Preparation of high-yield N-doped biochar from nitrogen-containing phosphate and its effective adsorption for toluene

Novel biochar was prepared from plant-based biomass by the addition of nitrogen-containing phosphates (NCPs), including ammonia phosphate (AP), ammonia polyphosphate (APP) and urea phosphate (UP). The results demonstrated that with the addition of NCPs, the yield of biochar could be significantly increased from about 30% to up to about 60%. The pore structure of the biochar was significantly improved, and the AP-prepared biochar obtained a higher S _BET and V _tot of 798 m² g^-1 and 0.464 cm³ g^-1, respectively. Moreover, the surface chemistry of the NCP-prepared biochar was affected, and N heteroatoms could be successfully doped on the surface of biochar, up to 4.16%. Furthermore, through TG-FTIR and XPS analysis, some possible interactions between plant-based biomass and NCPs during the pyrolysis process were proposed to explore the mechanisms of the preparation process, including the P route and N route, in which the H₃PO₄ and NH₃ gradually generated during the heating process played the dominant roles for the high yield N-doped biochar. All the NCP-prepared biochar presented good toluene adsorption capacities from 175.9 to 496.2 mg g^-1, which were significantly higher than that of blank char (6.5 mg g^-1).