Investigating the Influence of Impurity Defects on the Adsorption Behavior of Hydrated Sc 3+ on the Kaolinite (001) Surface Using Density Functional Theory.

In natural kaolinite lattices, A l 3 + can potentially be substituted by cations such as M g 2 + , C a 2 + , and F e 3 + , thereby influencing its adsorption characteristics towards rare earth elements like S c 3 + . Density functional theory (DFT) has emerged as a crucial tool in the study of adsorption phenomena, particularly for understanding the complex interactions of rare earth elements with clay minerals. This study employed DFT to investigate the impact of these three dopant elements on the adsorption of hydrated S c 3 + on the kaolinite (001) Al-OH surface. We discerned that the optimal adsorption configuration for hydrated S c 3 + is S c (H 2 O) 8 3 + , with a preference for adsorption at the deprotonated Ou sites. Among the dopants, Mg doping exhibited superior stability with a binding energy of −4.311 eV and the most negative adsorption energy of −1104.16 kJ/mol. Both Mg and Ca doping enhanced the covalency of the Al-O bond, leading to a subtle shift in the overall density of states towards higher energies, thereby augmenting the reactivity of the O atoms. In contrast, Fe doping caused a pronounced shift in the density of states towards lower energies. Compared to the undoped kaolinite, Mg and Ca doping further diminished the adsorption energy of hydrated S c 3 + and increased its coordination number, while Fe doping elevated the adsorption energy. This study offers profound insights into understanding the role of dopant elements in the adsorption of hydrated S c 3 + on kaolinite. [ABSTRACT FROM AUTHOR]