Electromagnetic and microwave absorbing properties of magnetite nanoparticles decorated carbon nanotubes/polyaniline multiphase heterostructures

Magnetite nanoparticles decorated CNTs/PANI multiphase heterostructures were prepared by polymerization of aniline monomer and an additional process of the coprecipitation of Fe²⁺ and Fe³⁺. Scanning electron microscopy and transmission electron microscopy observation indicated that the monodispersed magnetite nanoparticles were uniformly decorated on the surface of CNTs/PANI. The formation of magnetite nanoparticles on CNTs/PANI was mainly through a preferentially position-selective precipitation process. More interestingly, a portion of Fe₃O₄ nanoparticles was found to form core–shell structures with PANI. The effects of different additional amounts of NH₂Fe(SO₄)₂·6H₂O reactant on the magnetic properties and microwave absorbing performances of CNTs/PANI/Fe₃O₄ heterostructures were investigated. The CNTs/PANI/Fe₃O₄ multiphase heterostructures were proved to be superparamagnetic. The microwave absorption measurement showed that the CNTs/PANI/Fe₃O₄ samples under 1.5 g of NH₂Fe(SO₄)₂·6H₂O condition exhibited much more effective absorption performance. These results suggested the novel CNTs/PANI/Fe₃O₄ multiphase heterostructures with PANI as the second phase may be potential candidate for microwave absorption systems.     

Nitrogen-doped multiwalled carbon nanotubes decorated with copper(I) oxide nanoparticles with enhanced capacitive properties

We report on the enhanced capacitive properties of a copper(I) oxide nanoparticle (Cu₂O NP)-decorated multiwalled carbon nanotube (MWCNT) forest with nitrogen (N) doping. A careful in situ solid-state dewetting and plasma doping method was developed that ensured homogeneous decoration and contamination-free Cu₂O NPs with N doping on the nanotube sidewalls. The morphology and structure of the hybrid materials were characterised by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Raman spectroscopy and X-ray photoemission spectroscopy. The electrochemical performance of the hybrid materials was investigated by cyclic voltammetry and galvanostatic charge/discharge tests in a 0.1 M Na₂SO₄ electrolyte. The electrochemical tests demonstrated that the Cu₂O NP/N-MWCNT electrode exhibits a specific capacitance up to 132.2 F g^?1 at a current density of 2.5 A g^?1, which is 30% higher than that of the pure MWCNT electrode. Furthermore, the electrode could retain the specific capacitance at 85% stability over 1000 cycles. These observations along with the simple assembly method for the hybrid materials suggest that the Cu₂O NP/N-MWCNT could be a promising electrode for supercapacitor applications.     

多壁碳纳米管/聚亚苯基苯并二噁唑复合材料的微结构与性能

以甲基磺酸(MSA)为溶剂通过溶液共混法制备了不同多壁碳纳米管(MWNTs)含量的多壁碳纳米管/聚亚苯基苯并二噁唑(MWNTs/PBO)复合材料, 用扫描电镜(SEM)对热处理前后复合材料的微结构进行了分析, 并对其导电、力学和耐热性能进行了研究。结果表明: MWNTs能均匀地分散在聚合物基体中, 并能形成一定的网络结构, 热处理后的复合材料较热处理前的结构更致密, 导电性能和力学性能都有所改善, 其中MWNTs质量分数为10％的热处理后复合材料与纯PBO聚合物相比, 体积电阻率降低约9个数量级, 而拉伸强度和拉伸模量分别提高了95％和53％, 耐热性能也有一定的提高。      

Fe3O4纳米粒子修饰碳纳米管的制备及其磁学性能（英文）

通过FeCl2.4H2O和FeCl3.6H2O混合共沉淀,合成平均粒径为6 nm和10 nm的Fe3O4纳米粒子。然后将两种Fe3O4纳米粒子分别与经HNO3氧化处理的多壁碳纳米管(MWCNTs)置于乙醇水溶液(水和乙醇的体积比为1∶1)中,在超声波作用下制备Fe3O4/MWCNT复合材料。用高分辨透射电子显微镜、X-射线光电子能谱、振动样品磁强计、X射线衍射仪、热重分析仪对所制备的Fe3O4/MWCNT复合材料进行表征。结果表明:由6 nm和10 nm Fe3O4纳米粒子所制备的Fe3O4/MWCNT复合材料中,Fe3O4的质量分数分别为26.65%和29.3%,相应的磁饱和强度分别为16.5 emug-1和7.5 emug-1。     

Physical properties of multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWNTs), which were prepared by hydrogen arc discharge, were purified by using an infrared radiation heating system. The morphology, structure, vibrational modes and crystalline perfection of purified MWNTs were investigated by using scanning electron microscopy, high-resolution transmission electron microscopy, an X-ray diffractometer and a Raman spectrometer. Moreover, the electrical conductivity of individual purified MWNTs was measured using a two-probe method using a micro manipulator system. It turned out that the MWNTs had a high degree of graphitization, an electrical conductivity of about 1.85×10³ S cm⁻¹ along the long axis, and an enormous current density of more than 10⁷ A cm⁻².     

Investigation of the microwave-absorbing properties of Fe-filled carbon nanotubes

Carbon nanotubes encapsulated Fe nanowire composites were synthesized via pyrolyzing of ferrocene. The reflection loss (R.L.), matching frequency (f_m) and matching thickness (d_m) were calculated using the theory of the absorbing wall. The electromagnetic properties and microwave-absorbing characteristic effects by the encapsulation of metal Fe were investigated in a frequency range of 8-18 GHz. With matching thickness of 3.5 mm, the maximum reflection loss is about − 22.73 dB for the absorber. The bandwidth corresponding to the reflection loss below − 10 dB is more than 4.22 GHz. With increasing thickness, the peak value of the reflection loss shifts to a lower frequency.     

Thermodynamic properties of multiwalled carbon nanotubes

The experimental study of the heat capacity of multiwalled carbon nanotubes has been conducted at a constant pressure and a temperature in the range from 60 to 300 K. The derived temperature dependence of the heat capacity has been shown to differ from that of graphite. The explanation of the fact has been given in terms of the special features of phonon spectra of the above materials. Based on the experimental results and reliable literature data standard values of the basic thermodynamic functions of multiwalled carbon nanotubes (enthalpy, entropy, and Gibbs reduced energy) have been calculated.     

Reaction of diphenylpicrylhydrazyl (DPPH) with antioxidants in presence of poly(epsilon-caprolactone)/ poly(N-vinyl-2-pyrrolidone) block copolymer nanoaggregates

The reaction of antioxidants with 2,2-diphenyl-l-picrylhydrazyl (DPPH) has been studied employing both, ethanol and nano aggregates biodegradable block copolymers (BBC) in aqueous solution, as reaction media. Gallate derivatives with different chain lengths (gallic acid, methyl, propyl and octyl gallate) were used as antioxidants model, and BBC containing a central section of poly-epsilon-caprolactone (PCL) and three arms of poly-vinylpirrolidone (PVP) were used to originate nano aggregates in aqueous solution. The course of the reaction was followed by the changes of the DPPH absorption band at 517 nm. In ethanol, using an excess of antioxidants, DPPH was consumed completely by all gallate derivatives. Nevertheless, when the same reaction was carried out in aqueous nano aggregates of BBC, only a partial consumption of DPPH was observed, suggesting the occurrence of a complex reaction mechanism.     

Fabrication and characterisation of multiwalled carbon nanotubes decorated by magnetic Ni nanoparticles

Abstract

Magnetic carbon nanotube (CNT) composites have been successfully fabricated by employing a microwave assisted method after sensitisation and activation. The phase structures and morphologies of the composites were characterised in detail by transmission electron microscope and X-ray powder diffraction. The results show that sensitisation and activation are absolutely necessary for a dense layer of magnetic nanoparticles obtained on the surface of CNTs. Magnetic measurements using a vibrating sample magnetometer demonstrate that the prepared composites are ferromagnetic.     

Preparation and characterization of chitosan/genipin/poly(N-vinyl-2-pyrrolidone) films for controlled release drugs

The study of the physicochemical and functional properties of chitosan films cross-linked with genipin and poly(N-vinyl-2-pyrrolidone) (PVP) was performed in this work. Cross-linked films were prepared by casting method from acetic acid solutions. The structure and physical properties of the films were analyzed by infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹³C NMR), differential scanning calorimetry (DSC) and mechanical testings. Propranolol hydrochloride was used like a model drug to determine the behavior of drug release from films. The drug release capacity was measured and compared with the degree of cross-linking, mechanical properties and swelling index.     

Preparation of poly (vinyl alcohol) fibers strengthened using multiwalled carbon nanotubes functionalized with tea polyphenols

Poly (vinyl alcohol) (PVA) fibers were strengthened using multiwalled carbon nanotubes (MWCNTs) functionalized using a green modifier tea polyphenols (TP). MWCNTs were first modified using TP to increase their dispersity in dimethyl sulfoxide (DMSO)/water solution, and then PVA was added to the dispersion to form new dispersion of PVA/MWCNTs/TP/DMSO/water. The homogeneous dispersion was extruded through a spinning hole into cold methanol to form continuous fibers using gel-spinning process followed by a hot-drawing. The tensile strength of the well-oriented PVA/MWCNTs composite fibers containing merely 0.6 wt% of MWCNTs was surprisingly more than 2.6 times that of pure PVA fiber. Structure characterization showed that well-dispersed MWCNTs were caused by the interfacial interactions between PVA matrix and MWCNTs through the bridge effect of TP.     

Physical properties of CVD boron-doped multiwalled carbon nanotubes

The effects of boron doping and electron correlation on the transport properties of CVD boron-doped multiwalled carbon nanotubes are reported. The boron-doped multiwalled carbon nanotubes were characterized by TEM as well as Raman spectroscopy using different laser excitations (viz. 488, 514.5 and 647 nm). The intensity of the D-band laser excitation line increased after the boron incorporation into the carbon nanotubes. The G-band width increased on increasing the boron concentration, indicating the decrease of graphitization with increasing boron concentration. Electrical conductivity of the undoped and boron-doped carbon nanotubes reveal a 3-dimensional variable-range-hopping conductivity over a wide range of temperature, viz. from room temperature down to 2 K. The electrical conductivity is not found to be changed significantly by the present levels of B-doping. Electron Paramagnetic Resonance (EPR) results for the highest B-doped samples showed similarities with previously reported EPR literature measurements, but the low concentration sample gives a very broad ESR resonance line.     

An efficient method for decoration of the multiwalled carbon nanotubes with nearly monodispersed magnetite nanoparticles

A one-pot method has been developed to prepare magnetite nanoparticles decorated carbon nanotubes (CNTs) by thermal decomposition of iron chloride on CNTs templates in diethylene glycol. The morphological and structural characterizations indicate that magnetite nanoparticles are coated on the surfaces of the CNTs to form CNT-based nanocomposites. The density of magnetite nanoparticles on CNTs could be easily tuned by adjusting the weight ratio of iron chloride to CNTs. Magnetic measurements showed that the nanocomposites are superparamagnetic at room temperature and the magnetic properties of the samples can also be tuned by adjusting preparing conditions. The nanocomposites can be readily dispersed in water to form a stable solution and can be manipulated using an external magnetic field. As-synthesized nanocomposites may have potential applications in target–drug delivery, detection and separations, and in clinical diagnosis.     

Electrorheological properties of poly(acrylonitrile) microspheres coated with multiwall carbon nanotubes

Poly(acrylonitrile) (PAN) particles coated with functionalized multiwall carbon nanotubes (fMCNTs) were prepared and applied to electrorheological (ER) fluids. First, carboxylic acid groups were introduced on the multiwall carbon nanotubes by chemical oxidation method. Then, nitrile groups on the surface PAN particles were modified to amine groups by Co catalysis reaction. Finally, fMCNTs were anchored on the surface of polymer particles by covalent bonding between carboxylic acid groups on fMCNTs and amine groups on particles. fMCNTs attached polymeric microspheres were characterized by scanning electron microscopy and optical microscopy. The ER properties of fMCNTs modified microspheres were measured under controlled electric fields. Although the amount of fMCNTs anchored on the surfaces of microspheres was 1 wt.% of polymers, good ER properties were observed. This improvement may be caused by fMCNTs enhancing the electrical properties of polymer microspheres.     

Rheologic and mechanical properties of multiwalled carbon nanotubes-reinforced poly(trimethylene terephthalate) composites

This paper investigates the rheologic and mechanical properties of melt-blended poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) composites and the effect of acid treatment of MWCNT on these properties. The microstructure of the composites was studied by SEM and TEM in terms of the dispersion state of the nanotubes and the polymer–nanotube interaction. Incorporation of MWCNTs into PTT matrix resulted in an increase in both complex viscosity and moduli than those of neat PTT. A dramatic increase in the melt viscosity of composites observed with loading of MWCNT in the range of 0.5 and 2 wt% showed the formation of interconnected network of MWCNT in the polymer matrix at a rheologic percolation threshold. Acid treatment of MWCNT showed significant effect on the rheologic properties of PTT and led to the enhancement of both complex viscosity and moduli due to strong interfacial interaction between acid-treated MWCNT and PTT matrix. The effect of acid treatment was also evident by mechanical properties of the PTT/MWCNT composites. The untreated MWCNT showed only increase in modulus of PTT matrix; whereas, after acid treatment, both tensile strength and modulus of PTT matrix enhanced significantly.     

多壁碳纳米管/杂萘联苯聚醚砜酮复合材料的制备及性能

采用溶液共混及原位复合法制备多壁碳纳米管/杂萘联苯聚醚砜酮复合材料.通过扫描电镜观察材料的形貌,并对材料性能进行研究.对比两种方法,结果表明通过原位复合法制备,碳管在基体中有较好的分散和界面结合,其力学性能和导电性优于溶液共混法制备的复合材料.当碳管含量为3%(质量分数)时,原位复合材料的拉伸模量和强度分别为2.4GPa和107.6MPa,其体积电阻率达到1.0×106 Ω·cm,5%热失重温度提高了20℃.     

Synthesis and electrochemical probing of water-soluble poly(sodium 4-styrenesulfonate-co-acrylic acid)-grafted multiwalled carbon nanotubes

Water-soluble poly(sodium 4-styrenesulfonate-co-acrylic acid)-grafted multiwalled carbon nanotubes (MWNT-g-P(SSS-co-AA)) with core-shell nanostructure were successfully synthesized by in situ free radical copolymerization of sodium 4-strenesulfonate (SSS) and acrylic acid (AA) in the presence of MWNTs terminated with vinyl groups; their structure was characterized by FTIR, (1)H NMR, Raman, TGA and TEM. The results showed that the thickness and content of the copolymer layer grafted onto the MWNT surface are about 7-12?nm and 82.3%, respectively. The P(SSS-co-AA) covalently grafted on MWNTs provides MWNT-g-P(SSS-co-AA) with good hydrophilicity and solubility in water. Then a novel MWNT-g-P(SSS-co-AA)-modified glassy carbon electrode was fabricated by coating; its electrochemical properties were evaluated by electrochemical probe of K(3)[Fe(CN)(6)], and its catalytic behaviors to the electrochemical oxidation processes of dopamine (DA) and serotonin (5-HT) were investigated. Since the MWNT-g-P(SSS-co-AA)-modified electrode possesses strong electron transfer capability, high electrochemical activity and catalytic ability, it can be used in sensitive, selective, rapid and simultaneous monitoring of biomolecules.     

Variability of the elastic properties of multiwalled carbon nanotubes

The results of numerous experimental investigations of carbon nanotubes show evidence of a considerable variability in their mechanical properties. Based on the common features of the structures of graphite and multiwalled carbon nanotubes (MWNTs), it is demonstrated that structural polytype transitions are among the probable factors responsible for this variability. Analysis of the MWNT behavior under torsion shows that the torsional stiffness of MWNTs depends on the elastic moduli, the number and magnitudes of which vary with the local symmetry of the MWNT structure (on the transition from rhombohedral to hexagonal and turbostratic modifications). The effect of structural transformations on the Young modulus in stretched MWNTs is evaluated.     

Covalent attachment of poly (acrylic acid) onto multiwalled carbon nanotubes functionalized with formaldehyde via electrophilic substitution reaction

The functionalization with formaldehyde via an electrophilic substitution reaction and graft with poly (acrylic acid) (PAA) by “grafting from” technology have been carried out for multiwalled carbon nanotubes (MWNTs) and MWNTs-PAA composites have been formed. The IR and TEM results show presence of covalent band and so-called “core-shell” structures for MWNTs-PAA. The MWNTs-PAA exhibits excellent suspendability in water, which is significant to explore the potential application of carbon nanotube in biological and medical systems.