Adsorption mechanism of hydroxyl calcium on two kaolinite (001) surface

The adsorption mechanisms of hydroxyl calcium on two (001) lattice planes of kaolinite were investigated using the DFT plane-wave pseudopotentials program. The calculation results indicate that the adsorption of hydroxyl calcium on two (001) surfaces with different nature could be achieved,but with different mechanism. In adsorption on the Al (001) surface,the bond between Ca and O atoms of hydroxyl calcium becomes weaker and the Ca atom tends to escape from the hydroxyl calcium. The main adsorption pattern is the bonding of the O atom of hydroxyl calcium and H atom of the Al (001) surface,and the most stable site is the threefold hollow enclosed by three H atoms;and also hydroxyl calcium has a weak electrostatic interaction with Al (001) surface. In adsorption on the Si (001) lattice plane,the Ca and O atoms bond closely in hydroxyl calcium. The bonding of electrostatic adsorption of Ca atom posses- sing large positive charge on the Si (001) surface which is negative charge is achieved,and the preferred adsorption site on the Si (001) surface is the twelve-fold hollow site consisted by Si and O atoms. In addition,there are obvious effect of water on Al (001) surface and minor effect on Si (001) surface in aqueous system.