Photocatalytic Oxidation of 5‑Hydroxymethylfurfuralto Selective Products by Noble Metal-Free Z‑Scheme Heterostructuresα‑Fe₂O₃/Zn_0.5Cd_0.5S

It is a promising endeavor to explore the photocatalytic oxidation for 5-hydroxymethylfurfural (HMF) to produce high-value-added derivatives. The absence of efficient photocatalytic systems has hindered the transformation of HMF to 2,5-diformylfuran (DFF), while DFF is susceptible to subsequent oxidation into 2,5-furandicarboxylic acid (FDCA). Herein, we design a Z-scheme heterojunction photocatalyst α-Fe₂O₃/Zn_0.5Cd_0.5S via hydrothermal methods, which exhibits superior activity toward the selective oxidation of HMF to DFF or FDCA in aqueous solution. Photocatalytic investigations demonstrated the highest activity for 15% Fe₂O₃/Zn_0.5Cd_0.5S, resulting in a DFF selectivity of 99% and conversion of 75%, affording FDCA selectivity of 85% and conversion of 99%. The high catalytic activity has been ascribed to the effective separation of photogenerated charge carriers and generation of reactive oxygen species (ROS) in different atmospheres with the Z-scheme mechanism. Research revealed that the oxidation to DFF is associated with ^•OH in an Ar environment, while the generation of FDCA is related to ^•O₂^– in the air. Moreover, selective oxidation may also exhibit significant potential for the utilization of sunlight and other benzene substrates. Overall, this study offers a unique demonstration of designing a noble metal-free Z-scheme heterojunction photocatalyst for the oxidation of HMF to selective products in water.