Band gap narrowing of SnS2 superstructures with improved hydrogen production†
Transition metal sulfides exhibit chemical and physical properties that are of much scientific and technological interest and can largely be attributed to their covalent bonding of 3d electrons. Hierarchical structures of these materials are suited for a broad range of applications in energy storage, as biological scaffold, and as sensors. In this work, hierarchical SnS2 structures have been synthesized and show excellent photocatalytic performance for the production of H2 under blue light (450 nm) irradiation. A combination of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy indicates the formation of layered SnS2/SnS superstructures with a lattice mismatch between the two alternating layers. This indicates the presence of S vacancies and results in a drastic decrease of the band gap by 0.3 eV compared to bulk SnS2. This strategy of self-narrowing of the band-gap demonstrates its great potential for the design of new materials with visible light reactivity. Finally, we have extended this strategy to the synthesis of other transition metal sulfides (Ni3S4, CuS, CuS@C, and FeS2) with similar hierarchical structures, which have potential applications such as supercapacitors and electrode materials for sodium/lithium ion batteries.