A density functional theory study on acetylene-functionalized BN nanotubes

Covalent functionalization of a zigzag boron nitride nanotube (BNNT) with acetylene has been investigated by density functional theory in terms of energetic, geometric, and electronic properties. It has been found that the most stable functionalized BNNT is the one in which the acetylene is diffused into the tube wall so that two heptagonal and two pentagonal rings are formed, releasing energy of 1.54 eV. In addition, the effect of substituting the hydrogen atoms of C₂H₂ by different functional groups including –F, –CH₂F, –CN, and –OCH₃ on the geometric and electronic properties of the BNNT has been investigated. The reaction energies are found to be in the range of ?1.03 to ?3.13 eV so that their relative magnitude order is as follows: C₂F₂ > (OCH₃)₂C₂ > C₂H₂ > (CH₂F)₂C₂ > (CN)₂C₂, suggesting that the functionalization energy is increased by increasing the electron donating character of the functional groups. Overall, chemical modification of BNNT by the studied groups results in little changes in electronic properties of the tube and may be an effective way for the purification of BNNTs.     

BN Nanotube Serving as a Gas Chemical Sensor for N<Subscript>2</Subscript>O by Parallel Electric Field

Density functional theory calculations were performed to understand the electronic properties of C₂₄, B₁₂N₁₂, B₁₂P₁₂, and (6, 0) BNNT interacted with N₂O molecule in the presence and absence of an external electric field using the B3LYP method and 6-31G** basis set. The adsorption of N₂O from O-side on the surface of (6, 0) BNNT has high sensitivity in comparison with B₁₂N₁₂ nano-cage. The adsorption energy of N₂O (O-side) on the sidewalls of B₁₂N₁₂ and BNNT in the presence of an electric field are ?21.01 and ?15.48 kJ mol^?1, respectively. Our results suggest that in the presence of an electric field, the B₁₂N₁₂ nano-cage is the more energetically notable upon the N₂O adsorption than (6, 0) BNNT, C₂₄, and B₁₂P₁₂. Whereas, our results indicate that the electronic property of BNNT is more sensitive to N₂O molecule at the presence of an electric field than B₁₂N₁₂ nano-cage. It is anticipated that BNNT could be a favorable gas sensor for the detection of N₂O molecule.     

A DFT study on the healing of N‐vacancy defects in boron nitride nanosheets and nanotubes by a methylene molecule

In the present work, density functional theory calculations are used to investigate the healing mechanism of a N‐vacancy defect in boron nitride nanosheet (BNNS) or nanotube (BNNT) with a CH₂ molecule. The healing process starts with the chemisorption of CH₂ at the defect site, followed by its dehydrogenation over the surface. Next, a H₂ molecule is produced which can be easily released from the surface due to its small adsorption energy. For the dehydrogenation of CH₂ molecule over the defective BNNS or BNNT, the first C? H bond dissociation is the rate determining step. Our results indicate that the dehydrogenation of CH₂ over BNNS is both thermodynamically and kinetically more favorable than over BNNT. Besides, this study proposes a novel method for achieving C‐doped BNNSs and BNNTs. Given that the healing process proceeds without using a metal catalyst, therefore, no any purification is needed to remove the catalyst.     

Excited electronic and ionized states of the nitramide molecule, H2NNO2, studied by the symmetry-adapted-cluster configuration interaction method

Symmetry-adapted-cluster configuration interaction (SAC-CI) wave functions were employed to compute 16 singlet and 13 triplet vertical transitions, and 14 ionized states including relative intensities of the nitramide molecule, H₂NNO₂. This molecule is the simplest neutral closed-shell molecule which has an N–NO₂ bond and is a member of the nitramine family, R,R′N(NO₂), an important class of energetic materials with practical applications. The present nitramide results showed strong similarities with the ones of the N, N-dimethylnitramine molecule, which has also an N–NO₂ bond and was previously studied using the SAC-CI method. Experimental ultraviolet and photoelectron band spectra of the nitramide molecule could be successfully assigned. All the singlet transitions have valence character. The computed singlet and triplet transitions, excepting a singlet one, result from excitation originating in the four highest occupied molecular orbitals, which have close energies. Most of the singlet and triplet transitions involved mixing of singly excited configurations. The strongest computed transition, at 6.8 eV, is a mixture of two nπ_NO2 → π^* configurations corresponding to excitations from the highest occupied molecular orbital (HOMO) to the first two virtual orbitals and has an optical oscillator strength value of 0.2665. The computed ionized states described the whole measured spectrum, have excellent agreement when compared with the measured ionization potentials and revealed an inversion of the ordering of the first states not expected according to Koopmanns’ theorem, thereby showing the limitations of the latter.     

Molecular docking evaluation of celecoxib on the boron nitride nanostructures for alleviation of cardiovascular risk and inflammatory

Celecoxib (CXB) is a nonsteroidal anti-inflammatory drug (NSAID) that can be used to treat rheumatoid arthritis and ischemic heart disease. In this research, density functional theory (DFT) and molecular docking simulations were performed to study the interaction of boron nitride nanotube (BNNT) and boron nitride nanosheet (BNNS) with CXB and its inhibitor effect on pro-inflammatory cytokines. The calculated adsorption energies of CXB with the BNNT were determined in aqueous phase. The results revealed that adsorption of CXB molecule via its SO₂ group on BNNT is thermodynamically favored than the NH₂ and CF₃ groups in the solvent environment. Adsorption of CXB on BN nanomaterials are weak physisorption in nature. This can be attributed to the fact that both phenyl groups in CXB are not on the same plane and require significant activation energies for conformational changes to obtain greater H-$\pi$ interaction. Both BNNT and BNNS materials had huge sensitivity in electronic change and short recovery time during CXB interaction, thus having potential as molecular sensor and biomedical carrier for the delivery of CXB drug. IL-1A and TNF-α were implicated as vital cytokines in diverse diseases, and they have been a validated therapeutic target to manage cardiovascular risk in patients with inflammatory bowel disease. A molecular docking simulation confirms that the BNNT loaded CXB could inhibit more pro-inflammatory cytokines including IL-1A and TNF-α receptors as compared to BNNS loaded to CXB.     

Functionalization of BN nanosheet with N2H4 may be feasible in the presence of Stone–Wales defect

Following recent experimental works, herein we investigated chemical functionalization of a BN graphene-like sheet with hydrazine (N₂H₄) molecule based on the density functional theory. We found that the functionalization of the pristine sheet is not possible; while the presence of some structural defects such as Stone–Wales is essential to make it feasible. Functionalization energy of the defected sheet is calculated to be in the range of ?6.1 to ?7.4 kcal/mol at B3LYP/6-31G (d) level. Based on the obtained results, the functionalized BN sheet is found to be more soluble in water in comparison with the pristine sheet which is in good agreement with previous experimental reports. Also, it was found that the electronic properties of the defected sheet are slightly changed upon the chemical functionalization.     

Electronic, Energetic, and Geometric Properties of Methylene-Functionalized C60

Chemical functionalization of C₆₀ fullerene with one to six carbene (CH₂) molecule(s) has been investigated using density functional theory. We have found that the reaction is regioselective so that a CH₂ molecule prefers to be adsorbed atop a C–C bond which is shared between two hexagonal rings of the C₆₀, releasing energy of ?3.95 eV. Singly occupied molecular orbital (SOMO) of the CH₂ interacts with LUMO of the C₆₀ via a [2 + 1] cycloaddition reaction. Energy of the reaction and work function of the system are decreased by increasing the number of adsorbed CH₂ molecules. The HOMO/LUMO energy gap of C₆₀ is slightly changed and the electron emission from its surface is facilitated upon the functionalization.     

一锅法合成二硝基五亚甲基四胺反应机理的研究

二硝基五亚甲基四胺(DPT)是高性能单质炸药奥克托金(HMX)的重要硝化前体.以尿素为起始原料,中间产物不分离,经硝化、水解、Mannich缩合等反应得到DPT,总收率63.2%.通过分离、捕获中间体以及同位素示踪实验研究了一锅法合成DPT的反应机理.分离出了稳定的中间体二硝基脲、硝酰胺和二羟甲基硝酰胺,用苯磺酰氯捕获到了活性中间体1-硝基-六氢均三嗪.以氘代甲醛、二羟甲基硝酰胺和氨缩合得到氘标记的DPT,1HNMR和MS分析结果表明:在反应过程中二羟甲基硝酰胺解离释放出甲醛和硝酰胺,小分子碎片随机组合生成了三嗪化合物,进而生成DPT.     

Molecular-level functionalization of electrode surfaces

An ultra-thin film of functional molecule(s) can be deposited on an electrode, which then serves as a device to amperometrically monitor compounds of biological interest. The methods of surface functionalization, mostly on tin oxide (SnO₂) electrodes, include: chemical modification (covalent bond formation between the surface OH group with a functional group of a molecule); the Langmuir-Blodgett technique, where the NH₂ group of a long-chain alkylamine is bound to an enzyme via a small dialdehyde molecule as spacer; and electropolymerization of pyrrole in an electrolyte containing a single enzyme or a sequentially operating bienzyme system. The results of such investigations by the author’s group are presented.     

The nature of chemical bonding in nitramide

The spatial and electronic structure studies of nitramide NH₂NO₂ suggest that the change in its molecular geometry upon transition from the gas phase to the condensed state is caused by an increase in the contribution of conjugation between functional groups. According to the analysis of the Bader atomic charges, the effects of such conjugation are to a considerable extent governed by intramolecular charge transfer from the amino to the nitro group. From estimation of the contribution of conjugation to the charge transfer it follows that conjugation remains in the isolated molecule. The influence of hydrogen bonding on the increase in the contribution of conjugation and the corresponding charge redistribution in the molecule was considered. Despite the presence of conjugation between functional groups, the planar configuration of the molecule in the crystal is not realized and the crystallographic twofold axis corresponds to superposition of two molecular configurations with C _s symmetry.     

DFT study on the adsorption and dissociation of hydrogen sulfide on MgO nanotube

The adsorption of a H₂S molecule on the surface of an MgO nanotube was investigated using density functional theory. It was found that H₂S molecule can be associatively adsorbed on the tube surface without any energy barrier or it can be dissociated into –H and –SH species overcoming energy barrier of 4.03–7.77 kcal/mol. The associative adsorption is site selective so that the molecule is oriented in such a way that the sulfur atom was linked to an Mg atom. The HOMO–LUMO energy gap of the tube has slightly changed upon associative adsorption, while they were significantly influenced by dissociation process. Especially, the highest occupied molecular orbital of the tube shifts to higher energies which can facilitate electron emission current from the tube surface. Also, energy gap of the tube dramatically decreased by about 0.93–1.05 eV which influences the electrical conductivity of the tube.     

A DFT study on carbon-doping at different sites of (8, 0) boron nitride nanotube

A density functional theory study is carried out to investigate the geometries and electronic structure of pristine and carbon-doped (8, 0) single-walled boron nitride nanotubes (BNNTs). In order to understand the effect of impurities or doping on (8, 0) single-walled BNNT, we simulated C-doping in six different ways. Geometry optimizations reveal that in the considered models, B–N bond lengths are not significantly influenced by C-doping. Based on the quantum theory of atoms in molecules analysis, charge density accumulation for axial B–N bond critical points (BCPs) of pristine BNNT is slightly larger than zigzag ones. However, due to C-doping at the B- or N-tips, the evaluated electron density tends to decrease slightly at both axial and zigzag B–N BCPs. Besides, results indicate that influence of C-doping on properties of the (8, 0) BNNT could be also detected by values of chemical shielding isotropy (σ _iso) and anisotropy (Δσ).     

Nitrogen monoxide storage and sensing applications of transition metal–doped boron nitride nanotubes: a DFT investigation

The structural properties, electronic properties, and adsorption abilities for nitrogen monoxide (NO) molecule adsorption on pristine and transition metal (TM = V, Cr, Mn, Nb, Mo, Tc, Ta, W, and Re) doping on B or N site of armchair (5,5) single-walled boron nitride nanotube (BNNT) were investigated using the density functional theory method. The binding energies of TM-doped BNNTs reveal that the Mo atom doping exhibits the strongest binding ability with BNNT. In addition, the NO molecule weakly interacts with the pristine BNNT, whereas it has a strong adsorption ability on TM-doped BNNTs. The increase in the adsorption ability of NO molecule onto the TM-doped BNNTs is due to the geometrical deformation on TM doping site and the charge transfer between TM-doped BNNTs and NO molecule. Moreover, a significant decrease in energy gap of the BNNT after TM doping is expected to be an available strategy for improving its electrical conductivity. These observations suggest that NO adsorption and sensing ability of BNNT could be greatly improved by introducing appropriate TM dopant. Therefore, TM-doped BNNTs may be a useful guidance to be storage and sensing materials for the detection of NO molecule.

     

Hydrogen adsorption on carbon-doped boron nitride nanotube

The adsorption of atomic and molecular hydrogen on carbon-doped boron nitride nanotubes is investigated within the ab initio density functional theory. The binding energy of adsorbed hydrogen on carbon-doped boron nitride nanotube is substantially increased when compared with hydrogen on nondoped nanotube. These results are in agreement with experimental results for boron nitride nanotubes (BNNT) where dangling bonds are present. The atomic hydrogen makes a chemical covalent bond with carbon substitution, while a physisorption occurs for the molecular hydrogen. For the H(2) molecule adsorbed on the top of a carbon atom in a boron site (BNNT + C(B)-H(2)), a donor defect level is present, while for the H(2) molecule adsorbed on the top of a carbon atom in a nitrogen site (BNNT + C(N)-H(2)), an acceptor defect level is present. The binding energies of H(2) molecules absorbed on carbon-doped boron nitride nanotubes are in the optimal range to work as a hydrogen storage medium.     

Dispersion-corrected DFT study on the carbon monoxide sensing by B<Subscript>2</Subscript>C nanotubes: effects of dopant and interferences

Electrical sensitivity of a boron carbon nanotube (B₂CNT) was examined toward carbon monoxide (CO) molecule by using dispersion-corrected density functional theory calculations. It was found that CO is weakly adsorbed on the tube, releasing energy of 3.5–4.1 kcal/mol, and electronic properties of the tube are not significantly changed. To overcome this problem, boron and carbon atoms of the tube were substituted by aluminum and silicon atoms, respectively. Although both Al and Si doping make the tube more reactive and sensitive to CO, Si doping seems to be a better strategy to manufacture CO chemical sensors due to the higher sensitivity without deformation of nanotube structure after adsorption procedure. Moreover, it was shown that some interference molecules such as H₂O, H₂S and NH₃ cannot significantly change the electronic properties of B₂CNT. Therefore, the Si-doped tube might convert the presence of CO molecules to electrical signal.     

Controlled Covalent Functionalization of 2 H-MoS2 with Molecular or Polymeric Adlayers

Most air-stable 2D materials are relatively inert, which makes their chemical modification difficult. In particular, in the case of MoS₂, the semiconducting 2 H-MoS₂ is much less reactive than its metallic counterpart, 1T-MoS₂. As a consequence, there are hardly any reliable methods for the covalent modification of 2 H-MoS₂. An ideal method for the chemical functionalization of such materials should be both mild, not requiring the introduction of a large number of defects, and versatile, allowing for the decoration with as many different functional groups as possible. Herein, a comprehensive study on the covalent functionalization of 2 H-MoS₂ with maleimides is presented. The use of a base (Et₃N) leads to the in situ formation of a succinimide polymer layer, covalently connected to MoS₂. In contrast, in the absence of base, functionalization stops at the molecular level. Moreover, the functionalization protocol is mild (occurs at room temperature), fast (nearly complete in 1 h), and very flexible (11 different solvents and 10 different maleimides tested). In practical terms, the procedures described here allow for the chemist to manipulate 2 H-MoS₂ in a very flexible way, decorating it with polymers or molecules, and with a wide range of functional groups for subsequent modification. Conceptually, the spurious formation of an organic polymer might be general to other methods of functionalization of 2D materials, where a large excess of molecular reagents is typically used.     

Modeling adsorbate‐induced property changes of carbon nanotubes

Because of their potential for chemical functionalization, carbon nanotubes (CNTs) are promising candidates for the development of devices such as nanoscale sensors or transistors with novel gating mechanisms. However, the mechanisms underlying the property changes due to functionalization of CNTs still remain subject to debate. Our goal is to reliably model one possible mechanism for such chemical gating: adsorption directly on the nanotubes. Within a Kohn–Sham density functional theory framework, such systems would ideally be described using periodic boundary conditions. Truncating the tube and saturating the edges in practice often offers a broader selection of approximate exchange–correlation functionals and analysis methods. By comparing the two approaches systematically for NH₃ and NO₂ adsorbates on semiconducting and metallic CNTs, we find that while structural properties are less sensitive to the details of the model, local properties of the adsorbate may be as sensitive to truncation as they are to the choice of exchange–correlation functional, and are similarly challenging to compute as adsorption energies. This suggests that these adsorbate effects are nonlocal. © 2017 Wiley Periodicals, Inc.     

Theoretical Study of Adsorption Behavior of Vemurafenib Drug over BNNT(5,5-9) as a Factor of Drug Delivery: a DFT Study

In this research, a density functional theory(DFT) calculation was performed for investigation adsorption behavior of the anticancer drug Vemurafenib on BNNT(5,5-9) by using the M06-2X/6-31 G* level of theory in the solvent water. The electronic spectra of the Vemurafenib drug, BNNT(5,5-9) and complex BNNT(5,5-9)/Vemurafenib in solvent water were calculated by Time Dependent Density Functional Theory(TD-DFT) for the study of adsorption effect. The non-bonded interaction effects of the Vemurafenib drug with BNNT(5,5-9) on the electronic properties, natural charges and chemical shift tensors have been also detected. The results display the change in title parameters after process adsorption. According to the natural bond orbital(NBO) results, the molecule Vemurafenib and BNNT(5,5-9) play as both electron donor and acceptor at the complex BNNT(5,5-9)/Vemurafenib. On the other hand, the charge transfer occurs between the bonding, antibonding or nonbonding orbitals in two molecules drug and BNNT. As a consequence, BNNT(5,5-9) can be considered as a drug delivery system for the transportation of Vemurafenib as anticancer drug within the biological systems.     

Detection of paracetamol by armchair BN nanotubes: a molecular study

We have investigated structural and electronic properties of single wall (5,5) boron nitride nanotubes functionalized on the surface and at the ends with paracetamol (C₈H₉NO₂). Studies have been done within the density functional theory as implemented in DMol³ quantum chemistry code. The exchange and correlation energies have been treated according to the generalized gradient approximation with the Perdew–Burke–Ernzerhof parameterization and a basis function with double polarization. The geometry optimization of the (5,5) BNNT-Paracetamol system has been done using the criterion of minimum energy considering eight possible atomic interacting configurations. Simulation results show that the preferential interaction (physisorption) site of the paracetamol is on the nanotube surface in a parallel configuration and making an angle of 45° in the perpendicular direction to the nanotube. The BNNT-Paracetamol system experiences an increase in the polarity which favors the possible dispersion and solubility. As a result of the interaction, the functionalized nanotube chemical reactivity is increased. Provided the work function of the nondoped BNNT-Paracetamol structure decreases as compared with the pristine BNNT, the functionalized nanotubes yielded conditions to improve field emission properties consequently, they may be used as biosensors of paracetamol. Finally, the nanotube doped with carbon atoms induces chemisorption and an increase in the polarity, reactivity, and reduction in the work function. Taking into account, these results it may be suggested the use of the system in sensor devices and optoelectronic systems.     

Boron nitride nanotube (BNNT) as a sensor of hydroperoxyl radical (HO<Subscript>2</Subscript>): A DFT study

In this present study, the adsorption behavior of HO₂ radical on the exterior surface of (5, 0) zigzag boron nitride nanotube (BNNT) has been investigated. The electronic structures and geometries of studied complexes were calculated at B3LYP-D3/6-31++G (d, p) computational level. The value of adsorption energy for the most stable configuration (A) is obtained ?0.68 eV, indicating physisorption process. Meaningful change of HOMO–LUMO gap after adsorption confirming BNNT can be introduced as a promising sensor for sensing of HO₂ radical.