Unexpected F- removal by Co2Al-LDHs: Performance and new insight

Abstract

F- removal has been one of the most concerned topics in aquatic pollution control. Here, we reported an unexpected ability of CoAl2-LDHs towards F- removal with adsorption capacity of 122.54 mg/g, which outperformed many classical Al-based LDHs. The underlying mechanism behind the outstanding adsorption performance was uncovered based on the density functional calculations, and spectroscopic characterizations. Typically, Co exhibited strong electron-attraction ability that could also alter the chemical environment of Al atoms, as compared with other Al-based LDHs. As a result, the Co-OH and Al-OH in the CoAl2-LDHs could attract the electron from F- and this behavior strengthens the F- - LDHs interaction. Moreover, combining the above analysis with ligand-field theory, we further disclosed that the unique valence electron configuration of Co3+ (3d-orbital), consisting of two unpaired and one paired electron in t2g and two unpaired electrons in eg, contributed mostly to the electron-attraction ability of Co in LDHs. This research not only developed the performing LDHs materials for F- removal, but also gave a deep insight in understanding how the atomic properties regulate the adsorption behavior of materials, which could potentially motivate a rational design of other adsorbents to promote the performance.