Activation of peroxymonosulfate by Cu-Ni-Fe layered double oxides for degradation of butyl 4-hydroxybenzoate: Synergistic effect of oxygen vacancy and Cu(I).

In this study, Cu hybridization coupling oxygen defect engineering was adopted to synthesis of CuNiFe layered double oxides (CuNiFe-LDOs) in peroxymonosulfate (PMS) activation for degradation of methyl 4-hydroxybenzoate. The morphology and crystal structure of CuNiFe-LDOs was characterized in detail, which exhibited regular layered-structure at a Cu:Ni doping ratio of 1:1 and annealing temperature of 400 °C, and presented the crystal of CuO@FeO-NiO. Besides, the X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) results demonstrated that abundant oxygen vacancies (OVs) and low oxidation state Cu species were composed in CuNiFe-LDOs400. The CuNiFe-LDOs400/PMS system showed excellent catalytic performance toward the degradation of butyl 4-hydroxybenzoate (BuP), and resistant to the effect of pH value and background inorganic anions. Based on quenching experiments and EPR measurements, singlet oxygen (O) was identified as the dominant active species during the heterogeneous catalytic process, which was generated by the synergistic interaction between OVs-Cu(I) site and PMS. In this process, the electron-drawing property of OVs promoted the adsorption of PMS molecule on Cu(I) site, followed by the accumulation of electron and cleavage of O-O bond to generate intermediate oxygen radical species, which donated one electron to eventually generate singlet oxygen.