Showing papers on "Photocatalysis published in 1987"
TL;DR: In this article, a photocatalytic oxidation of organic impurities in water is described, where the aqueous stream passes over illuminated titanium dioxide attached to glass mesh, or coated as a thin film on the inside of a glass coil.
193 citations
TL;DR: A pretreated NiO-TiO 2 powder system is an active catalyst for photocatalytic decomposition of H 2 O into H 2 and O 2 in aqueous alkaline solution (3 N NaOH) as well as under NaOH coating conditions as discussed by the authors.
128 citations
110 citations
TL;DR: In this paper, a novel synthesis for the covalent linkage of cobalt tetrasulfophthalocyanine (Co^(II)TSP) to the surface of titanium dioxide (TiO_2) particles (d ≤ 0.5 µm) is described.
Abstract: A novel synthesis for the covalent linkage of cobalt(II) tetrasulfophthalocyanine (Co^(II)TSP) to the surface of titanium dioxide (TiO_2) particles (d ≤ 0.5 µm) is described. Upon irradiation with light that exceeds the bandgap energy (E_g) of TiO_2 (i.e., ⋋ 5 380 nm), Co^(II)TSP is reduced to Co^ITSP under anoxic conditions both as a dry powder and in aqueous suspension. The photochemical reduction is shown to be fully reversible in the presence of molecular oxygen (O_2). Hydrogen peroxide (H_2O_2) is produced upon irradiation of an aerated aqueous suspension of the 'hybrid" catalyst, TiO__2-Co^(II)TSP. Formation kinetics are followed in situ with a polarographic detector (detection limit ≃ 10^(7-) M H_2O_2); quantum yields, ϕ_(H_2O_2) between 0.16 and 0.49 have been determined. The reactive photocatalytic center appears to be generated by the attachment of molecular oxygen in the open apical coordination site of the hybrid Co^(II)TSP complex. Formation of Co^(II)TSP-O_2^(•-) is enhanced by the binding of TiO^- surface groups in the opposite apical position. Hydrogen peroxide is produced in a two-step electron transfer from the conduction band via the Co(III) center. The involvement of free radical intermediates in this mechanism appears to be highly unlikely. On the basis of its observed chemical and photochemical stability and the high quantum yields for O_2 reduction, the newly developed hybrid material is proposed to be applicable as a potent and stable oxidation catalyst.
82 citations
TL;DR: In this article, the authors reported an unprecedented type of photocatalysis with metalloporphyrin, in which the formation of carbon-carbon bonds proceeds by the effect of visible light.
Abstract: Photocatalysis with metalloporphyrin has been studied mainly in connection with biological photosynthesis. Electron transfer from excited metalloporphyrin to an acceptor resulting in charge separation, eventually leading to hydrogen evolution from water, has been the subject of much interest. In the present communication, they report an unprecedented type of the photocatalysis with metalloporphyrin, in which the formation of carbon-carbon bonds proceeds by the effect of visible light. The reaction is the polymerization of alkyl methacrylate catalyzed by (tetraphenylporphinato)aluminum methyl((TPP)AlMe) upon irradiation with visible light to give a polymer of narrow molecular weight distribution.
75 citations
TL;DR: In this paper, the X-ray diffractograms of the powder showed line broadening and a high concentration of lattice defects in these crystallites, and the optical spectra of the particle suspensions in water showed that the absorption around the band gap is considerably broadened, together with the appearance of maxima in the far ultraviolet.
67 citations
TL;DR: In this article, the effect of temperature and light intensity on the degradation of 3,4-DCB on the TiO2 surface was investigated and it was shown that increases in both parameters cause enhanced kinetic rates with increases in light intensity being more efficient.
48 citations
TL;DR: In this paper, a kinetic model that integrates the photon absorption properties of the solid, the heterogeneous redox reactions on the catalyst surface, and the homogeneous reactions of S(IV) is presented.
Abstract: Cobalt(I1) 4,4'4″4‴-tetrasulfophthalocyanine, Co^(II)TSP, covalently linked to the surface of titanium dioxide particles, TiO_2-CoTSP, is shown to be an effective photocatalyst for the oxidation of sulfur(IV) to sulfur(VI) in aqueous suspensions. Upon band-gap illumination of the semiconductor, TiO_2, conduction-band electrons and valence-band holes are separated; the electrons are channeled to the bound Co^(II)TSP complex resulting in the reduction of dioxygen while the holes react with
adsorbed S(IV) to produce S(VI) in the form of sulfate. The formation of S(V) radicals indicates that the reaction proceeds via successive one-electron transfers. Quantum yields in excess of unity were observed and attributed to desorption of SO_3^- from the TiO_2 surface and subsequent initiation of a homogeneous free radical chain reaction. Observed quantum yields between 0.5 and 300 depend on the concentration and nature of free radical inhibitors present in the suspension. A kinetic model that integrates the photon absorption properties of the solid, the heterogeneous redox reactions on the catalyst surface, and the homogeneous reactions of S(IV) is presented.
47 citations
TL;DR: In this article, the Pschorr reaction by Ru(bpy) 3 2+ in the fluorenone, fluorene and dibenzofuran series occurs with a low yield and slow rate in contrast with the photocatalysis previously observed for the phenanthrene series.
47 citations
TL;DR: In this paper, an aqueous suspension of hydrous ferric oxide photocatalyses was used for the reduction of molecular nitrogen to ammonia with oxidation of water; the catalytic activity of this material was attributed to the strongly negative flat band potential and chemisorption of N2.
Abstract: An aqueous suspension of hydrous ferric oxide photocatalyses reduction of molecular nitrogen to ammonia with oxidation of water; the catalytic activity of this material is attributed to the strongly negative flat band potential and chemisorption of N2.
39 citations
Journal Article•
TL;DR: In this article, the use of photo-sensitive coordination compountis catalysts for organic syntheses is discussed, focusing on photo-induced cyclisation reactions of unsaturated hydrocarbons in the presence of azido complexes.
Abstract: Electronic excitation of both WERNER-type complexes and light-sensitive orf;anometallics may lead to coordinatively unsaturated complex fragments, metal complexes with unusual formal oxidation numbers of the c entral atoms, free ligznds and 1iL;and oxidation. products, respectively, hich may exhibit catalytic activity. For the description of processes involviq5 photo- generation of catalytically a ctive species and subsequent catalyzed reactions, the terms photoinLuced catalg-ti c reactions md photoassisted reactions, respectively, have been applied. General features of 3hotoinduced catalytic and. photoassisted rextions md their applications are discussed. Particular emphasis is placed on the use of photosensitive coordination compountis catalysts for organic syntheses. Photooxygenation of phenols and terpenes in the presence of copper(I)/(II) complexes and metalloporphyrins, respectively, as well as photoinduced cyclisation reactions of unsz'iurated hydrocarbons in !;he presence of azido complexes of nickel(II), plladium(I1) and platinLun(1I) are discussed in more detail.
Patent•
07 May 1987
TL;DR: In this paper, a salt of a metal selected from cobalt, palladium, silver, chromium, lead copper, vanadium, platinum, tungsten, mercury, lanthanum, bismuth, and molybdenum (e.g., vanadium trichloride, cobalt chloride) is provided.
Abstract: PURPOSE: To improve the light fastness, weather resistance, etc., of a coating film, by incorporating a salt of a particular metal selected from Co, Pd, Ag, Cr, etc., into a binder vehicle of a coating paint contg. titanium oxide particles. CONSTITUTION: A salt of a metal selected from cobalt, palladium, silver, chromium, lead copper, vanadium, platinum, tungsten, mercury, lanthanum, bismuth, and molybdenum (e.g., vanadium trichloride, cobalt chloride) is provided. One or more members selected from such salts are incorporated into the binder vehicle of a coating compsn. contg. titanium oxide particles having a particle size of about 1W100mμ. Since the incorporated metal salt works as a catalyst poison against the photocatalytic activity of titanium oxide, the light fastness, weather resistance, etc., of a coating film can be improved. COPYRIGHT: (C)1988,JPO&Japio
TL;DR: In this paper, the mechanism of oxygen formation is analyzed in detail and it is proven that the oxygen is not produced by direct hole transfer from CdS via a catalyst to the solution.
TL;DR: The dependence of H2 evolution on the amounts of CdS, Pt, [S2−] and pH has been studied in this article, where the photodecomposition of H 2S into H2 and S in aqueous solutions under visible light irradiation is investigated.
Abstract: CdS/Pt colloids sensitize the photodecomposition of H2S into H2 and S in aqueous solutions under visible light irradiation. The dependence of H2 evolution on the amounts of CdS, Pt, [S2−] and pH has been studied.
TL;DR: In this paper, 2-Propanol was catalytically converted to acetone on niobium oxide supported on porous Vycor glass in the presence of oxygen or nitrogen monoxide under UV irradiation.
Abstract: 2-Propanol was catalytically converted to acetone on niobium oxide supported on porous Vycor glass in the presence of oxygen or nitrogen monoxide under UV irradiation. The light of wavelength shorter than 300 nm was effective for the reaction. The VIS-UV absorption measurements showed that niobium oxide was reduced by 2-propanol under the irradiation and Nb4+ formed by the photoreduction was reoxidized by oxygen. The kinetics of the reoxidation was investigated by means of spectroscopic measurements. The redox mechanism is proposed for the photocatalytic oxidation of 2-propanol.
TL;DR: In this article, a photoelectrochemical polymerization of 1-vinylpyrene has been achieved in a semiconductor photocatalyst suspension under visible light irradiation (λ > 480 nm).
Abstract: Photoelectrochemical polymerization of 1-vinylpyrene has been achieved in a semiconductor photocatalyst suspension under visible light irradiation (λ > 480 nm). Bandgap excitation of CdS, CdSe or Fe2O3 led to the oxidation of 1-vinylpyrene, which initiated the polymerization process. A 25–47% yield of poly(1-vinylpyrene) could be obtained upon irradiation of these semiconductor photocatalyst suspensions with 1-vinylpyrene in acetonitrile. Dependence of the polymer yield on various experimental conditions is described.
TL;DR: In this article, the photocatalytic deposition of noble metals on photosensitive supports is proposed to synthesize well dispersed metal catalysts in mild conditions of preparation, and the effects of various parameters governing the kinetics of photo-deposition (light flux, solution, concentration, temperature, nature of ions) have been studied.
Abstract: The photocatalytic deposition of noble metals on photosensitive supports is proposed to synthesize well dispersed metal catalysts in mild conditions of preparation. The effects of various parameters governing the kinetics of photo-deposition (light flux, solution, concentration, temperature, nature of ions) have been studied. Noble metals, such as Pt, Pd, Ag, Rh, Au, Ir have been deposited on titania. Other photosensitive supports such as oxides (ZnO, Nb2O5, ZrO2, ThO2, etc.) or sulfides (CdS) have also been employed. Bimetallic catalysts (Pt-Pd, Pd-Ag, Pt-Ir) on TiO2 have been prepared with a probable alloy formation according to STEM analysis. Although common insulating supports are theoretically unsuitable for photodeposition, a limited deposition of Pt was observed on alumina. A photodeposited 0.5 wt% Pt/TiO2 was used in two bi functional photocatalytic reactions. It exhibited a higher activity than a well dispersed analogue obtained by impregnation and H2 reduction, possibly because the support did not undergo a severe reduction treatment.
01 Jan 1987
TL;DR: In this paper, it was shown that interparticle electron transfer takes place from the conduction band of CdS to that of TiO2, resulting in an irreversible charge separation.
Abstract: The photodegradation of H2S in alkaline aqueous media is mediated by CdS under visible light excitation to give H2 and S. The new strategy of coupling CdS with another semiconductor (TiO2 or TiO2/redox catalyst), as well as with a redox catalyst deposited on an ‘inert’ support has been used. The results suggest inter-particle electron transfer takes place from the conduction band of CdS to that of TiO2effecting an irreversible charge separation: e cb − on TiO2 and h vb + on CdS. Photoelectrochemical experiments (rotating graphite electrode) under nearly identical conditions to those used in the photocatalysis work, with sulfite ions present, support the vectorial displacement of electrons from illuminated CdS to TiO2 and then to the graphite electrode. Further evidence for inter-particle electron transfer is presented from photoconductivity measurements carried out in vacuo for TiO2, CdS, CdS/TiO2 and CdS/SiO2 mixtures, as well as CdS + TiO2 double pellet. Under these conditions, inter-particle electron transfer also occurs, but from TiO2 to CdS. However, the two results are not inconsistent with one another, in view of the different treatments of the semiconductor materials and the different experimental conditions used. That inter-particle electron transfer does occur is inescapable. The strategy has been used and is worth further exploration to improve photocatalytic efficiencies.
TL;DR: In this article, the authors showed that the photocatalytic activity observed upon illumination in the sensitization band is due to absorption of light quanta by adsorbed molecules of the dye.
Abstract: Quantum efficiency of the photocatalytic hydrogen evolution upon illumination in the self-and dyesensitized absorption bands of suspended titanium dioxide has been determined. The photocatalytic activity observed upon illumination in the sensitization band is shown to be due to absorption of light quanta by adsorbed molecules of the dye.
TL;DR: In this article, the authors investigated the oxygen generation in aqueous suspensions of ZnO containing Hg(II), Ag(I) and CrO 2−4 ions as conduction band electron acceptors.
Journal Article•
01 Jan 1987
TL;DR: In this article, the authors report how the reaction of 2,5-DHF depends on the method of catalyst preparation, on the concentration of water, 2,3-DFD and zinc sulfide, and on the substitution of zinc sulfides by cadmium sulfide or homogeneous solutions of ZnS/CdS.
Abstract: Metallized semiconductor powders like titanium dioxide and cadmium sulfide may photocatalyze the reduction of water and reactions of organic compounds. In the latter case no new materials were obtained (Fox 1983) except in the dehydrodimerization of cyclic ethers by photoexcited zinc sulfide (Bucheler 1982; Zeug 1985; Yanagida 1985). This reaction affords from 2,5-dihydrofuran (2,5-DHF) and 2,3-dihydrofuran (2,3-DHF) the hitherto unknown compounds \(\underset{=}1\) - \(\underset{=}3\) in preparative amounts, and from THF the 2,2’-bitetrahydrofuryl (\(\underset{=}4\)) without traces of the 2,3’-isomer. Their formation is coupled to hydrogen evolution from water which occurs with- out a noble metal catalyst. In the following we report how the reaction of 2,5-DHF depends on the method of catalyst preparation, on the concentration of water, 2,5-DHF and zinc sulfide, and on the substitution of zinc sulfide by cadmium sulfide or homogeneous solutions of ZnS/CdS. Competition and inhibition experiments give some basic insights into the nature of interfacial electron transfer processes.
TL;DR: In this article, a significant effect of pore size has been found on the yield of photolysis of water to hydrogen, ozone (oxidising product) and methane (decomposing product of catalyst or solvent) using [pol-Ti(OBu)4 + CH3OH]-complex/SiO2.
Abstract: A significant effect of pore size has been found on the yield of photolysis of water to hydrogen, ozone (oxidising product) and methane (decomposing product of catalyst or solvent) using [pol-Ti(OBu)4 + CH3OH]-complex/SiO2. The pore structure of silica gel has been found to provide good conditions for forming this type of catalyst.
TL;DR: In this paper, the authors reported an unprecedented type of photocatalysis with metalloporphyrin, in which the formation of carbon-carbon bonds proceeds by the effect of visible light.
Abstract: Photocatalysis with metalloporphyrin has been studied mainly in connection with biological photosynthesis. Electron transfer from excited metalloporphyrin to an acceptor resulting in charge separation, eventually leading to hydrogen evolution from water, has been the subject of much interest. In the present communication, they report an unprecedented type of the photocatalysis with metalloporphyrin, in which the formation of carbon-carbon bonds proceeds by the effect of visible light. The reaction is the polymerization of alkyl methacrylate catalyzed by (tetraphenylporphinato)aluminum methyl((TPP)AlMe) upon irradiation with visible light to give a polymer of narrow molecular weight distribution.
TL;DR: It has been found that illumination in the impurity absorption region of silica-supported zirconium oxides intensifies considerably their ability to catalyze the oxidation of isobutylene to acetone.
Abstract: It has been found that illumination in the impurity absorption region of silica-supported zirconium oxides intensifies considerably their ability to catalyze the oxidation of isobutylene to acetone. A correlation has been established between the photocatalytic activity of these compounds and their photoluminescence intensity in vacuum.
TL;DR: In this article, the photocatalytic reactions of NO at ppm level with O2 were studied in the presence of TiO2 (anatase), PbO, and ZnO using a chemical luminescence NOX analyzer and a second derivative spectrometer.
Abstract: Photocatalytic reactions of NO at ppm level with O2 were studied in the presence of TiO2 (anatase), PbO, and ZnO using a chemical luminescence NOX analyzer and a second derivative spectrometer. The rate of oxidation of NO was very high, e.g. 1930% cm−2 h−1 in a photocatalytic reaction on TiO2 (anatase). Photoadsorption of NOX also took place on these metal oxides.
TL;DR: In this article, the photolysis of perchloric acid solutions of titanium(IV) with additions of ethanol was detected, which correspond to pseudo-octahedral aqua-complexes of Titanium(III) compounds.
Abstract: In the photolysis of perchloric acid solutions of titanium(IV) with additions of ethanol, the formation of titanium(III) compounds was detected. Irradiated solutions ([HClO4]=0.8 M) at 77‡K are characterized by an anisotropic ESR signal with parameters g1=1.994, g1=1.904, which correspond to pseudo-octahedral aqua-complexes of titanium(III). With the passage of time, the signal intensity of the titanium(III) compounds decreases, which is explained by their oxidation by ClO4 ions. During prolonged photolysis of titanium(IV) compounds in 7 M HClO4 with an addition of ethanol, a multicomponent signal of the paramagnetic chlorine oxide ClO2 with parameters gxx=2,004, axx(37Cl)=6.0. mTl axx(35Cl)=7,30 mTl, is recorded instead of the signal of titanium(III) compounds. Evidently ClO2 is formed as a result of a rapid dark reaction between compounds of trivalent titanium (products of the photochemical step) and chlorate ions, which are accumulated in the solution as a result of successive photochemical and dark redox conversions of the titanium compounds, perchlorate ions, arid free radicals from the alcohol molecules. The formation of free radicals in the system was established by the ESR method after irradiation of frozen solutions.