Title : Tuning core–shell-like structural evolution of Cu–ZnS photocatalysts for selective conversion of biomass-derived carbon to hydrogen and lactic acid
Abstract:
Photocatalytic reforming of biomass-derived organics offers a promising pathway to simultaneously produce H? and valorise waste-derived carbon resources. While H? is an important clean-energy carrier, the oxidation half-reaction can generate value-added organic products that may have a higher economic value on a mass basis and substantially improve the overall viability of the process. Lactic acid is particularly attractive because of its broad applications in food, pharmaceutical, chemical, and biodegradable polymer production. However, oxidation products are often treated as secondary by-products, and the composition- and structure-dependent trade-off between H? evolution and selective liquid-product formation remains insufficiently understood. In this context, ZnS-based photocatalysts offer an attractive platform due to their relatively simple synthesis and lower reliance on costly noble metals or toxic Cd-based sulfides. Cu incorporation is particularly appealing as a low-cost approach to tune light absorption, charge behaviour, and surface reaction pathways, yet its role in switching product selectivity remains unclear.
Cu–ZnS photocatalysts were evaluated for glucose photoreforming under neutral aqueous conditions. Cu loading strongly influenced the balance between H? evolution and liquid-product formation. Low Cu loading promoted higher H? production, whereas higher Cu loading shifted the reaction toward lactic acid formation. Structural and electronic characterization suggest that Cu loading influences the spatial distribution of CuS and Cu-doped phases, resulting in a core–shell-like of segregated CuS-rich/ZnS-rich structure. These results indicate that Cu does not simply act as an activity promoter, but can alter the photocatalytic reaction pathway through changes in its chemical environment and nanoscale distribution. The enhanced lactic acid formation over Cu-rich samples is proposed to arise from CuS-associated changes in charge-transfer behaviour and surface acid–base properties. These findings highlight the importance of controlling both the Cu chemical environment and nanoscale phase distribution to direct photocatalytic biomass-conversion pathways.
