Peroxymonosulfate enhanced photocatalytic degradation of Reactive Black 5 by ZnO-GAC: Key influencing factors, stability and response surface approach

Abstract

• ZnO-GAC was used in the photocatalysis of RB5 with the presence of PMS. • Cooperative effects of UV, ZnO surf e − and GAC mediated by PMS were observed. • The mineralization and degradation pathway of RB5 were investigated. • Effect of reaction parameters was evaluated by response surface methodology. Zinc oxide supported on granular activated carbon (ZnO-GAC) was synthesized for the photocatalysis of Reactive Black 5 (RB5) with the presence of peroxymonosulfate (PMS). RB5 removal was improved with increasing temperature and dosage of PMS or catalyst, but declined with increasing pH and RB5 concentration. The reaction followed first-order kinetic model and the activation energy was determined to be 16.15 kJ mol −1 . After 60 min treatment, 43.6% of TOC was removed and further extending the reaction time to 90 min resulted in 51.9% TOC removal. The evolution profile of ammonium and nitrate ions was monitored during the treatment, and the organic degradation products of RB5 oxidation were identified by LC-MS analysis with a plausible degradation pathway being proposed. Quenching experiments indicated that electron hole (h + ) and reactive radicals (e.g. HO • /SO 4 •− ) were mainly responsible for RB5 removal in the UV/ZnO-GAC/PMS system. The catalyst reuse experiment shows that ZnO-GAC had no obvious deactivation after four cycles, which implied the reusability and stability of the prepared catalyst. Response surface methodology (RSM) with Box-Behnken design (BBD) was used to evaluate the effect of operating conditions, including PMS concentration, reaction temperature and initial pH on the removal rate of RB5. The result of adequacy check indicated the proposed RSM model was reliable and accurate to analyze the operating parameters of the UV/ZnO-GAC/PMS system.