A review on photodegradation mechanism of bio-resistant pollutants: Analytical methods, transformation products, and toxicity assessment

Abstract

The photocatalysis process has been employed to degrade various organic micropollutants (OMPs). The photocatalytic degradation of pristine photocatalysts can be enhanced by doping metals and/or non-metals to the lattice structure or merging with co-catalysts to form highly active nanocomposites. However, the partial degradation of OMPs and the formation of transformation products (TPs) that may be more toxic than parent compounds can take place via different pathways (e.g., hydroxylation, deamination, cleavage). Most studies reported the full degradation of various pollutants but with modest mineralization due to the generated by-products and the poor optimization of operating conditions which may result in the increase of toxicity after full degradation. The integration of mass spectroscopy (MS) with chromatography techniques has revolutionized the ability to identify the generated TPs. The toxicity of TPs is usually assessed by the exposure of experimental animals, microorganisms, and plants to the treated solutions and monitoring their attitudes. Recently, some studies have employed software to improve the prediction of water toxicity due to TPs. In this review, we covered the degradation mechanisms, pathways, and various techniques of TPs identification and toxicity evaluation of a wide spectrum of pollutants. Furthermore, we tackle the limitations that may hinder the application of the photocatalysis process on a full-scale.