羟基钙在高岭石两种(001)晶面的吸附机理

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

利用基于密度泛函理论的平面波赝势方法,研究了羟基钙在高岭石2个不同的(001)面的吸附机理。研究结果表明,羟基钙在高岭石2个性质不同的(001)晶面均可发生稳定吸附,但在这2个表面,羟基钙的吸附机理不同。在铝氧羟基(001)面,羟基钙中钙离子有脱离羟基钙的趋势,羟基钙以氧原子与表面氢原子成键吸附为主,且在由表面3个H原子围成的穴位处最为稳定,同时与表面有较弱的静电作用;而在硅氧(001)面,羟基钙中钙原子与氧原子结合紧密,钙原子带有大量正电荷与荷负电底面以静电吸附方式结合,稳定作用于底面硅氧原子围成的十二元环中心处。在溶液环境中,水分子对羟基钙在铝氧(001)面吸附影响大而对硅氧(001)面影响较小。

The adsorption mechanisms of hydroxyl calcium on two（001） lattice planes of kaolinite were investigatedusing the DFT plane-wave pseudopotentials program. The calculation results indicate that the adsorption of hydroxylcalcium on two（001） surfaces with different nature could be achieved,but with different mechanism. In adsorption onthe Al（001） surface,the bond between Ca and O atoms of hydroxyl calcium becomes weaker and the Ca atom tendsto escape from the hydroxyl calcium. The main adsorption pattern is the bonding of the O atom of hydroxyl calcium andH atom of the Al（001） surface,and the most stable site is the threefold hollow enclosed by three H atoms;and alsohydroxyl calcium has a weak electrostatic interaction with Al（001） surface. In adsorption on the Si（001） latticeplane,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 adsorptionsite on the Si（001） surface is the twelve-fold hollow site consisted by Si and O atoms. In addition,there are obviouseffect of water on Al（001） surface and minor effect on Si（001） surface in aqueous system.