Discoloration of methylene blue at neutral pH by heterogeneous photo-Fenton-like reactions using crystalline and amorphous iron oxides

Different iron oxides were evaluated for the discoloration of methylene blue (MB) at neutral pH by heterogeneous photo-Fenton-like reactions with a UV-LED lamp. Fe , α-Fe , and a-FeOOH catalysts were synthesized and characterized by X-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy, and adsorption isotherms of N . The results show high crystallinity and relatively low surface areas for Fe and α-Fe , and amorphous structure with high surface area for the case of a-FeOOH. The discoloration of MB by iron oxides as catalysts was studied using UV-Vis spectroscopy. Despite the relative high adsorption of MB for magnetite (12%) compared to the other oxides, it shows a slow discoloration kinetics. Besides, amorphous oxide (named a-FeOOH) shows a higher discoloration kinetics with negligible adsorption capacity. The pseudo first-order kinetic constant values for Fe , α-Fe , and a-FeOOH are 5.31 × 10 , 6.89 × 10 , and 13.01 × 10 min ; and the discoloration efficiencies at 120 min were 56, 60, and 82%, respectively. It was testified that low crystallinity iron oxide can be used in the efficient discoloration of MB by photo-Fenton process with a hand UV-A lamp.