Photocatalytic Oxidation of 5-Hydroxymethylfurfural to Selective Products by Noble Metal-Free Z-Scheme Heterostructures α-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/Zn0.5Cd0.5S 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/Zn0.5Cd0.5S, 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.