U.S. patent application number 15/527635 was filed with the patent office on 2017-11-30 for benzene sensors using metal oxides and associated methods.
The applicant listed for this patent is Honeywell International Inc.. Invention is credited to Cornel Cobianu, Bogdan Serban, Alisa Stratulat.
Application Number | 20170343501 15/527635 |
Document ID | / |
Family ID | 54771181 |
Filed Date | 2017-11-30 |
United States Patent
Application |
20170343501 |
Kind Code |
A1 |
Serban; Bogdan ; et
al. |
November 30, 2017 |
BENZENE SENSORS USING METAL OXIDES AND ASSOCIATED METHODS
Abstract
In an embodiment, a method for fabrication of VOC sensor
comprises dissolving one or more metal precursors in a reagent to
form a solution, adding a reducing agent to precipitate a metal
oxide compound, subjecting the solution to acoustic energy,
recovering a nanoscale metal oxide, and forming a sensing layer in
a chemo-resistance sensor using the nanoscale metal oxide.
Inventors: |
Serban; Bogdan; (Bucharest,
RO) ; Cobianu; Cornel; (Bucharest, RO) ;
Stratulat; Alisa; (Bucharest, RO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Honeywell International Inc. |
Morris Plains |
NJ |
US |
|
|
Family ID: |
54771181 |
Appl. No.: |
15/527635 |
Filed: |
November 11, 2015 |
PCT Filed: |
November 11, 2015 |
PCT NO: |
PCT/US2015/060187 |
371 Date: |
May 17, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62081657 |
Nov 19, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 21/33 20130101;
G01N 21/75 20130101; G01N 33/54366 20130101; G01N 2021/7773
20130101; G01N 31/22 20130101; G01N 33/0047 20130101; G01N
2021/7756 20130101; G01N 27/127 20130101 |
International
Class: |
G01N 27/12 20060101
G01N027/12; G01N 33/00 20060101 G01N033/00 |
Claims
1-15. (canceled)
16. A method for fabrication of VOC sensor, the method comprising:
dissolving one or more metal precursors in a reagent to form a
solution, adding a reducing agent to precipitate a metal oxide
compound, subjecting the solution to acoustic energy, recovering a
nanoscale metal oxide, and forming a sensing layer in a
chemo-resistance sensor using the nanoscale metal oxide.
17. The method of claim 16, further comprising: adding a surfactant
to the solution prior to subjecting the solution to the acoustic
energy.
18. The method of claim 17, wherein the one or more metal
precursors comprise copper nitrate and chromium nitrate, wherein
the nanoscale metal oxide comprises CuO and Cr.sub.2O.sub.3
nanocomposite powders having a Cu/Cr molar ratio between about 0.01
and about 0.8.
19. The method of claim 18, wherein the solution comprises
hydrazine, and wherein the surfactant comprises
cetyltrimethylammonium.
20. The method of claim 18, wherein the reducing agent comprises an
aqueous solution of NaOH, urea, or a combination thereof, and
wherein the surfactant comprises CTAB, oleyl amine, or any
combination thereof.
21. The method of claim 17, wherein the one or more metal
precursors comprise cobalt (II) nitrate and cerium (III) nitrate,
wherein the nanoscale metal oxide comprises
Co.sub.3O.sub.4--CeO.sub.2 nanocomposite powders having a Co/Ce
molar ratio between about 1:1 and about 16:1.
22. The method of claim 21, wherein the reducing agent comprises
NaOH, urea, or any combination thereof, wherein the surfactant
comprises CTAB, olyel amine, or any combination thereof.
23. The method of claim 17, wherein the one or more metal
precursors comprise cerium (III) nitrate and manganese (II)
nitrate, and wherein the nanoscale metal oxide comprises
Ce.sub.2O.sub.3--MnO.sub.x nanocomposite powders having a Ce/Mn
molar ration between about 1:7 and about 5:7.
24. The method of claim 22, wherein the reducing agent comprises
NaOH, urea, or any combination thereof, wherein the surfactant
comprises CTAB, olyel amine, or any combination thereof.
25. The method of claim 17, wherein the one or more metal
precursors comprise cerium nitrate, aluminum nitrate, and
hexachloroplatinic acid.
26. The method of claim 25, wherein the nanoscale metal oxide
comprises Pt, Al.sub.2O.sub.3, and CeO.sub.2, wherein the Pt is
present in an amount between about 0.5-1.5 wt %, and wherein the
CeO.sub.2 is present in an amount of between about 10-40 wt %.
27. The method of claim 25, wherein the reducing agent comprises
NaOH, urea, or any combination thereof, wherein the surfactant
comprises CTAB, olyel amine, or any combination thereof.
28. The method of claim 16, wherein forming the sensing layer
comprises forming thin films or thick films using the nanoscale
metal oxide.
29. A VOC sensor comprising: a substrate, a plurality of leads
disposed on the substrate, and a metal oxide nanocomposite film
disposed in electrical contact with at least two of the plurality
of leads.
30. The VOC sensor of claim 29, wherein the metal oxide
nanocomposite film comprises a semiconductor film.
31. The VOC sensor of claim 29, wherein the metal oxide
nanocomposite film comprises a nanostructured CuO--Cr.sub.2O.sub.3
composite.
32. The VOC sensor of claim 30, wherein the metal oxide
nanocomposite film comprises a nanostructured
Co.sub.3O.sub.4--CeO.sub.2 composite.
33. The VOC sensor of claim 29, wherein the metal oxide
nanocomposite film comprises a nanostructured CeO.sub.2--MnO.sub.x
composite.
34. The VOC sensor of claim 29, wherein the metal oxide
nanocomposite film comprises a nanostructured
Pt--Al.sub.2O.sub.3--CeO.sub.2.
35. The VOC sensor of claim 29, wherein the nanocomposite film
comprises a plurality of nanoscale metal oxide particles.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 62/081,657 (entitled GAS-PHASE BENZENE SENSOR
AND ASSOCIATED METHODS filed Nov. 19, 2014), which is incorporated
herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
BACKGROUND
[0004] Detection of benzene and similar volatile organic compounds
(VOC) is of high importance for safety and process control in
chemical, petrochemical, steel and other manufacturing industries,
as well as for minimizing environment pollution with these harmful
gases. Benzene (C.sub.6H.sub.6) is a highly flammable, toxic, human
carcinogen, organic hydrocarbon. It is widely used as an
intermediate in processes leading to plastics, nylon, lubricants,
coke, fertilizers, detergents, etc. In recent years, in many
regions, including US and EU, benzene has replaced lead in gasoline
composition. Due to its increased harmful potential, severe
regulations have been imposed against its industrial use. In EU,
gas can contain maximum 1% benzene by volume, while in US the upper
limit is 0.62%. Monitoring benzene concentration is a vital
requirement for the personal protection of people working in oil
and gas storage and transportation, oil refineries, petrochemical
industry. At concentration levels higher than 10,000 ppm, benzene
can be lethal, while repeated exposures at much lower levels can
lead to cancer, heart and brain failures, and endocrine diseases.
The level over which benzene becomes harmful is currently set at
the threshold limit value (TLV) of 0.5 ppm.
[0005] Currently, benzene sensing is performed by employing several
techniques: multi-gas monitors, metal-oxides (MOx) based
chemo-resistors, electrochemical detectors, fixed or portable gas
chromatographs, single gas (colorimetric) detection tubes, and/or
photoionization detectors (PIDs). A combination of the last two
technologies leads to Ultra RAE3000, a portable benzene and
compound-specific VOC monitor commercialized by Honeywell's RAE
Systems. Ultra RAE3000 employs a PID, a low energy UV lamp and
pre-filter tubes. Honeywell top-solution has an accuracy of
+/-10%.
[0006] Other sensors that are commercially available for such
industrial applications, as well as breath alcohol portable
detectors, include a thick film of SnO.sub.2 deposited on ceramic
substrate, which is heated on the other side by a platinum heater.
Even if this sensor is recommended not only for domestic
applications, but also for portable applications, it is consuming
about 660 mW for heating the substrate to the optimum sensing
temperature and reading the detector response. Such a level of
power consumption is determining a frequent battery replacement in
portable applications, which may raise safety issues in the field
operation.
[0007] In addition, the above noted sensors are detecting these
VOC's gases only at relatively high concentrations, above 50 ppm,
while the present requirements for benzene in the ambient are as
follow: the threshold limit value (TLV) is 0.5 ppm, the short term
exposure limit (STEL) is 2.5 ppm, while the immediately dangerous
to health and life (IDHL) level is 500 ppm. Therefore, in safety
applications, it is useful to detect much lower gas concentrations
and then give an alarm and take an early stage action against any
hazardous situation. Therefore, there is a strong motivation for
increasing the sensitivity of the existing commercial sensors, as
well as decreasing power consumption of VOC sensors so that an
electric power much below 100 mW to be used and concentrations much
below 50 ppm to be detected for VOC gases.
[0008] It is already largely accepted by the business and
scientific community that the use of nanostructured sensing
materials is increasing the sensitivity due to its material
architecture and it is allowing the reduction of the power
consumption, due to their large specific area and increased
porosity, which are thus increasing the number of active sensing
sites, while their surface energy is high enough for the sensing
reactions to take place without too much thermal energy added from
outside.
SUMMARY
[0009] In an embodiment, a method for fabrication of VOC sensor
comprises dissolving one or more metal precursors in a reagent to
form a solution, adding a reducing agent to precipitate a metal
oxide compound, subjecting the solution to acoustic energy,
recovering a nanoscale metal oxide, and forming a sensing layer in
a chemo-resistance sensor using the nanoscale metal oxide.
[0010] In an embodiment, a VOC sensor comprises a substrate, a
plurality of leads disposed on the substrate, and a metal oxide
nanocomposite film disposed in electrical contact with at least two
of the plurality of leads.
[0011] These and other features will be more clearly understood
from the following detailed description taken in conjunction with
the accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the present disclosure,
reference is now made to the following brief description, taken in
connection with the accompanying drawings and detailed description,
wherein like reference numerals represent like parts.
[0013] FIG. 1 schematically illustrates another benzene sensor
according to an embodiment.
DETAILED DESCRIPTION
[0014] It should be understood at the outset that although
illustrative implementations of one or more embodiments are
illustrated below, the disclosed systems and methods may be
implemented using any number of techniques, whether currently known
or not yet in existence. The disclosure should in no way be limited
to the illustrative implementations, drawings, and techniques
illustrated below, but may be modified within the scope of the
appended claims along with their full scope of equivalents.
[0015] The following brief definition of terms shall apply
throughout the application:
[0016] The term "comprising" means including but not limited to,
and should be interpreted in the manner it is typically used in the
patent context;
[0017] The phrases "in one embodiment," "according to one
embodiment," and the like generally mean that the particular
feature, structure, or characteristic following the phrase may be
included in at least one embodiment of the present invention, and
may be included in more than one embodiment of the present
invention (importantly, such phrases do not necessarily refer to
the same embodiment);
[0018] If the specification describes something as "exemplary" or
an "example," it should be understood that refers to a
non-exclusive example;
[0019] The terms "about" or approximately" or the like, when used
with a number, may mean that specific number, or alternatively, a
range in proximity to the specific number, as understood by persons
of skill in the art field; and
[0020] If the specification states a component or feature "may,"
"can," "could," "should," "would," "preferably," "possibly,"
"typically," "optionally," "for example," "often," or "might" (or
other such language) be included or have a characteristic, that
particular component or feature is not required to be included or
to have the characteristic. Such component or feature may be
optionally included in some embodiments, or it may be excluded.
[0021] Disclosed herein are two VOC sensors that can detect
benzene. In an embodiment, a nanocomposite metal oxide can be
formed and used in a chemo-resistor sensor. In this sensor, a metal
oxide film or layer can be disposed over two interdigitated
electrodes. A resistance detected between the two electrodes can be
changed by the presence of benzene reacting with the metal oxide.
The resistance can increase or decrease based on the specific metal
oxide used. A sonochemical synthesis method can be used to form the
metal oxides used in the sensor described herein. This preparation
technique can produce a nanoscale metal oxide material having a
relatively high surface area. By increasing the surface area
relative to other metal oxide detectors, the operating power can be
reduced to provide a similar detection level. This may provide a
sensor having a longer battery life.
[0022] FIG. 1 schematically illustrates a cross-sectional view of a
chemo-resistor sensor 100. The sensor 100 generally comprises a
substrate 102 having two or more electrically conductive leads 104,
106 and a sensing layer comprising a semiconductor film 108 in
electrical contact with the leads 104, 106 (e.g., metal electrodes,
etc.). The substrate 102 can be electrically insulating (e.g.,
silicon dioxide, alumina, polymer, etc.). The leads 104, 106 can be
disposed adjacent one another, and in some embodiments, the leads
can be interdigitated. A housing 112 can be disposed about the
various elements of the sensor 100 to protect the internal
components and provide a controlled entrance for the various
chemical compounds to enter and react at the semiconductor film
surface. For example, an aperture 114 may control the exposure of
the semiconductor film 108 to a component such as benzene present
in the atmosphere adjacent the sensor 100.
[0023] The leads 104, 106 and/or the heating element 110 can be
coupled to a suitable control and detection circuitry. The control
circuitry can be configured to detect a resistance between the
leads 104, 106, which can be affected by one or more reactions
occurring in the semiconductor film 108. Semiconductor
manufacturing techniques such as sputtering, vapor deposition,
masking, and the like can be used to deposit the leads 104, 106 and
the optional heating element 110 on the substrate 102. Any suitable
film deposition techniques such as maskless direct printing, screen
printing, or the like can be used to dispose the semiconductor film
108 on the sensor 100, where one method is described in more detail
below.
[0024] An optional heating element 110 can be disposed in thermal
contact with the substrate 102. Since the substrate 102 can also be
thermally insulating, the heating element 110 can be disposed on
the side of the substrate with the leads 104, 106 and the
semiconductor layer 108. For example, the heating element 110 can
comprise a resistive heating element interdigitated with the leads
104, 106.
[0025] In an embodiment, the sensing metal oxide semiconductor film
108 can be formed from metal oxide nanocomposites. The sensing
layer can comprise different metal oxide combinations to which
noble metal can be added, and in some embodiments, a sonochemical
synthesis method can be used for the preparation of the sensing
layer.
[0026] The use of the sonochemical synthesis method can allow for a
one-pot synthesis. Further, this preparation method has the
advantage that the layer (nano)structuring can be controlled by the
value of power and intensity of acoustic radiation to be applied
during cavitation-activated chemical reactions between desired
precursors and reagents (like CTAB or triblock copolymer P123), the
last ones having a major role in guiding the nanostructuring
(nanowires, nanoflowers, nanofibers, etc).
[0027] The result of the sonochemical synthesis is a metal oxide
nanocomposite, which may be present as a powder of nanostructured
metal oxide. The powder can be collected at the end of process, by
washing, filtrating and drying the reaction products. The
nanostructured powder can then mixed with a binder to provide a
slurry of controlled viscosity. The slurry can then be deposited as
a thick or thin sensing film on the leads 104, 106 (e.g.,
interdigitated metal electrodes deposited on the substrate 102).
After thermal consolidation of the sensing layer to remove the
organic binder, the chemo-resistor can then be used for gas
detection, including the detection of various VOC gases including
benzene.
[0028] In some embodiments, a noble metal can be added to the metal
oxide nanocomposite as a doping. The noble metal doping can serve
as a catalyst to activate the oxidation of short and long chain
hydrocarbons, thereby allowing the reactions to take place at much
lower temperatures than in the ambient. In some embodiments, the
metal oxides can also act as catalysts (and a source of lattice
oxygen in the case of ceria for preventing noble metal sintering)
as well as semiconductor support for the charge transfer
reactions.
[0029] In an embodiment, the sonochemical synthesis method can
include the use of various metal precursors being dissolved in a
reagent. The metal precursors can include nitrates of copper,
chrome, cobalt, cerium, aluminum, manganese, or any combination
thereof. If a noble metal is to be included, a precursor comprising
a noble metal such as platinum, gold, palladium, rhodium, iridium,
ruthenium, silver, or any combination thereof. For example, if
platinum is being included in the metal oxide, hexachloroplatinic
acid can be included with the precursors.
[0030] The reagents can include any solvent suitable for dissolving
the precursors, and can include, but are not limited to, water,
ethanol, a reducing agent (e.g., hydrazine, sodium hydroxide, urea,
etc.), or any combination thereof. Surfactants can be added to
order the resulting precipitates into the desired shapes. Examples
of suitable surfactants include, but are not limited to,
cetyltrimethylammonium bromide (CTAB) (C.sub.19H.sub.42BrN), oleyl
amine (C.sub.18H.sub.37N), or any combination thereof.
[0031] The precursors, the reagents, and the surfactants can be
combined and an initiator such as a basic solution of sodium
hydroxide or urea can be added to the solution dropwise. The
resulting solution and/or slurry can be subjected to acoustic waves
to produce the desired precipitate particle size. In an embodiment,
the solution can be subject to between about 50 W and 150 W of
acoustic energy for between about 10 minutes and about 5 hours as
part of the sonochemical treatment. The resulting precipitate can
then be washed and dried in an oven. The powder can then be
calcined at between about 350.degree. C. and about 650.degree. C.
to produce the nanocomposite metal oxide powder having nanoscale
dimensions (e.g., between about 1 nanometers and about 500
nanometers).
[0032] Metal oxide nanocomposite thin films useful as the sensing
layer can be obtained by mixing the nanocomposite powders with
water-glycerol-bicine solution for getting a nanoink with
controlled rheological properties so that to be compatible with
maskless direct printing tool like that provided by "OPTOMEC" or
"Nanoink". In order to remove the organic additives, film drying
and firing in air at about 500.degree. C. to about 600.degree. C.
can be used. The resulting film can serve as a semiconductor layer
used to detect organics based on a reaction at the materials.
[0033] In some embodiments, screen printing or other techniques can
be used to provide a thick or thin film on the substrate over the
leads 104, 106. For example, a thick film fabrication method for
chemo-resistive VOC gas detection consists in mixing the metal
oxide nanocomposite powders described above with terpineol for
making a paste which can be screen printed on the electrode
structure and thermally treated at 500.degree. C.-600.degree. C. in
air to produce a thick solid film for the sensor 100.
[0034] The resulting semiconductor material can comprise a
relatively high surface area. The ability to increase the surface
area relative to other metal oxide layers may allow for a greater
rate of reaction, and thus resistance change, which can be detected
at lower power levels. In addition, the temperature is usually
increased to increase the reaction rate. By providing a larger
surface area, a detectable resistance change can be produced at a
lower temperature, thereby reducing the overall power requirements
for the sensor.
EXAMPLES
[0035] The disclosure having been generally described, the
following examples are given as particular embodiments of the
disclosure and to demonstrate the practice and advantages thereof.
It is understood that the examples are given by way of illustration
and are not intended to limit the specification or the claims in
any manner.
Example 1
[0036] In this example, sonochemical synthesis is used to prepare
CuO--Cr.sub.2O.sub.3 nanocomposite powders from metal nitrates. The
components include: precursors: copper nitrate
Cu(NO.sub.3).sub.2*3H.sub.2O, chromium (III) nitrate
Cr(NO.sub.3).sub.3*9H.sub.2O; reagents: solvent: H.sub.2O, ethanol,
reducing agent: hydrazine (N.sub.2H.sub.4) or sodium hydroxide
(NaOH) or urea CO(NH.sub.2).sub.2; and surfactant:
cetyltrimethylammonium bromide (CTAB) (C.sub.19H.sub.42BrN) or
oleyl amine (C.sub.18H.sub.37N).
[0037] The preparation method is carried out as follows:
[0038] 1. Dissolve appropriate amount copper nitrate in water;
[0039] 2. Dissolve appropriate amount of chromium nitrate in
water;
[0040] 3. Add the solution from step 2 to the solution from step
1;
[0041] 4. Dissolve the appropriate amount of CTAB or oleyl amine in
water;
[0042] 5. Add the CTAB or oleyl amine solution from step 4 to the
mixture of dissolved copper nitrate and chromium nitrate;
[0043] 6. Dissolve the hydrazine in water;
[0044] 7. Alternative, prepare an aqueous solution of NaOH or
urea;
[0045] 8. Add drop wise the CTAB (or oleyl amine) solution to the
solution of dissolved copper nitrate and chromium nitrate;
[0046] 9. Alternative, add drop wise the NaOH (or urea) solution to
the solution of dissolved copper and chromium nitrates;
[0047] 10. Stir the final solution for 10 minutes and then expose
it to the high power (100-200 W) high acoustic intensity
sonochemical treatment for about 3 hours;
[0048] 11. Separation and washing (in H2O and ethanol) of the
resulting powder;
[0049] 12. Dry the powder in an oven at a temperature of
100.degree. C.-120.degree. C.
[0050] 13. Calcination of the dried powder in an oven, at a
temperature of in the range from 350.degree. C. to 650.degree.
C.;
[0051] 14. Use the above calcinated powder for sensing layer.
Example 2
[0052] In this example, sonochemical synthesis is used to prepare a
Co.sub.3O.sub.4--CeO.sub.2 nanocomposite powder from cobalt and
cerium nitrates for VOC detection.
[0053] The component include: precursors: Cobalt (II) nitrate
Co(NO.sub.3).sub.2.6H.sub.2O and cerium (III) nitrate
Ce(NO.sub.3).sub.3.6H.sub.2O; chemical reagents: ethanol, reducing
agent: NaOH (or urea) and surfactant: CTAB (or
oleylamine:C.sub.18H.sub.37N).
[0054] The preparation method is carried out as follows:
[0055] 1. Dissolve the appropriate amount of cobalt nitrate in
ethanol, while stirring for about 1 hour;
[0056] 2. Dissolve the appropriate amount of cerium (III) nitrate
in ethanol, while stirring for about 1 hour;
[0057] 3. Mix the solutions from steps 1 and 2;
[0058] 4. Dissolve the appropriate amount of CTAB (or oleyl amine)
in water;
[0059] 5. Add in a drop wise manner the CTAB (or oleyl amine)
solution to the mixture from step 4, to dissolved nitrates mixture
from step 3 while stirring;
[0060] 6. Dissolve the appropriate amount of NaOH (or urea) in
water;
[0061] 7. Add in a drop wise manner the dissolved metal
nitrates-CTAB (oleyl amine)-solution obtained at step 5 to the NaOH
(or urea);
[0062] aqueous solution from step 6 while stirring;
[0063] 8. Stirring of the final solution of metal nitrates-CTAB (or
oleyl amine)-NaOH (or oleyl amine) for about 10 minutes;
[0064] 9. Expose the mixture from step 8 to high power (100-200 W)
high intensity acoustic radiation for about 3 hours;
[0065] 10. Separation of the resulting powder and washing it in
ethanol water mixture;
[0066] 11. Drying the resulting power in an oven at temperature of
about 100.degree. C.-120.degree. C.;
[0067] 12. Calcination of the dried powder at a temperature of
about 500.degree. C.-600.degree. C.;
[0068] 13. Use of the dried calcinated powder for VOC sensing film
preparation.
Example 3
[0069] In this example, sonochemical synthesis is used to prepare a
CeO.sub.2--MnO.sub.x nanocomposite powder from cerium and manganese
nitrates for VOC detection. The component include: precursors:
cerium nitrate hexahydrate Ce(NO.sub.3).sub.3.6H.sub.2O and
manganese (II) nitrate Mn(NO.sub.3).sub.2; solvent: H.sub.2O,
ethanol, reducing agent: NaOH or urea; and surfactant: CTAB or
oleyl amine.
[0070] The preparation method is carried out as follows:
[0071] Dissolve the appropriate amount of cerium III nitrate in
ethanol, while stirring for about 1 hour;
[0072] Dissolve the appropriate amount of manganese nitrate in
ethanol, while stirring for about 1 hour;
[0073] Mix the solutions from steps 1 and 2 so that to obtain Ce/Mn
molar ratio=1/7 to 5/7;
[0074] Dissolve the appropriate amount of CTAB (or oleyl amine) in
water;
[0075] Add in a drop wise manner the CTAB (or oleyl amine) solution
to the mixture from step 4, to dissolved nitrates mixture from step
3 while stirring;
[0076] Dissolve the appropriate amount of NaOH (or urea) in
water;
[0077] Add in a drop wise manner the dissolved metal nitrates-CTAB
(or oleyl amine)-solution obtained at step 5 to the NaOH (or urea)
aqueous solution from step 6 while stirring;
[0078] Stirring of the final solution of metal nitrates-CTAB (or
oleyl amine)-NaOH (or urea) for about 10 minutes;
[0079] Expose the mixture from step 8 to high power (100-200 W)
high intensity acoustic radiation for about 3 hours;
[0080] Separation of the resulting powder and washing it in ethanol
water mixture;
[0081] Drying the resulting power in an oven at temperature of
about 100.degree. C.-120.degree. C.;
[0082] Calcination of the dried powder at a temperature of about
500.degree. C.-600.degree. C.;
[0083] Use of the dried calcinated powder for VOC sensing film
preparation as it will be described below;
[0084] The material was calcinated at 550.degree. C. for 4
hours.
Example 4
[0085] In this example, sonochemical synthesis is used to prepare a
CeO.sub.2--MnO.sub.x nanocomposite powder from cerium and manganese
nitrates for VOC detection. The component include: Precursors:
cerium nitrate, Ce(NO.sub.3).sub.3.6H.sub.2O, aluminum nitrate
nonahydrateAl(NO.sub.3).sub.3.9H.sub.2O and hexachloroplatinic acid
H.sub.2PtCl.sub.6*6 H.sub.2O; and chemical reagents: solvent:
distilled water (H.sub.2O), ethanol, reducing agent: sodium
hydroxide (NaOH) or urea, and surfactant: CTAB or oleyl amine.
[0086] The preparation method is carried out as follows:
[0087] Dissolve the appropriate amount of cerium III nitrate in
water, while stirring for about 1 hour;
[0088] Dissolve the appropriate amount of aluminum nitrate in
water, while stirring for about 1 hour;
[0089] Dissolve the appropriate amount of H.sub.2PtCl.sub.6*6
H.sub.2O in water, while stirring;
[0090] Mix the solutions from steps 1-3 so that to obtain (0.5-1.5)
wt % Pt in (Al.sub.2O.sub.3-30 wt % CeO.sub.2);
[0091] Dissolve the appropriate amount of CTAB in water;
[0092] Add in a drop wise manner the CTAB or oleyl amine) solution
to the mixture from step 5, to the dissolved nitrates-Pt mixture
from step 4 while stirring;
[0093] Dissolve the appropriate amount of NaOH (or urea) in
water;
[0094] Add in a drop wise manner the dissolved metal nitrates-CTAB
(or oleyl amine)-solution obtained at step 5 to the NaOH (or urea)
aqueous solution from step 7 while stirring;
[0095] Stirring of the final solution of metal nitrates-Pt-CTAB (or
oleyl amine)-NaOH (or urea) for about 10 minutes;
[0096] Expose the mixture from step 9 to high power (100-200 W)
high intensity acoustic radiation for about 3 hours;
[0097] Separation of the resulting powder and washing it in ethanol
water mixture;
[0098] Drying the resulting power in an oven at temperature of
about 100.degree. C.-120.degree. C.;
[0099] Calcination of the dried powder at a temperature of about
500.degree. C.-600.degree. C.;
[0100] Use of the dried calcinated powder for VOC sensing film
preparation.
[0101] Having described the various systems and methods herein,
various embodiments can include, but are not limited to:
[0102] In a first embodiment, a method for fabrication of VOC
sensor comprises: dissolving one or more metal precursors in a
reagent to form a solution, adding a reducing agent to precipitate
a metal oxide compound, subjecting the solution to acoustic energy,
recovering a nanoscale metal oxide, and forming a sensing layer in
a chemo-resistance sensor using the nanoscale metal oxide.
[0103] A second embodiment can include the method of the first
embodiment, further comprising: adding a surfactant to the solution
prior to subjecting the solution to the acoustic energy.
[0104] A third embodiment can include the method of the second
embodiment, wherein the one or more metal precursors comprise
copper nitrate and chromium nitrate, wherein the nanoscale metal
oxide comprises CuO and Cr.sub.2O.sub.3 nanocomposite powders
having a Cu/Cr molar ratio between about 0.01 and about 0.8.
[0105] A fourth embodiment can include the method of the third
embodiment, wherein the solution comprises hydrazine, and wherein
the surfactant comprises cetyltrimethylammonium.
[0106] A fifth embodiment can include the method of the third or
fourth embodiment, wherein the reducing agent comprises an aqueous
solution of NaOH, urea, or a combination thereof, and wherein the
surfactant comprises CTAB, oleyl amine, or any combination
thereof.
[0107] A sixth embodiment can include the method of the second
embodiment, wherein the one or more metal precursors comprise
cobalt (II) nitrate and cerium (III) nitrate, wherein the nanoscale
metal oxide comprises Co.sub.3O.sub.4--CeO.sub.2 nanocomposite
powders having a Co/Ce molar ratio between about 1:1 and about
16:1.
[0108] A seventh embodiment can include the method of the sixth
embodiment, wherein the reducing agent comprises NaOH, urea, or any
combination thereof, wherein the surfactant comprises CTAB, olyel
amine, or any combination thereof.
[0109] An eighth embodiment can include the method of the second
embodiment, wherein the one or more metal precursors comprise
cerium (III) nitrate and manganese (II) nitrate, and wherein the
nanoscale metal oxide comprises Ce.sub.2O.sub.3--MnO.sub.x
nanocomposite powders having a Ce/Mn molar ration between about 1:7
and about 5:7.
[0110] A ninth embodiment can include the method of the eighth
embodiment, wherein the reducing agent comprises NaOH, urea, or any
combination thereof, wherein the surfactant comprises CTAB, olyel
amine, or any combination thereof.
[0111] A tenth embodiment can include the method of the second
embodiment, wherein the one or more metal precursors comprise
cerium nitrate, aluminum nitrate, and hexachloroplatinic acid.
[0112] An eleventh embodiment can include the method of the tenth
embodiment, wherein the nanoscale metal oxide comprises Pt,
Al.sub.2O.sub.3, and CeO.sub.2, wherein the Pt is present in an
amount between about 0.5-1.5 wt %, and wherein the CeO.sub.2 is
present in an amount of between about 10-40 wt %.
[0113] A twelfth embodiment can include the method of the tenth or
eleventh embodiment, wherein the reducing agent comprises NaOH,
urea, or any combination thereof, wherein the surfactant comprises
CTAB, olyel amine, or any combination thereof.
[0114] A thirteenth embodiment can include the method of any of the
first to twelfth embodiments, wherein forming the sensing layer
comprises forming thin films or thick films using the nanoscale
metal oxide.
[0115] In a fourteenth embodiment, a VOC sensor comprises a
substrate, a plurality of leads disposed on the substrate, and a
metal oxide nanocomposite film disposed in electrical contact with
at least two of the plurality of leads.
[0116] A fifteenth embodiment can include the VOC sensor of the
fourteenth embodiment, wherein the metal oxide nanocomposite film
comprises a semiconductor film.
[0117] A sixteenth embodiment can include the VOC sensor of the
fourteenth embodiment, wherein the metal oxide nanocomposite film
comprises a nanostructured CuO--Cr.sub.2O.sub.3 composite.
[0118] A seventeenth embodiment can include the VOC sensor of the
fourteenth embodiment, wherein the metal oxide nanocomposite film
comprises a nanostructured Co.sub.3O.sub.4--CeO.sub.2
composite.
[0119] An eighteenth embodiment can include the VOC sensor of the
fourteenth embodiment, wherein the metal oxide nanocomposite film
comprises a nanostructured CeO.sub.2--MnO.sub.x composite.
[0120] A nineteenth embodiment can include the VOC sensor of the
fourteenth embodiment, wherein the metal oxide nanocomposite film
comprises a nanostructured Pt--Al.sub.2O.sub.3--CeO.sub.2.
[0121] A twentieth embodiment can include the VOC sensor of any of
the fourteenth to nineteenth embodiments, wherein the nanocomposite
film comprises a plurality of nanoscale metal oxide particles.
[0122] While various embodiments in accordance with the principles
disclosed herein have been shown and described above, modifications
thereof may be made by one skilled in the art without departing
from the spirit and the teachings of the disclosure. The
embodiments described herein are representative only and are not
intended to be limiting. Many variations, combinations, and
modifications are possible and are within the scope of the
disclosure. Alternative embodiments that result from combining,
integrating, and/or omitting features of the embodiment(s) are also
within the scope of the disclosure. Accordingly, the scope of
protection is not limited by the description set out above, but is
defined by the claims which follow, that scope including all
equivalents of the subject matter of the claims. Each and every
claim is incorporated as further disclosure into the specification
and the claims are embodiment(s) of the present invention(s).
Furthermore, any advantages and features described above may relate
to specific embodiments, but shall not limit the application of
such issued claims to processes and structures accomplishing any or
all of the above advantages or having any or all of the above
features.
[0123] Additionally, the section headings used herein are provided
for consistency with the suggestions under 37 C.F.R. 1.77 or to
otherwise provide organizational cues. These headings shall not
limit or characterize the invention(s) set out in any claims that
may issue from this disclosure. Specifically and by way of example,
although the headings might refer to a "Field," the claims should
not be limited by the language chosen under this heading to
describe the so-called field. Further, a description of a
technology in the "Background" is not to be construed as an
admission that certain technology is prior art to any invention(s)
in this disclosure. Neither is the "Summary" to be considered as a
limiting characterization of the invention(s) set forth in issued
claims. Furthermore, any reference in this disclosure to
"invention" in the singular should not be used to argue that there
is only a single point of novelty in this disclosure. Multiple
inventions may be set forth according to the limitations of the
multiple claims issuing from this disclosure, and such claims
accordingly define the invention(s), and their equivalents, that
are protected thereby. In all instances, the scope of the claims
shall be considered on their own merits in light of this
disclosure, but should not be constrained by the headings set forth
herein.
[0124] Use of broader terms such as comprises, includes, and having
should be understood to provide support for narrower terms such as
consisting of, consisting essentially of, and comprised
substantially of. Use of the term "optionally," "may," "might,"
"possibly," and the like with respect to any element of an
embodiment means that the element is not required, or
alternatively, the element is required, both alternatives being
within the scope of the embodiment(s). Also, references to examples
are merely provided for illustrative purposes, and are not intended
to be exclusive.
[0125] While several embodiments have been provided in the present
disclosure, it should be understood that the disclosed systems and
methods may be embodied in many other specific forms without
departing from the spirit or scope of the present disclosure. The
present examples are to be considered as illustrative and not
restrictive, and the intention is not to be limited to the details
given herein. For example, the various elements or components may
be combined or integrated in another system or certain features may
be omitted or not implemented.
[0126] Also, techniques, systems, subsystems, and methods described
and illustrated in the various embodiments as discrete or separate
may be combined or integrated with other systems, modules,
techniques, or methods without departing from the scope of the
present disclosure. Other items shown or discussed as directly
coupled or communicating with each other may be indirectly coupled
or communicating through some interface, device, or intermediate
component, whether electrically, mechanically, or otherwise. Other
examples of changes, substitutions, and alterations are
ascertainable by one skilled in the art and could be made without
departing from the spirit and scope disclosed herein.
* * * * *