Electron-transfer-dominated non-radical activation of peroxydisulfate for efficient removal of chlorophenol contaminants by one-pot synthesized nitrogen and sulfur codoped mesoporous carbon

Synergistic adsorption and oxidative degradation (via persulfate activation) on metal-free carbonaceous mate-rials are expected to be environmentally friendly and highly efficient approach toward contaminants removal. Herein, nitrogen and sulfur codoped mesoporous carbon (NSDMC) were firstly synthesized via co-carbonization of calcium citrate and thiourea without any templates. NSDMC samples exhibit remarkably enhanced adsorption capacity and oxidative degradation (by activating PDS) for chlorophenols elimination. Increased SBET and introduced N-containing functional groups are beneficial for chlorophenols adsorption, PDS accessibility and successive activation. Doped sulfur species (especially for thiophenic S) can enhance the electron-transport performance of NSDMC, further promoting PDS activation and chlorophenols degradation. It can be ascribed to the synergistic effect of N and S codoping. NSDMC-30 (containing 5.83 at.% nitrogen and 2.15 at.% sulfur, and possessing SBET of 1935.9 m(2) g(-1)) exhibits the optimal adsorption and catalytic oxidation capability for 4-CP removal. Degradation rate constant of NSDMC-30 is 0.125 min(-1), which is 3.0 times and 7.8 times higher than nitrogen-doped MC and pristine MC, respectively. Radicals quenching experiments and EPR tests demon-strate that non-radical pathways play dominant role for PDS activation and chlorophenols degradation. Based on the influences of catalyst loading, initial 4-CP concentration, and PDS dosage on degradation kinetics of 4-CP, the pre-adsorption is unveiled to be the critical step determining oxidation rate of chlorophenols. More importantly, the results of in-situ Raman and electrochemical tests show that the surface-confined and activated PDS complex (carbon-PDS*) and continuous electron transfer from co-adsorbed 4-CP are mainly responsible for the oxidative degradation of chlorophenols. The intermediate products and TOC removal indicate that chlorophenols can be efficiently degraded and mineralized by as-synthesized NSDMC via activating PDS. Besides, the present NSDMC/ PDS system is also applicable for purification of actual polluted water samples. This work provides in-depth knowledge of carbon-driven nonradical process for PDS activation and contaminants remediation.

Automated summary

The nitrogen and sulfur codoped mesoporous carbon (NSDMC) shows significantly enhanced adsorption and oxidative degradation capabilities for chlorophenols, attributed to increased surface area, introduced N-containing functional groups, and enhanced electron-transport performance. Synergistic effect of N and S codoping plays a key role in promoting PDS activation and chlorophenols degradation.