U.S. patent application number 12/114625 was filed with the patent office on 2008-12-25 for gas sensor devices comprising organized carbon and non-carbon assembly.
Invention is credited to Sean Imtiaz Brahim, Steven G. Colbern, Leonid Grigorian, Robert L. Gump, Fikret Nuri Kirkbir.
Application Number | 20080317636 12/114625 |
Document ID | / |
Family ID | 39615702 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080317636 |
Kind Code |
A1 |
Brahim; Sean Imtiaz ; et
al. |
December 25, 2008 |
GAS SENSOR DEVICES COMPRISING ORGANIZED CARBON AND NON-CARBON
ASSEMBLY
Abstract
This invention relates generally to gas sensors comprising
organized assemblies of carbon and non-carbon compounds. The
invention also relates to devices containing such gas sensors and
analysis units. In preferred embodiments, the organized assemblies
of the instant invention take the form of nanorods or their
aggregate forms. More preferably, a nanorod is made up of a carbon
nanotube filled, coated, or both filled and coated by a non-carbon
material.
Inventors: |
Brahim; Sean Imtiaz;
(Camarillo, CA) ; Grigorian; Leonid; (Camarillo,
CA) ; Colbern; Steven G.; (Fillmore, CA) ;
Gump; Robert L.; (Camarillo, CA) ; Kirkbir; Fikret
Nuri; (Studio City, CA) |
Correspondence
Address: |
HOWREY LLP-CA
C/O IP DOCKETING DEPARTMENT, 2941 FAIRVIEW PARK DRIVE, SUITE 200
FALLS CHURCH
VA
22042-2924
US
|
Family ID: |
39615702 |
Appl. No.: |
12/114625 |
Filed: |
May 2, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60916104 |
May 4, 2007 |
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60981412 |
Oct 19, 2007 |
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60986167 |
Nov 7, 2007 |
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61032333 |
Feb 28, 2008 |
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61033630 |
Mar 4, 2008 |
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61035306 |
Mar 10, 2008 |
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Current U.S.
Class: |
422/98 |
Current CPC
Class: |
Y10T 436/204165
20150115; B82Y 15/00 20130101; B82Y 30/00 20130101; G01N 27/127
20130101; Y10S 977/953 20130101 |
Class at
Publication: |
422/98 |
International
Class: |
G01N 27/00 20060101
G01N027/00 |
Claims
1. A device for detecting an analyte gas, comprising: a sensor
comprising a carbon nanotube filled with one or more non-carbon
materials comprising a titanium compound, zirconium, zirconium
hydride, hafnium, hafnium hydride, vanadium, vanadium hydride, a
manganese compound, iron, iron hydride, cobalt, cobalt hydride,
nickel, nickel hydride, palladium, palladium hydride, platinum,
platinum hydride, copper, copper hydride, zinc, zinc hydride, or
the combination thereof; an analysis unit connected to the sensor,
and detects or determines the concentration of the analyte gas in a
background gas by measuring the Electronic Property Response of the
sensor due to the analyte gas; wherein the sensor and the analysis
unit are designed such that the average Electronic Property
Response is .gtoreq.1% when the analyte gas has concentrations of
10, 25, 50, 75, and 100 ppm.
2. The device according to claim 1, wherein the sensor provides
higher Electronic Property Response than a sensor comprising a
carbon nanotube provides.
3. The device according to claim 1, wherein said carbon nanotube is
a single wall carbon nanotube or a multi wall carbon nanotube.
4. The device according to claim 3, wherein said carbon nanotube is
a single wall carbon nanotube with an outer diameter varying in the
range of 1.0 nm to 1.8 nm.
5. The device according to claim 1, wherein said Electronic
Property Response is Resistive Response, Resistive Response derived
from Circuit, or Capacitive Response derived from Circuit.
6. The device according to claim 1, wherein said non-carbon
material comprises a titanium compound, a manganese compound, iron,
cobalt, nickel, palladium, platinum, or the combination
thereof.
7. The device according to claim 6, wherein said non-carbon
material comprises a titanium compound having a formula
TiH.sub.wB.sub.xN.sub.yO.sub.z, wherein w=0 to 2, x=0 to 2, y=0 to
1, and z=0 to 2.
8. The device according to claim 7, wherein said titanium compound
is titanium.
9. The device according to claim 7, wherein said titanium compound
is titanium hydride.
10. The device according to claim 6, wherein said non-carbon
material comprises a manganese compound having a formula
MnH.sub.wB.sub.xN.sub.yO.sub.z, wherein w=0 to 4, x=0 to 2, y=0 to
1, and z=0 to 2.
11. The sensor according to claim 10, wherein said manganese
compound is manganese.
12. The device according to claim 6, wherein said non-carbon
material comprises iron.
13. The device according to claim 6, wherein said non-carbon
material comprises cobalt.
14. The device according to claim 6, wherein said non-carbon
material comprises nickel.
15. The device according to claim 6, wherein said non-carbon
material comprises palladium.
16. The device according to claim 6, wherein said non-carbon
material comprises platinum.
17. The device according to claim 1, wherein said carbon nanotube
is further coated with a second non-carbon material.
18. The device according to claim 17, wherein said second
non-carbon material comprises a second titanium compound,
zirconium, zirconium hydride, hafnium, hafnium hydride, vanadium,
vanadium hydride, a second manganese compound, iron, iron hydride,
cobalt, cobalt hydride, nickel, nickel hydride, palladium,
palladium hydride, platinum, platinum hydride, copper, copper
hydride, zinc, zinc hydride, or the combination thereof.
19. The device according to claim 17, wherein said second
non-carbon material comprises the second titanium compound, the
second manganese compound, iron, cobalt, nickel, palladium,
platinum, or the combination thereof.
20. The device according to claim 1, wherein the said analyte gas
is nitrogen oxide, ethanol vapor, hydrogen, carbon dioxide, or
oxygen.
21. The device according to claim 1, further comprising: one or
more sensors each comprising a carbon nanotube or a filled carbon
nanotube, one or more analysis units connected to the one or more
sensors respectively, wherein the one or more analysis units detect
or determine the concentrations of the analyte gas and one or more
analyte gases in a background gas by measuring the Electronic
Property Response of the one or more sensors due to the analyte
gases, wherein each sensor provides a different Electronic Property
Response.
22. The device according to claim 21, wherein the filled carbon
nanotube of the one or more sensors is filled with one or more
non-carbon materials comprising a titanium compound, zirconium,
zirconium hydride, hafnium, hafnium hydride, vanadium, vanadium
hydride, a manganese compound, iron, iron hydride, cobalt, cobalt
hydride, nickel, nickel hydride, palladium, palladium hydride,
platinum, platinum hydride, copper, copper hydride, zinc, zinc
hydride, or the combination thereof.
23. The device according to claim 21, wherein the carbon nanotube
or the filled carbon nanotube of the one or more sensors is coated
with a second non-carbon material.
Description
[0001] This application claims priority to U.S. Provisional Patent
Application Nos. 60/916,104, filed May 4, 2007; 60/981,412, filed
Oct. 19, 2007; 60/986,167, filed Nov. 7, 2007; 61/032,333, filed
Feb. 28, 2008; 61/033,630, filed Mar. 4, 2008; and 61/035,306 filed
Mar. 10, 2008; all of which are incorporated herein by reference in
their entirety.
TECHNICAL FIELD
[0002] This invention relates generally to devices for detecting
analyte gases. The devices comprise gas sensors comprising
organized assemblies of carbon and non-carbon compounds. In
preferred embodiments, the organized structures of the instant
invention are made up of nanorods or their aggregate forms.
BACKGROUND OF THE INVENTION
[0003] There are many applications of carbon nanotubes (CNTs)
because of their unique mechanical, physical, electrical, chemical
and biological properties. For example, ultra low resistance
conductors, semiconductors, highly efficient electron emitters,
ultra-strong lightweight fibers for structural applications, and
lasers can all be manufactured by using CNTs. For reviews of CNT
technology, properties and applications, see Baughman et al.,
"Carbon Nanotubes--the Route Toward Applications", Science, volume
297, pages 787-792 (2002); Michael J. O'Connell (Editor) "Carbon
Nanotubes--Properties and Applications", CRC Taylor & Francis,
New York (2006); and Yury Gogotsi (Editor) "Nanomaterials
Handbook", CRC Taylor & Francis, New York (2006).
[0004] A great deal of research effort has been directed toward the
development of small dimensional inexpensive gas sensing devices
for applications including monitoring and controlling environmental
pollution; providing small, low-power, rapid and sensitive tools
for process and quality control in industrial applications; and
implementing or improving detection and quantification of harmful
gases.
[0005] In many industries, gases have become increasingly important
as raw materials and it has thereby become very important to
develop highly sensitive gas detectors. Such devices should allow
continuous monitoring of the concentration of particular gases in
the environment in a quantitative and selective way. However, many
of these efforts have not yet reached commercial viability because
of problems associated with the sensor technologies applied to
gas-sensing micro-systems. Inaccuracies and inherent
characteristics of the sensors themselves have made it difficult to
produce fast, reliable and low-maintenance sensing systems
comparable to other micro-sensor technologies that have grown into
widespread use commercially.
[0006] The practical application of environmental monitoring
requires developing sensing devices that are smaller and cheaper
than the analytical instruments currently used. Much of the
research on gas sensors to date has been carried out using either
thick-film or thin-film metal oxide semiconductor sensors.
Development of such sensors may have resulted in devices with
reasonable sensitivities. For environmental purposes, however,
greater sensitivities are required.
[0007] Among the gaseous species to be observed in air as
contaminants (polluting gases) are nitrous oxide (NO), nitrogen
dioxide (NO.sub.2), carbon monoxide (CO), carbon dioxide
(CO.sub.2), hydrogen (H.sub.2), hydrogen sulfide (H.sub.2S), sulfur
dioxide (SO.sub.2), ozone (O.sub.3), ammonia (NH.sub.3), and
organic gases such as methane (CH.sub.4), propane (C.sub.3H.sub.8),
liquid petroleum gas (LPG) organic vapors (ethanol, formaldehyde)
and the like.
[0008] For detection and quantification of carbon dioxide in gas
mixtures, there are two types of conventional sensors, i.e.
infrared spectroscopy (IR) based sensors and electrical resistance
based metal oxide semiconductor (MOS) sensors. The IR sensors take
advantage of the large IR stretching band for C.dbd.O functionality
at 2349 cm.sup.-1. Although commercially available portable IR
sensors exist, this approach is still limited by its power
consumption, size and cost. The MOS sensors utilize the change of
electrical resistance of a semiconductor film in the presence of
carbon dioxide. These sensors are also commercially available.
However, since such sensors operate at high temperatures, they
increase the power consumption.
[0009] There is a need for new or improved sensors that can be used
for fuel cell equipment in monitoring the hydrogen concentration in
the fuel stream (thereby its purity) and detection of equipment
leakages.
[0010] Detection and quantification of ethanol is also becoming
important for a variety of purposes including ethanol production,
chemical processing, fuel processing and use, societal
applications, and physiological research on alcoholism. A large
number of commercial ethanol measurement systems are available for
several of these applications. However, in general, these systems
are designed exclusively for vapor-phase measurements, operate at
relatively high power levels, are bulky, and possess functionality
that is more limited than required for a number of applications.
For the most precise measurements, high performance liquid
chromatography (HPLC) and infrared spectroscopy (IR) can be used
for ethanol concentration measurements. However, these are
expensive and involve large equipment. For portable detection,
smaller handheld devices such as breathalyzers are used for
measurements that are proportional to blood alcohol concentration
(BAC). Breathalyzer devices acquire ethanol from exhaled breath and
require direct and intimate exhalation into the apparatus.
Different versions of these devices have been integrated into some
models of various commercial vehicles. The driver is required to
breathe into a special mouthpiece to measure the level of alcohol
in the breath, and a computer decides whether or not to allow the
engine to start. In all these cases the measured breath alcohol is
indiscreet and can be difficult to correlate to the blood alcohol
concentration, since there can be a lot of variation in the breath
collection method. Moreover, while semiconductor metal oxides such
as SnO.sub.2 and ZnO have typically been employed for alcohol
sensing, these materials operate at elevated temperatures
(>150.degree. C.) and are sensitive to adsorption of other
gaseous species apart from ethanol such as gasoline, CO,
hydrocarbons and hydrogen which interfere with the alcohol
measurements.
[0011] With the increasing demand for superior but inexpensive gas
sensors of higher sensitivity and greater selectivity, intense
efforts are being made to find more suitable materials with the
required surface and bulk properties for use in gas sensors.
[0012] The carbon nanotubes (CNTs) are investigated as materials
suitable for manufacturing such sensors. For example, Robinson et
al. in "Improved Chemical Detection Using Single-Walled Carbon
Nanotube Network Capacitors" Sensors and Actuators A, volume 135,
pages 309 to 314 (2007); Varghese et al. in "Gas Sensing
Characteristics of Multi-wall Carbon Nanotubes" Sensors and
Actuators B, volume 81, pages 32 to 41 (2001); Valentini et al. in
"Highly Sensitive and Selective Sensors Based on Carbon Nanotubes
Thin Films for Molecular Detection" Diamond and Related Materials,
volume 13, pages 1301 to 1305 (2004); Snow et al. in "Chemical
Vapor Detection Using Single-Walled Carbon Nanotubes" Chemical
Society Reviews, volume 35, pages 790 to 798 (2006); and Star et
al. in "Gas Sensor Array Based on Metal-Decorated Carbon Nanotubes"
Journal Physical Chemistry B, volume 110, pages 21014 to 21020
(2006) have described the detection and quantification of gaseous
species in gas mixtures by sensors manufactured by using CNTs.
[0013] Sensors arrays have also been proposed for detection or
determination of concentration of more than one analyte, e.g. by Lu
et al., in "A carbon nanotube sensor array for sensitive gas
discrimination using principal component analysis", J. Electrochem.
Chem., volume 593, pages 105 to 110 (2006); by Qi et al. in "Toward
Large Arrays of Multiplex Functionalized Carbon Nanotube Sensors
for Highly Sensitive and Selective Molecular Detection", Nano
Lett., volume 3, pages 347 to 351 (2003); and by Graf et al., in
"Smart single-chip CMOS microhotplate array for metal-oxide-based
gas sensors" 12th International Conference on Transducers,
Solid-State Sensors, Actuators and Microsystems, volume 1, pages
123 to 126 (2003).
[0014] Methods of preparation of variety of sensors and sensor
arrays have also been proposed, for example, by Eranna et al., in
"Oxide Materials for Development of Integrated Gas Sensors--A
Comprehensive Review", Critical Reviews in Solid State and
Materials Sciences, volume 29, pages 111 to 188 (2004); and by
Sabate et al., in "Multisensor Chip for Gas Concentration
Monitoring in a Flowing Gas Mixture", Sensors and Actuators B,
volume 107, pages 688 to 684 (2005).
[0015] In summary, in all these applications, there is a high
demand for improved sensitivity, accuracy, reliability, selectivity
and stability beyond what is currently offered by commercially
available sensors. There exists a need for new or improved sensor
devices for detecting analyte gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram of the types of the organized
carbon and non-carbon assembly of the instant invention.
[0017] FIG. 2 schematically shows the preparation of a gas sensor
comprising organized carbon and non-carbon assembly.
[0018] FIG. 3 schematically shows the model electrical circuit used
to analyze the responses of various sensors comprising the
organized carbon and non-carbon assemblies.
[0019] FIG. 4 shows the Nyquist plot for the Ti.sup.f-SWCNT sensor
responding to 10 ppm NO.sub.2 gas at room temperature.
[0020] FIG. 5 shows the Nyquist plots of the Ti.sup.f-SWCNT sensor
as a function of NO.sub.2 gas concentration.
[0021] FIG. 6 shows the Resistive Response of the Ti.sup.f-SWCNT,
Ti.sup.f&c-SWCNT, TiH.sub.w.sup.f-SWCNT and the Starting SWCNT
sensor as a function of NO.sub.2 gas concentration.
[0022] FIG. 7 shows the Resistive Response of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and Starting SWCNT sensors as a function of NO.sub.2 gas
concentration.
[0023] FIG. 8 shows the Resistive Response of the
Ni.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Pt.sup.f&c-SWCNT
and Starting SWCNT sensors as a function of NO.sub.2 gas
concentration.
[0024] FIG. 9 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT, Ti.sup.f&c-SWCNT, TiH.sub.w.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of NO.sub.2 gas
concentration.
[0025] FIG. 10 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and Starting SWCNT sensors as a function of NO.sub.2 gas
concentration.
[0026] FIG. 11 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Pt.sup.f&c-SWCNT
and Starting SWCNT sensors as a function of NO.sub.2 gas
concentration.
[0027] FIG. 12 shows the Capacitive Response (Circuit) of the
Ti.sup.f-SWCNT, Ti.sup.f&c-SWCNT, TiH.sub.w.sup.f-SWCNT and the
Starting SWCNT sensor as a function of NO.sub.2 gas
concentration.
[0028] FIG. 13 shows the Capacitive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and Starting SWCNT sensors as a function of NO.sub.2 gas
concentration.
[0029] FIG. 14 shows the Capacitive Response (Circuit) of the
Ni.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Pt.sup.f&c-SWCNT
and Starting SWCNT sensors as a function of NO.sub.2 gas
concentration.
[0030] FIG. 15 shows the sensor enhancement factors calculated from
Resistive Response (Circuit) of the sensors in the NO.sub.2
concentration range of 0 ppm-10 ppm. (The enhancement factor of the
Ti.sup.f&c-SWCNT sensor was calculated in the concentration
range of 0 ppm to 100 ppm.).
[0031] FIG. 16 shows the sensor enhancement factors calculated from
Capacitive Response (Circuit) of the sensors in the NO.sub.2
concentration range of 0 ppm-10 ppm. (The enhancement factor of the
Ti.sup.f&c-SWCNT sensor was calculated in the concentration
range of 0 ppm to 100 ppm.).
[0032] FIG. 17 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, TiH.sub.w.sup.f-SWCNT sensor,
Ti.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of ethanol vapor concentration.
[0033] FIG. 18 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of ethanol vapor
concentration.
[0034] FIG. 19 shows the Resistive Response (Circuit) of the
Pd.sup.f&c-SWCNT, Pt.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of ethanol vapor
concentration.
[0035] FIG. 20 shows the sensor enhancement factors calculated from
Resistive Response (Circuit) of the sensors in the ethanol
concentration range of 0 ppm to 10 ppm.
[0036] FIG. 21 shows the Nyquist plot for the Pt.sup.f&c-SWCNT
sensor responding at room temperature to about 1% hydrogen and
nitrogen mixture.
[0037] FIG. 22 shows the Nyquist plots for the Pt.sup.f&c-SWCNT
sensor responding at room temperature to hydrogen and nitrogen
mixtures in the range of 0% to 3%.
[0038] FIG. 23 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of hydrogen concentration.
[0039] FIG. 24 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of hydrogen concentration in the range of 0% to 0.05%.
[0040] FIG. 25 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of hydrogen
concentration.
[0041] FIG. 26 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of hydrogen
concentration in the range of 0% to 0.05%.
[0042] FIG. 27 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of hydrogen concentration.
[0043] FIG. 28 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of hydrogen concentration in the range of 0% to 0.05%.
[0044] FIG. 29 shows the sensor enhancement factors calculated from
Resistive Response (Circuit) of the sensors in the hydrogen
concentration range of 0 ppm to 50 ppm (0% to 0.005%).
[0045] FIG. 30 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of carbon dioxide concentration.
[0046] FIG. 31 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of carbon dioxide concentration in the range of 0 ppm to
100 ppm.
[0047] FIG. 32 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of carbon dioxide
concentration.
[0048] FIG. 33 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of carbon dioxide
concentration in the range of 0 ppm to 100 ppm.
[0049] FIG. 34 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of carbon dioxide concentration.
[0050] FIG. 35 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of carbon dioxide concentration in the range of 0 ppm to
100 ppm.
[0051] FIG. 36 shows the Capacitive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of carbon dioxide concentration.
[0052] FIG. 37 shows the sensor enhancement factors calculated from
Resistive Response (Circuit) sensitivities in the carbon dioxide
concentration range of 0 ppm to 10 ppm.
[0053] FIG. 38 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of oxygen concentration.
[0054] FIG. 39 shows the Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of oxygen concentration in the range of 0 ppm to 100
ppm.
[0055] FIG. 40 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of oxygen
concentration.
[0056] FIG. 41 shows the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of oxygen concentration
in the range of 0 ppm to 100 ppm.
[0057] FIG. 42 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of oxygen concentration.
[0058] FIG. 43 shows the Resistive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of oxygen concentration in the range of 0 ppm to 100
ppm.
[0059] FIG. 44 shows the Capacitive Response (Circuit) of the
Ni.sup.f&c-SWCNT sensor, Pd.sup.f&c-SWCNT sensor,
Pt.sup.f&c-SWCNT sensor and the Starting SWCNT sensor as a
function of oxygen concentration.
[0060] FIG. 45 shows the Capacitive Response (Circuit) of the
Mn.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and the Starting SWCNT sensor as a function of oxygen
concentration.
[0061] FIG. 46 shows the Capacitive Response (Circuit) of the
Ti.sup.f-SWCNT sensor, Ti.sup.f&c-SWCNT sensor,
TiH.sub.w.sup.f-SWCNT sensor and the Starting SWCNT sensor as a
function of oxygen concentration.
[0062] FIG. 47 shows the sensor enhancement factors derived from
Resistive Response (Circuit) sensitivities in the oxygen
concentration range of 0 ppm to 10 ppm.
[0063] FIG. 48 schematically shows a device comprising a
Ni.sup.f&c-SWCNT sensor connected to a Resistive Response
(Circuit) analysis unit and a Mn.sup.f&c-SWCNT sensor connected
to a Resistive Response (Circuit) analysis unit.
SUMMARY OF THE INVENTION
[0064] The present invention is directed to a device for detecting
an analyte gas. The device comprises (a) a sensor comprising a
carbon nanotube filled with one or more non-carbon materials
comprising a titanium compound, zirconium, zirconium hydride,
hafnium, hafnium hydride, vanadium, vanadium hydride, a manganese
compound, iron, iron hydride, cobalt, cobalt hydride, nickel,
nickel hydride, palladium, palladium hydride, platinum, platinum
hydride, copper, copper hydride, zinc, zinc hydride, or the
combination thereof; and (b) an analysis unit connected to the
sensor, the analysis unit detects or determines the concentration
of the analyte gas in a background gas by measuring the Electronic
Property Response of the sensor due to the analyte gas; wherein the
sensor and the analysis unit are designed in such way that the
average Electronic Property Response is .gtoreq.1% when the analyte
gas has a concentration of 10, 25, 50, 75, and 100 ppm.
[0065] The carbon nanotube of the sensor is a single wall carbon
nanotube or a multi wall carbon nanotube. Preferably, the carbon
nanotube is a single wall carbon nanotube with an outer diameter
varying in the range of 1.0 nm to 1.8 nm. The Electronic Property
Response that the analysis unit measures includes, but is not
limited to, Resistive Response, Resistive Response derived from
Circuit, or Capacitive Response derived from Circuit.
[0066] The present invention is also directed to an array sensor
device, which comprises the above-described device and one or more
sensors each comprising a carbon nanotube or a filled carbon
nanotube.
[0067] The devices of the present invention also comprise carbon
nanotubes further coated with a second non-carbon material
comprising a second titanium compound, zirconium, zirconium
hydride, hafnium, hafnium hydride, vanadium, vanadium hydride, a
second manganese compound, iron, iron hydride, cobalt, cobalt
hydride, nickel, nickel hydride, palladium, palladium hydride,
platinum, platinum hydride, copper, copper hydride, zinc, zinc
hydride, or the combination thereof.
[0068] The device of the present invention is suitable for
detection or quantification of analyte gases such as nitrogen
oxide, ethanol vapor, hydrogen, carbon dioxide, or oxygen.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0069] In order to provide a clear and consistent understanding of
the specification and claims, including the scope given to such
terms, the following definitions are provided:
[0070] An "Electronic Property Response" as used herein, refers to
a normalized electronic property variation of a sensor due to the
presence of an analyte gas. It is calculated as:
Electronic Property Response(%)=100.times..DELTA.E/E.sub.b
[0071] E.sub.b is an electronic property of the background gas.
E.sub.mix is the electronic property of the mixture gas that
contains the analyte gas and the background gas.
.DELTA.E=E.sub.mix-E.sub.b, which is the variation of the
electronic property of the sensor (i.e. the sensor response) due to
the analyte gas.
[0072] An Electronic Property Response includes, but is not limited
to, Resistive Response, Resistive Response derived from Circuit, or
Capacitive Response derived from Circuit.
[0073] An "enhancement factor," as used herein, quantifies the
degree of improvement or attenuation in the sensor's response to an
analyte gas due to incorporation of one or more non-carbon
materials into a carbon nanotube over a range of various
concentrations. An enhancement factor can be determined by dividing
the sensitivity of a sensor comprising filled or filled and coated
carbon nanotube by that of a sensor comprising the starting carbon
nanotube.
[0074] The "minimum detection limit" of a sensor, as used herein,
is calculated by using the Nyquist plots as follows.
Minimum Detection Limit=the lowest resistive resolution of the
analyzer in ohms.times.10 ppm/.DELTA.Z'
[0075] where .DELTA.Z'=Z'.sub.b-Z'.sub.mix, and Z'.sub.b and
Z'.sub.mix are the real (resistive) parts of the impedance curves
for the background gas and for the 10 ppm analyte gas (in
background gas) respectively in ohms. The calculation of Minimum
Detection Limit is illustrated in Example 12.
[0076] The "sensitivity of a sensor" as used herein, is calculated
from the slope of the Electronic Property Response vs. the analyte
gas concentration curve, for example, by using the following
formulae:
Resistive Sensitivity(Circuit)=.DELTA.Resistive
Response(Circuit)/.DELTA.ppm of analyte gas
Capacitive Sensitivity(Circuit)=.DELTA.Capacitive
Response(Circuit)/.DELTA.ppm of analyte gas
[0077] A "sensor" as used herein, refers to a solid material that
has one or more electronic properties that are affected by the
surrounding gas.
[0078] This invention is directed to a sensor device for detecting
one or more analyte gases. The device comprises a sensor and an
analysis unit. The sensor comprises organized assemblies of carbon
and non-carbon materials. The sensor preferably comprises a carbon
nanotube filled with one or more non-carbon materials. The analysis
unit is connected to the sensor, and detects or determines the
concentration of the analyte gas in a background gas by measuring
the Electronic Property Response of the sensor due to the analyte
gas. In the present invention, the sensor and the analysis unit are
designed such that the average Electronic Property Response is
.gtoreq.1% when the analyte gas has concentrations of 1-100 ppm,
for example, 10, 25, 50, 75, and 100 ppm.
Organized Assemblies
[0079] These organized assemblies are made up of one or more types
of a repeating unit and may adopt different shapes, such as a rod,
spherical, semi-spherical, or egg shape. At least one dimension of
the repeating unit is typically smaller than 1000 nm, preferably
smaller than 100 nm, or more preferably smaller than 10 nm. A
cross-section of a repeating unit may resemble a circular, oval, or
rectangular shape. Typically, individual repeating units (or
different types of repeating units) aggregate to nanometer size
fragments. In a preferred embodiment, a repeating unit of this
invention may be a nanorod comprising nanocarbon and non-carbon
materials.
[0080] Many forms of carbon are suitable for the sensor of this
invention. These forms of carbon include for example amorphous
carbon, graphite, MWCNTs, SWCNTs, or a mixture thereof. In
preferred embodiments of this invention, the carbon may be a MWCNT,
a SWCNT, or a mixture thereof. In another preferred embodiment of
this invention, the carbon may be a SWCNT. In yet another preferred
embodiment, the carbon may be a SWCNT that has an external diameter
varying in the range of 1 nanometer to 1.8 nanometers.
[0081] Many non-carbon materials are suitable for incorporation
into the carbon nanotubes of this invention. Non-carbon materials
may comprise a metal (or a metal compound) or a non-metal material.
For example, a non-carbon material may comprise a metal, metal like
compound, metal nitride, metal oxide, metal hydride, metal boride,
mixture, or alloy thereof. Some examples of a non-carbon material
include magnesium (Mg), magnesium hydride, magnesium diboride
(MgB.sub.2), magnesium nitride (Mg.sub.3N.sub.2), magnesium oxide
(MgO), strontium (Sr), scandium (Sc), scandium nitride (ScN),
yttrium (Y), titanium (Ti), titanium hydride, titanium nitride
(TiN), titanium diboride (TiB.sub.2), titanium oxide (TiO.sub.2),
zirconium (Zr), zirconium diboride (ZrB.sub.2), zirconium nitride
(ZrN), hafnium (Hf), hafnium nitride (HfN), vanadium (V), vanadium
diboride (VB.sub.2), niobium (Nb), niobium diboride (NbB.sub.2),
niobium nitride (NbN), tantalum (Ta), chromium (Cr), chromium
diboride (CrB.sub.2), manganese (Mn), iron (Fe), cobalt (Co),
nickel (Ni), palladium (Pd), platinum (Pt), boron (B), boron
hydrides, boron nitride (BN), boron oxide (B.sub.2O.sub.3), and a
mixture (or alloy) thereof. Non-stoichiometric compounds of the
non-carbon material are also within the scope of this invention. In
addition, the non-carbon material may be amorphous or crystalline.
The crystalline form could be distorted, for example by having
deficiencies in the crystal structure. In the instant invention,
the non-carbon material does not comprise a halogen and/or a
halogenated compound.
[0082] In one embodiment of this invention, the non-carbon material
comprises a titanium compound. A titanium compound, as used herein,
refers to a compound that contains titanium. For example, a
titanium compound may be titanium, a titanium hydride, a titanium
boride, a titanium nitride, a titanium oxide, or a mixture thereof.
In particular, a titanium compound may be abbreviated with a
formula TiH.sub.wB.sub.xN.sub.yO.sub.z, where w varies in the range
of 0 to 2, x varies in the range of 0 to 2, y varies in the range
of 0 to 1, and z varies in the range of 0 to 2. Non-stoichiometric
titanium compounds are also within the scope of this invention. For
example, the titanium compound may be TiO.sub.1.354.
[0083] In another embodiment of this invention, the non-carbon
material comprises a manganese compound. A manganese compound, as
used herein, refers to a compound that contains manganese. For
example, a manganese compound may be manganese, a manganese
hydride, a manganese nitride, a manganese oxide, or a mixture
thereof. In particular, a manganese compound may be abbreviated
with a formula MnH.sub.w'B.sub.x'N.sub.y'O.sub.z', where w' varies
in the range of 0 to 4, x' varies in the range of 0 to 2, y' varies
in the range of 0 to 1, and z' varies in the range of 0 to 2.
Non-stoichiometric manganese compounds are also within the scope of
this invention. For example, the manganese compound may be
MnO.sub.1.782.
[0084] The non-carbon material may also comprise limited amount of
metal carbides, such as titanium carbide, silicon carbide, vanadium
carbide, tantalum carbide, or a mixture thereof, with an amount
preferably less than 10 volume percent.
[0085] As a repeating unit, the non-carbon material may fill, coat,
or both fill and coat the carbon nanotube (CNT). These three cases
are schematically shown in FIG. 1 (a) to (c). In the first case
shown in FIG. 1(a), the non-carbon material fills the core of the
CNT. The articles of the first case are abbreviated hereafter as
"non-carbon material filled carbon," for example, as Ti filled
SWCNTs. In the second case shown in FIG. 1(b), the non-carbon
material coats the CNT. The articles of this case are hereafter
abbreviated as "non-carbon material coated carbon," for example, as
Ti coated SWCNTs. In the third case shown in FIG. 1(c), the
non-carbon material both fills and coats the CNT. The articles of
this case are hereafter abbreviated as "non-carbon material filled
and coated carbon," for example, as Ti filled and coated SWCNTs.
The sensor of the present invention preferably comprises carbon
nanotubes filled with one or more non-carbon materials. The filled
nanotubes are optionally coated with one or more non-carbon
materials.
[0086] The repeating unit may be partially hollow. For example, the
core of a SWCNT, may be partially empty. The empty portion of the
core may be in less than 95, 75, 50, 25, or 10 volume percent. The
coating, filling, or coating and filling by the non-carbon material
may have a continuous or non-continuous form. For example, they may
be in the form of a continuous film deposited on the outer or inner
surface of a SWCNT, islands deposited on the outer or inner surface
of a SWCNT, beads deposited on the surface of a SWCNT, or
particulates deposited in the core of a SWCNT.
Method for Preparing an Organized Assembly
[0087] The organized assembly of carbon and non-carbon materials of
the present invention is prepared by the following method.
[0088] The method comprises the steps of reacting a carbon
precursor with a halogenated precursor to generate a halogenated
intermediate and removing halogen from the halogenated intermediate
to obtain the organized assembly of the carbon and the non-carbon
materials (hereinafter "the halide method"). If the non-carbon
material includes a hydride, nitride, oxide, or a mixture thereof,
the method may further comprise the step of hydrogenation,
nitrogenation, and/or oxidation after the halogen removal step to
obtain a composition comprising (1) carbon and (2) a non-carbon
hydride, boride, nitride, oxide, or a mixture thereof. In the
instant invention, the non-carbon material is not a halogen.
[0089] Many forms of the carbon precursor are suitable for the
halide method. In a preferred embodiment, these forms of carbon
precursors comprise a MWCNT, a SWCNT, or a mixture thereof. These
carbon precursors are hereafter referred as "carbon nanotubes" or
"starting carbon nanotubes", for example, a carbon nanotube,
MWCNTs, starting MWCNTs, SWCNTs, or starting SWCNTs.
[0090] A SWCNT or MWCNT precursor suitable for this invention may
be prepared by any synthesis method. Such methods may include, but
are not limited to, carbon arc, laser vaporization, chemical vapor
deposition (CVD), high pressure carbon monoxide process (HiPco),
cobalt-molybdenum catalyst process (CoMoCat). A SWCNT precursor may
be a mixture of SWCNT precursors prepared by more than one
synthesis method.
[0091] In one preferred embodiment of this invention, the carbon
precursor may comprise a SWCNT. In another preferred embodiment,
the carbon precursor may comprise a SWCNT that has an external
diameter varying in the range of 1 nanometer to 1.8 nanometers.
[0092] In one embodiment of the halide method, the SWCNT precursor
may be used as purchased. In another embodiment, amorphous carbons
and/or catalysts may be removed from the as-purchased SWCNTs before
the application of the disclosed method. The amorphous carbon
and/or the catalyst removal may be complete or partial. Thus, a
SWCNT precursor may contain any level of amorphous carbon and/or
catalyst. The invention is not limited to any particular method of
removing the amorphous carbon and/or the catalyst from the starting
SWCNTs. As an example, the method disclosed by Delzeit et al. in
U.S. Pat. No. 6,972,056 may be used for this removal.
[0093] A halogenated precursor may comprise a halogenated compound
and a halogen. Examples of the halogenated compound include
magnesium iodide (MgI.sub.2), scandium iodide (ScI.sub.3), scandium
bromide (ScBr.sub.3), yttrium iodide (YI.sub.3), titanium iodide
(TiI.sub.4), titanium bromide (TiBr.sub.4), vanadium iodide
(VI.sub.3), vanadium bromide (VBr.sub.3), molybdenum iodide
(MoI.sub.3), manganese iodide (MnI.sub.2), iron iodide (FeI.sub.2),
cobalt iodide (CoI.sub.2), nickel iodide (NiI.sub.2), palladium
iodide (PdI.sub.2), platinum iodide (PtI.sub.2), boron iodide
(BI.sub.3), lead iodide (PbI.sub.2), bismuth iodide (BiI.sub.3) or
a mixture thereof. Examples of the halogen include iodine, bromine,
an interhalogen compound (such as IBr, ICl.sub.3, BrF.sub.3) or a
mixture thereof.
[0094] Ends of the as-purchased carbon nanotubes are typically
closed, i.e. they are end-capped. The end-caps may prevent direct
filling of cores of the as-purchased carbon nanotubes with the
non-carbon materials. In some previously disclosed filling methods,
the end-caps are removed prior to the filling step by using acids
such as nitric acid or by controlled oxidation at elevated
temperatures. Such end-cap removal methods may cause partial or
excessive removal of carbon and formation of defects, thereby
degrading the useful properties of the carbon nanotubes.
[0095] The presence of the halogen in the halogenated precursor may
aid in filling of the carbon nanotubes with the non-carbon
materials without necessitating a separate end-cap removal step
prior to the filling, thereby simplifying the process. Also, such
filling may be achieved without any degradation of useful
properties of the carbon nanotubes. The presence of halogen may
also increase the amount of filling of carbon nanotubes by
non-carbon materials, thereby improving the yield and desired
properties of the organized assembly. Furthermore, the presence of
halogen may decrease the viscosity of the halogenated precursor,
thereby promoting better infiltration and shorter process
duration.
[0096] Some halogenated compounds may have impractically high
melting points (e.g., 587.degree. C. for FeI.sub.2, 780-797.degree.
C. for NiI.sub.2, 613-638.degree. C. for MnI.sub.2), and if the
reaction is carried out at such high temperatures, the carbon
nanotubes may irreversibly be damaged, diminishing the useful
properties of the organized assembly. However, incorporating
halogens such as bromine with a melting point of -7.3.degree. C. or
iodine with a melting point of 113.6.degree. C. into the
halogenated precursor may substantially reduce the reaction
temperature and prevent any property degradation.
[0097] Thus, there are several advantages of incorporating a
halogen into the halogenated precursor, including achieving filling
with no end-cap removal prior to the filling, increasing the
filling yield, and reducing the reaction temperature and time.
[0098] The amount of the halogenated compound in a halogenated
precursor may be at least 0.001 weight %. In other embodiments, the
amount of the halogenated compound in a halogenated precursor may
be at least 0.01 weight %, 0.1 weight %, 1 weight %, 10 weight %,
50 weight %, or 80 weight %. The amount of halogen in a halogenated
precursor may be at least 0.001 weight %. In other embodiments, the
amount of halogen in a halogenated precursor may be at least 0.01
weight %, 0.1 weight %, 1 weight %, 10 weight %, 50 weight %, or 80
weight %.
[0099] The amount of non-carbon material present in the halogenated
precursor controls the amount of non-carbon material incorporated
into the assembly. Thus, by varying the ratio of the non-carbon
material amount to the carbon precursor, the non-carbon material
content of the final composition can be varied. The ratio of
non-carbon material present in the halogenated precursor to carbon
present in the carbon precursor may be at least 0.01 weight %. In
other embodiments, the ratio of non-carbon material present in the
halogenated precursor to carbon present in the carbon precursor may
be at least 1 weight %, 10 weight %, or 25 weight %.
[0100] As a first process step, a carbon precursor is reacted with
a halogenated precursor. This reaction results in the incorporation
of the carbon precursor with the halogenated precursor to form a
halogenated intermediate. This incorporation may be in any form.
For example, the halogen may be incorporated on the outer or inner
surface or into the chemical structure of the carbon precursor.
This incorporation may be through chemical or physical bonding.
[0101] The reaction between the carbon precursor and the
halogenated precursor may occur at a temperature at which the
halogenated precursor is a liquid. Typically, it is at or above the
melting temperature of the halogenated precursor. In one
embodiment, the carbon precursor and the halogenated precursor may
be reacted at a temperature above 20.degree. C., 100.degree. C.,
150.degree. C., or 200.degree. C. for a period longer than 1
minute, 10 minutes, or 20 minutes.
[0102] In an optional process step, the carbon precursor may be
heated above room temperature to remove volatile compounds, such as
water, before the step of reacting the carbon precursor with the
halogenated precursor. The volatile compound removal may be
achieved by heating the carbon precursor above 100.degree. C. or
200.degree. C. for a period longer than 10 minutes.
[0103] After the reaction between the carbon precursor and the
halogenated precursor, a halogenated intermediate is produced.
[0104] As a second process step, the halogen is removed from the
halogenated intermediate. It is expected that, during the reaction,
the halogenated precursor may open the end caps of the carbon
nanotubes and fill their cores, coat the carbon nanotube, or both
fill (i.e., intercalate) and coat the carbon nanotube. As a result,
the halogenated intermediate may contain halogen, in a free form,
such as iodine, and/or in a form incorporated with the non-carbon
compound, such as TiI.sub.4. The presence of the halogen in the
final assembly in high quantities may deteriorate its properties as
compared to the halogen free assembly. It may be necessary to
reduce the halogen level, for example, below 10 weight %, to obtain
a commercially viable product.
[0105] The halogen removal may be achieved by sublimation,
evaporation, or thermal degradation. The halogen removal may also
be achieved by reacting the halogenated intermediate with a
suitable reactant, for example, hydrogen.
[0106] In particular, the halogen removal step may comprise heating
the halogenated intermediate at a temperature for a period
sufficient enough to reduce the halogen content of the intermediate
below 10 weight %. For example, the halogen removal step may be
carried out at a temperature above 200.degree. C., 300.degree. C.,
500.degree. C., or 800.degree. C. for a period longer than 5
minutes, 10 minutes, 30 minutes, or 1 hour. This heating may be
carried out below 1 atmosphere pressure. In one embodiment, this
heating may be carried out in a gas mixture comprising hydrogen at
a temperature for a period sufficient enough to reduce the halogen
content of the intermediate below 10 weight %. For example, the
halogen removal step may be carried out in a gas mixture comprising
at least 0.01 volume % or 1 volume % hydrogen at a temperature
above 200.degree. C., 300.degree. C., 500.degree. C., or
800.degree. C. for a period longer than 5 minutes, 10 minutes, 30
minutes, or 1 hour. The heating may be carried out below 1
atmosphere pressure. By adjusting these halogen removal conditions,
the level of hydride formation can be controlled and as a result
essentially hydride-free or partially or fully hydrogenated forms
of the non-carbon material may be obtained.
[0107] After the halogen removal step, an organized assembly
comprising a carbon and a non-carbon material (such as metal, metal
like compound, metal boride, or a mixture thereof) is obtained.
Specific examples of such non-carbon material include magnesium
(Mg), magnesium diboride (MgB.sub.2), strontium (Sr), scandium
(Sc), yttrium (Y), titanium (Ti), titanium diboride (TiB.sub.2),
zirconium (Zr), zirconium diboride (ZrB.sub.2), hafnium (Hf),
hafnium nitride (HfN), vanadium (V), vanadium diboride (VB.sub.2),
niobium (Nb), niobium diboride (NbB.sub.2), tantalum (Ta), chromium
(Cr), chromium diboride (CrB.sub.2), manganese (Mn), iron (Fe),
cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), boron (B),
boron nitride (BN), and a mixture thereof.
[0108] For an organized assembly comprising (1) a carbon and (2) a
non-carbon hydride, boride, nitride, oxide, or a mixture thereof,
the method may further include hydrogenation, reaction with boron
compounds, nitrogenation, and/or oxidation of the product after the
halogen removal step. This is an optional step for some hydrides
and borides. For example, if the halogen removal step is carried
out in a gas mixture comprising hydrogen, the non-carbon hydrides
may readily be obtained after the halogen removal without
necessitating this additional step. Also, if the halogenated
precursor includes a boron compound, the borides may also readily
be obtained after the halogen removal step without necessitating
this additional step. The hydrogenation may be carried out above
room temperature in a gas mixture containing hydrogen, ammonia, or
hydrazine. A preferable hydrogenation temperature is below
500.degree. C. In one embodiment of this invention, a hydrogenation
temperature in the range of 100.degree. C. to 300.degree. C. may
also be applied. The reaction with boron compounds may be carried
out by reacting the product with boron hydrides, for example
B.sub.2H.sub.6, B.sub.5H.sub.11. The nitrogenation may be carried
out above room temperature in a gas mixture containing nitrogen,
ammonia, hydrazine, or a mixture thereof. The oxidation may be
carried out at room temperature or above in a gas mixture
containing oxygen. As a result of hydrogenation, reaction with
boron compounds, nitrogenation, and/or oxidation, the assembly
comprising (1) a carbon and (2) a non-carbon (such as metal)
hydride, boride, nitride, oxide, or a mixture thereof is formed.
Some examples of such non-carbon material include magnesium hydride
(MgH.sub.2), magnesium nitride (Mg.sub.3N.sub.2), magnesium oxide
(MgO), scandium nitride (ScN), titanium hydride (TiH.sub.2),
titanium nitride (TiN), titanium oxide (TiO.sub.2), zirconium
nitride (ZrN), hafnium nitride (HfN), niobium nitride (NbN), boron
hydrides, boron nitride (BN), boron oxide (B.sub.2O.sub.3), and a
mixture thereof.
[0109] In one embodiment of the halide method, the organized
assembly comprising non-carbon material filled and coated carbon,
such as Ti filled and coated SWCNT may be prepared by both filling
and coating the carbon nanotube by the halogenated compound. To
achieve the filling, the size of the core should be larger than the
size of the halogenated compound. For example, a halogenated
compound, TiI.sub.4 has a size of about 1 nm. During the
halogenation reaction, this compound can fill the cores of SWCNTs
that have inner diameters larger than 1 nm. Thus, for example,
since the SWCNTs prepared by the carbon arc process have inner
diameters larger than 1 nm, these carbon precursors may be both
filled and coated with TiI.sub.4 and after the removal of iodine,
Ti filled and coated SWCNTs are generated.
[0110] In another embodiment of the halide method, the non-carbon
material coated carbon, such as Ti coated SWCNTs may be prepared by
coating the carbon nanotube by the halogenated compound. To achieve
the coating but not filling, the size of the core should be smaller
than the size of the halogenated compound. For example, a
halogenated compound TiI.sub.4 has a size of about 1 nm and the
SWCNTs prepared by CoMoCat process have inner diameters smaller
than 1 nm. Then, it is expected that during the halogenation
reaction, TiI.sub.4 can coat but not fill the cores of these
SWCNTs. As a result, after the iodine removal, Ti coated SWCNTs may
be produced.
[0111] In yet another embodiment of the halide method, the
non-carbon material filled carbon, such as Ti filled SWCNTs may be
prepared by washing the halogenated compound coated and filled
carbon nanotubes with a suitable solvent, such as ethanol. This
washing may remove the halogenated compound coating, but not the
filling at the carbon nanotube core. Then, after the halogen
removal, Ti filled SWCNTs are produced. This washing may completely
remove the halogenated compound coating if a suitable solvent is
used and/or if the solvent washing step is repeated several times.
This washing may also partially remove the halogenated coating, for
example, thereby incorporating a coating that has a particulate
form to the carbon. The amount of the coating then may be varied by
controlling the solvent type, solvent amount, and number of
repetition of washing steps.
[0112] Thus, by choosing the core size of the carbon nanotube or
incorporating a solvent wash step when the core size is larger than
size of the halogenated compound, the form of non-carbon material
incorporation may be controlled to prepare non-carbon filled,
coated, both filled and coated carbon assemblies, or their
mixtures.
[0113] In one embodiment of the invention, the method comprises
first filling the carbon nanotube and then further filling and/or
coating the filled carbon nanotube with a second non-carbon
material. The further filling and/or coating with the second
non-carbon may be achieved by following the method disclosed
above.
Sensor Device
[0114] This invention is particularly directed to a sensor device
comprising a sensor and an analysis unit. A "sensor," as used
herein, refers to a solid material that has one or more electronic
properties that are affected by the surrounding gas(es). The sensor
comprises a carbon nanotube filled with one or more non-carbon
materials. The analysis unit measures electronic properties of the
sensor. The device detects or quantifies an analyte gas by
measuring variation of an electronic property of the sensor as
explained below.
[0115] The sensors of this invention are used for detection or
quantification of analyte gases (or vapors) such as NO.sub.2,
ethanol, hydrogen, carbon dioxide and oxygen that may be present in
the environment surrounding the sensor. In a preferred embodiment
of this invention, the sensor comprises a carbon nanotube filled
with one or more non-carbon materials comprising a titanium
compound, zirconium, zirconium hydride, hafnium, hafnium hydride,
vanadium, vanadium hydride, a manganese compound, iron, iron
hydride, cobalt, cobalt hydride, nickel, nickel hydride, palladium,
palladium hydride, platinum, platinum hydride, copper, copper
hydride, zinc, zinc hydride, or the combination thereof.
[0116] These sensors may have any structure suitable for detection
or quantification of an analyte gas. In one embodiment of this
invention, the sensor comprises a repeating unit of the organized
carbon and non-carbon assembly. For example, the sensor comprises a
Ti filled SWCNT. A single repeating unit of the organized assembly
may also work as a sensor and thereby it is within the scope of
this invention. For example, the sensor may be one Ti filled SWCNT.
The repeating unit may also be combined with other materials, for
example with polymers, metals or metal oxides to form the sensors
of this invention. A coating comprising the repeating unit of the
organized assembly on a suitable substrate (for example, a glass
slide) may also form the sensor. There may be many more forms of
the sensor. All of them are within the scope of this invention.
[0117] The sensors of this invention may be prepared by any method
suitable for the present invention. The sensor can be prepared by
depositing the sensing material (e.g., the filled carbon nanotube)
over electrodes by sputtering, printing or dropping methods. One
method of preparation of a sensor is illustrated in Example 10
below and schematically shown in FIG. 2. There may be many more
methods for preparation of the sensors of this invention. All of
them are within the scope of this invention.
Analysis Unit
[0118] The sensors of this invention detect or quantify an analyte
gas by using an analysis unit that measures the variation of an
electronic property of the sensor caused by the presence of the
analyte gas. First, an electronic property of the background gas,
i.e. E.sub.b is measured. Then, the electronic property of the gas
that contains the analyte gas and the background gas, i.e.
E.sub.mix is measured. The difference between these two
measurements, i.e. .DELTA.E=E.sub.mix-E.sub.b is the variation of
the electronic property of the sensor (i.e. the sensor response).
The variation might be negative or positive, depending on the
electronic property measured. Both variations are within the scope
of this invention. The absolute value of the variation is used
hereafter.
[0119] This is explained in a simplified example as follows. A
sensor has an electronic property of electrical resistance. To
measure the concentration of an analyte gas (NO.sub.2) in a
background (nitrogen) gas, an analysis unit first measures the
electrical resistance of this sensor in nitrogen as 100 ohm. The
analysis unit then measures the electrical resistance of the sensor
in NO.sub.2--nitrogen gas as 101 ohm. Then, the analysis unit
determines the variation of the electric resistance by subtracting
100 ohm from 101 ohm, which equals to 1 ohm. This 1 ohm variation
is due to the presence of NO.sub.2.
[0120] The normalized sensor response is defined as:
Electronic Property Response(%)=100.times..DELTA.E/E.sub.b
[0121] There may be many electronic property variations that can be
measured by the analysis unit. In one embodiment of this invention,
the detection or quantification is determined by measuring the
variation of electrical resistance of the sensor. This variation is
hereafter abbreviated as "Resistive Response".
[0122] In another embodiment, the detection or quantification is
determined by measuring the variation of resistive and capacitive
properties derived from a model electrical circuit. One example of
such model electrical circuit, shown in FIG. 3, is formed by a
resistor R.sub.1, another resistor R.sub.2, and a non-Debye
capacitor C.sub.2. The values of R.sub.1, R.sub.2 and C.sub.2 for
each sensor in response to each analyte and analyte concentration
are obtained by first resolving the total impedance (Z) into a real
part (Z') and an imaginary part (Z''), then plotting the imaginary
part against the real part (i.e. Nyquist plot), and finally fitting
this plot to the model electrical circuit by using a suitable
software.
[0123] The variations measured by using this method are hereafter
abbreviated as "Resistive Response (Circuit)" and "Capacitive
Response (Circuit)". There may be many such equivalent circuits
that can be used for the electronic property variation measurement.
All these circuits are within the scope of this invention.
[0124] There may be many more electronic property variations that
can be measured by the analysis unit. All these electronic property
variations that can be used to detect or quantify the analyte gas
are within the scope of this invention.
[0125] In the present invention, the sensor and the analysis unit
are designed in such a way that the average Electronic Property
Response is .gtoreq.1% when the analyte gas has concentrations of
1-100 ppm. This limitation ensures that the device of the present
invention detects a sufficient normalized variation of the
electronic property above the background noise due to a particular
analyte gas, such that the result is accurate and reliable. The
average Electronic Property Response is determined by averaging the
Electronic Property Responses when the analyte gas concentrations
are between 1-100 ppm; preferably, determined by averaging at least
3, 4, or 5 analyte gas concentrations throughout the entire range,
for example, at 10, 25, 50, 75, and 100 ppm.
[0126] When a sensor has a particular average Electronic Property
Response of less than 1% averaged in the analyte concentration
range of 1 ppm to 100 ppm (e.g., 10, 25, 50, 75, and 100 ppm), this
variation is negligible above the background noise and thereby the
device is not sufficient for detection or quantification of the
analyte gas. Therefore, a sensor device comprising only one such
sensor and an analysis unit that measures the variation of this
particular electronic property is not within the scope of this
invention. For example, as disclosed below in Example 12, a
manganese filled and coated SWCNT sensor had Capacitive Responses
(Circuit) of 0.034%, 0.102%, 0.135%, 0.237%, and 0.270% at NO.sub.2
concentrations of 10, 25, 50, 75, and 100 ppm respectively. Thus,
the average Capacitive Response (Circuit) for this sensor was
0.156% at the NO.sub.2 concentrations ranging from 1 to 100 ppm.
Therefore, the sensor device comprising one manganese filled and
coated SWCNT sensor and an analysis unit that measures the
Capacitive Response (Circuit) can not detect or quantify NO.sub.2.
This sensor device is thereby not within the scope of this
invention.
[0127] However, such sensor can be used together with other
analysis units that measure variation of other electronic
properties. Such devices are within the scope of this invention.
For example, as disclosed below in Example 12, a manganese filled
and coated SWCNT sensor had an average Resistive Response (Circuit)
higher than 1% at NO.sub.2 concentrations 10, 25, 50, 75, and 100
ppm. The sensor device comprising one manganese filled and coated
SWCNT sensor and an analysis unit that measures the Resistive
Response (Circuit) may detect or quantify NO.sub.2. This sensor
device is thereby within the scope of this invention.
[0128] Furthermore, such sensors can also be used together with
other types of sensors in a sensor array to detect or quantify gas
mixtures comprising more than one analyte. This embodiment of this
invention is explained by way of example in Example 21 in
detail.
[0129] As explained below, it was found that most of the sensors
comprising the organized assemblies of this invention had
Electronic Property Responses improved over the sensors comprising
as purchased SWCNTs (i.e. starting SWCNTs). For example, the
Resistive Response (Circuit) of the starting SWCNTs is very low,
less than 2% to ethanol vapor, less than 1.5% to hydrogen, less
than 2.5% to carbon dioxide, less than 2.6% to oxygen in the
analyte concentration range of 1 ppm and 100 ppm. Most of the
sensors comprising the organized assemblies had higher Resistive
Responses (Circuit) to these analytes, as explained in detail in
Examples below.
[0130] Therefore, in one preferred embodiment of this invention,
the device of the present invention comprises a sensor that
comprises a carbon nanotube filled, or filled and coated with one
or more non-carbon materials; the sensor yields an electronic
variation (i.e. Electronic Property Response) higher than that of a
sensor comprising only carbon nanotubes that do not contain
non-carbon material (i.e. the starting carbon nanotube). This
preferred sensor of the present invention, for example, has
Resistive Responses, Resistive Responses (Circuit) and/or
Capacitive Responses (Circuit) higher than those of the sensor
comprising only carbon nanotubes. This preferred sensor of the
present invention also has sensitivities higher than those of the
sensor comprising only carbon nanotubes. This preferred sensor of
the present invention has enhancement factors higher than 1.00.
[0131] As also explained below, the Starting SWCNT sensors
sometimes had Electronic Property Responses better than those of a
few sensors comprising the organized assemblies of this invention.
However, such sensors comprising the organized assemblies of this
invention may have better sensitivities at certain analyte
concentrations as compared to the Starting SWCNT sensors.
Therefore, such sensors are also within the scope of this
invention.
[0132] The device determines the analyte concentration by
calibrating the analysis unit. For example, the device may
determine the analyte concentration by measuring the electrical
resistance of the sensor as follows. First, the analysis unit
measures electrical resistance R.sub.b of the sensor in a gas that
does not contain an analyte gas (i.e. a background gas). This gas
may be a single component gas or multi-component gas such as air.
Next, a known amount of analyte gas is introduced into the
background gas and the resistance of the sensor in this gas mixture
R.sub.mix is measured. The difference between the two resistance
values, .DELTA.R=R.sub.mix-R.sub.b is caused by an increase in
concentration of the known amount of analyte gas, which is
hereafter abbreviated as .DELTA.ppm. The absolute Resistive
Response of the sensor caused by the known amount of analyte
concentration increase is:
Resistive Response(calibration)(%)=100.times..DELTA.R/R.sub.b
[0133] The ratio .DELTA.Resistive Response (calibration)/.DELTA.ppm
is the Resistive Sensitivity of the sensor derived from electrical
resistance measurements of the known amount of analyte
concentrations. The Resistive Sensitivity value is used to
determine unknown analyte concentration by simply dividing the
Resistive Response of the sensor in the background gas that
contains unknown amount of analyte concentration with the Resistive
Sensitivity:
Unknown Analyte Concentration(ppm)=Resistive Response(%)/Resistive
Sensitivity
[0134] The sensitivity of each sensor may vary with varying analyte
concentration and analyte type. This variation might be linear or
non-linear. Therefore, the sensitivity variation for each analyte
is determined for each sensor at a wide analyte concentration range
before determination of the unknown concentration. The sensitivity
vs. analyte concentration (i.e. calibration plots) thereby obtained
may be used to determine the unknown concentration.
Sensor Device for Detection or Quantification of NO.sub.x Gas
[0135] In one embodiment, the devices of the instant invention are
for detection or quantification of nitrogen oxide (NO.sub.x) gases,
such as nitric oxide (NO), nitrogen dioxide (NO.sub.2), nitrous
oxide (N.sub.2O), dinitrogen trioxide (N.sub.2O.sub.3), dinitrogen
tetraoxide (N.sub.2O.sub.4), dinitrogen pentoxide (N.sub.2O.sub.5),
or mixtures thereof. In another embodiment, the NO.sub.x sensor
device of this invention is suitable for detection or
quantification of NO.sub.2. In another embodiment, the NO.sub.x
sensor device is suitable for detection or quantification of
NO.sub.2 in air.
[0136] These NO.sub.x sensor devices comprise a sensor and an
analysis unit, and the sensor comprises a carbon nanotube filled
with one or more non-carbon materials, as discussed above.
[0137] However, as disclosed below in Example 12 in detail, it was
found that the contribution of R.sub.1 to the Resistive Response
(Circuit) was less than 0.03% when the response was averaged in the
NO.sub.2 concentration range of 1 ppm to 100 ppm. It was thereby
concluded that the device comprising only one NO.sub.x sensor of
this invention and the analysis unit that measures the Electronic
Property Response R.sub.1 is not within the scope of this
invention. This device may be used together with other devices in
an array device to detect or quantify gas mixtures comprising more
than one analyte.
[0138] It was also found that a manganese filled and coated SWCNT
sensor had a Capacitive Response (Circuit) less than 0.27% at the
NO.sub.2 concentrations ranging from 1 ppm to 100 ppm. Therefore,
the sensor device comprising one manganese filled and coated SWCNT
sensor and the Capacitive Response (Circuit) analysis unit is not
within the scope of this invention. This device may be used
together with other devices in an array device to detect or
quantify gas mixtures comprising more than one analyte.
Sensor Device for Detection or Quantification of Ethanol Vapor
[0139] In one embodiment, the devices of the instant invention are
for detection or quantification of ethanol vapor mixed with a
background gas. These ethanol vapor sensor devices comprise a
sensor and an analysis unit, and the sensor comprises a carbon
nanotube filled with one or more non-carbon materials, as discussed
above.
[0140] However, as disclosed below in Example 14 in detail, it was
found that the contribution of R.sub.1 to the Resistive Response
(Circuit) was less than 0.03% when the response was averaged in the
ethanol vapor concentrations ranging from 1 to 100 ppm. Likewise,
the Capacitive Response (Circuit) C.sub.2, was less than 1% when
this response was averaged for this concentration range. It was
thereby concluded that the device comprising only one ethanol vapor
sensor of this invention and the analysis unit that measures the
Electronic Property Response R.sub.1 or the Capacitive Response
(Circuit) is not within the scope of this invention. This device
may be used together with other devices to detect or quantify gas
mixtures comprising more than one analyte.
[0141] It was also found that a nickel filled and coated SWCNT
sensor had a Resistive Response (Circuit) less than 0.53% at the
ethanol vapor concentrations ranging from 1 to 100 ppm. Therefore
the sensor device comprising one nickel filled and coated SWCNT
sensor and the Resistive Response (Circuit) analysis unit is not
within the scope of this invention. This device may be used
together with other devices in an array device to detect or
quantify gas mixtures comprising more than one analyte.
Sensor Device for Detection or Quantification of Hydrogen
[0142] In one embodiment, the devices of the instant invention are
for detection or quantification of hydrogen mixed with a background
gas. These hydrogen sensor devices comprise a sensor and an
analysis unit, and the sensor comprises a carbon nanotube filled
with one or more non-carbon materials, as discussed above.
[0143] However, as disclosed below in Example 15 in detail, it was
found that the contribution of R.sub.1 to the Resistive Response
(Circuit) was less than 0.03% when the response was averaged in the
hydrogen concentrations ranging from 1 to 100 ppm. Likewise, the
Capacitive Response (Circuit) C.sub.2, was less than 1% when this
response was averaged for this concentration range. It was thereby
concluded that the device comprising only one hydrogen sensor of
this invention and the analysis unit that measures the Electronic
Property Response R.sub.1 or the Capacitive Response (Circuit) is
not within the scope of this invention. This device may be used
together with other devices to detect or quantify gas mixtures
comprising more than one analyte.
[0144] It was also found that manganese filled and coated SWCNT
sensor had a Resistive Response (Circuit) less than 0.8% at the
hydrogen concentrations ranging from 1 to 100 ppm. Therefore the
sensor device comprising one manganese filled and coated SWCNT
sensor and the Resistive Response (Circuit) analysis unit is not
within the scope of this invention. This device may be used
together with other devices to detect or quantify gas mixtures
comprising more than one analyte.
Sensor Device for Detection or Quantification of Carbon Dioxide
[0145] In one embodiment, the devices of the instant invention are
for detection or quantification of carbon dioxide mixed with a
background gas. These carbon dioxide sensor devices comprise a
sensor and an analysis unit, and the sensor comprises a carbon
material filled with one or more non-carbon materials, as discussed
above.
[0146] However, as disclosed below in Example 18 in detail, it was
found that the contribution of R.sub.1 to the Resistive Response
(Circuit) was less than 0.03% when the response was averaged in the
carbon dioxide concentrations ranging from 1 to 100 ppm. Likewise,
the Capacitive Response (Circuit) C.sub.2, was less than 1% when
this response was averaged for this concentration range, except for
the titanium filled and coated SWCNT sensor. It was thereby
concluded that the device comprising only one carbon dioxide sensor
of this invention and the analysis unit that measures the
Electronic Property Response R.sub.1 is not within the scope of
this invention. It was further concluded that the device comprising
only one carbon dioxide sensor of this invention and the analysis
unit that measures the Capacitive Response (Circuit) is not within
the scope of this invention, except the device comprising titanium
filled SWCNT sensor. These devices may be used together with other
devices to detect or quantify gas mixtures comprising more than one
analyte.
[0147] It was found that the device comprising titanium filled and
coated SWCNT sensor had a Capacitive Response (Circuit) higher than
1% in the carbon dioxide concentrations ranging from 1 to 100 ppm.
Therefore, the device comprising the titanium filled and coated
SWCNT sensor and the Capacitive Response (Circuit) analysis unit is
within the scope of this invention.
Sensor Device for Detection or Quantification of Oxygen
[0148] In one embodiment, the devices of the instant invention are
for detection or quantification of oxygen mixed with a background
gas. These oxygen sensor devices comprise a sensor and an analysis
unit, and the sensor comprises a carbon material filled with one or
more non-carbon materials, as discussed above.
[0149] However, as disclosed below in Example 20 in detail, it was
found that the contribution of R.sub.1 to the Resistive Response
(Circuit) was less than 0.03% when the response was averaged in the
oxygen concentration ranging from 1 to 100 ppm. It was thereby
concluded that the device comprising only one oxygen sensor of this
invention and the analysis unit that measures the Electronic
Property Response R.sub.1 is not within the scope of this
invention. This device may be used together with other devices in
an array device to detect or quantify gas mixtures comprising more
than one analyte.
Sensor Device for Detection or Quantification of a Gas Mixture
Comprising at Least Two Analytes
[0150] In one embodiment of this invention, the device is for
detection or quantification of a gas mixture comprising at least
two analytes. This type of device is hereafter abbreviated as
"array device". The array device comprises at least two sensors and
at least one analysis unit for each sensor. Each sensor and its
analysis unit form a device subunit. Each subunit provides an
Electronic Property Response that is different than the other. One
of the sensors of the array device is a sensor comprising a carbon
nanotube filled with one or more non-carbon materials as discussed
above. The additional sensor or sensors comprise a carbon nanotube
or a carbon nanotube filled with a non-carbon material as discussed
above. Each carbon nanotube or filled nanotube is optionally coated
with one or more non-carbon materials. The sensors of the array
device comprise different carbon nanotubes or filled carbon
nanotubes from each other.
[0151] Some of the sensors of the array device may comprise an
organized assembly that yields negligible Electronic Property
Responses to some analyte gases. For example, the subunit
comprising nickel filled and coated SWCNT sensor and the Resistive
Response (Circuit) analysis unit has negligible response to the
ethanol vapor. However, this unit responds to the NO.sub.x gases.
Therefore, in a gas mixture comprising an NO.sub.x gas and ethanol
gas, the array device comprising this subunit may detect or
quantify the NO.sub.x gas.
[0152] Some of the sensors of the array device may comprise a
carbon nanotube. As explained above, such sensors may have very low
or negligible electronic responses to some analyte gases as
compared to most of the sensors comprising the organized assemblies
of this invention. However, the negligible response can be utilized
in a sensor array, for example, as a reference sensor.
[0153] The invention is illustrated further by the following
further examples that are not to be construed as limiting the
invention in scope to the specific procedures or products described
in them.
EXAMPLES
Example 1
Ti Filled SWCNT Article
[0154] In this example, the single-wall carbon nanotubes (SWCNTs)
were filled with titanium (Ti). This experiment was conducted with
minimal exposure to the external environment. SWCNTs were purchased
from Carbon Solutions Inc. (Riverside, Calif.) with a catalog
number P2-SWNT. They are manufactured by using the arc process and
have external diameters varying in the range of 1 nanometer and 1.8
nanometers. These SWCNTs are designated as "starting SWCNT."
[0155] The starting SWCNTs were processed as follows. The SWCNTs,
weighed about 82 mg, were placed in a 50 ml three-necked round
bottom Pyrex flask, which was equipped with a heating mantle, a
thermocouple, and an addition arm. The flask was connected to a
vacuum system through a liquid nitrogen trap.
[0156] The titanium iodide crystals (TiI.sub.4) used in this
Example were purchased from Aldrich with a catalog number 41,359-3.
The iodine crystals (12) were purchased from Aldrich with a catalog
number 20,777-2. TiI.sub.4 (about 1.8 gram) was mixed with 12
(about 1.8 gram) in a nitrogen-filled glove box and placed in the
flask addition arm. The end of the addition arm was covered to
protect the mixture from atmospheric moisture. The addition arm was
then taken out of the glove box and connected to the reaction
flask. Thus, the SWCNTs and the TiI.sub.4/I.sub.2 mixture initially
were kept in separate locations in the flask.
[0157] After the connection, the flask was immediately evacuated to
a pressure below 1 Torr. The contents of the flask were then heated
to about 150.degree. C. in vacuum for about 15 minutes to remove
volatile species from the SWCNTs. After this heating, the vacuum
valve was closed and the TiI.sub.4/I.sub.2 mixture was poured on
the SWCNTs by tipping the addition arm. The heating was continued
in order to melt the TiI.sub.4/I.sub.2 mixture and soak the SWCNTs
in the melt as follows. First, after the mixture was poured, the
flask was heated to about 200.degree. C. within about 6 minutes.
Then, it was further heated to about 275.degree. C. within about 12
minutes. Upon reaching about 275.degree. C., the vacuum valve was
opened to remove some un-reacted TiI.sub.4/I.sub.2 by evaporation
into the cold trap. The heating was continued in vacuum at about
275.degree. C. for about 1 hour. The contents of the flask were
then cooled to room temperature by cutting power to the heating
mantle. At this step, the nanorods comprised TiI.sub.4/I.sub.2
coated and filled SWCNTs.
[0158] This article was processed to remove TiI.sub.4 and 12
coating by an ethanol washing step as follows.
[0159] After the cooling, the flask was transferred to the glove
box filled with nitrogen, and the article was washed with ethanol
(Aldrich, catalog number 45, 984-4) to further remove un-reacted
TiI.sub.4/I.sub.2 mixture. The nanorods were first mixed with about
25 ml ethanol to prepare a suspension. This suspension was then
centrifuged at a centrifugal force of about 10,000 g for about 15
minutes to obtain a supernatant phase and a precipitate phase. The
supernatant phase was carefully removed by using a pipette and
discarded. This washing step was repeated once. The precipitate
phase was then transferred back to the glove box and it was dried
at about 25.degree. C. to remove residual ethanol. The precipitate
phase was characterized by 633 nm Raman spectroscopy. In the
ethanol washing step, the centrifugation step may be replaced with
a filtration step to recover the nanorods from the suspension. At
this step, the nanorods comprised TiI.sub.4/I.sub.2 filled
SWCNTs.
[0160] The TiI.sub.4/I.sub.2 filled SWCNTs were processed to remove
iodine by a heat treatment step as follows.
[0161] The precipitate phase was then placed in a quartz tube,
which was inserted in a tube furnace. The tube was sealed,
connected to a vacuum system and evacuated to about 30 mTorr
pressure. The furnace was then heated to about 500.degree. C.
within one hour. The heating was continued at about 500.degree. C.
for about 30 minutes.
[0162] After this heating period, a gas mixture consisting
essentially of about 3% hydrogen and about 97% argon was introduced
into the quartz tube and the pressure was raised to about 10 Torr.
The heating was further continued at a furnace temperature of about
500.degree. C. for about two hours at about 10 Torr in the flowing
gas mixture, after which the furnace was cooled to room
temperature. The Ti filled SWCNTs were thereby obtained.
Example 2
Ti Filled and Coated SWCNT Article
[0163] In this example, the SWCNTs were both filled and coated with
titanium (Ti). This example was carried out in the same manner as
described in Example 1, except that the contents of the reaction
flask were heated at about 275.degree. C. for about 15 to 20
minutes prior to opening the vacuum valve and that the ethanol
washing step was not carried out after the preparation of the
article comprising TiI.sub.4/I.sub.2 coated and filled SWCNTs.
Thus, after the cooling of the flask, TiI.sub.4/I.sub.2 coated and
filled SWCNTs were directly placed in a quartz tube, which was
inserted in a tube furnace. The Ti filled and coated SWCNTs were
thereby obtained.
Example 3
TiH.sub.w Filled SWCNT Article
[0164] In this example, TiH.sub.w filled SWCNTs were prepared,
where w varies in the range of 0 to 2. First, Ti filled SWCNTs were
prepared in the same manner as described in Example 1. Then, these
nanorods were placed in an air-free chamber and heated to about
650.degree. C. in vacuum for at least 2 hours to remove volatile
compounds. After the removal of volatile compounds, the temperature
was decreased to about 500.degree. C. and the chamber was
pressurized to about 500 Torr with hydrogen. The nanorods were
hydrogenated by keeping them at this temperature for at least one
hour. Finally, the hydrogenated nanorods were cooled to a room
temperature. TiH.sub.w filled SWCNT articles were thereby
prepared.
[0165] These nanorods were later heated to a temperature in the
range of 400.degree. C. to 650.degree. C. to release the hydrogen
from the nanorods. The hydrogen evolution was followed by using a
mass spectrometer. The evolution started at about 200.degree. C.
and became considerable at about 400.degree. C. The total amount of
hydrogen evolved from the nanorods indicated that at least 80% by
weight of titanium was hydrogenated, i.e., forming TiH.sub.0.800.
This result demonstrated that Ti filled SWCNTs may be used in
preparation of hydrogen storage devices and the hydrogen evolution
may be achieved at temperatures as low as 200.degree. C.
Example 4
Ni Filled and Coated SWCNT Article
[0166] This Example was carried out in the same manner as described
in Example 1, except that 0.9 gram of nickel iodide and 1.1 grams
of iodine were used instead of about 1.8 grams of TiI.sub.4 and
about 1.8 grams of 12, that the annealing was carried out at about
500.degree. C. for about 30 minutes, followed by about 600.degree.
C. for about 2 hours instead of about 500.degree. C. for about 2
hours, and that during the cooling, a gas mixture consisting
essentially of about 50 percent nitrogen, about 2.5 percent
hydrogen and about 47.5 percent argon was flowed at a pressure of
about 20 Torr, instead of the gas mixture consisting essentially of
about 5 percent hydrogen and about 95 percent argon at a pressure
of about 10 Torr. The article comprising Ni filled and coated
SWCNTs was thereby prepared.
Example 5
Fe Filled and Coated SWCNT Article
[0167] This Example was carried out in the same manner as described
in Example 1, except that about 0.9 gram of ferric iodide and about
1.8 grams of iodine were used instead of about 1.8 grams of
TiI.sub.4 and about 1.8 grams of 12, that the annealing was carried
out at about 500.degree. C. for about 30 minutes, followed by about
600.degree. C. for about 2 hours instead of about 500.degree. C.
for about 2 hours, and that during the cooling, a gas mixture
consisting essentially of about 50 percent nitrogen, about 2.5
percent hydrogen and about 47.5 percent argon was flowed at a
pressure of about 20 Torr, instead of the gas mixture consisting
essentially of about 5 percent hydrogen and about 95 percent argon
at a pressure of about 10 Torr. The article comprising Fe filled
and coated SWCNTs was thereby prepared.
Examples 6 to 9
Metal Filled and Coated SWCNT Articles
[0168] In these examples, the starting SWCNTs were filled with
various metals in the same manner as described in Example 5, except
that iodides of Mn, Co, Pd or Pt were used instead of ferric
iodide. The articles comprising Mn filled and coated SWCNTs, Co
filled and coated SWCNTs, Pd filled and coated SWCNTs, or Pt filled
and coated SWCNTs were thereby prepared.
Example 10
Preparation of a Sensor Comprising Ti Filled SWCNT Article
[0169] Preparation of a gas sensor is shown in FIG. 2. First, a
quartz slide with a thickness of about 1.0 mm (Ted Pella, Inc.
Prod. #26011) was cut into an about 1 cm.times.about 1 cm square
substrate (FIG. 2A). These substrates were cleaned in two steps as
follows. In a first cleaning step, the substrates were placed in a
4 to 5 weight percent detergent/water solution and sonicated for
about 5 minutes. These substrates were then washed with deionized
water for at least one minute and finally dried by blowing dry
nitrogen gas. In a second cleaning step, a solution was prepared to
contain deionized water, hydrogen peroxide and ammonium hydroxide
with a volume ratio of about 5:1:1 respectively. The quartz
substrates cleaned in the first step were placed in this solution
and heated at about 80.degree. C. for at least 20 minutes. These
substrates were then washed with deionized water for at least one
minute and finally dried by blowing dry nitrogen gas. About 2
mm.times.about 1 cm strip of polyimide tape was then placed at the
center of the cleaned quartz substrate to function as a mask for
subsequent evaporation and sputtering of chromium and gold
respectively onto the top surface of the quartz substrates (FIG.
2B). The masked quartz substrate was then placed inside a sputter
coater (Denton Vacuum DV-502A). A chromium layer of average
thickness less than about 100 .ANG. was first deposited on this
substrate to act as an adhesion layer (not shown in FIG. 2). Then,
a gold layer with an average thickness of about 2000 .ANG. was
deposited on this chromium layer and the mask was removed (FIG.
2C). The gold-deposited quartz substrate was then covered with a
strip of polyimide tape, cut to provide a window of dimension about
4 mm.times.about 2 mm and placed onto the substrate so as to bridge
the sputtered gold areas (FIG. 2D). Two pairs of shielded copper
wire, each piece terminating in gold pins, were soldered onto each
gold deposited area (FIG. 2E) to allow for four-point impedance
measurement over the quartz surface.
[0170] The titanium filled SWCNT article prepared in Example 1
(about 1 mg) was mixed with about 5.0 milliliter of anhydrous
dimethylformamide (DMF, Acros Cat. #61032-0010). This mixture was
then sonicated using a horn sonicator (Sonics Materials, Model
VC600) at about 600 W power and about 20 MHz frequency for about 5
minutes. This sonication step was repeated three times. A
dispersion of the titanium filled SWCNT article was thereby
obtained.
[0171] This dispersion was deposited drop by drop on the open area
of the polyimide tape by using a syringe (3 mL capacity) equipped
with a blunted needle (18G). This deposition was continued until
all the open area was covered with a dispersion layer. The
dispersant was first allowed to slowly evaporate from the
dispersion layer by forced air flow at room temperature. Then, the
quartz substrate was placed in a forced air convection oven at
about 130.degree. C. for about 30 minutes for further removal of
the dispersant. After this drying, a coating of the titanium filled
SWCNT article connecting the two gold layers was formed and a gas
sensor was thereby prepared. This sensor is hereafter designated as
the Ti.sup.f-SWCNT sensor, where superscript "f" refers
"filled".
[0172] Another sensor was prepared in the same manner described in
this example, except that the starting SWCNTs purchased from Carbon
Solutions Inc. with a catalog number P2-SWNT were used instead of
the Ti filled SWCNT article. This sensor is hereafter designated as
the Starting SWCNT sensor.
Example 11
Sensor Comprising Ti Filled SWCNT Article for Detection or
Quantification of NO.sub.2 Gas
[0173] The variation of electrical properties of sensors prepared
in Example 10 was analyzed as follows. First, the electrical
connection between the two gold layers was tested by using a
multimeter (Fluke Model 189) and measuring the resulting finite
contact resistance. After it was ensured by this measurement that
the electrical connection between the gold layers was formed by the
coating of the titanium filled SWCNT article, the sensor was
assembled into a gas chamber and connected to an impedance analyzer
(Novocontrol Technologies Model Alpha A). The impedance analyzer
was the analysis unit. The electrical connection was done through a
15-pin sub D type connector (MDC Inc. Part#D15-K200) mounted on an
NW50 KF flange (MDC, Inc.) for use as the top plate assembly of the
gas chamber. The D type connector allowed electrical connection
between the impedance analyzer test interface and the sensor, while
supporting the wired sensor inside the vacuum (test) side of the
chamber.
[0174] As a pre-conditioning step, before the impedance measurement
was carried out, the chamber was first evacuated to a pressure
below 1 Torr at room temperature and kept at this pressure for
about 4 hours by using a vacuum pump.
[0175] An interrogating sinusoidal voltage of about 50 mV.sub.rms
(about 70 mV.sub.peak-to-peak) was applied to the sensor by varying
the frequency in the range of 10 MHz to 10 mHz. Gas sensing
experiments were carried out in the following sequence. For
impedance measurements of the sensor in vacuum, all valves were
closed to the atmosphere and the chamber was evacuated below 1 Torr
pressure by using the vacuum pump. Then, the pump was switched off.
After it was ensured that the pressure did not increase above 1
Torr within a predetermined period of time, the impedance
measurements were started. For impedance measurements in air, the
ultra-high purity (UHP) air line was opened and the chamber was
filled with air until the pressure in the chamber reached about 760
Torr. Then a release valve was opened to an ambient atmosphere to
allow a flow of the UHP air into the chamber, regulated at about
100 milliliter per minute by means of a mass flow controller. For
impedance measurements in nitrogen, the release valve was closed
and the chamber was evacuated to a pressure below 1 Torr. The UHP
N.sub.2 line was then opened and the chamber was filled with
nitrogen until a pressure of about 760 Torr was reached and the
release valve opened to an ambient atmosphere. The flow of UHP
nitrogen into the chamber was regulated at about 100 milliliter per
minute by means of a mass flow controller.
[0176] For sensor impedance measurements in a test gas such as
NO.sub.2, the parent NO.sub.2 gas (about 1000 ppm in nitrogen) was
diluted with the ultra-high purity N.sub.2 to yield concentrations
of NO.sub.2 varying in the range of 0 ppm to 250 ppm. The flow rate
of the diluted test gas was controlled at about 100 milliliter per
minute by means of an MKS multi-gas controller (Model 647C). Each
concentration of NO.sub.2 gas mixture was allowed to flow over the
assembled sensor for about 10 minutes prior to acquiring the
frequency dependent impedance values.
[0177] The total impedance (Z) was resolved into a real part (Z')
and an imaginary part (Z'') and a semicircular Nyquist plot was
obtained, which intersected the Z' axis at two points. The
difference between these two intersection points yielded the real
part of the resistance. For example, as shown in FIG. 4, the real
resistance was about 48,900 ohms for the Ti.sup.f-SWCNT sensor at
about 10 ppm NO.sub.2 concentration. Same measurements were
repeated at various NO.sub.2 concentrations to determine the sensor
response as a function of the gas concentration. The same
measurement was also repeated for UHP N.sub.2 to determine the
response of the sensor to the diluent (i.e. background) gas. The
measurement results are shown in FIG. 5.
[0178] The normalized resistive response of the sensor was
calculated by using the following formula:
Resistive Response(%)=100.times.(R.sub.N2-R.sub.mix)/R.sub.N2
where R.sub.N2 and R.sub.mix are the real resistances of the sensor
in nitrogen (i.e. background gas) and the NO.sub.2--N.sub.2 gas
mixture respectively. The variation of the Resistive Response of
the sensor as a function of NO.sub.2 gas concentration is shown in
FIG. 6. Same impedance measurements were repeated for the Starting
SWCNT sensor. As shown in FIG. 6, the normalized resistive response
of the Ti.sup.f-SWCNT sensor was higher than that of the Starting
SWCNT sensor for all NO.sub.2 concentrations.
[0179] This sensor was further analyzed by modeling the impedance
data in the Nyquist plot using an equivalent circuit method. This
model electrical circuit, shown in FIG. 3, is formed by a resistor
R.sub.1, another resistor R.sub.2, and a non-Debye capacitor
C.sub.2. The values of R.sub.1, R.sub.2 and C.sub.2 for each sensor
in response to each gas concentration were obtained by fitting the
Nyquist plot to the model electrical circuit by using an
electrochemical impedance spectroscopy measurement software
manufactured by Scribner Associates (Southern Pines, N.C.).
[0180] It was found that R.sub.1, the uncompensated ohmic
resistance of the sensor did not show any dependence to the
NO.sub.2 concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the Resistive
Response was averaged in the NO.sub.2 concentrations ranging from 1
to 100 ppm. It was thereby concluded that the Electronic Property
Response R.sub.1 is not suitable for detection or quantification of
NO.sub.2 with Ti.sup.f-SWCNT sensor.
[0181] The other circuit parameters R.sub.2 and C.sub.2 decreased
in the presence of NO.sub.2. Same impedance measurements were
repeated for the Starting SWCNT sensor.
[0182] The normalized resistive and normalized capacitive responses
of the sensor were calculated by using the formula:
Resistive
Response(Circuit)(%)=100.times.(R'.sub.N2-R'.sub.mix)/R'.sub.N2
[0183] where R'.sub.N2 and R'.sub.mix individually equal to the sum
of their R.sub.1 and R.sub.2 components derived by using the model
electrical circuit. As shown in FIG. 9, the Resistive Response
(Circuit) of the Ti.sup.f-SWCNT sensor was higher than that of the
Starting SWCNT sensor for all NO.sub.2 concentrations.
[0184] Likewise, the normalized capacitive response of the sensor
was calculated by using the formula:
Capacitive
Response(Circuit)(%)=100.times.(C.sub.2,N2-C.sub.2,mix)/C.sub.2,N2
[0185] where C.sub.2,N2 and C.sub.2,mix are the capacitance of the
sensor in nitrogen and the NO.sub.2--N.sub.2 gas mixture
respectively, which is derived by using the model electrical
circuit. As shown in FIG. 12, the Capacitive Response (Circuit) of
the Ti.sup.f-SWCNT sensor was higher than that of the Starting
SWCNT sensor for all NO.sub.2 concentrations.
[0186] All these results disclosed above indicated that the
incorporation of non-carbon material into the carbon nanotubes
improved the response of the sensor.
Example 12
Sensors for Detection and Quantification of NO.sub.2 Gas
[0187] Various sensors were prepared and analyzed in the same
manner as described in Example 11, except that the SWCNT articles
prepared in Examples 2 to 9 were used instead of the Ti filled
SWCNT article prepared in Example 1. The results are shown in FIGS.
6 to 16. If a sensor is prepared by using a non-carbon filled and
coated SWCNT article, it is designated, for example, as
Fe.sup.f&c-SWCNT sensor, where "f&c" refers "filled and
coated".
[0188] It was found that R.sub.1, the uncompensated ohmic
resistance of these sensors did not show any dependence to the
NO.sub.2 concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the response
was averaged in the NO.sub.2 concentration range of 1 ppm to 100
ppm. It was thereby concluded that the Electronic Property
Response, R.sub.1 is not suitable for detection or quantification
of NO.sub.2 with these sensors.
[0189] As shown in FIGS. 6 and 9, the Resistive Response and
Resistive Response (Circuit) of the Ti.sup.f-SWCNT sensor was
higher than those of the Ti.sup.f&c-SWCNT sensor and
TiH.sub.w.sup.f-SWCNT sensor as well as that of the Starting SWCNT
sensor for NO.sub.2 concentration in the range of 0 ppm to 250 ppm.
Also, the Resistive Response and Resistive Response (Circuit) of
the Starting SWCNT sensor were higher than those of the
Ti.sup.f&c-SWCNT sensor and the TiH.sub.w.sup.f-SWCNT
sensor.
[0190] These results indicated that the Ti.sup.f-SWCNT sensor,
Ti.sup.f&c-SWCNT sensor or TiH.sub.w.sup.f-SWCNT sensor
together with the Resistive Response analysis unit or Resistive
Response (Circuit) analysis unit can detect and quantify NO.sub.x
gases. They are thereby within the scope of one preferred
embodiment of this invention. In another preferred embodiment, the
sensor devices comprising a Ti.sup.f-SWCNT sensor and a Resistive
Response analysis unit or Resistive Response (Circuit) analysis
unit are used to detect or quantify NO.sub.x gases.
[0191] The variation of the Capacitive Response (Circuit) of the
sensors as a function of NO.sub.2 gas concentration is shown in
FIGS. 12 to 14. As shown in FIG. 12, the slope of the
TiH.sub.w.sup.f-SWCNT sensor increased as compared to the
Ti.sup.f-SWCNT sensor and the Ti.sup.f&c-SWCNT sensor,
indicating that it had a better Capacitive Response (Circuit). This
result further indicated that the sensors comprising hydrides of
non-carbon materials such as hydrides of Zr, Hf, V, Cr, Mn, Fe, Co,
Ni, Pd, Pt, or mixtures of such non-carbon materials may have
improved Capacitive Responses (circuit) as compared to those
sensors comprising non-hydride non-carbon materials.
[0192] As shown in FIGS. 7, 8, 10 and 11, the Resistive Responses
and the Resistive Responses (Circuit) of the Fe.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT and Ni.sup.f&c-SWCNT sensors were higher
than that of the Starting SWCNT sensor, particularly for NO.sub.2
concentrations higher than 50 ppm. Mn.sup.f&c-SWCNT sensor
showed higher Resistive Response and Resistive Response (Circuit)
as compared to the Starting SWCNT sensor for NO.sub.2
concentrations at about 50 ppm or below. Pd.sup.f&c-SWCNT and
Pt.sup.f&c-SWCNT sensors showed lower Resistive Response and
Resistive Responses (Circuit) as compared to the Starting SWCNT
sensor.
[0193] These results indicated that the Fe.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT, Mn.sup.f&c-SWCNT,
Pd.sup.f&c-SWCNT or Pt.sup.f&c-SWCNT sensor together with
the Resistive Response analysis unit or Resistive Response
(Circuit) analysis unit can detect and quantify NO.sub.x gases.
They are thereby within the scope of one preferred embodiment of
this invention. In another preferred embodiment, the sensor devices
comprising Fe.sup.f&c-SWCNT sensor, Co.sup.f&c-SWCNT sensor
or Ni.sup.f&c-SWCNT sensors and the Resistive Response analysis
unit or Resistive Response (Circuit) analysis unit are used to
detect or quantify NO.sub.x gases.
[0194] As shown in FIGS. 13 and 14, the Fe.sup.f&c-SWCNT
sensor, the Co.sup.f&c-SWCNT sensor, the Ni.sup.f&c-SWCNT
sensor, the Pd.sup.f&c-SWCNT sensor and the
Pt.sup.f&c-SWCNT sensor had an increased Capacitive Response
(circuit) to varying NO.sub.2 concentration, whereas the response
of the Starting SWCNT sensor and the Mn.sup.f&c-SWCNT sensor
was very low. Furthermore, the slope (i.e. sensitivity) for some of
these sensors considerably increased above a threshold NO.sub.2
concentration, indicating that these sensors may be used for
selective identification of NO.sub.x gases in gas mixtures as well
as determination of their concentration. This threshold value
varied with the sensor type. For example, the Co.sup.f&c-SWCNT
sensor showed considerably increased response above about 50 ppm
NO.sub.2, the Ni.sup.f&c-SWCNT sensor above about 100 ppm
NO.sub.2, the Pd.sup.f&c-SWCNT sensor above about 50 ppm
NO.sub.2 and the Pt.sup.f&c-SWCNT sensor above about 75 ppm
NO.sub.2.
[0195] These results indicated that the Fe.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT or
Pt.sup.f&c-SWCNT sensor together with the Capacitive Response
(Circuit) analysis unit can detect and quantify NO.sub.x gases.
They are thereby within the scope of one preferred embodiment of
this invention.
[0196] The Capacitive Response (Circuit) of the Starting SWCNT was
very low, less than 0.26% at the NO.sub.2 concentrations ranging
from 1 to 100 ppm. This result indicated that a sensor device
comprising only one Starting SWCNT sensor and a Capacitive Response
(Circuit) analysis unit cannot be used for detection or
quantification of NO.sub.x gases. However, this sensor can be used
together with other sensors in a device comprising a sensor array
to detect or quantify analyte gas(es).
[0197] Similarly, the Capacitive Response (Circuit) of the
Mn.sup.f&c-SWCNT was very low. This sensor had Capacitive
Responses (Circuit) of 0.034%, 0.102%, 0.135%, 0.237%, and 0.270%
at NO.sub.2 concentrations of 10, 25, 50, 75, and 100 ppm
respectively. Thus, the average Capacitive Response (Circuit) for
this sensor was 0.156% at the NO.sub.2 concentrations ranging from
1 to 100 ppm. This result indicated that a sensor device comprising
only one Mn.sup.f&c-SWCNT sensor and a Capacitive Response
(Circuit) analysis unit cannot be used for detection or
quantification of NO.sub.x gases. However, this sensor can be used
together with other sensors in a device comprising a sensor array
to detect or quantify analyte gas(es).
[0198] Sensor sensitivities are calculated from the slopes of the
Electronic Property Response (Resistive Response (Circuit) or the
Capacitive Response (Circuit)) vs. the analyte concentration, for
example, by using the following formulae:
Resistive Sensitivity(Circuit)=.DELTA.Resistive
Response(Circuit)/.DELTA.ppm
Capacitive Sensitivity(Circuit)=.DELTA.Capacitive
Response(Circuit)/.DELTA.ppm
[0199] These sensitivities were calculated at two analyte
concentration ranges, (a) 0 ppm to 10 ppm (i.e. .DELTA.ppm=10-0)
and (b) 100 ppm to 250 ppm (i.e. .DELTA.ppm=250-100). The first
analyte concentration range for the Ti.sup.f&c-SWCNT sensor was
0 ppm to 100 ppm. At these concentration ranges, the response
curves were relatively linear. These calculated sensitivities are
summarized in Tables 1 to 4.
[0200] The results showed that the sensitivities varied from sensor
to sensor for each concentration range. Such sensitivity variations
may be used in detection or quantification of more than one analyte
gas by constructing a sensor array comprising at least two sensors
where each sensor comprises a non-carbon material that is different
than that of the other. In such an array, one sensor may also
comprise only a carbon nanotube, since, as shown in this Example,
the Starting CNT sensor had a sensitivity value distinctly
different than that of the others.
[0201] From these sensitivity values, the sensor enhancement factor
for the NO.sub.2 detection may be determined by dividing the
sensitivity of a sensor comprising filled or filled and coated
SWCNT by that of a sensor comprising the starting SWCNT. The
enhancement factor quantifies the degree of improvement or
attenuation in the sensor's response to NO.sub.2 due to
incorporation of one or more non-carbon materials to a carbon
nanotube over the range of various concentrations. The enhancement
factors are shown in Tables 1 to 4.
[0202] These enhancement factors may also be used, instead of the
sensor sensitivity, in detection or quantification of more than one
analyte gas by constructing a sensor array device. Since each
sensor may respond to each analyte in a unique manner, providing a
unique enhancement factor; the array device comprising these
sensors produces a unique smell-print for each analyte. For
example, a smell-print for NO.sub.2 gas is schematically shown in
FIG. 15 and numerically on Table 1. Such smell-prints may be used
for detection or quantification purposes. Lu et al., in "A carbon
nanotube sensor array for sensitive gas discrimination using
principal component analysis", J. Electrochem. Chem., (2006),
volume 593, at section starting on page 108, left column-last
paragraph and ending on page 109, right column-first paragraph
disclose how to use such smell-prints for detection or
quantification in detail.
TABLE-US-00001 TABLE 1 Resistive Sensitivities (Circuit) of the
sensors in the concentration range of 0 ppm-10 ppm NO.sub.2. (The
sensitivity of the Ti.sup.f&c-SWCNT sensor was calculated in
the concentration range of 0 ppm to 100 ppm.) Resistive Minimum
Sensitivity (Circuit) Enhancement detection limit Sensor (%
ppm.sup.-1) factor (ppm) Ti.sup.f-SWCNT 3.4 1.70 4.7 .times.
10.sup.-4 Mn.sup.f&c-SWCNT 2.4 1.20 2.4 .times. 10.sup.-5
Fe.sup.f&c-SWCNT 2.2 1.10 1.4 .times. 10.sup.-3
Ni.sup.f&c-SWCNT 2.1 1.05 6.5 .times. 10.sup.-3 Starting SWCNT
2.0 1.00 4.3 .times. 10.sup.-5 Co.sup.f&c-SWCNT 1.7 0.85 6.9
.times. 10.sup.-3 TiH.sub.w.sup.f-SWCNT 0.4 0.20 2.0 .times.
10.sup.-1 Pt.sup.f&c-SWCNT 0.2 0.10 7.1 .times. 10.sup.-1
Ti.sup.f&c-SWCNT 0.17 0.28 7.0 .times. 10.sup.-3
Pd.sup.f&c-SWCNT 0.1 0.05 5.0 .times. 10.sup.-1
TABLE-US-00002 TABLE 2 Resistive Sensitivities (Circuit) of the
sensors in the concentration range of 100 ppm to 250 ppm NO.sub.2.
Resistive Sensitivity (Circuit) Sensor (% ppm.sup.-1) Enhancement
factor Pt.sup.f&c-SWCNT 0.25 2.72 Ti.sup.f&c-SWCNT 0.18
2.57 Pd.sup.f&c-SWCNT 0.16 1.74 TiH.sub.w.sup.f-SWCNT 0.15 1.63
Co.sup.f&c-SWCNT 0.095 1.03 Ni.sup.f&c-SWCNT 0.095 1.03
Starting SWCNT 0.092 1.00 Ti.sup.f-SWCNT 0.08 0.87
Fe.sup.f&c-SWCNT 0.07 0.76 Mn.sup.f&c-SWCNT 0.012 0.13
TABLE-US-00003 TABLE 3 Capacitive Sensitivities (Circuit) of the
sensors in the concentration range of 0 ppm-10 ppm NO.sub.2. (The
sensitivity of the Ti.sup.f&c-SWCNT sensor was calculated in
the concentration range of 0 ppm to 100 ppm.) Capacitive Minimum
Sensitivity (Circuit) Enhancement detection limit Sensor (%
ppm.sup.-1) factor (ppm) TiH.sub.w.sup.f-SWCNT 0.100 33.3 0.06
Fe.sup.f&c-SWCNT 0.060 20.0 0.05 Pt.sup.f&c-SWCNT 0.030
10.0 0.17 Pd.sup.f&c-SWCNT 0.014 4.7 0.25 Co.sup.f&c-SWCNT
0.010 3.3 0.25 Ni.sup.f&c-SWCNT 0.009 3.0 0.34 Ti.sup.f-SWCNT
0.009 3.0 0.33 Ti.sup.f&c-SWCNT 0.009 3.0 1.11
Mn.sup.f&c-SWCNT 0.003 1.0 0.99 Starting SWCNT 0.003 1.0
1.00
TABLE-US-00004 TABLE 4 Capacitive Sensitivities (Circuit) of the
sensors in the concentration range of 100 ppm to 250 ppm NO.sub.2.
Capacitive Sensitivity (Circuit) Sensor (% ppm.sup.-1) Enhancement
factor Pt.sup.f&c-SWCNT 1.54 770 Pd.sup.f&c-SWCNT 0.310 155
Ni.sup.f&c-SWCNT 0.100 50 TiH.sub.w.sup.f-SWCNT 0.084 42
Co.sup.f&c-SWCNT 0.075 38 Fe.sup.f&c-SWCNT 0.030 15
Ti.sup.f&c-SWCNT 0.022 11 Ti.sup.f-SWCNT 0.004 2
Mn.sup.f&c-SWCNT 0.004 2 Starting SWCNT 0.002 1
[0203] The minimum detection limits of the sensors were calculated
by using the Nyquist plots as follows. First, the sensor resistance
was measured for the background gas (i.e. nitrogen). Then, the
sensor resistance was measured for the 10 ppm NO.sub.2--N.sub.2 gas
mixture. The variation of the real part (Z') of the impedance curve
obtained from these measurements was .DELTA.Z'=Z'.sub.b-Z'.sub.mix.
This variation was caused by 10 ppm increase in NO.sub.2
concentration. The lowest resolution of the impedance analyzer was
about 1 ohm for analysis with these sensors. Therefore, the minimum
detection limit was 1 ohm.times.10 ppm/.DELTA.Z'. For example, the
detection limit for the Ti.sup.f-SWCNT sensor was calculated as
follows. Z'.sub.b for this sensor in N.sub.2 was about 70,100 ohm
and Z'.sub.mix in about 10 ppm NO.sub.2--N.sub.2 mixture was about
48,900 ohm. Then, .DELTA.Z'=70,100-48,900=21,200 ohm. Therefore,
the detection limit of this sensor for NO.sub.2 corresponded to 1
ohm.times.10 ppm/21,200 ohm=4.7.times.10.sup.-4 ppm or 0.47
ppb.
[0204] As shown in Tables 1 and 2, the minimum detection level of
NO.sub.2 concentration varied from sensor to sensor. For example,
the minimum detectable concentration for the Ti.sup.f-SWCNT sensor,
as determined by the Resistive Response (Circuit), was 0.47
parts-per-billion (ppb) NO.sub.2. It was 500 ppb NO.sub.2 for the
Pd.sup.f&c-SWCNT sensor. The results also demonstrated that
some of the sensors may measure NO.sub.2 concentrations down to ppb
levels.
[0205] The minimum detection level depends on the resolution
provided by the impedance analyzer when the sensors are analyzed
for the electronic property variation. Thus, with analyzers that
offer better resolutions than that of the Novocontrol analyzer, the
minimum detection level may further be decreased below the levels
discussed above. Therefore, these detection limits are for
illustration purpose and do not limit the scope of the instant
invention.
[0206] Above results indicated that the SWCNT sensors comprising
Ti, titanium hydrides, Fe, Co, Ni, Pd, Pt or combinations thereof
may be suitable for detection or quantification of NO.sub.2 above
the minimum detection limits of these sensors. These results
further indicated that a device comprising the Mn.sup.f&c-SWCNT
sensor, and the Resistive Response analysis unit or the Resistive
Response (Circuit) analysis unit may also be suitable for detection
or quantification of NO.sub.2 above the minimum detection limits of
these sensors.
Example 13
Sensor Comprising Ti Filled SWCNT Article for Detection or
Quantification of Ethanol Vapor
[0207] In this example, the sensors were prepared and analyzed in
the same manner as described in above examples, except the
following. The analyte gas was ethanol vapor.
[0208] For sensor impedance measurements in ethanol vapor as a test
gas, the parent ethanol vapor (about 1000 ppm in nitrogen) was
diluted with the ultra-high purity N.sub.2 to yield concentrations
of ethanol vapor varying in the range of 0 ppm to 250 ppm. The flow
rate of the diluted test gas was controlled at about 100 milliliter
per minute by means of an MKS multi-gas controller (Model 647C).
Each concentration of ethanol-nitrogen mixture was allowed to flow
over the assembled sensor for about 10 minutes prior to acquiring
the frequency dependent impedance values.
[0209] This sensor was then analyzed by modeling the impedance
using an equivalent circuit method shown in FIG. 3. The total
impedance (Z) was resolved into a real part (Z') and an imaginary
part (Z'') and a semicircular Nyquist plot was obtained, which was
modeled to intersect the Z' axis at two points. The difference
between these two intersection points yielded the real part of the
resistance.
[0210] It was found that R.sub.1, the uncompensated ohmic
resistance of the sensor, did not show any dependence to the
ethanol vapor concentration. That is, the contribution of R.sub.1
to the Resistive Response (Circuit) was less than 0.03% when the
response was averaged in the ethanol concentration range of 1 ppm
to 100 ppm. Likewise, the parameter C.sub.2, representing the
capacitance of the sensor, did not exhibit any meaningful
dependence on adsorbed ethanol concentration. That is, in the
concentrations ranging from 1 to 100 ppm, the average Capacitive
Response (Circuit) was less than 1%. It was thereby concluded that
the Electronic Property Responses, R.sub.1 and C.sub.2 are not
suitable for detection or quantification of the ethanol vapor with
Ti.sup.f-SWCNT sensor.
[0211] The other circuit parameter R.sub.2, showing the only
observable response, decreased in the presence of ethanol vapor.
The variation of the Resistive Response (Circuit) of the sensor as
a function of ethanol vapor concentration is shown in FIG. 17. Same
impedance measurements were repeated for the Starting SWCNT
sensor.
[0212] As shown in FIG. 17, the Resistive Response of the Starting
SWCNT sensor increased with increasing ethanol vapor concentration,
attaining about 5% at about 250 ppm ethanol vapor concentration.
This result indicated that the Starting SWCNT sensor is not very
sensitive, particularly at low ethanol concentrations.
[0213] As compared, the Ti.sup.f-SWCNT sensor showed considerably
higher response. These results indicated that the incorporation of
non-carbon material to the carbon not only significantly improved
the response of the sensor, but also made such sensors viable
alternatives to commercially existing sensors.
Example 14
Sensors for Detection and Quantification of Ethanol Vapor
[0214] In this example, the sensors were prepared and analyzed in
the same manner as described in above examples, except the
following. The analyte gas was ethanol vapor.
[0215] It was found that R.sub.1, the uncompensated ohmic
resistance of these sensors, did not show any dependence to the
ethanol vapor concentration. That is, the contribution of R.sub.1
to the Resistive Response (Circuit) was less than 0.03% when the
response was averaged in the ethanol concentration range of 1 ppm
to 100 ppm. Likewise, the parameter C.sub.2, representing the
capacitance of the sensor, did not exhibit any meaningful
dependence on adsorbed ethanol concentration. That is, in the
concentrations ranging from 1 to 100 ppm, the average Capacitive
Response (Circuit) was less than 1%. It was thereby concluded that
the Electronic Property Responses, R.sub.1 and C.sub.2, are not
suitable for detection or quantification of the ethanol vapor with
these sensors.
[0216] The variation of the Resistive Response (Circuit) of these
sensors as a function of ethanol vapor concentration is shown in
FIGS. 17 to 19. All sensors showed higher resistive responses than
the Starting SWCNT sensor for ethanol concentrations lower than 10
ppm. The Fe.sup.f&c-SWCNT, Co.sup.f&c-SWCNT,
Ti.sup.f-SWCNT, Pd.sup.f&c-SWCNT, Mn.sup.f&c-SWCNT,
Ti.sup.f&c-SWCNT and Pt.sup.f&c-SWCNT sensors showed
significantly higher resistive responses than the Starting SWCNT
sensor for all ethanol concentrations investigated. The
TiH.sub.w.sup.f-SWCNT sensor did not show significant resistive
response increase for ethanol concentrations above 10 ppm. This
sensor may be suitable for detection of ethanol vapors for
concentrations lower than 10 ppm.
[0217] The average Resistive Response (Circuit) of the
Ni.sup.f&c-SWCNT was very low, less than 0.53% at the ethanol
vapor concentrations ranging from 1 to 100 ppm. This result
indicated that a sensor device comprising only one
Ni.sup.f&c-SWCNT sensor and a Resistive Response (Circuit)
analysis unit cannot be used for detection or quantification of
ethanol vapor. However, this sensor can be used together with other
sensors in a device comprising a sensor array to detect or quantify
analyte gas(es).
[0218] The sensor sensitivities to ethanol vapor were calculated
from the slope of each sensor's response curve in the range of 0
ppm to 10 ppm ethanol concentration. These calculated sensitivities
are summarized in Table 5. The results showed that all the sensors
had sensitivities significantly higher than that of the Starting
SWCNT sensor for ethanol concentrations at about or below 10 ppm.
As shown in FIG. 20, all sensors comprising the organized
assemblies of this invention exhibited at least about one order of
magnitude enhancement in sensitivity to ethanol detection versus
the Starting SWCNT sensor.
TABLE-US-00005 TABLE 5 Resistive Sensitivities (Circuit) of the
sensors in the concentration range of 0 ppm to 10 ppm ethanol.
Resistive Sensitivity (Circuit) Minimum detection Sensor (%
ppm.sup.-1) limit (ppb) Fe.sup.f&c-SWCNT 2.5 0.23
Co.sup.f&c-SWCNT 2.2 31 Ti.sup.f-SWCNT 1.7 0.35
Pd.sup.f&c-SWCNT 1.2 14 Mn.sup.f&c-SWCNT 0.7 29
Ti.sup.f&c-SWCNT 0.5 14 Pt.sup.f&c-SWCNT 0.5 91
TiH.sub.w.sup.f-SWCNT 0.3 1000 Ni.sup.f&c-SWCNT 0.04 1000
Starting SWCNT 0.00045 500
[0219] As shown in Table 5, minimum detection level varied from
sensor to sensor. For example, minimum detectable signal for the
Fe.sup.f&c-SWCNT sensor was 0.23 parts-per-billion (ppb) of
ethanol at about 1 ohm. While the Starting SWCNT sensor produced a
minimum detection limit at about 500 ppb of ethanol, all other
sensors, with the exception of the TiH.sub.w.sup.f-SWCNT and
Ni.sup.f&c-SWCNT sensors, showed much lower minimum detection
limits. The minimum detection limits of the Fe.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT, Ti.sup.f-SWCNT, Pd.sup.f&c-SWCNT,
Mn.sup.f&c-SWCNT, Ti.sup.f&c-SWCNT and Pt.sup.f&c-SWCNT
sensors were lower than 100 ppb. Two of the metal-CNT hybrid
sensors, Fe.sup.f&c-SWCNT and Ti.sup.f-SWCNT, were capable of
detecting ethanol down to the parts-per-trillion (ppt) level.
[0220] Above results indicated that the SWCNT sensors comprising
Fe, Co, Ti, Pd, Mn, Pt, or mixtures (or alloys) thereof may
particularly be suitable for detection of ethanol at concentrations
above the minimum detection limits of these sensors. As for the
TiH.sub.w.sup.f-SWCNT sensor, the minimum detection limit is 1,000
ppb (i.e. 1 ppm). Therefore, this sensor may be suitable for
detecting ethanol vapor at concentrations in the range of 1 ppm to
10 ppm.
Example 15
Sensor Comprising Pt Filled and Coated SWCNT Article for Detection
or Quantification of Hydrogen Gas
[0221] A Pt.sup.f&c-SWCNT sensor and a Starting SWCNT sensor
were prepared and analyzed in the same manner as described in above
examples, except the following. The analyte gas in this example was
hydrogen.
[0222] For sensor impedance measurements in hydrogen as an analyte
gas, the parent hydrogen (about 5% in nitrogen) was diluted with
the ultra-high purity N.sub.2 to yield concentrations of hydrogen
varying in the range of 0% to 3%.
[0223] This sensor was then analyzed by modeling the impedance
using an equivalent circuit method, shown in FIG. 3. The total
impedance (Z) was resolved into a real part (Z') and an imaginary
part (Z'') and a semicircular Nyquist plot was obtained. This plot
was shown in FIG. 21 for about 1% hydrogen concentration. This plot
was modeled to intersect the Z' axis at two points. The difference
between these two intersection points yielded the real part of the
resistance. For example, the real resistance was about 1,420 ohms
for the Pt.sup.f&c-SWCNT sensor at about 1% hydrogen
concentration. Same measurements were repeated at various hydrogen
concentrations to determine the sensor response as a function of
the concentration. The same measurement was also repeated for UHP
N.sub.2 to determine the response of the sensor to the background
gas. The measurement results are shown in FIG. 22.
[0224] It was found that R.sub.1, the uncompensated ohmic
resistance of the sensor, did not show any dependence to the
hydrogen concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the response
was averaged in the hydrogen concentration range of 1 ppm to 100
ppm. Likewise, the parameter C.sub.2, representing the capacitance
of the sensor, did not exhibit any meaningful dependence on
adsorbed hydrogen concentration. That is, in the concentrations
ranging from 1 to 100 ppm, the average Capacitive Response
(Circuit) was less than 1%. It was thereby concluded that the
Electronic Property Responses, R.sub.1 and C.sub.2, are not
suitable for detection or quantification of hydrogen with the
Pt.sup.f&c-SWCNT sensor.
[0225] The other circuit parameter R.sub.2, showing the only
observable response, increased in the presence of hydrogen. The
variation of the Resistive Response (Circuit) of the sensor derived
from R.sub.2 as a function of hydrogen concentration is shown in
FIGS. 23 and 24. Same impedance measurements were repeated for the
Starting SWCNT sensor.
[0226] As shown in FIG. 23, the normalized resistive response of
the Starting SWCNT sensor was less than 3% for all hydrogen
concentrations.
[0227] As compared to this sensor, the Pt.sup.f&c-SWCNT sensor
showed considerably higher responses to all hydrogen
concentrations. These results indicated that the incorporation of
non-carbon material to the carbon significantly improved the
response of the sensor, thus it made such sensors viable
alternatives to commercially existing sensors.
Example 16
Sensors for Detection and Quantification of Hydrogen Gas
[0228] Various sensors were prepared and analyzed in the same
manner as described in above examples, except the following. The
analyte gas was hydrogen.
[0229] It was found that R.sub.1, the uncompensated ohmic
resistance of these sensors, did not show any dependence to the
hydrogen concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the response
was averaged in the hydrogen concentration range of 1 ppm to 100
ppm. Likewise, the parameter C.sub.2, representing the capacitance
of the sensor, did not exhibit any meaningful dependence on
adsorbed hydrogen concentration. That is, in the concentrations
ranging from 1 to 100 ppm, the average Capacitive Response
(Circuit) was less than 1%. It was thereby concluded that the
Electronic Property Responses, R.sub.1 and C.sub.2 are not suitable
for detection or quantification of hydrogen with these sensors.
[0230] The other circuit parameter R.sub.2, showing the only
observable response, increased in the presence of hydrogen for some
sensors. The variation of the Resistive Response (Circuit) of these
sensors as a function of hydrogen concentration derived from
R.sub.2 is shown in FIGS. 23 to 28. The Pt.sup.f&c-SWCNT,
Fe.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Ti.sup.f&c-SWCNT,
Ni.sup.f&c-SWCNT, Co.sup.f&c-SWCNT and
TiH.sub.w.sup.f-SWCNT sensors showed higher resistive responses
than the Starting SWCNT sensor for all hydrogen concentrations
investigated.
[0231] However, the Ti.sup.f-SWCNT sensor and the
Mn.sup.f&c-SWCNT sensor had average Resistive Responses
(Circuit) less than 1% and 0.45% respectively in the concentrations
ranging from 1 to 100 ppm. It was thereby concluded that the
Resistive Response (Circuit) derived from R.sub.2 is not suitable
for detection or quantification of the hydrogen with the
Ti.sup.f-SWCNT sensor and the Mn.sup.f&c-SWCNT sensor.
[0232] The calculated sensitivities for these sensors are
summarized in Table 6. The results showed that the
Pt.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT,
Ti.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT, Co.sup.f&c-SWCNT
and TiH.sub.w.sup.f-SWCNT sensors had sensitivities higher than
that of the Starting SWCNT sensor for hydrogen concentrations at
about or below 50 ppm.
[0233] As shown in FIG. 29, the Pt.sup.f&c-SWCNT,
Fe.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Ti.sup.f&c-SWCNT,
Ni.sup.f&c-SWCNT, Co.sup.f&c-SWCNT and
TiH.sub.w.sup.f-SWCNT sensors exhibited at least about three-fold
enhancement in sensitivity to hydrogen detection over that of the
Starting SWCNT sensor.
[0234] The minimum detection limits, as shown in Table 6, varied
from sensor to sensor. For example, the minimum detection limit for
the Fe.sup.f&c-SWCNT sensor was about 0.159 ppm of hydrogen at
about 1 ohm. While the Starting SWCNT sensor produced a minimum
detection limit at about 1.61 ppm of hydrogen, the minimum
detection limits of the Fe.sup.f&c-SWCNT and
Pt.sup.f&c-SWCNT sensors were lower than 1 ppm.
TABLE-US-00006 TABLE 6 Resistive Sensitivities (Circuit) of the
sensors at two different hydrogen concentration ranges. Resistive
Sensitivity (Circuit) (% ppm.sup.-1) High Concen- Minimum Low
Concen- tration Range detection tration Range (1-3% limit Sensor
(0-50 ppm hydrogen) hydrogen) (ppm) Pt.sup.f&c SWCNT 0.110 7.9
.times. 10.sup.-5 0.714 Fe.sup.f&c SWCNT 0.086 2.0 .times.
10.sup.-6 0.159 Pd.sup.f&c SWCNT 0.084 8.7 .times. 10.sup.-6
3.03 Ti.sup.f&c SWCNT 0.082 3.0 .times. 10.sup.-6 3.57
Ni.sup.f&c SWCNT 0.077 4.1 .times. 10.sup.-5 3.33
Co.sup.f&c SWCNT 0.077 4.0 .times. 10.sup.-6 2.70
TiH.sub.w.sup.f SWCNT 0.070 1.6 .times. 10.sup.-6 2.78 Ti.sup.f
SWCNT 0.013 2.6 .times. 10.sup.-5 1.43 Mn.sup.f&c SWCNT 0.003
1.8 .times. 10.sup.-6 5.56 Starting 0.018 1.4 .times. 10.sup.-5
1.61 SWCNT
[0235] Above results indicated that the SWCNT sensors comprising
Pt, Fe, Pd, Ti, Co, Ni, or mixtures (or alloys) thereof, with the
exception of the Ti.sup.f-SWCNT sensor, may particularly be
suitable for detection and quantification of hydrogen at
concentrations above the minimum detection limits of these
sensors.
Example 17
Sensor Comprising Pt Filled and Coated SWCNT Article for Detection
or Quantification of Carbon Dioxide
[0236] A Pt.sup.f&c-SWCNT sensor and a Starting SWCNT sensor
were prepared and analyzed in the same manner as described in above
examples, except the following. The analyte gas in this example was
carbon dioxide.
[0237] For sensor impedance measurements in carbon dioxide as an
analyte gas, the parent carbon dioxide (about 1000 ppm in nitrogen)
was diluted with the ultra-high purity N.sub.2 to yield
concentrations of carbon dioxide varying in the range of 1 ppm to
1000 ppm.
[0238] It was found that R.sub.1, the uncompensated ohmic
resistance of the sensor, did not show any dependence to the carbon
dioxide concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the response
was averaged in the carbon dioxide concentration range of 1 ppm to
100 ppm. Likewise, the parameter C.sub.2, representing the
capacitance of the sensor, did not exhibit any meaningful
dependence on adsorbed carbon dioxide concentration. That is, in
the concentrations ranging from 1 to 100 ppm, the average
Capacitive Response (Circuit) was less than 1%. It was thereby
concluded that the Electronic Property Responses, R.sub.1 and
C.sub.2 are not suitable for detection or quantification of the
carbon dioxide with the Pt.sup.f&c-SWCNT sensor.
[0239] The other circuit parameter R.sub.2, showing the only
observable response, increased in the presence of increasing carbon
dioxide. The variation of the Resistive Response (Circuit) of the
sensor as a function of carbon dioxide concentration, derived from
R.sub.2, is shown in FIGS. 30 and 31.
[0240] Same impedance measurements were repeated for the Starting
SWCNT sensor. As shown in FIG. 30, the Resistive Response of the
Starting SWCNT sensor was less than 3.2% for all carbon dioxide
concentrations.
[0241] As compared to this sensor, the Pt.sup.f&c-SWCNT sensor
showed considerably higher responses to all carbon dioxide
concentrations. These results indicated that the incorporation of a
non-carbon material to the carbon not only significantly improved
the response of the sensor, but also made such sensors viable
alternatives to commercially existing sensors.
Example 18
Sensors for Detection and Quantification of Carbon Dioxide
[0242] Various sensors were prepared and analyzed in the same
manner as described in above examples, except the following. The
analyte gas was carbon dioxide.
[0243] It was found that R.sub.1, the uncompensated ohmic
resistance of these sensors, did not show any dependence to the
carbon dioxide concentration. That is, the contribution of R.sub.1
to the Resistive Response (Circuit) was less than 0.03% when the
response was averaged in the carbon dioxide concentration range of
1 ppm to 100 ppm. Likewise, the parameter C.sub.2, representing the
capacitance of the sensor, did not exhibit any meaningful
dependence on adsorbed carbon dioxide concentration, except for the
Ti.sup.f&c-SWCNT sensor. That is, in the concentration range of
1 ppm to 100 ppm, the Capacitive Response (Circuit) was less than
1% when the response was averaged for this concentration range. It
was thereby concluded that the Electronic Property Responses,
R.sub.1 and C.sub.2 are not suitable for detection or
quantification of the carbon dioxide with these sensors, except
with the Ti.sup.f&c-SWCNT sensor.
[0244] The other circuit parameter R.sub.2, showing the only
observable response, increased in the presence of increasing carbon
dioxide for some sensors. The variation of the Resistive Response
(Circuit) of these sensors, derived from R.sub.2, as a function of
carbon dioxide concentration is shown in FIGS. 30 to 35. The
Pt.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Mn.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT, Ti.sup.f&c-SWCNT, and
TiH.sub.w.sup.f-SWCNT sensors showed higher Resistive Responses
than that of the Starting SWCNT sensor for all carbon dioxide
concentrations investigated. The Ni.sup.f&c-SWCNT sensor showed
higher Resistive Responses than that of the Starting SWCNT sensor
up to about 400 ppm carbon dioxide concentration. However, the
Ti.sup.f-SWCNT and Fe.sup.f&c-SWCNT sensors showed lower
Resistive Responses than that of the Starting SWCNT sensor.
[0245] Moreover, the Ti.sup.f&c-SWCNT sensor, as shown in FIG.
36, had an observable C.sub.2 response, i.e. Capacitive Response
(Circuit). It reached as high as 12.5%. Therefore, a device
comprising the Ti.sup.f&c-SWCNT sensor and the analysis unit
that measures the Capacitive Response (Circuit) are within the
scope of this invention for detection or quantification of the
carbon dioxide.
[0246] The calculated sensitivities, derived from R.sub.2, are
summarized in Table 7. The results showed that the
Pt.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT, Mn.sup.f&c-SWCNT,
Ni.sup.f&c-SWCNT, Co.sup.f&c-SWCNT, Ti.sup.f&c-SWCNT,
and TiH.sub.w.sup.f-SWCNT sensors had sensitivities higher than
that of the Starting SWCNT sensor for carbon dioxide concentrations
at about or below 10 ppm. These results, however, further showed
that the Ti.sup.f-SWCNT and Fe.sup.f&c-SWCNT sensors had lower
sensitivities than the Starting SWCNT sensor.
TABLE-US-00007 TABLE 7 Resistive Sensitivities (Circuit) of the
sensors at two different carbon dioxide concentration ranges.
Resistive Sensitivity (Circuit) (% ppm.sup.-1) High Concen- Minimum
Low Concen- tration Range detection tration Range (100-1000 limit
Sensor (0-10 ppm CO.sub.2) ppm CO.sub.2) (ppm) TiH.sub.w.sup.f
SWCNT 0.30 7.0 .times. 10.sup.-4 1.10 Pt.sup.f&c SWCNT 0.24 7.0
.times. 10.sup.-4 0.31 Pd.sup.f&c SWCNT 0.20 8.0 .times.
10.sup.-4 0.39 Mn.sup.f&c SWCNT 0.17 8.0 .times. 10.sup.-4 1.18
Ti.sup.f&c SWCNT 0.15 1.0 .times. 10.sup.-3 2.50 Ni.sup.f&c
SWCNT 0.15 1.0 .times. 10.sup.-4 0.66 Co.sup.f&c SWCNT 0.14 5.0
.times. 10.sup.-4 0.87 Ti.sup.f SWCNT 0.12 5.0 .times. 10.sup.-4
1.50 Fe.sup.f&c SWCNT 0.08 2.0 .times. 10.sup.-4 0.05 Starting
0.13 6.0 .times. 10.sup.-4 0.90 SWCNT
[0247] As shown in FIG. 37, the Pt.sup.f&c-SWCNT,
Pd.sup.f&c-SWCNT, Mn.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT, Ti.sup.f&c-SWCNT, and
TiH.sub.w.sup.f-SWCNT sensors exhibited enhanced sensitivity to
carbon dioxide detection over that of the Starting SWCNT
sensor.
[0248] The minimum detection limits, as shown in Table 7, varied
from sensor to sensor. For example, the minimum detectable signal
for the Fe.sup.f&c-SWCNT sensor was about 0.05 ppm of carbon
dioxide at about 1 ohm. While the Starting SWCNT sensor produced a
minimum detectable signal at about 0.90 ppm of carbon dioxide, the
detection limits of the Fe.sup.f&c-SWCNT, Pd.sup.f&c-SWCNT,
Ni.sup.f&c-SWCNT, Co.sup.f&c-SWCNT and Pt.sup.f&c-SWCNT
sensors were lower than 0.90 ppm.
[0249] The above results indicated that the SWCNT sensors
comprising Pt, Pd, Ti, Co, Ni, Mn, or mixtures (or alloys) thereof,
with the exception of the Ti.sup.f-SWCNT and Fe.sup.f&c-SWCNT
sensors, may particularly be suitable for detection and
quantification of carbon dioxide at concentrations above the
minimum detection limits of these sensors.
Example 19
Sensor Comprising Pt Filled and Coated SWCNT Article for Detection
or Quantification of Oxygen
[0250] A Pt.sup.f&c-SWCNT sensor and a Starting SWCNT sensor
were prepared and analyzed in the same manner as described in above
examples, except the following. The analyte gas in this example was
oxygen.
[0251] For sensor impedance measurements in oxygen as an analyte
gas, the parent oxygen (about 1000 ppm in nitrogen) was diluted
with the ultra-high purity N.sub.2 to yield concentrations of
oxygen varying in the range of 1 ppm to 1000 ppm.
[0252] It was found that R.sub.1, the uncompensated ohmic
resistance of the sensor, did not show any dependence to the oxygen
concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the response
was averaged in the oxygen concentration range of 1 ppm to 100 ppm.
It was thereby concluded that the Electronic Property Response
R.sub.1 is not suitable for detection or quantification of the
oxygen with the Pt.sup.f&c-SWCNT sensor.
[0253] The other circuit parameters R.sub.2 and C.sub.2 increased
in the presence of oxygen. The variation of the Resistive Response
(Circuit) of the sensor, derived from R.sub.2, as a function of
oxygen concentration is shown in FIGS. 38 and 39.
[0254] Same impedance measurements were repeated for the Starting
SWCNT sensor. As shown in FIG. 38, the Resistive Response of the
Starting SWCNT sensor was less than 3.0% for all oxygen
concentrations. As compared to this sensor, the
Pt.sup.f&c-SWCNT sensor showed considerably higher responses to
all oxygen concentrations.
[0255] The variation of the Capacitive Response (Circuit) of the
sensor as a function of oxygen concentration is shown in FIG. 44.
Same impedance measurements were repeated for the Starting SWCNT
sensor. As shown in FIG. 44, the Capacitive Response of the
Starting SWCNT sensor was less than 0.5% for all oxygen
concentrations. As compared to this sensor, the
Pt.sup.f&c-SWCNT sensor showed considerably higher responses to
all oxygen concentrations.
[0256] These results indicated that the incorporation of a
non-carbon material to the carbon not only significantly improved
the response of the sensor, but also made such sensors viable
alternatives to commercially existing sensors.
Example 20
Sensors for Detection and Quantification of Oxygen
[0257] Various sensors were prepared and analyzed in the same
manner as described in above examples, except the following. The
analyte gas was oxygen.
[0258] It was found that R.sub.1, the uncompensated ohmic
resistance of these sensors, did not show any dependence to the
oxygen concentration. That is, the contribution of R.sub.1 to the
Resistive Response (Circuit) was less than 0.03% when the response
was averaged in the oxygen concentration range of 1 ppm to 100 ppm.
It was thereby concluded that the Electronic Property Response
R.sub.1 is not suitable for detection or quantification of the
oxygen with these sensors.
[0259] The variation of the Resistive Response (Circuit) of these
sensors, derived from R.sub.2, as a function of oxygen
concentration is shown in FIGS. 38 to 43. The Pt.sup.f&c-SWCNT,
Pd.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT, Fe.sup.f&c-SWCNT,
Co.sup.f&c-SWCNT, and TiH.sub.w.sup.f-SWCNT sensors showed
higher resistive responses than the Starting SWCNT sensor for all
oxygen concentrations investigated. The Ti.sup.f-SWCNT sensor
showed similar Resistive Responses to that of the Starting SWCNT
sensor over all oxygen concentrations. However, the
Ti.sup.f&c-SWCNT and Mn.sup.f&c-SWCNT sensors showed lower
Resistive Responses than that of the Starting SWCNT sensor.
[0260] The variation of the Capacitive Response (Circuit) of the
sensors as a function of oxygen concentration is shown in FIGS. 44
to 46. All the sensors had an increased Capacitive Response
(circuit) to varying oxygen concentration compared to the response
of the Starting SWCNT sensor.
[0261] The calculated sensitivities, derived from R.sub.2 and
C.sub.2, are summarized in Table 8. The results showed that all
non-carbon containing SWCNT sensors had sensitivities higher than
that of the Starting SWCNT sensor for oxygen concentrations at
about or below 10 ppm.
[0262] The sensor enhancement factors calculated from R.sub.2
sensitivities are shown in FIG. 47. The Pt.sup.f&c-SWCNT,
Pd.sup.f&c-SWCNT, Ni.sup.f&c-SWCNT, Co.sup.f&c-SWCNT,
Ti.sup.f&c-SWCNT, and TiH.sub.w.sup.f-SWCNT sensors exhibited
enhanced resistive sensitivity to oxygen detection over that of the
Starting SWCNT sensor.
TABLE-US-00008 TABLE 8 Resistive and Capacitive Sensitivities of
the sensors for oxygen gas. Resistive Sensitivity Capacitive
Sensitivity (Circuit), (Circuit), Sensor (% ppm.sup.-1) (%
ppm.sup.-1) Ti.sup.f-SWCNT 0.14 0.12 Ti.sup.f&c-SWCNT 0.16 0.55
Mn.sup.f&c-SWCNT 0.18 0.05 Fe.sup.f&c-SWCNT 0.11 0.16
Co.sup.f&c-SWCNT 0.15 0.10 Ni.sup.f&c-SWCNT 0.19 0.30
TiH.sub.w.sup.f-SWCNT 0.23 0.03 Pd.sup.f&c-SWCNT 0.17 0.09
Pt.sup.f&c-SWCNT 0.21 0.10 Starting SWCNT 0.15 0.02
[0263] Table 9 summarizes results of Examples 11-20: the Electronic
Property Responses of different sensors to different analyte gases.
The NO.sub.2 results are summarized from Examples 11-12. The
ethanol vapor results are summarized from Examples 13-14. The
H.sub.2 results are summarized from Examples 15-16. The CO.sub.2
results are summarized from Examples 17-18. The O.sub.2 results are
summarized from Examples 19-20.
TABLE-US-00009 TABLE 9 Electronic Property Responses of the sensors
to different analytes, when this response is averaged at an analyte
concentration range of 1 ppm to 100 ppm. Ethanol NO.sub.2 Vapor
H.sub.2 CO.sub.2 O.sub.2 Resistive Capacitive Resistive Resistive
Resistive Capacitive Resistive Capacitive Resistive Response
Response Response Response Response Response Response Response
Sensor Response (Circuit) (Circuit) (Circuit) (Circuit) (Circuit)
(Circuit) (Circuit) (Circuit) Starting-SWCNT X X X X Ti.sup.f-SWCNT
X X Ti.sup.f&c-SWCNT TiH.sub.w.sup.f-SWCNT X
Mn.sup.f&c-SWCNT X X X X Fe.sup.f&c-SWCNT X
Co.sup.f&c-SWCNT X X Ni.sup.f&c-SWCNT X X
Pd.sup.f&c-SWCNT X Pt.sup.f&c-SWCNT X Sensors denoted with
the symbol " " have Electronic Property Responses equivalent to or
higher than 1%. Sensors denoted with the symbol "X" have Electronic
Property Responses lower than 1 %.
Example 21
Sensor Array Device for Detection or Quantification of a Gas
Mixture Comprising Two Analytes, NO.sub.2 and Ethanol Vapor
[0264] In this example, an array device is constructed for
detection or quantification of a gas mixture comprising two
analytes, NO.sub.2 and ethanol vapor. This device works in the
concentration range of 0 ppm to 100 ppm range for each analyte gas.
The background gas is nitrogen.
[0265] This array device comprises two sensors: one
Ni.sup.f&c-SWCNT sensor connected to a Resistive Response
(Circuit) analysis unit and one Mn.sup.f&c-SWCNT sensor
connected to another Resistive Response (Circuit) analysis unit.
The construction of such a device is schematically demonstrated in
FIG. 48.
[0266] As disclosed in Example 12, the Ni.sup.f&c-SWCNT sensor
had a Resistive Response (Circuit) to NO.sub.2 gas. However, as
disclosed in Example 14, the average Resistive Response (Circuit)
of the Ni.sup.f&c-SWCNT sensor was very low, less than 0.53% in
the ethanol concentrations ranging from 1 to 100 ppm. Thus, the
response of this sensor to ethanol is negligible. Therefore, this
sensor may only detect or quantify the NO.sub.2 gas, but not the
ethanol vapor. In other words, any response of this sensor is due
to the NO.sub.2 gas.
[0267] As disclosed in Example 14, the Mn.sup.f&c-SWCNT sensor
had a Resistive Response (Circuit) to the ethanol vapor. As also
disclosed in Example 12, this sensor also had a Resistive Response
(Circuit) to the NO.sub.2 gas.
[0268] The detection or quantification is carried out as follows.
First, the NO.sub.2--N.sub.2 gas mixture is introduced at various
known concentrations. Then, the Ni.sup.f&c-SWCNT sensor and the
Mn.sup.f&c-SWCNT sensor are calibrated and their sensitivity is
determined. After this step, the Mn.sup.f&c-SWCNT sensor is
calibrated and its sensitivity is determined by introducing the
ethanol--N.sub.2 gas mixture at various known concentrations.
[0269] After these calibrations, the gas mixture with unknown
analyte gas concentration is introduced. During the quantification,
first the unknown concentration of NO.sub.2 is determined by using
the Resistive Response (Circuit) of the Ni.sup.f&c-SWCNT
sensor. By using this measured amount, the Resistive Response
(Circuit) of the Mn.sup.f&c-SWCNT sensor to NO.sub.2 gas is
calculated.
[0270] After this step, the Resistive Response (Circuit) of the
Mn.sup.f&c-SWCNT sensor is measured. The calculated response of
this sensor to NO.sub.2 gas is then subtracted from this
measurement to yield this sensor's response to the ethanol vapor.
The unknown concentration of the ethanol vapor is thereby
determined.
[0271] The invention, and the manner and process of making and
using it, are now described in such full, clear, concise and exact
terms as to enable any person skilled in the art to which it
pertains, to make and use the same. It is to be understood that the
foregoing describes preferred embodiments of the present invention
and that modifications may be made therein without departing from
the scope of the present invention as set forth in the claims. To
particularly point out and distinctly claim the subject matter
regarded as invention, the following claims conclude this
specification.
* * * * *