Dual-functional Z-scheme photocatalysis: Synergistic hydrogen generation and biomass-derived 5-hydroxymethylfurfural valorization over g–C3N4–nitrogen-doped TiO2 heterostructures

The concurrent production of renewable hydrogen and valorization of biomass represents a promising strategy to tackle energy sustainability and environmental concerns. However, designing efficient bifunctional photocatalytic systems capable of driving both reactions remains a significant challenge. This study introduces a Z-scheme heterojunction composed of graphitic carbon nitride (g-C 3 N 4 ) and titanium dioxide (TiO 2 ), synthesized through a combined hydrothermal and self-assembly approach, for simultaneous photocatalytic H 2 evolution and selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF). The heterostructure establishes an internal electric field that directs photogenerated electrons to g-C 3 N 4 and holes to TiO 2 , thereby facilitating effective charge-carrier separation while preserving their strong redox potentials . Structural analyses confirm the uniform growth of TiO 2 nanorods with reduced diameter of less than 10 nm on g-C 3 N 4 nanosheets, which enhances light harvesting and exposes abundant reactive sites. Under optimized conditions, the composite exhibited exceptional performance, achieving H 2 and DFF production rates of 481.9 μmol g −1  h −1 , respectively, with 92.8 % DFF selectivity. This represents a 3.8-fold enhancement in activity compared to pristine g-C 3 N 4 . The improved efficiency is attributed to the Z-scheme charge-transfer pathway, which mitigates recombination losses and optimizes the utilization of electrons and holes for respective reduction and oxidation reactions. This work provides a scalable framework for integrating green hydrogen generation with biomass refining, advancing the development of multifunctional photocatalysts for sustainable energy and chemical synthesis.