Molybdenum co-catalytic promotion for Fe3+/peroxydisulfate process: performance, mechanism, and immobilization

In this work, we proposed that molybdenum (Mo) powder as the cocatalyst could promote the sulfamethoxazole (SMX) decomposition in the Fe3+/peroxydisulfate (PDS) Fenton-like process. Efficient SMX elimination (96.7%) was reached after 20 min under the circumstances of 0.20 g·L−1 Mo, 0.50 g·L−1 PDS, 0.07 g·L−1 Fe3+, and beginning pH 5.4. Sulfate radicals were verified as the main active species according to the quenching experiment and electron spin resonance spectroscopy analysis. The Mo cocatalyst improved the Fe3+ reduction and PDS activation. According to the investigation of X-ray photoelectron spectroscopy for the valence state change of Mo before and after the reaction, the mechanism of Fe3+/Fe2+ circulation being initiated through the Mo4+ and Mo0 was presented. There was no obvious change of surface structure between the original and used Mo, as certified through X-ray diffraction and scanning electron microscope analyses. The mass spectrometry was used to determine the SMX degradation byproducts, and their toxicities were evaluated by the computational toxicology. Importantly, even after five cycles, the Mo still displayed excellent recyclability, and above 93% SMX was degraded in the fifth recycle. In the end, the immobilization of Mo was attempted by fixing Mo on the cyanoacrylate and agar, which also both showed the good co-catalytic effect. This research affords a promising inorganic co-catalytic Fenton-like system for water treatment.