U.S. patent application number 14/520328 was filed with the patent office on 2015-04-23 for photocatalytic thin film devices.
The applicant listed for this patent is Jeffrey F. Roeder, Peter C. Van Buskirk. Invention is credited to Jeffrey F. Roeder, Peter C. Van Buskirk.
Application Number | 20150111725 14/520328 |
Document ID | / |
Family ID | 52826347 |
Filed Date | 2015-04-23 |
United States Patent
Application |
20150111725 |
Kind Code |
A1 |
Van Buskirk; Peter C. ; et
al. |
April 23, 2015 |
PHOTOCATALYTIC THIN FILM DEVICES
Abstract
Novel photocatalytic devices are disclosed, that utilize
ultrathin titania based photocatalytic materials formed on optical
elements with high transmissivity, high reflectivity or scattering
characteristics, or on high surface area or high porosity open cell
materials. The disclosure includes methods to fabricate such
devices, including MOCVD and ALD. The disclosure also includes
photocatalytic systems that are either standalone or combined with
general illumination (lighting) utility, and which may incorporate
passive fluid exchange, user configurable photocatalytic optical
elements, photocatalytic illumination achieved either by the
general illumination light source, dedicated blue or UV light
sources, or combinations thereof, and operating methodologies for
combined photocatalytic and lighting systems. The disclosure also
includes photocatalytic materials incorporated on the surface of
packaged LEDs, LED lamps and LED luminaires, with photocatalytic
materials incorporated on optically useful luminaire surfaces or on
the surface of the remote phosphor. The disclosure also includes
ultrathin photocatalytic materials incorporated on surfaces to
affect antibacterial and antiviral properties.
Inventors: |
Van Buskirk; Peter C.;
(Newtown, CT) ; Roeder; Jeffrey F.; (Brookfield,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Van Buskirk; Peter C.
Roeder; Jeffrey F. |
Newtown
Brookfield |
CT
CT |
US
US |
|
|
Family ID: |
52826347 |
Appl. No.: |
14/520328 |
Filed: |
October 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61893823 |
Oct 21, 2013 |
|
|
|
Current U.S.
Class: |
502/200 ;
502/242; 502/302; 502/303; 502/304; 502/325; 502/338; 502/339;
502/344; 502/345; 502/347; 502/350; 502/351 |
Current CPC
Class: |
B01J 21/063 20130101;
A61L 2/232 20130101; A61L 2/238 20130101; A61L 9/00 20130101 |
Class at
Publication: |
502/200 ;
502/350; 502/302; 502/303; 502/304; 502/325; 502/339; 502/338;
502/344; 502/345; 502/347; 502/351; 502/242 |
International
Class: |
B01J 21/06 20060101
B01J021/06 |
Claims
1. A thin film photocatalytic material on a substrate, the thin
film photocatalytic material comprising titanium oxide and
constituents modifying two or more of the optical absorption,
carrier recombination rate or photocatalytic characteristics of the
thin film, the constituent chosen from the list of cation dopants,
anion dopants, lanthanide series oxide, transition metal dopants
and metallic nanoparticles.
2. The material of claim 1, wherein the substrate has at least one
of high optical transmittance (>90%) or high optical reflectance
(>95%) for light wavelengths capable of stimulating a
photocatalytic effect in the thin film photocatalytic material.
3. The material of claim 1, wherein at least one constituent in the
photocatalytic thin film comprises an oxide of an element chosen
from the group of La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Co, W, V, W, Zr, Cu, Mn, Fe Cr or from the anion group of N or
C.
4. The material of claim 1, wherein the thin film photocatalytic
material incorporates metal particles, wherein the elements in the
metal particles are chosen from the group of Pt, Pd, Ru, Ir, Ag,
Cu, Au, and Fe.
5. The material of claim 1, wherein the thin film photocatalytic
material is predominantly anatase crystal phase.
6. The material of claim 1, wherein the thin film photocatalytic
material has a thickness in the range of 1-30 nm.
7. The material of claim 1, wherein the thin film photocatalytic
material has a thickness less than or equal to 5 times the optical
skin depth of the light wavelengths capable of stimulating a
photocatalytic effect in the thin film photocatalytic material.
8. The material of claim 1, wherein the thin film photocatalytic
material is deposited by Atomic Layer Deposition.
9. The material of claim 8, wherein the constituents are
incorporated in a nano laminate structure.
10. The material of claim 8, wherein the photocatalytic thin film
comprises a titanium oxide nano-laminate, which may include
materials chosen from the group of suboxides to modify optical
properties of the titanium oxide thin film and additional oxides
including Al2O3, SiO2, SiN, ZrO2, and yttria stabilized zirconia to
modify hardness or chemical properties of the thin film.
11. The material of claim 1, wherein the thin film photocatalytic
material has thickness variation of less than .+-.5% over the
substrate.
12. The material of claim 1, wherein the surface area of the
photocatalytic thin film is at least 1.5 times greater than it
would be if the surface formed a simple geometric shape by using a
combination of surface roughening and formation of the substrate
into a complex geometric shape.
13. The material of claim 1, wherein the substrate is comprised of
a material chosen from the group of fused silica, glass, silica
containing glass, inorganic or polymeric materials or other
materials with low optical absorption at the photocatalytic
illumination wavelength.
14. The material of claim 13, wherein the substrate has high
porosity with a surface area greater than 50 square meters per
gram.
15. A method of forming a photocatalytic thin film on a high
surface area substrate, comprising; choosing a substrate material
with optical transparency above 80% at optical wavelengths suitable
for stimulation of a photocatalytic effect in a photocatalytic thin
film; forming the substrate material into a substrate having a
complex geometric shape, the shape having high surface area;
placing the substrate into a chamber capable of providing a
controlled atmosphere at low pressure; removing the air from the
chamber and providing a controlled atmosphere; and depositing a
photocatalytic thin film comprising titanium oxide.
16. The method of claim 15, wherein depositing the photocatalytic
thin film produces a thin film in which the thickness variation of
the photocatalytic material is less than .+-.5% over the active
area of the device.
17. The method of claim 15, wherein an additional step comprises
depositing on the substrate at least one coating to modify its
optical properties.
18. The method of claim 15, wherein depositing the photocatalytic
thin film is carried out until it reaches a thickness in the range
of 1-30 nm.
19. The method of claim 15, wherein depositing the photolytic thin
film takes place on a substrate wherein a combination of roughening
the substrate surface and forming the substrate into a complex
geometric shape increases the surface area of the photocatalytic
thin film to at least 1.5 times greater than it would be if the
surface formed a simple geometric shape.
20. The method of claim 15, wherein that method is Atomic Layer
Deposition.
21. The method of claim 20, wherein the substrate has a high degree
of open cell porosity, with surface area greater than 50 square
meters per gram.
22. The method of claim 15, wherein depositing the photolytic thin
film comprises adding lanthanide elements during deposition.
23. The method of claim 15, wherein depositing the photocatalytic
thin film comprises incorporating an oxide of an element chosen
from the group of La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Co, W, V, W, Zr, Cu, Mn, Fe Cr or from the anion group of N or
C.
24. The method of claim 15, wherein depositing the photocatalytic
thin film comprises incorporating metal particles during
deposition, wherein the elements in the metal particles are chosen
from the group of Pt, Pd, Ru, Ir, Ag, Cu, Au, and Fe.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. Utility application taking
priority from U.S. Provisional application No. 61/893,823 filed
Oct. 21, 2013, and herein incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to novel photocatalytic
devices, fabrication methods for those devices, and novel systems
that combine lighting and photocatalytic air purification
functions.
BACKGROUND
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[0050] The plethora of chemical contaminants in our environment is
a major concern, and their deleterious health effects are only
partially understood but believed to be enormous. Commercially
practical techniques for removal of these contaminants are
therefore of great interest. Examples of contaminants include, but
are by no means limited to formaldehydes, aromatic hydrocarbons,
various mitogen oxides, pesticides, specific bacteria, viruses,
etc.
[0051] Titanium dioxide is the archetypal photocatalyst, due to its
highly oxidizing properties when irradiated by UV light, physical
robustness, insolubility in water, low cost, low toxicity and other
attributes. Photocatalysis using titanium dioxide (titania, TiO2)
has received huge interest for purifying gases and fluids, in
particular air and aqueous fluids, via oxidizing chemical reactions
at a surface, via creation of electron-electron hole pairs.
[0052] A wide variety of titania-based materials, doping schemes,
physical configurations have been proposed to enhance and utilize
photocatalysis at TiO2 surfaces, although so far there has not been
widespread adoption of the technology for purification of air,
fluids or surfaces. The inventors of the present invention believe
that several technical and economic factors have reduced the
utility, effectiveness, commercial viability of photocatalytic air
purification systems.
[0053] Photocatalysis is typically achieved by a low or medium
pressure UV lamp, or in some cases a Xenon lamp, irradiating the
front surface of a ceramic or powder based titania surface, i.e.
from the direction of the medium that is targeted to be purified.
UV LEDs have also been employed, although these devices typically
have very short product lifetimes and are unreliable.
[0054] Photocatalysis utilizing titanium dioxide is typically
excited by illumination in the UV or near UV 240-400 nm spectral
region, which is hazardous to humans, more technologically
complicated and more expensive than visible light based
illumination sources.
[0055] Other challenges with conventional standalone photocatalytic
systems include the difficulty of uniform radiation, purification
media (i.e. media to be purified) interfering with illumination,
high voltage lamp power supplies and control, mercury content in
the lamp, air exchange and the large system sizes. The need for a
dedicated illumination source increases system complexities and
therefore reduces the viability of commercial devices.
[0056] The chemical activation at the surface of a photocatalytic
surface originates with the formation of electron-electron hole
pairs that arise from optical stimulation. Activation at the
surface typically has a finite lifetime that is limited by
illumination and recombination of electron-electron hole pairs.
Mitigation of these effects has been investigated primarily via
chemical modification of the titania particles, although there has
been no consensus in technical approach for manufacturing practical
photocatalyst materials and systems.
[0057] Widespread proliferation of new technologies is often highly
constrained by financial considerations such as return on
investment and the availability of adequate capital. Currently the
general lighting industry (estimated market size over $30B), is
undergoing a revolution characterized by both technological and
capital investment aspects; adoption of solid state lighting (SSL)
is gaining momentum. SSL technology has made enormous strides since
the invention of efficient blue LEDs in the 1990's, and completely
new vertically integrated supply chains have arisen to address the
needs for specialized raw materials, opto-electronic semiconductors
(LEDs and eventually OLEDs), phosphor and packaging materials,
manufacturing equipment, interconnects, LED controllers and
microcontrollers (MCUs), power supplies, fixturing, luminaires,
etc.
[0058] The inventors of the innovations described herein believe
that technically superior and commercially viable photocatalytic
systems may be achieved by leveraging semiconductor technology and
the capital investment environment of microelectronics and SSL
industries.
SUMMARY OF THE INVENTION
[0059] One aspect of the invention relates to fabrication methods
to form ultra-thin and highly uniform photocatalytic materials
based on titanium dioxide, titanium dioxide doped with rare earth
oxides, (e.g. TiO2-CeO2 or any other lanthanide or combination
thereof), with transition metals (e.g. Co, W, V, W, Zr, Cu, Fe Cr)
or the aforementioned materials combined with metal nanoscale or
microscale metal particles at the titania surface, e.g. Pt, Ag, Cu,
Fe etc. All of these composite, doped and metal article containing
titanium oxide based materials, including but not limited to the
stoichiometric TiO2 formulations, will be referred to as "titania"
in the description and claims of this invention. Combinations
formulated for photocatalytic activity will be referred to as
`photocatalytic titania based materials` in the description and
claims of this invention. In this context ultrathin may be defined
as the minimum thickness required to exhibit desired photocatalytic
surface properties, i.e. typically 3-50 nm. physical thickness.
Such ultrathin layers of the subject invention will be particularly
useful when formed on optically useful substrates such as those
with high optical transmissivity, high reflectivity, and high
incoherent reflectivity (e.g. scattering surfaces, either
Lambertian or otherwise).
[0060] These ultrathin layers may also be particularly useful when
formed on high surface area or high porosity open-cell substrates,
for example those which have moderate B.E.T. surface area in the
range of 5-50 m2/g, or with high BET surface area, e.g. greater
than 50 m2/g.
[0061] It will be understood to those practiced in the art of
photocatalytic materials that the subject invention will also be
useful and directly applicable to photo-electrochemical (PEC)
cells, super-hydrophilic surfaces, antimicrobial surfaces,
self-cleaning surfaces and other related applications of
titania-based materials.
[0062] Photocatalysis is a surface phenomenon, and therefore the
thickness of photocatalytic material may be very small in order to
present a suitable chemically activated surface., i.e. in principle
less than 10 nm. physical thickness, It evident that such a titania
layer must be adequately uniform in order to take full advantage of
a high surface area substrate and hence maximize the active area.
Microelectronics thin film technologies, especially metal organic
vapor deposition (MOCVD) and atomic layer deposition (ALD), are
particularly well suited to deposition of thin films of
materials.
[0063] It is desirable that such photocatalytic films be formed
with a high degree of precision in thickness and properties, as
well as uniform in thickness across the device and conformal where
the substrate has topological surface enhancement. Suitable methods
to form films of the subject photocatalytic titania based materials
include vacuum sputtering, ion beam deposition, chemical vapor
deposition (CVD)/metalorganic chemical vapor deposition (MOCVD),
and atomic layer deposition (ALD), in order of increasing inherent
uniformity and conformality.
[0064] Films of photocatalytic titania based materials may be
deposited by vacuum sputtering using metal targets or alloyed metal
targets and a reactive oxidizing gas such as oxygen. The process
may also employ oxide targets or alloyed oxide targets. In the case
of unalloyed targets, the targets may be used simultaneously or in
alternating fashion Vacuum sputtering is carried out at reduced
pressures, typically in the pressure range of 10-5 Torr. Ion beam
deposition is carried out at reduced pressure and results in very
smooth films.
[0065] These processes are carried out in a chamber capable of
producing suitable vacuum pressures and the substrate may be
stationary or moved in a linear or other manner, and may be called
Physical Vapor Deposition (PVD).
[0066] Any of these techniques for thin film deposition may
individually and collectively be referred to as "low pressure"
deposition techniques in the description and claims of this
invention.
[0067] Other "in air" deposition techniques can be used to deposit
the photocatalytic films herein described, such as, but not limited
to, spin coating and heat treating, flame jet deposition, and roll
coating. These atmospheric pressure techniques typically have
reduced thickness control and conformality capabilities relative to
low pressure techniques, but lower costs for manufacturing as well
because the atmosphere for the deposition process is not highly
controlled, as in the case of low pressure deposition techniques.
It is intended that the scope of this invention include both low
pressure and "in air" atmospheric pressure deposition techniques
for deposition of photocatalytic films.
[0068] Deposition of one or more other coatings to modify the
optical properties of substrates may also be carried out. These
additional coatings, if any, may be deposited in the same chamber
or chambers as the photocatalytic thin films are deposited in, or
in different chambers. The additional coatings may be deposited by
the same techniques as those which are used to deposit the
photocatalytic thin films, or may be deposited by different
techniques.
[0069] CVD, MOCVD and ALD may be carried out with gaseous, solid or
liquid precursors, which may be dispensed to the low pressure
coating chamber by passing a carrier gas over the source, or
dissolved in solvent for liquid delivery to a vaporizer and thence
to the vacuum coating chamber. Suitable precursors include halides,
amides, amidinates, beta-diketonates, alkoxides, iminates,
kitiminates, guanidinates and various Lewis base coordinated
molecules. Suitable organic solvents include straight and cycling
alkanes, alkenes, and alkynes, alcohols, and aromatic liquids.
Deposition may be carried out at atmospheric pressure, in which
case the gases used for deposition are typically controlled such as
to exclude air, or preferably sub-atmospheric pressures.
[0070] The deposition of the film via CVD and MOCVD preferably uses
precursors with compatible ligands that do not result in
detrimental ligand exchange. Examples of such precursors include
Ce(thd).sub.4 and Ti(OiPr).sub.2(thd).sub.2, Ce(thd).sub.3-L and
Ti(OiPr).sub.2(thd).sub.2, CeNR.sub.1R.sub.2, TiNR.sub.1R.sub.2,
where R.sub.1 and R.sub.2 comprise H, methyl, ethyl, propyl, etc.
For ALD, the aforementioned precursors may be used together in
dosing pulses to create an alloyed film, or separate pulses of Ti
and the lanthanide may be used to create a layered film. Additional
precursors suitable for ALD include Ti(Cp).sub.4 and Ce(Cp).sub.4
along with variously modified cyclopentadienyls where H is
substituted by alkyls. Ti(OiPr).sub.4 or other alkoxides may be
used, as well as Ti halides, e.g., TiCl.sub.4, TiBr.sub.4,
TiI.sub.4.
[0071] Additionally, the CVD/MOCVD process may be carried out in a
pulsed manner in which the precursors are separated from the
co-reactant.
[0072] Co-reactants suitable for CVD and MOCVD include oxygen and
nitrous oxide. For ALD, oxygen and nitrous oxide may be used, or
more reactive species such as plasmas of the oxidizing gas(es),
ozone, or water.
[0073] The ultrathin characteristic of the subject photocatalytic
material has high utility in that the optical function of the
substrate/optical element may be predominantly unaffected. In some
cases the subject ultrathin material may be incorporated and
optimized as the outer layer in that element's optical interference
coating design.
[0074] A related aspect of the invention are fabrication methods to
conformally deposit the subject titania or titania based thin film
materials on a substrate that has a high degree of nanoscale or
microscale roughness, in order to increase the surface area of the
resultant photocatalytic titania based material and to enhance the
photocatalytic effect.
[0075] A related aspect of the invention describes fabrication
methods to form the subject photocatalytic titania based materials
with a crystallographic structure that is optimized for efficient
photocatalytic activity (e.g. anatase crystal structure) and to
therefore enhance the photocatalytic effect.
[0076] A related aspect of the invention describes fabrication
methods to form the photocatalytic titania based materials with
optical absorption shifted to longer wavelengths (e.g. >400 nm.)
in order to utilize visible light LEDs to stimulate the
photocatalytic effect.
[0077] Another aspect of the invention relates to the geometry of
the UV or visible light irradiation, such as from the back surface
of a substrate, or via waveguide propagation through the substrate
that supports the ultrathin photocatalytic titania based material.
It is evident that such titania based photocatalytic layers need to
be extremely thin and highly uniform in order to allow some
fraction the illumination photons to reach and be absorbed near the
front surface of the photocatalytic material.
[0078] The use of the subject ultrathin catalytic materials on
transmissive optical elements open many possibilities for purifier
designs in applications where it is constraining, difficult or
impossible to use front surface illumination, i.e. to avoid
positioning the UV or visible illumination system in the medium to
be purified. This configuration may be useful for both gaseous
media and liquid media purification.
[0079] For purposes of this invention, liquid may refer to any
mixtures of liquids, colloids and solids, capable of flowing via
gravity or being pumped. Said liquids may contain dissolved gasses
or solids. In an exemplary embodiment, said liquid is primarily
water. Gas may refer to any mixture of gaseous elements, whether
free flowing or pumped. Said gases may include entrained liquid or
solid particles. In an exemplary embodiment, said gas is primarily
air. For purposes of this invention, flowable media may refer
either to gasses or liquids.
[0080] The invention includes monolithic integration of a ultrathin
titania based photocatalytic material on the surface of a solid
state light emitting device such as an LED or OLED. In this context
the LED devices may be individually packaged die, multiple die
modules, LED lamps (e.g. conventional light bulbs, MR-16s, etc.),
lighting fixtures and luminaires. For LED packages and modules, the
photocatalytic material would be back surface illuminated in these
integrated devices. For LED lamps, fixtures and luminaires, the
photocatalytic material may be either from or back surface
illuminated, depending on technical and aesthetic aspects of the
device design.
[0081] Several aspects of LED lamp products and technology may be
especially useful to create fluid purification functionality via
incorporation of ultrathin photocatalytic materials on an LED die,
module or lamp envelope or luminaire transmissive, reflective or
scattering surface. For example, LEDs may have white or blue
optical output which may be adapted for purposes of this invention
as the photocatalytic illumination source.
[0082] Integral LED driver ICs Lamps and high power LED modules
often incorporate or are packaged with control ICs. In an
embodiment of this invention, these control ICs, if present, may be
straightforwardly adapted to communicate with and control
additional UV LED die and for control algorithms, both being
applicable to auxiliary photocatalytic illumination source.
[0083] High performance packaged LEDs incorporate physical optics
techniques such as surface roughening and texturing, in order to
increase optical out-coupling, light output and hence output
efficiency. Surfaces of this type, when modified by the addition of
an ultrathin photocatalytic material in an embodiment of this
invention, will have larger surface area and hence higher
purification efficiency.
[0084] High performance LED lamps are engineered to remove waste
heat, which would otherwise cause the device to operate at high
temperatures, thereby reducing device lifetime. Airflow parallel to
the lamp surface is optimized to remove heat. This concept of
engineered airflow may be adapted in an embodiment of this
invention to efficiently exchange air to be purified at a
photocatalytic surface. In a preferred embodiment, that
photocatalytic surface may be back surface illuminated, i.e. via a
transmissive substrate that has high transmissivity at the
photocatalytic illumination wavelength.
[0085] Another aspect of the invention relates to front surface
illumination geometry of the UV or visible light irradiation. The
subject ultrathin photocatalyst layer may be formed on a highly
reflective surface, such as on a metallic layer, on an
all-dielectric interference coating, or on a dielectric enhanced
metal reflector, and the photocatalyst-reflector system may be
optimized to enhance the photocatalytic effect. Reflector surfaces
may be formed either on an opaque metallic, plastic or ceramic
material via conventional optical coatings or other treatments, or
on a glass or plastic transparent surface, employing similar
techniques.
[0086] A related aspect of the invention utilizes front surface
illumination of a particle, ceramic coated or other preexisting
surface that has optical utility, onto which the titania based
photocatalytic surface has been formed. That surface may have a
high degree of optical scattering, e.g. a highly Lambertian
scatterer for the visible, ultraviolet or infrared spectral
regions. That particle or ceramic coated surface may also be a
remote phosphor used in a blue or UV LED pumped white light
luminaire, i.e. a phosphor that is not configured on the LED
package material, but at transmissive, reflective or scattering
surfaces at distances typically ranging from 1-200 mm from the
packaged LED die or LED array.
[0087] Several further aspects of the invention incorporate
photocatalytic fluid purification systems that utilize the
photocatalytic materials and illumination inventions cited above.
One such invention relates to purification of surfaces of medical
tools, kitchen counter top surfaces, or other implements or
everyday items, either during use or when in storage.
[0088] Another aspect of the invention relates to air purifier
systems that incorporate the inventions cited above. These air
purifier systems may be provided as standalone systems, or as
systems that are integral to a room or isolated space that requires
ambient conditions, walls and other confining surfaces to have a
high degree of purity with respect to contaminating chemicals or
contagion.
[0089] It is evident that such purification systems will maintain
extremely low levels of contamination on the surfaces of the system
and hence the subject inventions include surface purification
systems.
[0090] Related aspects of the invention include purification of
other flowable media besides air, such as, but not limited to,
water, other aqueous liquids including in-vivo fluids, and
non-aqueous liquids.
[0091] Several related aspects of the invention are methods to
enhance the photocatalytic purifying process by increasing the
exchange of flowable media at the purifying photocatalytic surface
or substrate. In the context of this patent, substrate refers to
any object or structure of any shape on which a photocatalytic thin
film may be disposed. This substrate may have simple geometric
forms, such as a flat plane or simple curves, or may be shaped into
more complex geometric forms with higher surface area such as, but
not limited to, fins, channels, or tubes. These complex geometric
forms may serve several purposes, such as, but not limited to,
increasing surface area of the photocatalytic film, improving or
controlling flow of the flowable media, and shedding or
transferring heat. A surface may be considered a complex geometric
form if it has at least 1.5.times. the surface area of a simple
geometric form, such as a plane, a cylinder or a sphere.
[0092] Flow of the flowable media to be purified may take place by
means such as, but not limited to, convection, gravity, fans or
pumping. Flow may take place past structures such as, but not
limited to, fins or channels. Flow may also take place through
structures such as tubes, which may be regular in shape and form or
which may be irregular, such as through a porous media. In a
preferred embodiment of this invention, the structure comprises an
open celled foam. Flow may be accomplished by active fluid pumping
systems, or by passive means, or by a combination of active and
passive means. Passive means may increase movement, turbulence and
exchange of fluid via convection, resulting from the shape and
orientation of the photocatalytic surface, and/or including
localized introduction of heat to the fluid. Such heat may be waste
heat from the UV or visible photocatalytic illumination source,
waste heat from an integral lighting system, or from other sources.
Systems including, but not limited to, pumps, directional
convection, valves, fans, pressure differences, and gravity may be
used to achieve anisotropic flow of the flowable media, that is,
flow primarily in a particular direction past the photocatalytic
device or film.
[0093] A further aspect of the invention relates to photocatalytic
air purifier systems that incorporate combined purifier and
lighting functions. These combined lighting and photocatalytic
purification systems may incorporate either back surface or front
surface illumination of the titania based photocatalytic material.
Such combined function systems may either be for specialized use,
such as, but not limited to, in operating room or other clean room
environments, or for general lighting, for example in private
residences, schools and workplaces.
[0094] The invention includes operational modes for the subject
photocatalytic fluid purification systems. In some cases for either
back surface or front surface photocatalytic illumination of the
photocatalytic surface, such as in the case where UV or visible
irradiation is employed, the illumination may be unhealthy or
unpleasing for people. In such cases the illumination may be
intermittently turned on & off based on daily schedules,
detection of people via movement or by electronic ID schemes, or by
other means and logical schemes.
[0095] In combined purification and lighting systems, the invention
includes combination of photocatalytic illumination sources with
the spectrally balanced general illumination lighting sources. In
one example, for an LED lighting array, white light LEDs may be
packaged together with short wavelength LEDs (e.g. blue, violet or
ultraviolet emitters) such as InGaN LEDs with emission wavelength
less than 450 nm. that have no phosphor. Such short wavelength LEDs
in the array may be controlled separately as described above or as
based on other logical schemes.
[0096] The present invention may include a number of the inventive
elements summarized above, in a variety of combinations and
configurations.
[0097] The Inventions summarized above are illustrated in several
examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0098] FIG. 1 is a schematic of a back surface illuminated
photocatalytic device, illustrating various geometries to couple
the light source configurations.
[0099] FIG. 2 is a schematic of back surface illuminated
photocatalytic device, illustrating a conformal thin film
photocatalytic material on a high surface area optically
transmissive substrate.
[0100] FIG. 3 is a schematic of a combined lighting and air
purification system utilizing front surface illumination of the
subject photocatalytic titania based material formed on a
reflector.
[0101] FIG. 4 is a schematic of a combined lighting and air
purification system utilizing front surface illumination of the
subject photocatalytic titania based material formed on a remote
phosphor in an LED powered white light luminaire.
[0102] FIG. 5 is a schematic of a combined lighting and air
purification system utilizing a predominantly white lighting
luminaire and an optically transmissive element that supports the
subject titania photocatalytic material.
[0103] FIG. 6 is a schematic of a combined lighting and air
purification system utilizing passive (i.e. convective) means to
exchange ambient fluids during purification.
[0104] FIG. 7 is a schematic of a combined lighting and air
purification system utilizing. an array of LED white light emitters
in a decorative and light directing luminaire assembly.
DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS
THEREOF
[0105] The present invention relates to novel photocatalytic
materials, fabrication methods for those materials, and novel
photocatalytic devices and systems. The invention also describes an
apparatus and associated methods of construction and operation for
combining a photocatalytic thin film with a light source in order
to purify a flowable media. Particular embodiments will focus on
LED light sources and use in air, but any of the embodiment
disclosed herein may be combined in any fashion in order to carry
out the purposes disclosed herein.
[0106] In one aspect, the invention relates to the use of vapor
phase or low pressure methods to deposit a uniform layer of
titanium dioxide film, a mixed titanium oxide lanthanide oxide
film, or a mixed film with metal particles incorporated on our near
the surface. Lanthanides include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm Yb, and Lu. These methods include, by way of
example, sputtering, evaporation, metalorganic chemical vapor
deposition (MOCVD), and atomic layer deposition (ALD), and they
typically take place in a chamber at pressures below atmospheric
pressure and with a controlled atmosphere.
[0107] Evaporation is the simplest method and co-evaporation of
oxide sources may be used to deposit a uniform substantially
homogeneous film over a planar substrate. Alternatively, elemental
sources may be used in an oxidizing environment. Sputtering from a
uniform or composite target may also be used on planar surfaces and
to some degree on curved surfaces.
[0108] MOCVD has the ability to form a uniform layer on curved
surfaces and surfaces with complex geometry that have a high degree
of topography. In the case of MOCVD, the deposition temperature is
kept in a range where conformality is high and the deposited film
is substantially amorphous. In one embodiment, a photocatalytic
film, ceria doped titania, is deposited by MOCVD. The precursors,
Ce(thd).sub.4 and Ti(OiPr).sub.2(thd).sub.2 are dissolved in an
organic solvent and delivered to a vaporizer in maintained at a
temperature in the range of 150-250.degree. C. Argon carrier gas is
flowed through the vaporizer at 100-200 sccm and into a deposition
chamber where the substrate is held at a temperature of
450-650.degree. C. and a pressure between 1 and 20 Torr. Oxygen is
flowed as a co-reactant gas at between 400 and 1000 sccm. A thin
ceria doped titania film is deposited on the substrate. The
thickness of the ceria doped titania film may be between 1 and 30
nm.
[0109] Atomic layer epitaxy (ALD) may be used to deposit uniform
layers onto the aforementioned surfaces and also on highly curved
surfaces or into features of very high aspect ratio (e.g.,
>3:1). In one embodiment the photocatalytic film is deposited by
ALD. The precursors, Ce(Cp).sub.3 and Ti(Cp).sub.4 are transported
together by argon carrier gas flowed at 100-200 sccm and into a
deposition chamber where the substrate is held at a temperature of
150-450.degree. C. and a pressure between 1 and 20 Torr. The
combined Ce(Cp).sub.3 and Ti(Cp).sub.4 gas phase precursor is
delivered for a specific time, followed by an inert gas purge, then
oxygen is flowed through a water bubbler held at between
5-15.degree. C. as a reactant gas, followed by an inert purge.
Reactant and inert gas purge flows are between 200-1000 sccm. This
set of pulses is repeated until a thin ceria doped titania film is
deposited on the substrate. In a preferred embodiment of this
invention, the ability of ALD to deposit layers on extremely high
aspect ratio structures may be used to form a photocatalytic thin
film on an interconnected porous structure such as, but not limited
to, that of an open celled foam.
[0110] In another embodiment, the ALD process employs separate
pulse trains of Ce(Cp).sub.3 and Ti(Cp).sub.4 precursor, each
followed by the oxidizing and purge steps as described above.
Composition of the resulting titania-lathanide material would in
those cases be determined by the ratio of Ce(Cp).sub.3 and
Ti(Cp).sub.4 ALD cycles.
[0111] MOCVD may be carried out with solid sources held in bubblers
through which a carrier gas is flowed to convey the source to the
deposition chamber. The sources may also be dissolved in an organic
solvent as individual sources or combined together. Key criteria of
a solvent system are (1) high boiling point to reduce the chance of
flash off of the solvent, (2) high solubility for the compound, (3)
low cost. Useful hydrocarbon solvents may include, for example:
octane, decane, isopropanol, cyclohexane, tetrahydrofuran, and
butyl acetate or mixtures comprising these and other organic
solvents. Lewis base adducts may also be incorporated as additions
to the solvent(s) for beneficial effects on solubility and to
prevent possible oligimerization of the precursor molecules.
Examples of useful Lewis Bases include polyamines polyethers, crown
ethers, and the like. Pentamethylenediamine is a one example of a
polyamine. Examples of polyethers include various glymes such as
mono-, di-, tri-, and tetraglyme.
[0112] Most MOCVD processes have two temperature regions of
interest: a surface reaction kinetic limited range at lower
temperature and a mass transport limited range at higher
temperature. Co-reactants useful for forming high quality mixed
ceria-titania films include oxygen and nitrous oxide. In general,
there is a large excess of oxygen in the process, so that carbon
incorporation in the film is minimized. The primary objective in
the present invention is the formation of a film of as homogenous a
nature as possible, preferably a film of substantially anatase
crystal structure.
[0113] Depending on the substrate and titania-lanthanide film
composition, seed layers or other thickness dependent
inhomogeneities may be utilized to enhance formation of the anatase
phase, optimize absorption of the photocatalytic illumination,
increase surface hardness or durability, or to otherwise enhance
the photocatalytic effect. In this context seed layers may be
introduced as part of an ALD, MOCVD or PVD process, or via an
different process.
[0114] In some embodiments, lateral composition, topographic or
microstructural inhomogeneities may be engineered in the surface,
in order to achieve specific hydrophilic or hydrophobic properties
in order to modify fluid flow characteristics at that surface.
[0115] The deposition system may have an automated throttle valve
that allows pressure to be controlled independently of flow. In
this way, residence times can be manipulated more directly. The
hot-wall type reactor is one type of reactor that may be used to
deposit the subject films. Alternatives include batch hot-wall
reactor or warm-wall showerhead type reactors.
[0116] Useful MOVCD process conditions span a range of temperature
from 250.degree. C.-650.degree. C. and total pressure between
0.5-50 Torr. Preferably, the process temperature is below
500.degree. C., and pressure is between 1 and 10 Torr.
[0117] The use of ALD to create a crystalline mixed titania-ceria
film affords a higher degree of conformality than MOCVD. ALD also
offers the possibility of batch processing. ALD is a surface
saturation limited method for depositing thin films in which
alternating pulses of reactants are introduced to the process,
generally separated by an inert purge pulse. Typically, one
reactant contains the cation and a second reactant contains the
anion (oxygen in this case). The advantage of ALD is that each
layer formed by a surface saturation limited cation containing
layer, that is subsequently purified and/or oxidized by the second
reactant pulse. A typical ALD cycle consists of the first reactant
pulse, a purge pulse, the second reactant pulse and another purge
pulse. The cation containing layer may be formed using any suitably
volatile precursor, e.g., a metalorganic, a metal halide, metal
hydride, or combinations thereof.
[0118] Forming a composite or multicomponent oxide film by ALD may
be accomplished using different approaches. In the first approach,
the substrate is exposed to two or more metal cations
simultaneously. The ratio of cations in the precursor (reactant) is
chosen to achieve the desired ratio of cations in the film.
[0119] In the second approach, the cations may be alternated by ALD
cycle. The desired composition is achieved by choosing the ratio of
one cation cycle to the other. As an example, for a 25% alloy of
species B in oxide A, 1 cycle of species B would be followed by 3
cycles of species A.
[0120] Similar precursors to the MOCVD process may be employed for
ALD. Cyclopentadienyl coordinated metal precursors may also be
advantageously used for ALD of ceria-titania films. For the case of
simultaneous introduction of the metal containing precursors,
source materials are chosen so that there is compatibility between
the chemistries such that unwanted ligand exchange is prevented.
Process conditions favorable for ALD are in the temperature range
of 100-375.degree. C. with pressures in the range of 1-5 Torr.
Co-reactants (oxidizers) include oxygen, nitrous oxide, plasmas of
these gases, ozone, or water. We note that surface preparation
(termination) can be very important in ALD. Pre-treatments to
promote uniform nucleation include aqueous acids/bases compatible
with the substrate and that result in --H or --OH termination of
the substrate surface.
[0121] Anion doping of the titania film may also be employed in the
films of the subject invention e.g., incorporation of nitrogen via
either ALD or MOCVD. This may be accomplished by using a nitrogen
containing co-reactant, e.g. ammonia or other amines, nitrogen
oxides, plasmas or combinations of these, with or without oxidizing
reactants.
[0122] Other materials may be incorporated below, above, or in the
oxide film. An example is a metal that substantially maintains its
metallic character that may act in an optically or
photocatalytically enhancing manner. The metal may be deposited by
any suitable means, including evaporation, sputtering, chemical
vapor deposition, or ALD. They may be deposited on the substrate
before film deposition takes place, during film deposition, or
after film deposition, or in any combination thereof. Noble or
precious metals that strongly segregate from the alloyed oxide may
be used, for example Pt or Ag. These could be incorporated into the
oxide ALD process or separately using the aforementioned methods.
Non-strongly segregating metals may also be used, provided that the
processing temperatures of the oxide film deposition method do not
cause the metal to incorporate into the oxide such that it loses
its metallic character. Optionally, thermal treatments such as
annealing may be used to promote agglomeration of the metal or
de-wetting to form island structures.
[0123] Metallic particles may be dispersed onto the film by
depositing the metal by physical vapor deposition means such as,
but not limited to, evaporation or sputtering. The metallic
particles may include transition, precious, or noble metals. For
example, Pt may be deposited by vapor phase means. In the case of
evaporation, the metal may be deposited by resistive heating of a
charge or by electron beam heating at reduced pressure. Preferable
reduced pressures are below 10-3 Torr. Sputtering of Pt may be
carried out at reduced pressure. In either evaporation or
sputtering, the metal may be deposited on the Ti-lanthanide film at
room temperature or at elevated temperature. The film is heat
treated to induce de-wetting to form small islands. This is
preferably performed in a oxidizing ambient, the temperature and
degree of oxidizing atmosphere chosen to be compatible with the
substrate upon which the titania film has been deposited. The
island size defining the lateral dimensions of the metal particles
may be between 200 nm and 1500 nm is preferably between 5 and
50
[0124] Doping of the photocatalytic titania based materials with
metallic species segregated on an atomic scale, such as Ag, Au, Cu,
Pt and Fe, may also be accomplished using the aforementioned
techniques.
[0125] Incorporation of metal particles in such titania based
photocatalytic materials may serve three separate and functionally
complementary functions: [0126] 1) Enhancement of optical
absorption. Ag is of particular interest because of the surface
plasmon resonances on the near UV-blue spectral regions [0127] 2)
Retardation of recombination of photocatalytic illumination
generated electrons and electron holes, especially Pt and platinum
group metals. This is a well known effect in particle based
catalyst systems. [0128] 3) Complementary antimicrobial effects of
metals that are highly electronegative, especially Cu and Ag.
[0129] The present invention may utilize one or several species or
size scales of metal particles incorporated in a thin film titania
or doped titania or composite titania thin film matrix, to achieve
one or more of these three phenomena depending on the desired
purpose or application. ALD of composite materials of this type are
of particular interest based on the capability of that technique to
form precise nano-laminates of dielectric and metal composite
structures.
[0130] Other aspects of the subject invention include geometric and
physical optics schemes to exploit the surface chemistry and hence
purification attributes of ultrathin titania based photocatalytic
materials as described above. We note that the principles described
below may also be utilized with previously identified
photocatalytic materials, both those based on titanium dioxide and
also based on other materials.
[0131] The photocatalytic materials of the present invention, such
as those described above, and others that include, may be deposited
on various substrates and in a variety of configurations also
identified in the present invention, thereby enabling a range of
photocatalytic fluid purification devices. Photocatalytic
purification may be used to remove organic and other chemical
species from a fluid that may be either gaseous (e.g. air) or
liquid (e.g. water). Impurity species in such a fluid are brought
into near proximity or adsorbed at the photocatalytic surface, and
are subsequently chemically dissociated.
[0132] In general gaseous fluids to be purified by such devices
include ambient air in residential, commercial, industrial and
public building environments, as well as specialized application
environments that include manufacturing clean rooms, hospital
operating and recovery rooms, etc. Liquid fluids to be purified
include drinking water as well as in-vivo and in-vitro purification
and chemical processing in medical and biomedical applications.
[0133] In general, a photocatalytic fluid purification system
requires three conditions: [0134] I) a photocatalytic surface
[0135] II) a source of radiation to excite the photocatalytic
effect ("photocatalytic illumination") [0136] III) a fluid exchange
means to move fluid across the surface of the photocatalytic
material.
[0137] The photocatalytic surface may be a solid substrate that has
had one or more surfaces modified to incorporate photocatalytic
material. Depending on the application, the fluid meant for
purification, the surface area necessary for efficient
purification, the geometry and wavelengths of the incident
photocatalytic illumination, a variety of substrates may be
employed.
[0138] The fluid exchange means III is comprised of mechanical
confinement to channel the fluid exchange flow, and a way to drive
that flow.
[0139] For titanium dioxide photocatalytic materials, and for some
embodiments of the present titania based photocatalytic materials,
photocatalytic illumination is necessarily in the 200-400 nm.
spectral region. For titania-lanthanide and titania-transition and
metal particle or metal doped materials of the present invention,
photocatalytic illumination may be in the 400-450 nm. spectral
region.
[0140] For some fluid purification applications, either gaseous or
liquid purification, the photocatalytic material and fabrication of
that material may be advantageously utilized on substrates of
various shapes and surface finishes that facilitate conditions II
and/or III in the preceding paragraph.
Combined Lighting and Purifications Functions
[0141] There are a range of embodiments for the present invention
that incorporate combined lighting and air purification functions.
In those applications and configurations certain attributes of the
lighting system may be advantageously adapted to provide either
Condition II and/or Condition III as described above.
[0142] These combined lighting and purification functions may be
enabled by fabricating a photocatalytic material on surfaces that
have optical utility for the lighting device, as a partial or
comprehensive way to satisfy Condition II. These "optically useful
surfaces" may be either specularly reflective, specularly
transmissive, non specular, (i.e. scattering) transmissive or
reflective surfaces, the surface of an up-wavelength converting
phosphor (i.e. Stokes shifting), or combinations of these optical
surface types, which are incorporated in the lighting device. In
such cases in which the photocatalytic material is applied to an
optically useful surface, such material may be the titania based
material of the present invention, or another photocatalytic
material that is known to in the art.
[0143] One potentially useful attribute of a lighting device or
light source is its optical output ("lighting illumination"), which
is typically broadband in the 400-700 nm ("visible spectrum")
spectral region. Whereas incandescent, metal halide and fluorescent
light sources tend to emit lighting illumination that is somewhat
broadband over the visible spectrum, light emitting diodes ("LED")
used in lighting often have a strong blue or violet spectral
emission.
[0144] Although the majority of the discussion below addresses
adaptations and use of LED light sources, we emphasize that any
light source may in principle be utilized if it offers suitable
short wavelength output, or has other attributes as described
below.
[0145] White light emitting LEDs typically employ either one of two
white light generating mechanisms. The most common mechanism uses a
blue/violet LED that excites a phosphor; the resulting lighting
illumination is comprised of the original blue/violet light, mixed
with longer wavelengths in the green, orange and red portions of
the visible spectrum.
[0146] The second, less common white light generating mechanism
employs three LEDs, typically red, green and blue (RGB). In these
cases the emission of these RGB spectral components are mixed to
generate white light, and in some LED devices the spectral
irradiancy of each RGB component may be controlled by a
microcontroller, e.g. using pulse width modulation, in order to
generate a continuum of white light color temperatures or different
colored light entirely.
[0147] For either of these two white light generating LED
mechanisms, the short wavelength components of LED lighting
illumination will typically be in the 400-470 nm. spectral region.
In the former of the two mechanisms, the short wavelength phosphor
pump wavelength may also be in the ultraviolet, with wavelength in
the 300-400 nm spectral range. In general, LED light sources that
have stronger relative output in the 360-420 nm spectral range may
offer greater utility and flexibility to incorporate the inventive
concepts herein.
[0148] In some embodiments of the present invention, certain short
wavelength spectral components of the lighting illumination may
usefully also serve as the photocatalytic illumination. Although
LED lighting devices are particularly well suited to provide such
short wavelength photocatalytic illumination, we note that other
lighting illumination sources may also be utilized in the subject
invention.
[0149] Combined lighting and purification systems that utilize
spectral components of the lighting illumination to serve as the
photocatalytic illumination source, without the use of auxiliary
photocatalytic illumination sources, will be denoted as "Mode
1".
[0150] In related and complimentary embodiments, the photocatalytic
illumination may be completely provided by an auxiliary
photocatalytic illumination source, and the lighting and
purification functions would in those cases share other attributes
of the combined system such as optically reflective, transmissive,
scattering surfaces, and fluid flow controlling surfaces. The
lighting illumination may also be usefully combined with an
auxiliary photocatalytic illumination source, in order to increase
the sum total of the photocatalytic illumination. Combined lighting
and purification systems that incorporate an auxiliary
photocatalytic illumination source will be denoted as "Mode 2".
[0151] Other embodiments of combined lighting and purification
systems may advantageously employ certain heat dissipation and
fluid dynamics/confinement attributes of select lighting device as
a means to completely or partially satisfy the photocatalytic
purification Condition III as described above.
[0152] In general, all electrical powered light sources are
inefficient to some extent, in that significant electrical input
power is not converted into visible light (lighting illumination),
but is instead converted to thermal energy that heats the light
source. This is especially true for tungsten-halogen lamps,
incandescent lamps, ceramic metal halide sources and solid state
light (SSL) sources such as LEDs and organic LEDs (OLEDs). Higher
temperature operation is typically not a major issue for all of
these except SSL sources, since increases in the source temperature
shift the predominant blackbody radiation to shorter wavelengths,
thus increasing the visible light output to some extent. On the
other hand, SSL sources such as LEDs are deleteriously affected by
operation at high temperature; device lifetimes are dramatically
reduced. Therefore, LED lighting devices, especially high
brightness LEDs (HB-LEDs), are designed and configured with
intrinsic cooling features. Typically the LED packaged die is
attached to a heat sink base in a high thermal conductivity
structure, and the base is in turn attached to cooling fins and/or
a large thermal capacity structure that can dissipate the heat.
Certain LED light sources, especially LED lamps and LED luminaires,
employ fairly sophisticated designs to remove the LED waste heat
using convective flow.
[0153] One embodiment of the subject combined lighting and
photocatalytic purification systems is to take advantage of the
waste heat and to harness the resultant convective flow across both
optically useful and convective flow confining surfaces in lighting
devices, especially for LED lamps and luminaires. There are a wide
variety of convective cooling/air exchange schemes that may be
established in concert with optical surfaces configurations, and
several such designs are provided in the Embodiments. These
embodiments are in no way limiting as to how the inventive design
principles may be utilized in these types of devices and
systems.
[0154] Convective flow across heated surfaces in such devices may
in some cases be augmented with mechanically driven flow such as
from an electrical blower, or in some cases the waste heat may be
predominantly driven be auxiliary blower systems. The exhaust for
LED lamps and luminaires, which will be made up of partially
purified input air, may directly enter the upper regions of that
room, may be recycled and reintroduced to the photocatalytic
surface, or in the case of recessed ceiling lighting, it may be
delivered back to that room or another space by a duct, or system
of ducts. Such ductwork may transport the purified air either from
one of the subject devices, or from a system of many devices, as in
a room with multiple ceiling recessed luminaires, for example.
[0155] We note that although the discussion is primarily using LED
light sources as an example, many other light source types may be
used to take advantage of these inventive principles. In
particular, fluorescent light sources are well suited to take
advantage of this invention, as they may be designed to emit short
wavelengths of light which may be useful to stimulate the
photocatalytic effect. As with the LED embodiments, photocatalytic
thin films may be directly integrated with the light emitting
object, or may be present on a reflector or on a transparent or
translucent diffuser sheet near the light emitting object. Such a
reflector or diffuser sheet may, regardless of the light source, be
designed for insertion into a system having a light source, without
replacement of the entire light fixture or luminaire.
[0156] Many LED lighting devices that may be utilized to affect the
combined lighting and purification functions described above. These
LED lighting devices include Packaged LEDs, LED Arrays, LED lamps
and LED Luminaires. Each of these types of LED lighting devices may
employ the subject inventions in specific ways as appropriate to
address specific applications and product markets. Some possible
embodiments to utilize these LED light sources in fluid
purification functions are described in the attached Table.
LED light sources and configurations for combined
lighting-photocatalytic utility Three criteria for photocatalytic
fluid purification are:
[0157] a photocatalytic surface
[0158] a source of radiation to excite the photocatalytic effect
("photocatalytic illumination")
[0159] a fluid exchange means to move fluid across the surface of
the photocatalytic material.
Two Modes to provide Photocatalytic Illumination in a combined
Lighting/Photocatalytic purification system are:
Mode 1
[0160] Combined lighting and purification systems that utilize
spectral components of the lighting illumination to serve as the
photocatalytic illumination source, without the use of auxiliary
photocatalytic illumination sources.
Mode 2
[0161] Combined lighting and purification systems that incorporate
an auxiliary photocatalytic illumination source that provides
either all or a fraction of the photocatalytic illumination. In the
case of that auxiliary source providing a fraction, the balance of
the photocatalytic illumination would be provided by violet or blue
spectral components of the lighting illumination.
TABLE-US-00001 TABLE 1 Light source Photocatalytic purification
criteria application Condition I: Condition II: Condition II: LED
light Light source for photocatalytic Photocatalytic Photocatalytic
Fluid exchange source type description purification material
illumination means Packaged Single LED die Packaged Photocatalytic
Mode 1 Light Extrinsic to light blue or (emission LED is material
formed on source directly source. violet LED wavelength 400-450
nm.) incorporated outer surface of excites back One embodiment is
in a in a fluid transparent surface of a liquid flow conventional
flow- package substrate. photocatalytic component made package.
purification Material is titania- material (substrate from fused
silica or system, based and optically side), via other materials
that preferably absorbing at LED transmission transmit the liquid,
due emission through substrate. photocatalytic to the wavelength.
illumination, with relatively the interior small area of surfaces
of the flow packaged passages coated LED. with an ultrathin
Packaged Single UV LED die Packaged Photocatalytic Mode 1 Light
titania based UV LED (emission LED is material formed or source
directly photocatalytic wavelength 200-400 nm.) incorporated
deposited on outer excites back material. The in a in a fluid
surface of UV surface of blue/violet or UV conventional flow-
transparent silica photocatalytic light source is package.
purification glass cover plate or material (substrate coupled into
a solid system, dome. Material is side), via portion of the silica
preferably titania-based and transmission flow element and liquid,
due optically absorbing through substrate. this photocatalytic to
the at LED emission illumination is relatively wavelength. confined
within the small area of element via wave- packaged guiding and/or
LED. reflective means. A related embodiment is a silica based
microfluidic waveguide structure, with blue/violet or UV LED
radiation coupled into the silica and propagated via waveguiding
and reflective structures to the substrate side of the
photocatalytic material deposited in the microfluidic flow
channels. Packaged A blue or violet or Blue- Photocatalytic Mode 1
Light Extrinsic to light White LED near ultraviolet violet/phosphor
material formed on source directly source [Blue-violet LED die
mounted White outer surface of excites back LED/Phosphor] in a
suitably packaged transparent surface of transparent LED is package
substrate. photocatalytic package such as incorporated Material is
titania- material (substrate epoxy or silicone. in a based and
optically side), via A wavelength combined absorbing at LED
transmission down-converting lighting & emission through
substrate. phosphor is fluid flow- wavelength. typically
purification impregnated or system. otherwise incorporated in the
transparent epoxy. White LED An integral Blue- Photocatalytic Mode
1 Light Extrinsic to light array assembly of violet/phosphor
material formed on source directly source [Blue-violet multiple
blue-violet White outer surface of excites back LED/Phosphor] LED
die in a single LED array is transparent surface of package, or
incorporated package substrate. photocatalytic multiple packaged in
a Material is titania- material (substrate LEDs, mounted on
combined based and optically side), via a board, a flexible
lighting & absorbing at LED transmission membrane or some fluid
flow- emission through other integrating purification wavelength.
transparent mechanical system. substrate. support, e.g. chip-
Alternatively, the on board (COB). blue or preferably LED arrays
may violet spectral integrated, components of the typically on a
lighting board, with illumination may electrical driver, be
incident on circuitry, and in photocatalytic some cases surfaces on
a lamp microcontroller or or luminaire. ASIC dimming and color
control, optics and other system components. LED modules that
produce white light may be either Blue- violet LED/phosphor or RGB.
Alternatively these functions may be provided on a separate board
and incorporated with the array in a lamp or luminaire. White LED
An integral Blue- Photocatalytic Mode 2 UV Extrinsic to light array
assembly of violet/phosphor material formed on LEDs are source
[Blue-violet multiple blue-violet White outer surface of
incorporated as LED/Phosphor] LED die in a single LED array is
transparent some fraction of package, or incorporated package
substrate. the blue-violet multiple packaged in a Material is
titania- LED array, and LEDs, with combined based and optically are
separately photocatalytic lighting & absorbing at LED powered
and illumination fluid flow- emission controlled, with producing UV
purification wavelength. the UV LEDs also system. photocatalytic
incorporated in the illumination array. The UV incident on the LEDs
may be in back surface of the UV-A (315-400 nm the photocatalytic
wavelength), material (substrate UV-B (280-315 nm) side), via or
UV-C (100-280 nm) transmission spectral through ranges as
transparent appropriate to substrate. efficiently produce
Alternatively, the the photocatalytic UV illumination effect. may
be incident on photocatalytic surfaces on a lamp envelope or in a
luminaire, as below. White LED An integral RGB LED Photocatalytic
Mode 1 Blue or Extrinsic to light array assembly of red, array is
material formed on violet emitting source [RGB] blue and green
incorporated outer surface of LEDs in the array LED die in a single
in a transparent are preferentially package, or combined package
substrate. powered and are multiple packaged lighting &
Material is titania- incident on the LEDs, mounted on fluid flow-
based and optically back surface of a board, a flexible
purification absorbing at LED photocatalytic membrane or some
system. emission material (substrate other integrating wavelength.
side) which has mechanical been deposited on support, e.g. chip-
the epoxy on board (COB). package, via transmission through that
transparent substrate. Alternatively, the blue or preferably violet
spectral components of the lighting illumination may be incident on
photocatalytic surfaces on a lamp or luminaire. White LED An
integral RGB LED Photocatalytic Mode 2 UV Extrinsic to light array
assembly of array is material formed on LEDs are source [RGB]
multiple LED die incorporated outer surface of incorporated with in
a single package, in a transparent the RGB LED or multiple combined
package substrate. array, and are packaged LEDs, lighting &
Material is titania- separately mounted on a fluid flow- based and
optically powered and board, a flexible purification absorbing at
LED controlled. The membrane or some system. emission UV
photocatalytic other integrating wavelength. illumination
mechanical incident on the support, e.g. chip- back surface of on
board (COB). the photocatalytic material (substrate side), via
transmission through transparent substrate. Alternatively, said UV
illumination may be incident on photocatalytic surfaces on a lamp
or luminaire. LED lamp An integrated & Combined Photocatalytic
Mode 1 or Mode Fluid flow across completely self- lighting &
material formed on 2 Blue violet or the surface of a contained LED
fluid flow- outer surface of UV spectral lamp or a nearby light
source, often purification lamp envelope, on components optically
referred to as a system. luminaire generated by transmissive flow
light bulb, MR-16, reflective, LEDs or arrays, as confining surface
PAR, etc. It is transmissive or above, are (e.g. a transparent
comprised of a scattering surfaces incident on the or scattering
packaged LED or or on a user lamp envelope or transmissive flue or
LED array, and configurable onto retrofitted configurable globe,
electrical power retrofit optical or optical and/or may be achieved
circuitry for mechanical fluid flow by convection, and voltage
conversion, element. constraining the design of that rectification
and In general the mechanical element may be constant current
thickness of the elements. optimized for generation. These
photocatalytic For Mode 2, i.e. maximum fluid functions may also
material on for cases where exchange and be integrally optically
useful UV auxiliary turbulence at the provided as an surfaces,
photocatalytic surface of the LED module (as (especially
illumination is photocatalytic above). The lamp transmissive or
used, borosilicate surface. is also comprised metallic reflectors
glass, plastic or of enclosing in the lamp or other UV mechanical
luminaire) is on the absorbing structure(s) & order of 10 nm.,
elements may be optical element(s) i.e. <.lamda./20 optical
employed to to scatter, reflect or thickness for most prevent UV
from transmit the of the visible escaping to the lighting spectrum,
in order local illumination to have a negligible environment, and
LED A complete Combined effect on intended to prevent that For
luminaires, luminaire lighting lighting & optical properties
threat to people or fluid flow may be assembly/system, fluid flow-
of that surface. the environment. similarly optimized (e.g.
recessed 1' .times. purification When formed on a Alternatively
across the 4' or 2' .times. 4' ceiling system. the surface of a
these UV LED photocatalytic or wall panels, dielectric enhanced
elements may surfaces on recessed lighting, metal reflector or have
scheduled reflective, track lighting, floor an all dielectric
on-cycles and/or transmissive or lamps or table reflector, the
brief duration in scattering surfaces, lamps, operating subject
titania order to achieve and driven by
room lighting based the same result. either purely fixtures, etc.)
photocatalytic convective forces, utilizing one or material may be
or an external more LED arrays incorporated into blower, either
and/or LED lamps the interference locally at the & lamp
fixturing, coating design and luminaire, or transmissive, the
reflector's centrally for an reflective or optical properties
assembly of scattering optical and color luminaires, or by a
elements, appearance may be combination of mechanical optimized
with the these. fixturing, and incorporated electrical power
ultrathin titania and controls material, based on interface.
standard thin film design techniques.
Surface Purifications Functions
[0162] In general, a photocatalytic surface purification system
requires two conditions: [0163] I) a photocatalytic surface [0164]
II) a source of radiation to excite the photocatalytic effect
("photocatalytic illumination")
[0165] Healthcare Associated Infections (HAI) are a major problem
that threatens life and increases costs of healthcare. The CDC
estimates that in the U.S. there are 1.7 million
hospital-associated infections annually, contributing to 99,000
deaths. One primary transmission mode for these infections involves
contact with contaminated surfaces, where bacteria and viruses can
reside for days or even weeks on touch surfaces near the patient.
MRSA, C. Difficile, MDRA and Staphylococcus are particularly
dangerous and stubborn contagions that may reside on surfaces close
to a patient. Many types are difficult to attack with antibiotics,
and antibiotic resistance is spreading to Gram-negative bacteria
that can infect people outside the hospital.
[0166] Outside the healthcare world, there are a similar and
increasing range of opportunistic mass-infections as evidenced by
recent Norovirus outbreaks on cruise ships. These outbreaks may be
spread by viruses, bacteria and spores that propagate both airborne
and from surfaces to surface.
[0167] It is well known that many standard disinfecting regimens
(typically liquids comprised of bleach or hydrogen peroxide) may
leave a residual contagion on a surface, which is known as
"Bioburden". Bioburden is comprised of biofilm or planktonic
species residing at a surface that is nominally `clean`. Its
presence may be due to failure of hospital staff to follow standard
procedures, species with exceptional physical, chemical and
biological robustness, or a combination of those. There are several
disinfectant treatments that are receiving wide attention as ways
to augment liquid treatments. UV-C radiation, ozone and
disinfectant vapors or mists are known to be very effective, but
are highly hazardous and are only viable when a hospital room has
been vacated.
[0168] Antimicrobial, or `self sterilizing` surfaces are highly
desirable to complement standard cleaning. They act continuously,
and ideally they should have a high killing efficiency for a broad
range of bacteria, viruses and spores, and be non-toxic to humans.
Silver and copper containing surfaces are the most widely
investigated, but these have shortcomings including toxicity, cost
and questions about long term efficacy, due to adaptation of
bacteria.
[0169] The ultrathin titania photocatalytic materials and
illumination schemes of the subject invention may be incorporated
in a wide range of devices in order to effect or enhance
antimicrobial characteristics of surfaces. These materials may be
directly applied to solid surfaces of interest, or applied to
flexible polymeric materials that are subsequently applied to
surfaces or formed into those products directly.
[0170] In one embodiment, these products may be incorporated in
"high touch" surfaces, surfaces which have a great deal of contact
by humans. Examples of these products include, but are not limited
to: personal or commercial devices, such as cell phones and
smartphones, tablet and computer touchscreens and keyboards,
hospital objects, such as bed hand rails over-bed tables,
doorknobs, elevator buttons, escalator or stair rails, writing
implements, medical tables, instrument panels, and protective face
masks, and in-vivo devices including but not limited to joint
implants, cardiac pacemakers and defibrillators, catheters or
neurological electro-stimulation devices and medical systems such
as dialysis equipment.
[0171] It is evident that these materials, when incorporated on
consumer, commercial and medical products, will be exposed to
considerable abrasion, mechanical impact and chemical agents used
to clean and sanitize these products on a daily basis.
[0172] One advantage of ALD in the subject invention is its
capability to engineer composite materials. In the case of
photocatalytic titania those concepts were described above.
Composite oxides of these types may be formed either by
co-deposition during a cation ALD deposition step or via
nano-laminates.
[0173] One other aspect of the subject invention is to further
compositionally modify the titania photocatalytic materials so as
to increase the mechanical hardness and chemical resistance of the
surface. This may be accomplished via ALD formation of
nano-laminates that combine titania with Al2O3, SiO2, ZrO2, yttria
stabilized zirconia (YSZ), or other oxides that have desirable
characteristics. In terms of hardness, titania is approximately
5.5-6.5 on the MHS hardness scale, while Al2O3 is 9. Incorporation
if intermittent Al2O3 ALD steps during ALD of the subject titania
photocatalytic materials, will increase the hardness and abrasion
resistance of the antimicrobial or fluid purification active
surface.
[0174] In those cases Al2O3 may be formed, for example, using an
ALD process that is well known to those practiced in this field,
for example using trimethylaluminum deposition with vapor phase
water as the oxidizing co-reactant.
[0175] The present invention and some of its various embodiments
are described below, with reference to figures as necessary.
Reference numbers are used to match particular elements described
in the text with those shown in figures.
[0176] One embodiment is shown schematically in FIG. 1. This device
100 is designed to purify the air or other flowable medium at
photocatalytic thin film surface 101 by oxidizing reactions with
chemical and biological contaminants. A transparent substrate 102
supports a thin film of the subject photocatalytic titania based
material 101 on a front surface of substrate 102. In any embodiment
of this invention, this photocatalytic thin film 101 may be on the
substrate 102 and thereby in direct contact with the substrate 102,
or may be over the substrate 102, having one or more intervening
layers (not shown) disposed between the photocatalytic thin film
101 and the substrate 102. In a preferred embodiment the
photocatalytic material is a solid solution of TiO2-CeO2 (90%/10%).
The material has the anatase crystal structure.
[0177] The layer 101 is illuminated from its back surface, i.e.
from the direction of the substrate side 102 of the material. This
back surface illumination may be accomplished using blue emitting
LED sources, such as those fabricated using the InGaN material
system, with suitable emission wavelengths that induce the
photocatalytic effect. In a preferred embodiment this wavelength
may be approximately 420 nm. Other types of light sources and
emission wavelength ranges may also be used and are also the
subject of the invention.
[0178] The back surface illumination may be through the thickness
of the transparent substrate, with illumination source 103, the
emitted light shown with the arrow and "hv" label. In a preferred
embodiment the back surfaced illumination may be near normal
incidence. In that case the back substrate surface may be coated
with an antireflection coating on surface 104 to increase the
illumination intensity incident on the photocatalyst.
[0179] Back surface illumination may also be achieved by
transmitting the illumination from source 105, into guiding modes
in the transparent substrate, via coupling structures such as a
surface relief grating 106. Alternatively, illumination via guiding
modes may be accomplished by illumination of the substrate edges
from source 107. Alternatively, the light source 108 may be
embedded in the transparent substrate. These techniques may be used
to substantially confine the optical radiation to the interior of
photocatalytic film 101.
[0180] The thickness of the layer 101 is sufficiently thin, e.g. in
the range of 10-100 nm., for the illuminating wavelength to be
optically absorbed throughout the thickness of the photocatalyst
including in the proximity of the outer surface. In that case the
photocatalyst may become chemically active and effective to drive
oxidation reactions with contaminants in the flowable medium in
front of surface 101, thereby purifying the flowable medium.
[0181] FIG. 2 illustrates a similar configuration as FIG. 1 in
which the transparent substrate 201 has had a surface 202
roughened, which has subsequently had the subject photocatalytic
titania based thin film 203 formed on that surface with a high
degree of conformality, composition and crystalline control. The
material thickness may be accurately controlled as needed to allow
the back surface illumination from source 204 to be absorbed
throughout the layer 203 including in the proximity of its outer
surface. Surfaces of this type may be used to increase the surface
area of the photocatalytic surface and enhance the photocatalytic
effect, thereby increasing the efficacy of the device to purify the
ambient environment in front of photocatalytic surface 203.
[0182] Note that the substrate 201 may have its surface roughened
202, or the substrate surface may be flat and the surface of the
photocatalytic film 203 may be roughened (not shown), or any
combination thereof. The roughening of either the substrate or the
film may be carried out by subtractive techniques, such as but not
limited to, wet etching, dry etching, sanding, machining, or bead
blasting. The roughening of either the substrate or the film may
also be carried out by additive techniques such as, but not limited
to, spray coating, powder coating, annealing, recrystallization, or
nucleation or island formation before or during a thin film
deposition process. Roughening may be in a nanoscale or
microscale.
[0183] The present invention also includes formation of titania
based materials on physically shaped or textured surfaces that have
specific affinity or specific lethality for biologic impurities.
For example certain micro topographies have been synthesized to
mimic the topographic character of shark skin, resulting in
corresponding antibacterial properties. Addition of the subject
titania based photocatalytic materials to those surfaces will add
an antiviral effect to that surface. Other engineered surface
topographies may attract or bind specific viruses or bacteria based
on the shape and spatial frequency power spectra of the surface
topography. The subject titania photocatalytic materials and
illumination schemes, or other photocatalytic materials, may be
added to such surfaces to increase the microbe lethality and hence
antimicrobial effects there. These antimicrobial effects may
include prevention of biofilms or reduction of bioburden i.e.
residual microbes and fomites present after other cleaning or
disinfection processes. Such surfaces that combine microbe specific
affinity surfaces with photocatalytic materials, may be used both
as antimicrobial surfaces and for active purification surfaces in
the subject fluid purification apparatuses of the subject
invention.
[0184] Photocatalyst devices of this type may be used to purify air
near medical instruments or other tools, or for example as wall
panels in rooms in which the photocatalytic illumination is provide
from behind the wall panel. It may also be used to purify the
surfaces of those instruments, or other high touch surfaces in
hospitals, home or in the workplace, to render them antimicrobial.
Back surface illumination in those cases may be provided by near UV
or visible light LEDs or other sources with adequate spectral
irradiancy at suitable wavelengths to stimulate the photocatalytic
effect.
[0185] FIG. 3 illustrates an embodiment combining a lighting and
flowable media purification system utilizing front surface
illumination of the subject photocatalytic titania based material
formed on a reflector. In this embodiment 300, the titania based
photocatalytic material 301 is applied to the front surface of a
pure metallic or dielectric enhanced metallic reflective surface
302, and is illuminated by a broadband light source 303 such as a
white LED that has significant optical emission in the UV or in the
400-450 nm. spectral regions. Alternatively the white light source
may comprise any combination of red, green and blue wavelengths
("RGB"). While the metallic reflector has high reflectivity in the
visible spectral region, the reflectivity and E-field
characteristics of the reflector at the photocatalytic illumination
wavelengths, and the thickness of the photocatalytic layer, may be
optimized to enhance the photocatalytic effect, and hence the
capability of the system to purify the flowable medium between the
light 303 and the photocatalytic thin film 301.
[0186] FIG. 4 illustrates a combined photocatalytic purifier and
LED lighting system employing a titania based photocatalyst formed
on a remote phosphor in an LED powered white light luminaire 400.
In this case white light for illumination 401 is generated by
irradiation of a remote phosphor layer 402 by a blue or UV light
source 403. The remote phosphor layer 402 is interposed between the
metallic or dielectric enhanced metallic high reflector 404, and
titania based photocatalytic material 405. Alternatively the
photocatalytic material 405 may be heterogeneously incorporated
onto the surface of remote phosphor particles prior to their
application in the luminaire system. Typically the short wavelength
light source 403 for remote phosphor luminaires emits in the 460
nm. wavelength range. In cases where the photocatalytic effect at
thin film 405 requires a different wavelength, a second source 406
may be included as needed to achieve the photocatalytic effect and
purification of the flowable media at surface 405. The
photocatalytic effecting source 403 may be operated intermittently,
or during overnight hours for example as needed to regenerate the
chemically active photocatalytic surface.
[0187] FIG. 5 illustrates a flowable media purification function
combined with a predominantly white lighting luminaire by utilizing
a optically transmissive element that supports the subject titania
photocatalytic material. One possible configuration for the
luminaire has photocatalytic illumination hv from source 501
incident on a broadband luminaire metallic or dielectric enhanced
metallic reflector 502 on a mechanical support 503. The reflector
coating 502 has average reflectivity >80% in the visible
spectral region (400-700 nm. wavelength), and >75% reflectivity
for the photocatalytic illumination which may be UV (<400 nm.
wavelength), or visible light, such as in the 400-500 nm portion of
the visible spectrum. In a preferred embodiment, reflectivity is
>90% in the visible spectral region (400-700 nm. wavelength),
and >85% reflectivity for the photocatalytic illumination which
may be UV (<400 nm. wavelength), or visible light, such as in
the 400-500 nm. portion of the visible spectrum. In a further
preferred embodiment, reflectivity is >95% in the visible
spectral region (400-700 nm. wavelength), and >90% reflectivity
for the photocatalytic illumination which may be UV (<400 nm.
wavelength), or visible light, such as in the 400-500 nm. portion
of the visible spectrum. Said reflected photocatalytic illumination
is incident on a transmissive support 504 and then on the back
surface of the photocatalytic material 505. Ambient flowable media
at the front or outer facing surface of photocatalytic material 505
and is thereby purified by oxidizing chemical reactions.
[0188] White light illumination from source 506 is also incident on
the reflector 502/503, and may be reflected through the
transmissive element 504/505, for general illumination purposes. In
another embodiment, a broadband antireflection coating may
optionally be applied to the back surface of 504 to increase
external transmittance of that element.
[0189] It is noted that for certain photocatalytic material
compositions 505, visible light illumination will stimulate the
photocatalytic effect, and in those cases the functions of sources
501 and 506 may be achieved by a single source or multiple sources
of a single type.
[0190] FIG. 6 shows a combined photocatalytic purifier and lighting
system utilizing passive or convective means to exchange ambient
fluids during purification. In an embodiment, a luminaire system
600 with light source 601 is used in a decorative and light
directing enclosure 602. Illumination from 601 is incident on the
back surface of the transmissive photocatalytic element 603 mounted
on support or substrate 604, and said illumination serves as both
general illumination and as illumination to stimulate the
photocatalytic effect. In this case the titania based
photocatalytic material is sensitive to visible light emitted by
601. In a preferred embodiment, ambient air 605 is drawn up to the
photocatalytic surface, across its chemically active surface, and
upwards through the lamp body. The purified air 606 exits the
assembly. Said gas flow through the assembly is driven by
convective forces via heating of the air around the light source
601, such as by waste heat from the source. Alternatively, if the
support or substrate is transparent in the proper wavelength
region, the photocatalytic material may be mounted on the side
opposite the light source 601, facing the bottom opening of the
enclosure 602, allowing the incoming air 605 to strike the
photocatalytic material directly.
[0191] FIG. 7 shows an embodiment 700 comprising an array of LED
white light emitters 701 in a decorative and light directing
luminaire assembly 702. The array is mounted on an air permeable
packaging material. In this case the outer surface 703 of the LED
emitters 701 has the subject titania based photocatalytic material
incorporated thereon, and the composition of said material has been
adjusted such that visible illumination from the white LEDs is
suitable to stimulate the photocatalytic effect. White light
general illumination 704 is generated by the luminaire. Ambient air
705 is drawn into, across and through the LED array by convective
forces from waste heat from the LED array. In so doing it is
purified by chemical reactions at the photocatalytic surfaces at
each LED emitter. The purified air 706 passes upward and out of the
top of the luminaire.
[0192] The subject invention may be embodied in the following
examples that are by no means restrictive, but intended to
illustrate the invention. It will be clear that the described
invention is well adapted to achieve the purposes described above,
as well as those inherent within. The citation of any publication
is for its disclosure prior to the filing date and should not be
construed as an admission that the present invention is not
entitled to antedate such publication by virtue of prior invention.
Numerous other changes may be made which will readily suggest
themselves to those skilled in the art and which are encompassed
both in the spirit of the disclosure above and the appended
claims.
* * * * *
References