Insights of the La promotion in CoFe-LDH as particle electrodes on degradation process of N-nitrosopyrrolidine in electrocatalytic continuous-flow system

Layered double hydroxides (LDH), as a green, easy to prepare and modify material, has been widely concerned in the field of electrochemical catalytic degradation of difficult to remove pollutants in water. In our work, modified LDH material is synthesized by doping La into the lattice of CoFe-LDH based on its unique electronic structure and large ionic radius, which is used to build the particle electrode to degrade the N-nitrosopyrrolidine (NPYR) in a three-dimensional continuous flow aerated electrocatalytic reactor. The LaCoFe-LDH particle electrodes can generate more active free radicals under electric field, which are beneficial to the degradation of pollutants. The degradation effect of NPYR in the system is satisfactory, and the removal rate reached 83.3% within 90min. According to the results of characterization analysis, radical quenching experiment and EPR test, La doping improves the electron transfer ability of the catalyst, which effectively accelerates the redox cycle of Fe2+/Fe3+ and Co2+/Co3+ to achieve sustainable catalysis of particle electrodes to form free radicals, thus enhancing the degradation of NPYR. The DFT calculation results of CoFeLa-LDH show that the energy required for oxygen adsorption by CoFeLa-LDH (-6.79eV) is lower than that of CoFe-LDH (-6.08eV), illustrating the improved adsorption properties of the material after La doping. According to the detection results of GC-MS and LC-MS, the possible degradation path of NPYR is proposed. Moreover, the toxicity of the products after degradation of NPYR is generally reduced, indicating that the system is environmentally friendly. The study provides new insights into the design of electrocatalytic materials in water treatment.