Synergistic enhancement of biochar in TiO2/g-C3N4 Z-scheme heterojunction photocatalysts: mechanistic insights into the degradation pathways of sulfonamide antibiotics

Abstract This study successfully synthesized a BC/TiO 2 /g-C 3 N 4 composite photocatalyst using the sol–gel method, conducted an in-depth analysis of the influence mechanism of BC on charge transfer performance in heterojunction materials, and revealed its key role in regulating the charge transport process. The introduction of biochar significantly increased the specific surface area of BC/TiO 2 /g-C 3 N 4 compared to the TiO 2 /g-C 3 N 4 catalyst, broadening the visible light absorption range. Under simulated sunlight irradiation with a wavelength greater than 420 nm, the three-component material MBC-500, calcined at 500 °C, exhibits the best catalytic performance, with an adsorption photocatalytic degradation rate of 98.13% for sulfadiazine (SDZ) within 60 min, which is 3.46, 3.40, and 2.36 times that of TiO 2 , g-C 3 N 4 , and TiO 2 /g-C 3 N 4 , respectively. Characterization analysis and density functional theory (DFT) calculations revealed the energy band structure and electron transfer pathways of the composite photocatalyst, indicating the significant role of biochar in electron transfer and storage. Additionally, the calculated adsorption energies demonstrated the good adsorption performance of MBC-500 for O 2 and sulfadiazine. This composite photocatalyst exhibited good stability and reusability even after five cycles of use. During the degradation process of SDZ, ·O 2 − , h + , ·OH play a major role. Graphical Abstract