Layer Thickness-Dependent Electronic and Mechanical Properties of Two-Dimensional Kaolinite Nanosheets

Layer thickness is an important parameter for regulating the electronic and mechanical properties of two-dimensional (2D) materials. However, the relationship between layer thickness and properties of layered clay minerals has not been fully studied yet. In this work, the influence of layer thickness on the properties of 2D kaolinite nanosheets was investigated by using GGA functional (PBE), hybrid functional (HSE06), and density functional-based tight-binding (DFTB) calculations. It is found that the nanosize effect leads to the increase of the interlayer spacing Δd and the elongation of the Al-O bond at the outmost surface of the kaolinite nanosheet, and the band gap E_g decreases with increasing layer thickness. The electronic local functions and orbital distributions indicate that as the layer thickness increases, the region above the AlO layer will exhibit some delocalized electrons. Furthermore, the 2D effective Young's modulus increases linearly with the increase in layer thickness, while the 3D Young's modulus decreases as the layer thickness increases. The reduction in the thickness will result in significant changes in the surface activity, electronic delocalization, band structure, and mechanical properties of kaolinite nanosheets. This could provide a theoretical basis for the functionalization design of 2D clay minerals at the atomic level.