Degradation of Acid Orange 7 using peroxymonosulfate catalyzed by granulated activated carbon and enhanced by electrolysis

•GAC as metal-free catalyst was combined with electrochemistry to catalyze PMS.•The π-electron density and hydroxyl group content of GAC favors the activation of PMS.•The generation of SO4− and OH was verified by EPR and radical scavenging experiments•The stability of GAC was significantly improved with the assistance of electrolysis.

Electrochemistry coupled with granulated activated carbon catalysis of peroxymonosulfate (electro/GAC/PMS) as a novel wastewater treatment process was performed for the degradation of Acid Orange 7 (AO7) in aqueous solution. The decolorization of AO7 was compared under different permutations and combinations of electro-oxidation, GAC and PMS. It showed that the electro/GAC/PMS process was the most effective and the decolorization of AO7 followed pseudo-first order kinetics. The surface chemistry of GAC samples was analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Compared with the fresh samples, π-electron density and hydroxyl group content decreased under the GAC/PMS system, but kept the similar values under the electro/GAC/PMS system. Electron paramagnetic resonance and radical scavenger studies were used to verify the formation of sulfate radicals (SO4−) and hydroxyl radicals (OH). The optimized conditions were found to be: current density 8 mA cm−2; PMS concentration 5 mM; GAC dosage 0.5 g L−1; and initial pH value 5.0. GAC recycling experiments over 4 runs showed some decrease in reactivity. Overall, the results indicate that 100% color removal was readily achieved and 50.4% of TOC was removed which shows high efficiency of the electro/GAC/PMS process.

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