Recent progress in photocatalytic degradation of chlorinated phenols and reduction of heavy metal ions in water by TiO2-based catalysts

ABSTRACT Among the various semiconductor photocatalysts reported so far, TiO2 is still the most promising material for real applications because of its excellent chemical and thermal stability, non-toxicity, low cost and highly oxidising photogenerated holes. This review summarises the recent progress (mainly over the last five years) in photocatalytic oxidation of non-biodegradable organic pollutants (chlorophenols) and reduction of toxic heavy metal ions in aqueous solution. The review details the recently developed strategies for improving the performance of TiO2-based photocatalysts, with particular respect to the visible light activity, charge separation efficiency, stability, separability and adsorption capacity for the remediation of the aforementioned categories of water contaminants, as these factors heavily affect the practical application of this technology. Next, the underlying semiconductor photocatalytic mechanisms have been thoroughly addressed experimentally and theoretically, together with the proposed defect engineering to improve the photocatalytic performance. Finally, the prospect of TiO2 photocatalysis was discussed.