Unique hierarchical SiO₂@ZnIn₂S₄ marigold flower like nanoheterostructure for solar hydrogen production

The novel marigold flower like SiO₂@ZnIn₂S₄ nano-heterostructure was fabricated using an in situ hydrothermal method. The nanoheterostructure exhibits hexagonal structure with marigold flower like morphology. The porous marigold flower assembly was constructed using ultrathin nanosheets. Interestingly, the thickness of the nanopetal was observed to be 5-10 nm and tiny SiO₂ nanoparticles (5-7 nm) are decorated on the surface of the nanopetals. As the concentration of SiO₂ increases the deposition of SiO₂ nanoparticles on ZnIn₂S₄ nanopetals increases in the form of clusters. The optical study revealed that the band gap lies in the visible range of the solar spectrum. Using X-ray photoelectron spectroscopy (XPS), the chemical structure and valence states of the as-synthesized SiO₂@ZnIn₂S₄ nano-heterostructure were confirmed. The photocatalytic activities of the hierarchical SiO₂@ZnIn₂S₄ nano-heterostructure for hydrogen evolution from H₂S under natural sunlight have been investigated with regard to the band structure in the visible region. The 0.75% SiO₂@ZnIn₂S₄ showed a higher photocatalytic activity (6730 μmol^-1 h^-1 g^-1) for hydrogen production which is almost double that of pristine ZnIn₂S₄. Similarly, the hydrogen production from water splitting was observed to be 730 μmol^-1 h^-1 g^-1. The enhanced photocatalytic activity is attributed to the inhibition of charge carrier separation owing to the hierarchical morphology, heterojunction and crystallinity of the SiO₂@ZnIn₂S₄.