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Journal ArticleDOI

Photocatalytic reduction of nitrite and nitrate ions over TiO2 semiconductors

01 Jan 1996-Journal of Materials Science Letters (Kluwer Academic Publishers)-Vol. 15, Iss: 10, pp 874-877
Abstract: Photocatalysis has recently gained attention in the field of pollutant degradation [1-4]. Among the various semiconductors employed, anatase phase of TiO2 appears to be a promising photocatalyst [5, 6]. TiO; has become a benchmark semiconductor, showing the best compromise between catalytic performance and stability at any pH value of aqueous dispersion. It has been reported that for the same photoreaction, the preparation of TiO2 and its thermal treatment significantly affect the activity of the semiconductors. Indeed, preparation parameters influence the photoactivity since the physico-chemical features are determined by the catalyst's origin and preparation. The sol-gel method provides a convenient method for the preparation of several inorganic oxides with tailored physical and chemical properties. We report here the synthesis and photocatalytic performance of TiO2 prepared by a sol-gel method and compare its activity with a commercial sample of T iQ (J. T. Baker, USA). TiO2 gels were prepared by the acid catalysed solgel method. The sol was prepared by mixing Ti(IV) isopropoxide with anhydrous 2-propanol, H20 and HNO3 at ambient temperature with stirring. A series of gels with varying ratio of alcohol, water content and different molar ratio between titanium (IV) isopropoxide and acid was prepared, The gels were dried at 383 K for 12h. Crystallization to anatase was achieved in air by heating at 823 K for 24 h. Titanium hydroxide was precipitated by reacting an aqueous solution of TiC14 with an aqueous ammonia solution (25 wt%). This was done by adding the latter drop-wise to the metal solution at room temperature, with vigorous stirring owing to the exothermicity of the reaction. After standing for 24 h at room temperature, the solid was filtered and repeatedly washed with double distilled water until free of chloride ions. The resulting solid was dried at 393 K for 24h and then fired in air at 823 K for 24 h. X-ray diffractograms were obtained for the powdered samples using a Philips diffractometer (Philips Generator, Holland; Model PW 1130) provided with an online recorder and dot-matrix printer (Tele type, USA). The diffraction patterns were recorded at room temperature using Ni-filtered CuKa radiation (/1, = 0.154 18 nm) for all samples. A more

Topics: Photocatalysis (54%), Aqueous solution (54%), Anatase (53%) more
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Journal ArticleDOI
Michael A. Henderson1Institutions (1)
Abstract: The field of surface science provides a unique approach to understanding bulk, surface and interfacial phenomena occurring during TiO2 photocatalysis. This review highlights, from a surface science perspective, recent literature that provides molecular-level insights into photon-initiated events occurring at TiO2 surfaces. Seven key scientific issues are identified in the organization of this review. These are: (1) photon absorption, (2) charge transport and trapping, (3) electron transfer dynamics, (4) the adsorbed state, (5) mechanisms, (6) poisons and promoters, and (7) phase and form. This review ends with a brief examination of several chemical processes (such as water splitting) in which TiO2 photocatalysis has made significant contributions in the literature. more

1,602 citations

Journal ArticleDOI
Abstract: Charge carrier transfer processes are very important and play a vital role in photocatalytic reactions. A fundamental understanding of the kinetics and mechanisms of these charge transfer processes is crucial from the viewpoint of developing efficient photocatalysis systems for large-scale industrialization. In this work, recent efforts concerning the understanding of the kinetics and the mechanisms of the charge transfer in photocatalytic processes have been reviewed. Fundamental aspects involved in these charge transfer processes, such as charge generation, charge trapping, charge recombination, and electron and hole transfer are primarily discussed. Moreover, some recent studies focusing on enhancing the photocatalytic efficiency by improving the charge transfer and separation are also reviewed. more

161 citations

Journal ArticleDOI
Abstract: Interfacial electron transfer at semiconductor nanoparticles is a fundamental process that is relevant to many applications in photocatalysis such as wastewater cleaning, air cleaning and energy production. Fundamental understanding of the dynamic of the electron transfer is of crucial importance for the understanding of the fundamental concepts of photocatalytic processes and hence results in understanding and industrialization of photocatalytic reactions as well as a rational design of the photocatalytic systems. This review summarizes the progress in understanding electron transfer dynamics from semiconductor nanoparticles to the electron acceptor molecules. The approaches to improve the electron transfer efficiency will be also reviewed. Of particular focus will be the advancement of methodology as well as overview of some new highlights in electron transfer reactions at TiO2/liquid interface. more

89 citations

Journal ArticleDOI
TL;DR: The kinetics and the mechanism of various multielectron transfer reactions initiated by stored electrons in TiO(2) nanoparticles have been investigated employing the stopped flow technique and the underlying reaction mechanisms are discussed in detail. more

Abstract: The kinetics and the mechanism of various multielectron transfer reactions initiated by stored electrons in TiO2 nanoparticles have been investigated employing the stopped flow technique. Moreover, the optical properties of the stored electrons in the TiO2 nanoparticles have been studied in detail following the UV (A) photolysis of deaerated aqueous suspensions of TiO2 nanoparticles in the presence of methanol. The reduction of common electron acceptors that are often present in photocatalytic systems such as O2, H2O2, and NO3− has been investigated. The experimental results clearly show that the stored electrons reduce O2 and H2O2 to water by multielectron transfer processes. Moreover, NO3− is reduced via the transfer of eight electrons evincing the formation of ammonia. On the other hand, the reduction of toxic metal ions, such as Cu(II), has been studied mixing their respective anoxic aqueous solutions with those containing the electrons stored in the TiO2 particles. A two-electron transfer is found to... more

77 citations

Journal ArticleDOI
Hideki Kato1, Akihiko Kudo1Institutions (1)
Abstract: Tantalate photocatalysts reduced nitrate ions to nitrite ions, dinitrogen, and ammonia under UV irradiation even without co-catalysts or reducing reagents such as organic compounds. The photocatalytic activities of tantalate photocatalysts were larger than those of TiO2 photocatalysts. The selectivity for the photocatalytic reduction of nitrate ions was affected by the addition of co-catalysts. In particular, the efficiencies of dinitrogen and ammonia formation increased by one to two orders of magnitude when a Ni co-catalyst was loaded. The selectivity was also affected by the amount of loaded Ni and the loading method. 44% and 39% of nitrate ions in an aqueous KNO3 solution (0.010 mol L−1, 400 mL) were reduced to dinitrogen and ammonia, respectively, over the Ni(1 wt.%)/KTaO3 photocatalyst after 25 h irradiation. more

70 citations

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Journal ArticleDOI
01 Jan 1995-Chemical Reviews
Abstract: The civilian, commercial, and defense sectors of most advanced industrialized nations are faced with a tremendous set of environmental problems related to the remediation of hazardous wastes, contaminated groundwaters, and the control of toxic air contaminants. For example, the slow pace of hazardous waste remediation at military installations around the world is causing a serious delay in conversion of many of these facilities to civilian uses. Over the last 10 years problems related to hazardous waste remediation have emerged as a high national and international priority. more

16,306 citations

01 Jan 1954-

4,154 citations

01 Oct 1989-
Abstract: The book is devoted to the study of photocatalysis, a very popular area of modern-day chemistry. The various chapters will cover aspects of the field that are of particular interest to those at the top in research expertise. Among the subjects discussed are: the theory and preparation of semiconductor mate- rials, the various types of heterogeneous photocatalysis methods, absorption and desorption in photocatalysis, and applied photoca- talysis in energy production. A knowledge of photochemistry is not essential as the format and selection of topics make the field evolve naturally. The student is first introduced to the meaning of photocatalysis and subsequently taken through the essentials of photochemistry towards bridging it to semiconductor materials. The reader is also introduced to the colloidal state of semiconductors followed by thermodynamic and kinetic aspects of photocatalysis. The book is aimed at professional, faculty and graduate students in inorganic and physical chemistry, organic chemistry, oganometallic chemistry, and catalysis. more

1,655 citations

Journal ArticleDOI
Abstract: Several commercial and homemade TiO{sub 2} samples were used as photocatalysts to prove that the physicochemical features as determined by the origin and preparation methods affect the photocatalytic behavior, in addition to the semiconducting properties. The photodegradation of aqueous phenol solution in TiO{sub 2} dispersion, carried out in a batch reactor, was used as a test reaction. The results show a great variability of photocatalytic behavior, and in particular it has been observed that the rutile phase is active or inactive according to the preparation conditions. more

397 citations

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