Photocatalysts based on bismuth oxyhalide, process for their preparation and uses thereof

Abstract

The invention provides a process for the preparation of bismuth oxyhalide, comprising a precipitation of bismuth oxyhalide in an acidic aqueous medium in the presence of a reducing agent. Also provided are bismuth oxyhalide compounds doped with elemental bismuth Bi.sup.(0). The use of Bi.sup.(0)doped-bismuth oxyhalide as photocatalysts in water purification is also described.

Claims

1. Bi.sup.(0)-doped bismuth oxyhalide, wherein the halide is chloride, bromide or mixed chloride-bromide, wherein the molar concentration of the Bi.sup.(0) dopant is from 0.1 to 7.0%, calculated relative to the total amount of trivalent and zerovalent bismuth.

2. Bi.sup.(0)-doped bismuth oxyhalide according to claim 1, wherein the molar concentration of the Bi.sup.(0)dopant is from 0.1 to 5.0%.

3. Bi.sup.(0)-doped bismuth oxyhalide according to claim 1, selected from the group consisting of Bi.sup.(0)doped-BiOCl, Bi.sup.(0)doped-BiOBr and Bi.sup.(0)doped-BiOCl.sub.yBr.sub.1−y wherein y is in the range from 0.6 to 0.95.

4. Bi.sup.(0)-doped bismuth oxyhalide according to claim 3, which is Bi.sup.(0)doped-BiOCl.sub.yBr.sub.1−y wherein y is in the range from 0.7 to 0.95.

5. Bi.sup.(0)-doped bismuth oxyhalide according to claim 1, characterized in that its X-ray photoelectron emission spectrum exhibits a peak at 157±1 eV which is assigned to metallic bismuth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a characteristic X-ray powder diffraction pattern of the BiOCl compound of the invention.

(2) FIG. 2 is an image recorded with a scanning electron microscope showing BiOCl particles with flower-like morphology.

(3) FIG. 3 shows the X-ray photoelectron emission spectrum of the Bi.sup.(0)doped-BiOCl of the invention.

(4) FIG. 4 is a characteristic X-ray powder diffraction pattern of the BiOCl compound obtained by a process of the invention involving a filtrate recycling.

(5) FIG. 5 is an image recorded with a scanning electron microscope showing BiOCl particles with flower-like morphology obtained by a process of the invention involving a filtrate recycling.

(6) FIG. 6 is a characteristic X-ray powder diffraction pattern of the BiOBr compound of the invention.

(7) FIG. 7 is an image recorded with a scanning electron microscope showing BiOBr particles with flower-like morphology.

(8) FIG. 8 is a characteristic X-ray powder diffraction pattern of a mixed bismuth oxyhalide BiOCl.sub.0.875Br.sub.0.125 compound of the invention.

(9) FIG. 9 shows the X-ray photoelectron emission spectrum of the Bi.sup.(0)doped-BiOCl.sub.0.875Br.sub.0.125 of the invention.

(10) FIG. 10 shows the X-ray photoelectron emission spectrum of the Bi.sup.(0)doped-BiOCl.sub.0.875Br.sub.0.125 of the invention.

(11) FIG. 11 shows the X-ray photoelectron emission spectrum of the Bi.sup.(0)doped-BiOBr of the invention.

(12) FIG. 12 shows the X-ray photoelectron emission spectrum of the Bi.sup.(0)doped-BiOCl.sub.0.67Br.sub.0.33 of the invention.

(13) FIG. 13 presents UV spectra demonstrating the progress of chlorobenzene degradation in an aqueous solution in the presence of the compound of the invention activated with light irradiation.

(14) FIG. 14 presents UV spectra demonstrating the progress of chlorobenzene degradation in aqueous solution in the presence of the compound of the invention activated with light irradiation.

(15) FIG. 15 presents UV spectra of chlorobenzene in aqueous solution in the presence of hydrogen peroxide.

(16) FIG. 16 presents UV spectra demonstrating the progress of chlorobenzene degradation in aqueous solution in the presence of both the compound of the invention activated with light irradiation and hydrogen peroxide.

(17) FIG. 17 presents UV spectra demonstrating the progress of phenol degradation in aqueous solution in the presence of the compound of the invention activated with light irradiation.

(18) FIG. 18 presents UV spectra of phenol in aqueous solution in the presence of hydrogen peroxide.

(19) FIG. 19 presents UV spectra demonstrating the progress of phenol degradation in water in the presence of the compound of the invention under light irradiation and hydrogen peroxide.

(20) FIG. 20 presents UV spectra demonstrating the progress of phenol degradation in water in the presence of both the compound of the invention activated with light irradiation and hydrogen peroxide.

(21) FIG. 21 presents C/C.sub.0 plot versus time, illustrating the degradation of toluene in an aqueous medium in the presence of the compound of the invention under light irradiation.

(22) FIG. 22 is C/C.sub.0 plot versus time, illustrating the degradation of methyl blue (MB) in water in the presence of a compound of the invention under light irradiation.

(23) FIG. 23 presents C/C.sub.0 plot versus time, illustrating the degradation of carbamazepine in an aqueous medium in the presence of the compound of the invention under light irradiation.

EXAMPLES

Methods

(24) XRD measurements were performed on D8 Advance diffractometer (Bruker AXS, Karlsruhe, Germany) with a goniometer radius 217.5 mm, Göbel Mirror parallel-beam optics, 2° Sollers slits and 0.2 mm receiving slit. Low background quartz sample holder was carefully filled with the powder samples. XRD patterns from 5° to 85°2θ were recorded at room temperature using CuKa radiation (λ=0.15418 nm) with the following measurement conditions: tube voltage of 40 kV, tube current of 40 mA, step scan mode with a step size 0.02° 2θ and counting time of is per step for preliminary study and 12 s per step for structural refinement. The instrumental broadening was determined using LaB.sub.6 powder (NIST-660a).

(25) Morphological observations and identification of chemical composition were performed with the HRSEM-High Resolution Scanning Electron Microscope-Sirion (equipped with EDS LN2 detector, Oxford instruments, UK).

(26) XPS analysis was conducted using XPS Kratos AXIs Ultra (Kratos Analytical Ltd., UK) high resolution photoelectron spectroscopy instrument.

(27) UV spectroscopy analysis was carried out by means of UV-vis spectrophotometer (Varian EL-03097225).

(28) Chemical Oxygen Demand (COD) was measured using COD meter-DIN38404-C3 standard.

(29) Total organic carbon (TOC) was measured using PF-11 photometer.

Example 1

Preparation of Bismuth Oxychloride in the Presence of a Reducing Agent and Ferric Ions

(30) Deionized water (40 ml), glacial acetic acid (40 ml) and bismuth nitrate pentahydrate Bi(NO.sub.3).sub.3.5H.sub.2O (9.7 g) are placed in 250 ml flask and stirred at room temperature for fifteen minutes until a clear solution is formed. The solution is added to a second flask which was previously charged with CTAC (25.6 g of 25 wt % CTAC aqueous solution) and ammonium iron(III) sulfate NH.sub.4Fe(SO.sub.4).sub.2 (0.096 g). Sodium borohydride (0.01 g) and ethanol (10 ml) are also added to the reaction mixture, which is stirred for additional 60 minutes at about 30° C.

(31) The precipitate thus formed is 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 product is then dried (3 hours in air). The weight of the dried solid collected is ˜7 g.

(32) The X-ray powder diffraction pattern of the resultant bismuth oxychloride is presented in FIG. 1. The product exhibits X-ray powder diffraction pattern having characteristic peaks at 12.02, 26.01, 32.25, 40.82, 58.73 2θ (±0.05 2θ). The product is characterized by average particle size of 3 μm and surface area of 31 m.sup.2/g. FIG. 2 presents SEM image of the particles showing their flower-like morphology. The particles are relatively uniform in size, e.g., a representative single particle size is about 3 μm.

(33) XPS was used for the analysis of the composition of the solid. FIG. 3 shows the X-ray photoelectron emission spectrum of the sample. The peaks at binding energies of ˜156.9 eV and 162.2 eV are assigned to the Bi (.sub.metal) 4f (7/2, 5/2) photoelectrons, respectively. The compound is identified as Bi.sup.(0) doped-BiOCl.

Example 2

Precipitation of Bismuth Oxychloride from a Recycled Filtrate in the Presence a Reducing Agent and Ferric Ions

(34) The filtrate obtained following the separation of the solid product in Example 1 was reused as a reaction medium in this Example. The filtrate contains acetic acid, ethanol, water and the cationic part of the surfactant. To this filtrate were added Bi(NO.sub.3).sub.3.5H.sub.2O (9.7 g), ammonium iron sulphate (0.096 g dissolved in 5 ml water), sodium borohydride (0.01 g), sodium chloride (1.17 g) and ethanol (10 ml). The reaction mixture was allowed to stand for 60 minutes under mixing at 30° C.

(35) The precipitate thus formed is 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 product is then dried (3 hours in air). The weight of the dried solid collected is ˜7 g.

(36) The X-ray powder diffraction pattern shown in FIG. 4 and the SEM image of FIG. 5 are comparable to the XRPD and SEM image of FIGS. 1 and 2, respectively, demonstrating that the crystallinity and particle morphology of bismuth oxyhalide which precipitates from a recycled filtrate and from a fresh reaction medium (Example 1) are essentially the same.

Example 3

Preparation of Bismuth Oxybromide in the Presence of a Reducing Agent and Ferric Ions

(37) Deionized water (40 ml), glacial acetic acid (40 ml) and bismuth nitrate pentahydrate Bi(NO.sub.3).sub.3.5H.sub.2O (9.7 g) are placed in 250 ml flask and stirred at room temperature for fifteen minutes until a clear solution is formed. The solution is added to a second flask which was previously charged with CTAB solution (7.28 g dissolved in 20 ml of water) and ammonium iron(III) sulfate NH.sub.4Fe(SO.sub.4).sub.2 (0.48 g). Sodium borohydride (0.04 g) and ethanol (10 ml) are added to the reaction mixture which is stirred for additional 60 minutes at about 30° C.

(38) The precipitate thus formed is 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 product is then dried (3 hours in air). About 7 g of a slightly hygroscopic product were collected, containing ˜5-10% water.

(39) The X-ray powder diffraction pattern of the resultant bismuth oxybromide is presented in FIG. 6. The product exhibits X-ray powder diffraction pattern having characteristic peaks at 11.00, 31.78, 32.31, 39.26, 46.31, 57.23, 67.53 (±0.05 2θ).

(40) The product is characterized by average particle size of 3 μm and surface area of 30 m.sup.2/g. FIG. 7 presents SEM image of the particles showing their flower-like morphology. The particles are relatively uniform in size; a representative single particle size is 3 μm.

Example 4

Preparation of Mixed Halide BiOCl.SUB.0.875.Br.SUB.0.125 .in the Presence of a Reducing Agent and Ferric Ions

(41) Deionized water (45 ml), glacial acetic acid (50 ml) and bismuth nitrate (14.69 g) are added to a flask and are mixed at room temperature for fifteen minutes until a clear, transparent solution is formed. CTAB (1.378 g dissolved in 10 ml of water), CTAC (8.48 g in the form of 25 wt % aqueous solution) and ammonium iron (III) sulfate (146 mg dissolved in ml water) are added to the bismuth solution. Finally, sodium borohydride (0.015 g) and ethanol (10 ml) are added to the reaction mixture, which is then stirred for additional 60 minutes at about 30° C.

(42) The precipitate thus formed is separated from the liquid phase by filtration, washed five with ethanol (5×50 ml) and then five times with water (5×200 ml). The solid is then dried in air. The weight of the solid collected is ˜10.5 grams.

(43) The X-ray powder diffraction pattern of the resultant mixed bismuth oxyhalide is presented in FIG. 8. The product exhibits X-ray powder diffraction pattern having a characteristic peak at 11.74 2θ (±0.05 2θ) and additional peaks at 32.56, 36.06, 46.70 and 49.41 2θ (±0.05 2θ). The product is characterized by average particle size of 1 μm and surface area of 34 m.sup.2/g.

(44) XPS was used for the analysis of the composition of the solid. FIG. 9 shows the X-ray photoelectron emission spectrum of the sample. The peaks at binding energies of ˜156.9 eV and 162.2 eV are assigned to the Bi (.sub.metal) 4f (7/2, 5/2) photoelectrons, respectively. The product is identified as Bi.sup.(0)doped-BiOCl.sub.0.875Br.sub.0.125.

Example 5

Preparation of Bi.SUP.(0) .Doped-Mixed Halide BiOCl.SUB.0.875.Br.SUB.0.125

(45) Deionized water (50 ml), glacial acetic acid (40 ml) and bismuth nitrate (14.69 g) are added to a flask and are mixed at room temperature for fifteen minutes until a clear, transparent solution is formed. The so-formed solution is added to a previously prepared solution consisting of CTAC (33.92 g of 25 wt % aqueous solution) and CTAB (1.38 g). Finally, sodium borohydride (11.456 mg) and ethanol (20 ml) are added to the reaction mixture, which is then stirred for additional 60 minutes at about 25-30° C.

(46) The precipitate thus formed is separated from the liquid phase by filtration, washed five with ethanol (5×50 ml) and then five times with water (5×200 ml). The off-white solid is then dried (3 hours in air). The weight of the solid collected is ˜9 grams.

Example 6

Preparation of Bi.SUP.(0) .Doped-Mixed Halide BiOCl.SUB.0.875.Br.SUB.0.125

(47) The procedure of Example 5 was repeated, with a twofold increase of the amount of the reducing agent (22.913 mg of sodium borohydride is added to the reaction mixture).

(48) The precipitate thus formed is separated from the liquid phase by filtration, washed five with ethanol (5×50 ml) and then five times with water (5×200 ml). The off-white solid is then dried (3 hours in air). The weight of the solid collected is ˜9 grams.

(49) XPS was used for the analysis of the composition of the solid. FIG. 10 shows the X-ray photoelectron emission spectrum of the sample. The peaks at binding energies of ˜157.15 eV and 163.8 eV are assigned to the Bi(.sub.metal) 4f (7/2, 5/2) photoelectrons, respectively. The product is identified Bi.sup.(0)doped-BiOCl.sub.0.875Br.sub.0.125.

Example 7

Preparation of Bi.SUP.(0) .Doped-BiOBr

(50) Deionized water (50 ml), glacial acetic acid (40 ml) and bismuth nitrate (9.7 g) are added to a flask and are mixed at room temperature for fifteen minutes until a clear, transparent solution is formed. The so-formed solution is added to a previously prepared aqueous ethanolic solution of CTAB (1.38 g CTAB dissolved in a mixture consisting of 30 ml ethanol and 10 ml deionised water). Finally, sodium borohydride (7.56 mg) is added to the reaction mixture, which is then stirred for additional 60 minutes at about 25-30° C.

(51) The precipitate thus formed is separated from the liquid phase by filtration, washed five with ethanol (5×50 ml) and then five times with water (5×200 ml). The off-white solid is then dried (3 hours in air). The weight of the solid collected is ˜7 grams.

(52) XPS was used for the analysis of the composition of the solid. FIG. 11 shows the X-ray photoelectron emission spectrum of the sample. The peaks at binding energies of ˜156.8 eV and 164.9 eV are assigned to the Bi (.sub.metal) 4f (7/2, 5/2) photoelectrons, respectively. The product is identified as Bi.sup.(0)doped-BiOBr.

Example 8

Preparation of Bi.SUP.(0) .Doped-Mixed Halide BiOCl.SUB.0.67.Br.SUB.0.33

(53) Deionized water (50 ml), glacial acetic acid (40 ml) and bismuth nitrate (3.27 g) are added to a flask and are mixed at room temperature for fifteen minutes until a clear, transparent solution is formed. The so-formed solution is added to a previously prepared solution consisting of CTAC (3.2 g in 25 wt % aqueous solution) and CTAB (1.82 g). Finally, sodium borohydride (5.70 mg) and ethanol (20 ml) are added to the reaction mixture, which is then stirred for additional 60 minutes at about 25-30° C.

(54) The precipitate thus formed is separated from the liquid phase by filtration, washed five with ethanol (5×50 ml) and then five times with water (5×200 ml). The off-white solid is then dried (3 hours in air). The weight of the solid collected is ˜5 grams.

(55) XPS was used for the analysis of the composition of the solid. FIG. 12 shows the X-ray photoelectron emission spectrum of the sample. The peaks at binding energies of ˜157.75 eV and 163.06 eV are assigned to the Bi (.sub.metal) 4f (7/2, 5/2) photoelectrons, respectively. The product is identified as Bi.sup.(0)doped-BiOCl.sub.0.67Br.sub.0.33.

(56) Some of the photocatalysts prepared in the foregoing examples are tabulated in Table A.

(57) TABLE-US-00001 TABLE A Example Compound Bi .sup.(0) 4f 7/2 XPS peak Dopant level 1 Bi.sup.(0) doped-BiOCl 156.9 eV (FIG. 3) ~1 mole % 4, 5 Bi.sup.(0) doped-BiOCl.sub.0.875Br.sub.0.125 156.9 eV (FIG. 9) ~1 mole % 6 Bi.sup.(0) doped-BiOCl.sub.0.875Br.sub.0.125 157.1 eV (FIG. 10) ~2 mole % 7 Bi.sup.(0) doped-BiOBr 156.8 eV (FIG. 11) ~1.5 mole %   8 Bi.sup.(0) doped-BiOCl.sub.0.670Br.sub.0.330 157.7 eV (FIG. 12) ~3 mole %

Examples 9-16

Water Decontamination: Decomposition of Organic Contaminants in Aqueous Medium in the Presence of the Compound of the Invention Under Light Irradiation

(58) Samples were prepared by adding an organic compound (either chlorobenzene or phenol) to 200 ml of water. The compound of Example 1 was added in varying amounts to the samples and was tested for its photocatalytic activity on destruction of the organic compound under irradiation with Xenon lamp (300 W) located at a distance of 10 cm from the sample, at wavelength 250-740 nm. The compound of Example 1 was used either alone or in combination with hydrogen peroxide (30% aqueous H.sub.2O.sub.2 solution). Table 1 below shows the concentration of the organic contaminant in the sample, the amount of the compound of Example 1 present in the sample and the volume of 30% hydrogen peroxide solution added to the sample. For the purpose of comparison, the oxidation activity of hydrogen peroxide alone was also evaluated, i.e., in the absence of the compound of the invention.

(59) The decomposition of the organic compound under the conditions set forth above was determined by periodically analyzing the tested sample by means of UV spectroscopy. The spectra obtained for each experiment are presented in FIGS. 13-20, which correspond to Examples 9 to 16, respectively. The spectra show that in the presence of the photocatalyst of the invention, the intensity of the characteristic UV absorbance peak assigned to the organic contaminant (for chlorobenzene ˜262 nm, phenol ˜270 nm) decreases gradually with the passage of time, until the peak finally vanishes, indicating full oxidation of the organic compound to carbon dioxide.

(60) TABLE-US-00002 TABLE 1 Organic Contaminant BiOCl of Hydrogen Example (concentration) Example 1 (mg) Peroxide (ml) Observations  9 Chlorobenzene 100 0 Full decomposition of (200 ppm) the contaminant after 12 minutes (FIG. 13) 10 Chlorobenzene 200 0 Full decomposition of (400 ppm) the contaminant after 20 minutes (FIG. 14) 11 Chlorobenzene 0 0.2 No decomposition comparative (200 ppm) (FIG. 15) 12 Chlorobenzene 200 0.2 Full decomposition of (400 ppm) the contaminant after 16 minutes (FIG. 16) 13 Phenol 100 0 Full decomposition of (50 ppm) the contaminant after 120 minutes (FIG. 17) 14 Phenol 0 0.2 Transformation of phenol comparative (500 ppm) into phenol derivatives (FIG. 18) 15 Phenol 150 0.2 During the first three (500 ppm) hours mainly transformation into phenol derivatives is observed; then the organic compounds begin to decompose and full decomposition is reached after 300 minutes (FIG. 19) 16 Phenol 200 0.5 During the first three (1000 ppm) hours mainly transformation into phenol derivatives is observed; then the organic compounds begin to decompose and full decomposition is reached after 540 minutes (FIG. 20)

(61) Comparative Examples 11 and 14 illustrate that hydrogen peroxide alone is unable to promote the oxidation of the organic compound. The results shown in Examples 10, 11 and 12 demonstrate that the combination of the bismuth oxyhalide and hydrogen peroxide exhibits a synergistic effect.

Example 17

Water Purification: Decomposition of Organic Contaminants in Aqueous Medium in the Presence of the Compound of the Invention Under Light Irradiation

(62) The Bi.sup.(0)-doped BiOCl compound of Example 1 was tested for its ability to purify water contaminated with chlorobenzene. The tested sample consisted of 200 ml aqueous solution which contains chlorobeneze (400 ppm) and the compound of Example 1 (200 mg). The sample was exposed to light irradiation as set out in previous examples, and the progressively reduced amount of the organic compound present in the sample was indirectly evaluated by periodically measuring the Chemical Oxygen Demand (COD). The time intervals at which the COD was measured and COD values are tabulated in Table 2.

(63) TABLE-US-00003 TABLE 2 Irradiation time (min) COD (ppm) 0 200 4 60 8 50 20 <30 30 <30

(64) The COD test is in line with the UV spectroscopy analysis reported in the foregoing examples: both methods indicate that the compound of the invention is highly effective in decontaminating water contaminated with chlorobenezene.

Examples 18-20

Water Purification: Decomposition of Organic Contaminants in Aqueous Medium in the Presence of the Compound of the Invention Under Light Irradiation

(65) The Bi.sup.(0) doped-BiOCl.sub.0.875Br.sub.0.125compound of Example 4 was tested for its ability to purify water contaminated with mixtures of organic compounds. The tested sample consisted of 200 ml aqueous solution which contains the organic contaminants as tabulated in Table 3 below and the compound of Example 4 (150 mg). The pH of the sample was approximately 5. The sample was exposed to light irradiation at wavelength 385-740 nm. Light intensity was 70 mW/cm.sup.2 and the lamp was located at a distance of 10 cm from the sample.

(66) The catalytic activity of the Bi.sup.(0)doped-BiOCl.sub.0.875Br.sub.0.125 compound of Example 4 is evaluated by determining the time needed in order to reduce the initial TOC value of the tested sample to a final level of about 10 ppm (TOC indicates the amount of carbon bound to organic compounds and hence serves as a measure for water quality). The relevant details of this set of experiments and results are tabulated in Table 3.

(67) TABLE-US-00004 TABLE 3 Initial TOC Final TOC Irradiation Ex. Contaminant (ppm) (ppm) time (min) 18 Phenol (50 ppm) 38 6 80 19 Chlorobenzene (50 ppm) + 70 11 60 Phenol (50 ppm) 20 Chlorobenzene (50 ppm) + 87 8 60 Dimethyl acetamide (100 ppm)

Examples 21-23

Water Purification: Decomposition of Organic Contaminants in Aqueous Medium in the Presence of the Compound of the Invention Under Visible Light Irradiation

(68) The compounds of Examples 5, 6 and 7 were tested for their ability to purify water contaminated with organic pollutants. The experiments were carried out in a 250 mL cylindrical-shaped glass vessel at room temperature under air and at a neutral pH. The tested catalyst (200 mg) was suspended in water (200 ml). The sample further contains the organic contaminant as tabulated in Table 4 (the mixture was stirred in the dark for about 1 hour followed by filtration and measurement of adsorbed molecules by UV).

(69) The sample was exposed to light irradiation at wavelength 385-740 nm. For visible light irradiation, a 422 nm cut-off filter was used. 300W Xe arc lam (Max-302, Asahi Spectra) was used as the light source. Light intensity was 70 mW/cm.sup.2 and the lamp was located at a distance of 10 cm from the sample. Experimental details are set out in Table 4.

(70) TABLE-US-00005 TABLE 4 Light Pollutant Irradiation Example Catalyst [concentration] (wavelength) 21 Bi.sup.0 doped-BiOCl.sub.0.875Br.sub.0.125 Toluene 420-740 nm of Example 5 [470 ppm] 22 Bi.sup.0 doped-BiOCl.sub.0.875Br.sub.0.125 MB 385-740 nm of Example 6 [10 ppm] 23 Bi.sup.0 doped-BiOBr Carbamazepine 420-740 nm of Example 7 [60 ppm]

(71) The sample was periodically tested to determine the concentration of the remnant organic pollutant. To this end, 5 ml aliquots were periodically taken from the sample and centrifuged at 6000 rpm for ten minutes to remove the catalyst particles (in Examples 21 and 23, the aliquots were taken at t=0 min, 5 min, 20 min and 30 min and in Example 22, aliquots were taken at t=0 min, 30 min, 60 min, 90 min and 120 min). UV absorption spectra of the pollutant in the aliquot were recorded. In order to illustrate the decrease of the concentration of the pollutant with the passage of time, the ratio C.sub.t/C.sub.0 was plotted as a function of time. FIGS. 21 to 23 show the plots generated for Examples 21 to 23, respectively. The concentration of the pollutant drops sharply in the presence of the Bi.sup.0 doped-catalyst of the invention under light irradiation.

Example 24 (Comparative) and 25 (of the Invention)

(72) The activity of the BiOCl.sub.0.875Br.sub.0.125photocatalyst disclosed in Example 5 of WO 2012/066545 was compared with that of the Bi.sup.(0) doped-BiOCl.sub.0.875Br.sub.0.125compound of Example 4 (supra). The photocatalysts were tested for their ability to reduce phenol pollution in water, in response to light irradiation. Two separate samples were prepared according to the experimental conditions set forth in respect to Example 18 (Example 25 corresponds to Example 18). The TOC values of the two samples were measured periodically and the results are tabulated below, showing the reduction in the TOC of the aqueous solution with the passage of time.

(73) TABLE-US-00006 TABLE 5 Example 24 (comparative) Example 25 BiOCl.sub.0.875Br.sub.0.125 (of the invention) Time* of WO 2012/066545 Bi.sup.(0) doped-BiOCl.sub.0.875Br.sub.0.125 (min) TOC (ppm) TOC (ppm) 0 38 38 10 36 31 20 35 23 40 33 19 60 30 11 80 29 6 *Time elapsed from the beginning of irradiation

(74) The results shown in Table 5 demonstrate that the presence of bismuth metal dopant in the catalyst accounts for stronger photocatalytic activity, allowing rapid and effective destruction of phenol pollutant in water.

Example 26

Thin Film Formulation

(75) Bi.sup.3+-Containing Adhesive Solution

(76) Tetraethyl orthosilicate (TEOS; 5.2 gram), de-ionized water (2.7 gram) and ethanol (6 gram) were mixed together in the presence of nitric acid (pH=2) at 60° C. for 20 minutes. Pluronic P123 (0.15 gram) and poly vinyl alcohol (0.18 gram), both dissolved in 4 gram of ethanol were then added and the stirring continued for an additional hour at 60° C. to form the “glue” solution siloxane. Bismuth nitrate (0.0066 mole) is then added to the siloxane solution and the resultant mixture is vigorously mixed using homogenizer to form homogeneous blend.

(77) Halide-Containing Solution

(78) In case of BiOCl Film: CTAC aqueous solution (8.53 g of 25 wt % solution) is placed in a spraying device.

(79) In case of BiOBr Film: CTAB ethanol solution (2.43 g of CTAB dissolved in 12 ml of EtOH) is placed in a spraying device.

(80) Coating Procedure

(81) Microscope glass slides were carefully cleaned using acid piranha (a 3:1 mixture of sulfuric acid and hydrogen peroxide). Then, the slide is immersed in the Bi.sup.3+-containing solution and dip coated, followed by spraying the halide-containing solution onto the coated glass slide. In order to achieve a full removal of the organic residues from the final film, and for a better adhesion of the siloxane matrix, a calcinations step is applied. To this end, the slide is placed in an oven at room temperature. The temperature of the oven is increased gradually at a rate of 3 degrees per minute up to a temperature of 400° C. The slide is held in the oven at 400° C. for four hours and is then cooled down to room temperature. A thin uniform film is obtained, in which the catalyst is affixed onto the surface of the glass slide.