Sunlight-activated heterostructure MoS2/CdS nanocomposite photocatalyst with enhanced photocatalytic activity: band alignment and mechanism study

Abstract

A high recombination rate is a major limiting factor in photocatalysis. Mitigating recombination through material engineering and photocatalyst optimization is key to enhancing photocatalytic performance. In this study, a heterostructure MoS₂/CdS nanocomposite was synthesized through a hydrothermal method in a Teflon-lined autoclave subjected to a temperature of 200 °C for 16 hours. The resulting photocatalysts were characterized using a variety of techniques to understand their structural, surface, and optical properties. The photocatalytic activity of the as-synthesized photocatalysts was investigated by degrading methyl orange dye under both sunlight and visible light irradiation. Regardless of its MoS₂ content, the heterostructure MoS₂/CdS NC exhibited enhanced degradation efficiency relative to that of pure CdS, MoS₂, and commercial TiO₂ P25, with 5 wt% MoS₂/CdS NCs exhibiting the highest degradation performance among all the evaluated photocatalysts. This behavior was justified by improved charge separation and reduced charge recombination, which were attributed to the valence band and conduction band offsets at the MoS₂/CdS interface, as evidenced by band alignment study. The enhanced charge separation and reduced charge recombination were further validated by photoluminescence (PL), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements. Furthermore, an active species trapping experiment confirmed that electron transfer to oxygen and the subsequent formation of superoxide anions (O₂⁻) radical play the most significant roles in photocatalytic degradation under visible light illumination. Finally, the ability to reuse the MoS₂/CdS NCs multiple times without substantial loss of activity evidenced their stability, thus paving the way for advancements in large-scale environmental remediation and other industrial applications.