The effects of transitional metal element doping on the Cs(I) adsorption of kaolinite (001): A density functional theory study

Highlights: • The effects of Ag, Pd, Rh, Tc, Zn, and Zr doping on the structures of kaolinite were analyzed by DFT. • Zn-kaolinite has the highest adsorption energy for cesium in all systems. • Some of the key factors that controlling the interactions between Cs and kaolinites are identified. The adsorption of cesium on kaolinite has been extensively studied because this clay mineral is particularly important for the fixation and migration of cesium in the environment. Doping kaolinite with atoms of different elements lead to defects in the internal crystal, which change the physical and chemical properties of kaolinite. In this work, we utilized density functional theory (DFT) calculations to explore the change in electronic structures of kaolinite before and after the elemental substitution of Al by Ag, Pd, Rh, Tc, Zn, and Zr. Then, the interactions between Cs and pristine or doped kaolinites (0 0 1) were systematically investigated by analysing the adsorption energy (E_ads), electron transfer and density of states. Redundancy analysis (RDA) was used to study the key factors that affect the adsorption energy of kaolinite/Cs. The results show that the distance from Cs atoms to the kaolinite (0 0 1) surface and the number of transferred charges after adsorption of Cs atoms are significantly related to the adsorption energy of the system. The results of a Pearson correlation analysis also verified the reliability of this conclusion. All findings in this work are expected to be significant to the development and utilization of clay minerals as host materials for radioactive metal adsorbents.