Novel sulfur vacancies featured MIL-88A(Fe)@CuS rods activated peroxymonosulfate for coumarin degradation: Different reactive oxygen species generation routes under acidic and alkaline pH

A novel rod-shaped MIL-88A(Fe)@CuS featured with sulfur vacancies (SV) were constructed as heterogeneous catalysts for activating peroxymonosulfate (PMS) for coumarin (COU) degradation. A series of x[email protected] were obtained according to the mass content of MIL-88A(Fe) in the composites (x, wt% = 50 %, 65 %, and 80 %). Among them, 65 % [email protected] hold the best performance, and realized a complete COU removal (30 μM) in 7 min (0.2 g/L 65 %[email protected] and 0.5 mM PMS). The degradation was much more favorable in acidic initial pH than alkaline initial pH. The calculated reaction rate constants at initial pH of 3.0, 5.0, 6.0 and 9.0 were 0.903, 0.729, 0.650 and 0.095 min−1, respectively. Electron paramagnetic resonance (EPR) analysis, radical scavenging tests and mechanism exploration indicated that the main difference in degradation under acidic and alkaline pH came from the yield of 1O2. In initial pH = 3.0 condition, SV and lattice oxygen on 65 %[email protected] participated in the generation of 1O2, greatly increasing the content of 1O2 (11.6 × 10−11 M) and promoting the degradation. While under initial alkaline condition (pH = 9.0), 1O2 were basically produced from the reaction between Cu(II) and PMS, resulting in a low yield (1.7 × 10−11 M) and lower degradation. Besides, 65 %[email protected] maintained excellent reusability with low metal ions leaching, and the degradation exceeded 98.0 % even in the fifth run. Overall, this work provided an efficient and stable activator for activating PMS to degrade refractory organics, and managed to disclose the activation mechanisms under acidic and alkaline pH.