Understanding the Decolorization Behavior of Dyes in Multicomponent Mixtures by Advanced Oxidation Processes: An Integrated Experimental and Theoretical Study

Advanced oxidation processes (AOPs) are considered efficient treatment methods owing to the high reactivity of the oxidizing species they generate. However, in multicomponent mixtures, individual dyes may exhibit different apparent decolorization kinetics. Studies investigating the decolorization kinetics of individual textile dyes in mixtures remain limited, as their determination using conventional spectroscopic techniques is challenging. In this study, a spectral deconvolution methodology based on the additivity of absorbance and the Beer–Lambert law was proposed to determine the individual decolorization kinetics of reactive dyes subjected to AOPs by O3/H2O2/UV-C. The process was optimized using a Taguchi design, with the area under the visible spectrum (AUC) as the response variable. The presence of glass-sphere filler had the greatest effect on decolorization, followed by UV-C irradiation (16 W), gas flow rate (2 L/min), temperature (50 °C), and H2O2 concentration (50 mM), reducing the AUC by 99.29% in 25 min. Spectral deconvolution identified RY-RR as the most persistent dye, with a decolorization rate approximately 35% lower than that of the other dyes. Furthermore, density functional theory (DFT) calculations provided a molecular-level interpretation of the differences in dye reactivity and supported the experimentally observed persistence of RY-RR. The persistence of RY-RR determines the treatment time and, consequently, affects energy consumption, resulting in an electrical energy per order (EEO) of 7.4 kWh/m3. Adjusting the initial pH reduced the decolorization time to 20 min and the EEO by 28%, while achieving 54% TOC removal after 60 min. These results demonstrate that individual dyes can exhibit different apparent decolorization kinetics under the same oxidation conditions, reflecting the influence of their molecular characteristics on their decolorization behavior.