Dynamic light scattering-assisted design of an optimized NiS–ZnS nanocomposite for efficient photocatalytic dye degradation: experimental and theoretical insights

Abstract

Industrial dye pollutants demand efficient photocatalysts for sustainable wastewater treatment. Here, we report the synthesis of pure NiS, ZnS, and a negatively charged, optimized NiS–ZnS nanocomposite (NC) via coprecipitation, with their size and stability controlled by adjusting the precursor ratio, pH, temperature, stabilizer concentration, and reactant addition rate. Dynamic light scattering (DLS) analysis was used to monitor hydrodynamic radius (H_R), ζ-potential, and polydispersity index (PdI), providing real-time insights into dye adsorption, degradation dynamics, and salt–nanocomposite interactions. Optimized NiS : ZnS 50 : 50 nanocomposite showed high colloidal stability, achieved 98% crystal violet (CV) degradation within 60 min under visible light, outperforming other cationic dyes while being less effective for anionic dyes. Characterization of the NiS–ZnS NC (UV-Vis spectroscopy, PL spectroscopy, XRD, FTIR spectroscopy, EDX, XPS, SEM, TEM, TGA, and BET analysis) confirmed its visible light activity, suppressed charge recombination rate, successful synthesis, agglomerated nature, thermal stability, and mesoporous structure. Density functional theory (DFT), density of states (DOS), and electrostatic potential analyses showed bandgap narrowing, favorable dye binding, and efficient charge transfer supported by strong interaction energies. Salt studies revealed surface-charge modulation and radical pathways, with NaNO₃ enhancing the degradation via ˙OH generation, while CaCl₂ and AgNO₃ suppressed the degradation activity. LC-MS and total organic carbon (TOC) analysis confirmed dye mineralization and reduced toxicity, with seed germination assays verifying the biocompatibility of the NiS–ZnS NC. The generation of the reactive species ˙OH and ˙O₂⁻ was confirmed using electron spin resonance (EPR) spectroscopy and quencher experiments. This integrated experimental-computational approach establishes NC as a robust, charge-engineered photocatalyst for visible-light-driven dye remediation.