Functionalization of carbon nanotubes with Vaska's complex: a theoretical approach

The functionalization of single-walled carbon nanotubes (CNTs) with Vaska's complex trans-Ir(CO)Br(PPh(3))(2) has been investigated by means of hybrid quantum mechanics/molecular mechanics (QM/MM) calculations. The formation of a stable adduct has been experimentally evidenced by Wong et al. (Nano Lett. 2002, 2, 49), but microscopical details on the metal-nanotube interaction are still unclear. Our calculations show a low propensity to eta(2) coordination of Vaska's complex with the perfect hexagonal network of CNTs. Rather, a stronger interaction takes place when the transition metal center coordinates to carbon atoms belonging to pentagonal rings, as in topological defects or end-caps.     

Carbon nanotubes and fullerene in the solution polymerisation of acrylonitrile

The radical activity of single wall carbon nanotubes (SWCNT) and fullerene C₆₀ in the radical polymerisation of acrylonitrile (AN) in N,N-dimethylformamide (DMF) initiated by 2,2′-azobis[2-methyl-ω-hydroxy-oligo(oxyethylene) propionate] [AIB-OOE(4 0 0)] and 2,2′-azoisobutyronitrile (AIBN) at 333 K was investigated in situ using a dilatometric method. The carbonaceous substances were sonicated in DMF before the polymerisation. The changes in the process proceeding in the presence of SWCNT and C₆₀ in a comparison to the course of AN polymerisation without the participation of carbonaceous substances (the decrease of the reaction rate, the induction time) indicated on the inhibition effect, which can be described quantitatively using the inhibition parameter F. Single wall carbon nanotubes were found to act as retarders whereas fullerene C₆₀ as an inhibitor in the AN polymerisation. The changes in the chemical structure of products reveal that the carbon nanotubes and fullerenes are chemically bonded with the polymer.     

Enabling electrochemical studies of chemically-modified carbon nanotubes in non-aqueous electrolytes using superparamagnetic nanoparticle-nanotube composites co-modified by diazirine molecular “tethers”

Multiwalled carbon nanotubes (MWCNTs) were covalently modified with polymer-coated superparamagnetic Fe₃O₄ nanoparticles via amide bond formation to surface oxo-groups located predominantly at the ends of the nanotubes to form “magnetic MWCNTs”. The sidewalls of the magnetic MWCNTs were then selectively covalently modified with ferrocenyl groups via the photolysis of 3-[3-(trifluoromethyl) diazirin-3-yl] phenyl ferrocene monocarboxylate, which uses an aryldiazirine moiety as a molecular “tether”. We demonstrate that the assembly of the chemically-modified magnetic MWCNTs onto the surface of a magnetic carbon electrode enables one to obtain stable voltammetric signals of chemically-modified carbon nanotubes in non-aqueous electrolytes even under vigorous hydrodynamic conditions of stirring at 3000 rpm for up to twenty minutes. In contrast, non-magnetic chemically modified MWCNTs are removed from the electrode surface within the first two minutes of stirring.     

Synthesis of polydopamine‐functionalized magnetic graphene and carbon nanotubes hybrid nanocomposites as an adsorbent for the fast determination of 16 priority polycyclic aromatic hydrocarbons in aqueous samples

A novel adsorbent made of polydopamine‐functionalized magnetic graphene and carbon nanotubes hybrid nanocomposite was synthesized and applied to determine 16 priority polycyclic aromatic hydrocarbons by magnetic solid phase extraction in water samples. FTIR spectroscopy, transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy consistently indicate that the synthesized adsorbents are made of core–shell nanoparticles well dispersed on the surface of graphene and carbon nanotubes. The major factors affecting the extraction efficiency, including the pH value of samples, the amount of adsorbent, adsorption time and desorption time, type and volume of desorption solvent, were systematically optimized. Under the optimum extraction conditions, a linear response was obtained for polycyclic aromatic hydrocarbons between concentrations of 10 and 500 ng/L with the correlation coefficients ranging from 0.9958 to 0.9989, and the limits of detection (S/N = 3) were between 0.1 and 3.0 ng/L. Satisfactory results were also obtained when applying these magnetic graphene/carbon nanotubes/polydopamine hybrid nanocomposites to detect polycyclic aromatic hydrocarbons in several environmental aqueous samples.     

In situ electrochemically tuned photoluminescence of [Ru(bpy)<Subscript>2</Subscript>(dppz)]<Superscript>2+</Superscript> aggregates with single-walled carbon nanotubes and DNA monitored by guanine oxidation

A classical ruthenium(II) complex [Ru(bpy)₂(dppz)]²⁺ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) was combined with guanine and single-walled carbon nanotubes dispersed with DNA (SWCNTs-DNA) to prepare electrochemically tunable photoluminescence materials. These multi-component aggregates were found to show enhanced luminescence by the electrocatalytic oxidation of guanine under the excitation of a continuous wave green laser at a constant anodic potential via an electrode-solution interface. The results from this study provide a significant foundation for better understanding of DNA-based luminescent devices.     

Hydrogen adsorption strength and sites in the metal organic framework MOF5: Comparing experiment and model calculations

Hydrogen adsorption in porous, high surface area, and stable metal organic frameworks (MOF’s) appears a novel route towards hydrogen storage materials [N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127; J.L.C. Rowsell, A.R. Millward, K. Sung Park, O.M. Yaghi, J. Am. Chem. Soc. 126 (2004) 5666; G. Ferey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guegan, Chem. Commun. (2003) 2976; T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille, G. Férey, Chem. Eur. J. 10 (2004) 1373]. A prerequisite for such materials is sufficient adsorption interaction strength for hydrogen adsorbed on the adsorption sites of the material because this facilitates successful operation under moderate temperature and pressure conditions. Here we report detailed information on the geometry of the hydrogen adsorption sites, based on the analysis of inelastic neutron spectroscopy (INS). The adsorption energies for the metal organic framework MOF5 equal about 800 K for part of the different sites, which is significantly higher than for nanoporous carbon materials (550 K) [H.G. Schimmel, G.J. Kearley, M.G. Nijkamp, C.T. Visser, K.P. de Jong, F.M. Mulder, Chem. Eur. J. 9 (2003) 4764], and is in agreement with what is found in first principles calculations [T. Sagara, J. Klassen, E. Ganz, J. Chem. Phys. 121 (2004) 12543; F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113]. Assignments of the INS spectra is realized using comparison with independently published model calculations [F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113] and structural data [T. Yildirim, M.R. Hartman, Phys. Rev. Lett. 95 (2005) 215504].     

Multiwalled carbon nanotubes reinforced poly (ether‐ketone) nanocomposites: Assessment of rheological,mechanical, and electromagnetic shielding properties

This study investigates the effect of multiwalled carbon nanotubes (MWCNTs) content on rheological, mechanical, and EMI shielding properties in Ka band (26.5‐40 GHz) of poly (ether‐ketone) [PEK] prepared by melt compounding using twin screw extruder. Transmission electron microscopy (TEM) and field emission gun scanning electron microscopy (FEG‐SEM) studies were adopted to identify dispersion of nanotubes in PEK matrix. TEM and SEM images showed uniform dispersion of MWCNTs in PEK/MWCNT composites even at loading of 5 wt%. The rheological studies showed that the material experiences viscous (fluid) to elastic (solid) transition at 1 wt% loading beyond which nanotubes form continuous network throughout the matrix which in turn promotes reinforcement. Additionally, Van‐Gurp Palmen plot (phase angle vs complex modulus) and values of damping factor further confirm that the material undergoes viscous to elastic transition at 1 wt% loading. This reinforcement effect of nanotubes is reflected in enhanced mechanical properties (flexural strength and flexural modulus). Flexural strength and flexural modulus of PEK showed an increment of 17% upon incorporation of 5 wt% of MWCNTs. Total shielding effectiveness (SE_T) of −38 dB with very high shielding effectiveness due to absorption (SE_A ~ −34 dB) was observed at 5 wt% loading of MWCNTs in PEK matrix in the frequency range of 26.5‐40 GHz (Ka band).     

Electrocatalytic reduction of NAD+ at glassy carbon electrode modified with single-walled carbon nanotubes and Ru(III) complexes

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes. First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (k _s), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III) complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used for acetaldehyde determination.     

Complexes of DNA bases and Watson-Crick base pairs with small neutral gold clusters

The nature of the DNA-gold interaction determines and differentiates the affinity of the nucleobases (adenine, thymine, guanine, and cytosine) to gold. Our preliminary computational study [Kryachko, E. S.; Remacle, F. Nano Lett. 2005, 5, 735] demonstrates that two major bonding factors govern this interaction: the anchoring, either of the Au-N or Au-O type, and the nonconventional N-H...Au hydrogen bonding. In this paper, we offer insight into the nature of nucleobase-gold interactions and provide a detailed characterization of their different facets, i.e., geometrical, energetic, and spectroscopic aspects; the gold cluster size and gold coordination effects; proton affinity; and deprotonation energy. We then investigate how the Watson-Crick DNA pairing patterns are modulated by the nucleobase-gold interaction. We do so in terms of the proton affinities and deprotonation energies of those proton acceptors and proton donors which are involved in the interbase hydrogen bondings. A variety of properties of the most stable Watson-Crick [A x T]-Au3 and [G x C]-Au3 hybridized complexes are described and compared with the isolated Watson-Crick A x T and G x C ones. It is shown that enlarging the gold cluster size to Au6 results in a rather short gold-gold bond in the Watson-Crick interbase region of the [G x C]-Au6 complex that bridges the G x C pair and thus leads to a significant strengthening of G x C pairing.     

Enhanced magnetoconductivity and electrical property of MWCNT-CdS nanocomposite embedded in polyaniline

PANI/MWCNT-CdS nanocomposites with different content of CdS wt.% has been synthesized by the chemical oxidative in-situ polymerization reaction of aniline in the presence of multi-walled carbon nanotubes (MWCNT). TEM, XRD, FTIR, and TGA studies were done for the structural and thermal characterization of the samples respectively. The particle size of CdS nanoparticles distributes in between 2.7 and 4.8 nm. XRD spectrum reveals that the co-existence of MWCNT, CdS in PANI matrix, where CdS forms a hexagonal structure. TGA result shows that nanocomposite becomes more thermally stable with the increase in CdS content. The dc electrical transport property of PANI/MWCNT-CdS nanocomposites has been investigated within a temperature range 77 ≤ T ≤ 300 K. The dc conductivity follows a 3D variable range hopping (VRH) model. A large magnetoconductivity change (19%) is observed for 2 wt% CdS content in PANI/MWCNT-CdS, which is explained by the wave function shrinkage model.     

Preparation of glass carbon electrode modified with nanocrystalline nickel-decorated carbon nanotubes and electrocatalytic oxidation of methanol in alkaline solution

Nanocrystalline nickel with an average diameter of about 16 nm and a face-centered cubic (fcc) structure was uniformly attached to the surface of carbon nanotubes (CNT) by wet chemistry. The sample was characterized by X-ray powder diffraction and transmission electron microscopy (TEM). A glass carbon electrode modified with nickel-modified multi-wall carbon nanotubes (MWCNTs-Ni/GCE) was prepared. The electrochemical behavior of the MWCNTs-Ni/GCE and the electrocatalytic oxidation of methanol at the MWCNTs-Ni/GCE were investigated by cyclic voltammetry in 1.0 mol/L NaOH solution. The cyclic voltammograms showed that the electron transfer between β-Ni(OH)₂ and β-NiOOH is mainly a diffusion-controlled quasireversible process, and that the electrode has high catalytic activity for the electrooxidation of methanol in alkaline medium, revealing its potential application in alkaline rechargeable batteries and fuel cells. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(5): 503–506 [译自: 应用化学]     

异型碳纳米管储氢性能的分子动力学模拟研究

采用分子动力学(MD)方法对三种理想的Y型碳纳米管[记为Y(4,4), Y(6,6), Y(10,0)]和三种L型碳纳米管[记为L(9,0), L(6,6), L(10,0)]之储氢性能进行了模拟研究, 并与相应的直线型碳纳米管的储氢能力进行了比较, 同时考察了温度、碳纳米管的直径和螺旋性以及缺陷的位置和大小对异型碳纳米管储氢性能的影响. 结果表明, 在室温和低温条件下, 异型碳纳米管的储氢量高于直线型碳纳米管的储氢量, 且其储氢量大小随温度的降低和碳管直径的增大而增加, 椅式碳纳米管的储氢性能优于齿式碳纳米管, 而缺陷的位置和大小对异型碳管之储氢性能的影响则因碳管的形貌和直径的大小不同而存在差异.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Solid‐phase microextraction based on an agarose‐chitosan‐multiwalled carbon nanotube composite film combined with HPLC–UV for the determination of nonsteroidal anti‐inflammatory drugs in aqueous samples

We describe the preparation, characterization, and application of a composite film adsorbent based on blended agarose‐chitosan‐multiwalled carbon nanotubes for the preconcentration of selected nonsteroidal anti‐inflammatory drugs in aqueous samples before determination by high performance liquid chromatography with ultraviolet detection. The composite film showed a high surface area (4.0258 m²/g) and strong hydrogen bonding between the multiwalled carbon nanotubes and agarose/chitosan matrix, which prevent adsorbent deactivation and ensure long‐term stability. Several parameters, such as sample pH, addition of salt, extraction time, desorption solvent, and concentration of multiwalled carbon nanotubes in the composite film were optimized using a one‐factor‐at‐time approach. The optimum extraction conditions obtained were as follows: isopropanol as conditioning solvent, 10 mL of sample solution at pH 2, extraction time of 30 min, stirring speed of 600 rpm, 100 μL of isopropanol as desorption solvent, desorption time of 5 min under ultrasonication, and 0.4% w/v of composite film. Under the optimized conditions, the calibration curve showed good linearity in the range of 1–500 ng/mL (r² = 0.997–0.999), and good limits of detection (0.89–8.05 ng/mL) were obtained with good relative standard deviations of < 4.59% (n = 3) for the determination of naproxen, diclofenac sodium salt, and mefenamic acid drugs.     

Spectroscopic and DFT studies of photoactivatable Mn(I) tricarbonyl complexes

A combined experimental study and density functional theory calculations of fac‐[MnBr (CO)₃L] complexes (L = 2‐(2′‐pyridyl)benzimidazole ligand, furnished with either morpholine (L^morph) or phthalimido (L^phth) side‐chain) were performed using different spectral and analytical tools. The synthesized complexes released carbon monoxide upon the exposure to LED source light at 468 nm. Illumination of fac‐[MnBr (CO)₃L] (10 μM) in the myoglobin solution (Mb) produced about 25 μM MbCO. The plateau of the CO release process is attained within 25 min. With the aid of time‐dependent density functional theory calculations, the observed lowest energy absorption transition at ~ 400 nm has a ground‐state composed of d (Mn)/π (pyridyl) and excited‐state of ligand π*‐orbitals forming MLCT/π‐π^*. Natural population analyses of fac‐[MnBr (CO)₃L] were carried out to get information about the strength of Mn–CO bonds, electronic arrangment and natural charge of manganese ion.     

Highly C6-selective and quantitative modification of cellulose: nucleoside-appended celluloses to solubilize single walled carbon nanotubes

Cellulose derivatives having thymidine and/or trimethylammonium appendages exclusively at C6 positions can be prepared in a convenient manner through C6-selective bromination/azidation on cellulose to afford 6-azido-6-deoxycellulose followed by chemoselective [3 + 2] cycloadditions using Cu⁺ as a catalyst. These cellulose derivatives take unique sheet-like structures and function as “wrapping papers” to effectively disperse single-walled carbon nanotubes in water.     

Ruthenium complex catalyzed oxidative conversion of aliphatic amines to carboxylic acids using bromamine-T: Kinetic and mechanistic study

Ruthenium(III) complex catalyzed oxidation of aliphatic amines with bromamine-T under alkaline condition proceeds efficiently to afford carboxylic acids in high conversion. Hexa-coordinated ruthenium(III) complex of the type [RuCl₂(PPh₃)(L)] (L, tridentate ligand derived by the condensation of o-phenylene diamine with salicylaldehyde) has been synthesized and it was used as a catalyst for the oxidative conversion of amines to carboxylic acids. The detailed mechanistic and kinetic investigations have been made for the oxidation reactions. Under similar experimental conditions all the amines proceed with a common oxidation mechanism and follows an identical kinetics with first-order dependence each on [Oxidant]_o and [Amine]_o, and fractional order with respect to [Catalyst] and [OH⁻]. To understand the detailed kinetics and mechanism of the reactions, the reactions have been subjected to changes in (i) dielectric permittivity, (ii) primary salt effect, (iii) halide ions and (v) temperature. The reactions were carried out at different temperature and the activation parameters have been calculated. From enthalpy–entropy relationships and Exner correlations, the isokinetic temperature (β) of 382 K, calculated is much higher than the experimental temperature (313 K), indicating that, the enthalpy factor controls the rate. The observed results have been explained by a plausible mechanism and the related rate law has been deduced. The present method developed for the oxidation of amines to carboxylic acids by bromamine-T offers several advantages including high conversion, short reaction times, and stable, cost effective and relatively non-toxic reagents which make the reaction process simple and smooth.     

A theoretical study of CO adsorption on aluminum nitride nanotubes

Adsorption of toxic CO molecule on single-walled aluminum nitride nanotubes (AlNNTs) was investigated using density functional theory calculations. A detailed analysis of the energetic, geometry, and electronic structure of various CO adsorptions on the tube exterior surface was performed. In contrast to carbon and BN nanotubes, our results indicated that AlNNTs can strongly interact with CO molecules. The adsorption energy of the most stable configuration was calculated to be about −0.25 eV. The Morokuma–Kitaura decomposition for molecular interaction energies was used to investigate the nature of C–Al bond in the most stable CO–AlNNT complex, demonstrating that electrostatic forces and polarization term are basic factors of attractive interaction between CO and AlNNT. They provide 37.9 and 40.4% of attractive interaction and charge transfer energies make a little contribution to the adsorption energy of CO.     

功能化碳纳米管的电化学性质及在6-巯基嘌呤分析检测中的应用

采用修饰单壁碳纳米管(SWNT、SWNT-COOH或SWNT-OH)及多壁碳纳米管(MWNT、MWNT-COOH或MWNT-OH)的石墨电极研究配位阴离子[Fe(CN)6]3-和配位阳离子[Co(phen)3]3+的电化学行为与吸附性能,借助[Co(phen)3]3+在碳纳米管(CNT)的强吸附特性制备[Co(phen)3]3+/CNT/C修饰电极,以其应用于6-MP的分析检测.结果表明:1)在CNT修饰电极上[Fe(CN)6]3-/4-呈现很好的氧化还原可逆性,而[Co(phen)3]3+则显示明显的吸附控制特征.2)[Co(phen)3]3+在多壁碳纳米管修饰电极上的吸附量较单壁碳纳米管大,但经羧基化或羟基化后,吸附量减小,而且在羧基化表面的吸附量较羟基化的大.3)[Co(phen)3]3+与6-MP间存在明显的相互作用,其配位产物的还原峰电流与6-MP浓度呈线性关系.     

Influence of redox molecules on the electronic conductance of single-walled carbon nanotube field-effect transistors: application to chemical and biological sensing

In an effort to develop sensitive nanoscale devices for chemical and biological sensing, we have examined, using liquid gating, the conductance of semiconducting single-walled carbon nanotube-based field-effect transistors (SWCNT-FETs) in the presence of redox mediators. As examples, redox couples K3Fe(CN)6/K4Fe(CN)6 and K2IrCl6/K3IrCl6 are shown to modulate the SWCNT-FET conductance in part through their influence via the electrolyte gate on the electrostatic potential of the solution, as described by Larrimore et al. (Nano Lett. 2006, 6, 3129-1333) and in part through electron transfer between the redox mediators and the nanotubes. In the latter case, the rate of electron transfer is determined by the difference in chemical potential between the redox mediator and the SWCNTs and by the concentrations of the oxidized and reduced forms of the redox couple. Furthermore, these devices can detect the activity of redox enzymes through their sensitivity to the change in oxidation state of the enzyme substrate. An example is given for the blue copper oxidase, Trametes versicolor laccase, in which the rate of change of the SWCNT device conductance is linearly proportional to the rate of oxidation of the substrate 10-(2-hydroxyethyl)phenoxazine, varied over 2 orders of magnitude by the laccase concentration in the picomolar range. The behavior described in this work provides a highly sensitive means with which to do chemical and biological sensing using SWCNTs that is different from the amperometric, capacitive, and field-effect type sensing methods previously described in the literature for this material.