Investigation of the Structural, Electronic, Optical and Photocatalytic Properties of Two-Dimensional MXene Nanostructures in order to Using in Water Splitting Process by Density Functional Theory Method

In this study, the structural, electronic, optical, and photocatalytic properties of two dimensional (2D) Hf2CO2, Hf2CS2, and Hf2NO2 MXenes nanostructures were investigated by density functional theory (DFT) calculations. These computations were used with GGA-PBE and HSE06 functionals. The unit cell of these three structures and their atomic positions are fully optimized. The results show that the lattice constants for these nanostructures are 3.3592, 3.4026 and 3.2378 Aͦ, respectively. Using calculations GGA-PBE functional, only nanostructure Hf2CO2 is semiconductor with a band gap 0.92 eV and the two nanostructures Hf2CS2 and Hf2NO2 are metal. So we did the calculations with a HSE06 hybrid functional, too. Hence the nanostructure Hf2CS2 changed from metal to semiconductor. The computed band gaps in HSE06 hybrid functional for nanostructures Hf2CO2 and Hf2CS2 were 1.75 and 0.22 eV, respectively. The results obtained in this study are in good agreement with other previous studies. The results show the overall form of band structures is independent of the functional. The distance between conduction and valence bands is the band gap, which is the main difference in calculating the band structure using two functionals. In this study, the band gap difference calculated by these functionals for Hf2CO2 and Hf2CS2 nanostructures is 0.83 and 0.22 eV, respectively. The real and imaginary parts of the dielectric function have been calculated to investigate the optical properties of these nanostructures. We show that the Hf2CO2 nanostructure has high absorption in visible and ultraviolet regions. Thus Hf2CO2 nanostructure may apply in designing optoelectronic devices.