基于DFT研究Ca^(2+)取代对高岭石晶体结构及表面性质的影响

The effect of Ca^(2+) substitution on crystal structure and surface properties of kaolinite: A DFT study

为探索Ca^(2+)取代对高岭石晶体结构及表面性质的影响机制,构建了Ca^(2+)取代高岭石晶胞模型,并采用密度泛函理论方法对其进行键长、键角、能带结构及态密度、前线轨道、Fukui指数及电荷等分析.模拟结果表明:取代后晶胞导电性增强,同时反应活性更强,其中Na^(+)平衡构型比K+平衡构型更稳定;在(001)面及■面上,取代后高岭石表面反应活性增强,其中H1,O3位点反应活性增强,而水分子相较于■面更倾向于吸附在(001)面.结合表面电荷分布,取代高岭石(001)面电负性增强,同时Na^(+)与(001)面及■面均以静电作用为主.Ca^(2+)取代Al^(3+),使得晶体产生局部膨胀,周围晶格结构产生变化;同时取代后改变晶体轨道电子分布,轨道能量及电荷密度随之变化,最终改变反应活性.

In order to explore the influence mechanism of Ca^(2+)substitution on the crystal structure and surface properties of kaolinite,the cell model of Ca^(2+)substituted kaolinite was constructed,and the bond length,bond angle,band structure and density of states,surface frontier orbit,Fukui index and charge were analyzed by density functional theory. The simulation results show that after substitution,the cell conductivity is enhanced and the reaction activity is stronger. The Na^(+)equilibrium configuration is more stable than the K+equilibrium configuration. On the ■ planes,the surface reactivity of kaolinite after substitution is enhanced,in which the reactivity of H1 and O3 sites is enhanced,while water molecules tend to be adsorbed on the(001) plane more than on the ■ plane. Combined with the surface charge distribution,the electronegativity of substituted kaolinite(001) surface is enhanced,and the electrostatic interaction between Na^(+)and(001) surface or ■ surface is dominated. Ca^(2+)replaces Al^(3+),resulting in local expansion of the crystal and changes in the surrounding lattice structure. At the same time,the orbital energy and charge density change with the change of orbital electron distribution,and finally change the reaction activity.