Synthesis of MnO2/potassium-doped carbon nitride heterojunction with abundant oxygen vacancies and intercalation structure for efficient photocatalytic oxidation of 5-hydroxymethylfurfural

Photocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) represents a promising pathway for the valorization of biomass. However, this process still encounters challenges including low conversion efficiency and limited selectivity. To address these issues, a MnO 2 /potassium-doped carbon nitride (MnO 2 /K-CN) heterojunction photocatalyst, featuring abundant oxygen vacancies and intercalation structure, was synthesized for highly efficient and selective photocatalytic oxidation of HMF to DFF. Characterizations reveal that MnO 2 /K-CN with a large specific surface area facilitates the exposure of active sites and the mass transfer of reactants. Concurrently, the S-scheme heterojunction not only broadened the visible-light absorption range but also increased the density of oxygen vacancies in MnO 2 , effectively promoting the separation of photogenerated electron‒hole pairs. MnO 2 /K-CN induced the selective generation of superoxide radicals (•O 2 − ) and singlet oxygen ( 1 O 2 ) while suppressing the formation of hydroxyl radical (•OH), achieving high selectivity toward DFF. MnO 2 /K-CN achieved a HMF conversion of 98.6% and a DFF yield of 94.4%, while maintaining excellent catalytic stability. Theoretical calculations further reveal that MnO 2 /K-CN significantly reduced the energy barrier for the oxidation reaction of HMF, accelerating the oxidation kinetics. This study provides new insights for developing highly efficient and stable photocatalytic systems to achieve high-value-added utilization of biomass resources.