Photocatalysis assisted by peroxymonosulfate and persulfate for benzotriazole degradation: effect of pH on sulfate and hydroxyl radicals

Recently, notable attempts have been devoted to removing emerging pollutants from water resources. Benzotriazole (BTA) as an emerging pollutant has widely been detected in the aquatic environment and water resources. In the current work, peroxymonosulfate (PMS) and persulfate (PS) were added to a TiO2/UV system for BTA degradation, as electron acceptors to overcome recombination of hole and electron. Additions of PMS and PS to the photocatalysis process considerably increased removal efficiency. The rate constants of UV/TiO2/PMS, UV/TiO2/PS and UV/TiO2 were 0.0217 min(-1), 0.0152 min(-1) and 0.0052 min(-1) respectively. The results showed that pH significantly affected the UV/TiO2/PMS system while it marginally affected UV/TiO2/PS. Scavenging experiments using alcohols indicated that in acidic pH, the dominant oxidant was sulfate radical in both systems. The contribution of hydroxyl radical in BTA degradation was boosted at alkaline and neutral conditions especially in the UV/TiO2/PMS system. Moreover, other scavenging experiments implied that reaction of radicals occurred at both the catalyst surface and in solution. The mineralization results showed that PMS and PS significantly increased chemical oxygen demand and total organic carbon removal efficiencies. In general, presence of PMS in the photocatalysis process had a better performance compared to PS in terms of BTA removal and mineralization.