Removal of pharmaceuticals and endocrine disrupting compounds from water by zinc oxide-based photocatalytic degradation: A review

The detection of pharmaceuticals and endocrine disrupting compounds (EDCs), known as emerging contaminants (ECs), in the environment has attracted growing concern due to their toxicity and potential hazard to the ecosystems and humans. These contaminants are consumed at high quantities worldwide and they are released deliberately or accidentally into the water resources. The conventional treatment technologies that use biological processes cannot effectively remove these contaminants. Therefore, the development of efficient and sustainable removal methods for these emerging contaminants is essential. Photocatalytic removal of emerging contaminants by using zinc oxide catalyst (ZnO) is a promising process due to the unique characteristics of this catalyst such as absorption of a larger fraction of the solar spectrum, wide band gap, biocompatibility, non-toxicity and low cost. Recently, a considerable effort has been made to improve the photocatalytic performance of ZnO by doping with elements, optimizing preparation methods, and using nano-ZnO. In addition, the efficiency of photocatalytic degradation processes have been shown to be dependent on the pH of solution, type and amount of ZnO, concentration of contaminants, presence of natural organic matter (NOM) and electron acceptor. This paper presents a review of parameters which affect the performance of photocatalytic degradation processes by using the ZnO catalyst, and discusses methods for the modification of zinc oxide structure.