Conjugated polymer covalently modified multiwalled carbon nanotubes for optical limiting

A new soluble multiwalled carbon nanotubes (MWNTs) covalently functionalized with conjugated polymer PCBF, in which the wt % of MWNTs is approximately calculated as 7.3%, and the average thickness of PCBF covalently grafted onto MWNTs is 10.4 nm, was synthesized by an amidation reaction. In contrast to the starting polymer PCBF‐NH₂, grafting of PCBF onto MWNTs led to a 0.3 eV red‐shift of the N1s XPS peak at 399.7 eV assigning to N in the unreacted NH₂moieties in the resulting copolymer structure and an appearance of new peak at 402 eV corresponding to N bound to the carbonyl C (i.e., NH? C?O). Unlike PCBF‐NH₂, which only displayed a weak optical limiting response at 532 nm, Z‐scan for MWNT‐PCBF exhibited a much broader reduction in transmission and a scattering accompanying on the focus of the lens at both 532 and 1064 nm, indicating a prominent broadband optical limiting response. The thermally induced nonlinear scattering is responsible for the optical limiting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

One-step solid-state thermolysis of a metal-organic framework: a simple and facile route to large-scale of multiwalled carbon nanotubes

We report a simple and facile solid-state approach to large-scale synthesis of multiwalled carbon nanotubes (MCNTs), for the first time, by one-step direct thermolysis of a metal-organic framework [Ni(3)(btc)(2).12H(2)O] (btc = benzene-1,3,5-tricarboxylato) in a one-end closed conventional horizontal tube furnace under relatively low temperature without using any additional carrier gas or catalyst.     

Diverse chemiresistors based upon covalently modified multiwalled carbon nanotubes

A diverse array of multiwalled carbon nanotube (MWCNT) sensory materials have been synthesized and used to create sensors capable of identifying volatile organic compounds (VOCs) on the basis of their functional groups. Functionalized MWCNTs with a series of cross-sensitive recognition groups were successfully synthesized via zwitterionic and post-transformation synthetic procedures. The incorporated chemical functional groups on MWCNT surfaces introduced greatly increased sensitivity and selectivity to the targeted analytes. The distinct response pattern of each chemical was subjected to statistical treatments, which led to a clear separation and accurate identification of 100% of the VOCs. These results demonstrate that covalent functionalized MWCNT-based sensor arrays are a promising approach for low-cost, real time detection and identification of VOCs.     

Selective decoration of nickel and nickel oxide nanocrystals on multiwalled carbon nanotubes

A simple route to selective decoration of nickel and nickel oxide nanocrystals on multiwalled carbon nanotubes (MWCNTs) using nickel acetylacetonate (NAA) was successfully achieved for the first time. The homogeneously decorated nanocrystals on MWCNTs were investigated for their structure and morphology by various techniques, such as powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, field emission scanning electron microscopy and thermogravimetric analysis. It was found that the size distributions of the nanocrystals on MWCNTs ranged from 8 to 15 nm and they were well resolved. The precursor, NAA, was effectively employed to impregnate the MWCNTs, which on calcination at suitable temperatures and in the presence of hydrogen and nitrogen atmosphere gave rise to nickel and nickel oxide nanocrystals, respectively.     

Determination of catecolamines on electrodes modified with multiwalled carbon nanotubes

The electrochemical behavior of several biologically active catecolamines in studied on a glassy carbon electrode with the surface preliminarily modified by a composite film containing preliminarily carboxylated multi-walled carbon nanotubes (MWNT). The coatings are characterized by the methods of cyclic voltammetry and scanning microscopy. It is shown that the use of hybrid composites prepared by immobilizing MWNT and gold nanoparticles into the film of poly(isonicotinic) acid provides the high diffusion permeability of the surface layers and the efficiency of the electron transfer as regards catecolamines. The possibility of using these electrodes for selective determination of these substances in drugs widely used in the modern practical medicine is demonstrated.     

Synthesis of multiwalled carbon nanotubes through a modified Wolff-Kishner reduction process

We report the synthesis of highly crystallized multiwalled carbon nanotubes through a modified Wolff-Kishner reduction process at a low temperature of 180 degrees C without adding the conventional catalysts of Fe/Co/Ni into the reaction vessel. The as-synthesized carbon nanotubes are about 10-40 nm in diameter and several tens of micrometers in length. The experimental results indicate that a high concentration of NaOH is essential to the formation of carbon nanotubes. This technique opens a new route for the synthesis of CNTs and other carbon nanostructured materials.     

Enhanced sensing of anthraquinone dyes using multiwalled carbon nanotubes modified electrode

The voltammetric behaviour of two anthraquinone dyes such as Alizarin Red S (ARS) and Reactive blue 4 (RB4) was investigated at plain glassy carbon electrode (GCE), multiwalled carbon nano tube modified GCE (MWCNT/GCE) and zeolite modified GCE (ZE/GCE) using cyclic voltammetry. Effects of pH, scan rate and concentration were studied. The surface morphology of the modified electrode in the absence and presence of dye molecules was characterized by scanning electron microscopy (SEM). A systematic study on the variation of experimental parameters with differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived. MWCNT/GCE performed well among the three electrode systems and the limit of detection (LOD) was 0.036?µg?mL^?1 for ARS and 0.05?µg?mL^?1 for RB4 on this modified system. Suitability of the differential pulse stripping voltammetric method for the trace determination of textile dyes in effluents was also realized.     

A simple chemical route to selectively eliminate metallic carbon nanotubes in nanotube network devices

Semiconducting-only single-walled carbon nanotube (SWNT) network field effect transistors (FETs) have been fabricated by selectively reacting all the metallic SWNTs in the devices with diazonium reagents in a controlled manner. We have shown that the concentration of diazonium reagents used is crucial for selectively eliminating metallic SWNTs and keeping semiconducting ones intact. Excessive amounts of diazonium reagents can indiscriminately react with both metallic and semiconducting SWNTs and thus degrade the performance of the devices. This new technique will facilitate the process of fabrication of high-performance SWNT-based electronic devices.     

Large‐compound vesicle‐encapsulated multiwalled carbon nanotubes: A unique route to nanotube composites

A simple and unique strategy for preparation of large‐compound vesicle (LCV)‐encapsulated multiwalled carbon nanotubes (MWCNTs) has been developed, and this involves dispersion of MWCNTs in H‐shaped copolymers solution in DMF and encapsulation of MWCNTs with LCVs formed from hydrolysis and polycondensation of ? Si(OCH₃)₃ groups in the amphiphilic H‐shaped copolymers, (PTMSPMA)₂PEG(PTMSPMA)₂. This unique noncovalent approach is nondestructive, and the original structure of MWCNTs remains in the resultant MWCNTs/LCVs nanocomposites. The morphologies of nanocomposites LCVs/MWCNTs are controlled by the chain length ratio (N_PTMSPMA/N_PEG) of PTMSPMA to PEG. For the H‐shaped copolymers with N_PMSPMA/N_PEG ≤ 1.7, they self‐assembled to form LCVs with dense cavities in the presence of MWCNTs in a mixture of DMF/H₂O. When this ratio was more than 2.0, the large‐compound micelle‐wrapped MWCNTs were produced. This approach is potentially useful for preparation of MWCNTs encapsulated with various morphologies of polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3669–3679, 2009     

Fabrication of multiwalled carbon nanotubes/polyaniline modified Au electrode for ascorbic acid determination

An ascorbate oxidase (AsOx) (E.C.1.10.3.3) purified from Lagenaria siceraria fruit was immobilized covalently onto a carboxylated multiwalled carbon nanotubes and polyaniline (c-MWCNT/PANI) layer electrochemically deposited on the surface of an Au electrode. The diffusion coefficient of ascorbic acid was determined as 3.05 × 10(-4) cm(2) s(-1). The behavior of different electrolytes on electro-deposition was also studied. An ascorbate biosensor was fabricated using a AsOx/c-MWCNT/PANI/Au electrode as a working electrode, Ag/AgCl (3 M/saturated KCl) as standard and Pt wire as an auxiliary electrode connected through a potentiostat. Linear range, response time and detection limit were 2-206 μM, 2 s and 0.9 μM respectively. The biosensor showed optimum response at pH 5.8 and in a broader temperature range (30-45 °C), when polarized at +0.6 V. The biosensor was employed for determination of ascorbic acid level in sera, fruit juices and vitamin C tablets. The sensor was evaluated with 91% recovery of added ascorbic acid in sera and 6.5% and 11.4% within and between batch coefficients of variation respectively for five serum samples. There was a good correlation (r = 0.98) between fruit juice ascorbic acid values by the standard 2,6-dichlorophenolindophenol (DCPIP) method and the present method. The enzyme electrode was used 200 times over a period of two months, when stored at 4 °C. The biosensor has advantages over earlier enzyme sensors in that it has no leakage of enzyme, due to the covalent coupling of enzyme with the support, lower response time, wider working range, higher storage stability and no interference by serum substances.     

Enzymatic degradation of multiwalled carbon nanotubes

Because of their unique properties, carbon nanotubes and, in particular, multiwalled carbon nanotubes (MWNTs) have been used for the development of advanced composite and catalyst materials. Despite their growing commercial applications and increased production, the potential environmental and toxicological impacts of MWNTs are not fully understood; however, many reports suggest that they may be toxic. Therefore, a need exists to develop protocols for effective and safe degradation of MWNTs. In this article, we investigated the effect of chemical functionalization of MWNTs on their enzymatic degradation with horseradish peroxidase (HRP) and hydrogen peroxide (H(2)O(2)). We investigated HRP/H(2)O(2) degradation of purified, oxidized, and nitrogen-doped MWNTs and proposed a layer-by-layer degradation mechanism of nanotubes facilitated by side wall defects. These results provide a better understanding of the interaction between HRP and carbon nanotubes and suggest an eco-friendly way of mitigating the environmental impact of nanotubes.     

Electro-oxidation of amino-functionalized multiwalled carbon nanotubes

We report the electrochemistry of amino-functionalized multiwalled carbon nanotubes (MWCNTs-NH₂) in the pH range from 0.3 to 6.4 using quantitative cyclic voltammetry (CV) and single entity electrochemistry measurements, making comparison with non-functionalized MWCNTs. CV showed the latter to both catalyze the solvent (water) decomposition and to undergo irreversible electro-oxidation forming oxygen containing surface functionality. The MWCNTs-NH₂ additionally undergo an irreversible oxidation to an extent which is dependent on the pH of the solution, reflecting the variable amount of deprotonated amino groups present as a function of pH. Nano-impact experiments conducted at the single particle level confirmed the oxidation of both types of MWCNTs, showing agreement with the CV. The pK_a of the amino groups in MWCNTs was determined via both electrochemical methods giving consistent values of ca. 2.5.

A new and generic approach to the study of the oxidation of different forms of CNTs is found by using quantitative single entity and ensemble electrochemistry measurements.     

Sonochemical oxidation of multiwalled carbon nanotubes

Functionalization of carbon nanotubes (CNTs) is important for enhancing deposition of metal nanoparticles in the fabrication of supported catalysts. A facile approach for oxidizing CNTs is presented using a sonochemical method to promote the density of surface functional groups. This was successfully employed in a previous study [J. Phys. Chem. B 2004, 108, 19255] to prepare highly dispersed, high-loading Pt nanoparticles on CNTs as fuel cell catalysts. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, cyclic voltammetry, and settling speeds were used to characterize the degree of surface functionalization and coverage. The sonochemical method effectively functionalized the CNTs. A mixture of -C-O-/-C=O and -COO- was observed along with evidence for weakly bound CO at longer treatment times. The integrated XPS C 1s core level peak area ratios of the oxidized-to-graphitic C oxidation states, as well as the atom % oxygen from the O 1s level, showed an increase in peak intensity (attributed to -CO(x)()) with increased sonication times from 1 to 8 h; the increase in C surface oxidation correlated well with the measured atom %. Most of the CNT surface oxidation occurred between 1 and 2 h. The sonochemically treated CNTs were also studied by cyclic voltammetry and settling experiments, and the results were consistent with the XPS observations.     

Graphite powder and multiwalled carbon nanotubes chemically modified with 4-nitrobenzylamine.

We demonstrate that graphite powder and multiwalled carbon nanotubes (MWCNTs) can be derivatised by 4-nitrobenzylamine (4-NBA) simply by stirring the graphite powder or MWCNTs in a solution of acetonitrile containing 10 mM 4-NBA. We propose that 4-NBA partially intercalates at localised edge-plane or edge-plane-like defect sites and this hypothesis with a range of experimental data provided by electrochemistry in both aqueous and nonaqueous media, electron microscopy and X-ray powder diffraction.     

The electrochemical behavior of dopamine at glassy carbon electrode modified by Nafion multiwalled carbon nanotubes

DFT (B3LY/6-31G (d, p) and B3LYP/cc-PVDZ) calculations are performed for deoxidized dopamine (DA_(R)) and its oxidized form (DA_(O)). The electrochemistry of dopamine (DA) was studied by cyclic voltammetry (CV) at a glassy carbon electrode modified by Nafion multiwalled carbon nanotubes (MWNTs) in phosphate buffers at pH 5.4, showing that the standard electrode potential of a half reaction for DA_(O), H⁺/DA_(R) is 0.74 V. This experimental standard electrode potential of the half reaction is consistent with those of 0.65 and 0.69 V calculated using the energies of solvation and the sum of the electronic and thermal free energies of DA_(R) and DA_(O). The frontier orbital theory and Mulliken charges of molecules explain the electrochemical behavior of CV at a modified electrode well. The effects of oxygen on DA_(R) in blood and drug are also discussed according to equilibrium theory. The modified electrode was successful for determination of the content of pharmaceutical DA. The text was submitted by the authors in English.     

Amperometric hydrazine sensor using a glassy carbon electrode modified with gold nanoparticle-decorated multiwalled carbon nanotubes

Microchimica Acta - Gold nanoparticles (AuNP) were deposited on the surface of multiwalled carbon nanotubes (MWCNT) by in-situ thermal decomposition of gold acetate under solvent and reducing agent...     

Biosensor based on a glassy carbon electrode modified with tyrosinase immmobilized on multiwalled carbon nanotubes

We describe a biosensor for phenolic compounds that is based on a glassy carbon electrode modified with tyrosinase immobilized on multiwalled carbon nanotubes (MWNTs). The MWNTs possess excellent inherent electrical conductivity which enhances the electron transfer rate and results in good electrochemical catalytic activity towards the reduction of benzoquinone produced by enzymatic reaction. The biosensor was characterized by cyclic voltammetry, and the experimental conditions were optimized. The cathodíc current is linearly related to the concentration of the phenols between 0.4???M and 10???M, and the detection limit is 0.2???M. The method was applied to the determination of phenol in water samples.

The thermodynamics of the transformation of graphite to multiwalled carbon nanotubes

The thermodynamic quantities associated to the transformation from graphite to multiwalled carbon nanotubes (MWCNTs) were determined by electromotive force (emf) and differential scanning calorimetry (DSC) measurements. From the emf versus T data of galvanic cell Mo|Cr(3)C(2), CrF2, MWCNTs|CaF2 s.c.|Cr(3)C(2), CrF2, graphite|Mo with CaF2 as solid electrolyte, Delta(r)H(T) degrees= 8.25 +/- 0.09 kJ mol(-1) and Delta(r)S(T) degrees= 11.72 +/- 0.09 JK(-1) mol(-1) were found at average temperature T = 874 K. The transformation enthalpy was also measured by DSC of the Mn(7)C(3) formation starting from graphite or MWCNTs. Thermodynamic values at 298 K were calculated to be: Delta(r)H(298) degrees = 9.0 +/- 0.8 kJ mol(-1) as averaged value from both techniques and Delta(r)S(298) degrees approximately Delta(r)S(T) degrees. At absolute zero, the residual entropy of MWCNTs was estimated 11.63 +/- 0.09 JK(-1) mol(-1), and transformation enthalpy Delta(r)H(0) degrees approximately Delta(r)H(298) degrees. The latter agrees satisfactorily with the theoretical calculations for the graphite-MWCNTs transformation. On thermodynamic basis, the transformation becomes spontaneous above 704 +/- 13 K.