PHOTOCATALYTIC AIR PURIFICATION AND DISINFECTION COMPOSITION AND SYSTEM

Abstract

A combination of bismuth oxyhalides is provided, which is a photooxidant, antibacterial and antiviral. The combination of bismuth oxyhalides is added to a filter medium (e.g., a multistage filter) to decompose VOCs and/or eliminate bacteria and/or viruses. Suitable designs of multistage filters are also provided.

Claims

1) A combination comprising at least two bismuth oxyhalide compounds selected from Groups A1, A2, A3 and B, wherein: Group A1 includes Bi.sup.(0) doped-bismuth oxyhalides; Group A2 includes bismuth oxyhalides of the formula BiOCl.sub.yBr.sub.1-y, with y≥0.5; Group A3 includes single halide bismuth oxyhalides; and Group B includes bismuth oxyhalides of the formula BiOCl.sub.yBr.sub.1-y, with y<0.5.

2) A combination according to claim 1, wherein: Group A1 includes Bi.sup.(0) doped-BiOCl, Bi.sup.(0) doped-BiOBr and Bi.sup.(0)doped-BiOCl.sub.yBr.sub.1-y with 0.6≤y≤0.95; Group A2 includes BiOCl.sub.yBr.sub.1-y with 0.6≤y≤0.95; Group A3 includes BiOHal wherein Hal is chloride or bromide; Group B includes BiOCl.sub.yBr.sub.1-y with 0.1≤y≤0.4.

3) A combination according to claim 1, comprising Group A1 compound.

4) A combination according to claim 3, comprising Group A3 compound and/or Group B bismuth oxyhalide.

5) A combination according to claim 4, comprising: Group A1 compound, which is Bi.sup.(0)doped-BiOCl.sub.yBr.sub.1-y [0.7≤y≤0.95]; and at least one of: Group A3 compound, which is BiOBr, in the form of flower-like microspheres; Group B compound, which is BiOCl.sub.yBr.sub.1-y [0.1≤y≤0.4] in the form of plates or flower-like microspheres; wherein the combination is a photooxidant, antibacterial and antiviral.

6) A composition comprising the bismuth oxyhalides combination of claim 1 in water, a volatile organic solvent or a mixture thereof.

7) A filter medium comprising a combination of bismuth oxyhalides as defined in claim 1, added to a flow-through support.

8) A filter medium according to claim 7, wherein the flow-through support is made of nonwoven or woven fabric.

9) A filter medium according to claim 7, where the flow-through support is in the form hollow cells defined by thin gypsum walls.

10) A filter medium according to claim 7, where the flow-through support is in the form hollow cells defined by thin metal walls.

11) A blend comprising activated carbon and combination of bismuth oxyhalides as defined in claim 1.

12) A multistage filter comprising VOC-decomposing and/or bacteria-eliminating and/or virus eliminating filter medium in the form of photocatalyst added to a flow-through support, placed downstream to a prefilter, with light source positioned between said prefilter and said photocatalyst.

13) A multistage filter according to claim 12, wherein the photocatalyst is Bi.sup.(0) doped-bismuth oxyhalide, to eliminate viruses.

14) A multistage filter according to claim 13, wherein the Bi.sup.(0) doped-bismuth oxyhalide is Bi.sup.(0)doped-BiOCl.sub.yBr.sub.1-y (0.7≤y≤0.95).

15) A multistage filter according to claim 12, wherein the photocatalyst added to the flow-through support comprises a combination of bismuth oxyhalides, optionally in admixture with activated carbon, the combination comprising at least two bismuth oxyhalide compounds selected from Groups A1, A2, A3 and B, wherein: Group A1 includes Bi.sup.(0) doped-bismuth oxyhalides; Group A2 includes bismuth oxyhalides of the formula BiOCl.sub.yBr.sub.1-y, with y≥0.5; Group A3 includes single halide bismuth oxyhalides; and Group B includes bismuth oxyhalides of the formula BiOCl.sub.yBr.sub.1-y, with y<0.5.

16) A multistage filter according to claim 12, comprising bismuth oxyhalides added to a flow-through support, optionally in admixture with activated carbon, wherein said flow-through support is disposed between a pre-filter layer and a post-filter layer, wherein said pre-filter and post-filter layers are particulate-trapping layers, and wherein the light source consists of a plurality of LED lamps illuminating the photocatalyst.

17) A multistage filter according to claim 16, which is a cabin air filter.

18) A multistage filter according to claim 16, which is an air conditioner filter installed in the air flowing area of an air tube or an air conditioning system.

19) A transparent photocatalytic cell, having an air inlet and an air outlet, comprising: bismuth oxyhalides-added filter medium mounted inside the cell; means for drawing outside air stream or circulated air stream into the cell and forcing said air stream across said filter medium, wherein the bismuth oxyhalides photocatalyst is activatable by daylight entering the cell or visible light source positioned to illuminate said photocatalyst.

20) A method for reducing biological load on surfaces, comprising forcing air in a space where the surfaces are placed to pass across a filter medium having a combination of bismuth oxyhalides applied on flow-through support, wherein said bismuth oxyhalides include bromide-predominant mixed halide of the formula BiOCl.sub.yBr.sub.1-y, with y<0.5, said bismuth oxyhalides being illuminated by visible light, to charge the air with oxidant species and reduce the level of microorganism on said surfaces without the direct application of oxidant species onto said surfaces.

Description

IN THE DRAWINGS

[0072] FIG. 1 is SEM image of BiOCl.sub.0.80Br.sub.0.20 microspheres.

[0073] FIG. 2A is SEM image of BiOCl.sub.0.20Br.sub.0.80 plates.

[0074] FIG. 2B is SEM image of BiOCl.sub.0.20Br.sub.0.80 microspheres.

[0075] FIG. 3 is a photo of a gypsum-made honeycomb-shaped filter.

[0076] FIG. 4 is a photo of a silicon template used to create the gypsum-made honeycomb-shaped filter.

[0077] FIGS. 5A and 5B illustrate the design of a photoreactor.

[0078] FIG. 6 illustrate the design of a cell housing a volatile solvent and the photoreactor placed in the cell.

[0079] FIG. 7 shows VOC (toluene) concentration versus time plots.

[0080] FIG. 8 shows VOC (ethanol) concentration versus time plot.

[0081] FIG. 9 is a photo of the experimental set-up used for the biological study.

[0082] FIG. 10 is a photo of air cabin filter.

[0083] FIG. 11 is toluene concentration versus time plot.

[0084] FIGS. 12A and 12B demonstrate the combined action of activated carbon and the photocatalysts of the invention.

[0085] FIG. 13 is formaldehyde concentration versus time plot.

[0086] FIG. 14 is a photo showing a multistage filter.

[0087] FIG. 15 illustrates a multistage filter with the illumination array incorporated therein.

[0088] FIG. 16 is toluene concentration versus time plot.

[0089] FIG. 17 is toluene concentration versus time plot.

[0090] FIG. 18 illustrates an experimental set-up of the photoreactor.

[0091] FIG. 19 is a photo showing a series of aluminum flow-through supports.

[0092] FIG. 20 is toluene concentration versus time plot.

[0093] FIG. 21 is toluene concentration versus time plot.

[0094] FIG. 22 shows the incorporation of a multistage filter inside air tube or air channel.

[0095] FIGS. 23A, B and C. FIG. 23A is a graph showing the virus infectivity assay (end-point dilution) performed as described in Example 8 for cells infected with viruses pre-treated with the compound Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 for 5 minutes in the light or for 25 minutes in the dark. Virus titers at 5 minutes (indicated in the graph by the label “Catalife Light”) and 25 minutes (indicated in the graph by the label “Catalife Dark”) are presented here as 1 IU/ml, while in fact the CPE was absent in all the dilutions tested. Vero-E6 cells in 96-well plates were fixed and stained with Crystal Violet 48 hours post infection in the absence (“Mock”, B) or in the presence of the compound (Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20, C). Blue-stained wells indicate no CPE detected, while empty (“white”) wells indicate CPE. Several dilutions of the virus out of 10.sup.−2 to 10.sup.−7 are presented. Triplicates are presented here for the virus dilution 10.sup.−3 and 10.sup.−4.

EXAMPLES

Preparation 1

Preparation of Component A1: Bi.SUP.(0) .doped-BiOCl.SUB.0.80.Br.SUB.0.20

[0096] Deionized water (75 ml), glacial acetic acid (35 ml) and bismuth nitrate (9.18 g) were added to a flask and were mixed at room temperature for fifteen minutes until a clear, transparent solution was formed. The so-formed solution was added to a previously prepared solution consisting of CTAC (4.85 g; in the form of 25 wt % aqueous solution) and CTAB (1.378 g dissolved in 10 ml of water). Finally, sodium borohydride (21.4781 mg) and ethanol (20 ml) were added to the reaction mixture, which was then stirred for additional 60 minutes at about 25-30° C. The precipitate formed was separated from the liquid phase by filtration, washed five times with ethanol (5×50 ml) and then five times with water (5×200 ml). The off-white solid was then dried (3 hours in air). The weight of the solid collected was ˜9 grams. Doping level was ˜3%.

Preparation 2

Preparation of Component A2: BiOCl.SUB.0.80.Br.SUB.0.20

[0097] Deionized water (75 ml), glacial acetic acid (35 ml) and bismuth nitrate (9.18 g) were added to a flask and mixed at room temperature for fifteen minutes until a clear, transparent solution was formed. CTAB (1.378 g dissolved in 10 ml of water) and CTAC (4.85 g; in the form of 25 wt % aqueous solution) were added to the solution, for additional 30 minutes of mixing at room temperature. The white precipitate formed was separated from the liquid phase by filtration, washed five times with ethanol and five times with water, in order to remove the non-reactive organic species. The solid was then dried (in air). The weight of the solid collected was 7 g. The product may be subjected to heating at 400° C. for approximately 1 hour. The entitled product is characterized by average particle size of 2.62 m, surface area of 25.75 m.sup.2/g and pore radius of 22 Å. As shown in FIG. 1, the so-formed BiOCl.sub.0.80Br.sub.0.20 has flower-like morphology.

Preparation 3

Preparation of Component A3: BiOBr

[0098] Deionized water (50 ml), glacial acetic acid (35 ml) and bismuth nitrate (9.70 g) were added into a 250 ml beaker and mixed at room temperature for fifteen minutes until a clear, transparent solution was formed. Cetyltrimethylammonium bromide-CTAB- (7.2879 g dissolved in 30 ml of water and 30 ml of ethanol) were added to the solution, for additional 60 minutes of mixing at room temperature. The yellowish precipitate thus formed was separated from the liquid phase by filtration, washed five times with water (50 ml) and washed five times with ethanol (30 ml), in order to remove the non-reactive species. The solid was then dried (in air or oven at 60° C./overnight).

Preparation 4

Preparation of Component B: BiOCl.SUB.0.20.Br.SUB.0.80 .(Using Inorganic Halides)

[0099] Deionized water (50 ml), glacial acetic acid (35 ml) and bismuth nitrate (9.18 g) were added into a 250 mL beaker and mixed at room temperature for fifteen minutes until a clear, transparent solution was formed. Sodium chloride-NaCl (0.2212 g dissolved in 10 ml of water) and potassium bromide-KBr (1.8017 g dissolved in 10 ml of water) were added to the solution, for additional 60 minutes of mixing at room temperature. The yellowish precipitate thus formed was separated from the liquid phase by filtration, washed five times with water (50 ml), in order to remove the non-reactive species. The solid was then dried (in air or oven at 60° C./overnight). The entitled product was characterized by average particle size of 7 μm, BET surface area of about 30 m.sup.2/g and pore radius of 22 Å. As shown in FIG. 2A, the so-formed BiOCl.sub.0.20Br.sub.0.80 has plate-like morphology.

Preparation 5

Preparation of Component B: BiOCl.SUB.0.20.Br.SUB.0.80 .(Using Organic Halides)

[0100] Deionized water (50 ml), glacial acetic acid (35 ml) and bismuth nitrate (9.18 g) were added into a 250 ml beaker and mixed at room temperature for fifteen minutes until a clear, transparent solution was formed. Cetyltrimethylammonium chloride-CTAC- (4.8448 g of 25 wt. % aqueous solution) and Cetyltrimethylammonium bromide-CTAB- (5.5178 g dissolved in 20 ml of water and 15 ml of EtOH) were added to the solution, for additional 60 minutes of mixing at room temperature. The yellowish precipitate thus formed was separated from the liquid phase by filtration, washed five times with ethanol (30 ml) and five times with water (50 ml), in order to remove the non-reactive organic species. The solid was then dried (in air or oven at 60° C./Overnight). As shown in FIG. 2B, the so-formed BiOCl.sub.0.20Br.sub.0.80 has flower-like morphology.

Example 1

Photooxidation Activity of [A1+A2]/B Combination Incorporated into Gypsum Model Filter: Decomposition of Toluene and Ethanol

[0101] The goal of the study was to determine the visible-light induced photooxidation generated by a combination of bismuth oxyhalides, to assess its potential benefit in air-purification, i.e., in decomposing volatile contaminants.

[0102] In the study reported in this Example, a combination of three active bismuth oxyhalides was formulated as an aqueous dispersion. The formulation was applied onto honeycomb-shaped, gypsum-made filter. The photocatalytic filter was mounted in a cell, equipped with visible light irradiation source (to “switch on” the photocatalytic activity) and a fan. Vapors of volatile organic solvents, generated in a sealed test chamber, were caused to flow through the cell and across the photocatalytic filter. The concentration of the gaseous organic material was measured as function of time for more than 10 hours, to assess the ability of the photocatalytic filter to decompose vapors of organic contaminants passing therethrough.

[0103] Experimental Set-Up

[0104] 1) A1+A2+B Aqueous Formulation

[0105] 30 g of component A (Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 of Preparation 1), 10 g of component A2 (BiOCl.sub.0.80Br.sub.0.20 of Preparation 2) and 20 g of component B (BiOCl.sub.0.20Br.sub.0.80 of Preparation 4) are added to 100 ml water, to afford an aqueous dispersion of the three photocatalysts.

[0106] 2) Photocatalytic Filter

[0107] The filter model is made of gypsum body shaped into a square prism (a=10 cm, b=10 cm, c=3 cm), as shown in FIG. 3, with an array of open cells arranged in honeycomb structure, to allow air flow across the gypsum block, that is, through the passages extending perpendicularly to the bases (note that each passage has hexagonal cross section).

[0108] The rectangular gypsum block is prepared with the aid of a corresponding template shown in FIG. 4. The open cells in the honeycomb-shaped gypsum filter of FIG. 3 correspond in shape, size and position to the hexagonal prisms of the template shown in FIG. 4. The template consists of an array of 216 silicon-made hexagonal prisms extending vertically from a silicon frame. Each hexagonal prism is 3.5 cm high; the side of the hexagonal base is 5 mm. The center-to-center distance between two adjacent hexagonal prisms in a row is 5 mm.

[0109] Gypsum powder (180 g) was added to the A1+A2+B aqueous dispersion, and the so-formed mixture was poured into the silicon template. The hardening process of the gypsum took a few hours, following which the photocatalysts-added gypsum filter was ready for use.

[0110] 3) Photocatalytic Reactor

[0111] The photocatalytic reactor is shown in the photo appended in FIG. 5A. It consists of a Perspex cell (length: 30 cm, width: 10 cm, height: 10 cm). The walls of the cell are 5 mm thick. The honeycomb-shaped gypsum cast was placed at distance of 10 cm from, and parallel to, one of the square faces of the Perspex cell. White LED lamp (6500K with optional 10-40 W power) extends from the opposite square face of the cell into the interior of cell, illuminating in the direction of the gypsum body. The distance between the gypsum cast and the lamp was about 10 cm. Air flow across the cell was aided by a fan mounted on one face of the cell (in the side of the gypsum filter) and apertures distributed over the opposite face of the cell (where the lamp is placed).

[0112] 4) Test Chamber

[0113] The test chamber, which is shown in FIG. 6, consists of 500 L sealable cell, rectangular in shape (1) designed to accommodate the photocatalytic reactor and allow a flow of vaporized organic pollutant across the photocatalytic reactor (2), and measurement of the concentration of the gaseous pollutant in order to determine the degree of decomposition that can be achieved with the aid of photocatalytic reactor.

[0114] A shelf (3) is mounted at the upper part of the test chamber. The purpose of the shelf is to hold a petri dish (4), which is filled with the tested volatile organic solvent. The test chamber was equipped with a pair of fans (5A and 5B), one located above the shelf, to facilitate the vaporization of the organic solvent. The other fan (5B) is located on one of the walls of the test chamber, to ensure effective distribution of the vaporized organic pollutant in the interior of test chamber and passage of the vapors through the photocatalytic reactor. The photoreactor (2) is equipped with its own fan (5C), as previously explained. The test chamber is provided with a sealable door (not shown).

[0115] The test chamber also includes an external tap (6) mounted in the center of one of its walls, where VOC measurement occurs. The test chamber is equipped with a humidity and a temperature meter. The gas concentration in the test chamber was measured using Tiger VOC detector (from Ion Science), a photoionization detector equipped with 10.6 eV ionization lamp which measures concentrations of a wide range of gases, from 20,000 ppm down to 1 ppb.

[0116] Experimental Protocol

[0117] The test chamber was ventilated before the experiment begun to ensure that the atmosphere inside the test chamber was the same as the outside atmosphere. This atmosphere was set as the zero point for the measurements of the Tiger photoionization detector, such that any reading of the detector was relative to the zero point.

[0118] A petri dish with a sample of the tested organic solvent was placed on the shelf in the test chamber and the chamber was sealed. The pair of fans inside the test chamber were turned on and allowed to operate for thirty minutes. During the thirty minutes time period, the photocatalytic reactor placed in the cell is inactive: neither the fan nor the lamp of the photocatalytic reactor was switched on. Meanwhile the vapors of the slowly evaporating volatile solvent in the sample were evenly distributed inside the test cell owing to the action of the fans.

[0119] After the thirty minutes time period has elapsed, the fan and the lamp of the photocatalytic reactor were turned on in order to start measuring the photocatalytic activity of the filter and its effect on an organic contaminant. The LED lamp (Eurolux) operated at 20 W. The fan (DC brushless QFR0812VH) operated at 4.5 V, such that air velocity was 1 m/sec and air flow rate across the photocatalytic reactor was 10 L/sec.

[0120] The measurement using the tiger detector was performed by connecting the tip of the detector (where the gaseous sample is drawn into the detector with the help of a built-in pump inside it) to the tap of the test chamber. The reading, which stabilizes after about 30 seconds, is the concentration in ppm of the tested organic gas inside the cell. Measurements were conducted periodically at one-hour intervals and continued until the concentration of the tested gas dropped below the detection limit owing the photocatalytic action of multiple combination of bismuth oxyhalides incorporated into the filter.

[0121] For comparison, the same experiment was carried out using titanium oxide-based photocatalytic device: “Air Oasis” photocatalytic air purifier, which was placed inside the 500 L test chamber.

[0122] It should be noted that the Tiger detector cannot tell which gas is in the cell, but calculates the concentration taking into consideration the response factor (RF) of the organic gas chosen, i.e. the concentration of the generated intermediates in the process is calculated using the RF of Toluene.

[0123] Results

[0124] The volatile organic solvents, the decomposition of which was tested (separately) in the study, were toluene and ethanol. Toluene samples of 4 microliters were used. Ethanol samples of 2 microliters were used.

[0125] The results are shown in FIGS. 7 and 8, respectively, in the form of concentration (ppm) versus time plots. Results measured for the photocatalytic filter of the invention are indicated in squares. Results obtained for the comparative commercial photocatalytic unit are marked by rhombuses (Air Oasis).

[0126] Generally, a characteristic concentration versus time curve of photooxidation process of an organic contaminant by the action of a photocatalyst shows an initial increase of concentration, indicating the build-up of successively generated oxidation products. For example, in the case of toluene, the methyl attached to the aromatic ring provides the first oxidizable site: —CH.sub.3.fwdarw.—CH.sub.2OH.fwdarw.—CH(═O).fwdarw.—COH(═O). Next, the aromatic ring is opened, followed by carbon chain breakage. An efficient photocatalyst should be able to proceed to decompose the oxidation products of the original contaminant, eventually reaching full mineralization, i.e., CO.sub.2 and H.sub.2O formation.

[0127] Turning now to the concentration versus time curves for toluene in FIG. 7, the results show that under the action of the photocatalytic filter of the invention, activated with visible light irradiation, the concentration of the organic matter increases over the first hour, in line with the explanation given above. The concentration then decreases gradually, dropping down to zero after 12 hours, indicating that toluene underwent full oxidation to carbon dioxide and water.

[0128] TiO.sub.2-based commercial photocatalytic units tested in the study did not perform well:

[0129] Air Oasis shows steady increase in the organic matter from 1.8 ppm at time=0 to 3.4 ppm after 12 hours. This means that toluene was partially oxidized, but its (relatively stable) oxidation products haven't got fully oxidized to carbon dioxide and water by the action of Air Oasis.

[0130] Turning now to the concentration versus time curves for ethanol in FIG. 8, it is seen again the photocatalytic filter of the invention achieves complete mineralization of the organic matter after sixteen hours.

Example 2

Antimicrobial Activity of A1/B Combination Incorporated into Gypsum Model Filter

[0131] The goal of the study was to determine antimicrobial activity exerted by the combination of bismuth oxyhalides, to assess its potential benefit in air-disinfection, i.e., in eliminating bacteria from contaminated surfaces.

[0132] In the study reported in this Example, a combination of two active bismuth oxyhalides was formulated as an aqueous dispersion. The formulation was applied onto honeycomb-shaped, gypsum-made filter. The photocatalytic filter was mounted in a cell (photocatalytic reactor) equipped with visible light irradiation source to “switch on” the photocatalytic activity, and a fan to facilitate air flow across the cell. The experimental work was divided into two parts.

[0133] In part A, the photocatalytic cell was placed in a test chamber. Bacterial colonies (Salmonella typhi and Bacillus subtilis) grown on microslides were inserted into the test chamber, externally to the photocatalytic cell. Bacterial counts were taken periodically to assess the antimicrobial effect of the photocatalytic filter.

[0134] In part B, the photocatalytic cell was placed on shelf in a refrigerator. Bacterial colonies (Listeria monocytogenes ATCC) grown on microslides were put into the refrigerator (at two different locations). Bacterial counts were taken periodically to assess the antimicrobial effect of the photocatalytic filter.

[0135] Experimental Set-Up

[0136] 1) A1+B Aqueous Formulation

[0137] 10 g of component A (Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 of Preparation 1) and 30 g of component B (BiOCl.sub.0.20Br.sub.0.80 of Preparation 4) were added to 100 ml water, to afford an aqueous dispersion of the two photocatalysts.

[0138] 2) Photocatalytic Filter

[0139] A honeycomb-shaped filter, with the A1+B aqueous dispersion applied thereto, was prepared as described in Example 1.

[0140] 3) Photocatalytic Reactor

[0141] The photocatalytic reactor is as described in Example 1 and shown in the photo appended in FIG. 5A.

[0142] 4) Test Chamber

[0143] The test chamber consists of a 70-liter plastic container to accommodate the photocatalytic reactor. The test chamber was partially open to protect against uncontrolled air flow, but to allow air exchange at the same time.

[0144] Part A

[0145] Experimental Protocol

[0146] The photocatalytic reactor and contaminated glass slides were placed in the test chamber which was located inside a biological hood for safety reasons. The tests were performed in sterile conditions to prevent cross contamination. Two different microorganisms were chosen (Salmonella typhi and Bacillus subtilis), which represent the variety of bacteria and molds which are common airborne pollutants. The test chamber is shown in the photograph appended in FIG. 9. The photocatalytic reactor is in active mode (light source turned on). Contaminated microslides are located at the right side of the container.

[0147] The photocatalytic reactor started working when the LED light and the fan were turned on.

[0148] The contaminated glass slides were taken out for the counting of the microorganisms at predetermined intervals. They were transferred into test tubes where they were washed in order to start the counting process of the living microorganisms.

[0149] Results

[0150] Bacterial counts are tabulated below.

TABLE-US-00002 TABLE 1 Salmonella typhi Time [Hr] CFU ((colony forming units) 0 900,000 1 540,000 2 3,000 3 600

TABLE-US-00003 TABLE 2 Bacillus subtilis Time [Hr] CFU ((colony forming units) 0 1,200,000 1 680,000 2 4,400 4 960 6 500

[0151] The results demonstrate that the photocatalytic filter of the invention exerted antimicrobial activity, indicated by four-fold reduction of surface contamination. It is of note that the effect was achieved even though there was no direct contact between the photocatalytic filter and the bacterial colonies. Without wishing to be bound by theory, it is believed that the creation of oxidant species in the atmosphere inside the photocatalytic cell (i.e., decomposition of water molecules to produce active hydroxyl radicals) ultimately led to elimination of bacterial colonies. The location of the bacterially contaminated glass slides inside the test chamber had no effect on the microorganisms count results; no differences were found when the glass slides were located on the front or on the side of the test chamber. This suggests that uniform atmosphere was created inside the test chamber, in terms of the distribution of oxidant species.

[0152] Part B

[0153] Experimental Protocol

[0154] The photocatalytic reactor was placed on a shelf inside a refrigerator (T=2-8° C.). Listeria monocytogenes-contaminated microslides were placed in the refrigerator at two different locations: [0155] Inside to the photocatalytic reactor: adjacent to the front wall of the photocatalytic reactor (i.e., the perforated wall opposite to the wall equipped with the fan). [0156] Externally to the photocatalytic reactor: on a shelf in the refrigerator below the photocatalytic reactor.

[0157] Listeria monocytogenes-contaminated tube served as a control sample. The tube was covered with aluminum foil to cancel out any effect generated by the photocatalytic reactor. The control tube was placed on the shelf below the photocatalytic reactor.

[0158] At two time points after the beginning of the experiment (marked by switching on the photocatalytic reactor), i.e. after twelve and twenty-four hours of continuous operation of the photocatalytic reactor, the treated microslides were taken out of the refrigerator for viable counts. As to the control sample, viable count was performed only once, at the end of the twenty-four hours period. Details are as follows:

[0159] Starter of Listeria monocytogenes was grown over night. Serial dilutions were made to count the viable cells and determine initial concentration. Next, a volume of 0.2 ml of the starter was put on each of four microslides (an internally located pair, consisting of a first microslide for the t.sub.1=12 h measurement and a second microslide for the t.sub.2=24 h measurements+an externally located pair, consisting of a first microslide for the t.sub.1=12 h measurement and a second microslide for the t.sub.2=24 h measurements).

[0160] For the counting measurements, a slide was taken out from the refrigerator, inserted into 50 ml tube and washed by 2 ml of PBS buffer. The tube was vortexed and its content was transferred to a petri dish, into which SMA medium was poured to serve as the plate count agar. Viable counts were made on serially diluted samples incubated for forty-eight hours at 37° C.

[0161] Results

[0162] The results are tabulated in Table 3.

TABLE-US-00004 TABLE 3 Listeria monocytogenes internally externally located samples located samples control t = 0 h.sup.  1.2 × 10.sup.8 CFU/g 1.2 × 10.sup.8 CFU/g 1.2 × 10.sup.8 CFU/g T = 12 h <100 CFU/g <100 CFU/g T = 24 h <10 CFU/g <10 CFU/g 1.0 × 10.sup.8 CFU/g

[0163] The results indicate the strong antimicrobial effect exerted by the multiple combination of bismuth oxyhalides.

Example 3

Photooxidation Activity of A1/A3 Combination Embedded in Non-Woven Fabric Filter

[0164] The goal of the study was to assess the visible-light induced photooxidation generated by a combination of bismuth oxyhalides, when this combination is set in non-woven fabric filter medium.

[0165] In the study reported in this Example, a combination of two active bismuth oxyhalides was dispersed in ethanol. The binder-free formulation was sprayed onto non-woven fabrics. The fabrics were dried under ambient temperature, following which the bismuth oxyhalides-loaded non-woven fabric was mounted in a cell, equipped with visible light irradiation source (to “switch on” the photocatalytic activity) and a fan. Vapors of volatile organic solvents, generated in a sealed test chamber, were caused to flow through the cell and across the photocatalytic fabric filter. The concentration of the gaseous organic material was measured as function of time, to assess the ability of the photocatalytic non-woven fabric filter to decompose vapors of organic contaminants passing therethrough.

[0166] Experimental Set-Up

[0167] 1) A1+A3 Ethanolic Formulation

[0168] 350 mg of component A1 (Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 of Preparation 1) and 150 mg of component A3 (BiOBr)) were dispersed in 4 ml ethanol using a homogenizer (10,000 rpm).

[0169] 2) Photocatalytic Filter

[0170] Different types of 1-2 mm thick non-woven fibers (some of which include activated carbon as an adsorbing agent) were cut into square-shaped pieces (10 cm×10 cm). A volume of 4 ml of the A1+A3 ethanolic dispersion was uniformly sprayed on each of the non-woven fabric pieces. The fabric pieces were dried by allowing the ethanol to evaporate at room temperature.

[0171] 3) Photocatalytic Reactor

[0172] The photocatalytic reactor was the same 3 L rectangular cell described in Example 1 and shown in the photo appended in FIG. 5, but this time a bismuth oxyhalide-incorporated non-woven fiber piece served as the filter medium in place of the honeycomb-shaped gypsum body. The 10 cm×10 cm fiber piece was mounted in the photocatalytic reactor, 15 cm apart from the rear wall where the fan is located. The fiber piece was fit into a suitable frame made of Perspex.

[0173] 4) Test Chamber

[0174] The test chamber is the same 500 L sealable cell, rectangular in shape, described in Example 1 and shown in FIG. 6. As mentioned above, the major elements of the test chamber include: a shelf mounted at the upper part of the test chamber, to hold a sample of a volatile organic solvent; a pair of fans to ensure distribution of the vaporized organic pollutant in the interior of cell and passage of the vapors through the photocatalytic reactor; a sealable door; and an external tap mounted in the center of one of its walls, to which the Tiger device is connected for VOC measurements; and humidity and temperature meters.

[0175] Experimental Protocol

[0176] The protocol was similar with the one described in Example 1 (pre-experiment ventilation of the test chamber, placement of petri dish with a volatile organic solvent on the shelf in the test chamber, evaporation of the volatile organic solvent to achieve uniform distribution of the gaseous contaminant in the test chamber, switching on the photocatalytic reactor (white LED lamp (Eurolux) 6500K, operated at 10 W; a fan (DC brushless QFR0812VH) operated at 4.5 V, such that air velocity was 1 m/sec and air flow rate across the photocatalytic reactor was 10 L/sec.

[0177] The measurements using the tiger detector were conducted periodically at 30 minutes intervals over a period of two hours.

[0178] Results

[0179] The volatile organic solvent, the decomposition of which was tested in the study, was toluene. Toluene samples of 2.13 microliters were used.

[0180] The results indicate that at the end of the two hours test period, the initial concentration of toluene (1 ppm) dropped significantly, with the photocatalytic filter achieving from 35 to 95% decomposition rates depending on the source of activated carbon and porosity of the fabric.

Example 4

Photooxidation Activity of A1/A3 Combination Embedded in Cabin Air Filter

[0181] The goal of the study was to assess the visible-light induced photooxidation generated by a combination of bismuth oxyhalides embedded in a cabin air filter. Such filters are loaded with activated carbon to capture particles, adsorb contaminants etc., to protect the heating ventilation and air conditioning system of the vehicle.

[0182] In the study reported in this Example, a combination of two active bismuth oxyhalides was dispersed in ethanol. The binder-free formulation was applied onto the filter. The bismuth oxyhalides-loaded pleated filter was mounted in a cell, equipped with visible light irradiation source to “switch on” the photocatalytic activity, and a fan. Vapors of volatile organic solvents, generated in a sealed test chamber, were caused to flow through the cell and across the photocatalytic cabin air filter. The concentration of the gaseous organic material was measured as function of time for more ten hours, to assess the ability of the photocatalytic cabin air filter to decompose vapors of organic contaminants passing therethrough.

[0183] Experimental Set-Up

[0184] 1) A1+A3 Ethanolic Formulation

[0185] 2 g of component A1 (Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 of Preparation 1) and 2 g of component A3 (BiOBr)) are dispersed in 25 ml ethanol using a homogenizer (10,000 rpm).

[0186] 2) Photocatalytic Filter

[0187] A volume of 25 ml of the A1+A3 ethanolic dispersion was uniformly sprayed on a 10 cm×10 cm×3 cm activated carbon-containing non-woven fabric filter. The filter was dried by allowing the ethanol to evaporate at room temperature. The pleated filter was fixed in a conventional frame (10 cm×10 cm open area), as shown in the photo appended in FIG. 10.

[0188] 3) Photocatalytic Reactor

[0189] The photocatalytic reactor is the same 3 L rectangular cell described in Example 1 and shown in the photo appended in FIG. 5, but this time the bismuth oxyhalide-added, activated carbon-containing cabin air filter served as the filter medium in place of the honeycomb-shaped gypsum body. The cabin air filter was placed in the photocatalytic reactor, 12 cm apart from the rear wall where the fan is located.

[0190] 4) Test Chamber

[0191] The test chamber is the same 500 L sealable cell, rectangular in shape, described in Examples 1 and 3, and shown in FIG. 6.

[0192] Experimental Protocol

[0193] The protocol was similar with the one described in Examples 1 and 3 (pre-experiment ventilation of the test chamber, placement of petri dish with a volatile organic solvent on the shelf in the test chamber, evaporation of the volatile organic solvent to achieve uniform distribution of the gaseous contaminant in the test chamber, switching on the photocatalytic reactor (white LED lamp (Eurolux) 6500K, operated at 20 W; a fan (DC brushless QFR0812VH) operated at 4.5 V, such that air velocity was 1 m/sec and air flow rate across the photocatalytic reactor was 10 L/sec.

[0194] The measurements using the tiger detector were conducted periodically every hour over a period of ten hours.

[0195] Results

[0196] The volatile organic solvent, the decomposition of which was tested in the study, was toluene. Toluene samples of 13.31 microliters were used.

[0197] The initial concentration of toluene in the test chamber was ˜6 ppm. A concentration versus time plot is shown in FIG. 11, indicating practically full mineralization of toluene at the end of the ten minutes test period.

Example 5

Testing the Action of Activated Carbon and Bismuth Oxyhalides: Adsorption and Photooxidation of Toluene and Formaldehyde

[0198] The goal of the study was to assess the ability of bismuth oxyhalides to aid activated carbon—the adsorbent used in filters—in eliminating volatile organic contaminants.

[0199] Experimental Set Up

[0200] The 3 L photocatalytic reactor described above, with its LED light source and fan positioned in the rear side, was used. However, a simplified configuration was adopted: in the comparative example, 500 mg of commercial activated carbon (Sigma-Aldrich Cat. 97876) were added to a Petri dish which was put inside the 3 L photocatalytic reactor. The photocatalytic reactor was placed in the 500 L test chamber.

[0201] In the experiment according to the invention, a powder blend consisting of:

[0202] 200 mg of component A1 (Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 of Preparation 1);

[0203] 50 mg of component A3 (BiOBr); and

[0204] 250 mg of component B (BiOCl.sub.0.20Br.sub.0.80 of Preparation 4) was added together with 500 mg of activated carbon to the petri dish in the photocatalytic reactor.

[0205] Experimental Protocol

[0206] The protocol was similar with the one described in Examples 1, 3 and 4 (pre-experiment ventilation of the test chamber, placement of petri dish with a volatile organic solvent on the shelf in the test chamber, evaporation of the volatile organic solvent to achieve uniform distribution of the gaseous contaminant in the test chamber, then switching on the photocatalytic reactor (white LED lamp (eurolux) 6500K, operated at 20 W; a fan (DC brushless QFR0812VH) operated at 4.5 V, such that air velocity was 1 m/sec and air flow rate across the photocatalytic reactor was 10 L/sec. Humidity % was ˜40%.

[0207] The measurements using the tiger detector were conducted periodically every thirty minutes over a period of twelve hours.

[0208] Results

[0209] Toluene sample of 8.52 microliters was added to the petri dish in the test chamber. The sample evaporated and the concentration of toluene inside the test chamber, before the experiment begun, was 4 ppm.

[0210] The elimination of toluene achieved with activated carbon alone (500 mg), and with a blend consisting of 500 mg activated carbon+500 mg of the [A1+A3]/B combination, was tested. The results are shown in FIG. 12A, in the form of concentration (ppm) versus time plots. It is seen that activated carbon alone cannot eliminate volatile organic contaminants effectively. The action of activated carbon/bismuth oxyhalides, combing adsorption and photooxidation, is much more effective. The results suggest that the photocatalyst, in addition to decomposing the pollutant, also attaches a self-cleaning functionality to the activated carbon adsorbent, thereby improving its performance.

[0211] FIG. 12B shows the results of FIG. 12A but adds two sets of data, collected with the same experimental set-up, using 1000 mg of activated carbon (the second closest curve to the abscissa) and a blend consisting of 500 mg activated carbon+500 mg of the [A1+A3]/B combination, but this time dark conditions (the uppermost curve). Notably, doubling the amount of the activated carbon (500 mg.fwdarw.1000 mg) achieves only slight improvement in the removal rate of toluene, as compared to the strong effect achieved by the blend of the invention. The results attest to the unique role of the photocatalyst in combination with activated carbon.

[0212] FIG. 13 is a concentration versus time curve illustrating the gradual elimination of formaldehyde (initial concentration in the test chamber 1 ppm) with the aid of activated carbon/bismuth oxyhalides blend. The formaldehyde photocatalytic oxidation process was monitored using a specific sensor produced by Graywolf.

Example 6

Antiviral Activity of A1 and A3 Photocatalysts

[0213] The goal of the study was to test antiviral activity of A1 and A3 of Preparation 1 and Preparation 3, respectively (both synthesized with the aid of quaternary ammonium halide salts) by neutralization of Vesicular Stomatitis Virus (VSV), which is an enveloped, negative-sense RNA virus with wide host range.

[0214] Experimental Set-Up

[0215] Virus stocks were prepared in monolayer cultures of HeLa cells growing in Dulbecco's modified Eagle's medium (DMEM). The DMEM was supplemented with 10% of fetal calf serum (FCS), 100 U/mL penicillin, 100 U/mL streptomycin, and 2 mM L-glutamine (Biological Industries, Beit Haemek, Israel).

[0216] Virus titration was held in 96 wells plates as follows: 50000 HeLa cells per well were plated 24 hours prior to infection. The cultures were infected with (50 μl) virus in decimal dilutions. Following an hour of absorption, the cultures were covered with 150 μl of DMEM supplemented with 2% FCS. The virus titer was determined 48 hours post infection. Cells were fixed with 1.7% formaldehyde for 30 minutes at room temperature, stained with 100 μl of 0.01% Crystal Violet, and then washed with tap water. The virus titer was determined by end-point dilution.

[0217] Experimental Protocol

[0218] Ten mg of each one of the A1 and A3 photocatalyst powders were mixed with the virus in 1 ml medium in transparent glass tubes. Each test was conducted for an hour, in room temperature, with continuous rotation, under controlled light conditions (LED lamp). Simultaneous control tests were conducted in tubes wrapped with aluminum foil to prevent light exposure (in the dark).

[0219] Photocatalyst co-incubated with the virus samples were collected at intervals of 10 minutes. Samples were centrifuged to separate the photocatalyst (a non-soluble powder) from the virus. Following centrifugation, each sample was serially diluted, and 50 μl of separated virus were added to the HeLa cell cultures growing in 96-well plate. After one hour of virus absorption, 150 μl of medium were added to each well, and the cells were incubated at 37° C. for 48 hours, when the virus titer was determined.

[0220] In parallel, the toxicity of the photocatalysts were assessed. “HeLa” cells cultures maintained as described above in DMEM media, were incubated with the catalysts in light and dark conditions. No cytotoxic effect was observed in the cell culture at all the concentration used for virus inactivation (10 mg/ml).

[0221] Results

[0222] The photocatalysts have shown a clear antiviral activity in lowering the virus concentration up to three orders within 30 minutes, and up to four orders within 50 minutes of virus incubation in light conditions. The results for the A1/A3 photocatalysts are tabulated below.

TABLE-US-00005 TABLE 4 Light exposure Dark (min) Light (control) 0 .sup.  10.sup.4 10.sup.4 10 .sup.  10.sup.2 10.sup.4 20 .sup.  10.sup.2 10.sup.3 30 <10 10.sup.3 40 <10 10.sup.3 50 <10 10.sup.4 60 <10 10.sup.4

Examples 7A-7D

Photooxidation Activity of A1 Photocatalyst: Decomposition of Volatile Organic Compound

[0223] A series of experiments were conducted to test the action of Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 of Preparation 1 on volatile organic compounds (VOCs).

[0224] In its most general form, the experimental set-up consisted of the previously described test chamber (see FIG. 6), in the form of 500 L Perspex cell, accommodating a 30 cm×10 cm×10 cm photoreactor (the design of photoreactor was modified compared to that used in previous examples, as explained below). Toluene was the VOC of choice the experiments; toluene was added to a petri dish that was placed on a shelf mounted in the upper section of the test chamber. A pair of fans installed in the test chamber as previously described in reference to FIG. 6 enabled evaporation of toluene and its uniform distribution in the interior test chamber, such that it can reach the photocatalytic reactor. Variation in toluene concentration in the test chamber was detected with Tiger VOC detector (from Ion Science).

[0225] As for the photoreactor, reference is made to the design shown in FIG. 5B. A fan (5C) (San Ace 80 model name: 109P0812M601) is installed in one of the square-shaped sides of the photoreactor (2) to move air from the test chamber into the reactor. LED strips were mounted inside the photoreactor, in place of the previously used LED lamp. A total of five LED strips (7) were affixed to a frame, in parallel to each other, separated by equal distances of 2 cm. The frame itself can be installed in the photoreactor at two different positions:

[0226] 1) perpendicularly to the longitudinal axis of the photoreactor, such that the LED strips are positioned vertically (e.g., at distance of 10 cm from the fan; the frame is movable and can be repositioned along the length of the photoreactor); and

[0227] 2) the frame can be suspended from the ceiling of the photoreactor, such that the LED strips (7) are positioned horizontally, facing the floor of the photoreactor.

[0228] The inner walls of the photoreactor are partially coated with mirrors to deflect the light beams in the direction of the tested sample.

[0229] The photocatalyst tested was placed inside the photoreactor in various ways, i.e., embedded in, or applied onto the surface of substrates designed to allow flow-through of moving air. For example, numeral (8) in the appended drawings indicates a flow-through support coated with the photocatalysts. But other modes of using the photocatalysts were tested, as shown in each of the experiments 7A-7D.

[0230] 7A (Direct Action of Photocatalyst Powder):

[0231] The powdery photocatalyst Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 (2 g) was added to a petri dish placed in the interior of the photoreactor, about 20 cm from fan. The LED array was mounted above the petri dish, i.e., the LED strips (7) are positioned horizontally, illuminating the powder that rests on the floor of the photoreactor.

[0232] Toluene was added to a petri dish in the test chamber and was evaporated to reach toluene concentration of 3 ppm in the sealed test chamber (i.e., initial VOC level).

[0233] Then the fan of the photoreactor was turned on (operating at 50% of its maximal intensity, achieving incoming air stream of 0.5 m/s velocity). The LED illumination was switched on (approximately 15 W power), to induce the photocatalytic action of the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 powder.

[0234] The results are shown in FIG. 16, where toluene concentration is plotted versus time. The results demonstrate degradation of toluene with the passage of time (toluene concentration dropped by 50%˜five hours after the experiment had begun).

[0235] 7B (Photocatalyst Embedded in a Flow-Through Gypsum Substrate:

[0236] The photocatalyst was incorporated into a gypsum filter by the following method. Gypsum powder (60 g), activated carbon (1.5 g; Sigma Aldrich 31616) and silica (1 g; Sigma Aldrich 60760) were added to double distilled water (50 ml) which contained the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 photocatalyst (10 g). Following the initial mixing, the resulting photocatalytic gypsum formulation was poured over a thin silicon-based template as previously described and left for a final drying over 2 hours. The hardened 10 cm×10 cm×1.5 cm photocatalyst-added honeycomb shaped gypsum block, with an array of open cells extending through the block having hexagonal cross-section, to enable passage of air across the gypsum block, was ready for use. The photocatalytic gypsum was installed inside the photoreactor to occupy the square cross section (10 cm×10 cm) of the photoreactor.

[0237] Toluene was added to a petri dish in the test chamber and was evaporated to reach toluene concentration of 5 ppm in the sealed test chamber (i.e., initial VOC level).

[0238] Then the fan of the photoreactor was turned on (operating at 70% of its maximal intensity). The LED illumination was switched on (full power), to induce the photocatalytic action of the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 powder embedded in the gypsum filter.

[0239] The results are shown in FIG. 17 in the form of concentration versus time curve, demonstrating rapid degradation of toluene:toluene concentration dropped by 90%, only two hours after the experiment had begun.

[0240] 7C (Photocatalyst Applied on a Flow-Through Metal Substrate):

[0241] The experimental set-up is shown in FIG. 18, schematically illustrating a side view of the photoreactor (2). A fan (5C) was installed in one face of the photoreactor and the array of LED strips (7) was positioned vertically as previously explained. The change is seen in the addition of a white LED lamp (9), positioned outside the photoreactor, about 5 cm apart from the face of the photoreactor opposite the fan, for illuminating an array of tested samples indicated by numeral (8).

[0242] A photograph of the array of tested samples is shown in FIG. 19. Each member of the array has a structure of a honeycomb, i.e., hollow cells formed between thin (1 mm) aluminum walls. The side of the hexagonal cross-section of the hollow cell is 3 mm. The aluminum-made honeycomb corresponds in size and shape to the dimensions of the photoreactor such that it can fitted inside the photoreactor in a transverse position, to force air moving in the photoreactor to pass through the hollow cells of the aluminum-made honeycomb. Each aluminum-made honeycomb is 6 mm thick. As pointed out above, a total of five aluminum-made honeycombs was used, positioned in parallel to each along the longitudinal axis of the photoreactor.

[0243] Adjacent aluminum-made honeycombs are spaced 1 cm apart. As shown in FIG. 19, the aluminum-made honeycombs are joined to a base (11) such that the entire array can be inserted into, and taken out from, the photoreactor.

[0244] To apply the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 powder onto the thin aluminum walls, each aluminum-made honeycomb was treated with a sprayable glue (suitable glues are available commercially; the binding agent is dispersed in organic solvent(s); sometimes a diluent is added just before application). After the volatile organic component has evaporated, the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 powder was applied onto the glue-coated aluminum walls, by spraying an isopropanol dispersion of the photocatalyst (˜1 g powder in 10 cc IPA), to create a thin layer of the photocatalysts onto the walls of the hollow cells of the structure. The amount of photocatalyst loaded onto each aluminum-made honeycomb, with the geometric features set out above, was 0.7 g. The array consisting of the five aluminum-made honeycombs was placed inside the photoreactor.

[0245] Toluene was added to a petri dish in the test chamber and was evaporated to reach toluene concentration of 3 ppm in the sealed test chamber (i.e., initial VOC level). Then the fan of the photoreactor was turned on (operating at 75% of its maximal intensity). The LED illumination was switched on (full power), and also the externally positioned white LED projector (10 W), to trigger the photocatalytic action of the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 powder applied onto the walls of the aluminum-made honeycombs.

[0246] The results are shown in FIG. 20, indicating a rapid decrease in the VOC level in the test chamber: toluene concentration was reduced by half after just one hour, achieving full degradation at the end of the experiment.

[0247] 7D (Photocatalyst Applied on a Flow-Through Fabric Substrate):

[0248] This time the photocatalyst was added to an elastic woven fabric made of polyester. Four pieces (10 cm×10 cm in size) fabric were used; each was uniformly coated with 0.7 g of the photocatalyst by the procedure set out above (i.e., first coating the fabric with a glue provided in an organic carrier, (using a spray gun), allowing the volatile carrier to evaporate and then applying an isopropanol dispersion of the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 photocatalyst on one face of the fabric, by brushing or spraying. The four square-shaped pieces of fabric, to which the photocatalyst was added, were affixed to a frame inside the photoreactor.

[0249] Toluene was added to a petri dish in the test chamber and was evaporated to reach toluene concentration of 3 ppm in the sealed test chamber (i.e., initial VOC level). Then the fan of the photoreactor was turned on (operating at 75% of its maximal power). The LED illumination was switched on (full power).

[0250] The good removal rate of the VOC by the action of the photocatalyst incorporated into the flow-through fabric is demonstrated by a concentration versus time plot shown in FIG. 21.

Example 8

Inactivation of SARS-CoV-2 Virus by Bi.SUP.(0) .Doped-BiOCl.SUB.0.80.Br.SUB.0.20

[0251] The anti-viral activity of Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 photocatalytic powder against SARS-CoV-2 virus was examined in infected cells.

[0252] Experimental Set-Up

[0253] Vero-E6 cells were grown in DMEM medium supplemented with penicillin (100 U/mL), streptomycin (100 U/mL), L-glutamine (2 mM) and FCS (10%). One day before infection, cells were seeded at 10.sup.4 cells/well in 96-well plates. After infection cells were grown in DMEM supplied with 1% FCS.

[0254] SARS-Related Coronavirus 2 Isolate USA-WA1/2020 (BEI Resources, Cat. number NR-52281) was used for production of viral stock for the experiment. Initial dilution of 1:100 was prepared for a working stock and for incubation with the photocatalyst compound powder.

[0255] Experimental Protocol

[0256] Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 photocatalyst powder (25 mg) was mixed with 1 ml of the working SARS-CoV-2 stock in sterilized glass vials and incubated in visible light (10 W Daylight LED lamp) or dark conditions for time intervals of 0.5, 5, 15, 25 and 40 minutes. After the incubation, the virus-compound mixtures were transferred to 1.5 ml tubes (Eppendorf) and briefly span down (by centrifugation at 2500 rpm, 3 minutes, 4° C.) to separate the virus from the non-soluble powder. The supernatants were subjected to serial dilutions in DMEM medium (without FCS) and 50 μl of the diluted viruses were added to the Vero-E6 cells for infecting thereof (by absorption). The experiment was performed at triplicates. After 1 hour of incubation, 150 μl of fresh medium were added to the infected cells (DMEM, 1% FCS final concentration). Cells were incubated for further 48 hours in an incubator (CO.sub.2 5%, 37° C.). Mock virus samples (control) were incubated in glass vials without any powder and were used to infect cells as detailed above. The experiments conducted with infective virus were carried out in the HUJI BSL3 laboratory (The Hebrew University—Hadassah Medical School, Ein Kerem), strictly according to the NIH safety Biosafety level 3 guidelines for work with infectious agents.

[0257] Calculation of the virus titer (end-point dilution assay) was performed as follows. After 48 hours of incubation (namely, post infection), cells were fixed with 4% Formaldehyde for 30 minutes, then washed with phosphate-buffered saline (PBS) and stained with Crystal Violet (0.05%) for 10 minutes. After removing the stain, the wells were examined for the Cytopathic Effect (CPE), namely structural changes in the host cells resulting from viral infection, while wells empty of cells were detected as CPE-positive and blue-stained monolayers were detected as CPE-negative. Calculation of the viruses' titers in each sample was performed according to the modified Ramakrishnan Formula (DOI:10.13140/2.1.4777.1209).

[0258] Results:

[0259] As shown in FIG. 23, the Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 photocatalyst successfully reduced the virus infectivity, from 10.sup.6 IU/ml to actually zero. It is noteworthy that FIG. 23A presents the infectivity at 5 minutes in visible light and at 25 minutes at dark conditions as 1 IU/ml, while in fact, no CPE was observed at the highest virus concentration, as evident from the results shown in FIG. 23C (this was done in order to plot the data at the logarithmic scale (y-axes)). In other words, 5 minutes of incubation under visible light was sufficient to inactivate the virus, while full inactivation was achieved also in dark conditions, after 25 minutes, indicating a possible antiviral activity over dark conditions due to the presence of Bi(0) nanoparticles in the compound doped-heterojunctioned material. It is also noteworthy that SARS-CoV-2 virus is apparently sensitive to light, since the incubation under light conditions without any compound decreases the virus titer by one order of magnitude (log 10) after 40 min of exposure (FIG. 23B).

SUMMARY

[0260] The Bi.sup.(0) doped-BiOCl.sub.0.80Br.sub.0.20 compound (at 25 mg/ml) completely inactivated the SARS-CoV-2 virus after 5 minutes of light exposure, when the initial titer was as high as 10.sup.6 IU/ml.