Preparation of biochar-doped nitrogen-rich carbon nitride composites and their photocatalytic performance in organic pollutant degradation

To mitigate environmental contamination from tetracycline antibiotics and volatile formaldehyde, a series of biochar-doped nitrogen-rich carbon nitride (C3N5/BC) composites were synthesized via an in-situ growth method. Phase composition, surface area, pore structure, visible-light response, and photogenerated carrier recombination behavior were systematically characterized. Photocatalytic degradation of tetracycline hydrochloride (TCH) and formaldehyde under simulated sunlight was evaluated. The results show that biochar (BC) doping functions as an electron acceptor, enhancing surface electron density of C3N5, extending π–π* conjugation, increasing surface area, and promoting effective separation of photogenerated charge carriers. The composite containing 3.0% BC exhibits optimal photocatalytic activity, achieving degradation efficiencies of 99.22% for TCH and 97.75% for formaldehyde. The C3N5/BC composite also demonstrates excellent stability and broad substrate applicability. Coexisting inorganic anions such as CO32−, HCO3−, SO42−, and NO3− and complex aqueous matrices significantly suppress photocatalytic performance. Radical trapping experiments identify superoxide radicals (·O2−) as the dominant reactive species, and a corresponding photocatalytic mechanism is proposed.