Accelerated depolymerization of rice straw-derived lignin to vanillin and guaiacol using γ-Fe2O3/N, Fe-TiO2 as novel photocatalyst under visible light in aqueous media

Vanillin and guaiacol, essential value-added chemicals widely utilized in the cosmetic and healthcare industries, have been sustainably derived from rice straw-derived lignin using a novel γ- Fe₂O₃/N, Fe-TiO₂ photocatalyst under visible light irradiation. A green approach employing a deep eutectic solvent (DES) was used to induce a bandgap shift, facilitating the activation of the photocatalyst in the visible range. The structural, physicochemical, and optical properties of the synthesized photocatalyst were well-analyzed using various analytical techniques. The optimal conditions for achieving maximum lignin depolymerization of 97.1% and a high yield of vanillin and guaiacol were determined to be an initial lignin concentration of 50 mg/L, a catalyst loading of 0.7 g/L, the addition of 1 mL/L H₂O₂, and a pH of 5, with a reaction duration of 4h. The enhanced photocatalytic activity of γ- Fe₂O₃/N, Fe-TiO₂, was attributed to its modified bandgap, enabling visible-light absorption and the generation of reactive oxygen species, as confirmed by scavenging studies. This study provides a significant contribution to the sustainable valorization of lignin from agricultural waste biomass, demonstrating the potential for the scalable production of vanillin and guaiacol under visible-light-driven photocatalysis.