SUMMARY

In one embodiment, a method of making a photocatalytic article is described comprising i) buffing a powder comprising photocatalytic particles against at least one major surface of a support to bond the photocatalyst particles to the major surface of support, thereby providing a photocatalytic substrate; ii) configuring at least one photocatalytic substrate such that there are at least two layers of photocatalytic substrate and space between layers.

In another embodiment, a method of making a photocatalytic article is described comprising i) providing a photocatalytic substrate prepared by buffing a powder comprising photocatalytic particles against a major surface of a substrate to bond the photocatalytic powder to the major surface of the support; ii) configuring at least one photocatalytic substrate such that there are at least two layers of photocatalytic substrate and space between layers.

In some embodiments, the step of configuring comprises i) folding a photocatalytic substrate to form a pleated photocatalytic article; or ii) winding a photocatalytic substrate to form a helical, coil shaped, or tubular photocatalytic article; or iii) stacking at least two photocatalytic substrates; or a combination thereof. Embodied combinations include stacking a plurality of tubular photocatalytic substrates such that the tubular photocatalytic substrates are nested within each other and stacking a plurality of pleated photocatalytic substrates.

In another embodiment, a photocatalytic article is described prepared by the buff-coating method described herein.

The major surface of the support can advantageously comprise low concentrations of a substantially pure coating of photocatalytic particles, wherein the photocatalytic activity is not hindered by the presence of an organic or inorganic binder.

In another embodiment, a photocatalytic article is described comprising a photocatalytic substrate comprising a support and photocatalytic particles bonded to at least one major surface of the support at an amount ranging from 10 to 400 micrograms/cm ² ; wherein at least one photocatalytic substrate is configured such that there is at least two layers of photocatalytic substrate and space between layers.

In other embodiments, photocatalytic reactors are described comprising at least one light source and the (e.g. multi-layer) photocatalytic articles as described herein. The space between layers provide fluid transport channels. In favored embodiments, light passes through the at least two layers of photocatalytic substrate during use of the reactor. In another embodiment, a method of treating a fluid is described comprising:

providing a photocatalytic reactor as described herein to degrade an organic material in a fluid, such as water.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A is a perspective view of a photocatalytic reactor comprising a pleated photocatalytic substrate; FIG. 1B is a perspective view of a photocatalytic reactor comprising multiple layers of a planar photocatalytic substrate;

FIG. 2 is a perspective view of a photocatalytic reactor comprising multiple layers of pleated

photocatalytic substrates;

FIG. 3 is a perspective view of a photocatalytic reactor comprising a nested stack of tubular

photocatalytic substrates;

FIGs. 4A and 4B depict the transmission and absorbance spectra with respect to time of the degradation of an aqueous solution of Rhodamine B by a photocatalytic substrate having a coating of bismuth oxychloride photocatalyst;

FIG. 5 depicts the absorbance spectra with respect to time of the degradation of an aqueous solution of Rhodamine B by another photocatalytic substrate having a coating of bismuth oxychloride photocatalyst; FIG. 6 depicts the absorbance spectra with respect to time of the degradation of an aqueous solution of Rhodamine B by another photocatalytic substrate having a coating of titania photocatalyst.

DETAILED DESCRIPTION

Presently described are photocatalytic reactors, photocatalytic articles, methods of making photocatalytic articles, and methods of use.

Photocatalysis is an advanced oxidation process based on a solid semiconductor material that is bombarded with (e.g. UV or visible) radiation to excite the electrons and holes within the semiconductor material to produce oxidation-reduction (redox) reactions.

Two methods of photocatalysis have been suggested in literature. The first concerns the formation of free radicals. Electron-hole pairs migrate to the surface of the catalyst and react with hydroxyl ions and dissolved oxygen (O2) to form hydroxyl radicals in solution. Hydroxyl radicals then react with organic materials in the fluid to oxidize them. Hydroxyl radicals have the highest oxidizing strength of common oxidizing species such as ozone, peroxide, and chlorine -based compounds.

The second method involves redox reactions that take place on the catalyst surface with the adsorbed organic species. At the anodic (oxidizing) area of the catalyst, holes are reacting with water to create hydroxyl radicals, and the organic species and their intermediate products. At the cathodic (reducing) area of the catalyst, the electrons are reacting with the oxygen to reduce it to the superoxide species, which in turn reacts with holes to assist in the organic matter oxidation. The articles described herein comprise a photocatalytic substrate; i.e. a support comprising a photocatalytic material.

Various photocatalyst materials are described in the art. In some embodiments, the photocatalyst material is based on a semiconductor material with an energy gap within the range of typical visible and/or UV spectra. Representative examples include inorganic materials such as TiCL-titanium dioxide (titania) and other titania-based photocatalysts; ZnS-zinc sulfide; ZnO-zinc oxide; WO3- tungsten(VI)oxide; CdS-cadmium sulfide; Fe203-iron(III)oxide; Sn0 ₂ -tin(IV)oxide; ALCF-aluminum oxide (alumina), MnCL-manganese oxide, and CuO-copper oxide.

Representative visible light photocatalysts include inorganic materials such as BiOBr (bismuth bromide), BiOI (bismuth oxyiodide), N-doped T1O2 (nitrogen doped titanium dioxide), Ag’PCri (silver phosphate), B1VO4 (bismuth vanadate), and g-C\N ₄ (graphitic carbon nitride).

Mixtures of two or more photocatalysts can be used. Many of the photocatalyst materials just described have a Mohs Hardness ranging from 3 to 9. For example, the Mohs Hardness of titania is reported to be 6.2.

In one embodiment, the photocatalyst is bismuth oxychloride.

In other embodiments, the photocatalyst is a titania-based photocatalyst. Various titania-based photocatalyst compounds have been described. Such compounds have the general formula RT1O3, where R is Sr, Ba, Ca, Al or Mg. Such compounds may be metallized with any individual or combination of metals such as Pt, Pd, Au, Ag, Re, Rh, Ru, Fe, Cu, Bi, Ta, Ti, Ni, Mn, V, Cr, Y, Sr, Li, Co, Nb, Mo, Zn, Sn, Sb or Al. These metals enhance the photocatalytic reactions by either reducing or oxidizing species to their desired form such as, for example, reducing oxygen to peroxides. In addition to, or as an alternative to metallizing the semiconductor, the catalyst may also be doped with any individual or combination of f- transition elements of the lanthanide or actinide series such as Ce, La, Nd and Gd.

Titania-based photocatalyst typically comprises at least 50, 55, 60, 65, 70 wt.% or greater of anatase titanium dioxide crystal, with the balance either rutile and/or amorphous. In some embodiments, the titania-based photocatalyst further comprises Pt, Ce, and La. Such metals can independently be present at concentrations ranging from 1 wt.% to 5 wt.%.

The photocatalyst material is present on a major surface of the support at an amount to achieve the desired photocatalytic activity objectives of specific applications. In some embodiments, the photocatalyst is present on the support at an amount of at least 25, 30, 35, 40, 45, 50, 55 or 60 micrograms/cm ² . The amount of photocatalyst present on the support typically ranges up to 500 or 1000 micrograms/cm ² . In some embodiments, the amount of photocatalyst present on the support is no greater than 400, 350, 300, 250, 200, 150, or 100 micrograms/cm ² .

In one embodiment, the method of making the photocatalytic substrate comprises buffing a powder comprising photocatalytic particles against at least one major surface of a (e.g. light transmissive) support to bond the photocatalyst particles to the major surface of support, thereby providing a photocatalytic substrate. In some embodiments, both major surfaces of the photocatalytic substrate comprise a (e.g. buff-coated) photocatalytic coating. The term“bond” does not necessarily imply a chemical bond. In some embodiments, the photocatalytic particles are partially embedded within the major surface of the support and thus may be characterized as mechanically fastened. In other embodiments, Van der Waals forces may bind the photocatalytic particles to the support surface as well as the (e.g. platy) particles to each other.

Suitable processes are described in US 6,511,701 and WO 2014/182457; incorporated herein by reference.

The photocatalytic particles can have various shapes. In some embodiments, the photocatalytic particles may be characterized as spherical, wherein the length, width, and thickness of the particle are about the same. In other embodiments, the photocatalyst particles may be non-spherical and

characterized by an aspect ratio, i.e. a ratio of the width and/or thickness to the length wherein the length is the greatest dimension of the particle. Elliptical particles may have an aspect ratio up to 2: 1; whereas other (e.g. platy) particles may have an aspect ratio of greater than 2: 1 such as an aspect ratio of at least 3: 1, 4: 1, 5: 1, 10: 1, 15: 1, 20: 1, 25: 1, 50: 1, 75: 1, 100: 1, 250: 1, 500: 1, 750: 1, or even at least greater than 1000: 1). In some embodiments, the width of the photocatalyst particles is greater than the thickness of the particles. In some embodiments, the length of the photocatalyst particles is at least two times the thickness. For particles having a variable thickness, the thickness of the particle is determined as the largest value of thickness.

The buffing process utilized to prepare the photocatalytic substrates described herein is suitable for powders having a relative large particle size, e.g. wherein the largest dimension of the photocatalytic particles ranges up to 100 micrometers. However, in the interests of providing a photocatalytic substrate having a low concentration of photocatalyst per surface area of support, it can be preferred that the photocatalyst particles have a smaller particle size. For example, in some embodiments the largest dimension of the photocatalyst particles is typically at least 0.5, 1, or 2 micrometers ranging up to 10, 20, 30, 40, or 50 micrometers. In other embodiments, the largest dimension of the photocatalyst particles is at least 2, 3, 4, or 5 nanometers ranging up to 10, 20, 30, 40, or 50 nanometers. In yet other embodiments, the largest dimension of the photocatalyst particles is typically at least 50, 60, 70, 80, 90, or 100 nanometers ranging up to 500 nanometers.

In some embodiments, the thickness of photocatalyst coating is about the same as or less than the particle size (e.g. thickness) of the photocatalyst particles. In other embodiments, the thickness of photocatalyst coating is greater than the particle size (e.g. thickness) of the photocatalyst particles.

Various inorganic and organic support materials are suitable for the photocatalytic articles and methods described herein.

In some embodiments, the transparent support is glass, ceramic, or an organic polymeric film. Various light-transmissive polymeric films are known in the art including for example poly(vinyl acetate), poly(vinyl chloride), polyester such as polyethylene terephthalate; acrylic polymers, such as poly(methyl methacrylate), polystyrene; polyurethanes; polyepoxies; polycarbonates; and polyolefins such as polypropylene.

In favored embodiments, the support is sufficiently transmissive to light that activates the photocatalyst. The light typically includes peak wavelengths within the ultraviolet spectrum (e.g. 100 nm to 400 nm) and/or peak wavelengths within the visible light spectrum (400 nm to 700 nm). In some embodiments, the support has a transmission of at least 80%, 85%, 90%, 95% or greater for visible and/or ultraviolet light (e.g. 365 nm) as measured with a spectrophotometer.

In other embodiments, the support is opaque, reflective, or has a lower transparency than just described. For example, WO2014/182457 describes rubbing a powder comprising titanium dioxide particles again a surface of an aluminum support.

In some embodiments, the (e.g. transparent) support is a planar support such as a film or sheet having parallel major surfaces defined by a length (i.e. largest dimension) and width (i.e. the larger of the two dimensions orthogonal to the length). The thickness (i.e. smallest dimension) of the support can vary. In typical embodiments the thickness is at least 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 micrometers and can range up to 200, 300, 400, 500 micrometers or greater.

Advantageously, the rubbing/buffing method provides a substantially pure coating without an organic or inorganic binder. A material acts as a binder if it is the means of attaching the photocatalyst particle to the support, and is not the photocatalyst particle itself. The inclusion of binders can reduce the photocatalytic activity of the photocatalyst, for example, if the binder blocks active photocatalyst surface. Reduction of photocatalytic activity can also be reduced when the photocatalyst material is solvent-coated onto a support that is at least partially soluble in the solvent. The solvent typically swells the support causing a portion of the photocatalyst particles to be submerged within the surface of the support.

The buffing method described can be characterized as a“dry” buffing process. As used herein "dry" means substantially free of liquid. Thus, the photocatalyst powder composition is provided in a solid form, rather than in a liquid or paste form.

In some embodiments, the photocatalyst particles form a continuous layer on the major surface of the support. In some embodiments, the photocatalyst particles form a discontinuous layer on the major surface of the support. For example, the major surface of the support comprises a plurality of discrete, partially embedded particles.

In some embodiments, the buffing method provides a uniform coating of photocatalyst particles. For purposes of the present invention, "uniform" means having a relatively consistent thickness of coating over the desired dimension of the article in the plane of the photocatalytic substrate. The uniformity of the coating may be evaluated, for example, by optical evaluation using an optical densitometer. To evaluate uniformity, a transmission reading (or, alternatively, reflectance) is taken at six points and compared to determine the variation. Preferably, the variation is no more than 10%, more preferably no more than 5%, and most preferably no more than 3%. The wavelength to be evaluated is dependent on the physical properties of the coating and of the support and is appropriately selected to accurately assess the uniformity of the coating. For example, a coating that is visible under ordinary light conditions is evaluated using a wavelength of light in the visible range, such as 550 nm, the generally accepted midpoint of visible light. In other embodiments, the photocatalyst coating may be non-uniform.

The method generally comprises moving a buffing pad in the plane of the support parallel to the support surface. The orbital motion of the pad is typically carried out with its rotational axis perpendicular to the support. Thus, the pad moves in a plurality of directions during the buffing application, including directions transverse to the direction of the support in the case where the support is moving past the buffing pad.

In some embodiments, the rotary buffing action can be provided by one or more air-driven orbital sanding devices and associated buffing pads.

Alternatively, an electric orbital sander such as available under the trade designation“Black and Decker model 5710” with 4000 orbital operations per minute and a concentric throw of 0.1 inch (0.2 inch overall) may be used. Typically, the concentric throw of the pad is greater than about 0.05 inch (0.1 inch overall). Another suitable buffing tool can be obtained from Meguair’s Inc., Irvine, CA, under the trade designation“MEGUAIR’S G3500 DA POWER SYSTEM TOOL”.

Excessive pressure can damage the support surface including such defects as scratches and melting or warping the support from the heating effects of friction. Generally, excessive pressure of the sanders/pads to the web does not produce a uniform coating of the web.

The buffing operation is carried out at a temperature below the softening temperature of the support. Optionally the support may be heated after the buffing operation to a temperature up to the softening temperature of the polymer of the support to assist in adhesion.

Applicator pads may be any appropriate material for applying particles to a surface. For example, the applicator pad may be a woven or non-woven fabric or cellulosic material. Alternatively, the pad may be a closed cell or open cell foam material. In yet another alternative, the pad may be a brush or an array of bristles. In some embodiments, the bristles of such a brush have a length of about 0.2-1 cm, and a diameter of about 30-100 micrometers. Bristles can be made from nylon or polyurethane. Suitable buffing applicators include foam pads, EZ Paintr™ pads (described in U.S. Pat. No. 3,369,268, incorporated herein by reference), lamb's wool pads, pads available from 3M under the trade designation "Perfect it" pads, as well as a buffing pad obtained from Meguair’s Inc. under the trade designation“G3509 DA WAXING POWER PADS”.

The buffing applicator moves in an orbital pattern parallel to the surface of the support with its rotational axis perpendicular to the plane of the support. The buffing motion can be a simple orbital motion or a random orbital motion. The typical orbital motion used is in the range of 1,000-10,000 orbits per minute. In some embodiments, the orbital motion is no greater than 5000, 4000, 3000, or 2000 orbits per minute (i.e. revolutions per minute).

The thickness of the buffed coating can be controlled by the amount of powder applied and varying the time of buffing. Generally, the thickness of the coating increases linearly with time after a certain rapid initial increase. The longer the buffing operation, the thicker the coating. Also, the thickness of the coating can be controlled by controlling the amount of powder on the pads used for buffing.

Finally, the thickness of the coating can be controlled by controlling the temperature of the support during coating. Thus, coating operations carried out at higher temperature tend to provide thicker coatings. In contrast, if the coating is carried out near the softening temperature of a (e.g. polymeric) support, it may be difficult to obtain a very uniform coating. Thus, in some embodiments, the coating process is conducted at a temperature at least 10 or 20 degrees C. less than the softening temperature of a (e.g. polymeric) support.

The photocatalytic coating has sufficient adherence to the support such that the photocatalytic particles remain fixed to the major surface of the support during use (e.g. in a photocatalytic reactor).

The method further comprises configuring the photocatalytic substrate such that there are at least two layers of photocatalytic substrate spaced apart from each other. Configuring refers to altering the shape of a single (e.g. planar) photocatalytic substrate and/or assembling two or more separate (e.g.

pieces) of photocatalytic substrate.

The open space (i.e. volume occupied by a fluid) between (e.g. two adjacent) photocatalytic substrate layers provides fluid transport channels when the photocatalytic substrate is utilized in a photocatalytic reactor. In favored embodiments, each of the photocatalytic substrates layers are spaced from each other. However, it is appreciated, that sufficient fluid transport channels can be provided with less than all the photocatalytic substrates layers being spaced apart from each other.

The spacing between photocatalyst substrates should be sufficient to provide movement of fluid within the space and create sufficient mixing and contact of the fluid with the photocatalytic particles of the coated surface(s). In some embodiments, the spacing is larger than the mean free path of the fluid. In the case of air at 1 atm pressure, the mean free path is 68 nm. In other embodiments, the spacing is larger than 100 nm, 500 nm, or 1000 nm. In practical, continuous flow systems, such as high-performance liquid chromatography (HPLC), columns comprising packed beds of particles as small as 2 micrometers have voids between particles as small as 1 micrometer. Thus, in some embodiments, the spacing is typically at least 1 micrometer, 10 micrometer, 100 micrometer or 1 mm. Larger spacing may be used as long as attenuation of the light traversing the inter-substrate spacing is not significant, and mixing of the fluid within the space if sufficient to contact the fluid with the photocatalyst surfaces. For example, spacing members such as fins or protrusions extending from the photocatalyst substrate surfaces into the space between substrates may be present to increase overall turbulence in the fluid flow. In some embodiments, the spacing may be up to 1 m, 0.5 m, 0.1 m, 10 cm, or 1 cm. In some embodiments, the spacing will be between 100 nm to 1 m, 1 micrometer to 1 m, 10 micrometer to 1 m, 100 micrometers to 1 m, or 1 mm to 1 m. In some embodiments, the surface roughness of the photocatalyst particles or variation in photocatalyst coating thickness can provide adequate spacing between photocatalyst substrates.

The photocatalytic substrate can be configured utilizing various techniques. In some embodiments, the photocatalytic substrate is a (e.g. continuous) single piece of a flexible (e.g. polymeric film) support comprising photocatalytic particles bonded to at least one major surface of the support.

In one embodiment, the method comprises folding the photocatalytic substrate to form a pleated photocatalytic article. These embodiments are depicted in the photocatalytic reactors of FIGs. 1 and 2. Another example of a pleated photocatalytic substrate is depicted in US6315963.

Maximizing the surface area of photocatalytic substrate per volume of reactor can enhance the photocatalytic activity. The distance between the folds can be varied. However, adequate space between the folds is of importance for obtaining the desired turbulence and fluid flow rate. In some embodiments, a photocatalytic substrate is folded, wound, or otherwise configured such that there are at least 2, 3, 4, 5,

6, 7 or 8 layers of photocatalytic substrate per linear inch of configured photocatalytic substrate. In some embodiments, the number of layers ranges up to 10, 15 or 20 layers of photocatalytic substrate per linear inch. The fold angle can also vary. In some embodiments, the minimum angle is at least 45, 50 or 55 degrees ranging up to about 75, 80, 85, or 90 degrees.

FIG. 1A depicts an embodied photocatalytic reactor 100 comprising a configured (e.g. pleated) photocatalytic substrate 120 having at least two layers of photocatalytic substrate spaced apart from each other. The photocatalytic substrate preferably comprises (e.g. buff-coated) photocatalytic powder on one or both major surfaces. The illustrative configured (e.g. pleated) photocatalytic substrate 120 of FIG. 1A comprises four layers, 121, 122, 123, and 124. The photocatalytic reactor further comprises a light source 190 that emits light onto the top surface 101 of the configured (e.g. pleated) photocatalytic substrate 120. In favored embodiments, the photocatalytic substrate is sufficiently transparent such that the light passes through each of layers 121, 122, 123, and 124 activating the photocatalyst present on each of the major surfaces of each layer. The configured (e.g. pleated) photocatalytic substrate 120 is typically provided in a (e.g. rigid) housing (not shown) such that the configured (e.g. pleated) photocatalytic substrate 120 maintains its configuration. A reflective member 180, such as a mirror or other reflective material, may optionally be provided on at least the opposing surface relative to the emitting light of the light source. A reflective member may also optionally be present on the side walls 161 and 162. The reflective member can recycle light that passes through all the layers 121, 122, 123, and 124 or light that reaches the side walls. During use, fluid (e.g. aqueous fluid or air) is conveyed through the openings (as indicated by arrows) between the layers.

In yet another embodiment, a (e.g. buff-coated) pleated photocatalytic substrate as described herein can be utilized with a central light source, such as described in US 6,315,963.

The pleated photocatalytic substrates described herein are embodiments of a continuous piece of a photocatalyst substrate having at least two layers spaced apart from each other. Another example of a continuous piece of a photocatalyst substrate having at least two layers spaced apart from each other is a helical or coil-shaped photocatalyst substrate. One example of a coil-shaped photocatalyst substrate is described in US2010/0176067. In yet another embodiment, a pleated photocatalytic substrate can be wound into a helix or coil thereby increasing the surface area of photocatalytic substrate per reactor volume.

In other embodiments, the step of configuring the photocatalytic substrate comprises stacking at least two (e.g. separate pieces of) photocatalytic substrates.

FIG. 1B depicts an embodied photocatalytic reactor 100 comprising a configured, i.e. stacked (e.g. planar) photocatalytic substrates 125 having at least two layers of photocatalytic substrate spaced apart from each other. The photocatalytic substrate preferably comprises (e.g. buff-coated) photocatalytic powder on one or both major surfaces. The illustrative configured photocatalytic substrate 125 of FIG.

1B comprises four layers, 121, 122, 123, and 124. The photocatalytic reactor further comprises a light source 190 that emits light onto the top surface 101 of the configured photocatalytic substrate 120. In favored embodiments, the photocatalytic substrate is sufficiently transparent such that the light passes through each of layers 121, 122, 123, and 124 activating the photocatalyst present on each of the major surfaces of each layer. The configured photocatalytic substrate 125 is typically provided in a (e.g. rigid) housing (not shown) such that the configured photocatalytic substrate (i.e. stack) 125 maintains its configuration. A reflective member 180, such as a mirror or other reflective material, may optionally be provided on at least the opposing surface relative to the emitting light of the light source. A reflective member may also optionally be present on the side walls 161 and 162. The reflective member can recycle light that passes through all the layers 121, 122, 123, and 124 or light that reaches the side walls. Spacing members 170 air gaps between photocatalytic substrate layers. During use, fluid (e.g. aqueous fluid or air) is conveyed through the openings (as indicated by arrows) between the layers.

FIG. 2 depicts another embodied photocatalytic reactor 200 comprising configured (e.g. pleated) photocatalytic substrates 220, 230, 240, and 250. The photocatalytic substrate may comprise (e.g. buff- coated) photocatalytic powder on one or both major surfaces. In the embodiment, each illustrative configured (e.g. pleated) photocatalytic substrate 220 comprises twelve layers, i.e. size pleats with two faces per pleat. Four of such photocatalytic substrates 220, 230, 240, and 250 are stacked on top of each other with a support member 290 between photocatalytic substrates. The support members may be reflective or opaque, but are preferably light transmissive, particularly for supports that are between configured (e.g. pleated) photocatalytic substrates 220, 230, 240, and 250. The photocatalytic reactor of FIG. 2 further comprises light sources 290 and 291 that emits light onto the surfaces of the pleats of the configured (e.g. pleated) photocatalytic substrates. In favored embodiments, the photocatalytic substrate is sufficiently transparent such that the light passes through each of twelve layers activating the photocatalyst present on the major surface of each layer. The configured (e.g. pleated) photocatalytic substrates 220, 230, 240, and 250 are typically provided in a (e.g. rigid) housing (not shown) such that the configured (e.g. pleated) photocatalytic substrates maintains their configuration. A reflective member, such as a mirror or other reflective material, may optionally be provided on the top 301 and bottom surfaces 302 surfaces. The reflective member can recycle light that passes through all the layers 220, 230, 240, and 250 or light that reaches the top and bottom surfaces of the configured (e.g. pleated) photocatalytic substrates. During use, fluid (e.g. aqueous fluid or air) is conveyed through the openings (a few of which are indicated by arrows) between the pleated layers.

FIG. 3 depicts another embodiment of stacking at least two (e.g. separate pieces of)

photocatalytic substrates. This illustrative assembly of photocatalytic substrates includes fives layers 320, 322, 323, 324, and 325 wherein planar photocatalytic substrates are formed into tubes of decreasing diameter and the tubular photocatalytic substrates are stacked such that the tubular photocatalytic substrates are nested within each other with spaces between photocatalytic substrate layers. Spacing members 370 are typically present to maintain the space/opening between photocatalytic substrates in their configuration. The space between the tubes serve as a fluid transport channel. The tubular photocatalytic substrates 320 and 325 typically comprise (e.g. buff-coated) photocatalytic material on the interior major surfaces; whereas tubular photocatalytic substrates 322, 323, and 324 comprise (e.g. buff- coated) photocatalytic material on one or both major surfaces. The photocatalytic reactor of FIG. 3 further comprises a central light source 390 that radially emits light onto the tubular photocatalytic substrates 320, 322, 323, 324, and 325. The configured nested tubular photocatalytic substrates are typically provided in a (e.g. rigid) housing (not shown) such that the nested tubular photocatalytic substrates maintain their configuration. A reflective member, such as a mirror or other reflective material, may optionally surround the outermost tubular photocatalytic substrate 320. The reflective member can recycle light that passes through all the layers 320, 330, 340 and 350. During use, fluid (e.g. aqueous fluid or air) is conveyed through the opening, as indicated by arrows, between the nested tubular photocatalytic substrates.

It is appreciated that the illustrative configured photocatalytic substrates of

each of the illustrative photocatalytic reactors can have various numbers of layers, as previously described. Further, the (e.g. buff-coated) photocatalytic substrate described herein can be configured in various other arrangements having at least two layers and a sufficient number of spaces between layers to provide channels for fluid flow.

Although it is preferred for the photocatalytic substrate to be light-transmissive, such light- transmissivity is not critical for some photocatalytic reactor. For example, WO 2014/182457 describes buff coating titania onto an aluminum substrate. Such aluminum substrate can be pleated or wound into a helix and provided in a tubular light-transmissive housing. A single light source or multiple light sources can be utilized to activate the (e.g. titania) photocatalyst.

The photocatalytic reactor can comprise various single and multiple light sources. Further, various arrangements of the light source(s) can be utilized. Suitable UV light sources include low- pressure and medium pressure bulbs, broad-band pulsed Xenon, narrow-band excimer, pulsed electric field, black light and fluorescent light that provide a UV spectra in the 100-400 nm range. Suitable visible light sources include light emitting diodes (LEDs), mercury lamps, halogen lamps, and solar energy. The power of the light source can vary. In some embodiments, the power ranges from 50 to 100, 150 or 200 mW/cm ² . In other embodiments, the power may be lower, e.g. at least 0.5, 1, 2, 3, 4, or 5 mW/cm ² ranging up to 10, 20, 30, 40 or 50 mW/cm ² . In other embodiments, the power may be higher, e.g. at least 0.2, 1, 2, 3, 4, or 5 W/cm ² ranging up to 10, 20, or 30 W/cm ² .

The photocatalytic reactor can be utilized in a method of treating a fluid. The method generally comprises providing a photocatalytic reactor as described herein and utilizing the photocatalytic reactor to degrade an organic material in a fluid (e.g. air or water). Degradation of an organic dye, such as Rhodmaine B, is commonly used to demonstrate the photocatalytic activity of a photocatalyst, and is of commercial relevance in the decolorization of wastewater effluents where dye pollutants are prevalent.

In some embodiments, the amount of photocatalytic (e.g. particles) material can be at least 140 micrograms for 2 mls of fluid (i.e., 70 micrograms/ml). In other embodiments, the amount of photocatalytic (e.g. particles) material can be at least 140, 280, 560, or 680 micrograms/mL.

As evident in the forthcoming examples, in some embodiments, the (e.g. multi-layer) photocatalytic article described herein can reach a saturation of 0 in no greater than 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, or 5 hours depending on the amount of photocatalytic particles present. In some embodiments, the amount of undegraded organic material (e.g. Rhodamine B), as calculated from the absorbance can reach 0 in no greater than 13, 12, 11, 10, 9, 8, 7, or 6 hours depending on the amount of photocatalytic particles present.

Materials

Transparency film: Copier transparency film, polyacetate, 110 micrometers thick, Catalog number 21828 from Staples, Inc., Framingham, MA.

Bismuth Oxychloride (BiOCl) Photocatalyst Powder-Stock# 17102, obtained from Alfa Inorganics, Beverly, MA - average particle size 2 microns

Titanium Oxide (T1O2) Photocatalyst Powder- X-ray diameter 7 nm, Specific Surface Area 250 m ² /g (ST- 31 Photocatalytic T1O2, obtained from ISK, ltd, MA

Solution: 5 mg/L Rhodamine B, obtained from Sigma-Aldrich, St. Louis, MO, in deionized water. The solution was prepared by diluting from a concentrated stock solution (75 mg/L Rhodamine B in deionized water).

Preparation of Photocatalvst Substrate - Buff Coating a Support

Transparency film, as described above was utilized as a support. The transparency film was taped using a transparent tape (obtained from 3M Company, St. Paul, MN, under trade designation“3M SCOTCH 600 TRANSPARENT TAPE”) along each edge onto an aluminum metal plate such that a smaller exposed region of the transparency film support was available for coating. The edge-taped transparency film support was then lightly coated with a sprinkling of an excess amount of photocatalyst powder.“Excess amount,” refers to an amount that produces uncoated particles after the buffing process. The photocatalyst powder was then buffed onto the entire exposed region of the transparency film support using a foam pad-based buffing tool (obtained from Meguair’s Inc., Irvine, CA, under the trade designation“MEGUAIR’S G3500 DA POWER SYSTEM TOOL) and a buffing pad (obtained from Meguair’s Inc. under the trade designation“G3509 DA WAXING POWER PADS”) attached to a drill press (WEN 4210 10” Drill Press, WEN Products, Elgin, IL) through a flexible coupling (FCMR25-10- 10-SS, 6 beam clamp coupling, Ruland Manufacturing Co., Inc., Marlborough, MA). The photocatalyst powder was buffed at a main shaft speed of 1700 revolutions per minute (RPM) and an applied pressure of approximately 0.2 psi (1.4 kPa) for approximately 120 seconds. Excess powder was then removed using a vacuum cleaner and air gun. The buffing pad was vacuum cleaned to remove loose powder, and the buffing process was repeated at 1700 RPM and about 0.2 psi (1.4 kPa) for an additional 60 seconds to produce a glossy coated film with minimal loose particles on the surface.

Photocatalvst loading calculation:

The weight of 1 sheet of transparency film was 8.53 g and BiOCl coated transparency film was 8.57 g. The coated area was 567 cm ² (21 cm x 27 cm). Therefore, approximately 70 micrograms/cm ² of BiOCl was present on the major surface.

The T1O2 was coated in the same manner and had approximately 85 micrograms/cm ² of T1O2 present on the major surface.

Measurement of UV Transparency of Photocatalvtic Substrates and Control

The UV transparency of the control (i.e. uncoated transparency film), and photocatalytic substrates were measured as follows. Each film was cut into 1 cm x 3 cm pieces. One piece of film was placed inside a cuvette holder (CUV-UV, from Ocean Optics, Largo, FL) facing the UV lamp (Model ENF-260C, available from Spectroline, Westbuy, NY) , with the UV lamp facing the spectrometer measurement beam input. The power of 365nm UV tube was 6 W and the area of the lamp window was 4.5cm x 14.5cm.

The power was 92 mW/cm ² based on input power and the lamp window. One side of the cuvette holder was unscrewed and open to UV lamp exposure (wavelength 365nm). The handheld UV lamp was used as a UV light source. The transmission spectra were measured using the spectrometer (Jaz-EL350, available from Ocean Optics). After measurement, an additional piece of film was added and the measurement was repeated, up to 3 layers of film. Table 1 shows measured transparency. Absorbance at 365 nm per layer was obtained from the plot of absorbance against number of layers.

Table 1. Measured transparency of various films

Length of Coated and Uncoated (i.c. control) film and corresponding amount of Photocatalyst:

The photocatalyst substrate was cut into various length and the total amount of photocatalyst present was calculated as follows:

Example 1: BiOCl coated film, 2 cm x 1 cm = 2 cm ² , (about 140 micrograms total of BiOCl).

Example 2: BiOCl coated film, 4 cm x 1 cm = 4 cm ² , (about 280 micrograms total of BiOCl).

Example 3: BiOCl coated film, 8 cm x 1 cm = 8 cm ² , (about 560 micrograms total of BiOCl).

Example 4: BiOCl coated film, 16 cm x 1 cm = 16 cm ² , (about 1120 micrograms total of BiOCl).

Example 5: T1O2 coated film, 16 cm x 1 cm = 16 cm ² , (about 1360 micrograms total of T1O2)

Control Example 1: Transparency film only, 16 cm x 1 cm = 16 cm ² , no photocatalyst.

Measurement of Transmission Spectra of Photocatalvtic Degradation of Rhodamine B

Each of the photocatalyst substrates and control were folded such that square 1 cm pleats were formed. The folded photocatalyst substrates were individually inserted into a UV-Visible spectrometer cuvette (Sarstedt Inc. acrylic cuvettes, Ref 67.755, 10x10x45 mm, Nuembrecht, Germany). The folded film was suspended inside the cuvette above the light path of the spectrometer beam, approximately 1 cm above the bottom of cuvette. The folded film was lodged between the cuvette walls such that the force of expansion (unfolding) caused the film to maintain its position within the cuvette.

2 ml of 5 mg/L Rhodamine B solution was injected into the cuvette. The cuvette was held using a cuvette holder (CUV-UV, from Ocean Optics, Largo, FL). One side of cuvette holder was unscrewed and open to ultraviolet (UV) lamp exposure. A handheld UV lamp (6 W, window size 4.5 cm x 14.5 cm, 92 mW/cm ² , 365 nm wavelength, ENF-260C from Spectroline, Westbury, NY) was used as the UV light source. The distance between the UV lamp and cuvette was 2.5 cm. The UV source was oriented perpendicular to the measurement beam of the spectrometer and in the direction that caused the UV light to pass sequentially through the pleated layers of the photocatalyst substrate.

The transmission spectra, color of the Rhodamine B solution, and absorbance spectra were recorded using a spectroscopy system. Optical fiber cables were used to connect the CUV-UV cuvette holder to a visible light source (Model HL-2000-FHSA, available from Ocean Optics) and a spectrometer (Jaz-EL350, available from Ocean Optics). The transmission spectra were measured in a direction perpendicular the direction of UV light. The scattered light of the UV light source was negligible to the transmission measurement since the light from the visible light source was quite intense. A spectrum from deionized water was taken as a reference spectrum for calculating transmission ratio at various wavelengths. The spectrum was acquired every 5minutes. The wavelength range of the spectra was from 340.58 nm to 1031.1 nm. The obtained transmission spectrum was expressed as a color as follows. The measured transmission spectrum was translated to CIE XYZ color space using the color matching CIE 1931 2° Standard Observer function. The CIE XYZ color space was linearly transformed to CIE RGB space using CIE color space chromaticity coordinates (xR=0.49, yR=0T77, xG =0.310, yG=0.8l2, xB =0.20, yB=0.0l). Then, Hue, Saturation, and Brightness, which are the main properties of color, were computed from RGB values. Saturation is defined as colorfulness of an area, the strength or purity of the color. Saturation represents the amount of gray in proportion to the Hue. Here, Saturation is scaled from 0 (no color, gray) to 100 (pure color, fully saturated). Hue is defined as the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, and blue. The color can be correlated to a location (Hue) in the color wheel from 0 degrees to 360 degrees. The color at 0 degrees is equal to that at 360 degrees. The transmission spectra were converted to absorbance spectra. All mathematical processing was done by a customized Lab view program (software available from National Instruments, Austin, Texas).

Examples 1-4 and Comparative Example

FIGs. 4A and 4B depict the transmission and absorbance spectra with respect to time for (2 ml solution of 5 mg/L) Rhodamine B by the photocatalyst substrate of Example 1. The spectra were measured every five minutes and displayed every hour. After 12 hours, the spectra were almost identical to that obtained from deionized water.

FIG. 5 is the absorbance spectra with respect to time of the degradation of (2 mls of 5 mg/L solution) Rhodamine B by the photocatalyst substrate of Example 4. The spectra were measured every five minutes and displayed every hour. The arrow in FIG.5 shows the change of spectra with respect to time.

Table 2 shows the saturation of solution color obtained from transmission spectra of Comparative Example 1 and Examples 1-4 with respect to time. The hue of the solution color of Examples 1-4 was in the range of 300 (Magenta) to 330 (Deep pink) before complete decolorization. Table 2. Saturation with respect to time

The amount of undegraded Rhodamine B can be calculated from the absorbance of FIG. 4B since absorbance at 554 nm is linearly proportional to the concentration of undegraded Rhodamine B, as reported in Table 3.

Table 3. Amount of undegraded Rhodamine B (micrograms)

Examnle 5

Similar experiments were performed with Example 5 (T1O2 coated fdm).

FIG. 6 is the absorbance spectra with respect to time of (2 mls of 5 mg/L solution) Rhodamine B and the photocatalyst substrate of Example 5. The spectra were measured every five minutes and displayed every hour. The arrow in FIG. 5 shows the change of spectra with respect to time.

Hue, saturation, and amount of undegraded Rhodamine B were obtained from measured transmission spectra and absorbance spectra and summarized in Table 4. In contrast with Example 1-4, the hue of the solution color was changed from 300 (Magenta), 330 (Deep pink), 0 (Red), to 40 (Orange). Between 4 hours and 14 hours of light exposure, the reddish intermediate materials having absorbance peaks at 497 nm were observed in the conversion of pinkish Rhodamine B to colorless degraded

Rhodamine B. After 15 hours of light exposure, the solution was colorless.

Table 4. Hue, saturation, and amount of undegraded Rhodamine B of Example 5.