Showing papers on "Photocatalysis published in 1999"
TL;DR: In this article, the basic fundamental principles are described as well as the influence of the main parameters governing the kinetics (mass of catalyst, wavelength, initial concentration, temperature and radiant flux).
2,424 citations
TL;DR: In this paper, the presence of transition metal ions in photocatalytic reactions is reviewed according to two main approaches: (a) the influence of metal ions on the rate of photocatalysis and (b) the transformation of the ions to less toxic species or their deposition on the semiconductor catalyst surface for recovery of expensive and useful metals.
Abstract: The presence of transition metal ions in photocatalytic reactions is reviewed according to two main approaches: (a) the influence of transition metal ions on the rate of photocatalytic reactions (mainly oxidation) and (b) the transformation of the ions to less toxic species or their deposition on the semiconductor catalyst surface for recovery of expensive and useful metals. Most of the proposed mechanisms are discussed, together with experimental physicochemical evidences that support the involved pathways. Practical applications related to environmental protection and industrial processes are described.
1,294 citations
TL;DR: In this paper, the authors give an overview of the development and implications of nanotechnology in photocatalysis, including the use of nanoparticles in doped, coupled, capped, sensitized and organic-inorganic nanocomposite semiconductor systems, with an effort to enhance photocatalytic and optical properties of commonly used semiconductor materials.
Abstract: The aim of this review paper is to give an overview of the development and implications of nanotechnology in photocatalysis. The topics covered include a detailed look at the unique properties of nanoparticles and their relation to photocatalytic properties. Current applications of and research into the use of nanoparticles as photocatalysts has also been reviewed. Also covered is the utilization of nanoparticles in doped, coupled, capped, sensitized and organic–inorganic nanocomposite semiconductor systems, with an effort to enhance photocatalytic and/or optical properties of commonly used semiconductor materials. The use of nanocrystalline thin films in electrochemically assisted photocatalytic processes has been included. Finally, the use of nanoparticles has made a significant contribution in providing definitive mechanistic information regarding the photocatalytic process.
606 citations
TL;DR: In this paper, the relationship between the photo reaction and the surface crystal structure was evaluated on the different crystal faces of rutile single crystal and also polycrystalline anatase titanium dioxide to clarify the dependence of the crystal structure on the photoinduced hydrophilic conversion.
564 citations
TL;DR: In this paper, the authors deal with doping titania by Cr 3+ and Mo 5+ ions and show the complex interactions between variations in lifetime of charge carriers, adsorption properties and photocatalytic behaviour.
Abstract: Titanium dioxide is one of the most efficient photocatalysts for the detoxification of organically charged waste water. However, this material suffers from the drawback of poor absorption properties because of a band gap of 3.2 eV. Thus, wavelengths shorter than 400 nm are needed for light induced generation of electron–hole pairs. Therefore, doping with transition metal ions is interesting for inducing a batho-chromic shift of the band gap. However, this doping changes other physical properties such as lifetime of electron–hole pairs and adsorption characteristics. This paper deals with doping titania by Cr 3+ and Mo 5+ ions. We want to show the complex interactions between variations in lifetime of charge carriers, adsorption properties and photocatalytic behaviour.
437 citations
TL;DR: In this paper, the photoelectrochemical properties of polycrystalline Cu2O electrodes are discussed with regard to the application of the oxide as a photocatalytic material for water splitting.
350 citations
TL;DR: In this article, a two-phase swirl-flow monolithic-type reactor was used to study the kinetics of heterogeneous photocatalytic processes and the effects of parameters such as catalyst dosage, pollutant concentration, temperature, partial pressure of oxygen, UV light intensity, catalyst-layer thickness, circulation flowrate and catalyst annealing temperature.
Abstract: In recent years, photocatalytic degradation mediated by illuminated TiO2 has received considerable attention as an alternative for treating polluted water. In the present study, a new two-phase swirl-flow monolithic-type reactor was used to study the kinetics of heterogeneous photocatalytic processes. Photocatalytic degradation of phenol, 4-chlorophenol (4-CP) and 4-nitrophenol (4-NP) both in aqueous suspensions and over immobilized Degussa P25 TiO2 has been studied in laboratory scale. Experiments were conducted to investigate the effects of parameters such as catalyst dosage, pollutant concentration, temperature, partial pressure of oxygen, UV light intensity, catalyst-layer thickness, circulation flowrate and catalyst annealing temperature. Simple model for predicting the optimal catalyst dosage in aqueous suspensions for different photo-systems was proposed. Pseudo first-order kinetics with respect to all the parent compounds was observed. Experimental data obtained under different conditions were fitted with kinetic equation to describe the dependency of degradation rate as a function of the above mentioned parameters. Consequently, kinetic parameters were experimentally determined. Adsorptive properties of all the organics were also experimentally measured and fitted with Langmuir equation. The extreme low surface coverage of the organics on the catalyst may be one of the main factors that result in the low efficiency of the photocatalytic process. Besides, mass transfer of organics and oxygen in the photocatalytic process has also been discussed in detail. ©1999 Elsevier Science B.V. All rights reserved.
335 citations
TL;DR: In this paper, the photoactivity of pure rutile is found to increase with increasing Sn in the solid solution of rutiles, and it peaks at a tin content of 0.075.
284 citations
TL;DR: In this article, photo-induced and dark Fenton/Fenton-like reactions were compared and evaluated for the removal of UV-254 nm, COD and TOC.
274 citations
TL;DR: In this article, a pyrex fixed-bed continuous photoreactor irradiated by a medium pressure Hg lamp was used for performing photoreactivity experiments, and the main oxidation product was benzaldehyde but benzene, benzyl alcohol and traces of benzoic acid, phenol and unidentified compounds were also detected.
Abstract: Photo-oxidation of toluene has been carried out in gas–solid regime by using polycrystalline anatase TiO2 as the catalyst. The reacting gaseous mixture was toluene, air and water in various molar ratios. A pyrex fixed-bed continuous photoreactor irradiated by a medium pressure Hg lamp was used for performing the photoreactivity experiments. The main oxidation product was benzaldehyde but benzene, benzyl alcohol and traces of benzoic acid, phenol and unidentified compounds were also detected. The molar conversion to benzaldehyde with respect to the initial amount of toluene was ca. 20% in the best experimental conditions. Benzene was produced only as a transient product during the first 3–4 h of irradiation. The dependence of feed composition and flow rate on the toluene fractional conversion was investigated. Selected experiments were performed by using N2 or CO2 instead of air. The presence of oxygen was essential for the occurrence of the photoreaction while water played an important role in order to maintain the catalyst activity. Moreover, a Fourier-transform infrared spectroscopy (FT-IR) investigation was carried out simulating the experimental conditions used during the photoreactivity experiments. The results indicated that toluene is weakly stabilised on the hydrated TiO2 particles by hydrogen-bonding with surface hydroxyl groups, and that it is photo-oxidised to benzaldehyde only in the presence of surface OH groups.
TL;DR: In this article, the dynamics of charge carriers generated by femtosecond UV (160 fs, 390 nm) excitation in five standard TiO2 photocatalytic powders (JRC-TIO-1, -2, -3, -4, and -5 supplied by the Catalysis Society of Japan) in a vacuum and air was investigated by means of time-resolved femto-cond diffuse reflectance spectroscopy, and discussed from the viewpoints of crystal structure (anatase and rutile), particle size, and surrounding condition around the
Abstract: Dynamics of charge carriers generated by femtosecond UV (160 fs, 390 nm) excitation in five standard TiO2 photocatalytic powders (JRC-TIO-1, -2, -3, -4, and -5 supplied by the Catalysis Society of Japan) in a vacuum and air was investigated by means of time-resolved femtosecond diffuse reflectance spectroscopy, and was discussed from the viewpoints of crystal structure (anatase and rutile), particle size, and surrounding condition around the particles. Anatase TiO2 catalysts showed very rapid (less than 1 ps) and very slow electron−hole recombination processes, while rutile ones did not show any rapid decay. For catalysts composed of small particles, slower electron−hole recombination was observed in air compared with that in a vacuum, which was well explained in terms of upward band bending near the surface due to adsorption of oxygen. The relationship between the observed charge carrier dynamics and photocatalytic reactivity is also discussed.
TL;DR: In this article, the efficiency of the electrochemically assisted photocatalytic process in the degradation of C. I. Reactive Blue 19 on a Ti/Ru 0,3 Ti 0,7 O 2 electrode was investigated.
Abstract: The aim of this study was to investigate the efficiency of the electrochemically assisted photocatalytic process in the degradation of C. I. Reactive Blue 19 on a Ti/Ru 0,3 Ti 0,7 O 2 electrode. By using the quartz device and the Ti-supported noble metal oxide coating, decolorizations ratios higher than 95% and TOC reduction of about 52% were observed during a period of 120 min. Comparing this value with the sum of the decolorization ratios obtained by a single application of electrochemical and photochemical procedures, it is possible to observe a significant synergic effect between both processes. The electrochemical process was conduced at 28°C (refrigeration with air) and pH of 11.0, and with a constant potential of 1.8 V versus Ag/AgCl. With these conditions, the mean current was 23 mA. The voltammetric results also confirm the synergic effect of the simultaneous process.
TL;DR: In this paper, the thermodynamics and kinetics of CO 2 binding to transition metal transition-metal complexes (CoHMD 2+ and Ru(bpy) 2 (CO)X n + (bpy=2,2′-bipyridine, X=CO, Cl, H, etc.).
TL;DR: In this article, the effect of operational parameters, i.e., dye concentration, photocatalyst content, pH of the solution and incident light energy on the degradation rate of aqueous solutions of acid orange 7 (AO7) was examined.
TL;DR: The relation between the effect and the amount of SiO2 addition on photo-generated hydrophilicity of TiO2 thin film was investigated by measuring the X-ray diffraction, the microstructure, the specific surface area and the TG-DTA.
Abstract: The relation between the effect and the amount of SiO2 addition on photo-generated hydrophilicity of TiO2 thin film, was investigated by measuring the X-ray diffraction, the microstructure, the specific surface area and the TG-DTA. It was found that the optimum range existed in the amount of SiO2 addition to TiO2, 10–30 mol % SiO2 addition was most effective for contact angle of water. The SiO2 addition less than 30 mol % has a suppressive effect on the transformation of anatase to rutile and on the crystal growth of anatase in calcination, and it has large surface area. With the consequence that the photocatalytic activity of TiO2 and the capability of holding absorbed water which increases during UV irradiation improved.
TL;DR: In this article, the complete photocatalytic oxidation of C2H4 with O2 into CO2 and H2O has been achieved on ultrafine powdered TiO2 photocatalyst and the addition of H 2O was found to enhance the reaction.
TL;DR: In this article, the degradation of 2-chlorobiphenyl (2-CB) with oxidant concentration of 10 −3 and 10 −2 M and TiO 2 concentration of 25 µm/l was investigated.
TL;DR: In this article, the H2 evolution reaction from an aqueous Na2SO3 solution proceeded with 3.7% quantum yield under visible light irradiation (λ > 420 nm) on a Zn0.957Cu0.043S solid solution photocatalyst without co-catalysts such as Pt.
Abstract: The H2 evolution reaction from an aqueous Na2SO3 solution proceeded with 3.7% quantum yield under visible light irradiation (λ > 420 nm) on a Zn0.957Cu0.043S solid solution photocatalyst without co‐catalysts such as Pt.
TL;DR: In this paper, the photocatalytic degradation of 4-chlorophenol, chosen as an aromatic model pollutant, has been performed in contact with a suspended mixture of titania and activated carbon (AC).
TL;DR: In this paper, it was found for the first time that controlling the charge density in oxide semiconductors with an acceptor was effective for improving the activity to photolysis of H2O.
Abstract: It was found for the first time that controlling the charge density in oxide semiconductors with an acceptor was effective for improving the activity to photolysis of H2O. Although the photodecomposition activity of NiO supported on nondoped KTaO3 was negligibly small, doping small amount of acceptors such as tri- or tetravalent cations to KTaO3 increased the formation rate of H2 and O2. In particular, it was found that NiO supported on KTaO3 doped with 8 mol % Zr4+ exhibits higher activity to the photocatalytic decomposition of H2O than that of a well-known photocatalyst of Pt/TiO2 .
TL;DR: In this paper, Ru-doped TiO2 particles were prepared and their properties as the photocatalyst were investigated, showing that the oxygen evolution reaction occurred by irradiation of visible light at wavelengths longer than 440nm using iron(III) ions as the electron acceptor.
Abstract: In order to expand the effective wavelength of TiO2 particulate photocatalyst into the visible region, Ru-doped TiO2 particles were prepared and their properties as the photocatalyst were investigated. With this photocatalyst, the oxygen evolution reaction occurred by irradiation of visible light at wavelengths longer than 440 nm using iron(III) ions as the electron acceptor. To clarify the mechanistic aspects of the effect of Ru-doping, photoelectrochemical properties of Ru-doped TiO2 sinter electrodes were investigated.
TL;DR: Spectroscopic studies show that the presence of these substitutional metal ion species are, in fact, responsible for the large shift in the absorption spectra of these catalysts toward visible light regions.
Abstract: The metal ion-implantation of titanium oxide with metal ions (Cr + or V +) at high energy acceleration and the subsequent calcination of these metal ion-implanted TiO 2 in oxygen at around 725 K resulted in a large shift in the absorption spectra toward visible light regions. These catalysts exhibited effective and remarkable photocatalytic reactivity for various reactions such as the decomposition of NO into N2, 02 and N20 at 275 K not only under UV but also under visible light irradiation. XAFS, ESR and UV-Vis studies have revealed that the implanted metal ions (Cr + or V +) are located at the lattice positions of Ti 4+ in TiO2 and stabilized as Cr 3+ or (V 3+ or V 4+) species after the calcination of the sample in 0 2 at around 775 K. Thus, these spectroscopic studies show that the presence of these substitutional metal ion species are, in fact, responsible for the large shift in the absorption spectra of these catalysts toward visible light regions.
TL;DR: Three processes were studied for degradation of an anthraquinone dye (C.I. reactive blue-19) and maximum decolorization degrees of about 30% are insignificant in relation to theDecolorization degree achieved by the other processes.
TL;DR: A detailed description of various mechanisms for the photocatalytic oxidation of alcohols and organochlorides in an aerated or a deaerated system is given in this article.
TL;DR: In this article, an AgBr/SiO2 catalyst prepared from Schumann emulsion has been used for photolysis of CH3OH/H2O solution under UV illumination, H2 generation was observed and hydrogen was continuously evolved for 200 h without destruction of AgBr although Ag0 was detected by X-ray diffraction analysis after the reaction.
Abstract: A AgBr/SiO2 catalyst prepared from Schumann emulsion has been used for photolysis of CH3OH/H2O solution. Under UV illumination, H2 generation was observed and hydrogen was continuously evolved for 200 h without destruction of AgBr although Ag0 was detected by X-ray diffraction analysis after the reaction. It is presumed that the hydrogen production from methanol in distilled water occurs on the Ag0 and the support plays important roles for the photocatalysis as well as TiO2/SiO2 (J. Phys. Chem. B 1997, 101, 2611).
TL;DR: In this paper, a photoreactor irradiated by a medium pressure Hg lamp was used for photo-oxidization of toluene to benzaldehyde, and a small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected.
TL;DR: In this paper, a combined photochemical and biological flow reactor for the degradation of p -nitrotoluene-ortho-sulfonic acid (p -NTS) was presented.
TL;DR: In this article, the photocatalytic efficiency of pure and 0.5 −20 wt.% Fe-containing ZrO 2 samples, prepared by a solgel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25).
Abstract: The photocatalytic efficiency of pure and 0.5‐20 wt.% Fe-containing ZrO 2 samples, prepared by a sol‐gel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25). All samples were active, although the efficiency was lower than that of TiO 2. Nevertheless, the presence of iron increased the activity for nitrite photooxidation, with the maximum efficiency at 5 wt.% Fe content. At higher Fe content, the efficiency decreased but it was always higher than that of the undoped sample. For EDTA oxidation and Cr(VI) reduction, the same trend was observed. Remarkably, Cr(VI) reduction in the presence of EDTA was strongly accelerated, all zirconia samples being as active as P-25, although initial rates were lower and somewhat detrimentally affected by the presence of iron. The photocatalytic activity depends on the structural, surface and optical properties of the sample, on the preparation conditions and on the nature of the photocatalytic reaction. ©1999 Elsevier Science S.A. All rights reserved.
TL;DR: In this paper, mass spectral analysis of the photocatalyzed microcystin-LR allowed tentative characterization of the reaction process and products, and showed that the disappearance of micro-cystins was paralleled by a reduction in toxicity.
Abstract: TiO 2 photocatalysis has been used to destroy microcystin-LR in aqueous solution. The destruction of this toxin was monitored by HPLC, and the disappearance was accompanied by the appearance of seven UV detectable compounds. Spectral analysis revealed that some of these compounds retained spectra similartothe parent compound suggesting that the Adda moiety, thought to be responsible for the characteristic spectrum, remained intact whereas the spectra of some of the other products was more radically altered. Six of the seven observed reaction products did not appear to undergo further degradation during prolonged photocatalysis (100 min). The degree to which microcystin-LR was mineralized by photocatalytic oxidation was determined. Results indicated that less than 10% mineralization occurred. Mass spectral analysis of the photocatalyzed microcystin-LR allowed tentative characterization of the reaction process and products. Reduction in toxicity due to the photocatalytic oxidation was evaluated using an invertebrate bioassay, which demonstrated that the disappearance of microcystin-LR was paralleled by a reduction in toxicity. These findings suggest that photocatalytic destruction of microcystins may be a suitable method for the removal of these potentially hazardous compounds from drinking water.