Multipath radical synergistic activation of hydrogen peroxide by colloidal-clay composite gel microspheres: Reaction mechanism and efficient photocatalytic degradation of p-Nitrophenol

To address the challenges of low hydrogen peroxide(H 2 O 2 ) utilization efficiency in traditional homogeneous systems, this study successfully developed a novel photocatalytic colloidal clay mineral composite gel microsphere system (Fe 0 -OA-P/Gel-H 2 O 2 ). This system achieved efficient degradation of p-nitrophenol (PNP, 50 mg/L) in aqueous solutions through the synergistic activation of O 2 and H 2 O 2 to generate hydroxyl radicals (·OH), demonstrated a remarkable H 2 O 2 utilization rate of 91.55 %. The system exhibited 89.45 % PNP degradation efficiency with 64.87 % total organic carbon (TOC) removal. Under optimized conditions, the pseudo-first-order kinetic model revealed a degradation rate constant of 0.0084 min −1 , representing a 28.84-fold enhancement compared with H 2 O 2 systems. Radical quenching experiments combined with in situ EPR analysis confirmed a multi-path synergistic degradation mechanism to PNP, involving ·OH, superoxide radicals (·O 2 − ), and singlet oxygen ( 1 O 2 ). Material characterization through EDS and XRD spectra identified Fe-O-Si active sites on the microsphere surfaces. FTIR and XPS analyses verified successful encapsulation of Fe 0 within the gel matrix and its subsequent oxidation to Fe 2+ /Fe 3+ during photocatalytic processes. TG analysis demonstrated excellent thermal stability (weight loss <15 % below 150 °C), superior water absorption capacity (8.0 g/g) and adsorption capability for strongly polar organic pollutants. The introduction of oxalic acid as an electron shuttle significantly enhanced photoelectron transfer efficiency, increasing ·OH generation by 2–3 folds and achieving a quantum efficiency of 27.07 %. This study innovatively develops an efficient heterogeneous photocatalytic activation system through colloidal-clay mineral composite gel microspheres, which demonstrating significant potential for treating refractory organic pollutants in water and soil environments.