Roles of intrinsic defects on nitrogen, sulfur-codoped biochar in peroxymonosulfate activation toward organic contaminates degradation

The utilization of nitrogen and sulfur-codoped biochar-activated peroxymonosulfate (PMS) has emerged as a promising advanced oxidation technology for the degradation of organic pollutants. However, the dominant active sites, especially the specific defect structures governing PMS activation and their subsequent activation mechanism remain ambiguous, posing challenges to the rational design of high-performance biochar catalysts. Herein, a series of nitrogen and sulfur-codoped biochar (NSBC) with varying pyrolysis temperatures and doping levels were synthesized. An investigation into the relationship between their properties and the reaction rate constants of 2,4-dichlorophenol (2,4-DCP) degradation by activated PMS revealed that intrinsic defects, thiophene S, and graphitic N were active sites in the oxidation reaction, with intrinsic defects identified as playing a predominant role. Density functional theory (DFT) calculations combined with electrochemical measurements further revealed the crucial role of single-vacancy defective configuration in mediating a direct electron transfer pathway for 2,4-DCP degradation. Moreover, double-vacancy and topological defects facilitated the transfer of electrons to adsorbed PMS, leading to the release of 1 O 2 and subsequent degradation of 2,4-DCP. The distinctive mechanism enabled the NSBC-activated PMS system to exhibit high selectivity and effectively remove 2,4-DCP from a complex aquatic environment. The findings from this study provide valuable insights into the role of specific structural defects in PMS activation and offer theoretical support for the design of biochar catalysts with heteroatom doping strategies.