Synthesis and applications of nano-sized zinc oxide in wastewater treatment: a review

Generally, environmental pollution is a global problem and the treatments of wastewater have been an outstanding challenge these days. Increased inhabitants, metropolitanism and industrialization have in one way or the other contributed to the environmental hazards. The delimitation of the conventional treatment of wastewater has made researchers to explore novel and viable techniques that can mineralize pollutants without leftover in wastewater to have an environment free of pollutants. Nanotechnology is a promising technology that uses nano-sized materials with unique properties such as small size and large surface area to remove pollutants in aqueous environment. Nano-sized zinc oxide is of great importance as it has high photocatalytic ability, no secondary pollutant, non-toxic, biologically safe, cost-effective, synthesized effortlessly and stable under harsh environment. The utilization of zinc as starting materials for the synthesis of n-sized ZnO was studied extensively, and its availability makes it to be synthesized in various ways such as green synthesis, wet chemical method, precipitation, sol–gel method, co-precipitation, microwave and electrochemical synthesis. It is worthy of note that the mechanism of degradation of pollutants by nano-sized zinc oxide via photocatalysis, sonolysis, adsorption, coagulation and ozonation is vital in achieving complete mineralizing of pollutants in wastewater.