583 ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 4, pp. 583−587. © Pleiades Publishing, Ltd., 2010. Original Russian Text © T.V. Rezchikova, E.N. Kurkin, L.S. Kiryukhina, E.N. Kabachkov, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 4, pp. 529−533. INORGANIC SYNTHESIS AND INDUSTRIAL INORGANIC CHEMISTRY A Technique for Assessment of the Photocatalytic Properties of Plasmochemically Synthesized Crystalline ТiO 2 Nanopowders T. V. Rezchikova, E. N. Kurkin, L. S. Kiryukhina, and E. N. Kabachkov Institute of Chemical Physics Problems, Russian Academy of Sciences, Chernogolovka, Moscow oblast, Russia Received April 2, 2009 Abstract—The photocatalytic activity of crystalline titania nanopowders synthesized in a stream of ultrahigh- frequency discharge oxygen-containing low-temperature plasma was assessed. To this end, oxidation of an organic dye was carried out in UV-irradiated aqueous suspensions of ТiO 2 at different concentrations and varied irradiation times. DOI: 10.1134/S1070427210040014 Semiconductor materials possessing photocatalytic properties are extensively examined with a view to application in removal of organic contaminants from air and water. Among the known photocatalysts (TiO 2 , ZnO, ZnS), titania is deemed to be the most promising material for practical use. The sequence of chemical reactions occurring on the TiO 2 surface under UV radiation exposure and the principle of photocatalytic operation of TiO 2 were described earlier [1–3]. Titania powders available in the market are produced by different technologies and differ in dispersity and particle morphology, as well as in the phase and chemical compositions. For this reason their photocatalytic properties strongly differ as well. High activity of a powder is difficult to predict, but key factors determining this parameter can be identified. These include: (1) Structure. Among the known TiO 2 modifications [4], anatase and rutile are mainly used as photocatalysts, with anatase being more photocatalytically active. (2) Particle morphology. (3) Impurity content. (4) Size effect. Morokhov et al. [5, 6] showed that the physicochemical properties of crystalline nanopowders differ from those of macropowders. This concerns above all the enhanced excitation energy transfer in the crystal lattice of nanopowders, which significantly decreases the energy barrier for many activation processes. As known, the photocatalytic activity tends to increase with decreasing particle size. In photocatalysis examinations, it may be presumed that, along with the above-mentioned features, small particles are characterized by a lower probability of electron-hole recombination. This is explained by faster, compared to recombination, diffusion of electrons and holes to the surface in the case of small particles [7]. Enhancement of the photocatalytic activity of powders with decreasing particle size can be interpreted in terms of the numbers of active sites and particles per unit volume: They tend to increase with decreasing particle size. The particle size of crystalline nanopowders typically lies within 2–100 nm. The size of plasmochemically synthesized powdered titania particles falls within the indicated range. Here, we attempted to assess the catalytic activity of such powders by a technique similar to that employed by Houas et al. [8]. That study was focused on the photocatalytic decomposition of an organic dye (Methylene Blue) by UV-irradiated aqueous suspension of titania (specific surface area 50 m 2 g –1 ). The quantum yield of the decomposition reaction was estimated at 0.12–0.14%.