This study compares the electrochemical oxidation of acid orange 74 (AO 74), a typical metal complex azo dye, on four anode materials (Ru, IrO 2 , PbO 2 , and boron doped diamond (BDD)). The results show that the BDD electrode was quite efficient in the anodic oxidation of AO 74 with a 100% removal of AO 74 and an 84.3% removal of COD. Analyzing the active species at different electrodes, we reported that oxidation on an inert electrode primarily depends on direct oxidation and indirect oxidation of active radicals ( OH and O 2 − for the BDD anode and OH for the PbO 2 anode), whereas active electrodes (Ru and IrO 2 ) primarily depend on direct oxidation. The UV–vis spectrum demonstrated that Cr 3+ could be oxidized only on the BDD anode, proving that the BDD electrode has the highest oxidation potential. Similar organic intermediates species were observed on different electrodes by GC–MS. Furthermore, the different organic products are attributed to the difference in the oxidation ability of the electrodes. From the UV–vis spectrum and GC–MS analysis, we speculate that AO 74 was first degraded to aromatic compounds and pyrazole because of the cleavage of the azo-bond. Then it formed amides and organic acid because of the cleavage of the benzene ring, and finally CO 2 and H 2 O were formed.
Hao Li,Jiahao Zhang,Yiqi Du,Meixia Shi,Xinmou Kuang,Xiaolan Shen,Wenting Si
Electrochemical activation of persulfate is an efficient and green technology. In this study, the differences in the pollutant degradation efficiency and peroxydisulfate (PDS) activation mechanism were compared via electrochemical activation of PDS using only an IrO 2 anode, an IrO 2 cathode, and both an IrO 2 anode and stainless steel (SS) cathode. In these methods, the degradation of acid orange (AO) 74 conformed to the pseudo-first-order kinetic degradation model. The electrochemical activation of PDS using an IrO 2 anode resulted in the highest AO 74 degradation efficiency of 81.7 % with a degradation rate constant of 0.58 h −1 . The results of radical quenching and cyclic voltammetry indicated that during the electrochemical activation of PDS using an IrO 2 anode, direct electron transfer and nonradical oxidation contributed to AO 74 degradation. Using an IrO 2 cathode, the contribution to AO 74 degradation was mainly OH, while using an IrO 2 anode and SS cathode, the contribution was the joint action of the nonradical and radical oxidation. Furthermore, during the electrochemical activation of PDS using an IrO 2 anode, the degradation rate exhibited a good linear relationship with the current density and PDS concentration. The addition of Cl − considerably enhanced AO 74 degradation.
Hao Li,Yongkang Qi,Minru Su,Jie Hu,Xiaolan Shen,Chen Shi
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 − , CO 3 2− , and SO 4 2− , 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 Ag 0 /Ag + /Ag 2+ 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.
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