The role of boron nitride nanotube as a new chemical sensor and potential reservoir for hydrogen halides environmental pollutants
Highlights
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Chemical reactivity of systems were predicted by DFT based descriptors.
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The positive value of ∇2ρ(r) in H
B and HN show the closed-shell interactions. - •
The Eg order is HCl/BNNT > HF/BNNT > HBr/BNNT.
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A potential reservoir for hydrogen halide gas based on BNNT was investigated.
Introduction
Pristine boron nitride nanotubes (BNNTs) were theoretical predicted in 1994 by Rubio et. al [1] and experimentally synthesis in 1995 by Chopra et. al [2]. Since then various promising applications of BNNTs have inspired broad researches in the field of nanotechnology [3], [4]. BNNTs consist co-axial hexagonal boron-nitride network. BNNTs with a Young's modulus of 1.18 TPa are stronger than carbon nanotubes (CNTs). BNNTs have ∼300 W/mK thermal conductivity and higher thermal oxidation resistant than CNTs and thus they are stable up to 1100○C in air [5]. As a type of one-dimensional nanostructures, they present high hardness, high mechanical resistance and specific surface, low density, thermal and chemical stability and heat and electric resistance [6]. Due to their uniform electronic properties, significant advantages of the armchair BNNT suggest various applications in electronic and mechanical devices [7], [8]. The noncytotoxic and biocompatible characteristics of these materials result in therapeutic and nanomedicine applications [9]. Unique properties of semiconducting BNNTs with constant bond gap are not sensitive to the chirality and the tube diameter which result in the controllable electronic properties [10]. For BNNT the polar BN bonds modify the adsorption properties of sidewall structures. Adsorption of small gases on the high reactive surface of BNNT have been reviewed [11].
Hydrogen halides which are encountered in industrial settings are often generated during the pyrolysis of various materials. Hydrogen fluoride is highly corrosive and penetrates living tissues, convert to hydrofluoric acid and cause blindness. The HX/BNNT system has an intermolecular hydrogen bonded structure where nitrogen atom is proton acceptor and the HX molecules are proton donors. Hydrogen bonds (HB) play important role in biological phenomena and chemical reactions. There are two specific features of HBs, Inter and interamolecular HB. Various methods were advised to estimate the HB energy determination. The geometry parameters of H-bonds illustrate the strength of this bond. The elongation of the proton donating bond is greater for stronger HB complexes. These geometrical changes are also observed in proton acceptors. Topological parameters have been applied to estimate the HB energy with electron density at the bond critical point and its Laplacian function. In this paper, we present the sidewall chemical reactivity of armchair (5,5) BNNT for the adsorption of hydrogen halide pollutant and toxic gases to predict the BNNT potential application in the chemical sensor.
Section snippets
Computational details
Theoretical calculations were performed using the Gaussian 09 program package [12]. Full geometry optimizations of equilibrium geometries, total energies and electronic densities were performed in the framework of DFT in conjugation with the B3LYP exchange correlation functional and 6-31G(d) basis set. Multiplicity value and the total charge of the investigated molecules were introduced as 1 and 0 respectively. Hydrogen halides adsorption on the (5,5) BNNT containing 45 boron, 45 nitrogen and
Structural properties
Fig. 1 shows the optimized geometry of pristine (5,5) BNNT model with their end saturated by hydrogen atoms. The average bond length of BN, and the diameter and the length of BNNT are 1.449 Å, 7.160 and 10.002 Å respectively. The free HF, HCl and HBr molecules achieved a linear structure with a H-X bond length of 0.947, 1.304 and 1.451 Å respectively. The optimized tube models with the hydrogen halide adsorbents are shown in Fig. 2. As can be seen both BNNT and HX molecules preserve their
Conclusion
A complete theoretical analysis of the structural and electronic properties of the armchair (5,5) BNNT model system for adsorption of HX (X=F,Cl, Br) on the tube surface in the gas phase were performed within the formalism of DFT. The adsorption energy values show that the HX molecules can be adsorbed on the surface of BNNT exothermically. Higher charge concentration on N than B atom would favor the N⋯H bond interaction for all complexes. The larger adsorption energy and ρ value for HF/BNNT
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