Elsevier

Computational Materials Science

Volume 82, 1 February 2014, Pages 197-201
Computational Materials Science

Hydrogen fluoride on the pristine, Al and Si doped BC2N nanotubes: A computational study

https://doi.org/10.1016/j.commatsci.2013.09.058Get rights and content

Highlights

  • Electronic sensitivity of a BC2N nanotube to a HF molecule was studied by DFT.

  • HF prefers to be weakly adsorbed on the tube with the adsorption energy of 23.1 kcal/mol.

  • Al and Si dopings into the wall of the tube increase the reactivity of the tube toward the HF.

  • Unlike Al doping, Si doping significantly enhances sensitivity of the tube to HF.

  • Si-doped BC2N nanotube can convert the presence of HF molecules to electrical signal.

Abstract

We investigated the electronic sensitivity of a BC2N nanotube to a HF molecule by density functional calculations at B3LYP (augmented with an empirical dispersion term) level of theory. It was found that the HF molecule prefers to be weakly adsorbed on the tube with the adsorption energy of 23.1 kcal/mol and without significant effect on its electronic properties. Al and Si dopings into the wall of the tube increase the reactivity of the tube toward the HF molecule, so that calculated adsorption energies are about 92.8 and 73.0 kcal/mol, respectively. Contrary to the Al doping, the Si doping significantly enhances the electronic sensitivity of the tube to the HF molecule. We believe that Si-doped BC2N nanotube can convert the presence of HF molecules to an electrical signal which will be useful in the detection process.

Introduction

Carbon exists in several forms in nature and one of the carbon allotropes is carbon nanotubes (CNTs) with cylindrical form that discovered in 1991 by Iijima [1]. CNTs have novel properties, making them potentially useful in many applications in nanotechnology, nanoelectronics, optics, and other fields of materials science [2], [3]. Nanotube-based electronic devices, such as diodes, transistors, or field emitters, rely on modifications of the electronic properties of CNTs caused by mechanical deformations, doping or topological defects. Substituting CNTs with other elements like B, N can tune their electronic properties efficiently and lead to novel applications [4]. The BC2N stoichiometry is believed to be one of the most stable forms of the ternary BCN layers and nanotubes [5]. Bariele et al. have investigated theoretically stability and hydrogen adsorption properties of BC2NNT [6], [7]. Considerable experimental and theoretical efforts have been devoted to the synthesis of BC2NNTs, and they have been successfully obtained by electrical pyrolysis, laser ablation, hot-filament chemical vapor deposition, and the template route [8], [9], [10], [11].

Nowadays, it is essential to be able to quickly analyze and control the surrounding atmosphere in order to prevent the possible risks of pollution. With this in mind, many groups decided to work on the development of gas sensors for measuring toxic chemical compounds. Nanotubes exhibit potential applications in this field because of their unique properties such as high surface to volume ratio. Basically, it is expected that the adsorption of gas molecules on the sensors is stable and conductivity changes should be observable. However, most of gases are found physisorbed on suspended intrinsic nanotubes [12], [13], [14]. On the contrary, the dopants and defects in nanotubes can strongly enhance the adsorption of molecules [15], [16], indicating that doped atoms and defects play important roles in their applications. Peyghan et al. [17] have investigated adsorption mechanisms of hydrogen cyanide on modified BC2NNT, including aluminum doping and double anti-site defect using density functional theory (DFT). It was found that the BC2NNT with double anti-site defect is more sensitive than perfect tube for detecting hydrogen cyanide.

In the present work, within the DFT framework, the interaction of hydrogen fluoride (HF) with BC2NNTs will be investigated based on analyses of structure, energies, electronic properties, etc. Among the dangerous chemical compounds for both human and the environment, one can distinguish HF. HF is involved in a very specific chemical process and it can be released in the atmosphere [18]. In this case, it is essential to be able to quickly analyze this molecule in order to prevent the possible risks of pollution. It is also a degradation product from fire suppression systems that use Halon 1301 (bromotrifluoromethane) and Halon 1211 (bromochlorodifluoromethane) as fire suppression agents [18]. We are interested in whether there is a possibility of BC2NNTs serving as a chemical sensor to HF molecule, and if not, can we find a method to improve the sensitivity of BC2NNTs to HF?

Section snippets

Computational methods

We selected a (8,0) BC2NNT consisted of 32 B, 32 N and 64 C atoms, in which the end atoms have been saturated with hydrogen atoms to reduce the boundary effects. Geometry optimizations, energy calculations, natural bond analysis (NBO) and density of states (DOS) analysis have been performed on BC2NNT and different HF/BC2NNT complexes using B3LYP functional augmented with an empirical dispersion term (B3LYP-D) with 6-31G (d) basis set as implemented in GAMESS suite of program [19]. GaussSum

Pristine BC2NNT

In Fig. 1a, we have shown the optimized structure of BC2NNT, where four types of bonds, namely B–N, B–CI, N–CII and CI–CII, can be identified, with corresponding lengths of 1.46, 1.52, 1.44 and 1.36 Å, respectively. CI is a carbon atom that is bonded to two B atoms and one C atom, while CII is bonded to two N atoms and one C atom. Buckling of B–N and C–C bonds was found in the wall of the tube. After optimization, this buckling moves N atoms slightly inward and B atoms outward of the nanotube

Conclusion

The adsorption of a HF molecule on the pure, Al- and Si-doped BC2NNTs was investigated using DFT calculations. It is found that HF molecule is adsorbed on the boron atom of pristine nanotube from its F head with Ead of 23.1 kcal/mol. The electronic properties of the pristine BC2NNT induce a very limited change after the adsorption of HF molecule. However, the HF molecule shows strong interactions with the Al- and Si-doped tubes. The larger adsorption energies and charge transfers of HF on the

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