Zinc cadmium sulphide-based photoreforming of biomass-based monosaccharides to lactic acid and efficient hydrogen production.

Abstract

Approaches that add value to biomass through the use of photoreforming reactions offer great opportunities for the efficient use of renewable resources. Here, we constructed a novel zinc cadmium sulphide/molybdenum dioxide-molybdenum carbide-carbon (Zn_xCd_1-xS-y/MoO₂-Mo₂C-C) heterojunction which was applied to photoreforming of biomass-based monosaccharides for hydrogen and lactic acid production. Bandgap engineering effectively modulated the redox capacity of Zn_xCd_1-xS-y and exposed more (101) crystalline surfaces, which improved the lactic acid selectivity. The MoO₂-Mo₂C-C (MC) co-catalysts had unique microstructures that increased the light absorption range and the number of active sites of Zn_xCd_1-xS-y. These features effectively promoted the separation and migration of photogenerated carriers, which in turn enhanced the photoreforming activity. The optimised Zn_0.4Cd_0.6S-0/MC composites exhibited superior photocatalytic activity with a hydrogen yield of 12.2 mmol/g/h. Conversion of biomass-based monosaccharides was approximately 100 %, where xylose had the greatest lactic acid selectivity (64.1 %). Active species, including h⁺, ⋅O₂^-, ⋅OH, and ¹O₂, all favoured lactic acid production, where ⋅O₂^- played a major role in the conversion. This study demonstrates that rational design of photocatalysts can achieve the selective conversion of biomass into high value-added chemicals as well as the generation of clean energy.