Papers by Author: Tadeusz Bak

Abstract: The purpose of this work is to consider the basic concepts on the present state of understanding of photocatalytic energy conversion using oxide semiconductors. This work also considers the approaches in derivation of theoretical models that allow explanation of the effect of properties on the performance of oxide-based photocatalysts in photocatalytic water oxidation. In this work we show that the performance of photocatalytic systems must be considered in terms of a range of the key performance-related properties (KPPs) that, in addition to the band gap, include the concentration of surface active sites, charge transport and Fermi level. Taking into account that all these KPPs are related to defect disorder, defect engineering may be applied in processing oxide semiconductors with optimal properties that are required to exhibit maximised performance in solar-to-chemical energy conversion.

Abstract: The present work considers the performance of TiO2-based photosensitive oxide semiconductors as photocatalysts for water purification. This paper brings together the concepts of solid state chemistry for nonstoichiometric compounds and the concepts of photocatalysis in order to discuss the reactivity between TiO2 and water including microorganisms (bacteria and viruses). The performance of TiO2 photocatalysts are considered in terms of a model of photoelectrochemical cell. The experimental data on photocatalytic removal of microorganisms from water are considered in terms of the effect of several properties, including pH, dispersion, light intensity, and temperature. It is argued that correct understanding of the performance of TiO2 photocatalysts requires recognition that properties of TiO2, which is a nonstoichiometric compound, are determined by defect disorder and the related ability to donate or accept electrons. The photocatalytic properties of TiO2 are considered in terms of the reactivity of both anodic and cathodic sites with water and the related charge transfer at the TiO2/H2O interface. It is shown that the formation of well defined photocatalysts requires knowledge of mass and charge transfer during processing and performance, respectively. The main hurdles in the development of high-performance photocatalysts are discussed.

Abstract: The present work considers the performance-related properties of TiO2-based photosensitive semiconductors as photocatalysts for water purification and photoelectrodes for water splitting. These properties, including electronic structure, charge transport, surface properties, and near-tosurface properties, have an effect on light absorption and its conversion into chemical energy, and are closely related to defect disorder. Therefore, defect chemistry may be used as a framework for their modification in order to achieve enhanced performance. The present work considers the relationships between these specific performance-related properties and defect disorder.