Photocatalytic degradation of pollutants in petroleum refinery wastewater by TiO2- and ZnO-based photocatalysts: Recent development

Environmental pollution by Petroleum refinery wastewater (PRW) raises vital call for attention to scientist and industrialists due to its impact on human and eco-system. This manuscript reviews methods on modification of semiconductors, effect of operating parameters, reusability/stability, along with recent development on TiO2- and ZnO-based photocatalysts towards degradation of PRW pollutants. TiO2 and ZnO can be successfully modified to visible/solar light responsive photocatalysts. In-depth knowledge of reaction mechanism between photocatalysts and sorbates, structure formation in modified photocatalysts with respect to generation/mobilization of photo-charged carriers, informs the choice of composition of photocatalysts. Petroleum refineries are yet to benefit from heterogeneous photocatalysis due to some setbacks such as: recovery of photocatalysts for reuse, inability of the catalyst to degrade high concentration of pollutants, inability to handle the complex nature of PRW, and its reusability. Thus, a multifunctional and cost effective photocatalyst with reusability/stability needs more exploration to enable commercialization of the photocatalysts.