Degradation of methylene blue with magnetic Co-doped Fe₃O₄@FeOOH nanocomposites as heterogeneous catalysts of peroxymonosulfate

Magnetic Co-doped Fe₃O₄@FeOOH nanocomposites were prepared in one step using the hydrothermal synthesis process for catalyzing peroxymonosulfate (PMS) to degrade refractory methylene blue (MB) at a wide pH range (3.0-10.0). The catalysts' physiochemical properties were characterized by different equipment; Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ were confirmed to coexist in the nanocomposite by X-ray photoelectron spectroscopy. The nanocomposite effectively catalyzed PMS's decoloration (99.2%) and mineralization (64.7%) of MB. The formation of Co/Fe-OH complexes at the surface of nanoparticles was proposed to facilitate heterogeneous PMS activation. Compared with the observation for Fe₃O₄@FeOOH, the pseudo-first-order reaction constant was enhanced by 36 times due to Co substitution (0.1620 min^-1vs. 0.0045 min^-1), which was assigned to the redox recycle of Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ in Co-doped Fe₃O₄@FeOOH. Besides, the catalyst could be easily reused by magnetic separation and exhibited relatively long-term stability.