Efficient charge transfer in rheum ribes waste-derived biochar-supported Bi₂MoO₆ nanocomposites for visible-light-driven photocatalytic degradation of antibiotics

The sustainable removal of emerging pharmaceutical pollutants from aqueous systems has become a critical environmental challenge, demanding the development of efficient and reusable photocatalysts. Herein, a novel Rheum ribes waste-derived biochar supported Bi₂MoO₆ (Bi₂MoO₆/BC) nanocomposite was synthesized and systematically evaluated for visible-light-driven tetracycline (TC) degradation. Structural and morphological analyses (XRD, FTIR, SEM, TEM, and EDX mapping) confirmed the successful anchoring of ultrathin Bi₂MoO₆ nanosheets onto a porous conductive biochar matrix, providing abundant surface-active sites. Optical and electrochemical characterizations (UV–Vis DRS, PL, EIS, and photocurrent) demonstrated enhanced visible-light absorption, narrowed band gap, quenched photoluminescence, lower charge-transfer resistance, and higher photocurrent density, all indicative of efficient charge separation. RSM optimization using Design-Expert revealed catalyst dosage, initial concentration, and solution pH as decisive parameters, with optimal conditions (1 g L⁻¹, 20 ppm, pH = 6) yielding degradation efficiencies above 95 %. Radical trapping experiments confirmed •O₂⁻ as the dominant species, with •OH and h⁺ also contributing, and the synergistic mechanism featuring rapid electron transfer to biochar and the subsequent production of reactive radicals ultimately enabled the complete degradation of TC into CO₂ and H₂O.