Efficient acid orange 74 degradation using electrochemically activated peroxydisulfate with silver nanoparticle–modified carbon paper: Long–term stability through alternating anode–cathode operation

Electrodes with high activation efficiency and stability are critical for the electrochemical activation of persulfate. In this study, the effective degradation of acid orange 74 (AO 74) was achieved using the electrochemically activated peroxydisulfate (PDS) with a Ag nanoparticle–modified carbon paper (AgNPs@CP) electrode, demonstrating a 2.5-fold enhancement in the AO 74 degradation rate compared with the CP electrode. The impact of reaction conditions, including AgNPs dosage, PDS content, current density, initial solution pH, and agitation rate, as well as water matrices, such as Cl−, CO32−, and SO42−, on AO 74 degradation was systematically investigated to establish optimal parameters. Radical quenching experiments and electron paramagnetic resonance analysis identified sulfate radical and hydroxyl radical as the dominant reactive species. Gas chromatography–mass spectrometry analysis revealed that AO 74 was primarily transformed into aliphatic organic compounds during electrochemical degradation. Remarkably, the 3-h AO 74 degradation efficiency remained stable over five consecutive cycles through alternating use of the AgNPs@CP anode and CP cathode, facilitated by Ag0/Ag+/Ag2+ redox cycling that enabled Ag recovery and minimized Ag leaching. The electrochemically activated PDS with the AgNPs@CP electrode shows promise as a pretreatment technology for dyeing wastewater with low biodegradability.