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

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2023-01, Vol.452, p.139400, Article 139400
• Main Authors: Liu, Fansong, Wan, Lei, Wang, Haiying, Zhong, Cheng, Min, Xiaobo, Zhang, Liyuan
• Format: Article
• Language: English
• Subjects: Al-based LDHs; chemical environment of Al; Cobalt; Density functional theory; F- adsorption mechanism; π-donation
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2022.139400

•A weak-ligand chemical environmental around Al3+ in Al-based LDHs was built;•Co is an excellent ability to improve the F- adsorption performance of Al-based materials;•Co element in Co2Al-LDHs acts as the electron acceptor from F-;•Co element in Co2Al-LDHs promotes the electron-attraction ability of Al3+ with π-donation on Co-O bond. 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.