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 Eg 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.