Recycled magnetite as a sustainable photo-catalyst for hydrogen peroxide and peroxydisulfate activation: insights into the efficiency and mechanism of picloram removal in water

Abstract

In this work, activation oxidants like H₂O₂ and peroxydisulfate (S₂O₈²⁻) were investigated in the presence of a recycled magnetite (rMG) obtained from Hymag'in company (France) both in the dark and under UVA light. The rMG is a micro-powder (0.5–1 μm particle size) predominantly composed of magnetite, but it also contains cubic γ-Fe₂O₃. Picloram (PIC) was employed as a model pollutant to investigate the performance of rMG. The effects of oxidants (type and concentration), light and water matrix were assessed. Better efficiencies were observed in systems containing peroxydisulfate (PDS) due to the better stability of sulfate radicals compared to hydroxyl radicals. In addition, iron leaching was observed in PDS-based systems, thus suggesting that homogeneous Fenton reactions increased the catalytic efficiency. The effect of light boosted the efficiency due to regeneration of Fe(II) by Fe(III) photolysis. The 0.2 g L⁻¹ rMG can completely degrade PIC under UVA light in the presence of PDS after only 2 h of reaction. In wastewater effluents, rMG exhibited promising results with the removal of about 60% of PIC after 4 h, and rMG was significantly better than commercial magnetite. The present work highlights the feasibility of using wastes from the iron industry to treat wastewater, which is an added value for the circular economy of water.