Regulating the band gap of ZnxCd1−xS in 3DOM CaTiO3 for high hydrogen evolution and gluconic acid selectivity

Abstract

Biomass photoreforming to coproduce sustainable hydrogen and valuable chemicals is a potential strategy for alleviating energy and environmental issues. However, the lack of bifunctional catalysts to efficiently achieve the “one stone kills two birds” scenario greatly limits its practical application. Herein, we have rationally designed a three-dimensionally ordered macro-porous structure (3DOM) CaTiO₃ (CTO) to address the mass diffusion and light harvesting issues and to load Zn_xCd_1−xS (Z_xC_1−xS) quantum dots (QDs), realizing the selective glucose photoreforming process. The regulatable band gap of Z_xC_1−xS endows 3DOM CTO-Z_xC_1−xS composites with sufficient light absorbance and adjustable redox potentials. As a result, the optimized 3DOM CTO-Z_0.5C_0.5S photocatalyst delivers the best performance for sustainable hydrogen evolution from glucose photoreforming with a rate of 4.05 mmol g⁻¹ h⁻¹ and an apparent quantum efficiency (AQY) of 6.48% under monochromatic light of 365 nm. In particular, the well-developed photocatalysts simultaneously produce gluconic acid with selectivity up to 83.8% from the targeted oxidation of the terminal aldehyde group of glucose. The DFT calculations on Gibbs free energy change of the HER and the energy difference between reactants and products of the OER further reveal that the constructed Z-scheme heterojunction contributes to the spatial separation of photogenerated electrons and holes leading to a good quantum efficiency and liquid product selectivity. This work demonstrates a sustainable technology for the coproduction of hydrogen and value-added chemicals from photocatalytic biomass valorization.