In this study, nanosecond pulsed discharge plasma is employed to treat the XAD-2 resins in the purpose of improving its adsorption capacity of polycyclic aromatic hydrocarbons. The discharge images, waveforms of pulse voltage and discharge current, and optical emission spectra are measured to investigate the plasma characteristics. The scanning electron microscopy, N2 adsorption-desorption analysis, Fourier transform infrared spectrum, and x-ray photoelectron spectroscopy are employed to characterize the physical and chemical properties of raw and modified XAD-2 resins. It is found that the adsorption capacity of modified XAD-2 resins for polycyclic aromatic hydrocarbons is obviously improved. The adsorption capacity of XAD-2 resins modified by plasma increased by 70% in 10 min adsorption time under the optimal conditions of 20 min treatment time and artificial air. The reason for the improved adsorption capacity is attributed to the increase of specific surface area, the number of 28–33 nm micro-mesopores, and relative intensity of oxygen-containing functional groups (C=O, C–O, and COOH). The possible mechanism of plasma modification of XAD-2 resin is also proposed.
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 Fe2+ and the heterogeneous catalyst nano-Fe3O4, 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/Fe2+ and the PS/Fe3O4 systems. After 20 min of treatment, the MB degradation efficiency reaches 97.5% and 83.1% in the hybrid plasma/PS/Fe2+ and plasma/PS/Fe3O4 systems, respectively, which is 37.9% and 35.6% higher than that in the PS/Fe2+ and PS/Fe3O4 systems. The synergistic mechanism and key reactive species responsible for MB degradation in hybrid plasma/PS/Fe2+ and plasma/PS/Fe3O4 were explored using the addition of radical scavengers and control experiments under various conditions. The homogeneous catalyst Fe2+ exhibits better activation performance in PS and plasma than that of the heterogeneous catalyst nano-Fe3O4.
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