Overlooked key role of Mo(VI) in Fe2(MoO4)3 for peroxymonosulfate activation with 1O2 dominated degradation pathway

Abstract

In this study, an eco-friendly Fe2(MoO4)3 was synthesized via template assistant methods for peroxymonosulfate activation to remove RodanminhB (RhB). X-ray photoelectron spectroscopy (XPS) and UV–vis results illustrated the high valence Mo(VI) was the active center to initiate the nonradical-dominated pathway. Electron paramagnetic resonance (EPR) with chemical quenching experiments confirmed the leading role of 1O2 in RhB degradation, which originated from the Mo(IV)/Mo(VI) redox cycle and Mo(VI) peroxo-complex MoO(O2)22–. Also, the improved Fe(II)/Fe(III) cycle produced radicals, like SO4•−and •OH, to assist the degradation process, and promoted Mo(VI) regeneration alongside. 10 mg/L RhB can be completely removed after adding 0.2 g/L Fe2(MoO4)3–4 and 0.1 g/L PMS within 30 min. The effects of PMS and catalyst dosages, initial pH, inorganic anions, and humic acid on RhB degradation were studied and analyzed. Due to the anti-interference of 1O2, Fe2(MoO4)3–4 could sustain its high reactivity from pH 3 to 11. It also contained its original crystal structure with a high degradation rate after five cycle runs. Multiple kinds of dyes and antibiotics were eliminated efficiently within 30 min. The intermediates involved in the reaction were examed by liquid chromatography-mass spectrometry (LC-MS) to propose the degradation pathway of RhB. This work shed light on the overlooked key role of high valence Mo(VI) during PMS activation, instead of traditional low valence Fe(II) or Mo(IV).