Metal Nanoshells for Plasmonically Enhanced Solar to Fuel Photocatalytic Conversion

Abstract : In this study, first, we prepared ternary component semiconductor powders of ZnmIn2S3+m (ZIS) by using microwave-assisted hydrothermal method. Microwaveassisted hydrothermal process is a facile way to produce nanomaterials at a shorter reaction time with less secondary impurities while changing the amount of zinc in a series of solid solutions. With little adjustment of the ratios of [Zn]/[In], the hydrogen production rate of the photocatalysts, particle sizes, and band gap are significantly different. In the following experiments, the core-shell of nanoshell@SiO2, as well as the nanostructure of photocatalyst, were further investigated. Solar energy in the visible-light range is expected to be absorbed by the photocatalyst first without any interference from the metal nanoshells. The presence of metal nanoshells as the core can absorb the solar energy in the IR and visible-light region ranging from 500 nm to 900 nm. Our data showed that the plasmonic-enhanced photocatalytic activity was a function of the absorption of Au nanoshells. At the absorption wavelength of 500 nm of the Au nanoshells, the enhancement of hydrogen production was probably due to the plasmonic effect. As opposed to the absorption wavelength at 900 nm, the enhancement was due to thermal effect. Furthermore, the nanoshell absorbing at 700 nm has the highest hydrogen production rate which may be due to both the plasmonic and thermal effect. Thickness of the silica layer also influenced hydrogen evolution. Steady-state photoluminescence measurement was used to investigate the electron-hole recombination mechanism. Results demonstrated that efficient electron-hole charge separation can be achieved when Au nanoshells were incorporated. Finally, the core-shell with various [Zn]/[In] compositions was used to identify the interaction between the Au nanoshell and the photocatalyst.