Nitrogen and phosphorus co-doped porous carbons (NPCs) for peroxydisulfate (PDS) activation towards tetracycline degradation: Defects enhanced adsorption and non-radical mechanism dominated by electron transfer

Nitrogen and phosphorus co-doped porous carbons (NPCs) were successfully prepared by pyrolysis of the mixture of PANI and phytic acid. The synthesized NPCs exhibited excellent degradation abilities to tetracycline (90.34% within 60 mins). Based on the results of quenching experiments and electron paramagnetic resonance (EPR), metastable reactive complexes mediated electron transfer was the major pathway and singlet oxygen (1O2) played an auxiliary role in the TC degradation. Graphitic N, pyridinic N and defects were identified as the catalytic sites. Linear sweep voltammetry, chronoamperometry tests and electrochemical impedance spectroscopy tests revealed that defects as the active sites to form metastable surface-confined reactive species. The density functional theory (DFT) calculations results indicated that the introduction of phosphorus could promote the peroxydisulfate (PDS) adsorption and activation by adjusting the electron density of the carbon skeleton. This study provides new insights into the designation of metal-free PDS activators towards the high-efficiency removal of contaminants.