Effects of the HCN adsorption on the structural and electronic parameters of the beryllium oxide nanotube

The adsorption behavior of the HCN on the surface of beryllium oxide nanotube (BeONT) is studied by the density functional theory. Geometrical parameters, electronic properties and adsorption energies have been calculated for the BeONT and fourteen different HCN configurations on the nanotube. According to the obtained results, the process of the HCN molecule adsorption on different sites on the external surface of the nanotube is exothermic and all of the configurations are stable, while the process of HCN molecule adsorption on the internal surface of the BeONT is endothermic. The adsorption energy values indicate that the HCN molecule can be physically adsorbed on the surface of the BeONT. Furthermore, the HOMO–LUMO gap (Eg) of the BeONT decreases upon the HCN adsorption, resulting in the enhancement of the electrical conductivity. The AIM theory has been also utilized to analyze the properties of the bond critical points: their electron densities and their Laplacians. NBO analysis indicates that the HCN molecule can be adsorbed on the surface of the nanotube with a charge transfer from nanotube to HCN molecule. Due to the physisorption, NQR parameters of nanotube are also altered. In order to examine the deformation degree of the nanotube after HCN molecule adsorption, deformation energy is calculated, which indicates that no significant curvature in the geometry of the nanotubes is occurred when HCN adsorbs onto the surface of BeONT.     

Density functional study on the sensing properties of nano-sized BeO tube toward H2S

Using density functional calculations, we have investigated the adsorption of a H₂S molecule on the pristine and Si-doped BeO nanotubes (BeONT). It was found that the H₂S molecule is physically adsorbed on the pristine BeONT with adsorption energies ranging from 3.0 to 4.2 kcal/mol. Substituting a Be or O atom of the tube by Si increases the adsorption energy to 6.9–17.2 kcal/mol. We found that substituting an O atom by Si makes the electronic properties of the BeONT strongly sensitive to the H₂S molecule. Therefore, the process of Si doping provides a good strategy for improving the sensitivity of BeONT to toxic H₂S, which cannot be trapped and detected by the pristine BeONT. Also, the emitted electron current density from the Si_O–BeONT will be significantly increased after the H₂S adsorption.     

Density-functional calculations of HCN adsorption on the pristine and Si-doped graphynes

Graphyne, a lattice of benzene rings connected by acetylene bonds, is one-atom-thick planar sheet of sp- and sp²-bonded carbons differing from the hybridization of graphene (considered as pure sp²). Here, HCN adsorption on the pristine and Si-doped graphynes was studied using density-functional calculations in terms of geometric, energetic, and electronic properties. It was found that HCN molecule is weakly adsorbed on the pristine graphyne and slightly affects its electronic properties. While, Si-doped graphyne shows high reactivity toward HCN, and, in the most favorable state, the calculated adsorption energy is about ?10.1 kcal/mol. The graphyne, in which sp-carbon was substituted by Si atom, is more favorable for HCN adsorption in comparison with sp²-carbon. It was shown that the electronic properties of Si-doped graphyne are strongly sensitive to the presence of HCN molecule and therefore it may be used in sensor devices.     

Fullerene(C_(60)) as a Potential Chemical Sensor for Hydrogen Cyanide Detection

To find a novel sensor for the detection and control of toxic hydrogen cyanide(HCN), the geometrical and electronic parameters of HCN adsorption on fullerene C60 were investigated using density functional theory(DFT) calculations by means of B3 LYP functional with 6-31 G* basis set. The calculated density of states(DOSs) shows that the electronic properties of fullerene C60 were very sensitive to the presence of HCN molecule, so that the Eg of C60 was significantly decreased from 2.76 eV in pristine form to 1.81 eV(34.4% change) after the HCN adsorption which would result in electrical conductance increment. The results demonstrated that the C60 may convert the presence of a HCN molecule to an electrical signal for using in HCN-sensor devices through doping, chemical functionalization. Also, based on calculated results, the C60 is expected to be a potential efficient adsorbent as well as a sensor for detecting the presence of toxic HCN.     

Enhancement of hydrogen physisorption on graphene and carbon nanotubes by Li doping

Density-functional calculations of the adsorption of molecular hydrogen on a planar graphene layer and on the external surface of a (4,4) carbon nanotube, undoped and doped with lithium, have been carried out. Hydrogen molecules are physisorbed on pure graphene and on the nanotube with binding energies about 80-90 meV/molecule. However, the binding energies increase to 160-180 meV/molecule for many adsorption configurations of the molecule near a Li atom in the doped systems. A charge-density analysis shows that the origin of the increase in binding energy is the electronic charge transfer from the Li atom to graphene and the nanotube. The results support and explain qualitatively the enhancement of the hydrogen storage capacity observed in some experiments of hydrogen adsorption on carbon nanotubes doped with alkali atoms.     

Pyrrole adsorption on aluminum nitride nanotubes on DFT data

The adsorption behavior of pyrrole molecule with external surface of (5.0) on zigzag aluminum nitride nanotube (AlNNT) was studied using density functional theory calculations. It was found that the adsorption energy (E_ad) of pyrrole on the surface of pristine nanotubes is about–11.99 kcal/mol. However, when nanotubes have been doped with P atom, the adsorption energy of pyrrole was increased. Calculation showed that for the phosphorus-doped nanotube the adsorption energy range is about–9.04 to?12.80 kcal/mol. AlNNT is a suitable adsorbent for pyrrole, so it can be used in adsorption and separation processes involving pyrrole. The doped AlNNT can potentially be used for pyrrole sensors for detection in environmental systems.     

Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

A theoretical study on the pure and doped ZnO nanoclusters as effective nanobiosensors for 5-fluorouracil anticancer drug adsorption

The electronic sensitivity and effectiveness of the pristine, Fe,- Mg-, Al- and Ga-doped ZnO nanoclusters interacted with 5-fluorouracil (5-FU) anticancer drug are theoretically investigated in the gas phase using the B3LYP/wB97XD density functional theory calculations with LANL2DZ basis set. It is concluded that 5-FU adsorption on the doped nanoclusters has relatively higher adsorption energy as compared with the pristine zinc oxide. A number of thermodynamic parameters, such as band gap energy (E_g), adsorption energy (E_ad), molecular electrostatic potential, global hardness (η) and density of electronic states, are attained and compared. Also, calculated geometrical parameters and electronic properties for the studied systems indicate that Mg- and Ga-doped Zn₁₂O₁₂ present higher sensitivity to 5-FU compared with the pristine nanocluster. Theoretical results reveal that adsorption of 5-FU on the doped nanoclusters is influenced by the electronic conductance of the nanocluster. Therefore, Mg- and Ga-doped ZnO can be considered as promising nanobiosensors for detection of 5-FU in medicine.     

Covalent Functionalization of Pristine and Ga-Doped Boron Phosphide Nanotubes with Imidazole

Abstract

Density functional theory (DFT) calculations at the B3LYP/6–31G* level were performed to investigate covalent functionalization of imidazole on pristine (in gas and H₂O phases) and Ga-doped BPNT models in terms of energetic, geometric, and electronic properties. The results show that imidazole, as a functional group, prefers to be adsorbed via its nitrogen atom on the pristine, Ga_B, and Ga_P nanotube models. The adsorption energy of imidazole on the (6,0) zigzag BPNT in gas and solvent phases is ?0.76 and ?1.11 eV, respectively, and about 0.38 and 0.43 electron are transferred from the imidazole to nanotube in the phases. The presence of a polar solvent increases the electron donor of imidazole molecule. The results show that Ga doping can significantly enhance the adsorption energy of imidazole on the nanotube models to about 95%.

Moreover, the imidazole adsorption on the pristine and Ga-doped BPNT models has not significant changes in the energy gap of the nanotube models and it is slightly changed after covalent functionalization process. This study may provide new insight to the development of functionalized boron phosphide nanotubes for generation of the new hybrid compounds especially in drug delivery systems for virtual applications.     

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.

     

Adsorption of nitrous oxide on the(6,0) magnesium oxide nanotube

Nitrous oxide adsorption on the pristine（6,0） magnesium oxide nanotube was studied by using density functional theory calculations.We present the nature of the N₂O interaction in selected sites of the nanotube.Adsorption energies corresponding to adsorption of the N₂O on the nanotube were calculated to be in the range -11.67 to -22.21 kJ mol^-1.Our results indicate that the N₂O molecule has a weak physical adsorption on the pristine models due to weak Van der Waals interaction between the nanotubes and N₂O molecule.The important results can be useful in production of the N₂O sensors.     

A DFT study of H<Subscript>2</Subscript>CO and HCN adsorptions on 3<Emphasis Type="Italic">d</Emphasis>, 4<Emphasis Type="Italic">d</Emphasis>, and 5<Emphasis Type="Italic">d</Emphasis> transition metal-doped graphene nanosheets

The binding of 3d (Sc, Ti, V), 4d (Y, Zr, Nb), and 5d (La, Hf, Ta) transition metals on graphene nanosheet (TM–GNS) with hydrogen-terminated edges and the adsorption of H₂CO and HCN molecules on the pristine and TM-doped GNSs were theoretically studied using a density functional theory method. The calculation showed that all TM atoms had strong binding with GNS, in which the Ta atom displayed the strongest interaction with GNS. The H₂CO and HCN molecules showed much stronger adsorption on the TM–GNSs than that on the pristine GNS. The H₂CO showed stronger interactions with TM–GNSs than that of HCN, in which the Ta-doping displayed the strongest interactions between the GNS and H₂CO or HCN. The adsorption interactions induced dramatic changes of TM–GNS electronic properties. The results revealed that the adsorption strength and sensor ability of GNS can be greatly improved by introducing appropriate TM dopants. Therefore, TM-doped GNSs are suitable for application in H₂CO and HCN storage and sensor.     

Adsorption of hydrogen molecules on the platinum-doped boron nitride nanotubes

Adsorption of hydrogen molecules on platinum-doped single-walled zigzag (8,0) boron nitride (BN) nanotube is investigated using the density-functional theory. The Pt atom tends to occupy the axial bridge site of the BN tube with the highest binding energy of -0.91 eV. Upon Pt doping, several occupied and unoccupied impurity states are induced, which reduces the band gap of the pristine BN nanotube. Upon hydrogen adsorption on Pt-doped BN nanotube, the first hydrogen molecule can be chemically adsorbed on the Pt-doped BN nanotube without crossing any energy barrier, whereas the second hydrogen molecule has to overcome a small energy barrier of 0.019 eV. At least up to two hydrogen molecules can be chemically adsorbed on a single Pt atom supported by the BN nanotube, with the average adsorption energy of -0.365 eV. Upon hydrogen adsorption on a Pt-dimer-doped BN nanotube, the formation of the Pt dimer not only weakens the interaction between the Pt cluster and the BN nanotube but also reduces the average adsorption energy of hydrogen molecules. These calculation results can be useful in the assessment of metal-doped BN nanotubes as potential hydrogen storage media.     

N2O reduction over hexagonal BN nanosheet: effects of Stone–Wales defect and carbon pair doping

Nitrous oxide (N₂O) adsorption on the pristine and Stone–Wales (SW)-defected hexagonal BN nanosheets were investigated using density functional calculations including dispersion correction. It was found that N₂O is weakly adsorbed on the pristine sheet (h-BN) through van der Waals interaction with adsorption energy of ?1.2 kcal/mol. SW-defected sheet was found to be more reactive toward N₂O molecule having no significant change in electronic properties. However, the formation of B–B and N–N bond pairs in SW-defected sheet can be avoided, if there is a C–C pair doped in sheet (C₂-SW-h-BN). In this case, a strong adsorption is found due to large adsorption energy (?23.7 kcal/mol) and short bond length compared to the SW-h-BN complex. Interestingly, it was indicated that the N₂O molecule could be reduced into the N₂ on the C₂-SW-h-BN.     

QM/MM study of the interaction between zigzag SnC nanotube and small toxic gas molecules

Adsorptions of small toxic molecules such as CO, N₂, HCN, SO₂, H₂CO, and NH₃ on a single‐walled (6,0) SnC nanotube (SnCNT) are investigated using Quantum Mechanics/Molecular Mechanics (QM/MM) methodology. The calculations are carried out at the B3LYP/6‐311++G(d,p)//LANL2DZ:UFF level of theory. The high layer of the model consists of a pyrene‐type ring on the nanotube surface as the adsorption site, where one gas molecule is allowed to interact. Conversely, for the adsorption of the two molecules, a larger site like a coronene ring is used for the high layer. Adsorption energy, Gibbs free energy change, Mulliken charge transfer, and total electron‐density maps are computed in each case. The adsorption strength of the gas molecule on the SnCNT surface is also analyzed from the density of states projected to different atoms (PDOS) of the nanotube–adsorbate complexes. The adsorptions of CO and N₂ on the (6,0) SnCNT surface require to cross potential barriers, and the corresponding transition structures are identified by ONIOM‐IRC calculations. For the remaining four molecules, the processes of adsorption are predicted to be barrier‐less. The calculations for the adsorption of H₂CO on (5,0) and (7,0) SnCNT surfaces are extended to study the effect of the size of the nanotube. Results for the adsorption of a single molecule on (6,0) SnCNT using B3LYP functional are compared with those obtained from a dispersion corrected functional such as M06‐2X. © 2015 Wiley Periodicals, Inc.     

Density functional theory study on the possibility of Si‐, Ge‐, and Sn‐doped carbon nanotubes as efficient support materials for platinum

PBEPBE‐D3 calculations were performed to investigate how platinum (Pt) interacts with the internal and external surfaces of single‐walled pristine, Si‐, Ge‐, and Sn‐doped (6,6) carbon nanotubes (CNTs). Our calculations showed that atomic Pt demonstrates stronger binding strength on the external surfaces than the internal surface adsorption for the same type of nanotube. In cases of external surface adsorptions, Si‐, Ge‐, and Sn‐doped CNTs show comparable binding energies for Pt, at least 1.40 eV larger than pristine CNT. This enhancement can be rationalized by the strong covalent interactions between Pt and X? C (X = Si, Ge, and Sn) pairs based on structural and projected density of states analysis. In terms of internal surface adsorptions, Ge and Sn doping could significantly enhance the binding of Pt. Pt atom shows much more delocalized and bonding states inside Ge‐ and Sn‐doped CNTs, indicating multiple‐site interaction pattern when atomic Pt is confined inside the nanotubes. However, the internal surface of Si‐doped CNT presents limited enhancement in Pt adsorption with respect to that of pristine CNT because of their similar binding geometries. © 2016 Wiley Periodicals, Inc.     

Si‐Doped B12N12 Nanocage as an Adsorbent for Dissociation of N2O to N2 Molecule

Adsorption of N₂O molecule by using density functional theory calculations at the B3LYP/6–31G* level onto pristine and Si‐doped B₁₂N₁₂ nanocage in terms of energetic, geometric, and electronic properties was investigated. The results of calculations showed that the N₂O molecule is physically adsorbed on the pristine and Si‐doped B₁₂N₁₂ (Si_N) models, releasing energies in the range of –1.13 to –2.02 kcal mol⁻¹. It was found that the electronic properties of the models have not changed significantly upon the N₂O adsorption. On the other hand, the adsorption energy of N₂O on the Si‐doped B₁₂N₁₂ (Si_B model) was about –67.20 kcal mol⁻¹and the natural bond orbital charge of 0.58|e| is transferred from the nanocage to the N₂O molecule. In the configuration, the O atom of N₂O molecule is bonded to the Si atom of the nanocage, so that an N₂ molecule escapes from the wall of the nanocage. The results showed that the Si_B model can be an adsorbent for dissociation of the N₂O molecule.     

NBO,AIM, and TD-DFT assisted screening of BNNT optimum diameter on ethyl phosphorodimethylamidocyanidate sensor design

A computational study based on DFT calculations was performed to investigate the effect of phosphorodimethylamidocyanidate (PDMAC) molecule adsorption on the surface of pure and Ga-doped (4,0), (5,0), (6,0), (7,0), and (8,0) zigzag boron-nitride nanotubes (BNNTs). Our results reveal that the interactions between PDMAC molecule and (5,0), (6,0), (7,0), and (8,0) BNNTs are weak. However, according to the AIM and NBO analysis the PDMAC exhibits strong affinity towards the (4,0) BNNT with appreciable adsorption energy (?111.03 kJ/mol). The adsorption of PDMAC molecule onto the (4,0) BNNT affect the electronic conductance, hypsochromic, and hyperchromic shifts in the calculated UV-Visible spectrum. Based on the obtained results, it is expected that the pristine and Ga-doped (4,0) BNNT could be promising candidates in gas sensor devices for detecting the PDMAC molecule.     

Synthesis of Mg(II) doped ferrihydrite-humic acid coprecipitation and its Pb(II)/Cd(II) ion sorption mechanism

A magnesium doped ferrihydrite-humic acid coprecipitation (Mg-doped Fh-HA) was synthesized by coprecipitation method. The removal of heavy metals such as Pb(II) and Cd(II) was assessed. The isotherms and kinetic studies indicated that the Mg-doped Fh-HA exhibited a remarkable Pb(II) and Cd(II) sorption capacity (maximum 120.43 mg/g and 27.7 mg/g, respectively.) in aqueous solution. The sorption of Pb(II) and Cd(II) onto best fitted pseudo-second-order kinetic equation and Langmuir model. The adsorption mechanism of Mg-doped Fh-HA on Pb(II) and Cd(II) involves surface adsorption, surface complexation and surface functional groups (such as carboxyl group, hydroxyl group). In addition, ion-exchange and precipitation cannot be ignored. The Mg-doped Fh-HA is a low-cost and high-performance adsorption material and has a wide range of application prospects.