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The role played by local pH and pore size distribution in the electrochemical regeneration of carbon fabrics loaded with bentazon

Delpeux-Ouldriane, Sandrine, Gineys, Mickaël, Cohaut, Nathalie, Béguin, François
Carbon 2015 v.94 pp. 816-825
activated carbon, adsorbents, adsorption, bentazon, desorption, dissociation, electric field, electrochemistry, electrolytes, electrostatic interactions, fabrics, micropores, nanopores, pH, porosity, texture
Adsorption of the herbicide bentazon on activated carbon fabrics was found to be enhanced in acidic medium, showing that bentazon is mainly adsorbed through dispersive interactions. Bentazon was reversibly desorbed by applying a cathodic polarization of the cloth, leading to its fast regeneration. The mechanisms involved were carefully examined in light of the nanoporous texture of carbon and surface functionality, using various electrolytes at different pH values. Results showed that bentazon was strongly adsorbed and that the negative charges on the carbon surface together with the local electrical field were not sufficient to induce desorption of anionic bentazon through electrostatic interactions. The pH increase inside the porosity, especially due to water decomposition, was crucial in favoring the dissociation of surface groups, thereby strengthening electrostatic repulsions between the negatively charged carbon surface and the anionic bentazon molecule. This mechanism occurred in the micropores and mesopores, the latter contributing to the desorption kinetics through transportation of the adsorbate from the carbon surface to the electrolyte. Additionally, the presence of acidic surface groups on the adsorbent or the use of a basic electrolyte improved the desorption process thanks to the increase in negatively charged functionalities and the promotion of electrostatic repulsions.