Visible-Light-Driven Selective Oxidation of Biomass-Derived HMF to DFF Coupled with H2 Generation by Noble Metal-Free Zn0.5Cd0.5S/MnO2 Heterostructures

The development of efficient photocatalysts for utilization of solar energy for water splitting coupled with oxidation of biomass-derivatives is of utmost importance for the simultaneous production of clean fuel (H2) and value-added chemicals. Consequently, herein we report the development of the Z-scheme photocatalytic system, Zn0.5Cd0.5S/xMnO2, which has the optimum band structure suitable for efficient visible-light-assisted photocatalytic H2 generation integrated with selective oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to a more value-added product, 2,5-diformylfuran (DFF). The electron microscopy analyses of the samples revealed the presence of Zn0.5Cd0.5S microspheres composed of smaller nanocrystals with the surface covered by the MnO2 nanostructure and the intimate contact between Zn0.5Cd0.5S and MnO2. Photocatalytic investigations revealed the highest activity for Zn0.5Cd0.5S/1%MnO2, affording a DFF yield of 46% and a simultaneous H2 generation rate of 1322 μmol g–1 in 24 h, which are, respectively, 9 and 4 times higher than those of parent sample, Zn0.5Cd0.5S. Further, the best heterostructure exhibits good catalytic activity even under natural sunlight irradiation, affording DFF with a 14% yield and H2 generation rate of 152.6 μmol g–1 in 6 h. The high catalytic activity of the heterostructure over the parent materials has been attributed to efficient separation of photogenerated charge-carriers with the aid of the Z-scheme mechanism and the synergistic catalysis between Zn0.5Cd0.5S and MnO2. Overall, this work represents a unique demonstration of noble metal-free selective oxidation of HMF to DFF integrated with H2 production under mild reaction conditions.