Interfacial and physico-chemical properties of polymer-supported CdSZnS nanocomposites and their role in the visible-light mediated photocatalytic splitting of water.

Nano-composite CdSZnS moieties coated over polyester strip were found to exhibit better visible-light-mediated photo-activity for splitting of water, as compared to corresponding pure CdS or ZnS containing coupons. This increase in activity depended upon the mol ratio of the two component sulphides in a particular sample. HRTEM experiments revealed the presence of 1-3 nm size CdS particles embedded over larger size ZnS clusters, the composite samples thus functioning as a highly dispersed guest-host system. In the case of CdS and ZnS dispersed individually over polyester, average crystallite size was found to be around 5 and 15 nm, respectively. A blue shift was observed in the UV-vis absorption spectrum of CdS on addition of ZnS, in conformation with the quantum size effects. Powder XRD, electron diffraction and XPS studies showed that the nanocomposites were comprised of the face-centered cubic (alpha) phases of both CdS and ZnS in a close contact with each other. At the same time, certain solid solution phases, i.e. Cd(1-x)Zn(x)S, were generated at the interfaces of these two semiconductors. Our study demonstrates that the increase in the number of reaction sites due to smaller size of CdS particles and the micro-structural properties associated with the nanostructured CdS or CdS/ZnS interfaces may together play a vital role in the augmented catalytic activity of CdSZnS composite photocatalysts.