Prompting direct single electron transfer to produce non-radical 1O2/H* by electro-activating peroxydisulfate process with core-shell cathode

A novel heteroatomic N, P and S co-doped core-shell material (MnFe3O4@PZS) was synthesized by a simple polycondensation hydro-thermal method, and used as the cathode to cooperate with electron-catalysis to activate persulfate (S2O82−) (E-MnFe3O4@PZS-PDS) for tetracycline (TTC) degradation. Radical scavenger studies demonstrated that non-radicals including atomic H* and singlet oxygen (1O2) rather than sulfate and hydroxyl radicals were the crucial reactive oxygen species (ROS). Electrochemical analysis indicated that Mn doping could promote electro-catalytic process via diverting pathway from four/two-electron to one-electron to generate non-radical H*/1O2 at the cathode, including one-electron oxygen reduction reaction (1e-ORR) (O2→1O2), and one-electron hydrogen reduction reaction (1e-HRR) (H2O+e−→H∗), as evidenced by the lowest onset potential (0.072 V) together with electron transfer number (n = 1.65). Besides, the regeneration/reduction of FeⅡ/Ⅲ/MnⅡ/Ⅲ/Ⅳ and persulfate will not cause excessive consumption of electron and chemicals due to that could directly get the electron individually from the cathode and anode, and finally TTC could be completely degraded with low energy consumption (0.655 kWh m−3). This study provides new insights into the direct single electron activating PDS to produce non-radical H*/1O2 via core-shell catalytic MnFe3O4@PZS, and displays a promising application in wastewater treatment.