Water Photolysis by UV Irradiation of Rhodium Loaded Strontium Titanate Catalysts. Relation between Catalytic Activity and Nature of the Deposit from Combined Photolysis and ESCA Studies

Abstract

Photochemical water splitting (H 20 -> H 2 +!02) has been shown to occur on UV irradiation of aqueous suspensions of strontium titanate, modified by surface photodeposition of rhodium species.' Further improvement of the catalytic materials has now been achieved, using thermal deposition techniques. The most active material, prepared by heating rhodium chloride impregnated SrTiO, powder at 500°C in air, allowed one to produce appreciable quantities of (H 2 +!02) gas and to reach high turnover numbers on the catalytic material. The photolysisefficiency presents a strong pH dependence with an optimum around pH -14 and increases markedly when the wavelength of the light decreases from 400 to 300 nm. The amount of rhodium deposited also has a marked effect with an optimum at about 0.2-0.3% Rh by weight. ESCA studies have provided information about the nature of the catalytic deposit and about its relation to the activity of the materials. Catalytic efficiency and mechanistic aspects are discussed. The oxidation state of the rhodium species has a drastic influence: whereas SrTiO, loaded with reduced rhodium shows no catalytic activity, the efficiency increases on progressive oxidation of the deposited metal to surface rhodium(III) species, as detected by ESCA. The photoactive step may involve both band-gap excitation of the semi-conductor support and direct UV excitation of the deposited Rh(III) species.* ERA N°265 of the CNRS. ** ERA W 385 of the CNRS. t The designation Rh/SrTi0 3 has no implication about the oxidation state of the deposited rhodium species; RhO./SrTiO, and Rho/SrTiO, will be used to designate, respectively,surface rhodium oxides of undefined nature and deposited metallic rhodium.

Preparation of S, C cation-codoped SrTiO3 and its photocatalytic activity under visible light

“…Therefore, the development of a SrTiO 3 photocatalyst that shows a high level of activity under visible light is needed. In the past, transition metal cations have been used as dopants to redshift the absorption edge of TiO 2 and SrTiO 3 to a visible light region [4][5][6][7][8][9][10][11][12][13]. Konta et al reported a noble metal iondoped SrTiO 3 that showed photocatalytic activity under visible light [14].…”

The electronic and optical properties of carbon-doped SrTiO3: Density functional characterization

“…C-doped SrTiO 3 with three different ionic sites (C@Sr, C@Ti or C@O) are considered and the stability of these three configurations explored. The calculated results indicate that the C impurity prefers to replace the Ti ion rather than the Sr and O ion in SrTiO 3 .…”

“…The ABO 3 perovskites have a special characteristic that they are susceptible to partial substitution of cations at cation (A or B) site. Among these ABO 3 perovskites, the cubic SrTiO 3 is one of the most promising candidates for solar energy utilization and environmental cleanup, and has been the center of attention in recent years.…”

“…Among these ABO 3 perovskites, the cubic SrTiO 3 is one of the most promising candidates for solar energy utilization and environmental cleanup, and has been the center of attention in recent years. [1][2][3][4][5][6][7] However, similar to TiO 2 , the photoreaction efficiency of SrTiO 3 is severely restricted by its large intrinsic band gap (>3 eV), which results in absorbing only about 5% of the solar energy in the ultraviolet (UV) region. Therefore, it is highly desirable to modulate the electronic structure of SrTiO 3 so as to extend the optical absorption edge to the visible-light region.…”

Na adsorption on SrTiO3 (0 0 1) surface and its interaction with water: A DFT calculation

“…For example, SrTiO 3 can be used as substrate for the epitaxial growth of other oxide thin films [1,2] and metals [3,4]. Moreover, SrTiO 3 is a promising photocatalyst for decomposing organic compounds [5,6] and overall water splitting [7][8][9][10][11][12][13]. For these usages, interaction between adsorbate and surface of SrTiO 3 is very important because the adsorbed surface may bring about new characteristics.…”