Nghiên cứu sự trao đổi và hấp phụ các cation kim loại trên bề mặt kaolinite từ lý thuyết phiếm hàm mật độ

Abstract

In this study, metal cations exchange and adsorption processes onto kaolinite surfaces are investigated using first-principles calculations. Obtained results indicate that the exchanges of cations are mostly unfavorable, and the Al sites are conveniently replaced compared to Si sites. The metal cations are adsorbed strongly onto kaolinite surfaces at both O-slab and H-slab. The adsorption ability of metal cations decreases in the order of Li⁺ > K⁺ > Na⁺ > Ca²⁺ > Al³⁺ > Fe³⁺ > Cr³⁺ > Mg²⁺ at the PBE functional. Remarkably, the insertions of Li⁺ and Mg²⁺ into the lattice structure of kaolinite are found at H-slab following the formation of Li-O and Mg-O new bonds, respectively. The intercalation into kaolinite by Ca²⁺ is observed in forming Ca-O bonds for both H-slab and O-slab. For Na⁺, K⁺, and Cr³⁺, the favorable attachment is located at the O-slab upon adsorption. Besides, the Al³⁺ and Fe³⁺ ions interact preferably on the H-slab. The analyses of the density of states and electron localization function clarify the appearance of M-O covalent bonds upon the adsorption process. Further, K⁺ is suggested as a promising addition to kaolinite surfaces for the efficient adsorption and removal of organic compounds in environments.