Photocatalytic degradation of crystal violet and Eosin Yellow dyes using ZnS-Co₃O₄ composite: Synthesis, characterization and process optimization under UV light

This study investigates the photocatalytic degradation of Crystal Violet (CV) and Eosin Yellow (EY) dyes using a ZnS-Co₃O₄ composite photocatalyst. The composite was synthesized through the wet impregnation method, combining zinc sulfide (ZnS) and cobalt oxide (Co₃O₄) nanoparticles. Characterization of the composite was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, UV–Vis absorption spectroscopy and energy-dispersive X-ray (EDX) analysis. The photocatalytic performance of the ZnS-Co₃O₄ composite was evaluated under UV light irradiation with optimization of key factors such as illumination time, pH, catalyst dose, initial dye concentration and temperature. The maximum degradation efficiencies achieved were 94.23 % for CV and 92.33 % for EY under optimal conditions: 20 min of UV exposure, pH 11 for CV and pH 3 for EY, and a catalyst dose of 0.01 g/50 mL. The temperature effect showed an increase in degradation efficiency with higher temperatures, achieving 100 % for CV and 99.07 % for EY at 45 °C. Kinetic studies revealed that the photocatalytic degradation followed a first-order reaction, with rate constants of 0.0605 s⁻¹ for CV and 0.0286 s⁻¹ for EY. Response Surface Methodology (RSM) was used to model the degradation process, achieving high R² values of 0.9978 for CV and 0.9969 for EY. ANOVA confirmed the statistical significance of the model (p < 0.0001). These findings demonstrate the potential of the ZnS-Co₃O₄ composite as an effective photocatalyst for dye removal in wastewater treatment.