Acid-treated Multi-walled Carbon Nanotubes Research Articles

Photo-Catalytic Properties of TiO2 Supported on MWCNTs, SBA-15 and Silica-Coated MWCNTs Nanocomposites.

Mesoporous silica, specifically SBA-15, acid-treated multi-walled carbon nanotubes and a hybrid nanocomposite of SBA-15 coated onto the sidewalls acid-treated multi-walled carbon nanotubes (CNTs) were prepared and used as supports for anatase TiO2. Sol-gel methods were adapted for the synthesis of selected supports and for coating the materials with selected wt% loading of titania. Physical and chemical properties of the supports and catalyst composite materials were investigated by powder X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis, scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), UV-vis diffuse reflectance spectroscopy and fluorescence spectroscopy. The photo-activity of the catalyst composites were evaluated on the decolorisation of methylene blue as a model pollutant. Coating CNTs with SBA-15 improved the thermal stability and textural properties of the nanotubes. All supported titania composites had high surface areas (207–301 m2/g), altered band gap energies and reduced TiO2 crystallite sizes. The TiO2/SBA-CNT composite showed enhanced photo-catalytic properties and activity than the TiO2/SBA-15 and TiO2/CNT composites. In addition, an interesting observation was noted with the TiO2/SBA-15 nanocomposites, which had a significantly greater photo-catalytic activity than the TiO2/CNT nanocomposites in spite of the high electron-hole recombination phenomena observed with the photoluminescence results. Discussions in terms of morphological, textural and physical-chemical aspects to account for the result are presented.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1137-3) contains supplementary material, which is available to authorized users.

Synthesis of aspartic acid-treated multi-walled carbon nanotubes based water coolant and experimental investigation of thermal and hydrodynamic properties in circular tube

Aspartic acid as a hydrophilic group is added to the main structure of multi-walled carbon nanotubes (MWNT) for synthesizing highly-dispersed MWNT-based water nanofluids with different concentrations. Chemical treatment is analyzed and functionalization is confirmed by TGA, FTIR, Raman spectroscopes. The present study is followed by investigation of thermo-physical properties as well as heat transfer rate of circular tube at constant heat flux in the presence of non-covalently and covalently-functionalized MWNT with aspartic acid. The prepared nanofluids in three weight concentrations of 0.05%, 0.1% and 0.2% are investigated in the flow rate range of 2.86–8.85ml/s. Thermophysical properties, convective heat transfer coefficient, pressure drop, friction factor, performance index and pumping power results suggest that functionalized MWNT with aspartic acid is one of the most appropriate alternative coolant for water in industry.

Hexagonal boron nitride (h-BN) nanoparticles decorated multi-walled carbon nanotubes (MWCNT) for hydrogen storage

Hydrogen is considered as the most promising clean energy carrier because of its abundance, environmental friendliness and high conversion efficiency. However, developing safe, compact, light weight and cost-effective hydrogen storage materials is one of the most technically challenging barriers to the widespread use of hydrogen as fuel. The present work reports the hydrogen storage performance of multi-walled carbon nanotubes (MWCNT)/hexagonal boron nitride (h-BN) nanocomposites (MWCNT/h-BN), where ultrasonication method is adopted for the synthesis of the MWCNT/h-BN nanocomposites. Hydrogenation process was carried out using Seiverts-like hydrogenation setup. Characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Nitrogen adsorption–desorption isothermal studies (BET), CHN-elemental analysis and Thermogravimetric Analysis (TGA) were used to analyze the samples at various stages of the experiment. A maximum of 2.3 wt% hydrogen storage is achieved in the case of acid treated MWCNTs (A-MWCNT) with 5 wt% of h-BN nanoparticles compared to pure MWCNTs that could store 0.15 wt% only. Moreover the calculated binding energy (0.42 eV) of stored hydrogen of A-MWCNT with 5 wt% of h-BN nanocomposite lies in the recommended range of binding energy (0.2–0.6 eV) for fuel cell applications. The TG study shows that 100% desorption is achieved at the temperature range of 120–410 °C and confirms that the prepared hydrogen storage medium will serve effectively in the realm of hydrogen fuel economy in near future.

Synthesis of TiO2 Nanoparticles and Decorated Multiwalled Carbon Nanotubes With Various Content of Rutile Titania

Synthesis of different phases of titania nanoparticles (TiO2) and decorated multiwalled carbon nanotubes (MWCNTs) with various content of rutile titania have been performed. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The XRD results showed that the amount of precursor strongly influenced by phase transition of TiO2 nanoparticles. TEM images showed that the outer surface of MWCNTs modified with TiO2 nanoparticles. The selected-area electron diffraction (SAED) of TiO2 nanoparticles and MWCNTs-TiO2 revealed the polycrystalline structure of the samples. FTIR analysis confirmed the presence of oxygen containing groups on the surface of oxidized MWCNTs and TiO2 on the surface of decorated MWCNTs. Optical properties of samples measured using UV-Vis spectrophotometer and the achieved results demonstrated that dispersibility of oxidized and decorated MWCNTs is higher than that of pristine MWCNTs. The XPS results showed that TiO2 nanoparticles were covalently attached on the side walls of acid-treated MWCNTs.

Enhanced Oxygen Reduction Activity of N-Doped Multiwalled Carbon Nanotubes in Alkaline Media

A great deal of work has been made to develop new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. In order to replace expensive and scarce Pt-based catalysts that have been primarily employed as cathode catalysts in low-temperature fuel cells, different carbon-based materials that possess lower price, better availability and improved chemical stability have been studied. Nitrogen-doped nanocarbons can be used as alternatives to Pt-based cathode catalysts. Previously, we have investigated the reduction of O2 on CVD grown nitrogen-doped carbon nanotubes,1 on CNTs heat-treated in the presence of urea2 and on N-doped graphene3 and few-layer graphene/multiwalled carbon nanotube (FLG/MWCNT) composites.4 In this work the electrocatalysis of oxygen reduction on nitrogen-doped carbon nanotube (NCNT) catalysts has been investigated. These NCNT materials were prepared from two different nitrogen precursors and acid-treated MWCNTs. Cyanamide (CM) and dicyandiamide (DCDA) were used as nitrogen precursors and the doping was achieved by pyrolysing MWCNTs in the presence of these nitrogen-containing compounds at 800 °C. The MWCNT-to-nitrogen precursor mass ratio was 1:20. The N-doped carbon nanotube catalyst samples were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The electrocatalysis of the ORR was studied in 0.1 M KOH on glassy carbon (GC) electrodes modified with N-doped CNT electrocatalysts employing the rotating disk electrode (RDE) method. The NCNT-DCDA material showed a better ORR performance than the NCNT-CM catalyst. Fig. 1 presents the ORR polarization curves on NCNT-DCDA at various rotation rates and Fig. 2 shows the Koutecky-Levich plots for this catalyst. As can be seen, the number of electrons transferred (n) is close to 4, which is advantageous from the point of view of fuel cell application. A comparison of the RDE results indicated that these metal-free NCNT catalysts possess remarkable electrocatalytic activity toward the ORR in alkaline media similar to that of commercial Pt/C catalyst (Fig. 3). The results obtained in this work are important for the development of Pt-free cathode catalysts for alkaline membrane fuel cells (AMFC). In the next stage of work these materials will be tested in AMFC conditions.

Enhanced conversion efficiency of dye-sensitized solar cells using a CNT-incorporated TiO2 slurry-based photoanode

A new titanium dioxide (TiO2) slurry formulation is herein reported for the fabrication of TiO2 photoanode for use in dye-sensitized solar cells (DSSCs). The prepared TiO2 photoanode featured a highly uniform mesoporous structure with well-dispersed TiO2 nanoparticles. The energy conversion efficiency of the resulting TiO2 slurry-based DSSC was ∼63% higher than that achieved by a DSSC prepared using a commercial TiO2 slurry. Subsequently, the incorporation of acid-treated multi-walled carbon nanotubes (CNTs) into the TiO2 slurry was examined. More specifically, the effect of varying the concentration of the CNTs in this slurry on the performance of the resulting DSSCs was studied. The chemical state of the CNTs-incorporated TiO2 photoanode was investigated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A high energy conversion efficiency of 6.23% was obtained at an optimum CNT concentration of ∼0.06 wt.%. The obtained efficiency corresponds to a 63% enhancement when compared with that obtained from a DSSC based on a commercial TiO2 slurry. The higher efficiency was attributed to the improvement in the collection and transport of excited electrons in the presence of the CNTs.

Carbon Nanotube Composite Electrode Coated with Polypyrrole for Microbial Fuel Cell Application.

Microbial fuel cells (MFCs) are bio-electrochemical system that can convert biomass spontaneously into electricity through the metabolic activity of microorganisms. We constructed MFCs of polypyrrole (PPy) coated carbon nanotube (CNT) composite as an electrode material and Shewanella oneidensis as the biocatalyst to increase power density. The PPy-coated CNT were synthesized by the in-situ chemical polymerization of pyrrole on CNT, and the electrochemical properties and performance of the modified electrode as an anode in MFC were then investigated. Treatment with 0.1 wt% Ge-132 on the acid-treated MWNTs helped to form better PPy-MWNT composite. The PPy-CNT/CF anode showed a noteworthy 38% power production improvement when compared to plain CF anode. The PPy-CNT composite could be a very efficient and promising electrode material for electricity generation of MFC.

The Characteristics of CNT/Cement Composites with Acid-Treated MWCNTs

This study investigated the effects of acid-treated MWCNTs on the workability, compressive and tensile strength, porosity, and microstructure of CNT/cement composites. While workability decreased with acid treatment of CNTs, compressive and tensile strength improved significantly. Strength was also enhanced by using acid-treated CNTs alone, compared to using a surfactant with acid-treated CNTs. MIP analysis revealed that the porosity decreases from using acid-treated CNTs and that using acid-treated CNTs without a surfactant was more effective in reducing the size of micropores. A SEM analysis revealed improved CNT dispersion and dense hydration products in cement composites containing acid-treated CNTs. Ultimately, the use of acid-treated CNTs improved the CNT dispersion within CNT/cement composites, enhanced the pore structure, and formed denser hydration products around CNTs.

A porous elastomeric polyurethane monolith synthesized by concentrated emulsion templating and its pressure-sensitive conductive property

The spontaneous distribution of acid-treated MWCNTs in the concentrated emulsion leads to the press-sensitive conductivity of the porous PU.

Properties enhancement in multiwalled carbon nanotube-magnetite hybrid-filled polypropylene natural rubber nanocomposites through functionalization and processing methods

Abstract The effect of multiwalled carbon nanotubes (MWCNTs)-magnetite (Fe3O4) hybrid content on the thermal, dynamic mechanical, and morphological properties of thermoplastic natural rubber (TPNR) nanocomposites was evaluated. TPNR/filler nanocomposites were prepared using a melt-blending method with a ball-milling technique as a premixed process. The acid treatment successfully shortened the lengths and disentangled the crowds of MWCNTs, which led to a better dispersion of MWCNTs in the polymer matrix, as revealed by optical microscopy and scanning electron microscopy. The improved dispersion of acid-treated MWCNTs-Fe3O4 in the TPNR matrix and the enhanced interfacial adhesion between acid-treated MWCNTs-Fe3O4 and the TPNR matrix increased the thermal stability and dynamic mechanical properties. Acid-treated MWCNTs acted as radical scavengers, which helped delay the onset of thermal degradation and hence improved the thermal stability. As expected, MWCNTs played a role as the nucleating agent in the TPNR matrix; however, the effect was more pronounced for the TPNR matrix containing pristine MWCNTs.

The influence of acid-treated multi-walled carbon nanotubes on the surface morphology and thermal properties of alanine-based poly(amide–imide)/MWCNT nanocomposites system

Carbon nanotubes (CNTs) corresponding to the high electrical and thermal conductivity and excellent mechanical properties are ideal fillers for polymer composites. In this work, 5, 10, and 15 wt % of functionalized multi-walled CNTs (f-MWCNT) were incorporated into the alanine-based poly(amide–imide) matrix using a solution mixing technique for the preparation of nanocomposites. Here, we show the effect of the addition of well-dispersed f-MWCNT as demonstrated by transmission electron microscopy and field emission scanning electron microscopy on the thermal behavior of the composites. Thermal analysis results showed self-extinguishing feature for the obtained NCs.

Fabrication of a superhydrophobic surface via spraying with polystyrene and multi-walled carbon nanotubes

A superhydrophobic surface was fabricated via spraying with polystyrene (PS) and multi-walled carbon nanotubes (MWCNTs). Spraying is one of the simplest and cheapest methods of fabricating superhydrophobic surfaces. First, MWCNTs were sonicated for 1 h with acetone solution and dried completely at room temperature. Acid-treated MWCNTs and PS were mixed with THF (tetrahydrofuran) solution for 5 h. Using the mixed MWCNT/PS solution, superhydrophobic cover-glass specimens were fabricated by the spraying technique. Spraying was performed by a simple airbrush having a 400-μm-diameter nozzle under the following spraying conditions: pressure of 2 bar, spraying distance from nozzle to specimen of 130 mm, and spraying time of 10, 20, or 30 s. After specimen fabrication, the superhydrophobicity of the surface was characterized via contact angle (CA) and sliding angle (SA) measurements using PS-sprayed specimens for reference. The specimen sprayed using PS (1 wt%)/MWCNT (0.08 wt%) mixture showed the highest superhydrophobicity (water CA = 163.8 ± 2.5°, water SA = 5.0 ± 0.9°) among the fabricated specimens in this study. Moreover, to observe the morphology of the fabricated specimens, field emission scanning electron microscopy (FESEM) was utilized. To analyze the nanostructures observed in the SEM images, Raman spectroscopy was utilized.

Intratracheal exposure to multi-walled carbon nanotubes induces a nonalcoholic steatohepatitis-like phenotype in C57BL/6J mice

The effects of multi-walled carbon nanotubes (MWCNTs) exposure have garnered great interest in the field of public health, due to the high aspect ratio of MWCNTs. Because of worldwide increases in obesity prevalence, nonalcoholic fatty liver disease (NAFLD) is now the most common prevalent liver disease and is considered to be a component of metabolic syndrome, which is a cluster of disorders that also includes dyslipidemia, diabetes mellitus, arteriosclerosis, and hypertension. Exposure to MWCNTs is known to be a risk factor for lung and cardiovascular diseases, but its effect on NAFLD is unknown. In this study, we investigated the effects of intratracheal exposure of two different types of MWCNTs, namely, pristine multi-walled carbon nanotubes (PMWCNTs) and acid-treated multi-walled carbon nanotubes (TMWCNTs), on liver pathogenesis. Direct instillation of a test material into the lungs has been employed as a quantitatively reliable alternative method of inhalation exposure. The 10% weight loss dose was assessed in three months of subchronic study and is defined here as the maximum tolerated dose (MTD) of PMWCNTs and TMWCNTs; by this metric, MTD for a 1-year exposure of MWCNTs was determined to be 0.1 mg/mouse. Mice exposed to PMWCNTs and TMWCNTs for one year developed a nonalcoholic steatohepatitis (NASH)-like phenotype, characterized by inflammation, hepatic steatosis, and fibrosis. Furthermore, PMWCNTs induced a more severe NASH-like phenotype than TMWCNTs, which was related to consistent up-regulation of interleukin (IL)-6 and plasminogen activator inhibitor (PAI)-1. Impaired cholesterol homeostasis, overexpression of NF-κBp65, and suppression of peroxisome proliferator-activated receptor gamma (PPARγ) in the liver were also observed.

Effect of dispersion condition of multi-walled carbon nanotube (MWNT) on bonding properties of solderable isotropic conductive adhesives (ICAs)

Carbon nanotubes have been considered as reinforcements in composite materials because of their exceptional mechanical, electrical, and thermal properties. In this paper, the effect of dispersion conditions of multi-walled carbon nanotubes (MWNTs) on bonding properties of solderable isotropic conductive adhesives (ICA) was investigated. Two types of ICAs, untreated pristine MWNT-filled ICAs and acid-treated MWNT (a-MWNT)-filled ICAs were formulated with 1 wt% MWNTs and 83 wt% low-melting-point alloy (LMPA) fillers. X-ray photoelectron spectroscopy analysis was conducted to characterize the surface chemical states of pristine and a-MWNTs and verify the effectiveness of a-MWNTs. The fracture surface of the polymer matrix and solderable ICAs with a-MWNTs showed good dispersion conditions through field-emission scanning electron microscope. After the interconnection process, the a-MWNT-filled solderable ICA showed uniform dispersion of MWNTs in the polymer matrix and formed a stable metallurgical conduction path because of the good rheology-coalescence-wetting behavior of LMPA. Alternatively, pristine MWNT-filled ICA showed poor dispersion and an unstable conduction path formed by aggregated MWNTs.

Sensitive spectrophotometric determination of fluoxetine from urine samples using charge transfer complex formation after solid phase extraction by magnetic multiwalled carbon nanotubes

In this study, magnetic multiwalled carbon nanotubes (MWCNTs/Fe3O4) were prepared by assembling magnetic nanoparticles onto the acid-treated multiwalled carbon nanotubes, and because of their excellent adsorption capability, the MWCNTs/Fe3O4 nanocomposites were used as the adsorbent in a magnetic solid phase extraction procedure (MSPE) to extract fluoxetine from human urine samples. A spectrophotometric detection was performed by the drug reaction with a π-acceptor reagent, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in nonaqueous media via the formation of a charge transfer complex and by coupling MSPE with visible detection, and a reliable, sensitive and cost-effective method for the determination of trace amounts of fluoxetine was developed. The main factors affecting extraction efficiency and complex formation, including the pH of the sample solution, extraction and desorption time, desorption conditions, sample volume, amount of magnetic adsorbent, DDQ volume and complexation time, were investigated. Under the optimized conditions, the calibration curve was linear (R2 ≥ 0.9995) over the concentration range of 0.15 to 2.5 μg mL−1 with an LOD and LOQ of 0.06 and 0.19 μg mL−1, respectively. The relative standard deviation (RSD%) of 2.6% (n = 6) for 1 μg mL−1 and the enrichment factor of 48 was achieved. The method was successfully applied to the extraction and preconcentration of fluoxetine from human urine samples.

Role of oxidant in surface modification of carbon nanotubes for tyrosinase immobilization

Studies on the development of interface between biological molecules and novel nanomaterials have attracted research worldwide. Carbon nanotubes(CNTs) have become an important matrix for the fabrication of biomaterials due to its unique properties. Surface properties of the CNTs and the medium of immobilization are critical in the immobilization of biological molecules such as enzymes. In this study surface modification of multi-walled carbon nanotubes (MWCNTs) for carboxylic moieties attachment was accomplished by acid treatment and reaction with potassium permanganate. The effect of these two oxidants on the surface modification of MWCNTs for the purpose Tyrosinase immobilization was studied. Commercial MWCNTs were treated with either concentrated sulfuric acid and nitric acid mixture with ratio 3:1 or with 0.1 M potassium permanganate via reflux, stirring and ultrasonication. The resulting surface modified MWCNTs were characterized with FT-IR spectrophotometer, FESEM, and TGA analyzer. The immobilized Tyrosinase was tested for leaching assay. The FTIR spectra of functionalized MWCNTs showed a significant peak in the range of 1700 cm- 1 to 1729 cm-1 indicating the presence of carboxyl double bond, which confirmed the successful functionalization of MWCNTs by chemical oxidation. The carboxylic peak of MWCNTs treated with KMnO4- showed higher intensity as compared to acid-treated MWCNTs. The acid-treated MWCNTs displayed a sparkling crystalline-like particles while the KMnO4-modified MWCNTs consists of smooth powdery particles. Both treated MWCNTs also showed good dispersion in aqueous solution with different amount of acidic and basic site present.

Effect of carbon nanotube functionalization on the structure and properties of poly(3-hydroxybutyrate)/MWCNTs biocomposites

Multi walled carbon nanotubes (MWCNTs) covalently functionalized with an alkyl chain exhibited a better dispersion in poly(3-hydroxybutyrate) (PHB) solutions and cast films as compared with acid-treated MWCNTs (MWCNT-COOH) due to the much improved solubility in chloroform. The alkylated MWCNTs more effectively strengthened PHB composites than non-alkylated MWCNTs due to their uniform dispersion as well as stronger interaction of alkylated MWCNTs with the PHB matrix. Both acid-treated and alkylated MWCNTs added to PHB matrix facilitated crystallization kinetics. However the crystallization kinetics were found to be slower for the alkylated MWCNTs/PHB composites than acid-treated MWCNTs composites. The results may be ascribed to the inhibitory effect on PHB crystallization caused by the steric hindrance of the long alkyl chains attached to MWCNTs. Open image in new window

A multiwalled carbon nanotube/tetra-β-isoheptyloxyphthalocyanine cobalt(ii) composite with high dispersibility for electrochemical detection of ascorbic acid.

A sensitive electrochemical sensor for ascorbic acid (AA) is designed and synthesized via the following steps. The novel tetra-β-isoheptyloxyphthalocyanine cobalt(ii) (PcCo) spontaneously adsorbs on the surface of acid-treated multi-walled carbon nanotubes (aMWCNTs). Then, the aMWCNT/PcCo composite was immobilized on the glassy carbon electrode (GCE). The results of UV-vis, FT-IR, TG, XPS, SEM and TEM revealed the successful self-assembly between PcCo and aMWCNTs via the π-π stacking interaction, and the aMWCNT/PcCo composite appears to have a uniform network-like structure on the GCE surface due to the four peripheral isoheptyl substituents of PcCo. Such a structure can effectively increase the electrode area, facilitate the mass transport of analytes and provide continuous conducting pathways for the transportation of electrons. Synchronously, benefitting from the synergistic effect between PcCo and aMWCNTs, the obtained electrochemical sensor has a high current and low potential for the oxidation of AA. The linear range for the AA detection is from 10 μM to 1.2 mM and the detection limit is as low as 4.0 μM. The developed biosensor exhibited good reproducibility and acceptable stability, providing a simple method for the analysis of AA.

Morphology and cure behavior of multi-walled carbon nanotubes-based thermally conductive adhesive

We evaluated the cure behavior of multi-walled carbon nanotubes (MWCNTs) based thermally conductive adhesive by comprehensively thermal analysis, which presented extremely complicated variability of conversion ratio α as a function of temperature with synergistic action of positive effect and negative volumeblocking effect of MWCNTs and cross-linked network of cured polymer molecules. Due to the decomposition of MWCNTs and degradation of polymer, the mass drop is dramatically obvious over the temperature range of 330–370 °C. Binary resins filled with acid -treated MWCNTs present similar reaction interval as neat epoxy and matrix resins, which is distinct from the material filled with raw MWCNTs. The alteration of the crystalline temperature and cure temperature of resins is attributed to heterogeneous nucleation of MWCNTs in matrix resins. The -COOH group of acid-treated MWCNTs reacts with epoxy groups and thus generates cross-linking, accelerates the reaction rate and reduces the cure temperature.

Preparation of Multi-walled Carbon Nanotube/Polyaniline/Fe3O4 Composites

A method to prepare multi-walled carbon nanotube/polyaniline/Fe3O4 nanocomposites was developed. Acid-treated multi-walled carbon nanotubes (MWCNTs) were first encapsulated with polyaniline (PANI) by an in-situ micro-emulsion polymerization and then reacted with Fe3O4 modified with aniline dimer (ADM-Fe3O4). Fourier transform infrared spectrometry demonstrated that there existed chemical linkages between the MWCNTs and the PANI as well as between the MWCNTs and the ADM-Fe3O4 nanoparticles. The morphology of the nanocomposites was examined using transmission electron microscopy. The bulk structure of the nanocomposites was investigated with X-ray diffraction. The resulting products could be separated from the deionized water under an external magnetic field within about several seconds.