Acid-treated Multi-walled Carbon Nanotubes Research Articles

Structure, electrical and mechanical properties of polyamide 66/acid-treated MWCNT composite films prepared by solution mixing in the presence of nonionic surfactant

Two different sets of polyamide 66(PA66)-based composite films containing 2.0-10.0 wt% acid-treated multiwalled carbon nanotubes (MWCNT) were manufactured by solution mixing and casting method in the presence or absence of a nonionic surfactant. For the improved dispersion and interfacial interaction of MWCNTs in the PA66 matrix, carboxylic acid-functionalized MWCNTs were prepared by the acid-treatment of pristine MWCNTs. The uniform dispersion of the acidtreated MWCNTs in the PA66 matrix was confirmed from FE-SEM images of the fractured composite film surfaces. DSC thermograms supported that the acid-treated MWCNTs served as nucleating agents for the melt-crystallization of PA66 in both composite films prepared with/without the addition of the surfactant. The electrical and tensile mechanical properties of the composite films prepared with the surfactant were ~20 % higher than those of the composite films manufactured without the surfactant. For both composite films, sheet resistivity and tensile mechanical properties were found to be highly decreased and increased, respectively, with the increment of the acid-treated MWCNT content.

Exploring the use of biosurfactants from Bacillus subtilis in bionanotechnology: A potential dispersing agent for carbon nanotube ecotoxicological studies

In this work, we evaluate the efficiency of biosurfactants produced by Bacillus subtilis LSFM-05 for the dispersion of acid-treated multi-walled carbon nanotubes (CNT-LQES1) and the effect of dispersion on toxicity testing with Daphnia similis. Carbon nanotubes are very hydrophobic materials and they readily agglomerate in mineral water. As a result, in order to determine their toxicity it is critical to evaluate methods to disperse these nanomaterials in a biologically compatible manner. The biosurfactant used in this work, termed BioS, which is a mixture of the lipopeptides (surfactin and fengycin), was found to be non-toxic to D. similis in an acute toxicity test (48h) and it was an excellent dispersing agent for CNT-LQES1 in reconstituted mineral water. Monitoring in real-time using the nanoparticle tracking analysis (NTA) showed that the colloidal stability of the CNT-LQES1 suspension dispersed with BioS was highly stable. These findings are encouraging for the application of biosurfactants as nontoxic dispersion agents in the emerging fields of bionanotechnology and nanotoxicology.

Highly active nitrogen-doped few-layer graphene/carbon nanotube composite electrocatalyst for oxygen reduction reaction in alkaline media

In this work the electrocatalysis of oxygen reduction on nitrogen-doped few-layer graphene/multi-walled carbon nanotube (FLG/MWCNT) composite catalyst has been investigated. These composite materials were prepared from different nitrogen precursors, acid-treated MWCNTs and graphene oxide (GO), which was synthesised from graphite by the modified Hummers’ method. Urea and dicyandiamide were used as nitrogen precursors and the doping was achieved by pyrolysing the mixture of GO and MWCNTs in the presence of these nitrogen-containing compounds at 800°C. The N-doped composite catalyst samples were characterised by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was studied in 0.1M KOH on glassy carbon electrodes modified with N-doped FLG/MWCNT electrocatalysts employing the rotating disk electrode (RDE) method. The RDE results indicated that these metal-free nitrogen-doped nanocarbon catalysts possess remarkable electrocatalytic activity towards the ORR in alkaline media similar to that of commercial Pt/C catalyst. The results obtained in this work are particularly important for the development of non-Pt cathode catalysts for alkaline membrane fuel cells.

Multiwalled carbon nanotube mixed matrix membranes containing amines for high pressure CO2/H2 separation

CO2-selective mixed matrix membranes capable of facilitated transport were synthesized for CO2/H2 separation at high pressures of at least1.52 MPa and high temperatures above373.15 K. A significant improvement in membrane stability was achieved by thoroughly dispersing multiwalled carbon nanotubes (MWNTs) as mechanical reinforcing fillers in a polyvinylalcohol matrix containing amines. With 2wt% MWNTs incorporated, the membrane performance, including a CO2/H2 selectivity of 43 and a CO2 permeability of 836Barrers (1 Barrer = 7.5×10−11 cm3(STP) cm/(cm2 s kPa)), showed no change for 444h (18.5 days) when operated at1.52 MPa and380.15 K. At the same conditions, the membrane containing 4wt% acid-treated MWNTs also showed good stability. The membranes synthesized in this work are the first of this kind, displaying exceptional CO2/H2 separation performance and high tolerance to feed gas at high pressures and high temperatures. Potentially, they could be used in a stand-alone membrane unit for energy-efficient precombustion carbon capture from coal-derived syngas or in conjunction with water-gas-shift reaction for CO clean-up to produce high-purity H2 for fuel cells and to simultaneously capture CO2.

A Simple Gas–Solid Route To Functionalize Ordered Carbon

The reaction of nitric oxide (NO) and carbonaceous materials generates nitrogen functionalities on and in graphitic carbons and oxidizes some of the carbon. Here, we have exploited these phenomena to provide a novel route to surface-functionalized multiwalled carbon nanotubes (MWCNTs). We investigated the impacts of NO on the physical and chemical properties of industrially synthesized multiwalled carbon nanotubes to find a facile treatment that increased the specific surface area (SBET) of the MWCNTs by ∼20%, with only a minimal effect on their degree of graphitization. The technique caused less material loss (∼12 wt %) than traditional gas-based activation techniques and grafted some nitrogen functional groups (1.1 at. %) on the MWCNTs. Moreover, we found that Ni nanoparticles deposited on NO-treated MWCNTs had a crystallite size of dNi = 13.1 nm, similar to those deposited on acid-treated MWCNTs (dNi = 14.2 nm), and clearly much smaller than those deposited under the same conditions on untreated MWCNTs (dNi = 18.3 nm).

FUNCTIONALLY GRADED EPOXY COMPOSITES USING SILANE COUPLING AGENT FUNCTIONALIZED MULTIWALLED CARBON NANOTUBES

Functionally graded multiwalled carbon nanotube (MWCNT) reinforced epoxy matrix composites are fabricated using a centrifugal method. Aggregation of the MWCNTs during the epoxy curing process is prevented using a two-step aminosilane modification. Chemical interaction of the silane with the oxidized nanotube surface is confirmed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Raman spectroscopy of acid-treated MWCNTs corroborates the formation of surface defects owing to the introduction of carboxyl groups. The mechanical and microwave absorption property gradients of the composites correspond with those produced via silane modification indicating potential application to microwave absorbing materials. The MWCNTs are better dispersed in the epoxy resin after the modification, making it possible for them to become efficiently graded in the epoxy matrix. We therefore show that it is possible to fabricate functionally graded nanofiller-reinforced materials using the centrifugal method by modifying the surface of the nanofiller.

Surface Modification of Multiwalled Carbon Nanotubes with Engineered Self-Assembled RAFT Diblock Coatings

A facile method to modify the surface of multiwalled carbon nanotubes (MWCNTs) via electrostatic interactions between polyelectrolytes and oxidized MWCNTs was developed. Diblock copolymers containing poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC), a positively charged block, and poly(ethylene glycol) methacrylate (PEGMA), a neutral block, with tailored molecular weights and low polydispersities were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Acid treated-MWCNTs were coated with the RAFT diblock copolymers to improve their dispersibility in aqueous phosphate buffered saline (PBS) solution. The short positively charged PMETAC block was designed to attach the block copolymers to the surface of MWCNTs via electrostatic interactions, whereas the PEGMA block improved dispersibility of the MWCNTs in aqueous solutions. Extensive screening of the diblock copolymers with different degrees of polymerization (DP) showed that the dispersion stability of the polymer-coated MWCNTs in PBS was greatly improved with increasing chain length of the PEGMA block. In particular, the MWCNTs coated with a diblock copolymer containing PEGMA (DP = 118, the longest block investigated) showed superior dispersion stability in both water and PBS solution.

Simultaneous reinforcement and toughening of polyurethane composites with carbon nanotube/halloysite nanotube hybrids

Abstract In this work, three-dimensional (3D) hybrid nanofillers, composed of acid-treated multi-walled carbon nanotubes (a-CNTs) and silane-treated halloysite nanotubes (s-HNTs), have been successfully prepared through covalent bonding. By using simple solution-casting method, polyurethane (PU) elastomers reinforced with these s-HNT/a-CNT (HC) hybrid nanofillers have been fabricated. The morphology and mechanical properties of the resultant hybrid and PU composites are characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), thermogravimetric analysis (TGA) and tensile tests. Tensile test data show that the tensile strength, Young’s modulus and elongation at break of the resultant PU composite with merely 1 wt% HC hybrids are significantly improved by 140%, 35% and 68% respectively. This clearly demonstrates the synergistic reinforcement of one-dimensional CNTs and HNTs within the hybrid in improving the strength and toughness of PU composite. Therefore, the s-HNT/a-CNT hybrid thus prepared is an ideal agent for simultaneous reinforcement and toughening of PU elastomers.

Silver Nanowire Catalysts on Carbon Nanotubes-Incorporated Bacterial Cellulose Membrane Electrodes for Oxygen Reduction Reaction

Silver nanowires have unique electrical, thermal and optical properties, which support their potential application in numerous fields including catalysis, electronics, optoelectronics, sensing, and surface-enhanced spectroscopy. Especially, their application such as catalysts for alkaline fuel cells (AFCs) have attracted much interest because of their superior electrical conductivity over that of any metal and their lower cost compared to Pt. In this study, multiwalled carbon nanotubes (MWCNTs)-incorporated bacterial cellulose (BC) membrane electrode with silver nanowire catalyst was prepared. First, acid-treated MWCNTs were incorporated into BC membranes and then freeze-dried after solvent exchange to tert-butanol in order to maintain the 3D-network macroporous structure. Second, silver nanowires synthesized by polyol process were introduced onto the surface of the MWCNTs-incorporated BC membrane through easy vacuum filtration. Finally, thermal treatment was carried out to confirm the effect of the PVP on the silver nanowire catalysts toward oxygen reduction reaction. The electrode with thermally treated silver nanowire had great electrocatalytic activity compared with non-treated one. These results suggest that the MWCNTs-incorporated BC electrode with silver nanowire catalysts after thermal treatment could be potentially used in cathodes of AFCs.

Quantitative characterization of acidic groups on acid-treated multi-walled carbon nanotubes using 1-aminopyrene as a fluorescent probe

Acidic functional groups produced on the surface of acid-treated multi-walled carbon nanotubes (MWCNTs) were quantified by fluorescence measurements using 1-aminopyrene (1-AP) as an in situ probe molecule. The 1-AP cation-like bands were observed on the HNO3/H2SO4 mixture-treated MWCNT surfaces because the 1-AP molecule was tightly immobilized by the hydrogen bonding interaction between its amino group and the Brönsted-acidic groups on the MWCNT surface. The fluorescence measurement allowed us to confirm the Langmuir-type adsorption of 1-AP on the functional groups of the MWCNTs, and estimate their amount of the functional groups and adsorption equilibrium constant. A longer acid treatment caused the chemical modification to generate higher amounts of the Brönsted-acidic functional groups and improve the adsorption ability on the MWCNT surface. About 2% of carbon in the MWCNTs was oxidized by the 24h acid treatment. This value corresponded to 15–22% of carbon in the surface layer.

Significantly Enhanced Actuation Performance of IPMC by Surfactant-Assisted Processable MWCNT/Nafion Composite

The performance of Ionic Polymer Metal Composite (IPMC) actuator was significantly enhanced by incorporating surfactant-assisted processable Multi-Walled Carbon Nanotubes (MWCNTs) into a Nafion solution. Cationic surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) was employed to disperse MWCNTs in the Nafion matrix, forming a homogeneous and stable dispersion of nanotubes. The processing did not involve any strong acid treatment and thus effectively preserved the excellent electronic properties associated with MWCNT. The as-obtained MWCNT/Nafion-IPMC actuator was tested in terms of conductivity, bulk and surface morphology, blocking force and electric current. It was shown that the blocking force and the current of the new IPMC are 2.4 times and 1.67 times higher compared with a pure Nafion-based IPMC. Moreover, the MWCNT/IPMC performance is much better than previously reported Nafion-IPMC doped by acid-treated MWCNT. Such significantly improved performance should be attributed to the improvement of electrical property associated with the addition of MWCNTs without acid treatment.

The AMWCNTs supported porous nanocarbon composites for high-performance supercapacitor

The porous nanocarbons supported by acid-treated multiwall carbon nanotubes (PC@ACNTs) were prepared by the combination of the hydrothermal polymerization of glucose on ACNTs, carbonization under N2 protection and final activation with ZnCl2. The materials were characterized by transmission electron microscopy, X-ray powder diffraction and Raman spectra. The results indicated that the ACNTs distributed uniformly into the framework of the porous carbon. The composites showed the high BET specific surface area up to 1712m2g−1 and good conductivity. The electrochemical measurements indicated that the composites processed good performances for electrochemical energy storage (210Fg−1 at 0.5Ag−1), and high stability (>99.9%), much higher than the corresponding ACNTs, porous carbons and the samples prepared by using raw MWCNTs as source. The good performance of PC@ACNTs composites was relative with the synergy of good conductivity of ACNTs and large specific surface areas of PC.

Thermal and mechanical properties of poly(trimethyelene terephthalate)/acid-treated multiwalled carbon nanotube composites

Poly(trimethylene terephthalate) (PTT) and acid-treated multiwalled carbon nanotubes (OMWCNTs) composites were prepared using melt processing, and effect of CNT loading on thermal and mechanical properties of PTT have been investigated. Addition of OMWCNTs showed no effect on thermal stability, crystallization, and melting temperature of PTT matrix. Wide angle X-ray diffraction also showed no change in the crystallite size of PTT on addition of OMWCNTs. The tensile testing results showed that tensile modulus and tensile strength of PTT increased significantly on addition of OMWCNTs. The reinforcing effect of OMWCNTs was further confirmed by dynamic mechanical analysis, which showed noticeable increase in storage modulus and shift in the glass transition temperature on addition of OMWCNTs. Scanning electron microscopy studies showed good interfacial interaction between OMWCNTs and PTT matrix.

Solid-state supercapacitors with ionic liquid based gel polymer electrolyte: Effect of lithium salt addition

Performance characteristics of the solid-state supercapacitors fabricated with ionic liquid (IL) incorporated gel polymer electrolyte and acid treated multiwalled carbon nanotube (MWCNT) electrodes have been studied. The effect of Li-salt (LiPF6) addition in the IL (1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate, EMImFAP) based gel electrolyte on the performance of supercapacitors has been specifically investigated. The LiPF6/IL/poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP) gel electrolyte film possesses excellent electrochemical window of 4 V (from −2.0 to 2.0 V), high ionic conductivity ∼2.6 × 10−3 S cm−1 at 20 °C and high enough thermal stability. The comparative performance of supercapacitors employing electrolytes with and without lithium salt has been evaluated by impedance spectroscopy and cyclic voltammetric studies. The acid-treated MWCNT electrodes show specific capacitance of ∼127 F g−1 with IL/LiPF6 containing gel polymer electrolyte as compared to that with the gel polymer electrolyte without Li-salt, showing the value of ∼76 F g−1. The long cycling stability of the solid state supercapacitor based on the Li-salt containing gel polymer electrolyte confirms the electrochemical stability of the electrolyte.

Comparison between exfoliated graphite, graphene oxide and multiwalled carbon nanotubes as reinforcing agents of a polyurethane elastomer

A highly crystalline aliphatic segmented polyurethane (PU) elastomer with 40 wt% hard segment (HS) content, based on 1,6-hexamethylene diisocyanate and 1,4-butanediol as the HS, and a block copolymer of hexamethylene carbonate and polycaprolactone as the soft segment (SS), has been used as the matrix to prepare carbon nanofiller/PU composites by solution casting. Composite films with different loadings of solvent-exfoliated graphene (G)/nanographite, graphene oxide (GO) obtained by the so-called modified Hummers method, and acid-treated multiwalled carbon nanotubes (MWCNT) were obtained and characterised. Tensile test results show that the effectiveness of increasing PU strength follows the trend MWCNT > GO > G. The ductility reduction in all the cases is related to the large sizes of nanofillers in relation to PU hard domains and the hindrance to allow plastic flow of PU SSs by larger fillers.

Acid-Treated Multi-Walled Carbon Nanotubes Coated with Lung Surfactant Protein SP-A Do Not Induce a Lung Inflammatory Response

Acid-Treated Multi-Walled Carbon Nanotubes Coated with Lung Surfactant Protein SP-A Do Not Induce a Lung Inflammatory Response

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO2/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO2 nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312m2·g−1) and a bimodal mesoporous structure (3.18nm and 12.4nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.

Functionalized multi-walled carbon nanotubes for enhanced photocurrent in dye-sensitized solar cells

The influence of the incorporation of nitric acid-treated (functionalized) multi-walled carbon nanotubes (f-MWCNTs) and unmodified MWCNTs in TiO2 films are investigated by observing the photocurrent-voltage characteristics of dye-sensitized solar cells (DSSCs) with and without MWCNTs. The short-circuit photocurrent (Jsc) of the modified DSSC increased by 46% compared with that of a cell with plain TiO2 film. The open-circuit voltage remained the same for all cases. The enhanced Jsc is explained by the increased surface area of the film, enhanced cluster formation of TiO2 particles around f-MWCNTs, and improved interconnectivity of TiO2 particles in the presence of f-MWCNTs. The efficiency of the cell increased by 45% due to Jsc enhancement.

Characteristics of nylon 6,6/nylon 6,6 grafted multi-walled carbon nanotube composites fabricated by reactive extrusion

Nylon 6,6 composites containing nylon 6,6 grafted multi-walled carbon nanotubes (nylon 6,6-g-MWCNT) were fabricated from nylon 6,6 and acyl chloride grafted MWCNT (MWCNT–COCl) by reactive extrusion. MWCNT–COCl was produced by reacting acid-treated MWCNTs with thionyl chloride. Formation of nylon 6,6-g-MWCNT by reactive extrusion was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and scanning electron microscopy. To quantify the interfacial adhesion energies of nylon 6,6 and pristine and functionalized MWCNTs, the contact angles of cylindrical drop-on-fiber systems were determined using the generalized droplet shape analysis. The interfacial adhesion energy of the nylon 6,6/nylon 6,6-g-MWCNT composite was twice that of the nylon 6,6/pristine MWCNT composite. Nylon 6,6-g-MWCNTs exhibited excellent dispersion in the composite, whereas pristine MWCNTs exhibited poor dispersion when composite films were prepared by solvent casting. The reinforcement level of the composite increased with increasing MWCNT content. Among the composites examined, the nylon 6,6/nylon-g-MWCNT composite with a fixed MWCNT content exhibited the highest level of reinforcement.

In-situ preparation of multi-walled carbon nanotube (MWNT)/cellulose nanocomposites and their physical properties

The multi-walled carbon nanotube (MWNT)/cellulose nanocomposites were prepared by using monohydrated Nmethylmorpholine-N-oxide (NMMO) as a solvent for dispersing the acid-treated MWNTs (A-MWNTs) as well as for dissolving the cellulose. The A-MWNTs were well dispersed in both monohydrated NMMO and the nanocomposite films. The nanocomposite films were prepared by a film-casting method onto a glass plate. The tensile strain at break, Young’s modulus, and toughness of nanocomposite films increased by ∼5, ∼2 and ∼12 times, respectively at ϕ (A-MWNT content in the nanocomposite)=0.8 wt%, as compared to those of the pure cellulose film. The thermal degradation temperature of the nanocomposite films also increased from 329 to 339 oC by incorporation of 1 wt% A-MENTs. The electric conductivities of the A-MWNT/cellulose nanocomposites at ϕ =1 and 10 wt% were 2.09×10−5 and 3.68×10−3 S/cm, respectively. The transmittances were 86, 69 and 55 % at 550 nm for 0.4, 0.8 and 1 wt% nanocomposite films, respectively. Thus, these nanocomposites are promising materials in terms of all the properties studied in this paper and can be used for many applications, such as toughened cellulose fibers, transparent electrodes, etc.