Showing papers on "Photocatalysis published in 1985"

Heterogeneous Photocatalytic Decomposition of Phenol over TiO2 Powder

Abstract: The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors investigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5. The products at the initial stage of the reaction were hydroquinone, pyrocatechol, 1,2,4-benzenetriol, pyrogallol, and 2-hydroxy-1,4-benzoquinone. These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O. A reaction scheme involving hydroxyl radicals as real reactive species has been proposed. Although H2O2 was formed via O2\ewdot produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction. About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction. These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2\ew...

Photolysis of water over metallized powdered titanium dioxide

Abstract: Photolysis of gas-phase water has been carried out on NaOH-coated Rh/TiO2 and Pd/TiO2 catalysts. Hydrogen and oxygen were simultaneously produced on both catalysts and the stoichiometric composition (H2/O2= 2) was obtained for most of the catalysts. The rate of water photolysis strongly depended upon the amount of NaOH loaded and the pressure of water vapour. The photolysis rate on the Rh/TiO2 catalyst was maximized at 15 wt % of NaOH coating and at ca. 2 Torr of water-vapour pressure. The photocatalytic activity depended upon the kind of metal deposited as well as the source of TiO2. Rh was more active but Pd was less active than Pt, which was tested previously. The highest formal quantum yield was ca. 29% when the Rh/TiO2 catalyst was used. The dependences of the photolysis rate on light intensity, wavelength and thermal back reaction rate have also been studied.

An advanced visible-light-induced water reduction with dye-sensitized semiconductor powder catalyst

Abstract: For visible-light-induced water reduction to hydrogen with use of a sacrificial electron donor (triethanolamine), an efficient and durable photocatalyst system with xanthene dye sensitization of particulate platinized semiconductor catalyst is presented. A reductive electron-transfer mechanism from the photoreduced dye to the particulate platinized semiconductor is proposed in the present hydrogen production. The excited triplet state of the dye is a precursor of the reduced dye by the amine, so that the efficiency is determined mainly by the real excited triplet quantum yield of the dye. On the basis of this consideration, a novel use of heavy-atom additives to increase the efficiency of durable xanthene dye sensitized systems is demonstrated. 27 references, 9 figures, 3 tables.

Correlation of the crystal structure of titanium dioxide prepared from titanium tetra-2-propoxide with the photocatalytic activity for redox reactions in aqueous propan-2-ol and silver salt solutions

Abstract: Titanium dioxide (TiO2) has been prepared by the hydrolysis of titanium tetra-2-propoxide, followed by calcination at various temperatures (Tc) up to 1000 °C. The content and crystallite size of anatase in the TiO2 powders increased upon increasing Tc up to 550 °C. In the Tc range 550–600 °C a mixture of anatase and rutile was obtained. A further increase in Tc resulted in TiO2 of rutile structure only. The photocatalytic activities of these TiO2 powders for redox reactions were evaluated in the following systems: (1) aqueous propan-2-ol solution, (2) aqueous Ag2SO4 solution and (3) aqueous Ag2SO4 solution containing propan-2-ol. The anatase TiO2 showed photocatalytic activity in all these systems, the activity increasing with crystal growth. In aqueous propan-2-ol solution the activity is dramatically enhanced by partial coverage of the TiO2 with platinum black. The photocatalytic activity of the rutile TiO2 powder was comparable to or even greater than that of anatase when the reaction system included the silver salt, but was negligibly small for aqueous propan-2-ol solution regardless of the partial Pt coverage.

Process for the sensitization of an oxidation/reduction photocatalyst, and photocatalyst thus obtained

Abstract: A photocatalyst for photodecomposition of liquids is sensitized to visible light by chemically bonding to the catalyst a complex of a transition metal with a bipyridyl or phenanthrolyl type ligand.

ESR and photoluminescence evidence for the photocatalytic formation of hydroxyl radicals on small TiO2 particles

Abstract: ESR and photoluminescence studies have clarified that UV irradiation of the small TiO2 particle in the presence of H2O leads to the formation of \overset•OH radicals, which are formed by trapping of photo-formed holes by the surface OH− groups.

Investigation of the mechanism of hydrogen evolution during photocatalytic water decomposition on metal-loaded semiconductor powders

Abstract: The active sites for photocatalytic hydrogen evolution are identified for some noble metals deposited on TiO/sub 2/ particles by measuring the hydrogen isotope effect of the gases produced by the photodecomposition of water using a series of metal-loaded TiO/sub 2/ suspensions (separation factor analysis). The mechanism of the hydrogen evolution process on metal-loaded TiO/sub 2/ particles is discussed in relation to the hydrogen electrode reaction of the same metals. By means of separation factor analysis the hydrogen evolution process on Pt/TiO/sub 2/, Pd/TiO/sub 2/, and Rh/TiO/sub 2/ is assigned to a slow recombination mechanism. 27 references, 2 figures, 2 tables.

Photocatalytic dehydrogenation of aliphatic alcohols by aqueous suspensions of platinized titanium dioxide

Abstract: Photoirradiation (λex > 300 nm) of Ar-purged aqueous propan-2-ol solution gave hydrogen and acetone in the presence of platinum- and/or ruthenium dioxide-loaded TiO2. The photocatalytic activity of anatase TiO2 depended significantly on the amount of metal or metal oxide present; the effect on the activity increased in the order platinum black ≫ platinum powder > ruthenium dioxide. The photocatalytic activity of rutile TiO2 was negligible even when loaded with platinum black. The effective wavelengths for the photocatalytic dehydrogenation of propan-2-ol were below ca. 390 nm, in agreement with the u.v. absorption spectrum of anatase TiO2. In a similar way primary, secondary and tertiary aliphatic alcohols underwent photocatalytic oxidation, accompanied by hydrogen liberation, by the platinized TiO2. The primary and secondary alcohols gave the corresponding carbonyl derivatives, while 2-methylpropan-2-ol and acetone gave dimeric products accompanied by stoichiometric hydrogen evolution. The initial rate of dehydrogenation in these photocatalytic systems was in proportion to the rate constants of hydrogen abstraction by hydroxyl radical in the homogeneous systems.

Integrated chemical systems: photocatalysis at titanium dioxide incorporated into Nafion and clay

Abstract: Activite catalytique des deux systemes dans la reduction du N,N'-dimethylbipyridylium-4,4' avec oxydation de la triethanolamine Mecanisme

Photoelectrochemistry, photocatalysis, and photoreactors : fundamentals and developments

Abstract: Electronic states in ionic solids.- Semiconductor electrodes and their interaction with light.- Kinetic aspects in photoelectrochemical solar cells.- Choosing a photoelectrode.- Materials engineering: General considerations.- Concluding remarks on: Photoelectrochemistry.- Fundamental aspects of photochemistry and photophysics of transition metal complexes.- Photostorage of solar energy in colloidal semiconductor systems.- Redox catalysis in photochemical and photoelectrochemical solar energy conversion systems.- Effect of organized assemblies on electron transfer reactions and charge separation processes.- Photoassisted cleavage of hydrogen sulfide with semiconductor particles. The thiosulfate cycle.- Photocatalytic reactions of organic compounds. Hydrogen generation from organics and degradation of wastes.- Prospectives of exploitation of photocatalytic and photoelectrochemical processes for solar energy conversion.- Applications of picosecond absorption and emission spectroscopy. The mapping of primary events in photochemistry and photocatalysis.- Concluding remarks on: Homogeneous photocatalysis.- Fundamental aspects of the adsorption and the desorption of gases at solid surfaces under illumination.- Adsorption of energy in photocatalytic reactors.- Photocatalytic reactions.- Heterogeneous photocatalysis.- Some experimental investigations of photosorption phenomena at the gas-solid interface.- Photocatalytic reactions: an overview on the water splitting and on the dinitrogen reduction.- Concluding remarks on: Heterogeneous photocatalysis at the gas/solid interface.- to the modelling and design of photoreactors.- Radiative transfer in photochemical processes.- Studies of photoreactions in homogeneous photoreactors.- Studies of photoreactions in heterogeneous photoreactors.- Absorption of light energy in photoreactors.- Current problems in the modelling of photochemical reactors.- Guidelines for photoreactor research.

Visible-light-induced photodissolution of α-Fe2O3 powder in the presence of chloride anions

Abstract: Haematite iron oxide (α-Fe2O3), an n-type semiconductor, has been shown to corrode in the presence of chloride anion in aqueous acidic media when in powder suspension. The rate of corrosion was enhanced by a factor of ten upon band-gap excitation using visible light. Surface adsorption and ease of complex formation with solution species are shown to be a major factor in the dissolution process. A mechanism for dissolution is proposed and implications for iron oxide powder photocatalysis are assessed.

Semiconductor photocatalysis. Part 4. Hydrogen evolution and photoredox reactions of cyclic ethers catalysed by zinc sulphide

Abstract: ZnS-catalysed photoredox reactions of aqueous solutions of cyclic ethers, i.e. tetrahydrofuran, dihydrofurans, 2,5-dimethyltetrahydrofuran, 3-methyloxetane, 1,4-dioxane, and tetrahydropyran are described. A freshly prepared ZnS suspension displays efficient and selective photocatalysis especially for furan derivatives under band-gap irradiation (> 290 nm); reduction of water by the conduction band electrons generates H2 and one-hole oxidation of the substrates leads to carbon–carbon bond formation through coupling of intermediary radicals. In the photolysis of tetrahydrofuran, oligomerization from the dimeric product (1) to octamer was observed with efficient H2 evolution (φ½H2= 0.13–0.62). Further oxidation of intermediary radicals and photoreduction of the resulting oxidation products were also confirmed; e.g. photolysis of 2,5-dimethyltetrahydrofuran gave exclusively the ring-opened product (9) with its photoreduced product, hexane-2,5-diol (10).

Heterogeneous photocatalytic oxidation of no2− in aqueous suspension of various semiconductor powders

Abstract: NO2− ion was shown to be oxidized to NO3− with or without O2 under illumination in aqueous suspension of some semiconductor powders. Photoactive substances were Ag2O, PbO, TiO2(anatase), Si, ZnO, SnO2, CdS, and Bi2O3. The reaction proceeded with band gap illumination of semiconductors.

Pressure dependence of the rate and stoichiometry of water photolysis over platinized TiO2 [anatase and rutile] catalysts

Abstract: Water photolysis over platinized TiO/sub 2/ (anatase and rutile) catalysts was carried out in the presence of inert gas (He) to examine the effect of ambient pressure on the reaction rate and stoichiometry. The evolution rates of hydrogen and oxygen were independent of the He pressure up to 1 atm over anatase and rutile catalysts. A thick water layer on the catalysts, however, gave a remarkable hindrance effect on the water photolysis even under reduced pressure. When the photolysis is very slow, a nonstoichiometric ratio of hydrogen to oxygen (H/sub 2//O/sub 2/ > 2) was observed due to the slow adsorption of oxygen on TiO/sub 3/. The photoadsorption of oxygen on the catalysts was trivial under the present experimental conditions. 26 references, 4 figures.

Zinc compound having photocatalytic activity

Abstract: PURPOSE: To obtain a zinc compd which excels in light absorption power and chemical stability and has photocatalytic activity grinding and mixing zinc oxide and cadmium oxide with an electromagnetic type oscillating mortar then subjecting the mixture to sulfidation and oxidation treatments as well as platinum addition, thereby forming Zn + and Cd + with a high degree of dispersion CONSTITUTION: A hydroquinone is added to a mixture composed of zinc oxide and cadmium oxide and the mixture is ground and mixed with the electromag netic oscillating mortar The mixture is then subjected to the sulfidation treat ment by using a weak sulfiding agent such as carbon disulfide or methyl sulfide then to the oxidation treatment in oxygen Since the mixture is ground by the electromagnetic type oscillating mortar, the concn of the specific points on the particle surface of zinc oxide to stabilize the isolated Zn + is increased, and since the hydroquinone is added thereto, the active state is maintained until the specific point is subjected to the sulfidation treatment Platinum is added to the resultant powder and a semiconductor catalyst having the high photocatalytic activity stable in the visible light region is obtd COPYRIGHT: (C)1987,JPO&Japio

Photocatalytic oxidation of sulfur on the doped TiO2 catalysts.

Abstract: TiO2(anatase) doped with various elements was used as the photocatalyst in the production of sulfuric acid from sulfur in water into which O2 was bubbled. The catalysts doped with typical elements having one and two valencies showed high catalytic activity, but some doped with typical elements having four and five valencies showed low activity. The intermediate, i.e., \dotO2H radical, in the O2 reduction produced by photoproduced electrons will probably play an important part in the production of sulfuric acid. Therefore, it was suggested that the Ti3+ ion in the TiO2 lattice which contribute to direct O2 reduction will inhibit sulfuric acid production. In the case of transition metal dopants, the transition metal cation in the TiO2 lattice will directly affect the O2 reduction. The catalyst doped (deposited) with Pt shows the highest catalytic activity of all the catalysts used in the present study.

Photogeneration of hydrogen from water with mixed semiconductor catalyst

Abstract: Alumina-supported mixed semiconductor catalyst, ZnS·CdS/Al2O3, showed a significant rate of hydrogen generation from water under UV irradiation without an assistance of any noble metals. Singly supported catalyst, ZnS/Al2O3 or CdS/Al2O3, showed, however, less activity for photogeneration of hydrogen. The activity was not improved by physical mixture of ZnS/Al2O3 and CdS/Al2O3 although the amount of ZnS and CdS were the same as those in the ZnS·CdS/Al2O3 catalyst. This indicates that the intimate contacts between ZnS and CdS particles are necessary to photogeneration of hydrogen.

Investigation of the mechanism of hydrogen evolution during photocatalytic water decomposition on metal-loaded semiconductor powders

Abstract: The active sites for photocatalytic hydrogen evolution are identified for some noble metals deposited on TiO/sub 2/ particles by measuring the hydrogen isotope effect of the gases produced by the photodecomposition of water using a series of metal-loaded TiO/sub 2/ suspensions (separation factor analysis). The mechanism of the hydrogen evolution process on metal-loaded TiO/sub 2/ particles is discussed in relation to the hydrogen electrode reaction of the same metals. By means of separation factor analysis the hydrogen evolution process on Pt/TiO/sub 2/, Pd/TiO/sub 2/, and Rh/TiO/sub 2/ is assigned to a slow recombination mechanism. 27 references, 2 figures, 2 tables.