A mesoporous TiO2/carbon dot heterojunction photocatalyst efficiently cleaves entire types of C–O bonds in lignin under visible light

Abstract

The progress of photocatalytic biomass depolymerization under mild conditions for the production of high-value chemicals has great potential. Previous studies showed that commercial TiO₂ effectively cleaved α-O-4 linkages, but 4-O-5 linkages were much harder to break due to higher bond energy. Here, we successfully synthesized mesoporous TiO₂ with a high specific surface area, while oxygen vacancies enhanced its visible light absorption and regulated the position of the energy band. Additionally, the Z-scheme heterojunction Pt@CDs-2/TiO₂-MP was successfully prepared by introducing carbon dots, thereby effectively promoting the separation and transfer of photogenerated hole–electron pairs. Pt@CDs-2/TiO₂-MP was employed for the cleavage of 4-O-5 type lignin model diphenyl ether (DPE), with DPE being almost completely converted under 365 nm LED irradiation and achieving a 90.0% conversion rate under visible light. Besides, Pt@CDs-2/TiO₂-MP effectively cleaved α-O-4 (benzyl phenyl ether, 77.8%) and β-O-4 (phenethoxybenzene, 99.6%) models. Even for the C–C bond with a high dissociation energy (biphenyl, 99.0%), it exhibited significant bond cleavage capability, achieving a cyclohexane yield of 10.0%. Furthermore, this photocatalytic method successfully converted different types of lignin into high-value aromatic monomers. This study presents a sustainable and efficient method for the conversion of lignin, thereby contributing significantly to the achievement of sustainable development goals.