Acid-modified Multi-walled Carbon Nanotubes Research Articles

Caffeic-Acid-Functionalized MWCNTs and PEDOT:PSS Formed Composite Flexible Films with "Reinforced Concrete" Structure for Electrical Heating and EMI Shielding.

Nowadays, flexible multifunctional composites are attracting much attention and are practically being used in various emerging electronic devices. However, most composites suffer from the disadvantages of high loadings of conductive fillers, complicated preparation processes, and low energy conversion efficiency. In this article, Caffeic acid-modified multiwalled carbon nanotubes (C-MWCNTs)/poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS)/polyimide (PI) composite films (CPFs) were prepared using a simple layer-by-layer deposition method. The "reinforced concrete" structure of the C-MWCNTs/PEDOT:PSS layer ensures high electrical conductivity of the film, while the PI layer provides excellent mechanical properties (72.69 MPa). The composite film exhibits excellent electrothermal response and thermal stability up to approximately 125 °C at 5 V. In addition, the good conductivity of the film provides its electromagnetic shielding effectiveness (32.69 dB). With these advantages, we expect that flexible CPFs will be widely utilized in wearable devices, electromagnetic interference (EMI) shielding applications, and thermal management of personal or electronic devices.

Nanoemulsions of Hydroxysafflor Yellow A for Enhancing Physicochemical and In Vivo Performance.

Stroke was always a disease that threatened human life and health worldwide. We reported the synthesis of a new type of hyaluronic acid-modified multi-walled carbon nanotube. Then, we produced hydroxysafflor yellow A-hydroxypropyl-β-cyclodextrin phospholipid complex water-in-oil nanoemulsion with hyaluronic acid-modified multi-walled carbon nanotubes and chitosan (HC@HMC) for oral treatment of an ischemic stroke. We measured the intestinal absorption and pharmacokinetics of HC@HMC in rats. We found that the intestinal absorption and the pharmacokinetic behavior of HC@HMC was superior to that of HYA. We measured intracerebral concentrations after oral administration of HC@HMC and found that more HYA crossed the blood-brain barrier (BBB) in mice. Finally, we evaluated the efficacy of HC@HMC in middle cerebral artery occlusion/reperfusion (MCAO/R)-injured mice. In MCAO/R mice, oral administration of HC@HMC demonstrated significant protection against cerebral ischemia-reperfusion injury (CIRI). Furthermore, we found HC@HMC may exert a protective effect on cerebral ischemia-reperfusion injury through the COX2/PGD2/DPs pathway. These results suggest that oral administration of HC@HMC may be a potential therapeutic strategy for the treatment of stroke.

Carbon Nanotube Incorporated Nanocomposite Membranes for CO2 Removal

Thin-film nanocomposite (TFN) membranes that consist of multi-walled carbon nanotube (MWNT) incorporated polyamide selective layer formed on polysulfone substrate were developed. The resultant TFN membranes were used for CO2 gas removal. For inclusion into these active layers, a grafting procedure for CNT was established in this study to enhance their hydrophobicity. MWNTs grafted with poly (methyl methacrylate) (PMMA) were synthesized via a micro emulsion polymerization of methyl methacrylate (MMA) in the presence of acid-modified multi-walled carbon nanotubes (c-MWNTs). Subsequently, polyamide TFN membranes containing PMMA–MWNTs were prepared via interfacial polymerization reaction between aqueous and organic phases. The resultants TFN were characterized by using FTIR and SEM. Morphology studies demonstrate that MWNTs have been successfully embedded into the active polyamide layer. The gas selectivity increased about 6.6 times compared to the thin-film composite membrane when using 0.35 w/v% amine in the aqueous phase, 0.28 w/v% trimesoyl chloride (TMC) in organic phase and 0.50g/L PMMA–MWNTs in coating layer.

Kinetic, equilibrium and thermodynamic studies of thiamethoxam adsorption by multi-walled carbon nanotubes

Because of their high adsorption capacity, carbon nanotubes have caught the attention of the scientific community and a number of experimental results confirmed their ability to adsorb many toxins from water. The aim of this work was to study the kinetics, equilibrium and thermodynamics of thiamethoxam adsorption by multi-walled carbon nanotubes in aqueous solutions. To further elucidate the influence of nanotube structure on the adsorption mechanism, the experiments were performed on both fresh (pristine) and nitric acid-modified multi-walled carbon nanotubes. The results of the kinetic studies were analyzed using three kinetic models, while the adsorption equilibrium was tested against four different adsorption models. Based on the results, and the physico-chemical properties of the adsorbent and adsorbate, it is proposed that the dominant mechanism for thiamethoxam molecules attaching to multi-walled carbon nanotubes is caused by aromatic π–π interactions (electron donor–acceptor interactions). The results of thermodynamic calculations based on the adsorption data indicate the exothermic nature of the process, regardless of the carbon nanotube type used. The decrease in entropy and the consequent negative change in Gibbs free energy, as expected, confirm the spontaneity of thiamethoxam adsorption on both pristine and functionalized multi-walled carbon nanotubes.

Hyaluronic acid-modified multiwalled carbon nanotubes for targeted delivery of doxorubicin into cancer cells

Development of novel drug carriers for targeted cancer therapy with high efficiency and specificity is of paramount importance and has been one of the major topics in current nanomedicine. Here we report a general approach to using multifunctional multiwalled carbon nanotubes (MWCNTs) as a platform to encapsulate an anticancer drug doxorubicin (DOX) for targeted cancer therapy. In this approach, polyethyleneimine (PEI)-modified MWCNTs were covalently conjugated with fluorescein isothiocyanate (FI) and hyaluronic acid (HA). The formed MWCNT/PEI–FI–HA conjugates were characterized via different techniques and were used as a new carrier system to encapsulate the anticancer drug doxorubicin for targeted delivery to cancer cells overexpressing CD44 receptors. We show that the formed MWCNT/PEI–FI–HA/DOX complexes with a drug loading percentage of 72% are water soluble and stable. In vitro release studies show that the drug release rate under an acidic condition (pH 5.8, tumor cell microenvironment) is higher than that under physiological condition (pH 7.4). Cell viability assay demonstrates that the carrier material has good biocompatibility in the tested concentration range, and the MWCNT/PEI–FI–HA/DOX complexes can specifically target cancer cells overexpressing CD44 receptors and exert growth inhibition effect to the cancer cells. The developed HA-modified MWCNTs hold a great promise to be used as an efficient anticancer drug carrier for tumor-targeted chemotherapy.

Preparation Thin Film Nanocomposite Membrane Incorporating PMMA Modified MWNT for Nanofiltration

Multiwalled carbon nanotubes (MWNTs) grafted by Poly(methyl methacrylate) (PMMA) can well disperse in organic solutions like toluene，which were synthesized via a microemulsion polymerization of methyl methacrylate (MMA) in the presence of acid-modified multiwalled carbon nanotubes (c-MWNTs). The polyamide thin-film nanocomposite (TFN) membranes with embedded PMMA-MWNTs were prepared using piperazine (PIP) and trimesoyl chloride (TMC) on a polyacrylonitrile (PAN) porous substrate via interfacial polymerization for selective permeability. PMMA-MWNTs’ structure was analyzed by Fourier transform infrared spectrophotometry (FTIR), Raman spectrophotmetry (RAM), Scanning electron microscope (SEM) and thermo gravimetric analysis (TGA). Orthogonal experiment was used to study the effect of PIP concentration, TMC concentration and concentration of PMMA-MWNTs in organic phase. The results showed that the membrane performances is good, Na2SO4 rejection is above 98% and water flux is up to 150% improvement over the TFC membrane as PIP in aqueous phase was 2g/L, TMC and PMMA-MWNTs in organic phase were 4g/L and 0.67g/L, respectively . Demonstrated PMMA-MWNTs in the nanofiltration membrane can improve selective permeability.

Preparation and characterization of thin-film nanocomposite membranes embedded with poly(methyl methacrylate) hydrophobic modified multiwalled carbon nanotubes by interfacial polymerization

Carbon nanotube enhanced thin-film nanocomposite membranes were prepared by incorporating carbon nanotubes (CNTs) into the active layers of membranes used for water treatment. For inclusion into these active layers, a grafting procedure for carbon nanotubes was set up to increase their hydrophobicity. Multiwalled carbon nanotubes (MWNTs) grafted by poly(methyl methacrylate) (PMMA) were synthesized via a microemulsion polymerization of methyl methacrylate (MMA) in the presence of acid-modified multiwalled carbon nanotubes (c-MWNTs). Subsequently, polyamide thin-film nanocomposite (TFN) membranes containing PMMA–MWNTs were prepared via interfacial polymerization. Morphology studies demonstrate that MWNTs have been successfully embedded into the active polyamide layer. The rejection of Na2SO4 was high (99%), and the water flux was about 62% increased compared to the thin-film composite membrane when using 2g/L piperazine (PIP) in the aqueous phase, 4g/L trimesoyl chloride (TMC) and 0.67g/L PMMA–MWNTs in the organic phase, which demonstrates that PMMA–MWNTs significantly improve selectivity and permeability.

The production of functionalized multiwall carbon nanotube/amino acid-based poly(amide–imide) composites containing a pendant dopamine moiety

The high compatibility of amino-acid based poly(amide–imide) (PAI) as a polymer matrix for acid-modified multi-walled carbon nanotubes (MWCNTs) is discussed. PAI was synthesized from the direct polycondensation reaction of N,N′-(pyromellitoyl)-bis-l-isoleucine with a dopamine-based diamine, 3,5-diamino-N-(3,4-dihydroxy-phenethyl)benzamide, in a medium consisting of a molten salt, tetrabutylammonium bromide, and triphenyl phosphite as the activator under microwave radiation. To obtain a homogeneous dispersion of MWCNTs in the PAI matrix, acid-functionalized MWCNTs were used. Composites containing 5, 10, and 15wt.% MWCNT–COOH exhibited a relatively good dispersion on the macroscopic scale. MWCNT/PAI composite films have been prepared by casting a solution of precursor polymer containing MWCNTs into a thin film and its tensile properties examined. Incorporation of MWCNTs improved the mechanical properties significantly. Composites were also characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy, and thermal gravimetric analysis. The thermal stability of the composites containing the CNTs was improved due to the increased interfacial interaction between the PAI matrix and the modified CNTs and their good dispersion.

Acid‐modified carbon nanotubes distribution and mechanical enhancement in polystyrene/elastomer blends

AbstractThe incorporation of carbon nanotubes (CNTs) is expected as an effective path for tailoring mechanical properties of polymer blends. In this study, acid‐modified multiwalled CNTs (A‐MWCNTs) were introduced into polystyrene/maleic anhydride‐g‐(styrene‐ethylene‐butadiene‐styrene) (PS/SEBS‐MA) blends. By altering the mass ratio of PS/SEBS‐MA from 80/20 to 60/40, the biphase structure of blend was changed from sea‐island‐like type to quasi co‐continuous structure, of different mechanical behaviors. In 80/20 mass ratio, the impact strength was improved while the tensile strength was unchanged with increasing A‐MWCNTs content, whereas a simultaneously toughening and strengthening effect was achieved for the compound with 60/40 mass ratio. Scanning electron microscopy, polarized light microscopy, dynamic mechanical analysis, and rheological measurements were carried out to detect the distribution of A‐MWCNTs in the blends. The results demonstrated as increasing the nanotube loading from 0 to 3 wt%, A‐MWCNTs might gradually migrate into continuous PS phase in 80/20 mass ratio, due to the low content of SEBS‐MA, while they were totally packed in SEBS‐MA region within the entire loading range used in 60/40 mass ratio due to its high content of SEBS‐MA. This study provides guidance on the design and preparation of high performance ternary polymer/elastomer/inorganic filler composites. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Study on Morphology and Characterization of Poly(mphenylene isophtalamide)/Multi-Walled Carbon Nanotubes Composite Nanofibers by Electrospinning

Electrospinning technique is the main method of preparing polymer nanofiber simply, directly and continuously at present. In this work, electrospinning blend solution was prepared by in-situ polymerization using acid-modified multi-walled carbon nanotubes (MWNTs), m-phenylenediamine (MPD) and isophthaloyl chloride (IPC). And then composite nanofibers were prepared by electrospinning. MWNTs played an important role in nanofiber's properties. The effects of MWNTs on the morphology and characterization of the MWNTs/PMIA composite nanofibers were investigated. Scanning electron microscopy (SEM), thermal gravimetric analyzer (TGA), and X-ray diffraction (XRD) were utilized to characterize the MWNTs/PMIA nanofibers morphology and properties. The experimental results indicated that the nanofibers diameter decreased and solution dynamic viscosity increased with increasing MWNTs contents. XRD data demonstrated that PMIA composite nanofibers had the same crystal type as the pure PMIA nanofiber, and crystallinity was improved with increasing MWNTs loading. Transmission electron microscopy (TEM) was used to confirm MWNTs aligned along the axis of composite nanofibers.

Preparation of carbon nanotube/chitosan/gold nanoparticle composite microspheres

The electrostatic layer-by-layer (LbL) assembly of acid-modified multi-walled carbon nanotubes (MWNTs) and biopolymer chitosan (CHIT) is realized on planar substrates and polystyrene (PS) microsphere templates, respectively. The successful stepwise growing process of the composite films on planar substrates is investigated and confirmed by scanning electron microscopy and UV–vis spectroscopy. The transfer of the LbL assembly of MWNTs and CHIT to spherical PS microspheres leads to novel (MWNT/CHIT)PS core-shell structure, on which the gold nanoparticles (GNPs) are deposited to fabricate GNP(MWNT/CHIT)PS composite microspheres. The glass carbon electrodes modified with such (MWNT/CHIT)PS or GNP(MWNT/CHIT)PS composites exhibit satisfactory electrocatalytic activities for biomolecule dopamine.

Influence of Polyethyleneimine Graftings of Multi-Walled Carbon Nanotubes on their Accumulation and Elimination by and Toxicity toDaphnia magna

Modifications of carbon nanotubes (CNTs) for different applications may change their physicochemical properties such as surface charge. Assessments of the extent to which such modifications influence CNT ecotoxicity, accumulation, and elimination behaviors are needed to understand potential environmental risks these variously modified nanoparticles may pose. We have modified carbon-14 labeled multi-walled carbon nanotubes (MWNTs) with polyethyleneimine (PEI) surface coatings to increase their aqueous stability and to give them positive, negative, or neutral surface charges. Uptake and elimination behaviors of Daphnia magna exposed to PEI-coated and acid-modified MWNTs at concentrations of approximately 25 and 250 μg/L were quantified. PEI surface coatings did not appear to substantially impact nanotube accumulation or elimination rates. Although the PEI-modified nanotubes exhibited enhanced stability in aqueous solutions, they appeared to aggregate in the guts of D. magna in a manner similar to acid-treated nanotubes. The MWNTs were almost entirely eliminated by Daphnia fed algae during a 48 h elimination experiment, whereas elimination without feeding was typically minimal. Finally, PEI coatings increased MWNT toxicities, though this trend corresponded to the size of the PEI coatings, not their surface charges.

Silane grafted MWCNT/polyimide composites – Preparation, morphological and electrical properties

Precursor of polyimide, polyamic acid has been prepared by reacting 4,4′-oxydianiline with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride. Acid modified multiwall carbon nanotubes (MWCNTs) were grafted with 3-isocyanato-propyltriethoxysilane. Silane grafted MWCNTs were then mixed with the polyamic acid and heated to 300 °C to form a carbon nanotube/polyimide composite. During the imidization processes, the silanes on the MWCNT surface reacted with each other. TEM microphotographs shows that the silane grafted MWCNTs were connected. The composite material possesses an interpenetrating network in which polyimide molecules were interpenetrated into the MWCNT network. The electrical resistivity of silane grafted MWCNT/polyimide decreased very significantly compared to those only containing acid treated MWCNTs for the same loading with MWCNTs.

Electromagnetic Interference Shielding and Mechanical Properties of Maleic Anhydride Functionalized MWNT and Poly (urea urethane) Nanocomposites

The functionalized multiwall carbon nanotubes (MWNTs) have been prepared by free radical reaction with maleic acid and maleic anhydride. The functionalized MWNT was further blended with poly(dimethylsiloxane) (PDMS) based Poly(urea-urethane) (PUU). Both maleic acid modified MWNT (Maa-g-MWNT) and maleic anhydride modified MWNT (Mah-g-MWNT) showed enhanced dispersion compared with that of pristine MWNT and PUU.For MWNT/PUU nanocomposites containing 5 phr functionalized MWNT, the maximum microwave absorption was -19.2 dB for Maa-g-MWNT/PUU nanocomposites and was -22 dB for Mah-g-MWNT/PUU nanocomposites.

Carbon Nanotube Capsules Self-Assembled by W/O Emulsion Technique

Carbon nanotube capsules (CNCs) with the diameter of 5-10 microm were fabricated from acid-modified multiwalled carbon nanotubes (CNTs) using water-in-oil (W/O) emulsion technique. The effects of the content of CNTs in water, the extent of acid treatment, and the length of CNTs used on the formation and morphology of CNCs were investigated. It was found that the amount of CNTs in water and the length of CNTs are the crucial factors for the formation of carbon nanotube capsules.

Preparation, morphology and properties of acid and amine modified multiwalled carbon nanotube/polyimide composite

The precursor of polyimide, polyamic acid, was prepared by reacting 4,4′-oxydianiline (ODA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA). Unmodified, acid-modified and amine-modified multiwall carbon nanotubes (MWCNT) were separately added to the polyamic acid and heated to 300 °C to produce polyimide/carbon nanotube composite. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) microphotographs reveal that acid-modified MWCNT and amine-modified MWCNT were dispersed uniformly in the polyimide matrix. The effect of the acid and amine-modified MWCNTs on the surface and volume electrical resistivities of MWCNT/polyimide composites were investigated . The surface electrical resistivity of the nanocomposites decreased from 1.28 × 10 15 Ω/cm 2 (neat polyimide) to 7.59 × 10 6 Ω/cm 2 (6.98 wt% unmodified MWCNT content). Adding MWCNTs influenced the glass transition temperatures of the nanocomposites. Modified MWCNTs significance enhanced the mechanical properties of the nanocomposites. The tensile strength of the MWCNT/polyimide composite was increased from 102 MPa (neat polyimide) 134 MPa (6.98 wt% acid modified MWCNT/polyimide composites).