Sulfur anchored on N-doped porous carbon as metal-free peroxymonosulfate activator for tetracycline hydrochloride degradation: Nonradical pathway mechanism, performance and biotoxicity

Dual heteroatoms doping is an efficient method to improve catalytic activity of carbon materials. In this research, N, S co-doped porous carbon material (S-NPC) was prepared by direct thermal reduction method of metal organic frameworks and proved to be an excellent metal-free heterogeneous Fenton-like catalyst for peroxymonosulfate (PMS) activation. Tetracycline hydrochloride (TC) could be completely degraded in a short time of 20 min with 20 mg S-NPC and 10 mg PMS at 25 °C, attributing that N, S co-doping provided more defects (ID/IG = 0.998) to produce more active sites for PMS activation. Based on the results from radical identification, scavenging tests, density functional theory (DFT) and electrochemical analysis, non-radical pathway based on singlet oxygen (1O2) and electron transfer was proposed to be the dominant way in the S-NPC/PMS system and the contribution rate was about 95.872 %. Three possible pathways of TC degradation were proposed by high resolution liquid chromatography-mass spectrometry (LC-MS) and the toxicity of intermediate products was lower than TC. This study provided a novel strategy to degrade pollutants by preparing efficient co-doping metal-free Fenton-like catalyst.