Insight into the roles of microenvironment and active site on the mechanism regulation in metal-free persulfate activation process coupling with an electric field.

The regulation of the persulfate activation mechanism is highly desirable and meaningful for the treatment of different wastewaters. The role of active sites for mechanism regulation in carbon-driven persulfate activation is still ambiguous due to the complex and easily neglected microenvironment (concentration distributions of organics and oxidants) nearby carbon catalyst. This work aims to reveal the critical roles of active site and microenvironment on the activation mechanism through N-doped modification and application of an electric field (AC/PS/EC). Several N-doped activated carbon catalysts were prepared by activating for different times to adjust the surface active center and adsorption selectivity under an electric field. The contribution ratio of radical pathway and non-radical pathway for organic elimination significantly varied with the concentration distribution of organics and oxidants nearby the microelectrodes. The increased electro-adsorption of persulfate anion was found to be the primary promoting factor for the radical pathway for organic oxidation, resulting in a synergistic increase in degradation rate in the AC/PS/EC system. The quantitative structure-activity relationships analysis also revealed that the electro-adsorption selectivity was dominated by the surface graphitic N and pore structure of catalyst. This study sheds new light on the oxidative pathway regulation to deal with complex wastewater in a flexible and efficient manner.