Hydrogen physisorption energies for bumpy,saturated, nitrogen-doped single-walled carbon nanotubes

Finite saturated regular carbon nanotubes (CNTs) are predicted to exhibit higher capacity as hydrogen storage media compared to unsaturated regular CNTs. In the present study, molecular hydrogen physisorption energies (MHPEs) for finite saturated and unsaturated bumpy defected CNTs were calculated by density functional theory (DFT-D3) methods at the B3LYP/6-31G(d) theory level, with rigorous inclusion of van der Waals interactions. The calculated MHPEs for both regular and bumpy defected armchair, chiral and zigzag CNTs with similar diameters and lengths, with and without nitrogen doping, were compared in terms of Eph/H₂, defined as the MHPE per hydrogen molecule adsorbed inside the nanotube. For all studied systems, Eph/H₂ increased with the number of physisorbed hydrogen molecules. Nitrogen doping of regular and bumpy CNTs resulted in an increase in the Eph/H₂ values, with the exception of bumpy chiral nanotubes. The results of this study demonstrate that bumpy defects are important nanotube structural features whose effects depend on nanotube chirality. For instance, bumpy defects were beneficial for undoped and doped zigzag nanotubes, resulting in a decrease in Eph/H₂ values for regular structures from 0.5 and 0.74 to 0.26 and 0.42 eV, respectively. By contrast, for doped armchair regular structures with an Eph/H₂ value of 0.38 eV, bumpy defects increased Eph/H₂ to 0.45 eV. These Eph/H₂ values for bumpy doped armchair and the zigzag nanotubes are all within the range of 0.1–0.5 eV/H₂ reported as ideal for reversible hydrogen storage under environmental conditions.     

A density-functional theory of hydrogen adsorption on indium nitride nanotubes

First-principles calculations based on density functional theory (DFT) are used to study the chemisorption properties of one, two, and four hydrogen atoms on the zigzag and armchair single-walled InN nanotubes (InNNTs).The results indicate that the H atom is strongly bounded to the exterior wall of (4, 4) InNNTs compared with the (7, 0) InNNTs, while the chemisorption energies corresponding to the most stable configuration of H₂ dissociation and a single H atom are found to be–3.85 and–3.26 eV, respectively. Furthermore, the effect of the hydrogen storage on the geometries and electronic properties of related InN nanotubes were also discussed. The computed density of states (DOS) indicates that the energy gap of the zigzag and armchair InN nanotubes on hydrogen adsorptions are significantly decreased which can increase the electrical conductance of the tubes. Therefore, InN nanotubes due to the high binding energy can be used for hydrogen storage.     

Nonempirical calculations of the electronic properties of new boron nitride graphyne-like nanotubes

The nonempirical density-functional tight-binding approach to band structure calculations was used to study the structural and electronic properties of new boron nitride graphyne-like nanotubes (α-BN-NT) constructed on the basis of the atomic motif of α-graphyne. All α-BN tubes were semiconductors with gap widths of 3.8–4.2 eV. The electron energy characteristics of zigzag and armchair α-BN-NTs are discussed in comparison with the known boron nitride graphite-like nanotubes. In addition, the special features of interatomic interactions in α-BN are analyzed using the nonempirical discrete variational method of density functional theory.     

Molecular dynamics assessment of doxorubicin–carbon nanotubes molecular interactions for the design of drug delivery systems

Carbon nanotubes (CNTs) constitute an interesting material for nanomedicine applications because of their unique properties, especially their ability to penetrate membranes, to transport drugs specifically and to be easily functionalized. In this work, the energies of the intermolecular interactions of single-walled CNTs and the anticancer drug doxorubicin (DOX) were determined using the AMBER 12 molecular dynamics MM/PBSA and MM/GBSA methods with the aim of better understanding how the structural parameters of the nanotube can improve the interactions with the drug and to determine which structural parameters are more important for increasing the stability of the complexes formed between the CNTs and DOX. The armchair, zigzag, and chiral nanotubes were finite hydrogen-terminated open tubes, and the DOX was encapsulated inside the tube or adsorbed on the nanotube surface. Pentagon/heptagon bumpy defects and polyethylene glycol (PEG) nanotube functionalization were also studied. The best interaction occurred when the drug was located inside the cavity of the nanotube. Armchair and zigzag nanotubes doped with nitrogen, favored interaction with the drug, whereas chiral nanotubes exhibited better drug interactions when having bumpy defects. The π-π stacking and N-H…π electrostatic interactions were important components of the attractive drug-nanotube forces, enabling significant flattening of the nanotube to favor a dual strong interaction with the encapsulated drug, with DOX–CNT equilibrium distances of 3.1–3.9 Å. These results can contribute to the modeling of new drug-nanotube delivery systems.

     

Nitrogen-doped carbon nanotubes for heat transfer applications

In this research, it is aimed to enhance the heat transfer properties of the carbon nanotubes through nitrogen doping. To this end, nitrogen-doped multiwall carbon nanotubes (N-CNTs) were synthesized via chemical vapor deposition method. For supplying carbon and nitrogen during the synthesis of N-CNTs, camphor and urea were used, respectively, at 1000 °C over Co–Mo/MgO nanocatalyst in a hydrogen atmosphere. N-CNTs with three different nitrogen loadings of 0.56, 0.98, and 1.38 mass% were synthesized, after which, water/N-CNT nanofluids of these three samples with concentrations of 0.1, 0.2, and 0.5 mass% were prepared. To obtain a stable nanofluid, N-CNTs were functionalized by nitric acid followed by stabilizing in water by employing the ultrasonic bath. Investigation on the stability of the samples showed a high stability level for the prepared water/N-CNT nanofluids in which the zeta potential of ??43.5 mV was obtained for the best sample. Also for studying the heat transfer properties, the thermal conductivity in the range of 0.1–0.5 mass% and convection heat transfer coefficients of nanofluids in the range of 0.1–0.5 mass%, and Reynolds number in the range of 4000–9000 were evaluated. The results showed 32.7% enhancement of the convection heat transfer coefficients at Reynolds number of 8676 and 27% increase in the thermal conductivity at 0.5 mass% and 30 °C.

     

The influence of nitrogen sources on nitrogen doped multi-walled carbon nanotubes

A range of nitrogen doped carbon nanotubes (N-CNTs) was produced by a nebulised floating catalyst method at 850 °C using a mixture of toluene and 1-8% nitrogen containing reagents (a range of amines and amides). The carbon nanotube (CNT) products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), CHN analysis as well as Raman spectroscopy. Differences due to the different N containing reagents were noted but in general all reagents gave aligned CNTs that at low concentration (1%) were longer and wider than those produced without nitrogen. Increased N content in the reactant mixture gave doped tubes that became shorter and showed more disorder. Treatment of the N-CNTs with nitric acid (microwave, 30 min) gave samples that were chemically modified by the acid (loss of alignment, narrower tubes and more facile oxidation). It appears in general that the amount of N in the nitrogen containing reagent is more important than the source and type of the N atoms used as revealed by trends in the morphology (diameter, length) of the N-CNTs produced.     

CVD synthesis of nitrogen doped carbon nanotubes using ferrocene/aniline mixtures

Nitrogen doped carbon nanotubes (N-CNTs) have been synthesized by the chemical vapour deposition (CVD) floating catalyst method using either 4-ferrocenylaniline or mixtures of varying concentrations of ferrocene/aniline together with toluene as added carbon source. The N-CNTs produced are less stable (thermal gravimetric analysis measurements), less graphitic and more disordered (transmission electron microscope measurements) than their undoped counterparts. The ratio of the Raman D- and G-band intensities increase with the nitrogen concentration used during the CNT growth. Furthermore, the transmission electron microscope (TEM) studies reveal that the CNTs are multi-walled (MW), and that the diameters of the N-MWCNTs can be controlled by systematically varying the concentrations of the nitrogen source. The TEM analysis also revealed that when ferrocenylaniline and ferrocene/aniline reactions are compared at similar Fe/N ratios, higher N doping levels are achieved (ca. 2-5×) when ferrocenylaniline is the catalyst.     

Nitrogen-Doped Carbon Nanotubes as an Effective Support of Heterogeneous Catalysts for Selective Alkene Oxidation

Kinetics and Catalysis - Nitrogen-doped carbon nanotubes (N-CNTs) with different degrees of nitrogen doping were synthesized. The effects of nitrogen in the N-CNTs on the...     

DFT calculations of NMR properties for GaP nanotubes

Abstract  

We performed density functional theory calculations for nitrogen-doped models of the representative structures of (6,0) zigzag and (4,4) armchair aluminum phosphide nanotubes (AlPNTs). Our results indicate that the optimized bond distances and tip diameters do not detect the effects of the N-doped regions; however, the effects are observed for the band gap energies and dipole moments. It is noted that substitution of the P atom by the N atom does not influence the value of band gap energy for this N-doped model. The results also indicate that the tendency of the Al atom for contribution to the Al–N bond is stronger than the tendency of the P atom for contribution to the N–P bond; therefore, the latter form of substitution makes the AlPNTs interesting as reactive materials towards other atoms or molecules, especially for the the zigzag AlPNT.     

Features of the chemical bonding in fluorinated and hydrogenated carbon: Nanotubes analysis of polarized NEXAFS spectra

The carbon K-edge NEXAFS spectra of initial and fluorinated and hydrogenated single-wall carbon nanotubes (SWCNTs) are analyzed theoretically with regard to the polarization dependence. Differences in the polarized theoretical spectra of SWCNTs with zigzag and chair chiralities are shown. As a result of the comparison of experimental and theoretical carbon K-edge NEXAFS spectra of hydrogenated and fluorinated SWCNTs it is found that it is most probable that hydrogen atoms attach to the outer surface of the tube wall and fluorine atoms to the outer and inner surfaces of the SWCNT wall. Based on the analysis of polarized theoretical spectra of fluorinated and hydrogenated SWCNTs differences in the symmetry of the final states of C-H and C-F bonds are shown.     

氮掺杂碳纳米管负载的Ru和Pd催化剂上异丙醇的转化(英文)

Ru and Pd (2 wt%) loaded on pure and on Ndoped carbon nanotubes (NCNTs) were prepared and tested using the isopropyl alcohol decomposition reaction as probe reaction. The presence of nitrogen functionalities (pyridinic, pyrrolic, and quaternary nitrogen) on the nitrogen doped support induced a higher metal dispersion: Pd/NCNT (1.8 nm) Pd/CNT (4.9 nm), and Ru/NCNT (2.4 nm) Ru/CNT (3.0 nm). The catalytic activity of the supports was determined first. Isopropyl alcohol conversion produces acetone on CNTs while on NCNTs it led to both dehydration and dehydrogenation products. At 210 °C and in the presence of air, the isopropyl alcohol conversion was higher on the NCNTs (25%) than on the CNTs (11%). The Pd loaded catalysts were more active and more selective than the Ru ones. At 115 °C, the Pd catalysts were 100% selective towards acetone for a conversion of 100%, whereas the Ru catalysts led to dehydration and dehydrogenation products. The nitrogen doping induced the appearance of redox properties when oxygen is present in the reaction mixture.     

Simulation of structure and stability of carbon nanoribbons

Results of carbon nanoribbons and nanotubes simulation by means of hybrid density functional method and using empirical potentials have been compared. Energy of the nanoribbons formation and their citting from graphene sheet as well as energy of the nanotubes folding from graphene and nanoribbons have been determined. The REBO force field satisfactorily reflects the result of quantum chemical simulations; however, it cannot reproduce the formation of triple bonds between the edge atoms of the nanoribbons in the armchair conformation and thus leads to underestimated stability of the latter. Energy of the nanotubes folding from the nanoribbons is linear with the nanotube diameter.     

Aluminum nitride nanotubes

An AlN nanotube (AlNNT) was theoretically predicted in 2003. In comparison with the carbon nanotubes, the AlNNTs are wide-band-gap nanostructures with high reactivity, high thermal stability and sharp electronic sensitivity toward some chemicals. The B3LYP predicts an HOMO–LUMO gap of 3.74–4.27 eV for zigzag AlNNTs, while the experimental bad gap of bulk AlN is about 6.28 eV. The lowest strain energy of AlNNTs relative to its AlN nanosheet compared to the nanosheets of carbon and BN nanotubes with an equivalent diameter suggests the feasibility of AlNNT synthesis from its nanosheet. Theoretical methods predict a Young’s Modulus of about 453 GPa for AlNNTs that is smaller than that of carbon (1 TPa), BN (870 GPa) and GaN (796 GPa) nanotubes. In 2003, the faceted single-crystalline hexagonal AlNNTs were synthesized and extensively explored by means of density functional theory calculations. Several works have suggested different potential applications for AlNNTs including chemical sensors, hydrogen storage, gas adsorbent, and electron field emitter. This review is a comprehensive study on the latest achievements in the structural analyses, synthesis, and property evaluations based on the computational methods on the AlNNTs in the light of the development of nanotubes.     

氮掺杂碳纳米管包覆碳化硅作为不含金属的催化剂(英文)

A hierarchical metal-free catalyst consisting of nitrogen-doped carbon nanotubes decorated onto a silicon carbide (N-CNTs/SiC) macroscopic host structure was prepared. The influence of N-CNTs incorporation on the physical properties of the support was evaluated using different characterization techniques. The catalyst was tested as a metal-free catalyst in the selective oxidation of H2S and steam-free dehydrogenation of ethylbenzene. The N-CNTs/SiC catalyst exhibited extremely good desulfurization performance compared to a Fe2O3/SiC catalyst under less conducive reaction conditions such as low temperature, high space velocity, and a low O2-to-H2S molar ratio. For the dehy-drogenation of ethylbenzene, a higher dehydrogenation activity was obtained with the N-CNTs/SiC catalyst compared to a commercial K-Fe/Al2O3 catalyst. The N-CNTs/SiC catalyst also displayed good stability as a function of time on stream for both reactions, which was attributed to the strong anchoring of the nitrogen dopant in the carbon matrix. The extrudate shape of the SiC support allowed the direct macroscopic shaping of the catalyst for use in a conventional fixed-bed reactor without the problems of catalyst handling, transportation, and pressure drop across the catalyst bed that are encountered with nanoscopic carbon-based catalysts.     

Computational studies on aluminum nitride and aluminum phosphide nanotubes: density functional calculations of 27Al electric field gradient tensors

Abstract  

Nuclear quadrupole resonance (NQR) parameters including the nuclear quadrupole coupling constant (C _Q) and asymmetry parameter (η _Q) at the sites of various ²⁷Al nuclei on (6,0) zigzag and (4,4) armchair AlN and AlP nanotubes (NTs) were calculated by using the density functional theory (DFT) method to study the properties of the electronic structures of the nanotubes. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 suite of programs. The calculated electric field gradient tensors were converted to the nuclear quadrupole resonance parameters, C _Q constant, and η _Q parameter. The quadrupole resonance parameters in each of the structures were divided into four layers with equivalent electric field gradient tensor eigenvalues in each layer. The results show that, in AlN and AlP nanotubes, the Al atoms at the edges of the nanotubes play dominant roles in determining the electronic behavior of the nanotubes and important roles in growth and synthesis processes of the nanotubes. Also the average values of C _Q(²⁷Al) for the AlNNT models were higher in comparison with the AlPNT models, while variations of C _Q(²⁷Al) in AlPNTs were greater in comparison with in AlNNTs.     

N-CNTs/NiCo-LDH复合材料的制备及电化学性能

通过高温碳化聚吡咯纳米管制备了氮掺杂碳纳米管(N-CNTs), 并采用共沉淀法将镍钴层状双氢氧化物(NiCo-LDH)原位生长在N-CNTs上, 制备出具有三维互联网状结构的N-CNTs/NiCo-LDH复合材料. 研究了镍钴摩尔比对N-CNTs/NiCo-LDH复合材料形貌结构和电化学性能的影响. 结果表明, 当镍钴摩尔比为1∶2时, N-CNTs/Ni₁Co₂-LDH具有最佳的电化学性能. 在1 A/g电流密度下, 其比电容可达1311.8 F/g; 当电流密度为 10 A/g时, 电容保持率高达88.3%, 展现出优异的倍率性; 在经过2500次循环后, 电容保持率仍可达76.4%, 具有良好的循环稳定性.由N-CNTs/Ni₁Co₂-LDH与活性炭(AC)电极所构建的N-CNTs/Ni₁Co₂-LDH//AC水系混合型超级电容器, 在750 W/kg功率密度下, 具有27.19 W·h/kg的高能量密度.     

Laser-induced pinpoint hydrogen evolution from benzene and water using metal free single-walled carbon nanotubes with high quantum yields

Metal-free photocatalytic hydrogen evolution occurred efficiently in benzene containing single-walled carbon nanotubes under laser irradiation at 532 nm with an extremely high turnover number of 2 000 000 and a high quantum yield of 130%. The rate of hydrogen evolution increased with increasing laser intensity to exhibit a fourth power dependence, suggesting that hydrogen was evolved via four-photon processes in which the coupling of two radical anions derived from benzene is the rate-determining step and the benzene radical anion is produced by electron transfer from benzene to the doubly excited state of single-walled carbon nanotubes, which requires two photons. Polymerisation of benzene was induced by the photogenerated C₆H₆˙^–, accompanied by hydrogen evolution, resulting in a leverage effect to increase the quantum yield of hydrogen evolution to well over the 25% expected for the four-photon process. Laser-induced hydrogen evolution also occurred in water containing single-walled carbon nanotubes. In contrast to the case of benzene, water was not oxidized but hydrogen evolution from water was accompanied by the multi-oxidation of single-walled carbon nanotubes. The yield of hydrogen based on one mole of single-walled carbon nanotubes with 1.4 nm diameter and 1–5 mm length was determined to be 2 700 000%, when oxidations of single-walled carbon nanotubes occurred to produce the polyhydroxylated product.     

Fluorination of multiwall nitrogen-doped carbon nanotubes

A film of oriented nitrogen-doped multiwall carbon nanotubes was grown on a silicon substrate as a result of the thermolysis of an acetonitrile + ferrocene mixture. The fluorination of the film by BrF₃ vapor at room temperature removed the substrate; however, the vertical orientation of the nanotubes was not destroyed. Analysis of micrographs of a fluorinated sample obtained with a high-resolution transmission electron micro-scope showed that only the surface walls of the nanotubes were fluorinated. The fluorine concentration of the product as determined from X-ray photoelectron spectroscopy was about 16%. A comparison of the N1s spectra of the starting and fluorinated samples showed that the nitrogen atoms of CN_x nanotubes changed their electronic state as a result of fluorination. Matching of the X-ray photoelectron spectroscopic data with the results of quantum-chemical calculations for fragments of fluorinated nitrogen-doped nanotubes showed that fluorine atoms preferred to attach to pyridine-like nitrogen atoms or to carbon atoms in the ortho or meta positions relative to a nitrogen atom.     

Insights into the enhanced tolerance to carbon monoxide on model tungsten trioxide-decorated polycrystalline platinum electrode

Polycrystalline platinum decorated by WO₃ nanoparticles (WO₃/Pt_pc) is used as a model electrode to gain insights into the enhanced tolerance to carbon monoxide (CO) observed on such composite materials. Bifunctional-type reactions involving WO₃ and Pt active sites are observed, such as hydrogen spill-over or the electrooxidation of CO molecules adsorbed on Pt sites neighboring the WO₃ nanoparticles. The resulting CO_ad-free Pt sites are active for the hydrogen oxidation reaction (HOR), thereby enhancing the HOR activity for WO₃/Pt_pc electrode relatively to bare Pt_pc in 300 ppm CO/H₂ saturated HClO₄ electrolyte. However, this bifunctional effect occurs exclusively for CO molecules weakly adsorbed on Pt, i.e. only for a small fraction of the CO_ad fully covering the Pt surface.     

A theoretical study of the dissociative chemisorption of hydrogen on carbon nanotubes

Potential profiles were obtained for the chemisorption of hydrogen on (n, n) and (n, 0) carbon nanotubes. The energy barriers and rate constants for hydrogen molecule sorption on and desorption from various nanotubes were determined. The constants for sorption and desorption were used to calculate sorption-desorption equilibrium constants. Sorption on outside nanotube surfaces was found to be more favorable energetically than sorption on inside surfaces.