Efficient Photocatalytic Hydrogen Generation from Ni Nanoparticle Decorated CdS Nanosheets

High-quality, thickness-controlled CdS nanosheets (NSs) have been obtained through the thermal decomposition of cadmium diethyldithiocarbamate in octadecene. Ensembles with discrete thicknesses of 1.50, 1.80, and 2.16 nm have been made with corresponding lateral dimensions on the order of 90 nm × 20 nm. These latter values make the 1–3 nm NSs the largest 2D CdS specimens made to date using colloidal chemistry. Associated Ni nanoparticle decorated counterparts have been made through the photodeposition of Ni onto NSs with an average nanoparticle diameter of 6 nm. Subsequent photocatalytic hydrogen generation measurements have compared the performance of CdS NSs with that of their Ni NP decorated counterparts in water/ethanol mixtures. Apparent quantum yields as large as 25% have been seen for Ni NP decorated NSs with transient yields as large as 64% within the first 2 h of irradiation. Results from ensemble femtosecond transient differential absorption spectroscopy reveal that the origin of this high efficiency stems from efficient electron transfer from CdS to Ni. In this regard, the CdS/Ni semiconductor/metal heterojunction acts to dissociate strongly bound excitons in CdS NSs, creating free carriers needed to carry out relevant reduction chemistries