A hierarchical SnS@ZnIn₂S₄ marigold flower-like 2D nano-heterostructure as an efficient photocatalyst for sunlight-driven hydrogen generation

Herein, we report the <i>in situ</i> single-step hydrothermal synthesis of hierarchical 2D SnS@ZnIn₂S₄ nano-heterostructures and the examination of their photocatalytic activity towards hydrogen generation from H₂S and water under sunlight. The photoactive sulfides rationally integrate <i>via</i> strong electrostatic interactions between ZnIn₂S₄ and SnS with two-dimensional ultrathin subunits, <i>i.e.</i> nanopetals. The morphological study of nano-heterostructures revealed that the hierarchical marigold flower-like structure is self-assembled <i>via</i> the nanopetals of ZnIn₂S₄ with few layers of SnS nanopetals. Surprisingly, it also showed that the SnS nanopetals with a thickness of ∼25 nm couple <i>in situ</i> with the nanopetals of ZnIn₂S₄ with a thickness of ∼25 nm to form a marigold flower-like assembly with intimate contact. Considering the unique band gap (2.0-2.4 eV) of this SnS@ZnIn₂S₄, photocatalytic hydrogen generation from water and H₂S was performed under sunlight. SnS@ZnIn₂S₄ exhibits enhanced hydrogen evolution, <i>i.e.</i> 650 μmol h^-1 g^-1 from water and 6429 μmol h^-1 g^-1 from H₂S, which is much higher compared to that of pure ZnIn₂S₄ and SnS. More significantly, the enhancement in hydrogen generation is 1.6-2 times more for H₂S splitting and 6 times more for water splitting. SnS@ZnIn₂S₄ forms type I band alignment, which accelerates charge separation during the surface reaction. Additionally, this has been provoked by the nanostructuring of the materials. Due to the nano-heterostructure with hierarchical morphology, the surface defects increased which ultimately suppresses the recombination of the electron-hole pair. The above-mentioned facts demonstrate a significant improvement in the interface electron transfer kinetics due to such a unique 2D nano-heterostructure semiconductor which is responsible for a higher photocatalytic activity.