Hydrothermal carbonization carbon derived from crop straw for efficient photocatalytic elimination of antibiotics: Promotion role of native trace metals on photocatalytic performance

Crop straw containing abundant carbohydrates and metals is regarded as an ideal precursor for preparing hydrothermal carbonization carbon (HTCC)-based photocatalysts, but the inherent role of native metals on the photocatalytic performance of HTCC remains unclear. Herein, HTCC derived from corn straw (HTCS) catalyzed by native trace metals was prepared by a green hydrothermal process for photocatalytic removal of antibiotics. Sulfamethoxazole (SMX) degradation kinetic constant (k) over HTCS was 5.4 times that of g-C3N4. The results showed the native Ca (0.56%), Mn (0.023%) and Fe (0.055%) in corn straw should catalyze the formation of HTCS, and then promote the photocatalytic SMX removal over HTCS. Pure carbohydrate experiments certified that the Mn and Ca additions could modify the structure of HTCC. More surface C--O formation and furan rings polymerization originated by Ca and Mn catalysis in hydrothermal process. Surface C--O provided electrondeficient connection sites for SMX to form HTCS-SMX complex, and then complex was excited under visible light illumination to transfer electrons from SMX's HOMO to CB of HTCS. Ploymerized furan rings promoted electron transfer in the process. This work provides a green conversion way from waste (agriculture residue) to treasure (efficient carbon-based materials) for water purification.