Sc- and Ti-doped silicon carbide nanotubes for NH3 sensing and storage applications: a DFT approach

Ammonia (NH₃) is highly hazardous gases, thus the investigation for a highly sensitive sensor of NH₃ molecule is desirable. The adsorptions of NH₃ molecule on Sc and Ti atoms doped silicon carbide nanotube (SiCNT) were investigated by using density functional theory calculation. The adsorption energies, adsorption distances, energy gaps, chemical hardness and softness, orbital distributions, charge transfers and density of states were examined. The calculated results display that NH₃ molecules can be adsorbed on the pristine SiCNT via a weak physical interaction, which is much weaker than those of NH₃ adsorption on Sc and Ti-doped SiCNTs. All of Sc and Ti-doped SiCNTs can absorb single and multiple NH₃ molecules with the greatest adsorption energy of − 41.56 kcal/mol for NH₃/Ti_Si–SiCNT system. In addition, there are shorter adsorption distance and larger charge transfer for Sc- and Ti-doped SiCNTs than that of pristine SiCNT with NH₃ molecule. The orbital distributions are occurred around the doping site may be due to the strong interaction between NH₃ and SiCNT. The energy gaps of Sc- and Ti-doped SiCNTs have much more significant change than that of pristine SiCNT in which 2NH₃/Ti_C–SiCNT show the largest change of energy gap about 22% compared with bare Ti_C–SiCNT. The density of states of Sc- and Ti-doped SiCNTs show significant shift than that of pristine SiCNT which the new impurity states near the − 2.5 eV is occurred. The chemical hardness and softness illustrate the enhancement stability and decreased the reactivity. A short recovery times and suitable desorption temperatures are observed for the NH₃ desorption on Sc- and Ti-doped SiCNT surface. Therefore, sensitivity to NH₃ molecule of Sc- and Ti-doped SiCNTs is a promising candidate for highly sensitive gas sensing and storage nanomaterials.

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