Sulphate radical oxidation of benzophenone: kinetics, mechanisms and influence of water matrix anions

Benzophenone (BP) is an emerging contaminant that is widely distributed in soil, groundwater, sediment and surface water. In this study, the degradation kinetics, mechanisms, and influence of anions on thermally activated persulphate (TAP) oxidation of BP were systematically investigated. BP degradation was promoted by elevated temperature. The BP degradation data fitted well to the Arrhenius equation with calculated activation energy of 122.8 kJ/mol. BP degradation was also promoted by alkaline pH and high persulphate concentrations. Radical scavenging experiments suggested that both SO₄^•− and HO^• were involved in BP oxidation. Ultra-high-performance liquid chromatography coupled to Orbitrap mass spectrometry (UHPLC-Orbitrap-MS) identified six degradation intermediates. Based on these results, two possible reaction pathways were proposed. Water matrix anions had complex impacts on BP degradation by TAP. Cl⁻ had dual effects on the reaction: low concentration promoted it while high concentration inhibited it. Br⁻ strongly suppressed the reaction. SO₄²⁻ and NO₃⁻ did not affect the reaction. Overall, this study shows that thermally activated persulphate can effectively remove BP and water matrix anions greatly influence the reaction.