A Bifunctional Nitrogen-Doped Hierarchical Porous Graphite Carbon for Adsorption and Catalytic Removal of Tetracycline Antibiotics : Performance and Nonradical Mechanism

A nitrogen(N)-doped 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 antibiotics tetracycline (TC) removal via synergistic adsorption and catalytic degradation process. 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 oxidation efficiency for TC removal with 451.62 mg/g maximum adsorption capacity and 69.5% mineralization rate within 180 min. The 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/peroxydisulfate (PDS) system showed a good anti-interference ability to pH, inorganic anions and humic acid. The investigation of catalytic mechanisms revealed that the nonradical process governed PDS activation process using defective edges, C=O, 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 the degradation intermediates was assessed. This study not only provides a facile rote 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