Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.     

Radiation-induced grafting of multi-walled carbon nanotubes in glycidyl methacrylate–maleic acid binary aqueous solution

With the aim to improve the compatibility between multi-walled carbon nanotubes (MWCNTs) and nylon-6, purified MWCNTs (p-MWCNTs) were grafted successfully with glycidyl methacrylate–maleic acid in aqueous solution using a single-step radiation method. The chemical structure and morphology of grafted p-MWCNTs (g-MWCNTs) was investigated by micro-FTIR, Raman spectroscopy and transmission electron microscopy. The prepared nylon-6/g-MWCNTs composite has higher mechanical strength and heat distortion temperature due to improved dispersion and compatibility than those of nylon-6/p-MWCNTs.     

水溶性多壁碳纳米管/铜酞菁染料自组装薄膜的制备与表征

Water soluble multi-wall carbon nanotubes (MWCNTs) were prepared via chemical oxidation. Under ultrasonication,the chemically treated MWCNTs can be dispersed in water to form colloids. The MWCNTs were characterized by FT-IR spectra. The FT-IR spectra reveal the presence of carboxylic groups on the nanotubes. The functional groups can improve the nanotubes-solubility in water. Alcian Blue 8GX (AB), a quaternary ammonium dye of the copper phthalocyanine group, was dissolved in water and used to form electrostaticcally self-assembled multilayer films. The MWCNT/AB composite films were characterized by UV-vis absorption spectra as well as AFM and fluorescence spectrum. The experimental results show that the MWCNT/AB composite films can be produced easily. Compared to those of the AB aqueous solutions, composite films exhibit pronounced differences in the absorption and fluorescence spectra, which suggests that AB molecules aggregated in the composite film, and that a charge transfer might exist between AB molecules and the MWCNTs.     

Effect of MWCNTs Doping on the Morphology,Structure and Properties of Chitosan Beads

A series of chitosan (CS)/multi-walled carbon nanotubes (MWCNTs) composite hydrogel beads with different MWCNTs contents are prepared via a solution blending method. The effects of MWCNTs on the morphology, structure and properties of chitosan beads have been investigated. Digital pictures show that the composite beads obtained are of good morphological characteristics, and the SEM micrographs indicate that the addition of MWCNTs into CS beads made the surface of the CS/MWCNTs hydrogel beads contain much larger wrinkles. Fourier transform infrared spectra (FTIR) show that the main chain of CS bead is not changed, but there are some electrostatic interactions between CS and MWCNTs, which lead to very significant changes in the crystallization behavior of CS and MWCNTs. The thermal stability of CS/MWCNTs composites at high temperatures is increased with the existence of MWCNTs, indicating a possible electrostatic interaction between MWCNTs and CS lattices to limit the motivation of CS. The adsorption capacity of CS beads doped with a lower percentage of MWCNTs (0.02 wt%) for acid fuchsin is 112.76 mg/g, higher than that of pure CS beads (35.62 mg/g).     

Conductive macroporous composite chitosan-carbon nanotube scaffolds

Multiwalled carbon nanotubes (MWCNTs) were used as doping material for three-dimensional chitosan scaffolds to develop a highly conductive, porous, and biocompatible composite material. The porous and interconnected structures were formed by the process of thermally induced phase separation followed by freeze-drying applied to an aqueous solution of 1 wt % chitosan acetic acid. The porosity was characterized to be 97% by both mercury intrusion porosimetry measurements and SEM image analysis. When MWCNTs were used as a filler to introduce conductive pathways throughout the chitosan skeleton, the solubilizing hydrophobic and hydrophilic properties of chitosan established stable polymer/MWCNT solutions that yielded a homogeneous distribution of nanotubes throughout the final composite matrix. A percolation theory threshold of approximately 2.5 wt % MWCNTs was determined by measurement of the conductivity as a function of chitosan/MWCNT ratios. The powder resistivity of completely compressed scaffolds also was measured and was found to be similar for all MWCNT concentrations (0.7-0.15 Omega cm powder resistivity for MWCNTs of 0.8-5 wt %) and almost five times lower than the 20 k Omega cm value found for pure chitosan scaffolds.     

Electrically conducting electrospun silk membranes fabricated by adsorption of carbon nanotubes

We present a simple method of obtaining electrically conducting electrospun silk non-woven membranes consisting of nanofibers with multi-walled carbon nanotubes (MWCNTs) adsorbed on their surface. Nanofibrous membranes with fibroin diameters of 460 ± 40 nm were formed from aqueous Bombyx mori fibroin solution by electrospinning. The MWCNTs adhered well to the surface of the highly porous silk nanofibrous membranes when Triton X-100 was used as the surfactant for the dispersion of the MWCNTs in aqueous media. The electrical conductivity of the membranes was 2.4 × 10⁻⁴ S/cm due to the presence of the MWCNTs on their surface. In addition, the strong interaction between the MWCNTs and nanofibers keeps them from separating each other, even after ultrasonication. The combination of the high conductivity of the membranes and the simple process used to fabricate them could lead to significant advances in the development of new materials, such as electromagnetic interference shielding or electrostatic dissipation membranes.     

Preparation and characterization of Fe_3O_4/Au composite particles

Colloid gold with different sizes has been widely used in immunoassay and nucleic acid detection mainly because of their properties for immobilization of biomolecules, such as antibodies and oligonucleo-tides, through chemical reactions via active group SH on the biomolecules. Magnetic particles modified with various chemical groups on their surface can not only exhibit good magnetic responsiveness to an external magnetic field but also immobilize biomolecules through these chemical groups. As…     

Carbon Nanofiber and Poly[2-(methacryloyloxy) ethyl] Trimethylammonium Chloride Composite as a New Benchmark Carbon-based Electrocatalyst for Sulfide Oxidation

There is an overwhelming desire to develop new sulfide oxidation electrocatalysts that perform at low potentials and exhibit high current density for the removal and efficient sensing of sulfide. This article describes a comparative electrochemical analysis of various commercially available carbon materials and polymer/surfactant composite electrocatalysts for direct electrooxidation of sulfide in an aqueous solution. The composites were prepared from five different carbon materials multiwalled carbon nanotubes, fullerene-C₆₀, graphene, glassy carbon, and carbon nanofibers (CNF) and four different polymers: chitosan, polyvinylidene fluoride, Nafion, and indigenously synthesized poly[2-(methacryloyloxy)ethyl] trimethylammonium chloride (PMTC). The carbon@polymer composites were prepared by a simple ultrasonication technique, and the electrodes were prepared by drop-drying the prepared composite on indium tin oxide (ITO) substrates. The CNF@PMTC showed the highest positive zeta potential that allowed an accumulation of many negatively charged sulfide ions at the CNF@PMTC surface. Cyclic voltammetry was used for the electrooxidation of sulfide in an aqueous solution of tris buffer (0.05 M; pH 8.0) and KNO₃ (0.1 M). The lowest sulfide oxidation peak potential (i. e., −51 mV vs. standard hydrogen electrode) with a high catalytic current response (730 μA/cm²) of the CNF@PMTC-modified ITO electrode among the tested and previously reported carbon-based electrode materials make it ideal for direct sulfide electrooxidation. Taking this and its simple preparation method into account, CNF@PMTC can be considered a benchmark carbon-based electrocatalyst for sulfide oxidation.     

Ice-templated porous polymer/UiO-66 monolith for Congo Red adsorptive removal

Chitosan/MOF composite porous monolith used in water remediation as adsorbent can realize high-efficient removal of pollutant in water and facile recycling from water. However, dissolution of chitosan (without crosslinking) in acidic aqueous solution will cause breakage of composite monolith. Herein, we report a chitosan/UiO-66 monolith prepared by ice-templating method. Specially, a pre-crosslinking treatment (by glutaraldehyde) is employed before the monolith formation, which obviously boosts its stability in aqueous solution. The composite monolith is evaluated by SEM, N₂ adsorption, XRD, and batch adsorption tests for Congo Red (CR). The results show that the composite monolith possesses a typical ice-templating structure with hierarchical (mirco- / meso- and macro-) pores. UiO-66 particles are embedded on the surface of chitosan matrix, and the crystal structure of UiO-66 is not changed obviously by the crosslinking and freezing process. The composite monolith exhibits high adsorption efficiency (90% of CR was removed from its aqueous solution in 60 min) and the maximum adsorption capacity of 246.21 mg/g (derived from Langmuir model) can be reached. After adsorption, the monolith is collected by a facile procedure and recovered using ethanol for evaluating its reusability. After 4 cycles, the CR removal efficiency of the composite monolith still remains ~90% of the initial efficiency. This work demonstrates that the simple crosslinking procedure before monolith formation can ensure the intact shape of the chitosan/MOF monolith during adsorption.     

Dispersion of multi-wall carbon nanotubes by an ionic liquid-based polyether in aqueous solution

Multi-wall carbon nanotubes (MWCNTs) can be effectively dispersed by an ionic liquid-based polyether, poly(1-glycidyl-3-methylimidazolium chloride) (PGMIC) in aqueous solution. The amount of dispersed MWCNTs increases with the increasing of PGMIC concentration, and then decreases. Reaggregation of MWCNTs is observed when PGMIC exceeded the optimal concentration, which may be due to the conformational change of PGMIC molecules around MWCNT. The ultrasonic dispersion method is better than stirring method in the PGMIC solution. Furthermore, the acidic solution is convenient to prepare stable MWCNTs suspensions. Through the characterizations of ultraviolet–visible–near infrared, thermogravimetric analysis and Fourier transform infrared, it can be concluded that electrostatic repulsions, hydrophobic effect, n–π, and cation–π interactions played important roles in the dispersion of MWCNTs.     

Removal of U(VI) from aqueous solutions by using MWCNTs and chitosan modified MWCNTs

In this paper, the multiwalled carbon nanotubes (MWCNTs) were modified with chitosan (CS) by using low temperature plasma grafting technique (denoted as MWCNT-CS). The prepared MWCNTs and MWCNT-CS were characterized by SEM, TEM, FTIR and Raman spectroscopy in detail and the results suggested that CS molecules were successfully grafted on the surfaces of MWCNTs. The materials were applied as adsorbents in the removal of U(VI) ions from large volumes of aqueous solutions as a function of environmental conditions. The removal of U(VI) from aqueous solution to MWCNTs and MWCNT-CS increased with increasing pH values at pH < 7, and then decreased with increasing pH values at pH > 7. The sorption of U(VI) on MWCNTs and MWCNT-CS was strongly dependent on pH and independent of ionic strength. The sorption of U(VI) on MWCNTs and MWCNT-CS was dominated by inner-sphere surface complexation rather than by ion exchange or outer-sphere surface complexation. The surface grafted chitosan molecules can enhances U(VI) sorption on MWCNTs obviously, which was also evidenced from the XPS spectroscopy analysis. The results of high sorption capacity of U(VI) on MWCNT-CS suggest that the MWCNT-CS nanomaterial is a suitable candidate in the preconcentration of U(VI) ions from large volumes of aqueous solutions.     

Electrochemical activities of platinum-decorated multi-wall carbon nanotube/chitosan composites for the oxidations of alcohols

Electrooxidation of alcohols including methanol, ethanol, and isopropanol is studied on the modified solid glassy carbon electrodes with various amounts of platinum nanoparticles (PtNPs) immobilized on a composite of functionalized multi-walled carbon nanotubes (MWCNTs) and chitosan in an acidic solution. Here the chitosan is available as a binder to tightly anchor Pt nanoparticles onto the MWCNTs surfaces. MWCNTs/chitosan composite support can significantly improve the activity of the catalyst for alcohol oxidation and reduce the Pt catalyst loading. The calculated electrochemical active surface area is 379.2 m²/g Pt for PtNP–MWCNT/chitosan. Cyclic voltammetry and chronoamperometry techniques are employed for catalytic activity evaluation. The effects of operational parameters including platinum loading, concentration of the corresponding alcohol, concentration of the acid solution, scanning rate, and the final limit of anodic potential on the performance of the electrodes are also investigated.     

氮杂石墨烯碳纳米管复合材料负载Pt催化剂在甘油选择性氧化中的应用

一直以来,以碳材料为载体负载的金属催化剂被广泛应用于甘油液相氧化反应.研究表明,催化剂活性与碳的孔径分布有关,随着碳载体微孔比例的增加,催化剂活性下降.此外,载体表面基团对金属活性有着重要影响.例如,载体表面含氧基团的吸电子作用可降低载体表面电子的流动性(电子密度和导电性),从而阻碍甘油氧化反应过程中OH–的吸附和再生,导致反应活性降低.因此,开发微孔比例小、富含负电性基团的碳载体成为甘油氧化过程中急需解决的问题之一.本文通过热解碳纳米管(MWCNTs)和三聚氰胺的混合物,在碳纳米管表面直接生长得到氮杂石墨烯(NG-MWCNTs),并采用SEM,N2吸附,TEM和XRD对所得复合材料进行了表征.实验发现,相比于单纯的MWCNTs和直接热解三聚氰胺所得的产物CNx,NG-MWCNTs具有更高的比表面积(173 m2/g)和更大的平均孔径.此外,NG-MWCNTs非常适合作为Pt催化剂的载体,Pt平均粒径可小至1.4±0.4 nm.所制备的Pt/NG-MWCNTs催化剂在甘油选择性氧化反应中具有很高的催化活性和甘油酸选择性(甘油转化率和甘油酸选择性分别可达64.4%和81.0%),且具有可重复使用性能.Pt/NG-MWCNTs催化剂优异的催化活性不仅与载体表面高分散的Pt有关,而且与N原子对Pt的给电子作用有关.     

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.     

原位沉析法制备碳酸钙/壳聚糖三维复合材料的研究

将含有Ca²⁺的壳聚糖溶液与含有CO^2-₃的碱溶液用离子可渗透膜隔离,根据膜渗透原理,使膜内壳聚糖与碱液原位沉析,生成碳酸钙,得到具有高强度的碳酸钙(CaCO₃)/壳聚糖(CS) 三维复合材料. XRD测试结果表明,生成的碳酸钙以方解石晶型存在. 从SEM可以观察到碳酸钙颗粒尺寸约为5～10 μm,并且颗粒呈有序分布,它们以棒材的纵轴为中心,围绕中心呈环状分布. 对不同碳酸钙含量的复合棒材进行了弯曲性能测试,其弯曲强度随碳酸钙含量的增大先上升后下降. 在碳酸钙质量分数为10％时,弯曲强度达到最大值(约为113 MPa),弯曲模量为2.6 GPa.     

Modification and dispersion of multi-walled carbon nanotubes in water

In the present work, the decorated purified raw multi-walled carbon nanotubes (R-MWCNTs) were obtained by chemical modification (CM) by treatment with concentrated sulfuric acid and concentrated nitric acid mixture with a certain volume ratio of 1: 3. The R-MWCNTs and CM-MWCNTs samples were investigated by X-ray Diffraction (XRD) analysis and Fourier transform infrared spectroscopy (FT-IR). The prepared MWCNTs were homogeneously dispersed in water using a commercial surfactant (Polyvinyl pyrrolidone, (PVP)) and ultra-sonication. The dispersion of MWCNTs was obtained by UV-Vis analysis. The results show that chemical modification purified MWCNTs and more effective functional groups were attached on the surface of MWCNTs. Meanwhile, R-MWCNTs and CM-MWCNTs were uniformly distributed in aqueous PVP solution and the dispersion of CM-MWCNTs in water was better.     

PLA/MWNTs/HA复合材料的制备和性能研究

采用超声辅助原位湿法合成多壁碳纳米管／羟基磷灰石纳米复合材料(MWNTs／HA),并通过溶液浇铸法制备了PLA／MWNTs／HA复合材料薄膜。考察了MWNTs／HA纳米粒子含量对复合膜性能的影响,并通过力学性能、SEM、FTIR、以及DMTA对复合膜性能进行了表征,结果表明：随着纳米粒子质量分数的增加,复合膜的拉伸强度呈下降趋势;拉伸模量和储能模量呈现先下降后上升的趋势;玻璃化转变温度则呈现不断上升趋势。     

Surfactants for CNTs dispersion in zirconia-based ceramic matrix by sol–gel method

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO₂ matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.     

The effect of mixing methods on the dispersion of carbon nanotubes during the solvent-free processing of multiwalled carbon nanotube/epoxy composites

Several solvent-free processing methods to disperse multiwalled carbon nanotubes (MWCNTs) in bisphenol F-based epoxy resin were investigated, including the use of a microfluidizer (MF), planetary shear mixer (PSM), ultrasonication (US) and combinations. The processed mixture was cured with diethyl toluene diamine. Three complimentary techniques were used to characterize the dispersion of the MWCNTs in cured composite samples: optical microscopy, micro Raman spectroscopy, and scanning electron microscopy (SEM). For sample MF + PSM, optical micrographs and Raman images showed reduced agglomeration and a homogeneous distribution of MWCNTs in the epoxy matrix. SEM analysis of fractured specimen after tensile testing revealed breakage of nanotubes along the fracture surface of the composite. A comparison of the MWCNT dispersion in the epoxy samples processed using different methods showed that a combination of MF and PSM processing yields a more homogeneous sample than the PSM or US + PSM processed samples. Mechanical testing of the composites showed about 15% improvement in the tensile strength of samples processed by the MF + PSM method over other methods. Thermogravimetric analysis (TGA) results showed a small decrease in the onset degradation temperature for poorly dispersed samples produced by PSM compared with the well-mixed samples (MF + PSM). These results strongly suggest that the MF + PSM processing method yield better-dispersed and stronger MWCNT/epoxy composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Biobased films prepared from NaOH/thiourea aqueous solution of chitosan and linter cellulose

In the present study, films based on linter cellulose and chitosan were prepared using an aqueous solution of sodium hydroxide (NaOH)/thiourea as the solvent system. The dissolution process of cellulose and chitosan in NaOH/thiourea aqueous solution was followed by the partial chain depolymerization of both biopolymers, which facilitates their solubilization. Biobased films with different chitosan/cellulose ratios were then elaborated by a casting method and subsequent solvent evaporation. They were characterized by X-ray analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal analysis, and tests related to tensile strength and biodegradation properties. The SEM images of the biofilms with 50/50 and 60/40 ratio of chitosan/cellulose showed surfaces more wrinkled than the others. The AFM images indicated that higher the content of chitosan in the biobased composite film, higher is the average roughness value. It was inferred through thermal analysis that the thermal stability was affected by the presence of chitosan in the films; the initial temperature of decomposition was shifted to lower levels in the presence of chitosan. Results from the tests for tensile strength indicated that the blending of cellulose and chitosan improved the mechanical properties of the films and that an increase in chitosan content led to production of films with higher tensile strength and percentage of elongation. The degradation study in a simulated soil showed that the higher the crystallinity, the lower is the biodegradation rate.