Enhanced photocatalytic ozonation degradation of organic pollutants by ZnO modified TiO2 nanocomposites

Advanced oxidation processes (AOPs) for wastewater treatment have attracted much attention for their efficient capability in destroying persistent and toxic organic compounds. In this study, we reported a simple impregnation-calcination method to fabricate ZnO modified TiO2 (Zn-TiO2) nanocomposites and employed them as catalysts for degradation of organic pollutants in water. The results show that 7at%Zn-TiO2 exhibits much better performances of photocatalysis, catalytic ozonation and photocatalytic ozonation than pure TiO2, which could be due to its richer surface hydroxyl groups and higher separation efficiency of photogenerated electron-hole pairs. The total organic carbon (TOC) removal efficiency of salicylic acid (SA) in UV/O3/7at%Zn-TiO2 is higher than the sum of those in UV/7at%Zn-TiO2 and O3 processes, indicative of a synergistic effect between photocatalysis and ozonation. Mechanism studies demonstrate that the active species such as H2O2, h+, OH, O2− and 1O2 are responsible for SA degradation. Meanwhile, the intermediates of SA mineralization were identified by HPLC–MS and its mineralization pathway was proposed. Reusability test verifies a high stability of 7at%Zn-TiO2 in the photocatalytic ozonation process, and the catalyst can be applied in a wide pH range of aqueous solution from 3.5 to 10.0. This work puts forward a new application of the easily available Zn-TiO2 nanocomposites and might drive the advance of photocatalytic ozonation approach for water purification.