Low-temperature constructing N-doped graphite-like mesoporous structure biochar from furfural residue with urea for removal of chlortetracycline from wastewater and hydrothermal catalytic degradation mechanism

A novel N-doped graphite-like mesoporous structure biochar (NBC) was prepared from furfural residue with urea under mild low temperature, its performance in the removal of chlortetracycline (CTC) from aqueous solution and the hydrothermal catalytic degradation mechanism were investigated. This preparation strategy of the adsorbent demonstrated the properties of urea as a crosslinking agent and reactive reagent in the heat treatment process from room temperature to 300 °C. In addition, the pore structure, species and number of surface active adsorption sites of NBC were verified through SEM/EDS, FTIR, BET, XRD, TG and XPS analyses. The results showed that N atoms could be uniformly distributed on the surface of NBC, up to 17.7%, which was about ten times higher than that of direct pyrolysis of biomass (pristine BC) and NBC with graphite-like mesoporous structure had the abundant surface nitrogenous functional groups, such as pyrrolic-N and graphitic-N species besides the oxygen-containing functional groups. Batch adsorption studies indicated that NBC achieved equilibrium faster for CTC adsorption (200 min) than other reported adsorbents. The maximum adsorption capacity of CTC onto NBC was 44.3 mg/g, and the adsorption efficiency was still 26.7 mg/g after four recycling. The adsorption experimental data fitted well with the pseudo-second-order kinetic model and the Freundlich isotherm model. Besides, its catalytic degradation of CTC with hydrothermal treatment also exhibited a potential catalytic activity, and catalytic degradation pathway was proposed through the identification of intermediates using LC-MS. The furfural residue is industrially relevant to the furfural production process and hence NBC may be a promising new environment-friendly material.