Structure–Dispersion–Performance Relationship in Fe-Functionalized Silicon Oxide for Enhanced Degradation of Recalcitrant Azo Dyes

Recalcitrant azo dyes in textile wastewater are a significant environmental concern due to their persistence and potential impacts on human and ecosystem health. Heterogeneous Fenton-like processes offer a promising approach for their removal, although catalyst performance depends strongly on the physicochemical characteristics of the active material. This study investigated Fe-functionalized silicon oxide (Fe-SiO) catalysts for sodium percarbonate (SPC)-activated removal of Reactive Orange 84 (RO84). The catalysts were prepared using silicon oxide supports with and without thermochemical pretreatment and different amounts of Fe during synthesis. Their structural, morphological, and elemental characteristics were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS), complemented by textural analysis. Increasing the amount of Fe used during synthesis shifted removal from adsorption-influenced to oxidation-associated, as reflected in the kinetic behavior. Thermochemical pretreatment promoted more homogeneous Fe dispersion and reduced aggregation in the S2 series, consistent with its higher catalytic response under several evaluated conditions. The PFO model empirically described the observed removal kinetics. Overall, the Fe-SiO materials showed potential for SPC-assisted RO84 removal under the evaluated conditions.