Synthesis of N-doped sludge biochar using the hydrothermal route-enabled carbonization method for the efficient degradation of organic pollutants by peroxymonosulfate activation

Nitrogen-doped biochar (HTNBC) was prepared from sewage sludge via hydrothermal route-enabled carbonization, and the optimized HTNBC was found to efficiently activate peroxymonosulfate (PMS) by aiming the less consumption of the chemicals. The optimal HTNBC degraded a 0.1 mM aqueous solution of bisphenol A (BPA) within 10 min at a rate of 0.62 min−1, exhibiting a significantly superior catalytic activity compared to that of pristine sludge biochar. The HTNBC/PMS system effectively oxidized various organic pollutants, including BPA, sulfamethoxazole, 4-chlorophenol, carbamazepine, and nitrobenzene with a low consumption of PMS (1.0 mM) and a low catalyst loading (0.2 g/L). The active sites for PMS activation were identified as graphitic-N, pyridinic-N, and carbonyl groups, besides structural defects and a high specific surface area were also important. The primary oxidation mechanism was anticipated to involve non-radical pathways followed by radical-induced oxidation, in which the surface-bound reactions dominate. The HTNBC/PMS system acts over a wide pH range and exhibits a high resistance to the inorganic anions of natural water. Our results indicate that nitrogen doping via a hydrothermal route allows the fabrication of biochar with a greater abundance of oxygen functional groups, and the specific nitrogen species present within the carbon matrix are also of importance in the development of advanced carbon catalysts.