Fabrication of Hierarchical Two-Dimensional MoS₂ Nanoflowers Decorated upon Cubic CaIn₂S₄ Microflowers: Facile Approach To Construct Novel Metal-Free p–n Heterojunction Semiconductors with Superior Charge Separation Efficiency

Abstract

Due to the enormous demand for effective conversion of solar energy and large-scale hydrogen production, cost-effective and long-lasting photocatalysts are believed to be necessary for global production of sustainable and clean hydrogen fuel. Robust and highly efficient p–n heterojunction photocatalysts have a striking ability to enhance light-harvesting capacity and retard the recombination of photoexcitons. A series of p-MoS2/n-CaIn2S4 heterojunction composites with different MoS2 contents have been synthesized via a facile two-step hydrothermal technique in which rose-like p-MoS2 nanoflowers are decorated upon n-type cubic CIS microflowers. In the synthesis protocol highly dispersed MoS2 nanoflowers provided more active edge sites for the growth of c-CIS nuclei, leading to a hierarchical architecture with intimate interfacial contact. The formation of a hierarchical flower-like morphology of the photocatalyst has been established by an HRTEM and FESEM study. Electrochemical characterization, especially the slope of the curve from Mott–Schottky analysis and nature of the current from LSV, reveals the p–n heterojunction nature of the composite photocatalyst. The fabricated heterojunction photocatalysts were further examined for visible light photocatalytic H2 evolution. Far exceeding those for the neat c-CIS and MoS2, it is seen that the p-MoS2/n-CIS heterojunction photocatalyst with an optimum content of MoS2 exhibited enhanced H2 evolution using a 0.025 M Na2S/Na2SO3 solution as hole quenching agent under visible light illumination. The 0.5 wt % p-MoS2/n-CIS photocatalyst presents a higher H2 production rate of 602.35 μmol h–1 with 0.743 mA cm–2 photocurrent density, 19 times and 8 times higher than those of neat c-CIS, respectively. This superior photocatalyic activity is due to the efficient separation of electron–hole charge carriers at the interface, as supported by a photoluminescence study and EIS measurements.