Size-dependent electron injection over sensitized semiconductor heterojunctions for enhanced photocatalytic hydrogen production

Mechanistic understanding of the effect of electron transfer rate across the semiconductor heterojunction interface on its photocatalytic activity remains elusive. Herein, a series of sensitized semiconductor heterojunctions consisting of monodisperse CdS quantum dots (QDs) with controllable sizes range of 2.2–6.5 nm and cadmium tetrakis(4-carboxyphenyl)porphyrin (Cd-TCPP) nanosheets are constructed through partial sulfidation strategy. The in situ resultant CdS/Cd-TCPP composites exhibit size-dependent photocatalytic hydrogen evolution reaction (HER) activity with the highest activity of 3150 μmol·h−1·g−1 obtained at a medium CdS QD size of 4.8 nm. It is demonstrated that the interfacial electron transfer rate and the corresponding photocatalytic HER activity can be regulated by tuning the CdS QD size that determines the conduction band position of CdS relative to Cd-TCPP. This work provides a new strategy that rationally controls the interfacial electron transfer rate for developing highly efficient photocatalysts.