Thiosulfate enhanced Cu(II)-catalyzed Fenton-like reaction at neutral condition: Critical role of sulfidation in copper cycle and Cu(III) production

Thiosulfate (S2O32-) has been proven to be an effective promoter of Fenton-like reactions by accelerating the metal ions cycle. However, up to now, little is known about the role of sulfur transformation and intermediate sulfur in the regulation of metal chemical cycle and reactive species production. Herein, free Cu(II) was selected as catalyst for the activation of H2O2. The introduction of S2O32- significantly enhanced the degradation of benzoic acid, and the degradation rate (kobs) was 5.8 times that of Cu(II)/H2O2 system. The kinetic model revealed the transformation of sulfur species and demonstrated that sulfides (i.e., HS-/S2-, S2O32-) and S0 were the dominant electron donor for the reduction of Cu(II) into Cu(I). Consequently, the reduction and complexation roles of S2O32- significantly resolve the rate-limiting step and broaden the pH range of in Fenton-like reactions. Evidence for the critical role of high-valent copper (Cu(III)) and HO• on BA degradation was obtained by scavengers experiments, electron paramagnetic resonance and fluorescent probes. Meanwhile, the Cu(II)/H2O2/S2O32- system also exhibited satisfactory anti-interference ability of the various matrix. Overall, this study offers mechanistic insight into sulfidation in Cu chemical cycle and Cu(III) generation, and highlights the potential of S2O32- for Fenton-like reactions to control pollutants.