Abstract
A classic carbon material—expanded graphite (EG), was prepared and proposed for a new application as catalysts for activating peroxydisulfate (PDS). EG samples prepared at different expansion temperatures were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and other methods. It was observed that there existed a remarkable synergistic effect in the EG/PDS combined system to degrade Acid Red 97 (AR97). Unlike other carbon material catalysts, sp2 carbon structure may be the main active site in the catalytic reaction. The EG sample treated at 600 °C demonstrated the best catalytic activity for the activation of PDS. Degradation efficiency of AR97 increased with raising PDS dosage and EG loadings. The pH of aqueous solution played an important role in degradation and adsorption, and near-neutrality was the optimal pH in this research. It was assumed that the radical pathway played a dominant role in AR97 degradation and that oxidation of AR97 occurred in the pores and interface layer on the external surface of EG by SO4·− and ·OH, generated on or near the surface of EG. The radical oxidation mechanism was further confirmed by electron paramagnetic resonance spectroscopy. The EG sample could be regenerated by annealing, and the catalytic ability was almost fully recovered.
Highlights
Advanced oxidation processes (AOPs) based on sulfate radical (SO4 ·− ) generated from peroxymonosulfate (PMS) and peroxydisulfate (PDS) have attracted much attention for the oxidation of water and soil contaminations
Scanning electron microscope (SEM) pictures and N2 sorption isotherms of the EG samples can Scanning electron microscope (SEM) pictures and N2 sorption isotherms of the EG samples can be seen in the Supplementary data of Figure S2
The regeneration of expanded graphite after catalyzing was explored, and the results showed that the catalytic ability of EG was almost 100% restored, with around 96.9% Acid Red 97 (AR97) removal in 80 minutes
Summary
Advanced oxidation processes (AOPs) based on sulfate radical (SO4 ·− ) generated from peroxymonosulfate (PMS) and peroxydisulfate (PDS) have attracted much attention for the oxidation of water and soil contaminations. The mechanism of electron conduction could account for the activation of PDS and PMS by carbonaceous-based materials. Carbon materials could donate an electron to PMS or PDS to form the reactive radicals [21] (Equations (3) and (4)). Sun et al [16] first reported that reduced graphene oxide prepared by a hydrothermal method demonstrated an excellent catalytic ability to activate PMS for pollutant oxidation. EG was prepared and applied as catalyst to catalytically oxidize organic dye Acid Red 97 (AR97) and the mechanism of PDS activation was discussed
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