Facile template free approach for the large-scale solid phase synthesis of nanocrystalline XIn2S4 (X = Cd/Zn) and its photocatalytic performance for H2 evolution

Abstract

In the present study, we have demonstrated a unique approach for the synthesis of nanostructured ternary metal sulphides, XIn₂S₄ (X = Cd, Zn), using a simple, template free and low temperature solid phase reaction. A stoichiometric amount of precursors including CdO/ZnO, In₂O₃ and thiourea were mixed homogeneously and heated at 150 °C for different time intervals to produce nanostructured XIn₂S₄. Various molar ratios of the precursors were tried and among the different ratios, the molar ratio of 1 : 1 : 8 was found to be optimum for the growth of phase pure nano crystalline XIn₂S₄. X-ray analysis confirms the formation of cubic spinel Cadmium Indium Sulfide (CdIn₂S₄) and hexagonal Zinc Indium Sulfide (ZnIn₂S₄). HRTEM analysis confirms the formation of nanostructures of XIn₂S₄ with spherical and rod like mixed morphology. The band gap of the as synthesized materials is within the visible region i.e. 2.25 and 2.6 eV for CdIn₂S₄ and ZnIn₂S₄, respectively. Therefore, the activity of both the photocatalyts was tested for hydrogen generation by H₂S and H₂O splitting under natural solar light. The ZnIn₂S₄ photocatalyst was found to be more active for both H₂S and H₂O splitting reactions with H₂ evolution rates of 6994 μmol h⁻¹ g⁻¹ and 243 μmol g⁻¹, respectively, whereas for CdIn₂S₄ the rates were found to be 6128 μmol h⁻¹ g⁻¹ and 128.4 μmol g⁻¹, respectively. The H₂ evolution rate by H₂S splitting was found to be much higher than various previously reported nanostructured photocatalysts. The simple, environmentally friendly and cost effective method reported herein can be applied for the large scale synthesis of XIn₂S₄ nanoparticles, which is the novelty of the present work.