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 (NHC800) 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 x 10-4 min-1). Moreover, the NHC800/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, 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 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.

Automated summary

A nitrogen-rich hierarchical porous graphite carbon (NHC) was synthesized with different hydrothermal carbonization temperatures, and the NHC800 exhibited optimal adsorption and catalytic activation of peroxydisulfate (PDS) for tetracycline (TC) removal. The investigation of catalytic mechanism revealed the active redox sites and electron-transfer process. The study also proposed a degradation pathway and assessed the acute toxicity of degradation intermediates.