Application of solar energy in wastewater treatment: Photocatalytic degradation of α-methylstyrene in water in presence of ZnO

Zinc oxide mediated photocatalytic degradation of trace amounts of the petrochemical pollutant α-methylstyrene (AMS) in water is investigated using sunlight as the energy source. The influence of various parameters such as catalyst dosage, initial concentration of AMS, pH, insitu formed intermediates, humic acid, H2O2, O2 etc., on the rate of degradation is investigated. Acetophenone (ACP) is identified as the major intermediate in the degradation. Both AMS and ACP inhibit the degradation of one another, the extent of inhibition being dependent on the relative concentration of one with respect to the other. H2O2 formed in the process acts as a reservoir of various Reactive Oxygen Species (ROS) which can enhance the degradation. However, H2O2 also acts as a scavenger for the ROS leading to its own concurrent decomposition. The degradation of AMS follows first order kinetics. The degradation is slow in deaerated system thereby reconfirming the role of O2 in the photocatalytic process. The catalyst can be recycled at least three times repeatedly before there is reduction in activity. The study clearly shows that zinc oxide mediated solar photocatalysis can be used as an effective tool for the tertiary treatment of AMS contaminated water thus indicating its potential for achieving the twin objectives of solar energy harvesting and wastewater treatment.