Ends Of Multiwalled Carbon Nanotubes Research Articles

A New Method for Dispersing Pristine Carbon Nanotubes Using Regularly Arranged S-Layer Proteins.

Homogeneous and stable dispersions of functionalized carbon nanotubes (CNTs) in aqueous solutions are imperative for a wide range of applications, especially in life and medical sciences. Various covalent and non-covalent approaches were published to separate the bundles into individual tubes. In this context, this work demonstrates the non-covalent modification and dispersion of pristine multi-walled carbon nanotubes (MWNTs) using two S-layer proteins, namely, SbpA from Lysinibacillus sphaericus CCM2177 and SbsB from Geobacillus stearothermophilus PV72/p2. Both the S-layer proteins coated the MWNTs completely. Furthermore, it was shown that SbpA can form caps at the ends of MWNTs. Reassembly experiments involving a mixture of both S-layer proteins in the same solution showed that the MWNTs were primarily coated with SbsB, whereas SbpA formed self-assembled layers. The dispersibility of the pristine nanotubes coated with SbpA was determined by zeta potential measurements (−24.4 +/− 0.6 mV, pH = 7). Finally, the SbpA-coated MWNTs were silicified with tetramethoxysilane (TMOS) using a mild biogenic approach. As expected, the thickness of the silica layer could be controlled by the reaction time and was 6.3 +/− 1.25 nm after 5 min and 25.0 +/− 5.9 nm after 15 min. Since S-layer proteins have already demonstrated their capability to bind (bio)molecules in dense packing or to act as catalytic sites in biomineralization processes, the successful coating of pristine MWNTs has great potential in the development of new materials, such as biosensor architectures.

Accurate assembly of ZnO nanoclusters at the ends of multi‐walled carbon nanotubes in a microemulsion system

A novel method is reported here to attach ZnO nanoclusters accurately at the end of multi-walled carbon nanotubes (MWCNTs) in a hydrothermal system. The ends of MWCNTs were selectively functionalised using gas-phase functionalisation in ammonia. ZnO/MWCNT heterojunctions are formed accurately at the nanotube-ends through hydrothermal microemulsion synthesis. The reverse micelle of sodium dodecyl sulphate combines with the positive nitrogen-containing basic groups at the MWCNT end and act as the microreactors for ZnO nanoclusters. The sidewalls of the MWCNTs remain intact without any ZnO particles functionalisation. The results represent a versatile approach that is highly scalable and could pave the way toward versatile heterojunction devices fabrication.

Giant magnetic moment at open ends of multiwalled carbon nanotubes**Project supported by the National Natural Science Foundation of China (Grant Nos. 10774032 and 51472057) and the Instrument Developing Project of the Chinese Academy of Sciences (Grant No. Y2010031).

The attractions of cantilevers made of multiwalled carbon nanotubes (MWNTs) and secured on one end are studied in the non-uniform magnetic field of a permanent magnet. Under an optical microscope, the positions and the corresponding deflections of the original cantilevers (with iron catalytic nanoparticles at the free end) and corresponding cut-off cantilevers (the free ends consisting of open ends of MWNTs) are studied. Both kinds of CNT cantilevers are found to be attracted by the magnet, and the point of application of force is proven to be at the tip of the cantilever. By measuring and comparing deflections between these two kinds of cantilevers, the magnetic moment at the open ends of the CNTs can be quantified. Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes, it is called giant magnetic moment, and its possible mechanisms are proposed and discussed.

A comprehensive study of sound pressure in a finite-length fluid-filled multi-walled carbon nanotube

The aim of this paper is to analyze vibrational behavior and the sound wave propagation in the finite-length fluid-filled multi-walled carbon nanotubes (MWCNTs) and to determine the exact sound pressure load effect on it, and compare it to what has been used by the other researchers. For this purpose, the solution of the modified complex Helmholtz equation is derived by considering the non-rigidity of the CNT and the wave reflections at the open ends of the MWCNT. These investigations are very important for potential application of CNT-filled polymeric foam that is used as sound absorber. In this paper, in formulating the sound pressure load exerted on the innermost tube of the finite-length fluid-filled MWCNT, the following points have been studied for the first time: (i) the energy loss in the fluid, which cannot be ignored in the high frequency analysis; (ii) the non-rigidity of the MWCNT through considering finite acoustical impedance for its walls; (iii) the wave reflections at the open ends of the finite-length MWCNT to calculate the sound pressure load term which is coupled with the dynamic equations of motion for the finite-length fluid-filled MWCNT. The results show that ignoring the mentioned points would cause errors in the prediction of the sound pressure load exerted on the finite-length fluid-filled MWCNT.

Adsorption of toluene, ethylbenzene and m-xylene on multi-walled carbon nanotubes with different oxygen contents from aqueous solutions

The purified and oxidized multi-walled carbon nanotubes (MWCNTs) with different oxygen contents are employed as adsorbents to study their physicochemical properties and adsorption behaviors of toluene, ethylbenzene and m-xylene (TEX) in aqueous solutions. The results demonstrate that adsorption capacity is significantly enhanced for 3.2% surface oxygen, but is dramatically reduced for 5.9% oxygen concentration. The adsorption kinetics is investigated and fitted with pseudo-second-order model. The adsorption isotherms are found to be fitted with Langmuir model. More interestingly, with the increasing of surface oxygen content, maximum adsorption capacities firstly increased, and then, began to decrease. In the first stage, dispersion is the most important factor. A better dispersive interaction increases the available adsorption sites, which consequently can be favorable for the aqueous phase adsorption. Therefore, maximum adsorption capacity is remarkably enhanced with the increasing of oxygen content, which is according with our results. However, in the second stage, when oxygen content increases to a certain extent, hydroxyl groups cause water clusters formation on the surface or tube end of MWCNTs, which hinder the interaction between TEX and MWCNTs. Consequently, more oxygen content leads to the decrease in maximum adsorption capacity. The decrease indicates that the formation of water clusters plays a more important role than the better dispersion of MWCNTs for TEX adsorption.

Chemical functionalization of multiwalled carbon nanotubes by hexamethylene diamine

Multiwalled carbon nanotubes (MWCNTs) were modified by grafting with hexamethylene diamine to obtain reactive amine groups. Acid treatment was used to shorten the MWCNTs by cutting at defect sites. Carboxyl groups produced by the acid treatment were converted to carbonyl chloride by thionyl chloride,and hexa￣methylene diamine was grafted to the ends of the cut MWCNTs by its substitutional reaction with carbonyl chloride. XPS,TEM and SEM were used to characterize the samples during the course of modification. Results indicated that MWCNTs were shortened from tens of microns to about 500 nm by the acid treatment. Hexamethylene diamine was successfully grafted onto the ends of the MWCNTs with a grafted N content as high as 3.29 mol%. The grafted MWCNTs can be dispersed uniformly in acetone.

The Effect of O-Functionalities for the Electrochemical Reduction of Oxygen on MWCNTs in Acid Media

The effect for oxygen reduction characteristics of O-functionalities formed on the edge planelike defects at the open ends of multiwalled carbon nanotubes (MWCNTs) and at the hole defects on the tube walls was investigated by using the rotating disk electrode technique. The onset potential of the electrochemical reduction of oxygen for MWCNTs shifts to the positive direction of 0.19 V, while the O-functionalities were removed from the defects sites. These results suggest that the control of functional groups is important for the control of the oxygen reduction reaction catalyst activity.

Nonenzymatic glucose voltammetric sensor based on gold nanoparticles/carbon nanotubes/ionic liquid nanocomposite

In this paper, a novel nonenzymatic glucose voltammetric sensor based on a kind of nanocomposite of gold nanoparticles (GNPs) embedded in multi-walled carbon nanotubes (MWCNTs)/ionic liquid (IL) gel was reported. The surface morphology of this nanocomposite was characterized using X-ray photoelectron spectrometer (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. It can be found that most of GNPs lie close to the ektexine of MWCNTs and the others have obviously inserted the inner of MWCNTs through the defects or ends of MWCNTs, due to the attraction between GNPs and MWCNTs as well as the repulsion between GNPs and IL. Voltammetry was used to evaluate the electrocatalytic activities of the nanocomposite biosensor toward nonenzymatic glucose oxidation in alkaline media. The GNPs embedded in MWCNTs/IL gel have strong and sensitive voltammetric responses to glucose, owing to a possible synergistic effect among GNPs, MWCNTs and IL. Under the optimal condition, the linear range for the detection of the glucose is 5.0–120 μM with the correlation coefficient of 0.998, based on the oxidation peak observed during cathodic direction of the potential sweep. The kinetics and mechanism of glucose electro-oxidation were intensively investigated in this system. This kind of nanocomposite biosensor is also highly resistant toward poisoning by chloride ions and capable of sensing glucose oxidation in the presence of 20 μM uric acid and 70 μM ascorbic acid. This work provides a simple and easy approach to the detection of glucose in body fluid with high sensitivity and excellent selectivity.

The influence of edge-plane defects and oxygen-containing surface groups on the voltammetry of acid-treated, annealed and “super-annealed” multiwalled carbon nanotubes

The role of edge-plane-like defects at the open ends of multiwalled carbon nanotubes (MWCNTs) and at hole defects in the tube walls is explored using cyclic voltammetry with two charged redox probes, namely potassium ferrocyanide and hexaamineruthenium(III) chloride in unbuffered aqueous solutions, and one neutral redox probe, norepinephrine, in pH 5.7 buffer. Further, the presence of oxygen-containing functional groups (such as phenol, quinonyl and carboxyl groups), which decorate the edge-plane defect sites on the voltammetric response of the MWCNTs, is also explored. To this end, three different pre-treatments were performed on the pristine MWCNTs made using the arc-discharge method (arc-MWCNTs). These were (a) arc-MWCNTs were subjected to acid oxidation to form acid-MWCNTs—open-ended MWCNTs also possessing numerous hole defects revealing a large number of edge-plane-like sites heavily decorated with surface functional groups; (b) acid-MWCNTs, which were subsequently vacuum-annealed at 900 °C to remove the functional groups but leaving the many undecorated edge-plane-like sites exposed (ann-MWCNTs); (c) ann-MWCNTs, which were subjected to a further vacuum “super-annealing” stage at 1,750 °C (sup-MWCNTs), which caused the hole defects to close and also closed the tube ends, thereby, restoring the original, pristine, almost edge-plane defect-free MWCNTs structure. The results of the voltammetric characterisation of the acid-, ann- and sup-MWCNTs provide further evidence that edge-plane-like sites are the electroactive sites on MWCNTs. The presence of oxygen-containing surface groups is found to inhibit the rate of electron transfer at these sites under the conditions used herein. Finally, the two charged, “standard” redox probes used were found to undergo strong interactions with the oxygen-containing surface groups present. Thus, we advise caution when using these redox probes to attempt to voltammetrically characterise MWCNTs, and by extension, graphitic carbon surfaces.

Investigation of Pt Catalysts Supported on Multi-Walled Carbon Nanotubes with Various Diameters and Lengths

Platinum electrocatalysts supported on multi- walled carbon nanotubes (MWCNTs) with various diame- ters and lengths were studied by using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) and Chronoampe- rometry. The results indicated that the MWCNTs with smaller diameter generated more amorphous carbon after a sonochemical oxidation treatment. Compared with the long MWCNTs, the short MWCNTs had more open ends, resulting in high-Pt dispersion and electrocatalytic activity towards methanol oxidation. Pt nanoparticles supported on short MWCNTs with a diameter of 30-50 nm exhibited the best Pt dispersion and highest methanol oxidation activity among the catalysts studied. The high activities of the cat- alysts based on short MWCNTs were due to both the intrinsic high activity of the ends of MWCNTs and a good Pt distribution.

Growing Multihydroxyl Hyperbranched Polymers on the Surfaces of Carbon Nanotubes by in Situ Ring-Opening Polymerization

An in situ ring-opening polymerization strategy was employed to grow multihydroxyl dendritic macromolecules on the convex surfaces of multiwalled carbon nanotubes (MWNTs), affording novel one-dimensional (1D) molecular nanocomposites. The crude MWNTs were oxidized using 60% HNO3 and then reacted with thionyl chloride, resulting in MWNTs functionalized with chlorocarbonyl groups (MWNT-COCl). MWNT-COCl, when reacted with an excess of glycol, produced hydroxy-functionalized MWNT supported initiators (MWNT-OH). Using the MWNT-OH as the growth supporter and BF3·Et2O as catalyst, multihydroxy hyperbranched polyetherstreelike macromoleculeswere covalently grafted on the sidewalls and ends of MWNTs via in situ ring-opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane (EHOX). TGA measurements showed that the weight ratio of the as-grown hyperbranched polymers on the MWNT surfaces lay in the 20−87% range. The products were characterized by FTIR, NMR, DSC, TEM, and SEM. TEM indicates that the MWNTs are envelop...

System optimization for the development of ultrasensitive electronic biosensors using carbon nanotube nanoelectrode arrays.

Vertically aligned multi-walled carbon nanotubes (MWCNTs) have been reported in fabricating nanoelectrode arrays. Further studies on optimizing this system for the development of ultrasensitive DNA sensors are reported here. The mechanical stability of the as-grown MWCNT array can be improved by polymer coating or SiO2 encapsulation. The latter method provides excellent electronic and ionic insulation to the sidewall of MWCNTs and the underlying metal layer, which is investigated with electrochemical impedance spectroscopy. The insulation ensures well-defined nanoelectrode behavior. A method is developed for selectively functionalizing biomolecules at the open end of MWCNTs while keeping the SiO2 surface passivated, using the unique graphitic chemistry. An ultrahigh sensitivity approaching the limit of fluorescence techniques is obtained with this system for DNA detection.

Self assembly of ordered artificial solids of semiconducting ZnS capped CdSe nanoparticles at carbon nanotube ends

The utilization of carbon nanotubes (CNTs) as building blocks for nanodevices can only be realized when their electronic properties are preserved in the device configuration. It has been shown that bending and overlapping of CNTs result in a decrease in their conductance. Heterojunctions of quantum dots (QDs) and multiwalled carbon nanotubes (MWCNTs) could become better alternatives for the synthesis of nanoscale devices which would preserve the electronic properties of MWCNTs. Here, we present a significant refinement of a previously reported technique to integrate QD at the ends of MWCNTs and report a novel MWCNT–QD–MWCNT heterostructure with detailed chemical and physical characterization of the heterojunctions conducted via Fourier transform infrared spectroscopy, transmission electron microscopy (TEM) and energy dispersive spectroscopy. We have discovered a novel phenomenon of mesoscale ordering of thiol stabilized ZnS capped CdSe QDs containing amine terminal groups at the ends of acid treated MWCNTs during the conjugation process, which has been investigated using high resolution TEM.

Anti localization due to spin–orbit interaction in metal-doped carbon nanotubes

Electrode atoms are diffused, with only about 5% volume ratio, into the top end of multi-walled carbon nanotubes (MWNTs), standing in nanopores of porous alumina membranes. We find that diffusion of heavy materials leads to an anti-localization in the Altshuler–Aronov–Spivak oscillations in the MWNT bulk. This effect is only observable when electrons are injected through the diffusion region, and undergo a π-phase shift in their electron waves, caused by polarized injection of spin-flipped electrons due to spin-orbit interaction in the diffusion region.

Weak localization and phase interference due to spin-orbit interaction in metal-doped carbon nanotubes

Electrode atoms are slightly diffused, with only about 5% volume ratio, into the top end of multiwalled carbon nanotubes (MWNT's), standing in nanopores of porous alumina membranes. Diffusion of light-mass materials (carbon and aluminum) leads to weak localization in the Altshuler-Aronov-Spivak (AAS) oscillations, which is qualitatively consistent with previous works on MWNT's. In contrast, we find that diffusion of heavy materials (gold and platinum) changes this weak localization into an antilocalization in the MWNT bulk. This effect is only observable when electrons are injected through the diffusion region and undergo a \ensuremath{\pi}-phase shift in their electron waves, caused by polarized injection of spin-flipped electrons due to spin-orbit interaction in the diffusion region of the MWNT bulk.

Drastic change of phase interference by small diffusion of heavy-mass electrode atoms in carbon nanotubes and phase switching device

We slightly diffuse atoms of electrode materials into one end of multiwalled carbon nanotubes (MWNTs), grown using nanoporous alumina membranes. Diffusion of the light-mass materials (carbon and aluminum) lead to weak localization in Altshuler–Aronov–Spivak oscillation, consistent with past reports. In contrast, we find that diffusion of heavy-mass materials (gold and platinum) at the volume ratio of only about 5% change this weak localization to antilocalization. It is understood by a drastic change of the phase interference caused by the injection of spin-flipped electrons due to spin–orbit interaction in the diffusion region, in the entire part of the MWNTs. We also propose an electron-wave phase switching circuit using this effect.

Injection of Polarized Spins and Anti-Localization Caused by Slight Doping of Heavy Impurities into One End of Carbon Nanotubes

AbstractElectrode atoms are slightly diffused, with only about 5% volume-ratio, into the top end of multi-walled carbon nanotubes (MWNTs), standing in nano-pores of porous Alumina membranes. Diffusion of light-mass materials (carbon and aluminum) leads to weak localization in the Altshuler-Aronov-Spivak (AAS) oscillations, which is qualitatively consistent with previous works on MWNTs. In contrast, we find that diffusion of heavy materials (gold and platinum) changes this weak localization into an anti-localization in the MWNT bulk. This effect is only observable when electrons are injected through the diffusion region, and undergo a φ-phase shift in their electron waves, caused by polarized injection of spin-flipped electrons due to spin-orbit interaction in the diffusion-region of the MWNT bulk.