Adsorption and diffusion of Pb(II) on the kaolinite(001) surface: A density-functional theory study

•We investigate the adsorption and diffusion of Pb(II) on kaolinite(001) surface.•The most stable adsorbed site for Pb(II) is the bridge site.•Increasing the coverage will increase the adsorption energy in Θ ≤ 1.•The Pb(II) atoms are easy to diffuse on kaolinite(001) surface.

The adsorption and diffusion of Pb(II) atom on the hydroxylated (001) surface of kaolinite were investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics was systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites was the two-fold bridge site followed by the one-fold top site, and the adsorption energy increased with the coverage, thus indicating the higher stability of surface adsorption and a tendency to the formation of Pb(II) islands (clusters) with increasing coverage. Moreover, the energy barrier for diffusion of Pb(II) atom between the one-fold top and the two-fold bridge adsorption sites on kaolinite(001) surface was 0.23 (0.31) eV, implying that the Pb(II) atom is prone to diffusing on kaolinite(001) surface. The other properties of the Pb(II)/kaolinite(001) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.