Nonradical-dominated peroxydisulfate activation by nitrogen-rich hierarchical porous graphite carbon for efficient degradation of tetracycline

A nitrogen(N)-rich hierarchical porous graphite carbon (NHC) was synthesized at different hydrothermal carbonization temperature (400, 600 and 800 °C) using a template-free and solvent-free method. The as-prepared materials possessed perfect bifunctional performance for tetracycline (TC) removal via synergistic adsorption and catalytic activation of peroxydisulfate (PDS). The carbonization temperature had a significant effect in the material structure and property adjustment. The carbonaceous material prepared at 800 °C (NHC-800) showed optimal adsorption and catalytic activation of PDS efficiency with 451.62 mg/g maximum TC adsorption capacity and 69.5% TC mineralization rate within 180 min. The pseudo-first-order rate constant for NHC-800 (0.0406 min−1) was 111.54-folders higher than NHC-400 (3.6400 × 10−4 min−1). Moreover, the NHC-800/PDS system had a good anti-interference ability to pH, inorganic anions and humic acid. The investigation of catalytic mechanism revealed that the nonradical process governed PDS activation process with defective edges, CO, graphitic N and pyridinic N as the active redox sites, while the large surface area of NHC-800 or the activated C(+) supported the adsorption of pollutants or PDS, further facilitated the electron-transfer process. Finally, the possible degradation pathway was proposed and the acute toxicity of degradation intermediates was assessed. This study not only provides a facile route for the synthesis carbonaceous materials, but also gives a detailed insight in N species and other reactive sites of carbonaceous materials in adsorption and catalytic degradation process.