An observed "sandwich" framework mediated via sulfate ions as electron shuttle for efficient electro-oxidation of...

"Electro-oxidation processes are effective in treating sulfate-rich organic wastewater. However, this technology development has been hindered by the poor understanding of the role of sulfate ions. This paper reports that high concentration of sulfate ions significantly enhanced the electro-oxidation of organic pollutants. High sulfate concentration did not affect radical activity or organic pollutant coverage on the electrode surface. We propose that the electrode interface forms a "sandwich" framework mediated by sulfate ions, consisting of the electrode surface, the sulfate ion layer, and the organic pollutant layer. High concentrations of sulfate ions selectively promote the protonated organic pollutant into the framework via electrostatic attraction when the solution pH is lower than the pKa of the organic pollutants. In this framework, the sulfate ion layer acts as an electron shuttle, creating a smooth electron transfer pathway between the electrode surface and the organic maters. In this way, the "sandwich" framework can efficiently electro-oxidize organic pollutants. This study offers new insights into the role of sulfate ions in electro-oxidation processes, redefining their role in pollutant degradation, and guiding the design of sulfate-rich wastewater treatment."