Multifunctional CdS Semiconductor Nanocrystals: Enhanced Photocatalytic and Supercapacitor Performance with DFT Insights

Cadmium sulphide (CdS) semiconductor nanocrystals are of interest because of their optical properties and potential in photocatalysis. Here, we examine their structural, optical, photocatalytic, electrochemical, antimicrobial, and theoretical characteristics for possible environmental and energy-related applications. CdS nanocrystals were prepared by aqueous co-precipitation. X-ray diffraction (XRD) confirmed the formation of hexagonal wurtzite CdS, while FESEM, HRTEM, and EDAX were used to examine morphology, crystallinity, and elemental composition. UV–visible spectroscopy and Tauc analysis gave an optical band gap of 2.15 eV. Under visible-light irradiation, the material degraded 89.93% of methylene blue within 120 min. Antibacterial activity was also observed against the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Pseudomonas aeruginosa. Cyclic voltammetry yielded a specific capacitance of 17.75 F g−1, indicating the potential of the material for further investigation in energy storage applications. Density functional theory (DFT) calculations were used to examine the electronic structure, charge distribution, and related features of the CdS nanoclusters. Taken together, the experimental and theoretical results provide an initial assessment of the multifunctional behaviour of the prepared CdS nanocrystals. Further work is needed to establish their performance and safety under application-specific conditions.