Acid-free solvothermal synthesis of BiVO4–C hybrid photocatalysts from orange peel extract for enhanced visible-light dye degradation

Acid-free solvothermal BiVO 4 –C hybrid photocatalysts were synthesized using orange peel extract as a natural complexing, templating, and carbon-donating agent. This green route avoids corrosive mineral acids and yields an oxide-based hybrid in which biomass-derived carbonaceous species remain partially integrated at the BiVO 4 surface, forming a functional organic–inorganic interface. Post-synthesis annealing (350–550 °C) enables precise tuning of crystallinity, porosity, and the amount of residual organic matter. The material annealed at 350 °C exhibits the highest photocatalytic activity, achieving near-complete degradation of methylene blue (MB) within 75 min at an optimized catalyst loading, together with highly efficient removal of malachite green (MG) under visible-light LED irradiation. This performance arises from a synergistic combination of the preserved carbon-rich layer, which enhances dye adsorption and interfacial charge transfer, and the improved crystallinity of the BiVO 4 phase, which promotes efficient charge separation, as evidenced by strong photoluminescence quenching. Mott–Schottky analysis reveals n-type behavior with a flat-band potential of −0.71 V vs Ag|AgCl and a donor density of 1.49 × 10 18 cm -3 , confirming favorable charge transport. Band alignment and scavenger experiments identify photogenerated holes as the dominant oxidative species. The optimized photocatalyst also shows excellent stability over five consecutive cycles. This study demonstrates a facile and sustainable strategy to engineer biomass-assisted BiVO 4 –C hybrid photocatalysts with coupled adsorptive and photochemical functionalities for water remediation applications.