Carboxyl-functionalized Multi-walled Carbon Nanotubes Research Articles

Preparation and Characterization of Multiwall Carbon Nanotube (MWCNT) Reinforced Chitosan Nanocomposites: Effect of Gamma Radiation

Nanocomposites of biodegradable chitosan and multiwalled carbon nanotubes (MWCNTs) were prepared using two kinds of MWCNTs, i.e., pristine multiwalled carbon nanotubes (p-MWCNTs) and carboxyl-functionalized multiwalled carbon nanotubes (f-MWCNTs). The nanocomposites were subjected to gamma irradiation (60Co) at different intensities (1–50 kGy), and the variation of different physicomechanical properties has been extensively studied. Various techniques such as Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), optical microscopy (OM), thermogravimetric analysis (TGA), differential scanning colorimetry (DSC), and universal testing machine (UTM) were used to investigate the physicochemical, morphological, and thermomechanical properties of the nanocomposites. FTIR spectra and OM confirmed that oxygen-containing functional groups were present on the surface of the tubes that helped better dispersion of f-MWCNTs in chitosan solution. The experimental results demonstrated that the tensile strength (TS) and modulus (TM) of nanocomposites were increased by 57 and 48 %, respectively, through the addition of 1 % MWCNTs with the chitosan matrix; however, no significant changes of TS and TM are observed for more MWCNTs (above 1 %) in the composites. Considering the effect of irradiation doses, it was observed that low irradiation doses (up to 10 kGy) significantly increases thermal stability and tensile properties of the nanocomposite compared with the nonirradiated samples.

Inactivation of bacteria by electric current in the presence of carbon nanotubes embedded within a polymeric membrane.

Uniform conductive composite membranes were prepared using a phase inversion method by blending carboxyl-functionalized multi-walled carbon nanotubes (CNTs) with a polysulfone polymer. At 6 % of the embedded CNTs, the membrane pore size measured by transmission electron microscopy (TEM) was approximately 50 nm. Electric current in the presence of the composite membranes markedly inactivated the model pathogenic bacteria Escherichia coli and Staphylococcus aureus, with the extent of bacterial inactivation rising when the current was increased. Over 99.999 % inactivation of both bacteria was observed in deionized water after 40 min at 5 mA direct current (DC); importantly, no appreciable inactivation occurred in the absence of either the electric field or the CNTs within the membranes under otherwise the same conditions. A much lower, although still pronounced, inactivation was seen with alternating current (AC) in a 25 mM NaCl aqueous solution.

Morphology, crystallization and mechanical properties of biodegradable poly(butylene succinate-co-butylene carbonate)/multi-walled carbon nanotubes nanocomposites

Biodegradable poly(butylene succinate-co-butylene carbonate) (PBSC)/carboxyl-functionalized multi-walled carbon nanotubes (f-MWCNTs) nanocomposites were prepared through a solution and casting method at low f-MWCNTs loadings. Scanning electron microscopy observations revealed a fine dispersion of f-MWCNTs in the PBSC matrix. Both the nonisothermal and isothermal melt crystallization processes of PBSC were enhanced, apparently by the presence of f-MWCNTs in the nanocomposites, because f-MWCNTs acted as an efficient heterogeneous nucleation agent for the crystallization of PBSC. The crystallization mechanism remained unchanged for both neat PBSC and the PBSC/f-MWCNTs nanocomposites, regardless of crystallization temperature; moreover, the crystal structures of PBSC were not modified by f-MWCNTs in the nanocomposites. The dynamical mechanical properties were also improved in the nanocomposites. Upon incorporating only 1 wt% of f-MWCNTs, the storage modulus of PBSC improved by about 30% at −60 °C. In addition, the glass transition temperature values of PBSC were increased slightly in the nanocomposites, relative to that of neat PBSC. Open image in new window

An Electrochemical Method for High Sensitive Detection of Thiabendazole and Its Interaction with Human Serum Albumin

In this study, a simple and highly sensitive electroanalytical method for the determination of thiabendazole (TBZ) was developed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) modified glassy carbon electrode (MWCNT-COOH/GCE) in phosphate buffer solution (pH = 6.0). MWCNT-COOH/GCE exhibits an enhanced effectiveness for the redox of TBZ. This constructed biosensor exhibited two linear relationships with TBZ concentration range from 5.00 × 10−7 to 4.95 × 10−6 mol/L and 4.95 × 10−6 to 9.80 × 10−5 mol/L, respectively. The detection limit was 3.0 × 10−7 mol/L (S/N = 3) and the relative standard deviation (R.S.D.) was lower than 4.2 % (n = 6). The proposed method was successfully applied to determine TBZ in real samples and the results were satisfactory. The MWCNT-COOH/GCE electrode showed good reproducibility, stability, and anti-interference. The electrochemistry method was also described for the evaluation of TBZ and human serum albumin (HSA) interaction. In the presence of HSA, the peak currents of TBZ decreased linearly due to the formation of a kind of electro-inactive complex. The binding constant between TBZ and HSA was obtained by DPV.

Determination of tetrabromobisphenol A and bisphenol A in environmental water using carboxylated multiwalled carbon nanotubes as sorbent for solid-phase extraction combined with liquid chromatography-tandem mass spectrometry

A method for the determination of tetrabromobisphenol A and bisphenol A in environmental water using carboxyl-functionalized multiwalled carbon nanotubes as solid-phase extraction sorbent and liquid chromatography-tandem mass spectrometry was established. Comparison of three nanomaterials including multiwalled carbon nanotubes, C60 and carboxyl-functionalized multiwalled carbon nanotubes used as solid-phase extraction sorbents was made. After preconcentration by solid-phase extraction, tetrabromobisphenol A and bisphenol A were separated on a Thermo Scientific Hypersil C18 column (150 mm x 4. 6 mm, 3 μm) and then detected by tandem mass spectrometry in negative electrospray ionization (ESI) mode. The results showed a good linear response in the concentration range of 0. 02-1. 0 mg/L for tetrabromobisphenol A and bisphenol A, and the limits of detection (S/N= 3) were 0. 04 pg/L and 0. 2 μg/L for tetrabromobisphenol A and bisphenol A, respectively. The application of the proposed approach has been carried out for the determination of tetrabromobisphenol A and bisphenol A in spiked lake water and sea water samples. The recoveries varied from 82% to 99% with the relative standard deviations below 5. 0%. The proposed method can be used for the determination of tetrabromobisphe- nol A and bisphenol A at trace level in complex environmental samples.

Chemical modification of multiwalled carbon nanotube with a bifunctional caged ligand for radioactive labelling

Carboxyl-functionalized multiwalled carbon nanotubes (MWCNTs) have been successfully radiolabelled with cobalt-57 (57Co) (T1/2=270days) via the attachment of the bifunctional caged ligand MeAMN3S3sar. In this study MeAMN3S3sar has been synthesized and coupled to MWCNTs to form the conjugate MWCNT–MeAMN3S3sar. Synthesis was confirmed with nuclear magnetic resonance. X-ray photoelectron spectroscopy (XPS) confirmed the conjugation. Non-radioactive labelling of this conjugate was completed with Cu(II) ions to confirm the stability of the MeAMN3S3sar after coupling with the MWCNTs. The complexation of the Cu(II) was also confirmed with XPS. Transmission electron microscopy was used to demonstrate that the coupling reaction had a negligible effect on the size and shape of the MWCNTs. Radiolabelling of the MWCNT–MeAMN3S3sar conjugate and pristine (untreated) MWCNTs (non-specific) with the gamma-emitting radioactive isotope 57Co were compared. The radiolabelling efficiency of the MWCNT–MeAMN3S3sar conjugate was significantly higher (95% vs. 0.1%) (P⩽0.001) than for the unconjugated pristine MWCNTs. This will allow for the potential tracking of nanoparticle movement in vitro and in vivo.

Carboxyl-functionalized MWCNT doped poly(o-toluidine) nanohybrids: Synthesis, characterization with AC electrical and dielectric properties

Nanohybrids of protonic acid doped poly(o-toluidine) (POT) with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) were synthesized by in situ chemical oxidation polymerization in the absence of any added acid. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) showed that carboxylic groups had been introduced onto the surface of MWCNT. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that a thin layer of POT is well coated on the surface of MWCNT-COOH with a thickness of ∼19nm. Based on π–π* electron and H-bonding interactions between functional groups of o-toluidine monomer and those of MWCNT-COOH, o-toluidine molecules were adsorbed and polymerized on the surface of nanotubes. AC conductivity and dielectric properties of POT/MWCNT-COOH nanohybrids were measured at 100Hz–1MHz and a temperature range of 25–125°C. Upon increasing the concentration of MWCNT-COOH an increase in the AC conductivity, dielectric permittivity and loss tangent of host POT are observed. The presence of polarons and bipolarons are responsible for the frequency dependence of AC conductivity in these nanohybrids. The variation of AC conductivity with frequency has been described by the power law. The decrease in activation energy is observed with increasing concentration of MWCNT-COOH in the nanohybrids. The incorporation of 4wt% MWCNT-COOH into POT matrix resulted in around ten-fold increase in dielectric permittivity with a negligible effect on loss tangent at 100Hz. The permittivity is found to be stable up to 75°C and then increase gradually with increasing temperature.

Self-assembly of multiwall carbon nanotubes on sulfonated poly (arylene ether ketone) as a proton exchange membrane

Membranes of sulfonated poly (arylene ether ketone) containing carboxyl groups (SPAEK-C) are modified by alternating deposition of oppositely charged polyelectrolytes [carboxyl-functionalized multiwalled carbon nanotubes (C-MWCNTs) and chitosan (CS)] in order to reduce methanol crossover and maintain high proton conductivity in a direct methanol fuel cell (DMFC). Fourier transform infrared spectroscopy confirms that C-MWCNTs and CS are assembled in the multilayers. The morphology of membranes is studied by scanning electron microscopy. The results confirm the presence of thin C-MWCNTs/CS multilayers coated on the SPAEK-C membrane. The SPAEK-C-(C-MWCNTs/CS)n membranes maintain high proton conductivity values up to 0.058 Scm−1 at 25 °C and 0.24 Scm−1 at 80 °C, which are superior to previous layer-by-layer assembled polyelectrolyte systems. Meanwhile, the methanol permeability of these modified membranes is effectively reduced. The selectivity of SPAEK-C-(C-MWCNTs/CS)n is two orders of magnitude greater than that of Nafion® 117, making these modified membranes a good alternative to be used in DMFCs. The thermal stability, water uptake, swelling ratio and proton conductivity of SPAEK-C and SPAEK-C-(C-MWCNTs/CS)n membranes are also investigated.

Sensing hydrogen peroxide by carbon nanotube/horseradish peroxidase bio-nanocomposite

H2O2 is a product of reactions catalysed by several oxidase enzymes and it is essential in environmental and pharmaceutical analyses. The most commonly used enzyme in understanding the biological behaviour of catalysed oxidation of H2O2 is horseradish peroxidase (HRP). In our experiments HRP was bound to carboxyl-functionalized multiwalled carbon nanotubes (MWNT-COOH) by N-hydroxysuccinimide (NHS) and 1-[3-dimethylaminopropyl]-3-ethyl-carbodiimide (EDC) crosslinkers. The activity of this bio-nanocomposite and the limit of detection (LOD) for H2O2 were determined by measuring the fluorescence of tetraguaiacol (which chemical is the product of guaiacol oxidation after addition of H2O2 to the reaction mixture) as a function of time. The hydrogen peroxide biosensor we developed exhibited a detection limit of 1.2 µM H2O2 s−1 which resolution was better than the one measured in solution by about a factor of eight (it was 10 µM H2O2 s−1 in solution). An attempt has been made to measure the concentration of H2O2 in an electrochemical cell with HRP immobilized on the surface of an electrode made of indium tin oxide (ITO, a transparent conductive oxide) and MWNT.

Improvement in Mechanical and Thermo-Mechanical Properties of Carbon fibre/Epoxy Composites Using Carboxyl Functionalized Multi-Walled Carbon Nanotubes

Investigations were carried out to optimize mechanical and thermal performances of carbon fibre/epoxy composites modified with functionalized carbon nanotubes. For fabricating carbon fibre/epoxy nanocomposites, 0.1-0.4 wt.% carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs-COOH) were incorporated in an epoxy system. Laminates were cured at a temperature of 65.55 °C. The effects of MWCNT on flexural, interlaminar shear strength (ILSS),tensile and thermo-mechanical properties of carbon fibre/epoxy composites were studied. The results obtained from flexural, ILSS, tensile and dynamic mechanical analysis (DMA) of carbon fibre/epoxy demonstrated a linearly increasing trend in properties up to 0.3 wt.% MWCNT loading. Results obtained from the thermal mechanical analysis showed a linearly decreasing trend in coefficient of thermal expansion up to 0.3 wt.% MWCNT loading. The properties were lower at 0.4 wt.%, due to agglomeration that may have resulted in poor wetting of the carbon fibres.

Thermal and mechanical stabilities of composite films from thiadiazol bearing poly(amide-thioester-imide) and multiwall carbon nanotubes by solution compounding

An amino acid containing poly(amide-thioester-imide) (PATEI) possessing a conjugated thiadiazol ring was shown to be effective for dispersing multiwall carbon nanotubes (MWCNTs) in N,N′-dimethylacetamide. Through casting of these dispersions, MWCNT/PATEI composite films were successfully fabricated on substrates and showed no signs of macroscopic aggregation. To increase the compatibility between PATEI matrix and MWCNTs, carboxyl-functionalized MWCNTs (f-MWCNTs) were used in this study. The f-MWCNTs were dispersed homogeneously in the PATEI matrix while the structure of the polymer and the MWCNTs structure were stable in the preparation process as revealed by transmission electron microscopy. Tensile tests and thermal analysis were carried out on free-standing composite films for different MWCNT loading levels. Results showed that overall mechanical and thermal properties of the composites were greatly improved as compared with the neat PATEI film. Fourier transform infrared spectroscopy, powder X-ray diffraction, and field emission electron microscopy were also used to evaluate the MWCNT/PATEI composite system.

Studies of Carboxyl-Functionalized Multi-Wall Carbon Nanotubes and Mechanical Properties of its MWCNTs-OPC Cement Composites

This study successfully grafted multiwalled carbon nanotubes (MWCNTs) with carboxyl group (MWCNTs-COOH) via concentrated nitric acid oxidation reaction. The morphologies of MWCNTs oxidized under various conditions and the extent of dispersion of the MWCNTs in the cement matrix were characterized using fourier transform infrared spectroscopy (FTIR). This investigation also optimized the mechanical properties of MWCNTs-OPC cement composites by utilizing pristine MWCNTs (P-MWCNTs) and modified MWCNTs (MWCNTs-COOH) through a combination of dispersion method. Micrographs of MWCNTs incorporated cement samples revealed uniform dispersion of MWCNTs in cement, good interfacial adhesion between MWCNTs and cement, and improved interfacial bonding between MWCNTs-OPC cement at 0.4 wt.% loading. An improved dispersion and hence an improved crosslink interaction between MWCNTs-COOH and cement lead to the stronger shift of the mechanical properties of the cement composites.

Polyaniline/carbon nanotube multi-layered hollow microspheres with sandwich structure and their electrochemical performance

Novel composite hollow microspheres with the unique “sandwich” structure were prepared by alternate coverage of polyaniline (PANI) and carboxyl-functionalized multi-walled carbon nanotubes (f-MWNTs) on the surface of spherical templates, formed by in situ polymerization. It was proved that the incorporation of f-MWNTs into the PANI layers could strengthen the stability of hollow microspheres, which had been demonstrated by other researchers in the preparation of carbon nanotubes-based hollow microcapsules. Specially, Raman spectra revealed that the driving force for adsorbing f-MWNTs was not electrostatic interaction, but hydrogen bond and additional π–π conjugated interaction. With the measurements of conductivity and electrochemical performance, it was also proved that the facile strategy to introduce f-MWNTs into the shells could effectively improve conductivity and electrochemical performance of PANI hollow microspheres.

Electrostrictive thermoplastic polyurethane-based nanocomposites filled with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH): Properties and improvement of electromechanical activity

The impact of small amounts of carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) added into a polyether-based thermoplastic polyurethane elastomer (TPU) was studied considering mainly on the morphological, mechanical, electrical and electrostrictive properties. The electrostrictive properties were measured by the analysis of the deformation response occurring under external electric fields E applied on 50 μm-thick films. Dielectric measurements were carried out in order to determine the percolation threshold fc, which was found near 1 v% loading. This volume fraction leads to a very high dielectric permittivity εr′ up to ≈330, i.e. about 50 times higher than that of the pure TPU, where εr′≈6–7.

Enhanced thermal and electrical properties of poly (D,L-lactide)/multi-walled carbon nanotubes composites by in-situ polymerization

Biodegradable poly (D,L-lactide) (PLA)/carboxyl-functionalized multi-walled carbon nanotubes (c-MWCNTs) composites were achieved via in-situ polymerization. These as-prepared composite materials were characterized with FT-IR, XRD, TG, DSC, SEM, and high insulation resistance meter. The results demonstrate that the multi-walled carbon nanotube was carboxyl functionalized, which improved the collection between c-MWCNTs and PLA, and further realized the graft copolymerization of c-MWCNTs and PLA. There is a higher glass transition temperature and a lower pyrolysis temperature of PLA/c-MWCNTs composites than pure PLA. The c-MWCNTs gave a better dispersion than unmodified MWCNTs in the PLA matrix, and an even coating of PLA on the surface of c-MWCNTs was obtained, which increased the interfacial interaction. High insulation resistance analysis showed that the addition of c-MWCNTs increased the electric conductivity, and c-MWCNTs performed against the large dielectric coefficient and electrostatic state of PLA. These results demonstrated that c-MWCNTs modified PLA composites were beneficial for potential application in the development of heat-resisting and conductivity plastic engineering.

Improvement in Mechanical and Thermo-Mechanical Properties of Epoxy Composite Using Two Different Functionalized Multi-Walled Carbon Nanotubes

In this study, two types of functionalized multi-walled carbon nanotubes were dispersed in an epoxy resin system (SC-15) at room and elevated temperatures using a combination of sonication and high shear mixing methods to determine optimal mechanical and thermal properties. At first, 0.1 wt% - 0.3 wt% of amino-functionalized multi-walled carbon nanotubes (MWCNT-NH2) and carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) were dispersed in part-A of SC-15 resin using a combination method. The mixture was then added to part-B of epoxy resin and cured using two different cycles (cycle A: at room temperature for 24 hours and post-cure at 93.33?C for 4 hours, cycle B: at 65.56?C for 5 hours). In addition, control samples (without MWCNTs) were also fabricated for baseline consideration under similar conditions. In all cases, epoxy with MWCNTs showed improved performance. Improvements in properties in MWCNT/epoxy samples prepared using cycle A were comparatively lower than samples prepared with cycle B. Flexural and thermo-mechanical results demonstrated maximum improvement in 0.2 wt% MWCNT-COOH modified epoxy samples prepared using cycle B. Improvements in performance for samples cured at elevated temperatures were attributed to better dispersion of MWCNTs due to reduced viscosity. On the other hand, increased number of functional groups present in MWCNT-COOH contributed to higher crosslinking resulting in the highest observed properties.

Synthesize procedures, mechanical and thermal properties of thiazole bearing poly(amid-imide) composite thin films containing multiwalled carbon nanotubes

This research is aimed at characterizing the thermal, mechanical, and morphological properties of carbon nanotubes (CNTs) reinforced poly(amide-imide) (PAI) composites having thiazol and amino acid groups which were prepared by sonication-assisted solution compounding. To increase the compatibility between the PAI matrix and CNTs, carboxyl-functionalized multiwall CNTs (MWCNTs-COOH) were used in this study. The MWCNTs were dispersed homogeneously in the PAI matrix while the structure of the polymer and the MWCNTs structure are stable in the preparation process as revealed by transmission electron microscopy. MWCNT/PAI composite films have been prepared by casting a solution of precursor polymer containing MWCNTs into a thin film, and its tensile properties were examined. The thermal stability, Young’s modulus, and tensile strength of PAI were greatly improved by the incorporation of MWCNTs and their good dispersion. Composites were also characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis.

Chitosan/Functionalized Multiwalled Carbon Nanotubes Multilayer Hollow Microspheres Prepared via Layer-by-Layer Assembly Technique

Novel multilayer hollow microspheres were fabricated via the layer-by-layer (LBL) assembly technique by the electrostatic interaction between the polycation chitosan (CHI) and the anion carboxyl-functionalized multiwalled carbon nanotubes (f-MWNTs) on sacrificial polystyrene sulfonate (PSS) microsphere templates. The successful stepwise growth of the CHI/f-MWNTs multilayers in different pH media was compared by zeta potential measurement and scanning electron microscopy (SEM) analysis. The morphologies of the hollow microspheres were characterized by transmission electron microscopy (TEM) and SEM. The swelling and collapse of the hollow microspheres occurred during the template removal by dissolution and the drying process. It was found that more f-MWNTs had been deposited onto the surface of the PSS microspheres at pH 3 than at pH 5, confirmed by SEM and thermogravimetric analysis (TGA). Furthermore, this result is consistent with the differences of the electrical conductivities of the hollow microspheres obtained from the different pH media. It is also found that in the etching process, the different etching reagents, such as DMF and toluene, obviously affected the electrical conductivity of the final hollow microspheres.

Effect of Low Multi-Walled Carbon Nanotubes Loading on the Crystallization Behavior of Biodegradable Poly(Butylene Adipate)

The effect of low carboxyl-functionalized multi-walled carbon nanotubes (f-MWCNTs) loading on the crystallization behavior of biodegradable poly(butylene adipate) (PBA) was studied with various techniques in this work. For the nonisothermal melt crystallization, f-MWCNTs accelerate the crystallization process of PBA apparently due to the heterogeneous nucleation effect. The Ozawa method fails to describe the nonisothermal crystallization process of neat PBA and its nanocomposite. Isothermal melt crystallization kinetics of neat PBA and its nanocomposite was analyzed by the Avrami equation. The overall isothermal crystallization rate of neat PBA and its nanocomposite increases with increasing crystallization temperature. The addition of f-MWCNTs accelerates the isothermal crystallization of PBA as compared with that of neat PBA at a given crystallization temperature, indicative of the nucleating agent effect of f-MWCNTs; however, the crystallization mechanism does not change. The crystal structure of PBA remains unchanged in the PBA/f-MWCNTs nanocomposite despite the presence of f-MWCNTs.

Imprinted electrochemical sensor for dopamine recognition and determination based on a carbon nanotube/polypyrrole film

An electrochemical sensor combining a molecular imprinted technique and an electropolymerization method was developed in this work. A molecular imprinted polymer (MIP) film was fabricated by electropolymerizing pyrrole in the presence of dopamine (DA) after electrodepositing carboxyl-functionalized multi-walled carbon nanotubes (MWNTs-COOH) onto a glassy carbon electrode (GCE) surface. Scanning electron microscopy (SEM), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were employed to characterize the constructed sensor. The effects of pH, the monomer concentration, the number of cycles for the electropolymerization, and the scan rate for the sensor preparation were optimized. The MIP-based sensor displayed an excellent recognition capacity toward DA compared with other structurally similar molecules. Additionally, the DPV peak current was linear to the DA concentration in the range from 6.25×10−7 to 1×10−4mol/L, with a detection limit of 6×10−8mol/L. The prepared sensor also showed stable reproducibility and regeneration capacity.