Showing papers on "Photocatalysis published in 1989"
TL;DR: In this article, the oxidation of liquid cyclohexane by O2 over UV-illuminated TiO2 at room temperature has been studied in a static slurry reactor.
Abstract: The oxidation of liquid cyclohexane by O2 over UV-illuminated TiO2 at room temperature has been studied in a static slurry reactor. From the effects of the mass of catalyst, the temperature, the radiant flux, the concentration of C6H12 (using acetonitrile as a solvent), it is concluded that the reaction is photocatalytic. Using mainly the 365 nm-ray of a mercury-lamp, an initial quantum yield of 0.1 is found for pure cyclohexane and radiant fluxes < ca.5mWcm−2 (6×1015 photons s−1 cm−2). A high selectivity to cyclohexanone is observed (83%), the other products being cyclohexanol (5%) and CO2 (12%). The low amount of cyclohexanol is explained by the higher rate of oxidation of this alcohol compared to that of cyclohexane. Smaller oxidation rates are observed when TiO2 is loaded with 0.5 to 10 wt%Pt and the cyclohexanone/cyclohexanol ratio decreases to ca. 4. Finally, the C6H12 oxidation has been employed as a test reaction to confirm the detrimental effect of the doping with several tri or pentavalent cations upon the photocatalytic activity of TiO2.
209 citations
TL;DR: In this paper, the adsorption parameter determined in the analysis of the kinetics of the photocatalytic data agreed with the ad-orption affinity parameter determined using the classical Langmuir adaption isotherm for the dark equilibrium data.
Abstract: Aqueous solutions of methylene blue are totally mineralized when recirculated over thin films of titanium dioxide illuminated with near-u.v. light. The rate of destruction obeys first-order kinetics with reasonable precision but the apparent first-order rate constant, k′, decreases with increasing initial concentration of solute. 1 dm3 of 10 µmol dm–3 methylene blue solution illuminated with a 20 W lamp, is decreased to 5 µmol dm–3 in 11.8 min. Sunlight from a 1 m2 parabolic trough is capable of destroying the methylene blue at 6.4 times this rate. The decrease in k′ values with increasing concentration is consistent with curves calculated using the integrated form of the Langmuir expression. The adsorption parameter determined in the analysis of the kinetics of the photocatalytic data agreed with the adsorption affinity parameter determined using the classical Langmuir adsorption isotherm for the dark equilibrium data; this indicated the key role played by adsorption in photocatalytic oxidation with titanium dioxide. The maximum quantum yield for methylene blue destruction at high flow rates with a 10 µmol dm–3 initial concentration was calculated to be 0.0092.
171 citations
TL;DR: In this paper, the photocatalytic activity of α-Fe2O_3 colloids is compared to the activities of colloids and suspensions of ZnO and TiO_2.
Abstract: The photocatalytic activity of α-Fe2_O_3 colloids is compared to the activities of colloids and suspensions of ZnO and TiO_2. The formation of H_2O_2 is investigated and the oxidation of organic molecules is studied with high sensitivity. While ZnO and TiO_2 are found to be quite active photocatalysts in the formation of hydrogen peroxide and in the degradation of chlorinated hydrocarbon molecules, only negligible photocatalytic activity is found for α-Fe_2O_3. Upper limits of quantum yields for several photoreactions of α-Fe_2O_3 are given.
140 citations
TL;DR: In this article, the authors present an etude de l'activite catalytique de TiO 2, Pt/TiO 2 and TiO2 -Al 2 O 3.
Abstract: Hydrogenolyse et hydrogenation photocatalytique d'alcenes et d'alcynes dans l'eau, sur TiO 2 . Isomerisation cis trans du butene-2. Etude de l'activite catalytique de TiO 2 , Pt/TiO 2 et TiO 2 -Al 2 O 3
119 citations
TL;DR: The use of titanium dioxide and titanium aluminosilicates in the photocatalytic destruction of chlorinated hydrocarbons is investigated in this paper, where it is shown that titanium dioxide is more active than titanium-exchanged clays, titanium-pillared clays and titanium dioxide in the amorphous, anatase, and rutile forms.
96 citations
TL;DR: In this article, the photocatalytic activity of thin Pt-TiO2 thin films was examined through the dehydrogenation of methanol in aqueous solution and the plot of the activity against the thickness of the film gave a sigmoidal curve.
Abstract: Photocatalytic Pt-TiO2 thin films of various thicknesses (ca. 20 to 100 nm) were prepared on Vycor glass substrates by spray-coating. The photocatalytic activity of the films was examined through the dehydrogenation of methanol in aqueous solution. The plot of the activity against the thickness of the film gave a sigmoidal curve. A drastic increase in activity was observed at about 50 nm thickness. From thin-film X-ray diffraction measurements of the films it was revealed that anatase was formed at a thickness of more than 50 nm, whereas amorphous TiO2 was formed at thicknesses of less than 50 nm. The increase of activity was, therefore, attributed to the formation of anatase. Compared with powder catalysts, the thin films showed a remarkable improvement in specific photocatalytic activity due to the high dispersion of the catalyst.
87 citations
Abstract: Photocatalytic activity and spectroscopic properties of ZnS suspensions for the two-electron reduction of aldehydes or related compounds in aqueous medium are described. The ZnS suspension (ZnS-O) prepared by cooling from aqueous ZnSO{sub 4} and Na{sub 2}S solutions catalyzes photoredox reactions of acetaldehyde, giving ethanol without much H{sub 2} evolution as a two-electron-reduction product, and acetic acid, biacetyl, and acetoin as oxidation products. When the ZnS-O suspension is refluxed (giving ZnS-100) or dried to powder, the resulting ZnS shows an increased activity for H{sub 2} evolution but a decreased activity for the two-electron reduction. The two-electron photoreduction is ascribed to the sequential transfer of active electrons in the conduction band of defect-free aggregates of ZnS microcrystallites (quantized ZnS). This mechanism is supported by product analysis, energetics at ZnS interfaces, the sharp and blue-shifted onset of absorption and excitation spectra, and the long-life band gap emission of the active ZnS-O suspension. UV, emission, and ESR spectra, as well as the enhancement of the particle size and crystallinity, suggest that the activity change observed after heating or drying to powder is due to the formation of surface states which may trap active electrons. This interpretation is also supported by the generated activity ofmore » ZnS-100 for the H{sub 2} photoevolution under >350-nm irradiation. ZnS photocatalysis under >350-nm irradiation relationship with spectroscopic properties are also discussed.« less
72 citations
TL;DR: The photocatalytic reaction of kraft lignin at titanium dioxide photocatalyst was investigated in this article, where it was completely decomposed into carbon dioxide and water through dehydrodimers of phenol derivatives.
Abstract: The photocatalytic reaction of kraft lignin at titanium dioxide photocatalyst was investigated. Kraft lignin was completely decomposed into carbon dioxide and water through dehydrodimers of phenol derivatives constituting kraft lignin, methanol and organic acids such as oxalic and formic acids. Aromatic compounds such as vanillin could not be recovered due to their tendency to dehydrodimerization and the strong oxidizing power of the photo-generated holes by the action of which the dehydrodimers were completely decomposed into carbon dioxide and water. The production of methane, ethane, and ethylene was much smaller than that in the decomposition with hydroxyl radicals in homogeneous solution.
71 citations
TL;DR: The effect of platinum loading on the efficiency of CdS-photocatalyzed hydrogen evolution from an aqueous solution of sodium sulfide and on the intensity of the green emission (510 nm) suspended in the same solution was studied in this paper.
Abstract: The effect of platinum loading on the efficiency of CdS-photocatalyzed hydrogen evolution from an aqueous solution of sodium sulfide and on the intensity of the green emission (510 nm) of CdS suspended in the same solution was studied The Fermi level of the CdS photocatalyst at the working condition can be estimated from the intensity of the green emission of the platinum-loaded CdS powder and the luminescence-potential curve of a CdS electrode When the amount of platinum deposited on CdS is increased, the Fermi level of CdS at the working stage is moved down toward more positive potential, leading to a stronger band bending, and the photocatalytic reaction is stimulated Too much Pt loading, however, lowers the photocatalytic activity because of the enhanced rate of electron-hole recombination as well as light absorption by platinum The temperature effect on the reactivity and the reason for the presence of an induction period of the reaction are also elucidated in relation with the band bending of the photocatalyst
64 citations
TL;DR: The degradation of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane by simulated sunlight ( > 340 nm) has been investigated in the presence of aqueous suspensions of semiconductor particulates (TiO2, ZnO, CdS, WO3, α-Fe2O3 and TiO2/5 wt.% Pt).
Abstract: The degradation of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) by simulated sunlight ( > 340 nm) has been investigated in the presence of aqueous suspensions of semiconductor particulates (TiO2, ZnO, CdS, WO3, α-Fe2O3 and TiO2/5 wt.% Pt). Titanium dioxide appears to be the most effective catalyst; the half-life for the processes is −40 min (at initial DDT concentration 1 mg L−1 and 2 g L−1 TiO2, photon flux 3 × 10−5 einstein/min, over a cell cross-section of 4 cm2).
The near quantitative recovery of chloride ions after long irradiation periods suggests that the end products of the degradative process are CO2 and HCl. To the extent that neither DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) nor DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) were observed by gas chromatographic techniques, the reaction proceeds through hydroxyl radical attack on the aromatic moieties with subsequent ring opening.
54 citations
Journal Article•
TL;DR: In this article, the optimum conditions have been established for the selective semiconductor-photocatalyzed oxidation by long-wavelength ultraviolet light of the primary alcohol functionality in 1,4-pentanediol.
Abstract: Optimum conditions have been established for the selective semiconductor-photocatalyzed oxidation by long-wavelength ultraviolet light of the primary alcohol functionality in 1,4-pentanediol. On platinized (2%) TiO{sub 2} powder suspended in oxygenated aqueous (4 vol %) acetonitrile, the initial rate ratio for oxidation of the primary/secondary alcohol site was >7. Analysis of further oxidation products allowed for mechanistic delineation of the course of the semiconductor-mediated reaction. The selectivity is attributed to the essential role of adsorption, with the critical photoinduced electron transfer occurring at the surface of the irradiated particle. ZrO{sub 2} and SnO{sub 2} samples were much less active than TiO{sub 2} as photocatalysts. The effects of oxygen pressure, metal cocatalyst loading, and water content of acetonitrile are discussed.
TL;DR: In this article, the authors show that the addition of sodium ions alters the composition of surface phases and enhances the photocatalytic activity of 2-propanol and propene.
TL;DR: In this paper, a polypropylene (PP) film containing 0.25 wt% of titanium dioxide (TiO 2 ) powder was photoirradiated for times up to 200 h at room temperature in air.
TL;DR: In this paper, the photoelectrocatalytic reduction of carbon dioxide in aqueous solution to C-1 organic compounds (formic acid and formaldehyde) in the presence of n-Bi2S3 and n-CdS semiconductor powders with band gap energies of 1.3 and 2.4 eV respectively was described.
TL;DR: In this article, the authors used bilayer phospholipid membranes to stabilize the catalyst particles, preventing their aggregation and thus increasing their activity and selectivity, and cyclodextrins were used as a support for the Mn catalytic centers.
TL;DR: In this paper, thin films of TiO 2 were prepared on fused silica and titanium substrates by chemical vapor deposition (CVD) using Ti[OCH(CH 3 ) 2 ] 4 under conditions of anatase formation.
Abstract: Thin films of TiO 2 were prepared on fused silica and titanium substrates by chemical vapor deposition (CVD) using Ti[OCH(CH 3 ) 2 ] 4 under conditions of anatase formation. The UV—visible transmission spectrum of the film deposited on the fused silica substrate showed an absorption edge 30 nm shorter than that of anatase powder. This blue shift may be attributed to size quantization, i.e. the film may consist of extremely small TiO 2 particles. The absorption edge shifted to slightly longer wavelength upon heating the film in air at high temperatures. The photocatalytic property of the film was examined using the photodeposition reaction of silver from aqueous AgNO 3 . The silver photodeposition rate increased with the calcination temperature, maximizing at around 400°C and then decreasing at higher temperature. To compare the photocatalytic property with the photoelectrochemical property, photocurrents were measured in a KOH solution using the film deposited on the titanium substrate. They decreased after calcination at temperatures above 400°C. Compared to bulk TiO 2 , the wavelength dependence of the current was shifted to considerably shorter wavelengths, in agreement with the absorption spectrum.
TL;DR: The photocatalytic efficiencies of these doped samples were investigated by carrying out the decomposition of peroxomonosulphate (PMS, HSO5−) over the doped and undoped WO3 particles as discussed by the authors.
Abstract: WO3 particles were doped with the transition metal ions TiIII, VIV, CrIII, MnII, FeIII, CoII, NiII, CuII, ZnII, RuIII and V2O5 to increase the visible light absorption. The photocatalytic efficiencies of these doped samples were investigated by carrying out the decomposition of peroxomonosulphate (PMS, HSO5−) over the doped and undoped WO3 particles. PMS is capable of reacting with both the photogenerated holes and electrons. The effect of initial concentrations of PMS, amount of catalyst, pH, dopants and percentage doping on the photocatalytic efficiency of WO3 are investigated and are discussed.
TL;DR: In this article, the reaction mechanism of the photocatalytic oxidation of 2-ethoxyethanol (Ethyl Cellosolve, EtOCH2CH2OH) on TiO2 powder was investigated by gas chromatography-mass spectrometry (GC-MS), infrared (IR) spectroscopy, and electron spin resonance (ESR) with spin trapping technique.
Abstract: The reaction mechanism of the photocatalytic oxidation of 2-ethoxyethanol (Ethyl Cellosolve, EtOCH2CH2OH) on TiO2 powder was investigated by gas chromatography-mass spectrometry (GC-MS), infrared (IR) spectroscopy, and electron spin resonance (ESR) with spin trapping technique. Irradiation of TiO2 powder with UV light in the presence of EtOCH2CH2OH under air led to the formation of ethyl formate, ethanol, acetaldehyde and carbon dioxide. The main product, ethyl formate was different from the product through the reaction pathway proposed before for primary alcohols. It was also different from the product of electrolysis on Pt. Reaction mechanism is proposed based on IR and ESR studies.
TL;DR: The photochemistry of ethanol solutions of 2,3,7,8,12,13,17,18-octaethylporphyrinatoiron(III), [Fe(oep)]+, has been investigated in the presence of CCl4 and of different amounts of oxygen as discussed by the authors.
Abstract: The photochemistry of ethanol solutions of 2,3,7,8,12,13,17,18-octaethylporphyrinatoiron(III), [Fe(oep)]+, has been investigated in the presence of CCl4 and of different amounts of oxygen. Continuous irradiation with 330–440 nm light induces an ethanol-to-oxygen electron transfer occurring with the assistance of an iron(III) porphyrin ethanolate complex. At a partial pressure of oxygen ranging from 0.1 to 1 Torr, the photoproducts, hydroxyethyl radical and hyperoxide ion O2– give rise to a catalytic process, with > 100 turnovers of [Fe(oep)]+, leading to the reduction of carbon tetrachloride to chloroform and chloride ions and with oxidation of ethanol to acetaldehyde. The rate of the photocatalytic process was observed to depend on the oxygen concentration, excitation wavelength, and the presence of a radical scavenger. A chain mechanism has been formulated involving radical species that can be quenched by oxygen to yield peroxyl radicals.
TL;DR: It is found that the nitrite in water is converted into nitrate by irradiation in the presence of oxygen and titanium dioxide which acts as a catalyst.
TL;DR: In this paper, it has been found that CBr4 may replace oxygen and functions in a similar way, and the concomitant formation of oxidation products in the TiO2-mediated aerobic reaction is avoided.
Abstract: Three reactions: the CdS-mediated valence isomerization of hexamethyldewarbenzene to hexamethylbenzene, the cycloreversion of dianthracene, and the TiO2-mediated cis–trans isomerization of stilbene are known to be suppressed when the semiconductor excitation takes place in the absence of oxygen. The oxygen, when present, is presumed to trap the electron delaying electron-hole recombination. It has been found that CBr4 may replace oxygen and functions in a similar way. In addition, the concomitant formation of oxidation products in the TiO2-mediated aerobic reaction is avoided. The mechanism is discussed. Keywords: cadmium sulphide, carbon tetrabromide, dianthracene, heterogeneous photocatalysis, hexamethyldewarbenzene, titanium oxide.
TL;DR: In this paper, the CdS1−xSex mixed-crystal powder was prepared for the purpose of reducing the band gap of CDS and expanding the effective wavelength region of the photocatalyst.
Abstract: The CdS1−xSex mixed-crystal powder was prepared for the purpose to reduce the band gap of CdS and expand the effective wavelength region of the photocatalyst. Hydrogen evolution was observed from an aqueous solution of 1 M sodium sulfite by use of the mixed-crystal photocatalyst loaded with platinum under illumination at wavelengths longer than 520 nm, where neither the platinum-loaded CdS nor CdSe photocatalyst is active. However, when the mixed-crystal catalysts were illuminated at wavelengths longer than 390 nm or with an AM 1 solar simulator, the rate of the hydrogen evolution was lower than that of CdS. The energy levels of the electronic bands in the mixed-crystals have been clarified from the results of the electrochemical studies, and the fact that the mixed-crystal powder has lower photocatalytic activity than CdS powder has been ascribed to the downward shift of the conduction band edge. These findings are useful in designing photocatalysts for hydrogen production.
TL;DR: In this paper, the selective photocatalytic oxidation of m-phenoxytoluene to mphenoxybenzaldehyde on titanium dioxide (TiO2) particles incorporated in Nafion membranes has been investigated.
Abstract: The selective photocatalytic oxidation of m-phenoxytoluene to m-phenoxybenzaldehyde on titanium dioxide (TiO2) particles incorporated in Nafion membranes has been investigated. No more than 0.1% of by-products was detected after 24 h irradiation, and the catalytic nature of the reaction is demonstrated with a turnover in excess of 100. In addition, a yield of at least 28% is achieved. Both the emission characteristics and catalytic activity of TiO2 are regenerated by washing the membrane in butanol.
TL;DR: In this article, the possible ways of increasing efficiency of light usage in the production photohydrogen process from the solution of complex compounds of the transient metals have been studied, including varying of the inner coordination sphere of a complex by varying of ligands, changing of its solvation of shells by using the mixed water-organic solvents and sensitization of hydrogen evolution process by using dyes.