MULTIWALLED CARBON NANOTUBE-BASED AROMATIC HYDROCARBON SENSOR USING ELECTRONIC DIPOLE SPECTROSCOPY

A novel electronic spectroscopy technique based on dipole-dipole interactions for the identification of chemical analytes has been developed. This technique is based on the measurement of the charge transfer of chemical analytes to a multiwalled carbon nanotube mat-based sensing system. This technique was used for the identification of three aromatic hydrocarbons, namely, benzene, toluene, and xylene, at 100 parts-per-billion concentration. This technique was evaluated with multiwalled carbon nanotube mats for rapid, reliable, and robust identification of the three chemicals that belong to the same genre. The technique involves the identification of electronic spectral signatures of these chemicals using frequency domain analysis of the voltage signals generated by the binding of the chemical analytes onto the multiwalled carbon nanotube mat surfaces. This technique has the potential for rapid and accurate identification of multiple chemical analytes in a multiplexed fashion using a single-sensor device. In addition, this particular device configuration in conjunction with the electronic dipole spectroscopy results is a powerful lab-on-a-chip device for chemical and biological sensing applications.     

Enabling nickel ferrocyanide nanoparticles for high-performance ammonium ion storage

Prussian blue and its analogs are extensively investigated as a cathode for ammonium-ion batteries. However, they often suffer from poor electronic conductivity. Here, we report a Ni₂Fe(CN)₆/multiwalled carbon nanotube composite electrode material, which is prepared using a simple coprecipitation approach. The obtained material consists of nanoparticles with sizes 30–50 nm and the multiwalled carbon nanotube embedded in it. The existence of multiwalled carbon nanotube ensures that the Ni₂Fe(CN)₆/multiwalled carbon nanotube composite shows excellent electrochemical performance, achieving a discharge capacity of 55.1 mAh·g^–1 at 1 C and 43.2 mAh·g^–1 even at 15 C. An increase in the ammonium-ion diffusion coefficient and ionic/electron conductivity based on kinetic investigations accounts for their high performance. Furthermore, detailed ex situ characterizations demonstrate that Ni₂Fe(CN)₆/multiwalled carbon nanotube composite offers three advantages: negligible lattice expansion during cycling, stable structure, and the reversible redox couple. Therefore, the Ni₂Fe(CN)₆/multiwalled carbon nanotube composite presents a long cycling life and high rate capacity. Finally, our study reports a desirable material for ammonium-ion batteries and provides a practical approach for improving the electrochemical performance of Prussian blue and its analogs.     

Preparation and Characterization of Polyvinylpyrrolidone-functionalized Multiwalled Carbon Nanotube (PVP/f-MWNT) Nanocomposites

Polyvinylpyrrolidone/hydroxyl-functionalized multiwalled carbon nanotube and sulfonyl-functionalized multiwalled carbon nanotube nanocomposites were prepared in aqueous media. The structure, morphology, and thermal characterization of the prepared nanocomposites were done by Fourier transform infrared, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry techniques. The polyvinylpyrrolidone/hydroxyl-functionalized multiwalled carbon nanotube and polyvinylpyrrolidone/sulfonyl-functionalized multiwalled carbon nanotube nanocomposites improved the thermal properties of polyvinylpyrrolidone. According to the differential scanning calorimetry analysis, the glass transition temperature of 101.6 and 84.6°C is observed for the polyvinylpyrrolidone/hydroxyl-functionalized multiwalled carbon nanotube (5% w/w) and polyvinylpyrrolidone/sulfonyl-functionalized multiwalled carbon nanotube (5% w/w) nanocomposites, respectively. The energy-dispersive X-ray spectroscopy image of polyvinylpyrrolidone/sulfonyl-functionalized multiwalled carbon nanotube (5% w/w) nanocomposite showed a homogenous distribution of sulfonyl-functionalized multiwalled carbon nanotube in the polyvinylpyrrolidone matrix.     

Asymmetric Flexible Supercapacitor Stack

Electrical double layer supercapacitor is very significant in the field of electrical energy storage which can be the solution for the current revolution in the electronic devices like mobile phones, camera flashes which needs flexible and miniaturized energy storage device with all non-aqueous components. The multiwalled carbon nanotubes (MWNTs) have been synthesized by catalytic chemical vapor deposition technique over hydrogen decrepitated Mischmetal (Mm) based AB₃ alloy hydride. The polymer dispersed MWNTs have been obtained by insitu polymerization and the metal oxide/MWNTs were synthesized by sol-gel method. Morphological characterizations of polymer dispersed MWNTs have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM and HRTEM). An assymetric double supercapacitor stack has been fabricated using polymer/MWNTs and metal oxide/MWNTs coated over flexible carbon fabric as electrodes and nafion^® membrane as a solid electrolyte. Electrochemical performance of the supercapacitor stack has been investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy.     

Scrutinization of Polystyrene Microsphere-grafted Multiwalled Carbon Nanotube and Silver Nanoparticle-based Hybrids: Morphology,Thermal Properties,and Antibacterial Activity

Polystyrene microsphere (emulsion polymerization) was grafted on pure multiwalled carbon nanotube and amine-modified multiwalled carbon nanotube. Silver nanoparticle was also decorated on nanotube using chemical reduction (dimethylformamide). Amine-modified multiwalled carbon nanotube secures better silver attachment on nanotube wall. Polystyrene/Ag–amine-modified multiwalled carbon nanotube depicted fine dispersion in polymer latex due to modification. The 10% decomposition temperature and maximum degradation temperature of polystyrene/Ag–amine-modified multiwalled carbon nanotube was increased to 352 and 424°C. Antibacterial properties of nanocomposite were studied against respiratory track demolishing Gram-positive Staphylococcus aureus bacteria and two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). Ag nanoparticle was found responsible to potential death rate of microbes.     

Charge transfer effects on the sensing properties of fiber optic chemical nano-sensors based on single-walled carbon nanotubes

The effects of charge transfer induced by analyte molecule adsorption on the sensing properties of single-walled carbon nanotube (SWCNT) fiber optic chemical nano-sensors has been investigated. Experimental evidence indicates that extrinsic fiber optic Fabry-Perot (FP) interferometers incorporating nano-scale sensitive layers of SWCNTs and cadmium arachidate exhibit responses of opposite sign on exposure to electron donating (xylene and ethanol vapors) or accepting (NO₂) analytes, at room temperature. This reveals the strong influence of the electrical nature of the adsorbed species on the optical properties of carbon nanotube overlays. To take account of this influence, the plasma optic effect has been considered, which allows one to relate the modulation of the optical properties of sensitive overlays to the changes of carrier concentration. The results reveal that in analogy with resistive sensors based on SWCNTs, charge transfer phenomena play a significant role in optical detection, providing the possibility of enhancing the sensing performance and discriminating between accepting or donating analytes.     

Role of Carboxylic Acid-Functionalized MWCNTs in Potentially Biodegradable Poly(Amide–Imide) Nanocomposites Based on N,N′-(Pyromellitoyl)-bis-S-valine: Preparation,Thermal and Morphological Properties

A simple solution-blending process was used to efficiently disperse of carboxyl-modified multiwalled carbon nanotubes into a potentially biodegradable poly(amide–imide) to obtain poly(amide–imide)/carboxyl-modified multiwalled carbon nanotubes bionanocomposites. Carboxyl-modified multiwalled carbon nanotubes were utilized to better dispersion of multiwalled carbon nanotubes into the polymer matrix. The poly(amide–imide)/carboxyl-modified multiwalled carbon nanotube bionanocomposites were prepared with different carboxyl-modified multiwalled carbon nanotube contents (5–15 wt%). The resulting bionanocomposites are characterized by several techniques, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Adding carboxyl-modified multiwalled carbon nanotube into polymer matrix significantly increased the thermal stability of bionanocomposites due to the increased interfacial interaction between the poly(amide–imide) matrix and carboxyl-modified multiwalled carbon nanotube.     

Carbon nanotube-nanoporous anodic alumina composite membranes with controllable inner diameters and surface chemistry: Influence on molecular transport and chemical selectivity

This work presents the fabrication of carbon nanotube composite membranes with controllable nanotube dimensions (inner diameters and lengths) and surface chemistry and explores their influence on the transport properties and chemical based transport selectivity. These membranes were prepared by growing of vertically aligned multiwalled carbon nanotubes (MWCNTs) inside nanoporous anodic alumina membranes (NAAMs) through a catalyst-free chemical vapour deposition (CVD) approach. The deposition time during CVD process and the length of NAAMs were used to control nanotube dimensions. The thermal annealing and wet and dry oxidation processes were used to control the surface chemistry of inner walls of nanotubes from highly graphitic-hydrophobic to oxygen rich and hydrophilic. The structural features and chemical composition of the prepared membranes are characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The influence of the nanotube dimensions and surface chemistry on molecular transport properties of prepared membranes are assessed by analysing the transport of two models molecules with different hydrophilic–hydrophobic and charge properties. The obtained results reveal that the diffusional flux of model molecules through CNTs-NAAMs can be controlled by nanotube dimensions and surface chemistry of graphitic surface and these parameters can be used to tailor their chemical based molecular separation for specific applications.     

Modification of pristine multiwalled carbon nanotube by grafting with poly(methyl methacrylate) using benzoyl peroxide initiator

Multiwalled carbon nanotube was successfully grafted with poly(methyl methacrylate) by free radical mechanism using benzoyl peroxide initiator. The reaction was carried out in situ, where the initiator and methyl methacrylate monomer generated the polymer‐free radical that was subsequently grafted to the surface of the pristine multiwalled carbon nanotube. The multiwalled carbon nanotube grafted poly(methyl methacrylate) (MWCNT‐g‐PMMA) were characterized using Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, ¹³ C‐solid NMR spectroscopy, X‐ray photoelectron spectroscopy, and scan electron microscopy. From the result of the characterizations, the grafting of poly(methyl methacrylate) on to multiwalled carbon nanotube was confirmed, and a percentage grafting of 41.51% weight was achieved under optimized conditions with respect to the temperature and the amount of the initiator. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43270.     

Radial followed by longitudinal unzipping of multiwalled carbon nanotubes

A hybrid structure of graphene nanoleaves attached on a carbon nanotube and rectangular graphene nanosheets (GNSs) were fabricated by means of radial followed by longitudinal unzipping of crystalline multiwalled carbon nanotubes (MWCNTs) grown by catalytic chemical vapor deposition, using a chemical method containing sulfuric acid and nitric acid. Consecutive unzipping in the radial direction and then in the longitudinal direction of a nanotube has never been reported. Our simple chemical approach will open the path to fabrication for rectangular GNSs in the hundred nanometers by few hundred nanometers scale and a broad application of MWCNTs to the novel carbon nanostructure.     

The Improvement of Electrical Property of Multiwalled Carbon Nanotubes with Plasma Modification and Chemical Oxidation in the Polymer Matrix

We prepared a series of multiwalled carbon nanotube/polymer nanocomposites with two types of tube. One was plasma-modified with maleic anhydride and the other was modified with acid and the same plasma treatment. The morphology of the modified multiwalled carbon nanotube was observed by transmission and scanning electron microscopy. The surface structure was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The optimum conductivity of multiwalled carbon nanotube/polymer nanocomposites with specific ratios was of the order of 10⁻³ S/cm for a total MWCNT content of 2.0 and 2.5 wt%.     

Synthesis and characterization of multiwalled carbon nanotubes-protoporphyrin IX composites using acid functionalized or nitrogen doped carbon nanotubes

In this research we describe the synthesis and characterization of composite materials based on multiwalled carbon nanotubes and protoporphyrin IX. We compare the results of using three types of carbon nanotubes: pristine (diameter < 10 nm), acid functionalized (diameter < 10 nm), and nitrogen doped carbon nanotubes (diameter ≈ 20 nm). Carbon nanotubes were mixed with protoporphyrin IX via two simple and straightforward methods using sonication, or heating-stirring. The characterization of the composites was done by Raman spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, ultraviolet-visible and fluorescence spectroscopy and infrared spectroscopy. A diversity of coatings of the nanotubes by protoporphyrin were obtained depending on the type of nanotube used or the method of synthesis. Some carbon nanotubes increased their diameter up to 40% after the reaction with protoporphyrin. Percentages by weight up to 20% of protoporphyrin were measured by thermogravimetric analysis. We obtained experimental evidences by different techniques of the electronic interaction and the formation of covalent bonds between both constituents, above all for the composites using nanotubes < 10 nm in diameter. Some of these evidences were ~ 98% of fluorescence quenching, reduction in the intensity of the absorption bands in ultraviolet visible spectroscopy, strong reduction in the intensity of some bands in Raman spectroscopy, red and blue shifts, as well as the presence of new absorption bands in infrared spectroscopy. Nitrogen doped carbon nanotubes showed low chemical reactivity to protoporphyrin IX, perhaps due to their lower acceptor character as they could have charge transfer from nitrogen dopants to the nanotube network, or because of their metallic character.     

Effects of thermal imidization on mechanical properties of poly(amide‐co‐imide)/multiwalled carbon nanotube composite films

In this study, experimental and numerical studies were performed to investigate the relationship among the functionalization method, weight fraction of MWCNTs, thermal imidization cycle, and mechanical properties of various PAI/MWCNT composite films. Poly(amide‐co‐imide)/multiwalled carbon nanotube composite films were prepared by solution mixing and film casting. The effects of chemical functionalization and weight fraction of multiwalled carbon nanotubes on thermal imidization and mechanical properties were investigated through experimental and numerical studies. The time needed to achieve sufficient thermal imidization was reduced with increasing multiwalled carbon nanotube content when compared with that of a pure poly(amide‐co‐imide) film because multiwalled carbon nanotubes have a higher thermal conductivity than pure poly(amide‐co‐imide) resin. Mechanical properties of pure poly(amide‐co‐imide) and poly(amide‐co‐imide)/multiwalled carbon nanotube composite films were increased with increasing imidization time and were improved significantly in the case of the composite film filled with hydrogen peroxide treated multiwalled carbon nanotubes. Both the tensile strength and strain to failure of the multiwalled carbon nanotube filled poly(amide‐co‐imide) film were increased substantially because multiwalled carbon nanotube dispersion was improved and covalent bonding was formed between multiwalled carbon nanotubes and poly(amide‐co‐imide) molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Green Synthesis of Salicylic Acid-Based Poly(amide-imide) in Ionic Liquid and Composite Formation with Multiwalled Carbon Nanotube

A new salicylic acid-containing diacid monomer was synthesized by an established synthetic procedure from readily available reagents. The obtained diacid was used in the preparation of a thermally stable poly(amide-imide) by direct polycondensation with 4,4′-diphenylmethanediamine using 1,3-diisopropylimidazolium bromide ionic liquid as a green medium. The prepared polymer was used as matrix for preparation of multiwalled carbon nanotube/poly(amide-imide) composites in three multiwalled carbon nanotube concentrations (5, 10, and 15?wt%). The products were characterized for assessing the spectroscopic, thermal, and morphological properties by several methods. A homogeneous dispersion of multiwalled carbon nanotubes in the poly(amide-imide) matrix was observed by microscopy techniques.     

Radical grafting of polyethylene onto MWCNTs: A model compound approach

Covalent functionalization of pentadecane-decorated multiwalled carbon nanotubes (MWCNTs) has been studied as a model compound approach for the grafting of poly(ethylene-co-1-octene) onto MWCNTs by reactive extrusion. It was accomplished through radical addition onto unsaturated bonds located on the MWCNTs' surface using dicumyl peroxide as hydrogen abstractor. It was found that this surface treatment results into the break-up of the native nanotube bundles and increases solubility in various solvents. Raman spectroscopy was utilized to follow the introduction of pentadecane on the MWCNTs' surface; while thermogravimetric analysis and elemental analysis indicated the extent of this grafting. Pentadecane functionalized MWCNTs were imaged by transmission electronic microscopy showing single long functionalized MWCNTs distinct from the starting pristine bundles.     

Fabrication and Characterization of High-Performance Diglycidyl Ether of Bisphenol-A/Tetrabromobisphenol-A Blend Reinforced with Multiwalled Carbon Nanotube Composite

The nanocomposite of diglycidyl ether of bisphenol-A and diglycidyl ether of bisphenol-A/tetrabromobisphenol-A blend with purified multiwalled carbon nanotube and acid-functional multiwalled carbon nanotube were processed by solution route. According to field emission scanning electron microscope, diglycidyl ether of bisphenol-A/purified multiwalled carbon nanotube depicted poor dispersion and aggregated morphology, however, diglycidyl ether of bisphenol-A/acid-functionalized multiwalled carbon nanotube revealed better dispersion in matrix. The diglycidyl ether of bisphenol-A/tetrabromobisphenol-A/purified multiwalled carbon nanotube had higher thermal stability as T₀ of 369°C and T_max of 569°C were observed. Nonflammability of diglycidyl ether of bisphenol-A/tetrabromobisphenol-A blend-based material was 44%, i.e., higher than diglycidyl ether of bisphenol-A/purified multiwalled carbon nanotube series. Diglycidyl ether of bisphenol-A/tetrabromobisphenol-A/purified multiwalled carbon nanotube 0.1 had crystalline morphology with diffractions at 12.77° and 26.8°. The diglycidyl ether of bisphenol-A/tetrabromobisphenol-A/multiwalled carbon nanotube nanocomposite revealed electromagnetic interference shielding effectiveness of ～12.1?dB, i.e., desired for aerospace applications.     

Linear carbon chains encapsulated in multiwall carbon nanotubes: Resonance Raman spectroscopy and transmission electron microscopy studies

In this paper we report the characterization of linear carbon chains encapsulated in multiwalled carbon nanotubes by using Raman spectroscopy and transmission electron microscopy. The chains are characterized by strong vibrational peaks around 1850 cm⁻¹ and both the frequency and intensity of these peaks were found to be dependent on laser excitation energy. Furthermore, resonance Raman spectroscopy was used for constructing the resonance window of the linear carbon chains. The Raman spectroscopy data showed that long chains have lower highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps and weaker carbon–carbon bonds. Besides the spectroscopy evidence for the linear carbon chain, we used scanning transmission electron microscopy/electron energy loss spectroscopy analysis of the nanotube cross section to unambiguously show the existence of a 1D structure present within the innermost carbon nanotube with an unprecedented clarity compared to previous reports on this kind of system.     

Conducting polymer composites of multiwalled carbon nanotube filled doped polyaniline

A multiwalled carbon nanotube (c‐MWNT)/polyaniline (PANI) composite was synthesized by an in situ chemical oxidative polymerization process. With the carbon nanotube loading increased from 0 to 30 wt %, the conductivity also increased and became weakly temperature‐dependent. Fourier transform infrared spectroscopy studies showed that the synthesis by an in situ process led to effective site‐selective interactions between the quinoid ring of the PANI and the multiwalled nanotubes, facilitating charge‐transfer processes between the two components. The morphological analysis indicated that the c‐MWNTs were well dispersed and isolated, and the tubes became crowded proportionally to the weight percentage of c‐MWNTs used in the composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of functionalized multiwalled carbon nanotubes on weather degradation and corrosion of waterborne polyurethane coatings

A series of waterborne polyurethane/functionalized multiwalled carbon nanotube (WBPU/f-MWCNT) nanocomposite dispersions was prepared using three defined concentrations of 0.5, 1.0 and 2.0 wt% carboxyl functionalized multiwalled carbon nanotubes (f-MWCNTs). All dispersions were coated on mild steel and exposed under natural weather condition for a maximum of 365 days. Both exposed and unexposed coatings were characterized by potentiodynamic polarization (PDP) and X-ray photoelectron spectroscopy (XPS) analyses. The pristine WBPU coating showed slight degradation and corrosion protection. Inclusion of a higher content of f-MWCNTs significantly improved both the degradation and corrosion protection efficiencies of the coatings. Maximal degradation and corrosion protection was observed when 2.0 wt% f-MWCNT was mixed with WBPU for all of the coatings.     

Electrocatalytic properties of carbon nanotube carpets grown on Si-wafers

Electrocatalytical activity of carbon nanotube carpets grown on oxidized silicon wafers by spray pyrolysis catalytic chemical vapor deposition has been examined for use in electrochemical devices. To determine the influence of electron donor doping on electrochemical quality, N-atoms were incorporated into the nanotube structure during growth. N-doping, as revealed by electron microscopy, Raman spectroscopy and X-ray diffraction data, led to essential changes of the tubule morphology and structure. For the electrochemical investigation of the carbon nanotube electrodes produced, cyclic voltammetry and electrochemical impedance spectroscopy were used, while ferrocene (FeCp₂) and uric acid served as reference redox systems. Results have revealed enhanced electron transfer kinetics on the N-doped electrodes. The electronic band structure of carbon nanotubes and electrochemical gating are shown to be responsible for the charge transfer kinetics on nanotube electrodes.