In-situ preparation of CuO/Cu₂O/Cu/N-codoped biochar from chitosan derivative: Adsorption property and photo-Fenton catalytic performance in removal of antibiotic

Nanosheets of chitosan-Schiff base copper complex (CS-Schiff-Cu) were synthesized by coordination of Cu²⁺ with chitosan-salicylaldehyde Schiff base. Then, nanoparticles of copper-nitrogen codoped biochar (Cu–N-C-700) were prepared by pyrolysis of CS-Schiff-Cu nanosheets in N₂ atmosphere at 700 °C. Morphological and structural characterizations indicated that, in Cu–N-C-700 the nanostructured CuO, Cu₂O, and Cu active sites were successfully implanted in-situ in the biochar matrix, and the N element was doped into carbon as pyrrolic and pyridinic structures. BET measurement revealed that Cu–N-C-700 possesses mesoporous structure with average pore diameter of 21 nm. The adsorption of tetracycline antibiotic on Cu–N-C-700 in aqueous solution was calculated to follow the Freundlich isotherm model and the pseudo-first-order kinetic model. The Cu–N-C-700/H₂O₂ system exhibited good catalytic performance in degradation of tetracycline with a degradation efficiency of 98.5% after irradiating for 15 min. The influence of H₂O₂ dosage and initial pH value on the degradation of tetracycline was discussed in detail. The possible degradation pathway of tetracycline was also investigated. The Cu–N-C-700 nanocomposite remained stable in five consecutive cycles, suggesting good reusability. Finally, a reasonable adsorption-photo-Fenton synergy mechanism was proposed based on the CuO/Cu₂O/Cu multi-active centers and the good adsorption and conductive performance of biochar.