Showing papers on "Photocatalysis published in 1988"
TL;DR: In this paper, the synthesis of transparent colloidal solutions of extremely small titanium dioxide particles (d < 3 nm) in water, ethanol, 2-propanol, and acetonitrile is presented.
Abstract: The syntheses of transparent colloidal solutions of extremely small titanium dioxide particles (d < 3 nm) in water, ethanol, 2-propanol, and acetonitrile are presented. Quantum-size effects are observed during particle growth and at the final stages of synthesis. They are quantitatively interpreted by using a quantum mechanical model developed by Brus. The particles prepared in aqueous solution possess the anatase structure and consist of about 200 TiO_2 molecules at their final growth stage. The colloidal particles can be isolated from solution as white powders that are soluble in water and ethanol with no
apparent change in their properties. In organic solvents the quantum-size TiO_2 particles appear to form with rutile structure. Excess negative charge on the particles resulting either from deprotonated surface hydroxyl groups or from photogenerated or externally injected charge carriers causes a blue shift in the electronic absorption spectrum, which is explained by an electrostatic model. Electrons can be trapped in the solid as a Ti^(3+) species, which has a characteristic visible absorption spectrum. As
much as 10% of the available Ti^(4+) ions can be reduced photochemically in the solid with a quantum yield of 3%. Molecular oxygen reoxidizes the Ti^(3+) centers, leading to detectable amounts of surface-bound peroxides. The pH of zero point of charge (pH_(zpc)) of the aqueous colloidal suspension has been determined to be 5.1 ± 0.2. The acid-catalyzed dissolution of the aqueous colloid yielding Ti(IV) oligomers has been studied, and an activation energy E_a = 58 ± 4 kJ/mol has been measured for this reaction. The photocatalytic activity of the small TiO_2 particles is demonstrated.
845 citations
TL;DR: In this paper, the photocatalytic degradation of phenol, 4-chlorophenol, 2,4-dichlorophenol and 2, 4,5-trichlorophenol over TiO/sub 2/ (anatase) has been investigated by using three photochemical reactors.
Abstract: The photocatalytic degradation of phenol, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,5-trichlorophenol over TiO/sub 2/ (anatase) has been investigated by using three photochemical reactors. TiO/sub 2/ was used as a thin film, coating the internal surface of a glass coil (reactors I and II) or the external surface of glass beads (reactor III). The degradation of the four phenolic compounds, in a continuous recirculation mode in all three reactors, approximates first-order kinetics to near-complete degradation. The Langmuir-Hinshelwood kinetics have been modified slightly to rationalize the first-order behavior in solid-liquid reactions and to argue in favor of a surface reaction; the degradation reactions occur on the TiO/sub 2/ particle surface. In the multipass mode experiments, both reactors I and II exhibit higher degradation rates for phenol at the higher flow rates. By contrast, the greater degradation is associated with the lower flow rates in the single-pass mode experiments.
603 citations
TL;DR: In this article, simple devices were described for the purification of water combining adsorption of organic impurities with in situ photocatalytic oxidation regeneration of the adsorbent/photocatalyst.
147 citations
130 citations
TL;DR: In this article, the complete photocatalytic degradation of two polychlorinated dibenzo-p-dioxins and one polychlorined biphenyl to CO 2 and HC 1 was investigated in aerated aqueous suspensions of several semiconductors (TiO 2, ZnO, CdS, TiO 2 Pt 5% by weight, and Fe 2 O 3 ) irradiated by simulated solar light.
103 citations
TL;DR: In this article, a thermal treatment of TiO2 powders with various surface hydroxyl densities has been conducted and their activity for photocatalytic oxygen evolution in aqueous suspensions has been investigated in the presence of various electron acceptors.
Abstract: TiO2 powders with various surface hydroxyl densities have been prepared by thermal treatment (600–1000 °C), and their activity for photocatalytic oxygen evolution in aqueous suspensions has been investigated in the presence of various electron acceptors, i.e. AgNO3, K2PtCl4 and KBrO3. The activity increased drastically with the thermal treatment. The oxygen evolution rate was found to be inversely proportional to the surface concentration of OH–, indicating an inhibitory effect of surface hydroxyl groups with respect to photocatalytic oxygen evolution. On highly hydroxylated samples the formation of surface bound peroxides appears to be favoured over oxygen generation.
87 citations
TL;DR: In this article, the photocatalytic activity of TiO/sub 2/ species in the oxide was found to be significantly enhanced by forming surface layers where TiO /sub 2 / species are surrounded by an Al/sub O/sub 3/ carrier acting as cocatalyst.
Abstract: Titanium-aluminum binary metal oxides prepared by coprecipitation have been used as photocatalysts for the hydrogenation reaction of propene with water and isomerization of cis-2-butene in the gas-solid system. Photocatalytic activity of TiO/sub 2/ species in the oxide was found to be significantly enhanced by forming surface layers where TiO/sub 2/ species are surrounded by Al/sub 2/O/sub 3/ carrier acting as cocatalyst.
85 citations
TL;DR: In this article, the photocatalytic activity of SrTiO3 powder prepared by the alkoxide method was examined on the photodecomposition of water, the evolution of H2 from aqueous methanol solution, and evolution of O2 from an ionized silver nitrate solution.
75 citations
62 citations
TL;DR: In this paper, the reaction mechanisms of the photocatalytic oxidation of several different alcohols on TiO2 were investigated by three experimental techniques: spin trapping, photocurrent measurement, and product analysis.
Abstract: The reaction mechanisms of the photocatalytic oxidation of several different alcohols on TiO2 were investigated by three experimental techniques: spin trapping, photocurrent measurement, and product analysis. The results are interpreted according to the band model of a semiconductor and current doubling. It was found that alcohols with α-hydrogens gave low concentrations of spin adducts since their photoproduced radicals have short lifetimes on TiO2 due to a current-doubling process. Also, it was found that oxygen participated in a radical chain mechanism in the photocatalytic oxidation of ethanol to acetaldehyde.
TL;DR: In this paper, the effect of the amount of TiO2 loading on the photocatalytic activity of H2 evolution from aqueous methanol solution over a platinized TiO 2/SiO2 catalyst was studied.
Abstract: The effect of the amount of TiO2 loading on the photocatalytic activity of H2 evolution from aqueous methanol solution over a platinized TiO2/SiO2 catalyst was studied. UV diffuse reflectance spectra of TiO2/SiO2 showed the blue shift of absorption edge for the catalyst of lower amount of TiO2 loading, which suggested the higher dispersion of TiO2 on SiO2. The activity decreased monotonously with the decrease of the amount of TiO2 loading over SiO2, i.e. with the increase of the dispersion.
TL;DR: In this paper, the elimination of cyanide from water by oxidation under UV illumination and using ZnO powder as catalyst has been studied, and it has been observed that after 2 h of solar exposure, 87% of the initial 10 −4 M of CN − has been transformed to CO 3 2−.
TL;DR: In this article, electron transfer from CdS to K4Nb6O17 under visible light irradiation was demonstrated to induce H2 evolution in sodium sulfite solution.
TL;DR: In this article, the role of surface hydroxylation of TiO2 particles as an essential characterestics for their photocatalytic activity can be verified by preparing TiO 2 powders by hydrothermal method since hydroxyated surface layers will be better retained on these particles formed in superheated water.
TL;DR: In this paper, a series of primary, secondary, saturated and unsaturated alcohols have been selectively oxidized photocatalytically to the corresponding aldehydes and ketones by using near visible and UV light.
01 Jan 1988
TL;DR: In this article, photocatalysis is defined and exemplified and the theories of photoelectrochemistry are used to construct model cells, and Mechanistic criteria needed to define a redox reaction pathway on a heterogeneous photocatalyst are reviewed, and a brief survey of functional group transformations on semiconductor surfaces is given.
Abstract: Photocatalytic oxidation of organic substrates occurs with high chemical yield on irradiated semiconductor surfaces. Photocatalysis is defined and exemplified and the theories of photoelectrochemistry are used to construct model cells. Mechanistic criteria needed to define a redox reaction pathway on a heterogeneous photocatalyst are reviewed, and a brief survey of functional group transformations which have been reported on semiconductor surfaces is given. The photocatalytic oxygenation of olefins is considered as a vehicle to illustrate these principles, and several practical applications of such investigations are cited.
TL;DR: In this article, the performance of the Ru(bipy)32+/MV2+/EDTA/colloidal RuO2 system for photochemical production of hydrogen has been investigated as a function of light intensity, pH, temperature and concentrations of the different components.
Abstract: The performance of the Ru(bipy)32+/MV2+/EDTA/colloidal RuO2 system for photochemical production of hydrogen has been investigated as a function of light intensity, pH, temperature and concentrations of the different components. Both the hydrogen production rate and the concentration of methylviologen radicals (MV+) were monitored. Also the development of a state electrical potential on the catalyst was registered using an RuO2 film electrode. In order to clarify the role of the colloidal catalyst and the coupling of the homogeneous and the heterogeneous processes, a model is presented which is based on steady state kinetics and electrochemical principles. The model predicts the steady state rate of hydrogen production, the MV+ concentration and the potential of the catalyst particles, and allows a satisfactory description of most of the experimental results. The principle findings from the experimental results and the model simulations are that hydrogen evolution at the catalyst surface takes place near the equilibrium potential of the H+/H2 redox couple, and that the overall rate of the heterogeneous processes is dominated by mass transport of MV+ to the catalyst surface.
TL;DR: In this article, the photocatalytic oxidation of aqueous I2 was investigated using suspensions of pure anatase and rutile, five doped rutiles and two commercial anatase pigments.
Abstract: The photocatalytic oxidation of aqueous I–, usually as neutral 0.1 mol kg–1 KI, has been investigated using suspensions of pure anatase and rutile, five doped rutiles and two commercial anatase pigments. Reaction only proceeded in the presence of both O2 and u.v. radiation to yield I2, which reacted with excess I– to form I3–; there was no evidence for IO– or IO3– formation. The dependence of initial reaction rate on the square root of the intensity of the incident 366 nm radiation, together with low quantum yields, reflect the recombinative loss of photoelectrons and photoholes greatly exceeding their consumption in productive reaction steps. No activation energy for I2 formation was observed with any of the catalysts, and in this respect the photo-oxidation of I– differs from that of liquid alcohols on the identical catalysts. A mechanism is proposed in which I2 and OH– result from electron transfer between charged and neutral species adsorbed on the TiO2 surface, leading to an overall reaction: 4I–+ O2+ 2H2O +hvâ†� 2I2+ 4OH–.
TL;DR: In this article, a TiO2 powder suspension in a methanolic solution of an azobenzene results in the formation of 1,2,4-triphenyl-1, 2, 4-triazolidines and a 2-phenylindazole in moderate yields.
Abstract: Irradiation of a TiO2 powder suspension in a methanolic solution of an azobenzene results in the formation of 1,2,4-triphenyl-1,2,4-triazolidines and a 2-phenylindazole in moderate yields.
TL;DR: In this paper, the authors showed that methyl propionate yielded methyl 4-propionyloxybutyrate (head-to-tail dimer) by photocatalysis in the presence of RhCl(CO)(PMe3)2 at room temperature.
Abstract: Dehydrogenation of methyl propionate yielded methyl 4-propionyloxybutyrate (head-to-tail dimer) by photocatalysis in the presence of RhCl(CO)(PMe3)2 at room temperature. Methyl aerylate is presumed to be an intermediate.
TL;DR: Several insoluble zinc porphyrins with N-methylpyridyl and n-nonyl meso-substituents are suggested as photocatalysts for a photocatalyst-Pt/TiO2-electron donor as discussed by the authors.
Abstract: Several insoluble zinc porphyrins with N-methylpyridyl and n-nonyl meso-substituents are suggested as photocatalysts for a photocatalytic system (photocatalyst-Pt/TiO2-electron donor) of water reduction.
TL;DR: Pt(alizarine)2 complex adsorbed on the surface of titanium dioxide has been found to cause spectral sensitization of the photocatalytic activity of TiO2 as mentioned in this paper.
Abstract: Pt(alizarine)2 complex adsorbed on the surface of titanium dioxide has been found to cause spectral sensitization of the photocatalytic activity of TiO2. Adsorption of the complex provides simultaneously sensitization of the photoprocess and catalysis of dark steps of dihydrogen formation.
TL;DR: In this article, the design and construction of a multistage high pressure photocatalytic reactor and sample transfer device with adaptation to a surface analysis chamber are reviewed in detail.
Abstract: The design and construction of a multistage high pressure photocatalytic reactor and sample transfer device with adaptation to a surface analysis chamber are reviewed in detail. The apparatus consists of four components: (i) a small stainless‐steel high‐pressure photocatalytic reactor with gas handling section, (ii) a gas product detection chamber with quadrupole mass spectrometer (QMS), (iii) an ultrahigh‐vacuum (UHV) surface analysis system, and (iv) a bellows‐type sample transfer device incorporated with a worm gear. The reactor, which has a total internal volume of ≂320 ml, is capable of operation under dynamic (flow) or static (batch) modes. It includes a sapphire view port to enable the study of the influence of UV‐visible photoirradiation on low surface area (≊1 cm2) metal and metal oxide catalysts in various heterogeneous catalytic reactions. The catalyst sample can undergo any chemical process within the pressure range of from ≂1×10−9 to 2×10+3 Torr and over a temperature range of 80–1100 K. The ...
01 Jan 1988
TL;DR: The use of colloidal semiconductors as light harvesting units in photocatalytic reactions is discussed in this paper, where a survey of the optical and electronic properties of small semiconductor particles is followed by the discussion of heterogeneous charge transfer reactions induced by light.
Abstract: The use of colloidal semiconductors as light harvesting units in photocatalytic reactions is discussed. A survey of the optical and electronic properties of small semiconductor particles is followed by the discussion of heterogeneous charge transfer reactions induced by light. Application of time resolved laser techniques allows to unravel the salient kinetic features of important redox reactions, such as the recombination of electron-hole pairs and the spectral sensitization of wide band gap materials. In the latter process very high light energy conversion efficiencies are achieved when the sensitiser is used in conjunction with a polycrystalline thin film electrode prepared by a sol gel process.
01 Jan 1988
TL;DR: In this paper, the effects of pretreatment, doping, metal deposits, and the existence of correlations between photoassisted isotopic exchanges and pnotocatalytic oxidations are discussed.
Abstract: Studies using 1802 and N18 0 heteroexchanges at room temperature over band-gap illuminated powder semiconductor oxides to characterize the light-induced lability of oxygen are reviewed. In particular, the effects of pretreatment, doping, metal deposits are presented, Existence of correlations between photoassisted isotopic exchanges and pnotocatalytic oxidations is shown. Information obtained from photoconductance measurements is then summarized. Correlations between the electrical behaviour of powder semiconductor oxides under vacuum or in an oxygen atmosphere and their activity in oxidations are discussed. Investigations of electron transfers between Pt (or Ni) and TiO2, as well as between CdS and TiO2, under various conditions (vacuum, presence of oxygen and hydrogen) are presented. Concerning the potential applications of heterogeneous photocatalysis, interests for the recovery of precious or toxic metals from dilute solutions and for the preparation of metallic or bimetallic supported catalysts are evaluated. Finally, the possibilities for water decontamination are examined through the case of the degradation of 4-chlorophenol.