Photocatalytic activity of a mesoporous TiO2/Ni composite in the generation of hydrogen from aqueous ethanol systems

Abstract

inTiO 2 /Ni metal-semiconductor composites were prepared from mesoporous titanium dioxide obtained by sol-gel precipitation in the presence of a structure-forming template. The photocatalytic activity of mesoporous TiO 2 /Ni composites in the generation of hydrogen from aqueous ethanol mixtures was discovered and studied in detail.The high activity of titanium dioxide as a photocatalyst in the redox reactions of many substrates has stimulated research on the development of the controlled synthesis of TiO 2 samples possessing given texture, phase state, and optical and electrophysical characteristics [1][2][3][4][5]. The photocatalytic activity of titanium dioxide was found to be very sensitive to particle size, crystallinity, and phase composition. We should note that powdered titanium dioxide photocatalysts commonly used in most redox reactions, as a rule, have a relatively small specific surface. A significant factor lowering the activity of such catalysts is the relatively low rate of reactions involving electrons of the TiO 2 conductance band in the absence of catalysts for the secondary "dark" steps featuring noble metals such as Pt [1, 2], Rh [1, 2], Pd [1, 3], Ag [1, 6], and Au [7] on the surface of the photocatalyst or an inert support. Hence, there are two directions for improving TiO 2 photocatalytic systems. The first direction involves the development of methods for the preparation of highly porous titanium dioxide samples (especially, mesoporous samples) with surface greater than 100 m 2 /g available for interaction with substrate molecules, ordered porous structure, and high content of anatase, which is the structural modification of TiO 2 most active in photocatalytic reactions. The second direction involves the development of composites, especially metal-semiconductor composites, in which a high degree of separation of the charges generated in the semiconductor may be achieved due to close electronic contact between the composite components and the use of these electrons in the reaction with adsorbed substrates.In the present work, both these approaches are followed for the development of the direct synthesis of a highly active mesoporous TiO 2 /Ni composite photocatalyst by the photoreduction of a nickel salt adsorbed on the mesoporous titanium dioxide surface. The photocatalytic properties of this composite in the generation of hydrogen from aqueous ethanol mixtures were studied.Samples of mesoporous titanium dioxide were obtained by sol-gel hydrolysis of Ti(IV) tetrabutoxide in 1-butanol by atmospheric moisture in the presence of a structure-forming template, namely, dibenzo-18-crown-6. After completion of the 26 0040-5760/05/4101-0026

Quantum Size Effects in Semiconductor Photocatalysis

“…However, after modification of the surface of nanostructural semiconductors with metal particles the quantum yield of this photoreaction increases sharply and in individual cases can reach 1.0. Increase in the rate of photocatalytic release of hydrogen was observed in the transition from the individual semiconductors to CdS/Rh [142], CdS/Ni [142,143], CdS/Co, CdS/Mn, CdS/Fe [143], TiO 2 /Ni [144,145], TiO 2 /Co, TiO 2 /Cu, TiO 2 /Ag [144] composites.…”

Photochemical formation of semiconducting nanostructures

“…The TiO 2 /Ni 0 metal-semiconductor nanocomposites, which are the products of the photocatalytic reduction of NiClO 4 on the surface of mesoporous TiO 2 with particle size 9-10 nm and pore diameter 7-10 nm, have high photocatalytic activity in the release of hydrogen from water-alcohol mixtures [208,209].…”

Semiconductor photocatalytic systems for the production of hydrogen by the action of visible light

“…Heterostructures consisting of a semiconductor (CdS), conducting organic polymers, and various types of sensitizers that had proved much more effective catalysts than cadmium sulfide for the release of hydrogen during the action of visible light were constructed for the first time [13,17,19]. Photocatalytic processes for the production of hydrogen involving metal sulfide microhetero transitions [8,10,12,16,19], photocatalysts based on mesoporous titanium dioxide [20,21,24,25,27], nanostructured semiconductors, etc. [14,15,18,19,22,23,26,28] were also investigated.…”