Predicted Photocatalytic Degradation Mechanism Of Reactive Orange 107 Dye

Reactive dyes are extensively used in textile applications; however, their persistence in wastewater poses significant environmental and health risks. In this study, the photocatalytic degradation mechanism of Reactive Orange 107 (RO-107) was theoretically investigated using conceptual density functional theory (CDFT) at the B3LYP/6-31G(d) level. The most susceptible sites for hydroxyl radical (•OH) attack were identified through Fukui function analysis. The results revealed that the N9 (f° = 0.06299) and N26 (f° = 0.06265) atoms are the primary reactive centers, indicating that the azo linkage is the most vulnerable site for oxidative degradation. The proposed mechanism demonstrated that •OH attack initiates azo bond cleavage, leading to the formation of two main fragments, followed by hydroxylation and ring-opening reactions, ultimately producing low-molecular-weight products and mineralization to CO₂ and H₂O. Toxicological evaluation using ProTox 3.0 indicated that RO-107 is relatively low in toxicity (class 5); however, some degradation intermediates exhibited increased toxicity. In particular, compound (6) was predicted to be carcinogenic (class 2), whereas compounds (1) and (2) were classified as relatively non-toxic (class 6). These findings highlight that although photocatalytic treatment promotes dye degradation, it may also generate intermediates with higher toxicological risk.