Effect of different type of organic compounds on the photocatalytic reduction of Cr(VI) in presence of ZnO nanoparticles

Effect of different type of organic compounds (humic acid, oxalate, ethylenediaminetetraacetic acid, nitrilotriacetic acid, phenol) on the photocatalytic reduction of Cr(VI) with illuminated ZnO was studied in this work with variation of solution pH, contact time, initial Cr(VI) concentration, and type of organic compounds. Maximum removal of Cr(VI) was observed at near neutral pH because of the reduced photocatalytic activity of ZnO at exceedingly low and high pH values originated from either acidic/photochemical corrosion of the catalyst and/or surface passivation with Zn(OH)(2). Removal efficiency of Cr(VI) increased in the presence of oxalate compared to that without presence of organic compound because of positive holes in the valence band of ZnO were scavenged by oxalate. However, it was decreased in the presence of the other organic compounds due to the blocking effects of electron transfer between ZnO surface and Cr(VI). The reduction pattern of Cr(VI) was better described by first-order kinetic model. Finally photocatalytic reaction with illuminated ZnO can be effectively applied to treat wastewater contaminated with Cr(VI).