SYNTHESIS OF COBALT-DOPED CERIUM SULFIDE PHOTOACTIVATION FOR DEGRADATION OF METHYLENE BLUE USING PEROXYMONOSULFATE IN AQUEOUS MEDIA

Abstract

The present study investigated the synthesis and photocatalytic application of cobalt-doped cerium sulfide (Co–CeS) for the degradation of methylene blue (MB) in aqueous media using peroxymonosulfate (PMS) under visible-light irradiation. The synthesized catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), Fourier-transform infrared spectroscopy (FTIR), and UV–visible spectroscopy. XRD analysis confirmed the formation of a crystalline cerium sulfide phase, while SEM revealed an irregular, agglomerated, and rough surface morphology. EDS confirmed the presence of Ce, S, and Co, indicating successful incorporation of cobalt into the sulfide-based material. FTIR analysis identified surface hydroxyl, adsorbed water, and metal–sulfur-related vibrations. UV–visible analysis showed enhanced optical absorption toward the visible region. The photocatalytic activity of Co–CeS was evaluated using 10 mg L⁻¹ MB in the presence of PMS under 450 nm visible-light irradiation. The effects of initial pH, catalyst dosage, PMS concentration, temperature, and irradiation time were systematically investigated. MB degradation increased with irradiation time, reaching 98.5% after 120 min under the selected conditions. The optimum catalyst dosage and PMS concentration were 0.5 g L⁻¹ and 1.0 mM, respectively, while pH 7 provided the highest degradation efficiency. Increasing temperature from 20 to 35 °C enhanced the degradation rate, with 99.1% degradation at 35 °C. The degradation kinetics followed an apparent pseudo-first-order model, with a maximum of 0.035 min⁻¹ and a half-life of approximately 19.8 min. The apparent activation energy was estimated to be 39.0 kJ mol⁻¹, indicating a temperature-dependent degradation process. The enhanced performance was attributed to the synergistic interaction of Co–CeS, visible light, and PMS, promoting charge separation and the generation of reactive oxygen species. Overall, the results demonstrate that Co–CeS is a promising photoactive catalyst for PMS-assisted degradation of cationic dyes in aqueous systems.