Evaluation of two types of TiO2-based catalysts by photodegradation of DMSO in aqueous suspension

Among the different methods to evaluate the photocatalytic activity of TiO2-based photocatalysts, the most employed has been the methylene blue method. However, several questions have emerged during the lasts years about its reliability, because this compound can absorb light in the visible range. In this work a new compound is used as photocatalytic test-substance, the dimethylsulfoxide (DMSO), which will be used in the ISO standard (ISO/CD 10676) for the determination of the photocatalytic efficiency of systems used for water treatment. This solvent is a hydroxyl scavenging agent, which can interact with OH. The study is focused on the degradation of this molecule by two different catalysts: Degussa P25 and Hombikat UV100. The reaction is studied by the monitoring of two of the intermediates formed during the reaction: the methansulfonate (CH3SO3−) and the sulfate (SO42−), by means of the ion chromatography technique, and by measuring the TOC. In general, TiO2 Degussa P25 shows better results in terms of generation of two intermediates (methansulfonate and sulfate), TOC removal, and photonic efficiencies. Although Hombikat UV100 has six times larger specific surface than the other photocatalyst, the reason for the higher photoactivity of Degussa P25 can lie in the slower recombination rate of the electron/hole pairs, and also in the kind of aggregates formed in aqueous solution.