Mg/Mn co-doped CdS nanoparticles: a multifunctional platform for wastewater purification and antibacterial applications

Abstract

Developing nanomaterials with multifunctional properties that can address both biomedical and environmental challenges is the focus area of this research study. This work presents Mg and Mn co-doped CdS synthesized in a controlled way by a co-precipitation method utilizing ammonia hydroxide as both a capping and stabilizing agent. While fixing the Mn concentration at 2%, the Mg concentration was varied from 1% to 7% based on prior studies of the optical and electronic properties of CdS at these doping concentrations. X-ray diffraction analysis confirmed lattice expansion and a hexagonal phase along with crystal size reduction from 49.08 nm (pure CdS) to 42.94 nm for Mg_5%–Mn_2%-CdS, which is evidence of successful substitution. The reduction in the optical bandgap from 2.80 eV (pure CdS) to 2.19 eV (optimally co-doped sample) is evidence of the absorption enhancement of visible light. Methylene blue exhibited 84.79% degradation under visible-light irradiation within 125 min, following psuedo-first-order kinetics with a rate constant of 0.014 min⁻¹ (R² = 0.98). The dominant reducing species, ˙O₂⁻ and ˙OH, were confirmed by scavenger experiments. The same sample exhibited strong antibacterial activity by producing inhibition zones of 17 ± 0.2 mm against E. coli and 40 ± 0.3 mm against S. aureus, which surpassed the activity of pure CdS, approaching the standard antibiotic efficiency. These results suggest that Mg–Mn-co-doped samples are stable, dual-functional, and suitable for both wastewater purification and antimicrobial applications.