Degradation of methylene blue in liquid using high-voltage pulsed discharge plasma synergizing iron-based catalyst-activated persulfate

Abstract In this work, high-voltage pulsed Ar gas–liquid discharge synergizing iron-based catalyst-activated persulfate (PS) was employed to degrade methylene blue (MB) in water. The catalytic performances of two types of iron-based catalysts, namely the homogeneous catalyst Fe 2+ and the heterogeneous catalyst nano-Fe 3 O 4 , were compared. Correspondingly, the plasma gas temperature and excited species were calculated and diagnosed using optical emission spectra. It was found that the introduced plasma process significantly enhanced the degradation efficiency of MB by the PS/Fe 2+ and the PS/Fe 3 O 4 systems. After 20 min of treatment, the MB degradation efficiency reaches 97.5% and 83.1% in the hybrid plasma/PS/Fe 2+ and plasma/PS/Fe 3 O 4 systems, respectively, which is 37.9% and 35.6% higher than that in the PS/Fe 2+ and PS/Fe 3 O 4 systems. The synergistic mechanism and key reactive species responsible for MB degradation in hybrid plasma/PS/Fe 2+ and plasma/PS/Fe 3 O 4 were explored using the addition of radical scavengers and control experiments under various conditions. The homogeneous catalyst Fe 2+ exhibits better activation performance in PS and plasma than that of the heterogeneous catalyst nano-Fe 3 O 4 .