Nitrogen-doped hollow carbon spheres with enhanced electrochemical capacitive properties

Nitrogen-doped hollow carbon spheres (N-HCS) with uniform size have been synthesized via the hydrothermal method using pyrrole as the precursor. After carbonization at 850 °C, the average diameter of N-HCS is ca. 370 nm with shell thickness of ～15 nm. The electrochemical capacitive behavior of N-HCS was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1.0 M H₂SO₄ aqueous solution. Results show that N-HCS have high specific capacitance (345.2 F g^?1 at 0.2 A g^?1) and high-rate capability with the increase of the scan rate from 10 to 1000 mV s^?1 due to the synergetic effects of the unique hollow nanostructure and the N-doped thin carbon shell. In addition, the capacitance retains 98.1% after 1500 cycles even at a high loading current density of 10 A g^?1.     

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。     

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.     

Electromagnetic and microwave-absorbing properties of magnetite decorated multiwalled carbon nanotubes prepared with poly(N-vinyl-2-pyrrolidone)

The magnetite (Fe₃O₄) decorated multiwalled carbon nanotubes (MWNTs) hybrids were prepared by an in situ chemical precipitation method using poly(N-vinyl-2-pyrrolidone) (PVP) as dispersant. The structure and morphology of hybrids are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron-microscopy (TEM). The TEM investigation shows that the Fe₃O₄/MWNTs hybrids exhibit less entangled structure and many more Fe₃O₄ particles are attached homogeneously on the surface of MWNTs, which indicated that PVP can indeed help MWNTs to disperse in isolated form. The electromagnetic and absorbing properties were investigated in a frequency of 2–18 GHz. The results show that the Fe₃O₄/MWNTs hybrids exhibit a superparamagnetic behavior and possess a saturation magnetization of 22.9 emu/g. The maximum reflection loss is ?35.8 dB at 8.56 GHz, and the bandwidth below ?10 dB is more than 2.32 GHz. More importantly, a new reflection loss peak occurs at the frequency of 14.6 GHz, which indicates that the Fe₃O₄/MWNTs hybrids have better absorption properties in the high-frequency.     

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.     

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.     

Electrodeposition of nickel nanoparticles onto multiwalled carbon nanotubes

The process of nickel nanoparticle nucleation and growth during galvanochemical deposition on the surface of multiwalled carbon nanotubes has been studied. The dependences of the morphology, size, and spacing of nickel nanoparticles on the deposition time at a current density of 5 and 0.5 A/dm² are determined.     

Designed fabrication of hierarchical porous carbon nanotubes/graphene/carbon nanofibers composites with enhanced capacitive desalination properties

Carbonaceous materials, one of the most important electrode materials for sea water desalination, have attracted tremendous attention. Herein, we develop a facile and effective two-step strategy to fabricate hierarchical porous carbon nanotubes/graphene/carbon nanofibers (CNTs/G/CNFs) composites for capacitive desalination application. Graphite oxide (GO), Ni²⁺, and Co²⁺ are introduced into polyacrylonitrile (PAN) nanofibers by electrospinning method. During the annealing process, the PAN nanofibers are carbonized into CNFs felt, while the CNTs grow in situ on the surface of CNFs and graphite oxide are reduced into graphene simultaneously. Benefiting from the unique hierarchical porous structure, the as-prepared CNTs/G/CNFs composites have a large specific surface area of 223.9 m² g^?1 and excellent electrical conductivity. The maximum salt capacity of the composites can reach to 36.0 mg g^?1, and the adsorbing capability maintains a large retention of 96.9% after five cycles. Moreover, the effective deionization time of the CNTs/G/CNFs composites lasts more than 30 min, much better than the commercial carbon fibers (C-CFs) and graphene/carbon nanofibers (G/CNFs) composites. Results suggest that the designed hierarchical porous CNTs/G/CNFs architecture could enhance the capacitive desalination properties of electrode materials. And the possible adsorption mechanism of the novel electrode materials is proposed as well.     

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.     

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。      

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.     

Synthesis and electromagnetic wave absorption properties of multi-walled carbon nanotubes decorated by BaTiO3 nanoparticles

A hybrid composite material, consisting of BaTiO3 and multi-walled carbon nanotubes, was synthesized by an efficient solvent-thermal route. Transmission electron microscopy images clearly indicate that the surfaces of the multi-walled carbon nanotubes were uniformly decorated by well-crystallized BaTiO3 particles, with diameters of 15-30 nm. Electromagnetic wave absorption properties analysis, determined by the electromagnetic parameters measured by a vector network analyzer, shows that the reflection loss in the BaTiO3/multi-walled carbon nanotube composite was higher than that occurring in pure multi-walled carbon nanotubes or BaTiO3 and that was resulted from a better matched characteristic impedance and an enhanced complex permeability in the high frequency, which was improved by the decrease of eddy currents owing to the finite increase in resistivity. The maximum reflection loss of -37.5 dB in the BaTiO3/multi-walled carbon nanotube composite was obtained at a frequency of 10.4 GHz and the absorption range under -10 dB was from 9.6-13.1 GHz range as the absorber thickness was 2 mm.     

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.     

Facile synthesis of copper oxide nanotubes decorated by TiO2 nanoparticles,optical and photocatalytic activity in water

Copper oxide nanotubes decorated by TiO₂ nanoparticles (CNTNs) were fabricated by simple three-step method. First, deposition of copper onto cellulose fibres, then thermal oxidation of copper and cellulose fibres and last simply mixing copper oxide nanotubes and TiO₂ nanoparticles (NPs). Scanning electron microscopy, transmission electron microscopy and X-ray diffraction showed that the synthesised nanotubes were monoclinic-structured polycrystalline CuO with diameter and wall thickness of approximately 50～100 nm and 20～25 nm, respectively. Moreover, the diameter of the TiO₂ NPs is about 20～30 nm. Optical properties of the solutions containing copper oxide nanotubes decorated by TiO₂ NPs were studied. Discrete dipole approximation was used for the calculation of absorption, scattering and extinction cross sections of the deposited CNTNs on a glass substrate. Our simulation results show that there are good agreements between the experimental date and the simulation results. Moreover, the photocatalytic tests were done by methyl orange under visible light (λ = 633 nm) irradiation for prepared samples.     

电场诱导多壁碳纳米管有序排列对多壁碳纳米管/环氧树脂复合材料性能的影响

采用交流（AC）电场诱导法制备了多壁碳纳米管（MWCNTs）均匀分散且定向有序排列的MWCNTs/环氧树脂复合材料。采用SEM、偏振拉曼光谱等研究了电场强度、MWCNTs含量、加电时间及温度（黏度）等因素对MWCNTs定向排列的影响,讨论了MWCNTs有序排列对MWCNTs/环氧树脂复合材料电学和力学性能的影响。结果表明：MWCNTs沿电场方向有序排列;MWCNTs/环氧树脂复合材料施加AC电场后的拉曼强度明显高于未施加电场的情况;当MWCNTs含量从0wt%增加到0.025wt%时,MWCNTs/环氧树脂复合材料导电率从2.3×10^-12 S/cm增加到1.3×10^-8 S/cm,增加了约4个数量级;MWCNTs含量为2.5wt%时,MWCNTs/环氧树脂复合材料拉伸强度提高了26.3%。     

Acoustic properties of polyurethane compositions enhanced with multi‐walled carbon nanotubes and silica nanoparticles

In this study, in order to enhance acoustic properties of polyurethane (PU) foams multi‐walled carbon nanotubes (MWCNT) and/or silica nanoparticles were added to polyol‐isocyanate composition up to 2 wt%, and acoustic properties of polyurethane foam samples with small amount of carbon nanotubes and silica nanoparticles (spherical and/or amorphous types) were determined in the frequency range from 50 Hz up to 6400 Hz. Acoustic properties, especially absorption coefficient of the produced samples were measured for all the prepared samples and results were investigated to come up with the best polyurethane samples that can be applied for sound absorption application at the desired frequency range. It was found that double combination of carbon nanotubes and silica nanoparticles, especially 0.7 wt% carbon nanotubes and 0.2 wt% spherical silica nanoparticle added polyurethane composition has better sound absorption ratio overall all frequencies levels compared to the other samples. Thus, it is possible to obtain polyurethane nanocomposite with a higher amount of carbon nanotube by weight at the same time enhancing sound absorption properties. Moreover, there is a synergic effect between carbon nanotubes and silica nanoparticles when mixed and added into polyurethane matrix at predetermined levels to get enhanced acoustic response with a higher level of carbon nanotube in polyurethane foam.     

纳米铜修饰多壁碳纳米管/石蜡相变驱动复合材料的制备及热性能

以油胺为分散稳定剂,在石蜡中热分解甲酸铜-碳纳米管复合物前驱体,单步制备了纳米铜修饰多壁碳纳米管(Cu-MWCNTs)/石蜡复合材料。通过XRD、TEM和DSC对Cu-MWCNTs/石蜡复合材料的物相、微观形貌及相变行为进行了表征和分析,并对其热敏性、热膨胀性和热稳定性及影响因素进行了分析研究。结果表明:纳米Cu原位沉积在MWCNTs外壁上,粒径为2~35nm。与纯石蜡相比,Cu-MWCNTs/石蜡复合材料的相变温度和相变潜热均明显降低。Cu-MWCNTs含量为0.2wt%的Cu-MWCNTs/石蜡复合材料具有较短的升温时间,体膨胀率降低较小,且多次加热后稳定性较好,可作为此类热敏微驱动器的理想材料。     

多壁碳纳米管对单质硫正极材料电化学性能的改性

为增强单质硫电极的导电性能和抑制活性硫在电解液中的溶解,选用高比表面积、强吸附能力的多壁碳纳米管作为非活性添加剂,通过密封分段加热的方式与单质硫形成复合材料。X射线衍射(XRD)、扫描电子显微镜(SEM)和比表面积(BET)测试均表明单质硫均匀分散到碳纳米管基体中。电化学测试显示添加碳纳米管的硫电极首次放电比容量高达1 487.0mAh.g-1,硫的利用率达到了88.9%,循环50次后比容量还保持在913.7mAh.g-1,较之普通硫电极其电化学性能得到显著改善。     

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.     

Synthesis and thermal transport studies of nanofluids based on metal decorated photochemically oxidized multiwalled carbon nanotubes

Nanoparticle fluid suspensions were prepared using photochemically functionalized multiwalled carbon nanotubes in polar base fluids. Multiwalled carbon nanotubes prepared by catalytic chemical vapour deposition technique have been functionalized by irradiating with ultraviolet light of wavelength 254 nm. The photochemical oxidation of multiwalled carbon nanotubes under UV irradiation introduces oxygen containing functional groups onto the surface of the nanotubes, generating new defects on their structure. Silver nanoparticles have been deposited over multiwalled carbon nanotubes by chemical method. The enhancement in thermal conductivity of the prepared nanofluids using functionalized multiwalled carbon nanotubes and Ag nanoparticles deposited functionalized multiwalled carbon nanotubes with volume fraction, temperature and aspect ratio has been demonstrated. Silver deposited functionalized multiwalled carbon nanotubes based nanofluids in DI water with 0.02% volume fraction exhibit a thermal conductivity enhancement of 9.9% and 47% at room temperature and at 50 degrees C respectively.