Enhanced degradation of nitrogen-containing disinfection by-products via radical attack in ZnAl particle electrode system: Mechanism and density functional theory calculations

Disinfection by-products (DBPs), in water receive attention because of their toxicity, mutagenicity and carcinogenicity. In this study, Nitrosopyrrolidine (NPYR) in water is electrocatalytically degraded by using ZnAl layered double hydroxide/activated carbon (ZnAl-LDH/AC) as a particle electrode in a three-dimensional electrode reactor (3DER). The results of SEM, TEM and XRD showed the successful synthesis of ZnAl-LDH, in which Zn2Al1-LDH had regular morphology and better crystallinity. The results of electrochemical characterization tests indirectly showed that Zn2Al1-LDH/AC had the largest OPE, the smallest mass transfer resistance, and higher mass transfer rate, and better electrocatalytic performance. The pollutant concentration had the greatest effect on the removal rate of NPYR in the one-way experiment, and the interaction effect between different influencing factors is determined by response surface optimization experiments. The optimal operating conditions showed a pollutant removal rate of 83.78%. A response surface prediction model is constructed. Hydroxyl radicals and superoxide radicals are demonstrated to be the main contributors to indirect oxidation by free radical quenching experiments and EPR. DFT calculations combined with GC-MS and LC-MS results deduced two possible degradation pathways. Toxicity prediction of NPYR and its intermediates is performed using software. Based on the above study, a mechanism for the degradation of NPYR by 3DER is proposed.