Acid-citrate sequential engineered Hangjin2# clay for photo-fenton degradation of methyl orange: electron transfer mechanism analysis

Technological advancements and industrialization resulted in a significant increase in the discharge of hazardous waste into aquatic environments, highlighting the urgent need for environmentally friendly remediation strategies. In this context, the present study introduces Hangjin2 # clay as a novel, eco-friendly heterogeneous photo-Fenton-like catalyst for the degradation of methyl orange, a representative model pollutant in wastewater treatment. The skeletal structure and ionic coordination environment of Hangjin2 # clay were altered via acid and sodium citrate modification, which triggered structural and coordination rearrangements. This modification also immobilized Fe 2+ and generated both Lewis and Brønsted acid sites on the Hangjin2 # clay surface. The Lewis acid sites enhanced the adsorption of H 2 O 2 , while the Brønsted acid sites facilitated the formation of hydroxyl radicals through proton transfer processes. These effects collectively promoted efficient Fe 3+ /Fe 2+ redox cycling, thereby enhancing the photo-Fenton catalytic performance. XPS and FTIR analyses revealed that acid-activated iron ions, chelated by sodium citrate, underwent isomorphous substitution with tetrahedral Si 4+ in Hangjin2 # clay, as evidenced by characteristic Si-O-Fe vibrational features and binding energy shifts in the Fe 2p 3/2 orbitals. In photo-Fenton degradation experiments using hydrated systems, the catalyst achieved a 98.9 % degradation rate of 50 mg/L methyl orange under optimal conditions (25 mM H 2 O 2 , pH 3, and 1 g/L catalyst) after 90 min. Additionally, stability tests demonstrated a maintained removal efficiency of 98 % after three successive catalytic cycles.