Tuning the Crystallinity and Coverage of SiO-ZnInS Core-Shell Nanoparticles for Efficient Hydrogen Generation.

The coverage, thickness, and crystallinity of ZnInS (ZIS) shells on SiO core nanoparticles (SiO@ZIS) were systematically investigated using microwave-assisted solvothermal methods aided by the addition of acid in ethanolic medium. The surface modification of the SiO cores with (3-mercaptopropyl)trimethoxysilane was found to be critical to generate a homogeneous coverage of ZnInS. The SiO@ZIS core-shell nanoparticles exhibited the best coverage but poor crystallinity when synthesized in pure ethanol, whereas best crystallinity but poor coverage was observed when synthesized in an aqueous solution. The addition of selected amounts of acid (HCl) led to improved crystallinity in the ethanolic medium. The thickness of the ZIS shell could be controlled in an ethanolic solution by judiciously varying the amounts of acid and the concentration of the ZIS precursor. Increasing the concentration of the ZIS precursor to twice the standard concentration in ethanolic solution with the addition of 100 μL of HCl afforded better crystallinity, homogeneous coverage, and optimal photocatalytic hydrogen production.