Self-Assembled/Oval-Shaped Iron Oxide Nanoparticles for Efficient Photo-Fenton Reaction at Neutral pH

Mass-production simple synthesis of self-assembled oval-shaped iron oxide nanparticles was achieved by 24 h solvothermal treatment at 100 °C using a ferric nitrate precursor in ethanol media. The Brunauer–Emmett–Teller (BET) surface area was measured to ~100 m²/g, and the XRD pattern results showed a hematite crystalline structure. With increasing heat-treatment temperature from 300 to 700 °C under a 4% H₂/96% Ar atmosphere for 3 h operation, the oval-shaped morphology of the iron oxide nanoparticles (NPs) was disrupted, leading to a sharp decrease in BET surface area with mixed hematite, magnetite, and wűustite phases. Taking into consideration H₂O₂ as a decomposition catalyst of iron oxide NPs, photo-Fenton degradation of methylene blue (MB) was investigated. The results showed the highest apparent rate constant of 5.36 × 10⁻³ min⁻¹ (r ² = 0.996) under the 0.2 g α-Fe₂O₃ powder dosage and 0.5 M H₂O₂ loading conditions; however, all of the phase-transformed α-Fe₂O₃ NPs showed smaller apparent rate constants. Notably, 50 L pilot-scale photo-Fenton reaction based on the optimal batch-scale MB-degradation conditions could be of significant potential catalytic utility in advanced oxidation processes (AOPs) for practical water/wastewater applications.