ZnS-CuS-Cu₂S nanocomposite heterostructures with improved charge separation for efficient mixed dye photodegradation

In this study, ZnS, CuS, and ZnS-CuS-Cu₂S nanocomposites are synthesized by the chemical co-precipitation method and evaluated for their photocatalytic efficiency in degrading acid yellow (AY), bromophenol blue (BPB), and mixed dye solutions under visible-light irradiation. The structural phase, morphology, particle size, and functional groups are characterised using important techniques such as XRD, FE-SEM, HR-TEM, XPS, FT-IR, and UV spectroscopy analysis. Structural and morphological analyses confirmed the formation of nanocrystalline phases of cubic ZnS, hexagonal CuS, and a well-integrated ZnS-CuS-Cu₂S heterostructure exhibiting strong interfacial contact. The highly crystalline nanocomposites have a typical size of ∼12 nm, and the ZnS-CuS-Cu₂S nanocomposite showed enhanced charge separation and reduced electron-hole recombination due to heterojunction formation between the ZnS and CuS domains. Photocatalytic experiments demonstrated that ZnS-CuS-Cu₂S achieved 91.84% degradation of AY and 97.49% degradation of BPB within 120 minutes, outperforming pure ZnS (71.07% and 82.96%, respectively) and CuS (67.53% and 74.1%, respectively). Furthermore, the catalyst effectively degraded mixed dye solutions (AY-BPB) with efficiencies of 97% and 90% for AY and BPB, respectively. The degradation of the organic dye pollutant containing an N[double bond, length as m-dash]N double bond over the ZnS-CuS-Cu₂S nanocomposites proceeds through a dual mechanism: reduction via electron transfer and oxidation through the generation of superoxide(˙O₂ ^-) radicals, which effectively break the conjugation bond. Furthermore, the ZnS-CuS-Cu₂S nanocomposite displays excellent chemical stability and maintains its photocatalytic efficiency over multiple reuse cycles.