Photocatalytic degradation of Reactive Orange 107 in wastewaters under UV irradiation using multiphase cobalt selenide (CoSex) nanocatalyst: Performance evaluation, kinetic assessment, and mechanistic insights

Abstract

This study reports the photocatalytic degradation of Reactive Orange 107 (RO 107) in media using synthesized CoSe nanoparticles. The catalysts were characterized by XRD, FT-IR, SEM-EDX, HRTEM, N2 adsorption–desorption, BET, and BJH analyses, verifying crystalline CoSe formation, porous architecture, morphology and elemental distribution. Under optimized conditions of 1.0 g L⁻1 catalyst dosage, 25 mg L⁻1 RO107 concentration, natural pH, and irradiation source UV-C, CoSe achieved 97.87% degradation within 120 min. Decreasing the RO 107 concentration to 5 mg L⁻1 increased the efficiency to 98.17%, confirming high activity at low pollutant loading. The degradation followed pseudo-first-order kinetics, with kapp values of 0.0110–0.0646 min⁻1 depending on catalyst dosage, 0.0111–0.0709 min⁻1 for initial RO 107 concentration, and 0.0116–0.0723 min⁻1 under pH conditions. Water matrix inhibition followed distilled water (97.87%) > tap water (94.92%) > river water (89.16%) > lake water (86.58%). Dye degradation followed BY2 (99.82%) > RO107 (97.87%) > AO7 (95.12%) > CR (92.78%) > MG (90.65%) > RB19 (86.35%). The degradation efficiency was strongly influenced by the irradiation wavelength, following the order UV-C > UV-B > UV-A. After 120 min of reaction, the highest degradation efficiency was achieved under UV-C irradiation (97.87%), while lower efficiencies were obtained under UV-B (89.17%) and UV-A (80.69%) irradiation. The best activity was obtained at 0.8–1.5 g L⁻1 catalyst dosage and 5–25 mg L⁻1 RO 107 concentration, while reusability tests showed a decrease from 97.87% to 81.23% after six cycles, indicating promising stability.