Hydrodesulphurisation activity of CoMo catalyst supported on multi wall carbon nanotube: sulphur species study

Multi wall carbon nanotube (MWCNT) supported CoMo catalyst was prepared and hydrodesulphurisation (HDS) activity of naphtha was evaluated in a fixed bed down flow reactor. Activity test experiments were conducted at a temperature of 310°C, pressure of 15?bar and liquid hourly space velocity of 4/h. The conditions were close to those of industrial practice. The structure of the MWCNT was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and accelerated surface area and porosity system (ASAP). The catalyst was characterised by X-ray diffraction, SEM, energy dispersive X-ray, inductively coupled plasma optical emission spectrometry, TEM and ASAP. Also for sulphur species study, naphtha feed and product were analysed by gas chromatography–sulphur chemiluminescence detection. Catalytic activity test indicated that MWCNT is a suitable support for HDS catalyst. Sulphur conversion of the catalyst was 88%. Also sulphur species comparison showed that all the sulphur types were converted.     

Metal-decorated multi-wall carbon nanotubes for low temperature gas sensing

We investigate the possibility of using, as a gas sensitive material, multi-walled carbon nanotubes (MWCNT) covered with gold or silver nanoclusters deposited by thermal evaporation. Metal-decorated MWCNT were dispersed in an organic vehicle, micro-deposited onto silicon micro-machined sensor substrates and subsequently annealed to remove the organic vehicle. The resulting sensors are shown to be sensitive to NO₂ when operated at room temperature and significantly more selective than sensors based on MWCNT without metal nanoclusters attached to their surface.     

RGO–MWCNT–ZnO based polypyrrole nanocomposite for ammonia gas sensing

Polypyrrole (PPy) nanocomposites were synthesized using ferric chloride (FeCl₃) as an oxidant by in situ polymerization at room temperature in which reduced graphene oxide- multi-walled carbon nanotubes (RGO–MWCNT) and zinc oxide (ZnO) were used as fillers. RGO–MWCNT and ZnO were synthesized by solution mixing and surfactant assistant precipitation respectively. The RGO–MWCNT–ZnO /PPy nanocomposites were prepared by loading 2, 5, 10 and 20 wt% of RGO–MWCNT:ZnO (1:1) in PPy to measure the electrical conductivity. The PPy nanocomposites were characterized by using FTIR, X-ray diffraction and FESEM. Furthermore, these RGO–MWCNT–ZnO/PPy nanocomposites were investigated to study sensing of ammonia gas at room temperature. The response of 20 wt% loading RGO–MWCNT–ZnO/PPy was observed to be 325% towards 200 ppm of ammonia gas.     

Sn/SnO2/Mwcnt composite anode and electrochemical impedance spectroscopy studies for Li-ion batteries

Tin/tinoxide/multi-walled carbon nanotube (Sn/SnO₂/MWCNT) core-shell structure nanocomposite anode is produced by thermal evaporation and subsequent plasma oxidation with using MWCNT buckypaper. Metallic tin is evaporated onto free-standing and flexible MWCNT buckypaper having controlled porosity and subsequent RF plasma oxidized in Ar:O₂(1:1) gas mixture. X-ray diffraction and scanning electron microscopy are used to determine the structure and morphology of the obtained nanocomposite. The electrochemical characteristics of the nanocomposite anode are examined by using electrochemical impedance spectroscopy and galvanostatic charge–discharge experiments. Family of Nyquist plots during first discharge process are obtained and studied at different voltage values.     

Sonication-assisted preparation of pristine MWCNT-polysulfone conductive microporous membranes

Conductive microporous membranes were fabricated by the phase inversion technique from pristine multiwalled carbon nanotubes (MWCNT)-polysulfone mixtures. A sonication-assisted method was used to disperse MWCNT in the polysulfone matrix without a covalent modification of the MWCNT or the use of surfactants. Electron Microscopy (SEM) and conduction tests were used to characterize the membranes. SEM pictures indicated that a concentration of 3% of MWCNT allowed a good dispersion of the nanotubes inside the hydrophobic polysulfone matrix. Current-voltage tests showed efficient electron percolation pathways across the membrane as a result of the successful dispersion of pristine MWCNT. These membranes will be applied in separation of charged species where microfiltration together with application of electric fields is needed.     

碳基采暖电热材料研究进展

近几年,由于节能与环保的需求,电取暖的方式得到大力的推广,电热材料的研究与应用受到人们广泛的重视。非金属碳基电热材料是新型的节能型电热采暖材料,本文重点对影响非金属碳基电热材料中的炭黑基电热材料、碳纤维基电热材料、碳晶电热材料电热性能的因素及相关应用进行了综述。     

Macrodispersion of multi-walled carbon nanotubes for conductive films

Understanding of the effect of the multi-walled carbon nanotube (MWCNT) dispersion process on physical properties of MWCNT film is crucial in process optimization of MWCNT film-based products. In the present work, the electrical conduction property of MWCNT films according to various conditions in MWCNT dispersion is investigated. Spectroscopic analysis of dispersed MWCNTs show that the electrical resistance of the MWCNT conductive film is affected by an increase in the electrical contacts between adjacent CNTs due to CNT debundling and physical damage caused by ultrasonic processing. Based on the two conflicting parameters, dispersion guidelines for highly conductive MWCNT film are presented.     

Scavenging phenomenon and improved electrical and mechanical properties of polyaniline–divinylbenzene composite in presence of MWCNT

A semi-doped polyaniline (PANI)–dodecylbenzenesulfonic acid (DBSA) complex is added with a suspension of multiwall carbon nanotubes (MWCNT)–divinylbenzene (DVB) to prepare PANI–MWCNT based thermosetting conductive resin system. Firstly, unreinforced nanocomposites with various loading of MWCNT are prepared. Continuous improvement in the electrical conductivity is observed with increasing MWCNT loading in the composite, while improvement in the mechanical properties is observed only up to 0.2 wt% MWCNT loading. On further MWCNT loading, the decrease in mechanical properties is observed. Flexural strength increased by 18% with 0.2 wt% of MWCNT in the unreinforced nanocomposite while electrical conductivity increased continuously to 0.68 S/cm (at 0.5 wt% of MWCNT loading) from 0.25 S/cm (neat sample). DSC and TGA analysis show that MWCNT effectively contributed to enhance the scavenging effect of PANI, affecting degree of DVB polymerization at higher loading of MWCNT. Samples were characterized by FTIR analysis. DMA analysis is also performed to understand the mechanical behavior of the cured unreinforced nanocomposite under dynamic loading. SEM observation has been employed to understand the dispersion behavior of MWCNT into the matrix. PANI-wrapping behavior on MWCNT is observed from the SEM images. Wrapping of PANI on MWCNT increased doping state and surface area of PANI which subsequently contribute to the increased scavenging behavior of PANI at higher MWCNT loading. A structural thermosetting nanocomposite with electrical conductivity of 0.68 S/cm, flexural modulus of 1.87 GPa and flexural strength up to 35 MPa is prepared. In addition, PANI–DBSA/DVB matrix with MWCNT is also used to impregnate carbon fabrics to prepare highly conductive CFRPs. A CFRP with 1.67 S/cm electrical conductivity in through-thickness direction and 328 MPa flexural strength is obtained with the addition of 0.2 wt% MWCNT into the resin system.     

Highly concentrated carbon nanotube admixture for nano-fiber reinforced cementitious materials

The use of effectively dispersed multiwalled carbon nanotube (MWCNT)/aqueous/surfactant suspensions in cement based materials have been shown to substantially improve their mechanical properties. The produced MWCNT suspensions have a high aqueous content, which corresponds to the mixing water. In the present work, a method for preparing highly concentrated MWCNT suspensions is presented, thus reducing the volume of the resulting admixture that is required in cement based materials. A centrifugal process, that uses two different ultracentrifuge rotors, was employed to reduce the quantity of water in the suspensions. Optical absorbance spectroscopy shows that the ultracentrifugation process increases the concentration of the MWCNT suspensions by a factor of 5. Using the highly concentrated MWCNT suspensions following dilution results in nanocomposites with mechanical properties that are comparable to the performance of samples prepared using the non-concentrated suspensions. These results verify that the ultracentrifugation concentration method successfully preserves the solubility of the MWCNT suspensions without affecting the reinforcing properties of the admixture. In this manner, the ultracentrifugation concentration method may constitute an effective preparation step for large-scale implementation of MWCNT admixtures.     

MWCNT/PEDOT复合材料的微观结构和热电性能

热电转换技术能将大量的废弃热能转换为电能以重新利用,是一种绿色能源转换技术,可以有效提高能源利用效率,缓解煤炭、石油等主要化石类能源过度开采、使用带来的能源危机及环境污染问题,因此受到科研工作者的广泛关注,是近年来的研究热点。基于此,本文以电子型导电高聚物中机能较优的聚(3, 4-乙烯二氧噻吩)(PEDOT)作为研究主体,通过化学原位氧化聚合将多壁碳纳米管(MWCNT)复合到载体中得到MWCNT/PEDOT复合材料。利用XRD、拉曼、TEM及正电子湮没寿命(PAL)等方法对MWCNT/PEDOT复合材料的形貌和微观结构进行了系统研究,研究表明:当MWCNT含量高于24.9wt%时,复合材料中出现MWCNT团聚现象,其分散性变差。同时,MWCNT/PEDOT复合材料的热电性能测试结果显示,未掺杂PEDOT的电导率仅为7.5 S·m?1,而MWCNT含量为30.1wt%时,该复合材料的电导率高达566.59 S·m?1,提高近76倍。同时,30.1wt%MWCNT/PEDOT的功率因子(814.3×10?4 μW·(m·K2)?1)相对于未掺杂PEDOT(14.5×10?4 μW·(m·K2)?1)提高约56倍,这主要是由于PEDOT分子链与MWCNT掺杂物间π-π相互作用及MWCNT的高导电性。随着MWCNT含量的增加,PAL测试结果中第一寿命成分τ₁(即正电子在材料中湮没的第一寿命成分)的下降证实了该复合材料中MWCNT与PEDOT间界面变小或者界面间相互作用减弱,导致其热导率相对于未掺杂PEDOT有一定的上升,但远远低于功率因子的升高。最终,该MWCNT/PEDOT复合材料的热电优值(即热电材料Z_T值)由0.015×10?4升至0.45×10?4,增加了约30倍。结果表明:掺杂的高电导率MWCNT能够极大地提高PEDOT类电子型导电聚合物的热电性能。      

The Effect of Hydrothermal Aging on the Low-Velocity Impact Behavior of Multi-Walled Carbon Nanotubes Reinforced Carbon Fiber/Epoxy Composite Pipes

Chemical transmission lines, petroleum and natural gas lines, pressure vessels, and pipes used in thermal facilities are expected to maintain their mechanical properties for many years without being damaged and not to be corroded in working conditions. The composite materials are the right candidate for these harsh conditions due to their superior properties. Reinforcement of nanoadditives to composite materials improves both the mechanical properties and the resistance to environmental conditions, thereby increasing the lifetime. In this study, multi-walled carbon nanotube (MWCNT) reinforced [±?55°] carbon fiber/epoxy composite pipes produced with filament wound method were used. It was hydrothermally aged in 80 °C distilled water for 1, 2, 3 weeks in order to examine the effect of environmental conditions. In order to investigate its resistance against loads that may occur in working conditions, ring tensile tests (ASTM D 2290–16 procedure A), and low-velocity impact tests at 5, 10, 15 J, energy levels were carried out. The effect of hydrothermal aging on neat and MWCNT added epoxy composite had been examined by considering the aging period. Consequently, the impact resistance of neat and MWCNT added samples decreased with the aging process. Besides, tangential tensile strength loss was 17% in MWCNT reinforced sample and 13% in the neat sample.

     

Synthesis and characterization of conductive polypyrrole/multi-walled carbon nanotubes composites with improved solubility and conductivity

High conductivity and solubility of polypyrrole (PPy)/multi-walled carbon nanotubes (MWCNT) composites has been successfully synthesized by in situ chemical oxidation polymerization using various concentrations of cationic polyelectrolyte poly(styrenesulfonate) (PSS) and ammonium peroxodisulfate (APS). Raman spectroscopy, FTIR, EPR, FESEM and HRTEM were used to characterize their structure and morphology. These images of FESEM and HRTEM showed that the fabricated PPy/MWCNT composites are one-dimensional core-shell structures with the average thickness of the PPy/MWCNT composites without PSS is about 250 nm and considerably decreases to 100–150 nm by adding the PSS content. The results of Raman spectrum, FTIR and UV–Vis indicate the synthesized PPy/MWCNT composites are in the doped state. The conductivities of PPy/MWCNT composites synthesized with the weight ratio of PSS/pyrrole monomer at 0.5 are about two times of magnitude higher than that of PPy/MWCNT composites without PSS. These results are perhaps due to the part of cationic electrolyte served as a dopant can be incorporated to the PPy structure to improve the conductivity of fabricated PPy/MWCNT composites.     

The effect of multiwall carbon nanotubes on the in-plane shear behavior of epoxy glass fiber reinforced composites

In this study, we investigate how multi-wall carbon nanotubes (MWCNTs) affect the in-plane shear mechanical behavior of glass fiber/epoxy composite. These multi-scale composites are fabricated using vacuum infusion: pristine MWCNT and amino-functionalized MWCNT are incorporated into epoxy resins at concentrations of both 0.1 and 0.3 wt.% and are subsequently evaluated. The MWCNT are mixed into the resins by mechanical stirring and sonication prior to resin infusion, and the MWCNT distribution in the cured laminate is then evaluated by performing a heat conduction assessment. Monotonic and cyclic quasi-static room temperature in-plane shear tests are performed following the ASTM D 4255 standard. The initial shear modulus, the deterioration of the shear modulus during plastic deformation and material hardening are evaluated. Incorporating MWCNT into the resins did not affect the parameters investigated under the imposed conditions.     

Effect of surface functionalization on mechanical properties and decomposition kinetics of high performance polyetherimide/MWCNT nano composites

In this investigation, Polyetherimide (PEI) reinforced with multi-walled carbon nanotube (MWCNT) using novel melt blending technique. Surface of MWCNTs are modified by acid treatment as well as by plasma treatment. PEI nano composites with 2 wt% treated MWCNT shows about 15% improvement in mechanical properties when compared to unfilled PEI. The thermal decomposition kinetics of PEI/MWCNT nano composites has been critically analyzed by using Coats – Redfern model. The increase in activation energy for thermal degradation by 699 kJ/mol for 2 wt% MWCNT implies improvement in the thermal properties of PEI. Studies under Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM) depict significant interfacial adhesion with uniform dispersion of MWCNT in polymer matrix due to surface functionalization. 0.5 wt% chemically modified MWCNT shows typical alignment of MWCNT. There is a significant improvement in mechanical properties and thermal properties for surface functionalized MWCNT reinforced.     

Fabrication of a room-temperature NO2 gas sensor based on WO3 films and WO3/MWCNT nanocomposite films by combining polyol process with metal organic decomposition method

Polyol process was combined with metal organic decomposition (MOD) method to fabricate a room-temperature NO₂ gas sensor based on a tungsten oxide (WO₃) film and another a nanocomposite film of WO₃/multi-walled carbon nanotubes (WO₃/MWCNTs). X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the structure and morphology of the fabricated films. Comparative gas sensing results indicated that the sensor that was based on the WO₃/MWCNT nanocomposite film exhibited a much higher sensitivity than that based on a WO₃ film in detecting NO₂ gas at room temperature. Microstructural observations revealed that MWCNTs were embedded in the WO₃ matrix. Therefore, a model of potential barriers to electronic conduction in the composite material was used to suggest that the high sensitivity is associated with the stretching of the two depletion layers at the surface of the WO₃ film and at the interface of the WO₃ film and the MWCNTs when detected gases are adsorbed at room temperature. The sensor that is based on a nanocomposite film of WO₃/MWCNT exhibited a strong response in detecting very low concentrations of NO₂ gas at room temperature and is practical because of the ease of its fabrication.     

A review of procedures of purification and chemical modification of carbon nanotubes with bromine

In this paper, bromination methods of three morphological forms of carbon nanotubes (CNT): single-walled, double-walled and multi-walled, are reviewed along with their characteristics and purification protocols using liquid bromine. Different functionalization methods of the CNT with bromine in the liquid, gas and plasma phases, using electrochemical and electrothermal method, under microwave conditions in the presence of Lewis acids or radical precursors are also discussed.     

Surface coating of multi-walled carbon nanotube nanopaper on shape-memory polymer for multifunctionalization

We are presenting a method of synthesizing three-dimensional self-assembled multi-walled carbon nanotube (MWCNT) nanopaper on hydrophilic polycarbonate membrane. The process is based on the very well-defined dispersion of nanotube and controlled pressure vacuum deposition procedure. The morphology and structure of the nanopaper are characterized with scanning electronic microscopy (SEM) over a wide range of scale sizes. A continuous and compact network observed from the microscopic images indicates that the MWCNT nanopaper could have highly conductive property. As a consequence, the sensing properties of conductive MWCNT nanopaper are characterized by functions of temperature and water content. Meanwhile, in combination with shape-memory polymer (SMP), the conductive MWCNT nanopaper facilitates the actuation in SMP nanocomposite induced by electrically resistive heating. Furthermore, the actuating capability of SMP nanocomposite is utilized to drive up a 5-gram mass from 0 to 30 mm in height.     

Effect of MWCNT alignment on mechanical and self-monitoring properties of extruded PET–MWCNT nanocomposites

Self-monitoring aligned MWCNT loaded PET composites, with different CNT content, were prepared via twin-screw extrusion starting from a PET/MWCNT masterbatch, and fully characterized. All electrically conductive samples showed self-monitoring ability, i.e. a variation in electrical resistance as a function of stress. Moreover, the insertion of MWCNTs resulted in mechanical reinforcement with respect to neat PET. It was found that both self-monitoring behavior and mechanical performance are directly related to MWCNT content and to the direction of applied stress with respect to CNT orientation. In particular, too high MWCNT content decreased sensitivity at low strain, whereas a minimum MWCNT content was required to insure ohmic conductivity.     

The influence of nanoadhesives on the tensile properties and Mode-I fracture toughness of bonded joints

Nanoadhesives of epoxy resin are synthesized and evaluated. They are organically modified by multiwalled carbon nanotubes (MWCNT) (1% by weight) as reinforcement. Tensile tests are conducted on multiple identical unnotched and notched specimens to evaluate the overloading and fracture behavior of the nanoadhesives and are compared with the neat epoxy resin. In comparison with the neat epoxy, it is found that the 1% MWCNT reinforcement increased the ultimate and residual strength by about 29% and 56%, respectively. In comparison with the neat resin, there is a 265% increase in the fracture toughness of the MWCNT adhesive. Fracture surface analysis revealed the various mechanisms by which the MWCNT adhesives acquire their superior strength and toughness in comparison with the neat resin.     

New approach to model the buckling and stable length of multi walled carbon nanotube probes near graphite sheets

Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out for the first time via two analytical approximation methods as well as a numerical one. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. In addition, minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers.