Hydrothermally tailored hematite nanorods for photo-fenton degradation of 4-nitrophenol: Influence of morphology on catalytic mechanism and environmental safety

Hematite rod nanoparticles were synthesized by alkaline hydrothermal modification of natural laterite for different durations (12, 24, 36, and 48 h). The impact of the modification duration on the morphology and physicochemical properties of the resulting modified varieties of hematite (H.12, H.25, H.36, and H.48) was assessed using different analytic techniques. The four derivatives were applied as potential catalysts during the decontamination of hazardous 4-nitrophenol (4-NP) by photo-Fenton’s oxidation. The modified H.36 displayed the best geometry as nanorods, the highest surface area (154.7 m²/g), and the most effective catalytic performances. The incorporation of H.36 at a dose of 0.4 g/L resulted in complete oxidation for the investigated 4-nitrophenol contaminants within 80 min (5 mg/L), 120 min (10 mg/L), and 180 min (15 mg/L). The mineralization studies validated the successful transformation of 4-NP molecules (5 mg/L) into safe end products over H.36 within 160 min. The mineralization pathway ended by the formation of H₂O, CO₂, NO₂⁻, and NO₃⁻ after a series of oxidation reactions involved interaction with the release of hydroxyl radicals and generation of different intermediaries (p-benzoquinone, hydroquinone, 4-aminophenol, and acetic acid). The eco-toxicity studies for the treated solutions over different durations, considering both chronic (ChV > 10) and acute toxicity (LC50 and EC50 > 100), signify remarkable impact for the applied oxidation reactions using H.36 in reducing the toxicity of 4-NP and inducing the safety of the treated samples, especially after 160 min.