From MOF to Al/N-doped porous carbon: Creating multiple capture sites for efficient capacitive deionization defluorination

Abstract

Fluorine pollution has been recognized as one of the major problems of global concern. Metal-organic frameworks (MOFs), as potential fluoride adsorbents, possess unique chemical reactivity and broad functionalities. However, their application is restricted by instability in fluoride or acid/base solution and difficult separation. Here, lotus flower-like Al/N-doped porous carbon composite was prepared by a simple pyrolysis method using Al-based MOF as a precursor and used for capacitive deionization (CDI) defluorination. Through pyrolysis, MOF-derived carbon not only obtained a larger specific surface area and N-rich structure, but also possessed multiple F− capture sites. These carbon substrate enabled the metal centers to be uniformly dispersed and contributed to enhanced electrical conductivity and chemical stability of electrode material. Through the CDI defluorination system, F− migrate rapidly with the aid of the electric field and was captured under the synergistic effect of metal sites and carbon substrate. According to the Langmuir isotherm, the maximum F− removal capacity was 76.28 mg g−1 at 1.2 V, and the adsorption kinetics followed pseudo-second-order model. The electroenhanced adsorption method exhibits high adsorption capacity and selectivity for F− due to combining the advantages of adsorbent adsorption and electrosorption, which already exceeds the capacities of most electrode material.