The heterojunction of NiO/MgFe-LDH promoted degradation of nitrogenous disinfection by-products in electrochemical system via accelerating singlet oxygen generation

Abstract

Nitrosopyrrolidine (NPYR), as a typical disinfection by-product, is a strong carcinogen and its effective removal is of great significance to protecting people’s health. In this study, a novel NiO/MgFe-LDH composite material as particle electrode is designed and used for the electrocatalytic degradation of NPYR in continuous flow three-dimensional aeration electrochemical reaction system (3DAER). MgFe-LDH nanosheets are loaded with NiO nanosheets on the surface, and the composites show a special laminated structure, which contributes to the formation of heterojunction between NiO and MgFe-LDH. In order to reveal the factors of heterojunction, we have carried out relevant revealing. The characterization and density functional theory (DFT) studies probe a strong interaction and charge transfer existed between NiO and MgFe-LDH, which alters the electronic structure and surface activity of the interface. Moreover, the energy barrier for adsorption and dissociation of H2O on NiO/MgFe-LDH is also significantly lower than that of MgFe-LDH, which will improve the adsorption capacity of pollutants. Interestingly, formation of singlet oxygen (1O2) is only existed in NiO/MgFe-LDH 3DAER system, which is produced by accelerating electron transfer from the function of heterojunction and promoting the generation of hydroxy (·OH) and superoxide (O2−) radicals to form 1O2. Finally, under the optimal conditions from response surface methodology (RSM-BBD), the degradation efficiency of NPYR in the NiO/MgFe-LDH 3D particle electron system reaches a maximum removal efficiency of 90.36 % within 150 min. At last, the relative electrocatalytic mechanism is also inferred by combining DFT theoretical calculations and degradation pathways.