Single-walled Carbon Nanotubes Composites Research Articles

SWCNT nano-composite optical sensors for VOC and gas trace detection

The feasibility of exploiting novel chemo-sensitive coatings based on cadmium arachidate (CdA)/single-walled carbon nanotube (SWCNT) composites for the development of high performance optical chemo-sensors has been experimentally investigated and proved. SWCNT nano-composite overlays have been transferred on the distal end of standard optical fibers by the Langmuir–Blodgett deposition technique in order to realize extrinsic low-finesse Fabry-Perot interferometers. A structural and morphological characterization of the fabricated optical probes has been carried out by scanning electron microscopy observations and Raman spectroscopy analysis. Reflectance measurements have been carried out to test the sensing performance of the proposed devices to volatile organic compound (VOC) and gas exposure. Also, VOC trace detection has been evaluated in different environments, such as air and water. Obtained results have also been compared in the same operating conditions to those obtained in the case of standard SWCNT overlays deposited by using the same deposition technique and optical transducers in order to outline the effect of the nano-composite matrix both on the material integration effectiveness and sensing performance. The results shown here demonstrate that the use of nano-composite coatings not only promotes a better adhesion of the sensitive overlay to the fiber surface, thus improving the robustness of the chemo-optical sensors, but also significantly enhances their sensitivities from three to seven times with respect to the SWCNT overlay directly deposited on the fiber surface. Moreover, resolutions in the range 30–250 part per billion (ppb) and 0.6–1.5 part per million (ppm) have been estimated in case of air and water environments, respectively.

Electrochemical and Raman spectroelectrochemical investigation of single-wall carbon nanotubes–polythiophene hybrid materials

Two types of polythiophene—single-wall carbon nanotubes (SWCNTs) composites are comparatively studied. Composites of the first type consisted of nonmodified SWCNTs and nonmodified regioregular poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene) (P3OT) or poly(dioctylterthiophenes) (PDOTT). Composites of the second type (molecular composites) were obtained by grafting carboxylic acid functionalized poly(alkylthiophene)s on amine functionalized SWCNTs. In AFM images of the composites of nonfunctionalized components, individual carbon nanotubes can be easily distinguished, which are well dispersed in the polymer matrix showing fibrilar morphology. Cyclic voltammetry and Raman spectroelectrochemical experiments unequivocally show that all characteristic redox and spectroscopic features of both SWCTs and the polymer are retained in the composite material. Moreover the percolating network of SWCTs facilitates the electrochemical doping of the polymeric component. These new, solution processible materials are good candidates for printable contact electrodes in organic electronics. Molecular composites obtained by grafting show a different morphology. It is characterized by a network of fibers of diameters ranging from few dozens to few hundreds nm. Individual composite components cannot be distinguished which is an obvious consequence of the grafting reaction. Combined voltammetric and Raman spectroelectrochemical studies show that the grafting reaction lowers the electrochemical activity of the polymer component and the resulting maximum doping level is, in this case, lower than that found in composites of nonmodified components.

Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/single-walled carbon nanotube composites

Electrochemical polymerization of 2,2′-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430–1450 cm −1 indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600–800 cm −1 resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH 4OH solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm −1.

Stiff and electrically conductive composites of carbon nanotube aerogels and polymers

Many challenges remain in the effort to realize the exceptional mechanical and electrical properties of carbon nanotubes in composite materials. Here, we report on highly electrically conductive and mechanically stiff composites of polymers and single-walled carbon nanotubes (SWNT). Conductive SWNT-based nanofoams (aerogels) are used as scaffolds to create polymer [poly(dimethylsiloxane)] composites. The resulting composites possess electrical conductivities over 1 S cm−1 and exhibit an ∼300% increase in the elastic modulus with as little as 1 vol% nanotube content.

The incorporation of single-walled carbon nanotubes into polymerized high internal phase emulsions to create conductive foams with a low percolation threshold

New methods for the incorporation of single-walled carbon nanotubes (SWCNTs) into styrene-divinylbenzene-based high internal phase emulsions (HIPEs) are addressed with specific attention to minimizing the SWCNT loading while maintaining a high level of conductivity of the final polyHIPE–SWCNT composites. Stable HIPEs were achieved using sodium dodecyl sulfate-stabilized SWCNTs, thus eliminating the necessity of SWCNT functionalization. PolyHIPE–SWCNT composites were made with water: oil ratios (vol/vol) of 75:25 and of 84:16. The percolation threshold was determined to be 0.2 and 0.1 wt%, respectively. These threshold values are lower than that obtained for non-porous, polystyrene–SWCNT composites made by means of a latex-based route followed by melt-processing.

Functionalization of Carbon Nanotubes with Water‐Insoluble Porphyrin in Ionic Liquid: Direct Electrochemistry and Highly Sensitive Amperometric Biosensing for Trichloroacetic Acid

A functional composite of single-walled carbon nanotubes (SWNTs) with hematin, a water-insoluble porphyrin, was first prepared in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]) ionic liquid. The novel composite in ionic liquid was characterized by scanning electron microscopy, ultraviolet absorption spectroscopy, and electrochemical impedance spectroscopy, and showed a pair of direct redox peaks of the Fe(III)/Fe(II) couple. The composite-[BMIM][PF(6)]-modified glassy carbon electrode showed excellent electrocatalytic activity toward the reduction of trichloroacetic acid (TCA) in neutral media due to the synergic effect among SWNTs, [BMIM][PF(6)], and porphyrin, which led to a highly sensitive and stable amperometric biosensor for TCA with a linear range from 9.0x10(-7) to 1.4x10(-4) M. The detection limit was 3.8x10(-7) M at a signal-to-noise ratio of 3. The TCA biosensor had good analytical performance, such as rapid response, good reproducibility, and acceptable accuracy, and could be successfully used for the detection of residual TCA in polluted water. The functional composite in ionic liquid provides a facile way to not only obtain the direct electrochemistry of water-insoluble porphyrin, but also construct novel biosensors for monitoring analytes in real environmental samples.

Effect of Doping Ions on Capacitance Properties of Polypyrrole/Functionalized Single-walled Carbon Nanotubes Composites

Polypyrrole/functionalized single-walled carbon nanotubes composites (PPy/F-SWNTs) were electrochemically prepared in dispersive solution of pyrrole (Py) and F-SWNTs with or without doping ions. The effect of in-situ doping ions including Cl-, ClO4-, toluenesulfonate (TOS-) and dodecylbenzenesulfonate (DBS-) on the capacitance performance of the composites was investigated by cyclic voltammetry (CV), galvanostatical charge/discharge and electrochemical impedance spectroscopy (EIS) techniques. Except the pristine composite and the composite doped by DBS-, the others exhibited notable electrochemical capacitance behaviors. Furthermore, the specific capacitance of PPy-Cl/F-SWNTs (polymerization charge was 2 mAh•cm-2) reached 241 Fg-1 at the scanning rate of 10 mVs-1. PPy-TOS/F-SWNTs (polymerization charge 2 mAhcm-2) had greater capacitance and charge/discharge rate than the former did. Even at the scanning rate of 200 mVs-1, its specific capacitance was still up to 172 Fg-1. But with heaver doping ion (TOS-), PPy-TOS/F-SWNTs (polymerization charge 2 mAhcm-2) had a slightly smaller specific capacitance, such as 196 Fg-1 at the scanning rate of 10 mVs-1.

Evaluation of Composite Electronic Materials Based upon Single-Wall Carbon Nanotubes and Highly Charged Poly(aryleneethynylene)s for Supercapacitor Applications

Although substantial improvement in capacitance, energy densities, and discharge times has been achieved for redox supercapacitors over the last several years, important challenges remain. These include high series resistance which limits the ability to quickly discharge these devices, excessive heat generation, and the coupled thermoelastic strain field which tends to deform the device materials. High stability composites based upon conjugated polymers that wrap single-wall carbon nanotubes (SWNTs) provide a platform to develop materials that can broadly impact these issues. This work compares the performance of a new class of hybrid materials, polymer-wrapped SWNTs to established electroactive polymer-based anode and cathode material benchmarks of poly(3,4-propylenedioxythiophene) for the construction of supercapacitors. These polymer-wrapped SWNT composites exploit rigid, polyanionic poly(aryleneethynylene)s which provide unusual solubility and dispersion characteristics for carbon nanotubes in several solvents.

Evidence for large hydrogen capacity in single-walled carbon nanotubes encapsulated by thin Pd layers onto a Pd substrate

We report a study of hydrogen storage and its mechanism in a novel material, representing single-walled carbon nanotubes (SWCNTs) encapsulated by thin Pd layers onto a Pd substrate. A synergetic effect resulting in combination of the Pd and the SWCNT properties with regard to hydrogen has been achieved. We showed that adding SWCNTs increases the H 2-capacity of the Pd–SWCNT composite under electrochemical loading only by up to 25% relative to the Pd metal alone. At the same time, with regard to the added SWCNTs, such synergetic approach (providing high H 2 pressure from highly H-loaded massive Pd substrate into a small fraction of deposited SWCNT) allowed us to achieve a net capacity of 8–12 wt.%. H 2, thus, bringing a unique chance to study hydrogen storage mechanism in highly H-loaded SWCNT. Using ESR technique it was established that the Pd–C x π-complexes forming at the openings of SWCNTs could be considered as hydrogen adsorption sites, providing both high gravimetric capacity (H/C > 1) and low hydrogen binding energy in the Pd encapsulated SWCNT.

Polyisoprene single-wall carbon nanotube composites synthesized under high pressure

The mechanical and thermal properties of high-pressure-synthesized composites of polyisoprene (PI) and single-walled carbon nanotubes (SWCNTs) (1 wt%) have been measured using a tensile tester and the transient hot-wire method. PI–SWCNT composites were prepared by ultrasonic mixing in toluene to obtain good dispersion of the nanotubes within the polymer matrix, which was verified by atomic force microscopy. The mixtures were dried for several days under dynamic vacuum and subsequently treated at a high pressure (∼0.5 GPa) and temperature (513 K) to improve the SWCNT–polymer interaction. As a result of the high-pressure treatment, PI becomes crosslinked, yielding an elastomeric PI–SWCNT composite. Preliminary results show that the tensile strength and Young's modulus of the composite are 2.8 and five times higher, respectively, than those of pure high-pressure-treated PI, and that the thermal conductivity increased ∼30% by adding 1 wt% SWCNTs.

SWNT–SOG composite for transparent field emission device

A transparent field emission device based on the composite of purified single-walled carbon nanotubes (SWNTs) and spin-on glass (SOG) was developed. Highly crystalline SWNTs were synthesized in situ on a tin-oxide-coated glass using the arc discharge method. A simple purification step by oxidation proved to be an effective process in enhancing the transparency and pureness of the SWNT film. The transparent SOG–SWNT composite was then formed by spin coating SOG on the SWNT film. The field emission device showed a maximum current density of 0.1 mA cm −2 and a low turn-on field emission of 1.6 V μm −1 with a high field enhancement factor of 1.5×10 5 cm −1.

The influence of single-walled carbon nanotube functionalization on the electronic properties of their polyaniline composites

The “in situ” preparation and characterization of composites of polyaniline (PANI) and single-walled carbon nanotubes (SWCNTs) are reported. To improve the dispersion and compatibility with the polymer matrix the raw SWCNTs were modified following different routes. SWCNTs oxidized by chemical or thermal treatments (nitric acid and air oxidation, respectively) were subjected to covalent functionalization with octadecylamine (ODA). SWCNT/PANI composites were prepared either from just oxidized SWCNTs, or from ODA functionalized SWCNTs. Temperature-programmed desorption, elemental analyses, ultraviolet–visible (UV–vis), UV–vis with near infrared and Raman spectroscopy, X-ray diffraction, scanning and transmission electron microscopy and conductivity measurements were used to characterize the functionalized SWCNT materials, dispersions and composites. The PANI composite prepared from air oxidized SWCNTs showed the best electrical conductivity indicating a better interaction with polyaniline than ODA functionalised SWCNTs. The improvement of conductivity is attributed to the doping effect or charge transfer of quinoide rings from PANI to SWCNTs.

Structural, wetting, and electronic properties of metal clusters adsorbed on carbon nanotubes

Atomic structures of M4(M=Ti and Fe) metal clusters on the surface of single-walled carbon nanotubes (SWNT) are studied by the first principles calculations. The various equilibrium structures and total energies of M4 cluster-SWNT composites are presented, which reveal that the relative energies between the tetrahedral and planar configurations correspond to the wetting properties of metal clusters adsorbed on carbon nanotubes. Electronic properties of the M4+SWNT composites are also presented to show the highly spin polarized behaviors. Our results suggest that the M4+SWNT composite is a simple and typical model to study the interactive effects and architectures of metal clusters absorbed on carbon nanotubes, which can be further exploited for the design of nanoscale electrodes and nanoelectronic devices.

Functionalization of Single-Walled Carbon Nanotubes with Metalloporphyrin Complexes: A Theoretical Study

We report a detailed theoretical investigation on the functionalization of semiconducting (10,0) and metallic (6,6) single-walled carbon nanotubes (SWNTs) with a series of metalloporphyrin (MP) complexes (MP = CoP, NiP, CuP, and ZnP) by using density functional theory (DFT) calculations. We find that similar to the free-base porphyrin, metalloporphyrin molecules can also be used to separate the semiconducting SWNTs from metallic SWNTs. The mechanisms for separation are mainly attributed to the difference in charge transfer and hybridization between metalloporphyrin molecules and SWNTs. However, contrasting with the porphyrin−SWNTs systems, the presence of the unpaired electrons in the metalloporphyrin−SWNTs assembly implies a nonzero magnetic moment of this material, making it possess interesting magnetic and optic properties. Moreover, the metalloporphyrin−SWNTs composites also have potential applications in further fabricating nanotube electronic devices for sensors, catalysts, or spintronic molecular d...

Composites of Single-Walled Carbon Nanotubes and Polystyrene: Preparation and Electrical Conductivity

Composites of single-walled carbon nanotubes (SWNT) and polystyrene have been prepared using three different types of SWNT: HiPco, CoMoCat, and pulsed laser vaporization (PLV). Nanotubes were incorporated into the polystyrene matrix by two methods: (1) evaporation of chloroform solutions of SWNT noncovalently functionalized with poly[(m-phenylenevinylene)-co-(2,5-dioctoxy-p-phenylenevinylene)] (PmPV) and polystyrene; (2) coagulation in water of DMF solutions containing polystyrene and nitric acid oxidized SWNT. From measurements of the electrical conductivities of the composites over a range of concentration from 0.1 to 6 wt % SWNT, the percolation threshold of conductivity was 0.17−0.3% SWNT for the PmPV-coated materials and 0.4–0.5% for those made by coagulation. Of the three types of SWNT, composites made with HiPco tubes had the highest conductivity.

Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping

The magnetic orientation of single-walled carbon nanotubes (SWNTs) or the SWNT composites wrapped with polymer using poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV) as the conducting polymer were examined. The formation of SWNT/MEHPPV composites was confirmed by examining absorption and fluorescence spectra. The N,N-dimethylformamide solution of SWNT/MEHPPV composites or the aqueous solution of the shortened SWNTs was introduced dropwise onto a mica or glass plate. The magnetic processing of the composites or the SWNTs was carried out using a superconducting magnet with a horizontal direction (8 T). The AFM images indicated that the SWNT/MEHPPV composites or the SWNTs were oriented randomly without magnetic processing, while with magnetic processing (8 T), they were oriented with the tube axis of the composites or the SWNTs parallel to the magnetic field. In polarized absorption spectra of SWNT/MEHPPV composites on glass plates without magnetic processing, the absorbance due to semiconducting SWNT in the near-IR region in horizontal polarized light was almost the same as that in vertical polarized light. In contrast, with magnetic processing (8 T), the absorbance due to semiconducting SWNT in the horizontal polarization direction against the direction of magnetic field was stronger than that in the vertical polarization direction. Similar results were obtained from the polarized absorption spectra for the shortened SWNTs. These results of polarized absorption spectra also support the magnetic orientation of the SWNT/MEHPPV composites or the SWNTs. On the basis of a comparison of the composites and the SWNTs alone, the magnetic orientation of SWNT/MEHPPV composites is most likely ascribable to the anisotropy in susceptibilities of SWNTs.

Electromagnetic interference shielding of carbon nanotube/ethylene vinyl acetate composites

Single-walled carbon nanotube (SWCNT) and ethylene vinyl acetate (EVA) composites were synthesized in an internal mixer by melt mixing. The electrical conductivity as well as electromagnetic interference (EMI) shielding effectiveness (SE) over the X-band (8–12 GHz) and microwave (200–2,000 MHz) frequency ranges of these composites were investigated. It was observed that the electrical conductivity of composites increases with increasing SWCNT loading. A percolation threshold of about 3.5 wt.% was obtained and the electrical conductivity of EVA was increased by ten orders of magnitude, from 10−14 to 10−4 Ω−1 cm−1. The effect of sample thickness on SE was investigated. The correlation between SE and conductivity of the composites is discussed. The experimental data showed that the SE of the composites containing higher carbon nanotube loadings (above 10 wt.%) could be used as an EMI shielding material and lower SWCNT loadings could be used for the dissipation of electrostatic charge.

Creation of Hierarchical Carbon Nanotube Assemblies through Alternative Packing of Complementary Semi‐Artificial β‐1,3‐Glucan/Carbon Nanotube Composites

Much attention has been focused on exploiting novel strategies for the creation of hierarchical polymer assemblies by the control of the assembling number or the relative location among neighboring polymers. We here propose a novel strategy toward the creation of "hierarchical" single-walled carbon nanotube (SWNT) architectures by utilizing SWNT composites with cationic or anionic complementary semi-artificial beta-1,3-glucans as "building blocks". These beta-1,3-glucans are known to wrap SWNTs helically, to create one-dimensional superstructural composites. If the cationic composite is neutralized by an anionic composite, a well ordered SWNT-based sheet structure was created. Transmission electron microscopy (TEM) observation revealed that this sheet structure is composed of highly-ordered fibrous assemblies of SWNTs. This suggests that the cationic and anionic composites are tightly packed through electrostatic interactions. Moreover, both of the final assembly structures are readily tunable by adjusting the cation/anion ratio. The self-assembling modulation of functional polymers is associated with the progress in ultimate nanotechnologies, thus enabling us to create numerous functional nanomaterials. We believe, therefore, that the present system will extend the frontier of SWNT research to assembly chemistry including "hierarchical" superstructures.

Immobilized enzyme–single-wall carbon nanotube composites for amperometric glucose detection at a very low applied potential

The behaviour of support electrodes modified with randomly dispersed single-wall carbon nanotube meshes containing adsorbed glucose oxidase with respect to amperometric glucose detection at a low potential is demonstrated.

Electrochemical capacitance of the composite of poly (3,4-ethylenedioxythiophene) and functionalized single-walled carbon nanotubes

The homogenous coating of poly (3,4-ethylenedioxythiophene) (PEDOT) on carbon nanotubes was realized by using functionalization of single-walled carbon nanotubes (SWNTs) in this study. Consequently, the PEDOT/functionalized SWNTs (PEDOT/F-SWNTs) composites, with size of around 100nm, which is much smaller than that of PEDOT, were prepared by the electrochemical method. Its small granule increased the active/nonactive mass ratio and reduced the ions diffusion length. Therefore, its specific capacitance of the composite was up to 200F g−1, which was remarkably greater than that of PEDOT. Furthermore, the PEDOT/F-SWNTs composites had very rapid charge/discharge ability with specific capacitance of 180F g−1 at scanning rate of 200mV s−1 and 170F g−1 at frequency of 1Hz, which is an important practical advantage. In addition, such composite had a good cycling performance and a wide potential window.