Chloride-mediated electrocatalytic radical generation on S,N co-doped Ti₃C₂T_x: Synergistic superoxide and singlet...

Heteroatom-doped Ti₃C₂T_x materials with tailored active sites and electron distributions are potential catalysts for the electrocatalytic degradation of pollutants. In this study, a series of S and N doped Ti₃C₂T_x (Px-Ti₃C₂T_x@NS) samples were synthesized to optimize the electrocatalytic degradation of tetracycline hydrochloride (TC). Furthermore, activation mechanisms involving direct oxidation and reactive oxygen species (ROS) and reactive chlorine species (RCS) generation and the contributions of surficial active sites were elucidated. Degradation rate constants for Ti₃C₂T_x, pretreated Ti₃C₂T_x (P-Ti₃C₂T_x), and the S/N co-doped samples P1-Ti₃C₂T_x@NS, P3-Ti₃C₂T_x@NS, and P10-Ti₃C₂T_x@NS were 0.14, 0.12, 0.15, 0.19, and 0.12 min⁻¹, respectively. Compared with Ti₃C₂T_x, P3-Ti₃C₂T_x@NS exhibited the best performance for TC degradation owing to its enhanced RCS generation. Experimental results revealed that HO^• can be generated through H₂O conversion with or without the assistance of Cl^- or RCS. However, the presence of Cl^- and the conversion products of RCS considerably enhanced the generation of O₂^•- and ¹O₂. The exceptional performance of P3-Ti₃C₂T_x@NS in the presence of Cl^- was attributed not only to RCS (especially Cl₂^•-) but also to their secondary products, O₂^•- and ¹O₂. Moreover, theoretical calculations confirmed the transfer of electrons from Ti to Cl, and the electron affinity of Ti atoms was enhanced by co-doping with N and S. These findings provide a beneficial approach for mechanism regulation based on ROS and RCS and insights into electrocatalytic degradation.