Adsorption of hydrated Al3+ on the kaolinite (001) surface: A density functional theory study
Adsorption of hydrated Al3+ on the kaolinite (001) surface: A density functional theory study
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DOI：
10.1016/j.clay.2022.106498
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发表时间：
2022-04-07
影响因子：
5.6
通讯作者：
Qiu, Tingsheng
中科院分区：
文献类型：
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作者：
Miao, Yuqi;Yan, Huashan;Qiu, Tingsheng
为了揭示高岭石表面离子稀土矿石中Al~(3+)杂质的微观赋存状态，采用密度泛函理论(DFT)建立了Al~(3+)在水体系中的稳定水合物模型。研究了水合物Al~(3+)在高岭石(001)表面的外层吸附和内层(单齿/双齿)吸附络合物的结构和键合机理。通过分子动力学模拟和吸附实验对DFT模拟结果进行了验证。结果表明，Al3+的稳定水合物形式为[Al(H2O)(6)](3+)。当水合Al~(3+)吸附在高岭石(001)表面外层时，Al~(3+)更倾向于吸附在Si-O表面。当水合Al3+吸附在高岭石(001)表面的内层时，Al倾向于与表面“直立”羟基脱质质子化形成的Ou原子成键，形成单齿吸附络合物，并与周围的5H2O保持配位；Al倾向于与表面“直立”和“卧倒”羟基脱质子化形成的Ou和Ol原子成键，形成双齿吸附络合物，由于空间位阻效应，Al只与周围的3H2O保持配位.分子动力学模拟结果验证了密度泛函理论计算的吸附构型的合理性。结合Mulliken布居、电荷密度和偏态密度(PDOS)分析表明，水合Al~(3+)单齿/双齿吸附络合物中的Al-Os键具有较强的离子性和较强的键填充性。水合Al3+优先在高岭石表面形成更稳定的双齿吸附络合物。吸附能的计算和吸附实验结果都支持这一结论。
In order to reveal the microscopic occurrence of Al3+ impurity in ionic rare earth ore on kaolinite surface, density functional theory (DFT) was used to construct the stable hydrate model of Al3+ in the water system. The structure and bonding mechanism of the complexes of outer layer adsorption and inner layer (monodentate/bidentate) adsorption of hydrate Al3+ on kaolinite (001) surface were studied. The DFT simulation results were verified by molecular dynamics (MD) stimulation and adsorption experiments. The results showed that the stable hydrate form of Al3+ is [Al(H2O)(6)](3+). When hydrated Al3+ is adsorbed on the outer layer of the kaolinite (001) surface, Al3+ is more inclined to be adsorbed on the Si-O surface. When hydrated Al3+ is adsorbed on the inner layer of the kaolinite (001) surface, Al tends to form a bond with Ou atoms formed by the deprotonation of the "upright " hydroxyl group on the surface to form monodentate adsorption complexes, and maintains coordination with the surrounding 5 H2O; Al tends to form bonds with the Ou and Ol atoms formed by the deprotonation of the "upright " and "lying " hydroxyl groups on the surface to form bidentate adsorption complexes, due to steric hindrance effect, Al only maintains coordination with the surrounding 3 H2O. The MD simulation results verified the rationality of the adsorption configuration calculated by DFT. Combined with Mulliken population, charge density and partial density of state (PDOS) analysis, it is shown that the Al-Os bond in the monodentate/ bidentate adsorption complex of hydrated Al3+ has the characteristics of strong ionicity and strong bond filling. The hydrated Al3+ preferentially forms a more stable bidentate adsorption complex on kaolinite surface. Both the calculation of adsorption energy and the results of adsorption experiments support this conclusion.