Promotion of tetracycline degradation by electro-Fenton: Controlling the reaction zone by N-doped modified activated carbon cathode

Abstract

The effective matching of ·OH produced by an electro-Fenton cathode with liquid-phase pollutants is the key to the efficient degradation of pollutants by using electro-Fenton systems. Therefore, tetracycline (TC) was enriched near a carbon cathode through N-doped modification, and the modified carbon cathode increased ·OH generation. The zone of TC degradation by ·OH and zone of ·OH generation were both controlled near the cathode. This phenomenon was called “controlling the reaction zone.” The adsorption capacities of NAC-1000/GF considerably increased by 9.16% and 31.09% for TC and H2O2, respectively. In addition, the modified cathodic electro-Fenton system (NAC-1000/GF) showed 17.15 mg L−1 improvement in the degradation effect of TC compared with the unmodified system. This improvement is substantially higher than that of the pure adsorption system (5.98 mg L−1). The degradation efficiency of TC reached 83.07% in 120 min. Structural characterization, molecular dynamics simulation, and electrochemical experiments revealed that pyrrolic-N enhanced the adsorption capacity of the activated carbon cathode, and pyridinic-N and graphitic-N further hindered TC desorption, which provided a favorable guarantee for controlling the reaction zone. Pyridinic-N and graphitic-N also enhanced the 2e-ORR selectivity of the cathode and promoted ·OH generation, which was conducive to the continuous and efficient degradation reaction in the zone. In addition, the theoretical calculation confirmed that an effective synergy existed between adsorption and electrolysis. This study provides a new direction and theoretical guidance for the development of electro-Fenton technology for water pollutant degradation.