Integrating anodic sulfate activation with cathodic H2O2 production/activation to generate the sulfate and hydroxyl radicals for the degradation of emerging organic contaminants

Abstract

Conventional electrocatalytic degradation of pollutants involves either cathodic reduction or anodic oxidation process, which caused the low energy utilization efficiency. In this study, we successfully couple the anodic activation of sulfates with the cathodic H2O2 production/activation to boost the generation of sulfate radical (SO4·−) and hydroxyl radical (·OH) for the efficient degradation of emerging contaminants. The electrocatalysis reactor is composed of a modified-graphite-felt (GF) cathode, in-situ prepared by the carbonization of polyaniline (PANI) electrodeposited on a GF substrate, and a boron-doped diamond (BDD) anode. In the presence of sulfates, the electrocatalysis system shows superior activities towards the degradation of pharmaceutical and personal care products (PPCPs), with the optimal performance of completely degrading the representative pollutant carbamazepine (CBZ, 0.2 mg L−1) within 150 s. Radicals quenching experiments indicated that ·OH and SO4·− act as the main reactive oxygen species for CBZ decomposition. Results from the electron paramagnetic resonance (EPR) and chronoamperometry studies verified that the sulfate ions were oxidized to SO4·−radicals at the anode, while the dissolve oxygen molecules were reduced to H2O2 molecules which were further activated to produce ·OH radicals at the cathode. It was also found that during the catalytic reactions SO4·−radicals could spontaneously convert into peroxydisulfate (PDS) which were subsequently reduced back to SO4·−at the cathodes. The quasi-steady-state concentrations of ·OH and SO4·−were estimated to be 0.51×10−12 M and 0.56×10−12 M, respectively. This study provides insight into the synergistic generation of ·OH/SO4·− from the integrated electrochemical anode oxidation of sulfate and cathode reduction of dissolved oxygen, which indicates a potential practical approach to efficiently degrade the emerging organic water contaminants.