Multidimensional Analysis of Chlorine Photolysis for Astrazon Red 6B Degradation: Kinetics, Synergistic Effects, and...

This study investigates the degradation of Astrazon Red 6B (AR 6B), a cationic textile dye, using the UV₂₅₄/chlorine advanced oxidation process. A multidimensional experimental approach was employed to evaluate the process performance and synergy under varying operational conditions, including chlorine dosage (100-1000 μM), dye concentration (10 and 20 mg L^-1), temperature (25°C-45°C), and pH (5, 7, and 9). Particular attention was given to pH, as it governs chlorine speciation and consequently the nature and reactivity of generated oxidative species. The combined UV/chlorine system exhibited significantly enhanced degradation compared to the individual processes (chlorination and UV irradiation), confirming a strong synergistic effect. By outperforming the UV/H₂O₂ system, the highest performance (with a synergy index [SI] of 9.76) of the UV/chlorine system was observed under mildly acidic conditions (pH 5 with 250 μM chlorine, 20 mg L^-1 dye, and 25°C), where reactive chlorine species (RCS) and hydroxyl radicals (the dominant oxidants) were simultaneously promoted, accelerating chromophore destruction and subsequent oxidative pathways. Neutral (pH 7) and alkaline (pH 9) conditions exhibited a different reactivity pattern, indicating a shift in the dominant radical species and reaction mechanisms. Variations in oxidant dose, pollutant concentration, and temperature further influenced the SI in a pH-dependent manner, highlighting the complex interplay among radical generation, scavenging reactions, and substrate availability. Overall, the results demonstrate that the UV/chlorine process is a highly tunable oxidation system whose efficiency is strongly controlled by chlorine speciation and radical dynamics. The mechanistic insights provided contribute to a deeper understanding of reactive species interactions and support the optimization of UV/chlorine treatment for textile wastewater remediation.