Two-dimensional sp2 carbon-conjugated COFs electrode for efficient electro-adsorption of uranium

Abstract

Electro-adsorption has been shown great potential for radionuclides separation from aqueous solution benefit from its advantages, such as energy conservation, environmental protection. Herein, a 2 D sp2 carbon-conjugated COFs was obtained by the Knoevenagel reaction between 1,4-phenylenediacetonitrile and 1,3,5-tris(p-formylphenyl)benzene, and then amidoximated by treatment with hydroxylamine, the sp2 carbon-conjugated COFs functionalized carbon felts achieved efficient electro-adsorption for uranium(VI). A variety of characterization techniques were used to determine the chemical structure and morphology of the prepared sp2 carbon-conjugated COFs. The adsorption equilibrium of the sp2 carbon-conjugated COFs for uranium(VI) can be reached within 10 min at pH 6.0 and 1.2 V, more than twice faster than physicochemical adsorption according to the kinetic constants (K2). The maximum electro-adsorption capacity was calculated to be 478.5 mg/g fitted by Langmuir isotherm model, which was much higher than 294.1 mg/g obtained by physicochemical adsorption. Meanwhile, the distribution coefficient Kd of the electrode for uranium was 1.07 × 105 mL/g, indicating the sp2 carbon-conjugated COFs possessed excellent selectivity for uranium(VI) against co-existing cations. XPS studies confirmed that both hydroxyl and amino groups of amidoxime in COFs-AO are involved in the coordination of uranium(VI). Most importantly, the electrode showed good reusability, which makes it possible to remove uranium(VI) from uranium-containing wastewater. This work could allow sp2 carbon-conjugated COFs to be expanded to efficiently cleanup other contaminants by rational topology construction and ligands design.