Additional O doping significantly improved the catalytic performance of Mn/O co-doped g-C3N4 for activating periodate and degrading organic pollutants

Metal-doped g-C3N4 materials have been extensively investigated and utilized as catalysts in the domain of wastewater treatment. In this study, additional O was introduced in Mn-doped g-C3N4 (MCN) to synthesize Mn/O co-doped material (MOCN), and a new non-radical oxidation system of periodate (PI) activation with MOCN was established for degradation of pollutants. The results indicated that additional O doping can enhance the catalytic performance of MOCN. This was primarily demonstrated by the 3.5-fold increase in the degradation rate (k) of sulfadiazine (SDZ) by MOCN/PI system compared to MCN/PI one. Simultaneously, density functional theory (DFT) calculations have revealed that MOCN material exhibit a higher affinity for adsorbing PI (adsorption energy Eads = −4.992 eV), resulting in an elongation of the I-O bond length (lI-O = 1.874 Å) and facilitating bond cleavage of PI to generate reactive active species (ROS). The reaction process was confirmed to be primarily driven by non-radical singlet oxygen (1O2), as demonstrated by electron paramagnetic resonance (EPR) and free radical quenching experiments. In addition, possible degradation pathways of SDZ were proposed based on the identified intermediate products and the calculated Fukui constants. The MOCN/PI catalytic system was highly efficient and environmentally friendly, with great potential for development in sewage treatment.