Adsorption of cyanogen chloride on the surface of boron nitride nanotubes for CNCl sensing

Adsorption of cyanogen chloride on the surface of boron nitride nanotubes for CNCl sensing

Chemical Physics Letters 700 (2018) 7–14 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locat...

2MB Sizes 0 Downloads 32 Views

Chemical Physics Letters 700 (2018) 7–14

Contents lists available at ScienceDirect

Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett

Research paper

Adsorption of cyanogen chloride on the surface of boron nitride nanotubes for CNCl sensing Tayebeh Movlarooy ⇑, Mahboobeh Amiri Fadradi Faculty of Physics and Nuclear Engineering, Shahrood University of Technology, Shahrood, Iran

a r t i c l e

i n f o

Article history: Received 11 January 2018 In final form 2 April 2018 Available online 3 April 2018 Keywords: Boron nitride nanotube CNCl molecule Density functional theory Adsorption Sensor

a b s t r a c t The adsorption of CNCl gas, on the surface of boron nitride nanotubes in pure form, as well as doped with Al and Ga, based on the density functional theory (DFT) has been studied. The electron and structural properties of pristine and doped nanotubes have been investigated. By calculating the adsorption energy, the most stable positions and the equilibrium distance are obtained, and charge transferred and electronic properties have been calculated. The most stable molecule adsorption position for pure nanotube is obtained at the center of the hexagon and for doped nanotube above the impurity atom from N side. Ó 2018 Elsevier B.V. All rights reserved.

1. Introduction Today sensors have a relatively high sensitivity and are capable of detecting small amounts of gas, heat, or radiation. Efforts have been made to improve the efficiency of the sensors, which include researchers on new materials, especially nanoscale structures, including nanotubes, nanomiles, nanobelts and nanowires [1–3]. Nanosensors are very important for their small size and nanometric dimensions, along with high degree of accuracy and reactivity, so that they even react in the presence of few atoms of a gas and are able to detect and respond to physical nanoscale stimuli. Nanosensors are also used to detect toxins, drugs, mines buried in ground, explosives, and nanoparticles in the air [4]. Sensors made from single-walled nanotubes have high sensitivity and have a low reaction time at room temperature. Cyanogen Chloride (CNCl), known as CK, is a colorless and highly toxic gas. The molecule of this gas contains three atoms C, N and Cl, which are linearly coupled with the covalent triple (C, N) and single (Cl, C) covalent bonds. Contact with water or moist air can produce flammable and/or toxic gases. CK is used in chemical warfare applications and is very toxic to the blood. It also causes respiratory failure and metabolic obstruction in the human body and animals. CNCl, after contact with the eyes or respiratory organs, causes immediate damage and decomposes rapidly in the human body [5]. Symptoms include sleepiness, runny nose, sore throat, cough, dizziness, nausea, seizure, paralysis, and death. ⇑ Corresponding author. E-mail address: [email protected] (T. Movlarooy). https://doi.org/10.1016/j.cplett.2018.04.001 0009-2614/Ó 2018 Elsevier B.V. All rights reserved.

Prolonged exposure may result in pulmonary edema. May cause damage to red blood cells and central nervous system. Cyanogen chloride is a flammable gas it may polymerize with the evolution of heat. It has a permissible exposure limit (PEL) of 0.6 mg/m3. Research has acknowledged that this gas is heavily influenced by the filter masks. A group of researchers studied the absorption of this gas on the surface of aluminum nitride nanotubes using DFT calculations [6]. Boron nitride nanotubes (BNNTs) have attracted particular attention in nanotechnology and optoelectronics applications [7–9]. For the first time, boron nitride nanotubes were predicted through theoretical calculations in 1994 [10] and the successful synthesis of these nanotubes was reported in 1995 [11]. Depending on the diameter of the tubes and chirality, Carbon nanotubes can be conductors or semiconductors [12–15], whereas boron nitride nanotubes have a large band gap that has a weak dependence on the diameter, chirality, and number of pipe walls and all kinds of them are semiconductors with band gap of about 5–6 eV [5]. One of the unique properties of BNNTs is its tensile strength, rigidity, and deformability; it also has unique physical properties and morphology, chemical stability, acid-alkaline resistance, and high oxidation resistance. All of these factors make BNNTs applicable in environments with oxidizer materials and high temperatures. One of the special uses of this material is radiation protection, multifunctional materials for energy storage, environmental protection, nuclear industry, sensors, external body of spaceships and medicine. In recent year’s different DFT calculation were performed to investigate the effect of nanotubes diameter on the adsorption

8

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14

energy, when the gas molecules adsorbed the surface of the nanotubes. Alireza Soltani, et al. [16] were performed DFT calculation to evaluate the ability of (8, 0), (10, 0) and (4, 4) BN nanotubes with different diameters as CNCl sensor. their results revealed that the length and diameter of tube have not significant effect upon the adsorption process. Maziar Noei and coworkers [17] have investigated the adsorption properties of CH3COOH on carbon nanotubes with different diameters they concluded that more efficient adsorption energies cannot be achieved by increasing the nanotube diameter. Peng Shao, et. al [18] investigated the CO2 molecule adsorption on a series of (n, 0) zigzag (n = 6, 8, 10, 12 and 14) Aldoped BNNT by DFT calculations. They found that the CO2 adsorption energies on Al-doped BNNT are almost independent of BNNT diameters. A. H. Javid and his coworker [19] studied chemical adsorption behavior of benzene on single-walled carbon nanotubes (9, 9) and (7, 7) in the gas phase by using DFT. They found that CNT (7, 7) with smaller diameter is more effective than (9, 9) in absorbing and removing benzene from the air. Alireza Soltani, et. al [6] investigated the influence of cyanogen chloride adsorption over the electronic properties of (5, 0), (8, 0), and (10, 0) AlN nanotubes. Their results revealed that AlN nanotube with smaller diameter would be more effective as adsorbent for adsorption of CNCl molecule. A. A. El-Barbary, and coworkers [20] studied adsorption of different gas molecules on (5, 0), (9, 0), (5, 5) and (6, 6) BNNTs, applying the DFT. They concluded that the best BNNT for adsorbing the CO2, CO, NO2 and NO gas molecules is (5, 0) BNNT. Motivation to these studies, in this research, we intend to simulate the CNCl nanosensor based on small diameter zigzag (6, 0) and armchair (3, 3) boron nitride nanotubes using the density functional theory (DFT).

2. Calculation method In this research, the adsorption of CNCl gas molecule, on singlewalled zigzag boron nitride (6, 0) and armchair (3, 3) nanotubes in pure form, as well as doped with Al and Ga, has investigated by using the density functional theory (DFT) [21,22] with SIESTA computational code [23]. To calculate the interaction between valence electrons and atomic nuclei, the pseudo-potential approximation is used, and for calculating the exchange- correction function, the generalized gradient approximation of Perdew-Burke-Ernzerh (GGA-PBE) [24,25] has been used. Although it is well-known that GGA/PBE underestimate the band gap and HSE method is more accurate. But the main focus of this study is the variation of the band gap due to the adsorption, so due to the high cost of HSE we used GGA approximation. However, in recent years, vast researches have been used GGA approximation to investigate gas molecule absorption on the surface of nanostructures [26–36]. The Kohn-Sham orbitals are expanded in linear combinations of atomic orbitals (LCAO) of finite range, using double zeta polarization (DZP) basis sets. The sampling for the Brillouin zone integrations is performed using the Monkhorst-Pack Scheme with a regular k-point grid of 1  1  100 and the optimized mesh cutoff energy was set around 500 Ry. A vacuum space of about 10 Å is used in the lateral directions of nanotubes to avoid the interatomic interactions. The adsorption energy has been calculated according to the following equation [9,37,38]:

Eads ¼ Enanotubeþmolecule  Enanotube  Emolecule

3. Results and discussion Initially, to study BNNTs as CNCl gas nanosensors, we simulate and discuss the best adsorption positioning of CNCl gas molecules on the surface of BNNTs, and then investigate the effect of adsorption of the molecule on the structural and electronic properties of the nanotubes. The Gauss View software [39] was used to model the molecular adsorption on the nanotube surface. The typical active positions for adsorption of the molecule on the nanotube surface are shown in Fig. 1. Now, in order to find the best position and the best adsorption equilibrium distance, we need to consider each of these situations. To absorb the CNCl molecule on the surface of both types of nanotubes, the molecule must get near from the side of the atoms N and Cl to the nanotube surface at different positions. Because the molecule of CNCl is geometrically linear, we examine its adsorption on the surface of the nanotubes in both horizontal and vertical states. Fig. 2 shows some configuration of the simulation of the adsorption of CNCl molecules in different positions on the surface of both nanotubes. In all of these cases, the molecular distance from the nanotube surface changes from 0.5 to 4 Å. In order to obtain the adsorption energy, according to Eq. (1), we must calculate the energy of the molecule and the desired surface separately before absorbing it, and subtract it from total energy of the gas-surface to obtain the amount of adsorption energy. The amount of adsorption energy for various distances, from 0.5 to 4 Å, to the nanotube surface at different positions is obtained with the GGA approximation. The results for both (3, 3) and (6, 0) nanotubes when the CNCl molecule approach to the surface of the nanotube in both horizontal and vertical state, are plotted in Figs. 3–6 and the most stable state for each configuration is summarized in Table 1. As shown in Table 1 and diagrams, the most stable state of CNCl molecule adsorption on both zigzag (6, 0) and armchair (3, 3) nanotubes and for horizontal and vertical states is positions 7 and 8 respectively which is on the hexagonal center when the molecule from the side of Cl and N atoms is approaching the hexagonal center. The optimized distance of the molecule relative to the surface of the nanotube for the horizontal and vertical states is 3 and 2.5 Å from the center of the hexagon respectively. The obtained results are comparable to the previous similar works [6,40,41]. Regarding the calculated adsorption energy in a steady state, it is observed that the adsorption energy values on both types of nanotubes are in the vertical stateless (negative) than the parallel state, which indicates that the system is more stable in these situations. Also, the amount of adsorption energy for the zigzag nanotube is less than that of the armchair, which indicates the greater stability of the zigzag nanotube compared to the armchair after adsorption of the CNCl molecule. So adsorption of CNCl

ð1Þ

where Eads is absorption energy, Enanotube + molecule is the total energy of the nanotube and the absorbed gas, Enanotube is the total energy of the nanotube in the absence of gas and the Emolecule is the total energy of the gas molecule in the absence of the nanotubes.

Fig. 1. Shows four configurations (active positions) for adsorption of CNCl gas molecule on the surface of the BNNT: 1- above the atom B. 2- above the atom N. 3on the bisector of the B–N bond. 4- above the hexagonal center of the BNNT.

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14

9

Fig. 2. Some configurations of CNCl adsorption on the surface of BNNT: a- the molecular axis is perpendicular to the nanotube axis; b) the molecular axis is parallel to the nanotube axis. The adsorption of the molecule in both parts is as follows: 1- above the atom B from the Cl side. 2- above the B from the N side. 3- above the atom N from the Cl side. 4- above N from the N side. 5- on the bisector of the B–N bond from the N side. 6- on the bisector of the B–N bond from the atom Cl side. 7- above the hexagonal center from Cl side. 8- above the hexagonal center from N side.

Fig. 3. Adsorption energy of the CNCl molecule on the surface of (6, 0) BNNT in terms of distance from its surface at different positions in the horizontal state (curves 1 to 8 related to different positions which described in Fig. 2).

Fig. 4. Adsorption energy of the CNCl molecule on the surface of (6, 0) BNNT in terms of distance from its surface at different positions in the perpendicular state.

molecule on the zigzag nanotube is stronger than absorption on the armchair nanotubes. As it’s shown, the amount of adsorption energy for both types of nanotubes is very small. On the other hand, after adsorption we did not see any bond between the molecule and the surface of the nanotubes, so the small amounts of adsorption energy, as well as the lack of bond between the molecule and the surface of the nanotubes indicates that adsorption of CNCl molecules on the surface of pure boron nitride nanotubes

is a physical adsorption and there is no strong bond that indicates the chemical adsorption of the molecule on the nanotube surface. The results of the tables and figures well indicate when the molecule of CNCl is far away from the surface of the nanotube, the position of the molecule relative to the surface of the nanotube does not have an effect on the energy of the system. This explanation shows that in nature, when the CNCl molecule approaches the surface of the BNNT, it gradually moves to the steady state, from

10

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14

Fig. 5. Adsorption energy of the CNCl molecule on the surface of (3, 3) BNNT in terms of distance from its surface at different positions in the horizontal state.

Fig. 6. Adsorption energy of the CNCl molecule on the surface of (3, 3) BNNT in terms of distance from its surface at different positions in the perpendicular state.

whatever state it is, to the stable position, the center of the hexagonal ring. In the following, we investigate the effect of adsorption of CNCl gas molecule on the structural and electronic properties of BNNTs. The band structure for the zigzag (6, 0) and armchair (3, 3) BNNTs before and after adsorption of CNCl molecule is shown in Fig. 7. It is observed that both types of zigzag and armchair BNNTs are a semiconductor, the zigzag (6, 0) nanotube with a direct band gap of 2.677 eV and armchair (3, 3) with an indirect band gap of 4.224 eV. Comparing the band structure of BNNTs before and after adsorption, we find that the band gap has changed rarely after adsorption. A number of bands have been added at the top and bottom of the Fermi level, which indicate the hybridization of the orbitals of the molecules with nanotube after adsorption. In Table 2, the difference in the minimum energy level of the conduction band and the Fermi energy (EC  EF) and the maximum energy level of the valence and the Fermi energy (EF  EV), the Fermi energy, the value and type of band gap for all of the considered stable structures have been reported. The energy units are in terms of the electron volt (eV). According to the reported results in Table 2, we see some changes in the Fermi energy level of both nanotubes after adsorption of the molecules. The low adsorption energy obtained for the stable structures, the limited charge transfer and the negligible band gap changes all represent the physical adsorption between the nanotubes and the molecules. In order to achieve better results, we doped the zigzag (6, 0) BNNT with Al and Ga atoms and again studied the effect of CNCl gas adsorption in the vertical state. One of the B atoms in the hexagonal ring of the nanotube is replaced with the Al and Ga impurity atoms as shown in Fig. 8. The formation energy for Aldoped and Ga-doped (6, 0) BNNT is obtained 127.28 and 104.29 eV respectively, which indicate these doped systems are stable. Then close the CNCl molecules in the vertical state to the surface of the doped nanotube and by finding the most stable

Table 1 Adsorption energy of the CNCl molecule on the surface of (6, 0) and (3, 3) BNNTs in terms of its distance from the surface at different positions (as described in Fig. 2) for the most stable state. Adsorption energy (eV) [distance (Å)] Positions configuration

1

(6, (6, (3, (3,

0.312 0.227 0.314 0.251

0)BNNT + Horizontal CNCl 0)BNNT + Vertical CNCl 3)BNNT + Horizontal CNCl 3)BNNT + Vertical CNCl

2 [2.5] [3.0] [3.0] [3.0]

0.118 0.391 0.410 0.311

3 [3.0] [2.5] [3.0] [2.5]

0.307 0.326 0.360 0.313

4 [3.0] [3.0] [3.0] [3.0]

0.322 0.239 0.360 0.198

5 [3.0] [3.0] [3.0] [3.0]

0.404 0.261 0.217 0.330

6 [3.0] [3.0] [3.0] [2.5]

0.383 0.285 0.196 0.279

7 [3.0] [3.0] [3.0] [3.0]

0.438 0.277 0.470 0.421

8 [3.0] [2.5] [3.0] [3.0]

0.127 0.523 0.350 0.475

[3.0] [2.5] [3.0] [2.5]

Fig. 7. Band structure of a) (6, 0) BNNT before adsorption, b) (6, 0) BNNT after adsorption of CNCl, c) (3, 3) BNNT before adsorption, d) (3, 3) BNNT after adsorption of CNCl and e) CNCl molecule.

11

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14 Table 2 The band gap and the Fermi level of the BNNTs before and after adsorption of the CNCl molecule (D = direct and ID = indirect band gap). Structure

Fermi level

EC  EF (eV)

EF  EV (eV)

Band gap (eV)

(6, (6, (3, (3,

4.316 3.239 2.7628 2.472

1.375 0.822 1.412 1.358

1.302 1.806 2.812 2.822

2.677 2.628 4.224 4.180

0) 0) 3) 3)

BNNT BNNT + CNCl BNNT BNNT + CNCl

Fig. 8. A sample simulation of CNCl molecule adsorption on the surface of doped zigzag (6, 0) BNNT.

Fig. 9. The hexagonal ring which is in front of the adsorbed CNCl.

D D ID ID

adsorption state, we examine their electronic properties. As in the previous section, we simulate and discuss the best adsorption positioning of CNCl gas molecules on the surface of doped BNNT and change its distance from 0.5 to 4 Å to obtain the best stable adsorption position and then investigate the effect of adsorption of the molecule on the structural and electronic properties of the doped nanotube. The optimized structural geometries of all considered stable systems, after and before CNCl adsorption has calculated. As shown in Fig. 9 the optimized B–N bond lengths and hexagonal angels of the ring which is in front of the adsorbed CNCl, are summarized in Tables 3 and 4. As shown, the average B–N bond lengths and hexagonal angels approximately increase after doping and molecule adsorption. The adsorption energies in terms of CNCl distances for Al and Ga doped BNNTs are plotted in Figs. 10 and 11 and for the most stable state is reported in Table 5. The energy variation trend in terms of CNCl molecule distance in doped BNNTs is similar to its trend in pure nanotubes. The lowest value of obtained adsorption energy indicates the most stable adsorption position. This stable position for absorption of CNCl molecule is when the N atom of the CNCl molecule approaches Al atom at distance of 2 Å and Ga atom at 2.5 Å. We calculated the charge transfer value between the molecule and the nanotube surface for all stable systems. In Table 6, the amount of adsorption energy, the amount of charge transfer, the equilibrium distance between the molecule and the surface of the nanotube, and the position of the most stable adsorption systems have been reported. As it clears from Table 5, the most stable adsorption position for doped BNNTs is the state in which the CNCl molecule is located on the Al and Ga impurity atoms. Adding impurity disturbs

Table 3 Optimized structural geometries of all considered stable systems, lattice constant (C), B–N bond lengths (d), all parameters are in angstrom (Å). System

C

d1-2

d2-3

d3-4

d4-5

d5-6

d6-1

Average d

(6, (6, (6, (6, (6, (6, (3, (3,

12.940 12.949 13.010 12.400 13.023 12.400 12.522 12.577

1.461 1.475 1.468 1.456 1.467 1.457 1.461 1.476

1.464 1.428 1.801 1.833 1.888 1.919 1.460 1.458

1.464 1.529 1.764 1.891 1.834 1.861 1.455 1.531

1.441 1.529 1.463 1.453 1.462 1.453 1.460 1.531

1.463 1.428 1.486 1.452 1.487 1.482 1.460 1.458

1.464 1.475 1.467 1.467 1.471 1.471 1.453 1.476

1.451 1.477 1.575 1.579 1.601 1.607 1.458 1.487

0) 0) 0) 0) 0) 0) 3) 3)

BNNT BNNT + CNCl Al-BNNT Al-BNNT + CNCl Ga-BNNT Ga-BNNT + CNCl BNNT BNNT + CNCl

Table 4 Optimized hexagonal angels for all considered stable systems, angles are in degrees. System

1-2-3 B-N-B

2-3-4 N-B-N

3-4-5 B-N-B

4-5-6 N-B-N

5-6-1 B-N-B

6-1-2 N-B-N

Average angel

(6, (6, (6, (6, (6, (6, (3, (3,

110.536 120.285 109.150 113.986 108.349 111.904 119.187 118.134

120.070 116.212 113.491 108.185 112.906 108.579 119.007 118.951

118.012 110.662 114.122 117.603 112.503 115.227 119.187 111.522

117.768 116.172 122.677 122.474 124.310 124.218 111.444 118.833

118.011 120.312 123.880 122.481 125.300 124.158 118.992 111.516

120.060 108.636 121.995 122.414 122.957 123.411 111.445 119.177

117.412 115.380 117.552 117.857 117.720 117.914 116.544 116.355

0) 0) 0) 0) 0) 0) 3) 3)

BNNT BNNT + CNCl Al-BNNT Al-BNNT + CNCl Ga-BNNT Ga-BNNT + CNCl BNNT BNNT + CNCl

12

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14

Fig. 10. The adsorption energy of the CNCl molecule on the surface of doped (6, 0) BNNT with Al in terms of distance at different positions (as described in Table 5).

Fig. 12. Band structure of zigzag (6, 0) BNNT a) pure and doped with b) Al c) Ga before adsorption.

Table 7 The band gap and the Fermi level of pure and doped (6, 0) BNNTs (D = direct band gap).

Fig. 11. The adsorption energy of the CNCl molecule on the surface of doped (6, 0) BNNT with Ga in terms of distance at different positions (as described in Table 5).

charge density symmetry, the magnetic moment is generated and the CNCl molecule is absorbed by the impurity atom. The amount of adsorption energy for all stable systems is greater than -1eV, which indicates that adsorption is in the range of chemical adsorption. That means the absorption has become stronger. Similarly, the best adsorption distance for all structures obtained about 2– 2.5 Å. The band structure of doped BNNT with Al and Ga is shown in Fig. 12. By comparing the band structure of doped and pure BNNTs, it’s seen that after doping, some bands have been created around the Fermi level, which has changed the entire band structure and

Structure

Fermi level

EC  EF (eV)

EF  EV (eV)

Band gap (eV)

BNNT Al (BNNT) Ga (BNNT)

4.316 4.2442 4.2445

1.375 1.334 1.089

1.302 1.265 1.288

2.677 D 2.599 D 2.377 D

its gap value. The band gap value and the Fermi energy level in doped BNNT have decreased compared to pure nanotubes. The reduction of the band gap in the Ga-doped nanotube is more than that of Al-doped. The difference between the minimum energy level of the conductance band and the Fermi level (EC  EF), the maximum valence band compared to the Fermi level (EF  EV), the value and type of the band gap and the position of the Fermi level in doped BNNTs are reported in Table 7. In Fig. 13, the electronic band structure for stable adsorption doped systems with Al and Ga has been plotted. Regarding the band structure of the stable systems in doped BNNTs and comparing them with the band structure of the stable adsorption systems on pure nanotubes, it is observed that around the Fermi level some bands have been created and the band gap has decreased in most of the adsorption structures. The band gap of doped BNNTs with Al and Ga after adsorption and their Fermi level position are summarized in Table 8.

Table 5 The adsorption energy of the CNCl molecule on the surface of (6, 0) BNNT doped with Al and Ga in terms of distance from its surface at different positions for the most stable state. 1- above the atom Al (Ga) from the Cl side. 2- above the Al (Ga) from the N side. 3- above the atom N from the Cl side. 4- above N from the N side. 5- on the bisector of the Al (Ga) N bond from the N side. 6- on the bisector of the Al (Ga) -N bond from the atom Cl side. 7- above the hexagonal center from Cl side. 8- above the hexagonal center from N side. Adsorption Energy (eV) [distance (Å)] Positions Configuration

1

2

3

4

5

6

7

8

Al-doped (6, 0) +Vertical CNCl Ga-doped (6, 0) +Vertical CNCl

0.309 [2.5] 0.277 [3.0]

1.754 [2.0] 1.113 [2.5]

0.578 [2.5] 0.273 [3.0]

0.246 [2.5] 0.3629 [3.0]

0.642 [2.5] 0.312 [2.5]

0.542 [2.5] 0.252 [3.0]

0.374 [3.0] 0.422 [2.0]

0.512 [2.5] 0.347 [2.0]

Table 6 The adsorption energy, adsorption position, and adsorption distance and charge transfer (QT(e)) of the most stable structures investigated for pure (6, 0) BNNT and doped with Al and Ga after CNCl adsorption. Structure

Distance (Å)

Adsorption energy(eV)

Adsorption position

QT(e)

CNCl +)BNNT) CNCl + Al)BNNT) CNCl + Ga)BNNT)

2.5 2.0 2.5

0.523 1.754 1.112

on the hexagonal center On the Al impurity On the Ga impurity

0.834 1.504 1.418

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14

13

Fig. 13. Band structure of doped BNNTs with: (a) Al before adsorption (b) Al after adsorption (c) Ga before adsorption d) Ga after adsorption of CNCl molecule.

Table 8 Band gap and Fermi level position for doped BNNTs with Al and Ga before and after CNCl adsorption. Structure

Fermi level

EC  EF (eV)

EF  EV (eV)

Band gap (eV)

Al)BNNT) Al)BNNT) + CNCl Ga) BNNT) Ga) BNNT)+CNCl

4.2442 3.9654 4.2444 3.7884

1.334 0.869 1.089 0.978

1.265 0.893 1.288 1.075

2.599 1.762 2.377 2.053

The reduction of the band gap in adsorption on Al-doped structures is more than Ga-doped. The band gap for adsorption of CNCl molecules on Al and Ga doped nanotubes was obtained 1.762 and 2.053 eV, respectively. According to the results summarized in Tables 6–8, after doping nanotube the band gap decreases and the charge transfer between the nanotube and the adsorbed CO molecule increases. So it can conclude by doping nanotube the electronic properties improved and increased conductance.

4. Conclusion In this study, we investigated the adsorption of CNCl gas molecules on the surface of single-walled BNNTs using the density functional theory with the SIESTA code. By calculating the adsorption energy, the most stable positions and the equilibrium distance were obtained and the amount of charge transferred and the electronic properties were calculated. The stable positions for pure structures were calculated on the hexagonal center of the nanotubes at 2.5 to 3 Å. For the linear molecule of CNCl, the adsorption in the case where the molecule is perpendicular to the nanotube axis was more stable than the adsorption in the horizontal state. It was also observed that it would be better to absorb the molecule from the side of the N atom. Adsorption on zigzag nanotube is more stable than absorbing on the armchair nanotube. The band gap changes, the transferred charge and the amount of adsorption energy on the pure nanotube were little which indicates that the interaction between the pure nanotube and molecule is vanderwaals and there is physical adsorption. Then the zigzag boron nitride (6, 0) nanotube was doped with Al and Ga. In doped structures, the most stable adsorption position was obtained at distance of 2 to 2.5 Å over the Al and Ga impurity atoms. The adsorption energy of doped systems was more negative than the pure state and was within the chemical adsorption range, which shows that the adsorption is stronger and more stable. The band gap variations and the amount of charge transferred between the molecule and

nanotube after doping the systems has increased. According to the results, the Al-doped boron nitride nanotube is more stable and a better absorber for detecting CNCl gas compared with Ga. References [1] Y.F. Sun, S.B. Liu, F.L. Meng, J.Y. Liu, Z. Jin, L.T. Kong, J.H. Liu, Metal oxide nanostructures and their gas sensing properties: a review, Sensors 12 (3) (2012) 2610–2631. [2] S. Capone, A. Forleo, L. Francioso, R. Rella, P. Siciliano, J. Spadavecchia, A.M. Taurino, Solid state gas sensors: state of the art and future activities, J. Optoelectron. Adv. Mater. 5 (5) (2003) 1335–1348. [3] J. Arbioli Cobos, Metal additive distribution in TiO2 and SnO2 semiconductor gas sensor nanostructured materials, Universitat de Barcelona, 2001. [4] S. Peng, J. O’Keeffe, C.Y. Wei, K. Cho, J. Kong, R. Chen, N. Franklin, H. Dai, Carbon nanotube chemical and mechanical sensors, in: Proceedings of the 3rd International Workshop on Structural Health Monitoring , 2001, September, pp. 1–8. [5] S. Chopra, K. McGuire, N. Gothard, A.M. Rao, A. Pham, Selective gas detection using a carbon nanotube sensor, Appl. Phys. Lett. 83 (11) (2003) 2280–2282. [6] A. Soltani, A. Sousaraei, M. Mirarab, H. Balakheyli, Interaction of CNCl molecule and single-walled AlN nanotubes using DFT and TD-DFT calculations, J. Saudi Chem. Soc. 21 (3) (2017) 270–276. [7] D. Vahedi Fakhrabad, T. Movlarooy, N. Shahtahmasebi, Density functional theory study of ultra small diameter (2, 2) boron nitride, silicon carbide and carbon nanotubes, Phys. Status Solidi B 249 (5) (2012) 1027–1032. [8] Z.Y. Deng, J.M. Zhang, K.W. Xu, Adsorption of SO2 molecule on doped (8, 0) boron nitride nanotube: a first-principles study, Phys. E: Low-Dimen. Syst. Nanostruct. 76 (2016) 47–51. [9] J. Kaur, S. Singhal, N. Goel, Effect of substitutional carbon-doping in BNNTs on HF adsorption: DFT study, Superlat. Microstruct. 75 (2014) 445–454. [10] A. Rubio, J.L. Corkill, M.L. Cohen, Phys. Rev. B 49 (1994) 5081. [11] N.G. Chopra, R.J. Luyken, K. Cherrey, V.H. Crespi, M.L. Cohen, S.G. Louie, A. Zettl, Science 269 (1995) 966. [12] T. Movlarooy, S.M. Hosseini, A. Kompany, N. Shahtahmasebi, Optical absorption and electron energy loss spectra of single-walled carbon nanotubes, Comput. Mater. Sci. 49 (2010) 450–456. [13] T. Movlarooy, S.M. Hosseini, A. Kompany, N. Shahtahmasebi, Ab-initio calculations of optical spectra of chiral (4, 1) carbon nanotube, Phys. Status Solidi B 247 (7) (2010) 1814–1821. [14] T. Movlarooy, S.M. Hosseini, A. Kompany, N. Shahtahmasebi, Ab initio calculations of electronic structure and optical spectra of (13–0) carbon nanotube, Int. J. Nanosci. 10 (4–5) (2011) 587–590. [15] T. Movlarooy, The effect of intraband transitions on the optical spectra of metallic carbon nanotubes, Chin. Phys. Lett. 30 (7) (2013) 077301. [16] Alireza Soltani, Mohammad T. Baei, A.S. Ghasemi, E. Tazikeh Lemeski, Komail Hosseni Amirabadi, Adsorption of cyanogen chloride over Al- and Ga-doped BN nanotubes, Superlat. Microstruct. 75 (2014) 564–575. [17] Maziar Noei, Ali-Akbar Salari, Mahsa Madani, Mina Paeinshahri, Hossein Anaraki-Ardakani, Adsorption properties of CH3COOH on (6, 0), (7, 0), and (8, 0) zigzag, and (4, 4), and (5, 5) armchair single-walled carbon nanotubes: a density functional study, Arabian J. Chem. 10 (2017) S3001–S3006. [18] Peng Shao, Xiao-Yu Kuang, Li-Ping Ding, Jing Yang, Ming-Min Zhong, Can CO2 molecule adsorb effectively on Al-doped boron nitride single walled nanotube?, Appl Surf. Sci. 285P (2013) 350–356. [19] A.H. Javid, M. Gorannevis, F. Moattar, A. Mashinchian Moradi, P. Saeeidi, Modeling of benzene adsorption in the gas phase on single-walled carbon

14

[20]

[21] [22] [23]

[24] [25] [26]

[27]

[28]

[29]

[30]

T. Movlarooy, M.A. Fadradi / Chemical Physics Letters 700 (2018) 7–14 nanotubes for reducing air pollution, Int. J. Nanosci. Nanotechnol. 9 (4) (2013) 227–234. A.A. El-Barbary, Kh.M. Eid, M.A. Kamel, H.O. Taha, G.H. Ismail, Adsorption of CO, CO2, NO and NO2 on boron nitride nanotubes: DFT study, J. Surface Eng. Mater. Adv. Technol. 5 (2015) 154–161. P. Blaha, D. Singh, P.I. Sorantin, K. Schwarz, Phys. Rev. B 46 (1992) 1321. C. Fiolhais, F. Nogueira, M. Margues, A Primer in Density Functional Therory, Springer, 2003. J.M. Soler, E. Artacho, J.D. Gale, A. Garcia, J. Junquera, P. Ordejon, D. SanchezPortal, The SIESTA method for ab initio order-N materials simulation, J. Phys: Condens. Matter 14 (2002) 2745. M. Peterson, F. Wanger, L. Hufnagel, M. Scheffler, P. Blaha, K. Schwarz, Comput. Phys. Commun. 126 (2002) 294. J. Perdew, K. Burke, M. Ernzhofer, Phys Rev Lett 77 (1996) 3865. Jyotirmoy Deb, Barnali Bhattacharya, Debolina Paul, Utpal Sarkar, Interaction of nitrogen molecule with pristine and doped graphyne nanotube, Physica E 84 (2016) 330–339. Fahimeh Shojaie, N2 adsorption on the inside and outside the single-walled carbon nanotubes by density functional theory study, Pramana – J. Phys. 90 (2018) 4. You Xie, Yi-Ping Huo, Jian-Min Zhang, First-principles study of CO and NO adsorption on transition metals doped (8, 0) boron nitride nanotube, Appl. Surf. Sci. 258 (2012) 6391–6397. Wei Li, Lu. Xiao-Min, Guo-Qing Li, Juan-Juan Ma, Peng-Yu Zeng, Jun-Fang Chen, Zhong-Liang Pan, Qing-Yu He, First-principle study of SO2 molecule adsorption on Ni-doped vacancy-defected single-walled (8, 0) carbon nanotubes, Appl. Surf. Sci. 364 (2016) 560–566. Zun-YiDeng, Jian-MinZhang, Ke-WeiXu, Adsorption of SO2 molecule on doped (8, 0) boron nitride nanotube: a first-principles study, Physica E 76 (2016) 47–51.

[31] Ruoxi Wang, Dongju Zhang, Chengbu Liu, The germanium-doped boron nitride nanotube serving as a potential resource for the detection of carbon monoxide and nitric oxide, Comput. Mater. Sci. 82 (2014) 361–366. [32] Zun-Yi Deng, Jian-Min Zhang, Xu. Ke-Wei, First-principles study of SO2 molecule adsorption on the pristine and Mn-doped boron nitride nanotubes, Appl. Surf. Sci. 347 (2015) 485–490. [33] Ernesto Chigo Anota, Gregorio H. Cocoletzi’, GGA based analysis of the metformin adsorption on BN nanotubes, Physica E56 (2014) 134–140. [34] Masoud Bezi Javan, Adsorption of CO and NO molecules on SiC nanotubes and nanocages: DFT study, Surf. Sci. 635 (2015) 128–142. [35] Michael Mananghaya, Dennis Yu, Gil Nonato Santos, Hydrogen adsorption on boron nitride nanotubes functionalized with transition metals, Int. J. Hydrogen Energy 41 (31) (2016) 13531–13539. [36] R. Bhuvaneswari, V. Nagarajan, R. Chandiramouli, Adsorption studies of trimethyl amine and n-butyl amine vapors on stanene nanotube molecular device – a first-principles study, Chem. Phys. 501 (2018) 78–85. [37] R. Wang, R. Zhu, D. Zhang, Adsorption of formaldehyde molecule on the pristine and silicon-doped boron nitride nanotubes, Chem. Phys. Lett. 467 (1) (2008) 131–135. [38] Y. Sun, L. Chen, F. Zhang, D. Li, H. Pan, J. Ye, First-principles studies of HF molecule adsorption on intrinsic graphene and Al-doped grapheme, Solid State Commun. 150 (39) (2010) 1906–1910. [39] Tutorial Gauss View, . [40] W. An, X. Wu, X.C. Zeng, Adsorption of O2, H2, CO, NH3, and NO2 on ZnO nanotube: a density functional theory study, J. Phys. Chem. C 112 (15) (2008) 5747–5755. [41] R.Q. Wu, M. Yang, Y.H. Lu, Y.P. Feng, Z.G. Huang, Q.Y. Wu, Silicon carbide nanotubes as potential gas sensors for CO and HCN detection, J. Phys. Chem. C 112 (41) (2008) 15985–15988.