Visible-Light-Driven Selective Oxidation of Biomass-Derived HMF to DFF Coupled with H 2 Generation by Noble Metal-Free Zn 0.5 Cd 0.5 S/MnO 2 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 (H 2 ) and value-added chemicals. Consequently, herein we report the development of the Z-scheme photocatalytic system, Zn 0.5 Cd 0.5 S/ x MnO 2, which has the optimum band structure suitable for efficient visible-light-assisted photocatalytic H 2 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 Zn 0.5 Cd 0.5 S microspheres composed of smaller nanocrystals with the surface covered by the MnO 2 nanostructure and the intimate contact between Zn 0.5 Cd 0.5 S and MnO 2 . Photocatalytic investigations revealed the highest activity for Zn 0.5 Cd 0.5 S/1%MnO 2, affording a DFF yield of 46% and a simultaneous H 2 generation rate of 1322 μmol g –1 in 24 h, which are, respectively, 9 and 4 times higher than those of parent sample, Zn 0.5 Cd 0.5 S. Further, the best heterostructure exhibits good catalytic activity even under natural sunlight irradiation, affording DFF with a 14% yield and H 2 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 Zn 0.5 Cd 0.5 S and MnO 2 . Overall, this work represents a unique demonstration of noble metal-free selective oxidation of HMF to DFF integrated with H 2 production under mild reaction conditions.