Functional and unmodified MWNTs for delivery of the water-insoluble drug Carvedilol - A drug-loading mechanism

The purpose of this study was to develop carboxyl multi-wall carbon nanotubes (MWNTs) and unmodified MWNTs loaded with a poorly water-soluble drug, intended to improve the drug loading capacity, dissolubility and study the drug-loading mechanism. MWNTs were modified with a carboxyl group through the acid treatment. MWNTs as well as the resulting functionalized MWNTs were investigated as scaffold for loading the model drug, Carvedilol (CAR), using three different methods (the fusion method, the incipient wetness impregnation method, and the solvent method). The effects of different pore size, specific surface area and physical state were systematically studied using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transformation infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), nitrogen adsorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The functional MWNTs allowed a higher drug loading than the unmodified preparations. The methods used to load the drug had a marked effect on the drug-loading, dissolution, and physical state of the drug as well as its distribution. In addition, the solubility of the drug was increased when carried by both MWNTs and functional MWNTs, and this might help to improve the bioavailability.     

Electrical properties of boron-doped MWNTs synthesized by hot-filament chemical vapor deposition

We have synthesized a large amount of boron-doped multiwalled carbon nanotubes (MWNTs) by hot-filament chemical vapor deposition. The synthesis was carried out in a flask using a methanol solution of boric acid as a source material. The scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy were performed to evaluate the structural properties of the obtained MWNTs. In order to evaluate the electrical properties, temperature dependence of resistivity was measured in an individual MWNTs with four metal electrodes. The Raman shifts suggest carrier injection into the boron-doped MWNTs, but the resistivity of the MWNTs was high and increased strongly with decreasing temperature. Defects induced by the plasma may cause this enhanced resistivity.     

Amino Functionalization of MWNTs and Their Effect on ILSS of Hybrid Nanocomposites

Multi-walled carbon nanotubes (MWNT) were oxidized by treatment with a mixture of sulfuric and nitric acids to introduce carboxyl groups on their surfaces. Triethylene tetraamine (TETA) was then grafted onto the oxidized MWNTs via a thionyl chloride route to obtain the amino-functionalized MWNTs (f-MWNT). The presence of amino functional groups on the MWNTs was confirmed using FT-IR, and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to compare the morphology of pristine MWNT (p-MWNT) and f-MWNT. Both the p-MWNT and f-MWNT were dispersed in epoxy resin using ultrasonic agitation and the suspensions were injected into E-glass fiber woven fabric using a specialized vacuum assisted resin transfer molding (VARTM) process in which a flow flooding chamber (FFC) was used to re-direct the suspension flow. Control samples were fabricated using the same E-glass fiber mat and unmodified epoxy resin following the same procedure. Compression shear testing (CST) was performed on all the manufactured samples to determine their Inter laminar shear strength (ILSS). Results show 41% increase in ILSS for hybrid composites containing p-MWNTs and a 61% increase for samples containing f-MWNTs relative to the control samples without MWCNT.     

Vertically aligned peapod formation of position-controlled multi-walled carbon nanotubes (MWNTs)

We have succeeded in making peapod structures with vertically aligned multi-walled carbon nanotubes (MWNTs), grown on a silicon substrate using hot filament chemical vapor deposition. Opening the tips of the MWNTs was performed at 600 C using oxygen and then C₆₀ molecules were deposited on them to fill their inner spaces. We confirmed that the MWNTs were open at the tips and filled with C₆₀ molecules using transmission electron microscopy. In addition, it has been determined that MWNTs can be filled with other materials, such as molybdenum oxide.     

Selfassembly of gold nanoparticles onto the surface of multiwall carbon nanotubes functionalized with mercaptobenzene moieties

We have developed a new and effective method to robustly self-assemble gold nanoparticles onto the surface of multiwall carbon nanotubes (MWNTs) functionalized with mercaptobenzene moieties. Fourier transform infrared and electron diffraction spectroscopy were used to verify whether or not the mercaptobenzene moieties have been attached to the π-conjugated body of MWNTs. Transmission electron microscope images give direct evidences for the success of selfassembly of gold nanoparticles onto the functionalized MWNTs.     

Elevated performances of SnS anodes with MWNTs as conductive agent for rechargeable lithium-ion batteries

SnS nanoparticles were mechanochemically synthesized and fabricated into electrodes with two kinds of conductive agents, acetylene black and multi-wall carbon nanotubes (MWNTs), respectively. The morphology and structure of as-synthesized SnS powder were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical properties of as-prepared electrodes were investigated by discharge–charge test, cyclic voltammogram, and electrochemical impedance spectrum. By comparing the variation of the charge-transfer impedance R _ct at different discharge states, it was found that the value of R _ct of the electrode with MWNTs as conductive agent was less than that of the electrode with acetylene black as conductive agent. The electrode with MWNTs as conductive agent had preferable cycling performances, which was believed to be attributed to the tenacity and good conductivity of MWNTs.     

A facile, green, and tunable method to functionalize carbon nanotubes with water-soluble azo initiators by one-step free radical addition

Versatile functional groups were covalently attached to the surface of multiwalled carbon nanotubes (MWNTs) by one-step free radical addition of water-soluble azo initiators. The coverage density of functional groups is rationally controlled either by adjusting the feed ratio of azo initiators to MWNTs or by utilizing the starting chemicals of multifunctional groups. TEM observations in conjunction with solubility data imply that the functionalized-MWNTs have much better dispersibility and stability than pristine MWNTs in polar solvents. The attached carboxylic groups were then used as scaffolds to chelate Ag⁺ ions affording Ag/MWNTs nanohybrids in the presence of NaBH₄ reductant. This shows that the reactive groups anchored on MWNTs can be further chemically functionalized. The proposed method might open many new opportunities for the development of high-performance nanomaterials containing CNTs.     

Preparation and Physical Properties of Carbon Nanotubes–PVA Nanocomposites

Nanocomposite materials were prepared by incorporating multiwall carbon nanotubes (MWNTs), obtained by acetylene catalytic chemical vapor deposition (CCVD) on Co/Fe‐modified MgO, within poly(vinyl alcohol) (PVA). Before incorporation, nanotubes were oxidized to obtain better compatibilization with the polymer. It has been found that the addition of COOH‐functionalized and purified MWNTs improves the mechanical response, increases the glass transition temperature, and delays the thermal oxidation of PVA. Furthermore, the PVA crystallinity seems to be enhanced by the presence of nanotubes.     

Preparation and characterization of aligned carbon nanotubes/polylactic acid composite fibers

Aligned functionalized multiwalled carbon nanotubes/polylactic acid (MWNTs-PCL/PLA) composite fibers were successfully prepared by electrospinning processing. The MWNTs bonded with the polycaprolactone chains exhibited excellent uniform dispersion in PLA solution by comparing with the acid-functionalized MWNTs and amino-functionalized MWNTs. Optical microscopy was used to study the aligned degree of the fibers and to investigate the influences of the electrodes distance on the alignment and structure of the fibers, and results showed that the best quality of aligned fibers with dense structure and high aligned degree were obtained at an electrodes distance of 3 cm. Moreover, the MWNTs embedded inside the MWNTs-PCL/PLA fibers displayed well orientation along the axes of the fibers, which was demonstrated by field emission scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

Large diameter MWNTs growth on iron-sprayed catalyst by CCVD method under atmospheric pressure

In this work, we have synthesized large diameter multi-walled carbon nanotubes (MWNTs), by simple catalyst chemical vapor deposition (CCVD). Fe powder was spread on quartz substrate as a catalyst by a simple method and then heated under Ar atmosphere. Carbon’s products can be synthesized by the decomposition of ethylene gas and deposition of carbon atoms on the Fe catalyst particles in Ar atmosphere at 930°C. XRD pattern, SEM and TEM images were used to investigate the characteristics, morphology and structure of carbon’s products.     

Electrically Conductive Multiwall Carbon Nanotubes/Poly(vinyl alcohol) Composites with Aligned Porous Morphologies

Electrically conductive multiwall carbon nanotubes (MWNTs)/poly(vinyl alcohol) (PVA) composites with aligned porous structure were obtained by a directional freeze-drying process. The results show that the morphologies of the MWNTs/PVA composite can be tailored by adding different contents of MWNTs in the PVA matrix. Because of the aligned porous structure of the MWNTs/PVA composites, the conductivity property of MWNTs/PVA composite does not coincide absolutely with the universal percolation theory. In the aligned porous MWNTs/PVA composites, the existence of the micro-pores destroys the uniform distribution of the conductive network along the direction perpendicular to the aligned pores and results in a nonuniform distribution conductive network. When being used to monitor flowing vapors in pipes, compared with a film sensor with the thickness from several decades to hundreds of microns, the aligned porous conductive MWNTs/PVA composite with micron-sized pores should be a much better sensor.     

Supercritical fluid-assisted synthesis of a carbon nanotubes-grafted biocompatible polymer composite

A nanocomposite consisting of multi-wall nanotubes (MWNTs) grafted with a biocompatible polymer poly(2-hydroxyethyl methacrylate) was prepared by in situ polymerization in supercritical carbon dioxide. The surface of the MWNTs was first surface modified with hydroxyl groups in the solution of KMnO₄ and a phase-transfer catalyst. MWNT-OH was then functionalized with vinyl groups using a silane coupling agent, γ-methacryloxypropyltrimethoxysilane. The silane groups can improve the dipersion of MWNTs in supercritical carbon dioxide, while the terminal vinyl groups help fabricate polymer chains on the MWNT surface. The as-synthesized products were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermo-gravimetric analysis. The SEM and TEM images showed that the nanotubes were well coated with the polymer shell. The composite had higher thermal stability than the pure polymer and dispersed well in methanol. This biocompatible polymer composite was prepared using a green method and is expected to be useful as a biomaterial composite with potential applications in the biological field.     

Green chemical functionalization of multiwalled carbon nanotubes with poly(?-caprolactone) in ionic liquids

Multiwalled carbon nanotubes (MWNTs) have been successfully functionalized by free radical addition of 4,4′-azobis(4-cyanopentanol) in aqueous media to generate the terminal-hydroxyl-modified MWNTs (MWNT-OH), followed by surface-initiated in situ ring-opening polymerization of ?-caprolactone in 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF₄) to obtain poly(?-caprolactone)-grafted MWNTs (MWNT-g-PCL). Spectroscopic methods in conjunction with electron microscopy clearly revealed that hairy PCL chains were chemically attached to the surface of MWNTs to form core-shell nanostructures with the latter as core and the former as shell. With increasing polymerization time from 2 to 8 h, the amount of the grafted-PCL synthesized in BmimBF₄ varies from 30.6 to 62.7 wt%, which is clearly higher than that (41.5 wt%) obtained in 1,2-dichlorobenzene under comparable conditions (8 h). The proposed methodology here uses water and room temperature ionic liquids (RTILs) as the reaction media and promises a green chemical process for functionalizing nanotubes.     

The synthesis of multi-walled carbon nanotubes (MWNTs) by catalytic pyrolysis of the phenol-formaldehyde resins

A series of carbon nanomaterials, particularly multi-walled carbon nanotubes (MWNT), are obtained as products from catalytic pyrolysis of the cross-linked phenol-formaldehyde resins with different ferrocene under inert atmosphere. The morphology and structure of the samples were evaluated by TEM and XRD techniques. CNTs morphology is dependent on the iron nanoparticles and their forms (Fe, Fe₃C) resulted from ferrocene decomposition. The amount of nanotubes increases with iron content released from ferrocene catalyst during the pyrolysis process. Fe₃C nanoparticles drive the nucleation and the growth of carbon nanotubes during the pyrolysis process. Long (up to microns) well-defined MWNTs with small defects, ropes and disordered carbon are representatives in the pyrolyzed resins composition.     

Functional multi-walled carbon nanotube/polyaniline composite films as supports of platinum for formic acid electrooxidation

Embedding of carbon nanotubes in conducting polymeric matrices for various nanocomposites material is now a popular area. In this article, a concise chemical method has been described for the preparation of homogeneous nanocomposite of multi-walled carbon nanotube (MWNT)/polyaniline (PANI) by electrochemical codeposition. For this we functionalized the MWNTs via the diazotization reaction. This helped to disperse the nanotubes in aniline. The composite films were dispersed Pt by electrodeposition technique. The presence of MWNTs and platinum in the composite films was confirmed by XRD analysis and transmission electron microscopy (TEM). Four-point probe investigations revealed that the MWNT/PANI composite films exhibited a good conductivity. Cyclic voltammograms (CV) showed that Pt-modified MWNT/PANI composite films perform higher electrocatalytic activity and better long-term stability than Pt-modified pure PANI film toward formic acid oxidation. The results imply that the MWNT/PANI composite films as a promising support material improves the electrocatalytic activity for formic acid oxidation greatly.     

Effect of multi-walled carbon nanotubes loaded with Ag nanoparticles on the photocatalytic degradation of rhodamine B under visible light irradiation

Multi-walled carbon nanotubes loaded with Ag nanoparticles (Ag/MWNTs) were prepared by two methods (direct photoreduction and thermal decomposition). The photocatalytic activity of Ag/MWNTs for the degradation of rhodamine B (RhB) under visible light irradiation was investigated in detail. The adsorption and photocatalytic activity tests indicated that the MWNTs served as both an adsorbent and a visible light photocatalyst. The photocatalytic activity of MWNTs was remarkably enhanced when the Ag nanoparticles were loaded on the surface of MWNTs. Moreover, the visible light photocatalytic activity of Ag/MWNTs depended on the synthetic route. On the basis of the experimental results, a possible visible light photocatalytic degradation mechanism was discussed.     

Comparative study on modification of multi-walled carbon nanotubes by a hydrophilic polymer with different approaches

The multi-walled carbon nanotubes (MWNTs) modified by a hydrophilic polymer were prepared with polymerization and blending approaches. The differences of both modified MWNTs were compared by Fourier transform infrared and Raman spectroscopies, thermogravimetric analysis and transmission electron microscopy. Chemical grafting reaction had occurred between MWNTs and polyvinyl pyrrolidone (PVP) after modification with polymerization and blending approaches. Polymerization modification can graft more PVP on the surface of MWNTs compared with blending modification. Polymerization modification of MWNTs belongs to the “grafting from” mechanism, while blending modification belongs to the “grafting to” mechanism. Modified MWNTs exhibit remarkable solubility in water, ethanol and dimethyl formamide.     

Studies on the Nonisothermal Crystallization Behavior of Polypropylene/Multiwalled Carbon Nanotubes Nanocomposites

Polypropylene/multiwalled carbon nanotubes (PP/MWNTs) nanocomposites were prepared by a melt compounding process. The morphology and nonisothermal crystallization of these nanocomposites were investigated by means of optical microscopy, scanning electron microscopy, and differential scanning calorimetry. Scanning electron microscope micrographs of PP/MWNTs composite showed that the MWNTs were well dispersed in the PP matrix and displayed a clear nucleating effect on PP crystallization. Avrami theory, modified by Jeziorny and Mo's method, was used to analyze the kinetics of the nonisothermal crystallization process. It was found that the addition of MWNTs improved the crystallization rate and increased the peak crystallization temperature of the PP/MWNTs nanocomposites as compared with PP. The results show that the Jeziorny theory and Mo's method successfully describe the nonisothermal crystallization process of PP and PP/MWNTs nanocomposites.     

真空热处理碳纳米管的储氢性能研究

研究了真空热处理对多壁碳纳米管(MWNTs)电化学储氢性能的影响.采用化学气相沉积法(CVD)制备碳纳米管，碳纳米管与LaNi₅储氢合金按质量比1∶10混合，制作成CNTs-LaNi₅电极.电解池采用三电极体系，6mol/L KOH为电解液，Ni(OH)₂为正极，Hg/HgO为参比电极.实验结果表明，在相同的充放电条件下，850℃时CNTs-LaNi₅电极的储氢性能最好，克容量最大为503.6mAh/g，相应的平台电压高达1.18V.从500—850℃随着温度升高，放电量有较大幅度的增加，但到950℃时放电量反而下降.由此可见，碳纳米管的热处理温度对碳纳米管的电化学储氢性能有着较大的影响. 关键词： 碳纳米管(CNTs) 储氢性能 5合金')" href="#">LaNi₅合金 化学气相沉积法(CVD法)