pH-Dependent Dye Protonation and the Effect of Iron on Dye Degradation During Fenton-Based Processes

This study investigated the degradation and removal efficiency of reactive and direct dyes using various treatment processes, including UV alone, peroxide alone, Fenton, photo-Fenton, and UV-peroxide. The decolorization results showed that UV and peroxide alone had limited performance, achieving only 8.8% to 14.4% decolorization for direct dyes DR28 and DB71. The Fenton and photo-Fenton processes exhibited rapid total organic carbon (TOC) degradation within the initial 30 minutes, reducing reactive dyes RBla5, RB19, and RO16 by 41.3% to 38.8%. However, the reaction stagnated due to the depletion of Fe2+ in the Fenton process. Interestingly, the UV-peroxide treatment demonstrated superior decolorization performance, achieving 72.9% to 99.2% decolorization for DR28 and DB71 at pH 3 and 7. In contrast, TOC removal efficiency fell below expectations for all processes. The iron-based processes, Fenton and photo-Fenton, resulted in low TOC removal values for both direct dyes, possibly caused by the mordanting phenomena between dyes and iron, shown by visible sediment formation Further research is needed to optimize TOC removal efficiency, especially for direct dyes, and to elucidate the mechanisms of protonation and mordant interactions in the dye degradation process.