Abstract

Solar energy-driven processes for biomass valorization are priority for the growing industrialized society. To address this challenge, efficient visible light-active photocatalyst for the selective oxidation of biomass-derived platform chemical is highly desirable. Herein, selective oxidation of 5‑hydroxymethylfurfural (HMF) to 2,5- diformylfuran (DFF) is achieved by visible light-driven photocatalysis over titania. Pristine titania is photocatalytically inactive under visible light, an unconventional approach is employed for the visible light (λ =515 nm) sensitization of titania via a formation of a visible light absorbing complex of HMF (substrate) on the titania surface. Surface-complexation of HMF on titania mediate ligand-to-metal charge transfer (LMCT) under visible light, which efficiently catalyzes the oxidation of HMF to DFF. A high DFF selectivity of 87% is achieved with 59% HMF conversion after 4 hours of illumination. Whereas, the apparent quantum yield obtained for DFF production is calculated to be 6.3%. It is proposed that the dissociative interaction of hydroxyl groups of HMF and the titania surface is responsible for the surface-complex formation. When the hydroxyl groups of titania are modified via surface-fluorination or calcination the oxidation of HMF is inhibited under visible light, signifying that hydroxyl groups are decisive for photocatalytic activity.