Heterogeneous activation of persulfate by CuMgAl layered double oxide for catalytic degradation of sulfameter

In this study, a series of CuMgAl layered double oxides (CuMgAl-LDOs) were obtained via calcination of CuMgAl layered double hydroxides (CuMgAl-LDHs) synthesised via a co-precipitation method. The results show that CuMgAl-LDO can be prepared using an optimal Cu:Mg:Al molar ratio of 3:3:2, NaOH:Na₂CO₃ molar ratio of 2:1, and calcination temperature of 600℃. CuMgAl-LDO is a characteristic of mesoporous material with a lamellar structure and large specific surface area. The removal efficiency of sulfameter (SMD) based on CuMgAl-LDO/persulfate (PS) can reach > 98% over a wide range of initial SMD concentrations (5-20 mg L^-1). The best removal efficiency of 99.49% was achieved within 120 min using 10 mg L^-1 SMD, 0.3 g L^-1 CuMgAl-LDO, and 0.7 mmol L^-1 PS. Kinetic analysis showed that the degradation of SMD was in accordance with a quasi-first-order kinetic model. The stability of the CuMgAl-LDO catalyst was verified by the high SMD removal efficiency (> 97% within 120 min) observed after five recycling tests and low copper ion leaching concentration (0.89 mg L^-1), which is below drinking water quality standard of 1.3 mg L^-1 permittable in the U.S. Radical scavenging experiments suggest that SO₄^·- is the primary active species participating in the CuMgAl-LDO/PS system. Moreover, our mechanistic investigations based on the radical scavenging tests and X-ray photoelectron spectroscopy (XPS) results indicate that Cu^(II)-Cu^(III)-Cu^(II) circulation is responsible for activating PS in the degradation of SMD and the degradation pathway for SMD was deduced. Accordingly, the results presented in this work demonstrate that CuMgAl-LDO may be an efficient and stable catalyst for the activation of PS during the degradation of organic pollutants.