Pristine Boron Nitride Nanotubes Research Articles

Zigzag boron nitride nanotube functionalization as a sensor for the recognition of group IIA (Mg2+, Ca2+) metal ions, quasi-metal (Si2+, Ge2+) ions, and transition metal (Cu2+, Zn2+) ions: a computational study.

Boron nitride nanotubes (BNNTs) provide an exceptional and sophisticated platform for detecting metal ions with high surface area and remarkable chemical stability. Metal cations tend to bind to the surface of BNNTs, which leads to significant changes in the electrical properties of nanotubes. BNNT-based metal ion sensors have shown promising results in various applications, including water quality monitoring, biomedical research, industrial quality control, and environmental monitoring. In the present study, we have explored the electronic sensitivity of the BNNT to metal ions (Si2+, Ge2+, Cu2+, Zn2+, Mg2+, and Ca2+). The interaction between the ions with the pristine BNNT is performed in the solution phase. The results show that ion adsorption on the nanotube surface is exothermic and favorable. The density of states calculation is presented to investigate the electronic properties of the nanotube during the adsorption process. The results display that an increase in the electrical conductivity of the complexes accompanies the reduction in the energy gap. Based on the obtained data, the Si2+ and Ge2+ cations adsorbed on the BNNT with satisfactory Eg changes (%ΔE) can be promising candidates for better sensing ability. All calculations are conducted within the density functional theory (DFT) using the ωB97XD functional and 6-31G(d,p) basis set. The present approach incorporates the utilization of empirical atom-atom dispersion in conjunction with long-range correction. The calculations are performed using the quantum chemistry package GAMESS, and the obtained results are visualized by employing the GaussView 6.0.16 program.

Deformation behaviors of hydrogen filled boron nitride and boron nitride - carbon nanotubes: Molecular dynamics simulations of proposed materials for hydrogen storage, gas sensing, and radiation shielding

Boron nitride nanotubes (BNNTs) have been extensively studied for hydrogen storage, sensing, and radiation shielding applications. The deformation behaviors of pristine, defective, and H2-encapsulated closed-end armchair BNNTs and BNNT-carbon nanotube (CNT) heterostructures are investigated using molecular dynamics employing the ReaxFF interatomic potential and a combination of Tersoff, adaptive intermolecular reactive empirical bond order, and Lennard-Jones potentials. The calculated elastic properties for pristine BNNTs and CNTs are in excellent agreement with published reliable data. The nanotube length and diameter, defects, entrapped hydrogen content, and temperature all affect the mechanical properties significantly. The ReaxFF potential predicts H2 molecule adsorption on B atoms of undeformed BNNTs whilst under strain, the H2 molecules show preference for the N atoms. Hydrogen adsorption leads to lowering of the elastic and fracture strength of BNNTs. The ReaxFF potential is shown to be a reliable forcefield for investigating the interaction of H2 molecules with BNNTs and BNNT-CNT heterotubes.

Ibuprofen adsorption and detection of pristine, Fe–, Ni–, and Pt–doped boron nitride nanotubes: A DFT investigation

The main challenge has been focused on ibuprofen drug detection and adsorption of boron nitride nanotube (BNNT) doping with transition metal (TM = Fe, Ni, and Pt) atoms using the density functional theory calculation in gas and water phases. The geometrical structures, adsorption energies, solvation energies, and electronic properties were examined. The optimized geometries show that the ibuprofen molecule oriented itself at different bond distances and angles with respect to BNNT surface. The calculated results display exothermic adsorption processes for all ibuprofen/BNNT and ibuprofen/TM–doped BNNT complexes. Ibuprofen molecule can absorb on the Fe–, Ni–, and Pt–doped BNNTs via a stronger interaction than those of pristine BNNT in both gas and water phases in which the Fe doping on N site of BNNT shows the strongest interaction with ibuprofen molecule. The H (head) site of ibuprofen molecule to BNNT surface shows stronger interaction than M (middle) and T (tail) sites. The short of adsorption distance and the large of charge transfer correspond to the high adsorption strength of TM–doped BNNTs toward ibuprofen molecule. Charge analysis confirms the partial charge transfer occurring from the ibuprofen molecule to the BNNTs. The solvation energies in water solution reveal that the ibuprofen molecule adsorbed on TM–doped BNNTs is more soluble than pristine BNNT. The work functions of BNNTs are reduced by ibuprofen adsorption. A short recovery times and suitable desorption temperatures are observed for the ibuprofen desorption on pristine BNNT and TM–doped BNNT surfaces. After ibuprofen adsorption, the energy levels and energy gaps of Fe–, Ni–, and Pt–doped BNNTs are changed in which Ni doping on B atom of BNNT displays the largest change. The quantum molecular characteristics of BNNT will be changed after ibuprofen adsorption. The orbital distributions are occurred around the ibuprofen molecule and doping site. The alteration in the density of states for TM–doped BNNT is considerably more pronounced compared to the pristine BNNT. Drawing from the achieved outcomes, it can be inferred that when employed for the delivery of ibuprofen in biological media, Fe–, Ni–, and Pt–doped BNNTs exhibits the greater suitability for the adsorption and detection of the ibuprofen molecule compared to pristine BNNT.

Chemical modifications of boron nitride nanotubes with heterocyclic molecules: A DFT study

The density functionals M06–2X and B3LYP were exploited for investigating the impact of modifying the surface of a boron nitride nano-tube (BNNT) with the furan molecule in terms of energy, electronics, and geometry. According to the density functional theory (DFT) results, BNNT had a strong interaction with the furan molecule. So, the adhesion of the furan molecule onto the surface of BNNT was consistent with the chemical functionalization. Furthermore, the computed density of states indicated that the electronic features of the BNNT were adjusted with a partial chemical modification. Also, the functional energy raised by enhancing the electron donation property of the functional groups, which was due to the rise in the electrical conductance of BNNT in contrast with the pristine BNNT. Retaining the electronic features of BNNT and the increased solubility demonstrated that using furan to chemically modify BNNTs could be a useful method to purify them.

Insights on the enhanced hydrogen sulfide adsorption on X (X = Cr, Ni, Al, C, Si, O, S) doped boron nitride nanotubes

This study investigates the enhanced hydrogen sulfide (H2S) gas adsorption on X (X = Cr, Ni, Al, C, Si, O, and S) doped boron nitride nanotubes (BNNT) through first-principle density functional theory calculations. The study also examined the electrostatic potential maps, HOMO-LUMO distributions, density of states plots, atomic charges, and reactivity descriptors of doped BNNT clusters before and after adsorption. The H2S orientation was different for each optimized doped BNNT-H2S cluster. The theoretical infrared spectra indicated a red shift in the SH symmetric stretching frequency of H2S gas molecule upon adsorption on pristine and doped BNNT. The examination of the atomic charges showed that during the interaction, the charge was transferred from the doped BNNT to the H2S gas molecule. The analysis revealed that Al/BNNT and S/BNNT exhibited better interactions and, therefore, better adsorption ability towards H2S gas than pristine and other doped BNNT. However, considering the recovery time aspect, C/BNNT, O/BNNT, and Si/BNNT were better adsorbent for H2S.

Adsorbing CNCl on pristine, C-, and Al-doped boron nitride nanotubes: A density functional theory study

The density functional theory (DFT) framework was used to investigate the intermolecular interactions between cyanogen chloride (CNCl) pollutant gas molecule with pristine boron nitride nanotubes (BNNT), Al-doped boron nitride nanotubes (BNAlNT), and carbon boron nitride nanotubes (BC2NNT). The geometric structures of the resulting systems have been optimized using different methods, including B3LYP-D3(GD3BJ)/6-311G(d), ωB97XD/6-311G(d), and M06-2X/6-311G(d). The computed adsorption energies suggest that the studied nanotubes can enhance adsorption of CNCl, and thus promote its detection when employed as sensing materials. Wave function analysis has been implemented to study the type of intermolecular interactions at ωB97XD/6-311G(d,p) level of theory. Natural bond orbital (NBO) analysis has been used to study the charge transfer and bond order. Quantum theory of atoms in molecules (QTAIM) analysis has also been used to determine the type of interactions between the target gas and the nanotubes. To investigate the weak intermolecular interactions we also carried out non-covalent interaction analysis (NCI). The results also indicate that the CNCl-nanotube systems are created through physisorption as they are dominated by non-covalent interactions. The predicted adsorption energies increase as follows: BNAlNT: −1.175 eV > BC2NNT: −0.281 eV > BNNT: −0.256 eV; this shows that the aluminum-doped boron nitride nanotube is the best option from promoting adsorption of the target gas among them. The HOMO–LUMO energy gaps were as follows: BNNT: 7.090, BNAlNT: 9.193, and BC2NNT: 7.027 eV at B3LYP-D3/6-311G(d) level of theory.

Quantum DFT methods to explore the interaction of 1-Adamantylamine with pristine, and P, As, Al, and Ga doped BN nanotubes

Nanostructures, nowadays, found growing applications in different scientific and industrial areas. Nano-coins, nanosheets, and nanotubes are used in medical applications as sensors or drug delivery substances. The aim of this study is to explore the adsorption of 1-Adamantylamine drug on the pristine armchair boron nitride nanotubes (BNNTs) with BNNT(5,5), BNNT(6,6), and BNNT(7,7) chirality along with the P, As, Al and Ga-doped BNNTs, using the quantum mechanical density functional methods. Considering the fact that dispersion effects are important in the case of weak Van der Waals interactions, computations have been done using B3LYP hybrid functional with the implementation of the D3(BJ) empirical dispersion correction methods. Quantum theory of atoms in molecules, natural bonding orbitals, and Kohn–Sham orbitals were used to investigate the nature and type of the adsorption process. The results showed that, while the adsorption of 1-Adamantylamine on the outer surface of pristine BNNT is physical in nature, doping can improve the ability of detracted BN to adsorb the drug through chemical bonds. Also, it was found that, by increasing the radius of the BNNT the adsorption energy was decreased. In conclusion, results of the present work suggest that, Ga doped nanotube, due the chemisorption, is not an ideal nanotube in drug delivery of 1-Adamantylamine drug, whereas, the other studied cases physiosorbed the drug, and may not have serious problem in release of the 1-Adamantylamine drug.

PRISTINE AND GROUP IV DOPED BORON NITRIDE SINGLE-WALL NANOTUBES FOR HYDROGEN STORAGE: A DENSITY FUNCTIONAL THEORY COMPUTATIONAL INVESTIGATION

In this report, a density functional theory (DFT) computational approach was used to investigate the structural and electronic properties of molecular hydrogens adsorbed on single-walled boron nitride nanotubes (BNNTs) with/without doped by group IV elements, such as carbon (C), silicon (Si), and germanium (Ge) atom. The twelve hydrogen molecules (H2) were added to the outer surfaces of BNNT frameworks. Geometry optimization calculations were performed to find the local energy minima of the BNNTs nanostructures with the molecular hydrogens at the DFT/B3LYP/6-31G level of theory. By employing single-point calculations at the B3LYP/6-31G* level of theory, the equilibrium geometric structures were then utilized to find the electronic structures of hydrogen molecules adsorbed on the surfaces of BNNT frameworks. The results showed that the bond lengths of B-N are in the range of1.44 Å – 1.48 Å. The optimized distances of hydrogen molecules from the surfaces of BNNTs were predicted to be 3.1 Å – 3.2 Å. Moreover, the computed HOMO-LUMO energies of molecular hydrogens adsorbed on the surface of BNNTs are about 2.2 eV – 4.3 eV. For the surface map of HOMO, the electron density distribution of hydrogen molecules adsorbed on the surface of pristine BNNT was localized in the N-tip. While in the case of doped BNNTs, the electron densities of HOMOs were focused on the group IV elements. The B-tips on the pristine and doped BNNTs possess the major contribution to the LUMO.

A DFT approach to the adsorption of the Levodopa anti-neurodegenerative drug on pristine and Al-doped boron nitride nanotubes as a drug delivery vehicle

The adsorption behavior of the anti-neurodegenerative drug Levodopa (LD) on pristine and aluminum-doped (Al-doped) boron nitride nanotubes (BNNTs) has been investigated in the current study using the density functional theory (DFT) approach at the B3LYP/6-31G** level of theory. The aim was to improve and expand boron nitride nanotubes drug carriers used in biomedical systems, i.e., drug delivery systems. The binding qualities of pure and doped BNNT complexes as adsorbents with LD were explored using the natural bond orbitals (NBO) analysis, density of state (DOS), electrical and structural characteristics, and atoms in molecules (AIM) properties. Due to doping heteroatoms in the adsorbent's molecular structure, the obtained data reveal a gradual shift in LD adsorption, with a significant rise in negative adsorption energy values. The electronic perturbation caused by doped atoms, particularly Al, improves boron nitride nanotube sensitivity to adsorbed Levodopa, and the electronic properties of the nanotubes are altered following Levodopa adsorption in the complex. As the frontier molecular orbital distributions were transferred from LD to BNNTs in the complex of BNNT–LD, it was also shown that LD drugs could be loaded on pristine and Al-doped BNNTs while remaining safe from interactions with other substances. Furthermore, AIM analysis based investigations revealed that O–Al interaction in LD adsorbed on Al-doped boron nitride nanotube and O–N interaction in the BNNT–LD complex are partially covalent. Finally, the findings showed that pristine and Al-doped BNNT could be used in drug delivery processes by controlling the loaded LD contribution to future interactions.

Al- and Ga-embedded boron nitride nanotubes as effective nanocarriers for delivery of rizatriptan

Motivated by earlier experimental and theoretical studies on the potential of different nanostructures for drug delivery, the adsorption and electrical sensitivity of pristine, Al- and Ga-embedded (8,0) boron nitride nanotubes (BNNTs) to a rizatriptan (RZ) molecule are explored using dispersion-corrected density functional density calculations. The RZ molecule is shown to be weakly adsorbed on pristine BNNT, with a modest adsorption energy of −0.46 eV and only a minor impact on its electronic properties. The replacement of a B atom with an Al or Ga promotes the reactivity of the BNNT toward the RZ molecule, as evidenced by calculated adsorption energies and charge-transfer values. Once the RZ molecule is introduced onto the BNNTs, the band gap of the tubes narrows. However, the amount of reduction in band gap values of Al- or Ga- embedded BNNT is more pronounced than that of pristine tube. As solvent effects are included, the desorption times of RZ from the surface of BNNTs are expected to be shortened. The influence of surface charge on the adsorption process of RZ molecules, as well as curvature effects, is thoroughly investigated. Overall, the high sensitivity, reasonable adsorption energies, and fast desorption suggest that Al- and Ga-embedded BNNTs might be served as effective drug delivery systems for RZ.

Molecular engineering of the surface of boron nitride nanotubes for manufacture of thermally conductive dielectric polymer composites

Recent developments in microelectronic devices have led to rising demand for polymeric nanocomposites that can simultaneously deliver enhanced thermal conduction and electrical insulation. Boron nitride nanotube (BNNT) is one of the most promising fillers for the fabrication of such composites. While being electrically insulating, effective crystal lattice vibrations allow BNNTs to achieve thermal conductivity values that can even surpass that of diamond. However, when BNNTs are surface functionalized and incorporated within polymers, their lattice vibrations are significantly suppressed, resulting in polymeric nanocomposites with thermal conductivity values only a fraction of what BNNTs can achieve in air. The aim of this study is to shed light on the underlying cause of this challenge for thermally conductive, dielectric polycarbonate (PC)/BNNT nanocomposites that were produced using two distinct surface functionalization approaches. By incorporation of BNNTs in PC, the thermal conductivity values were significantly increased. However, depending on nanotubes’ concentration, the thermal conductivity of pristine BNNTs in PC were comparable or superior to those of the functionalized nanotubes. Theoretical analysis and experimental characterization have been conducted to elucidate the fundamental impacts of surface functionalization on the lattice vibrations of BNNTs and their subsequent effects on the thermal properties of dielectric BNNT composites.

DFT Study for Adsorbing of Bromine Monochloride onto BNNT (5,5), BNNT (7,0), BC2NNT (5,5), and BC2NNT (7,0)

The study of intermolecular interactions is of great importance. This study attempted to quantitatively examine the interactions between bromine monochloride (BrCl) with pristine boron nitride nanotube (BNNT) armchair (5,5) and zigzag (7,0) as well as armchair (5,5) BC2NNT and zigzag (7,0) BC2NNT in vacuum. Quantum mechanical studies of such systems are possible in the density functional theory (DFT) framework. For this purpose, various functionals, such as B3LYP-D3, [Formula: see text]B97XD, and M062X, have been used. One of the most suitable basis functionals for the systems studied in this research is 6-311G (d), which has been used in both optimization calculations and calculations related to wave function analyses. The main part of this work is the study of various analyses that reveal the nature of the intermolecular interactions between the two components introduced above. The results of conceptual DFT, natural bond orbital, non-covalent interactions, and quantum theory of atoms in molecules (QTAIM) were consistent and in favor of physical adsorption in all systems. Gallium had more adsorption energy than other dopants. The HOMO–LUMO energy gaps were as follows: BNNT (5,5): 10.296, BNNT (7,0): 9.015, BC2NNT (5,5): 7.022, and BC2NNT (7,0): 5.979[Formula: see text]eV at B3LYP-D3/6-311G (d) model chemistry. The strongest interaction is related to the BC2NNT (7,0)/BrCl cluster: [Formula: see text][Formula: see text]eV. The results of QTAIM and NCI analysis identified the intermolecular interactions of the type of strong van der Waals interaction for these nanotubes. The sensitivity of the adsorption increased when a gas molecule interacted with carbon-doped BNNT, and the change in the frontier orbital gap could be used to design nanosensors to detect BrCl gas.

Structural, magnetic, and electronic properties and stability of 3d-TM substituted single-walled zigzag BNNTs: A density functional theory study

We investigate the effects of the substitution of all the first series transition-metal (TM) atoms on the physical properties of (10,0) boron nitride nanotube (BNNT) using the DFT calculation. Three interesting results are as follows: First, the formation energies show a more stable system for the born (B) site substitution than nitrogen (N) site substitution. Second, reducing the bandgap of the TM-substituted BNNT with respect to the pristine BNNT can be mainly related to the presence of the new impurity states induced near the Fermi level by the d electrons of the TM atom, and a half-metal behavior has been obtained for Ti-, V-, Ni-, Co-, Cu-substitution at B-site and Fe-, V-, Ni-substitution at N-site. Third, besides the appearance of two up-and-down-spin channels, a new spin-crossover has been observed for Fe-, Ni-, Co-, Cu-substitution at B-site and Ti-, V-substitution at N-site which make them suitable to use in spintronic applications.

Theoretical investigation on 5–fluorouracil anti–cancer drug adsorption on Sc– and Ti–doped armchair and zigzag boron nitride nanotubes

The application of nanomaterials as a drug delivery system for anticancer is now becoming an important for control drug release near the tumor cell. Herein, the adsorption properties of 5–fluorouracil (5FU) drug on pristine armchair and zigzag single wall boron nitride nanotubes (BNNT) and their doping with Sc or Ti atom in gas phase and water solution conditions were investigated through density functional theory calculations. The interactions of 5FU molecule and BNNTs on the geometrical stabilities, adsorption abilities and electronic properties were also determined and discussed. The calculations reveal that there are shorter adsorption distance, higher adsorption ability, higher solubilities, and larger charge transfer when 5FU molecule is adsorbed on Sc– and Ti–doped BNNTs in comparison with adsorptions on pristine BNNT. According to the results, the doping of transition metal atom is improved the reactivity of BNNTs toward 5FU molecule. Thermodynamic analyses demonstrate that interactions between 5FU molecule and Sc– and Ti–doped BNNTs are exothermic and spontaneous processes. The recovery time is attained to be 272.63 s for the 5FU desorption from the Ti doping on N site of armchair BNNT. The electronic properties reveal that after 5FU adsorption, the energy gap and density of state of Sc– and Ti–doped BNNTs are clearly changed than that of pristine BNNT, which suggests that Sc and Ti doping is improved the sensitivity of BNNTs to 5FU molecule. Therefore, Sc– and Ti–doped BNNTs can be a good candidate for sensors or catalyst to adsorb and detect 5FU molecule for drug delivery system in the nanomedicine domain.

DFT study of X-doped (X= Cu, Ag, Au) boron nitride nanotubes for spintronic and optoelectronic applications

In this paper, first-principle calculations of (3,0) and (5,5) single-walled boron nitride nanotubes (BNNT) doped with X-atoms (X = Cu, Ag and Au), in the boron and the nitrogen sites are carried out. A systematic approach based on Pseudo-Potential Plane-Wave (PPPW) method combined with the generalized gradient approximation (GGA) within the density functional theory (DFT) is used to study the influence of X atoms doping on the structural, electronic, optic and magnetic properties of the analyzed BNNT. The structural arrangement in equilibrium conditions shows an outward radial deformation around the X atom in the tube, leading to affecting the electronic properties of the BN nanotubes. Moreover, it is revealed that the doping has a profound implication in inducing significant modification on the band energy of the pristine BNNT. Optoelectronic properties can be estimated by using different empirical models, which are mainly related to the fundamental energy gap, where high optoelectronic proprieties have been recorded. Moreover, the obtained results show that the adsorption of Cu and Au atoms can induce magnetization while no magnetism is observed for the Ag-doped BNNT. Therefore, the magnetic properties of BNNTs can be modified by introducing appropriate doping using X atoms. This makes the Cu and Au-doped BNNT structure potential alternative for developing magnetic and optic nanostructures, which are highly suitable for spintronic and optoelectronic applications.

The adsorption of bromochlorodifluoromethane on pristine, Al, Ga, P, and As-doped boron nitride nanotubes: A study involving PBC-DFT, NBO analysis, and QTAIM

Nanostructures such as nanotubes and nanosheets are widely used in the medical industry for drug delivery, prevention, and treatment. These nanostructures are used as sensors or carriers by adsorbing functional groups. In this study, the adsorption rates of the bromochlorodifluoromethane (CBrClF2) molecule, which is used as an effective gaseous fire suppression agent, onto the outer surfaces of pristine, Al, Ga, P, and As-doped boron nitride nanotubes are investigated. A periodic boundary condition density functional theory method using both Perdew, Burke, and Ernzerhof exchange–correlation (PBEPBE) and B3LYP-D3 functionals together with the 6-311G (d) basis set were used. Subsequently, the B3LYP, CAM-B3LYP, ωB97XD, and M06-2X functionals with the 6-311G (d) basis set were used to consider the single-point energies. Natural bond orbital analysis and the quantum theory of atoms in molecule were considered using the PBEPBE/6-311G (d) method, and the results were compatible with the expected electronic properties, namely the Wiberg bond index, natural charge, natural electron configuration, donor–acceptor natural bond orbital interactions, and second-order perturbation energies. All the calculations and analyses denoted that the adsorption of the CBrClF2 molecule onto the surfaces of pristine boron nitride nanotubes occurred due to physical adsorption and van der Waals interactions. Among the doped nanotubes, the Al nanotube exhibited the highest adsorption energy compared to the other doped nanotubes.

A CAM-B3LYP DFT Investigation of Atenolol Adsorption on the Surface of Boron Nitride and Carbon Nanotubes and Effect of Surface Carboxylic Groups

The adsorption behavior of atenolol molecule over the pristine carbon nanotube and boron nitride nanotube as well as functionalized carbon nanotube was performed employing the B3LYP and CAM-B3LYP methods with 6-311G(d, p) basis set in two phases (gas and water solution). We used natural bond orbital, non-covalent interactions and the quantum theory of atoms in molecules to investigate the hydrogen bonds, interaction energies and charge transfers between the atenolol drug and nanosystems. In all cases, the process of intermolecular interaction between atenolol and nanosystems is exothermic showing that the optimized complexes are stable. The hydrogen-bonding interactions between drug and CNT–(COOH)3 play an important role for the different kinds of adsorption. In addition, data showed that there is a large charge donation and back-donation for atenolol adsorption on the surface of CNT–(COOH)3. Results indicated that although in the case of pristine carbon nanotube, the adsorption is weak, functionalization of carbon nanotube with –COOH groups can effectively modify the surface of nanotubes towards atenolol molecules adsorption and improve their solubility in water solution.

Enhancing the piezoelectric properties of boron nitride nanotubes through defect engineering

In this work, the piezoelectric coefficients of boron nitride nanotubes (BNNTs) containing vacancies were predicted using molecular dynamics simulations (MDS) with a Tersoff potential force field. The piezoelectric coefficients were determined by applying the electric field in the axial direction of BNNTs. The effect of diameter as well as different types of atom vacancies and their positions were taken into consideration. The smaller diameter BNNTs showed higher electromechanical response than larger diameter tubes. Our results reveal that the vacancy defects significantly influence the piezoelectric coefficients of BNNTs, and in some cases, in fact increase the electromechanical response of defective tubes over that of pristine ones. For instance, the piezoelectric coefficient of (8, 0) BNNT with boron (B) mono-vacancy enhances by 17% compared to pristine tube. The converse is true in case of nitrogen (N) mono-vacancies. The removal of B–N bond I, aligned along the tube axis, results in the reduction of piezoelectric coefficient of (8, 0) BNNT by 41%. The removal of bond II, inclined to the tube axis, increases the piezoelectric coefficient of (8, 0) BNNT by 13%. The same phenomenon was observed for other zigzag BNNTs containing mono-vacancies and di-vacancies (absence of B–N bonds). The results showed that the piezoelectric coefficients of BNNTs strongly depend on the position of vacancies and the maximum enhancement was observed as 17% and 13% for B mono-vacancy and di-vacancy of B–N bond II, respectively, over that of pristine (8, 0) BNNT. Apart from mono- and di-vacancies, we also considered multi-vacancies in BNNTs and observed maximum enhancement by as much as 36% in the piezoelectric coefficient of defective (8, 0) BNNT containing 2B and 2 N vacancies at particular locations. Moreover, the concerned results reveal that the enhancement of electromechanical response largely depends on the symmetry of vacancy defect pore and not the vacancy concentration. The present work shows that we can enhance/alter the piezoelectric properties of BNNTs via a novel pathways of defect engineering by introducing different types of vacancies and changing their positions to suit a particular NEMS applications.

Adsorption of NO2, HCN, HCHO and CO on pristine and amine functionalized boron nitride nanotubes by self-consistent charge density functional tight-binding method

The adsorptions of toxic gases including NO2, HCN, HCHO and CO molecules on the pristine and amine functionalized (5,0) single-wall boron nitride nanotubes (BNNTs) are investigated based on self-consistent charge density functional tight-binding (SCC-DFTB) method. The calculated results indicate that the pristine (5,0) BNNT exhibits weak adsorption for the gas molecules. Based on the calculated adsorption energy, interaction distances and charge transfer, amine functionalization at a boron atom of the pristine (5,0) BNNT enhances the sensitivity of the pristine (5,0) BNNT toward the gas molecules. The electronic densities of state results reveal that new local states in the vicinity of Fermi level for adsorption between amine functionalized BNNT and the gas molecules significantly appear. This confirms the improved sensitivity of the pristine (5,0) BNNT functionalized with amine for adsorption of the toxic gases. This study is expected to provide a useful guidance on gas sensing application of pristine and amine functionalized BNNTs for detection of the toxic gases at room temperature.

Enhancement of chlorobenzene sensing by doping aluminum on nanotubes: A DFT study

Chlorobenzene (CB) is a harmful, aromatic volatile organic compound and has been demonstrated to be a primary precursor of dioxin formation in industrial processes. Single-walled carbon nanotubes (SWCNT) and boron nitride nanotubes (BNNT) have attracted tremendous attention in a wide range of applications, including chemical gas sensors. In this work, we studied the sensing behavior of both semiconducting (8, 0) SWCNT and BNNT via aluminum doping by using DFT calculations. Our results reveal that CB can only adsorb on pristine SWCNT and BNNT via physisorption, while the Al-doped nanotubes greatly enhance the adsorption energies of the CB molecule. This is caused by the electron donating from the Cl atom to the Al atom to form an AlCl dative bond. The strong interaction caused by this AlCl dative bond formation leads to the breaking of the partial-double-bond characteristic of the CCl bond of the CB molecule so that the adsorption energies of CB can be enhanced. Moreover, we also found that Al-doped (8,0) BNNT displays a huge conductivity increase because of the considerable change in the band gap value after detecting the CB molecule. Our results imply that the Al-doped nanotubes, especially Al-doped BNNT, might be highly sensitive to chlorine-containing species.