Biomineralization of Nanocrystalline CdS/ZnS Photocatalysts via Controlled Surface Passivation for Enhanced Hydrogen Evolution

The high-temperature processing and organic solvents used in the synthesis of heterojunction photocatalysts is a challenge for the large-scale manufacturing that will be necessary for impact at the societal scale. While syntheses under more benign conditions have been demonstrated, the resulting material performance is often not competitive. Herein, we demonstrate the controlled, aqueous phase, and ambient temperature biomineralization-based synthesis of nanocrystalline CdS/ZnS core/shell hydrogen evolution photocatalysts using a purified form of the enzyme, cystathionine γ-lyase. Photocatalytic hydrogen evolution measurements show that controlled Zn2+-based passivation of the surface of CdS improves the hydrogen evolution activity from 1300 μmol h–1 g–1 to 3200 μmol h–1 g–1 in the presence of a Na2S/Na2SO3 sacrificial reagent, which is on par with reported hydrogen evolution rates of CdS/ZnS core/shell photocatalysts synthesized through traditional chemical routes. The steady-state photoluminescence (PL) intensity and PL lifetime measurements coupled with energy-dispersive X-ray spectroscopy indicate that Zn2+ passivates the surface of biomineralized CdS nanocrystals, with the extent of passivation controlled by the concentration of the zinc precursor added directly to the synthesis solution. Photodeposition of a platinum cocatalyst onto the highest-performing CdS/ZnS photocatalyst further boosts the hydrogen evolution rate to 7200 μmol h–1 g–1 in the presence of a Na2S/Na2SO3 sacrificial reagent, establishing biomineralization as an effective platform for the controlled synthesis of high-performing heterojunction hydrogen evolution photocatalysts.