Combination effect of carbon nanotubes with graphene on intumescent flame-retardant polypropylene nanocomposites

A novel polypropylene (PP) nanocomposite was fabricated by the incorporation of intumescent flame retardant (IFR), carbon nanotubes (CNTs) and graphene into the PP matrix. Results from TEM indicate that IFR, CNTs and exfoliated graphene nanosheets are dispersed finely in the PP matrix, which is supported by the XRD analysis results. Thermogravimetric (TGA) results show that the addition of IFR, CNTs and graphene improved the thermal stability and the char yields of PP. The PP/IFR/CNTs/RGO nanocomposites, filled with 18 wt% IFR, 1 wt% CNTs and 1 wt% graphene, achieve the limiting oxygen index value of 31.4% and UL-94 V0 grade. Cone calorimeter data reveal that combustion behavior, heat release rate peak (PHRR) and average specific extinction area (ASEA) of PP decrease substantially when combination effects of IFR, CNTs and graphene intervene. For the PP/IFR/CNTs/RGO nanocomposites, the PHRR exhibits an 83% reduction and the time of ignition is delayed 40 s compared with neat PP.     

Eco-friendly polyvinyl alcohol (PVA)/bamboo charcoal (BC) nanocomposites with superior mechanical and thermal properties

Carbon-based nanofillers, such as carbon nanotubes (CNTs) and graphene sheets are considered as effective nanoreinforcements due to their unique structures and material performance. However, the utilisation of such nanofillers can be hindered owing to a high level of nanotoxicity via human inhalation and high material cost for CNTs, as well as the tendency to form agglomerates of graphene sheets in polymer matrices. Bamboo charcoals (BCs) are eco-friendly and sustainable carbon-based particles, which possess good affinity with polyvinyl alcohol (PVA), one of popular water soluble biopolymers, to achieve excellent properties of PVA/BC nanocomposites. In particular, porous structures of BC particles enable polymeric molecules to easily penetrate with the strong internal bonding. In this study, fully eco-friendly PVA/BC nanocomposite films were successfully fabricated using a simple solution casting method to achieve the high dispersibility of BCs. With the inclusion of only 3 wt% BCs, tensile modulus and tensile strength of PVA/BC nanocomposite films were enhanced by 70.2 and 71.6%, respectively, when compared with those of PVA films. Better thermal stability is manifested for resulting nanocomposite films as opposed to that of pristine PVA, which is evidenced by the maximum increase of 17.8% in the decomposition temperature at the weight loss of 80%. It is anticipated that BCs can compete against conventional carbon-based nanofillers with a great potential to be developed into eco-friendly nanocomposites used for thin-film packaging application.     

Hybrids of carbon nanotubes and graphene/graphene oxide

This paper reviews recent progress in hybrids based on carbon nanotubes (CNTs) and graphene (G) or graphene oxide (GO). The combination of CNTs, including single-walled (SW), double-walled (DW) and multi-walled (MW), and G or GO resulted in various hybrids. CNTs–G/GO hybrid thin films are usually prepared by using solution/suspension casting and layer-by-layer (LbL) deposition, free-standing sheets are fabricated by using vacuum filtration and 3D hierarchical structures are produced by using chemical vapor deposition (CVD). CNTs–G/GO hybrids have also been used as fillers to fabricate polymer composites with synergistic effects. The composites have significantly improved electrical, mechanical and thermal properties, which make them very useful for various potential applications, such as transparent electrodes replacing ITO, electrodes for supercapacitors, lithium-ion batteries and dye-sensitized solar cells.     

Influence of Fe nanoparticles diameters on the structure and electron emission studies of carbon nanotubes and multilayer graphene

In this paper we report the effect of Fe film thickness on the growth, structure and electron emission characteristics of carbon nanotubes (CNTs) and multilayer graphene deposited on Si substrate. It is observed that the number of graphitic shells in carbon nanostructures (CNs) varies with the thickness of the catalyst depending on the average size of nanoparticles. Further, the Fe nanoparticles do not catalyze beyond a particular size of nanoclusters leading to the formation of multilayer graphene structure, instead of carbon nanotubes (CNTs). It is observed that the crystallinity of CNs enhances upon increasing the catalyst thickness. Multilayer graphene structures show improved crystallinity in comparison to CNTs as graphitic to defect mode intensity ratio (I_D/I_G) decreases from 1.2 to 0.8. However, I_2D/I_G value for multilayer graphene is found to be 1.1 confirming the presence of at least 10 layers of graphene in these samples. CNTs with smaller diameter show better electron emission properties with enhancement factor (γ_C = 2.8 × 10³) in comparison to multilayer graphene structure (γ_C = 1.5 × 10³). The better emission characteristics in CNTs are explained due to combination of electrons from edges as well as centers in comparison to the multilayer graphene.     

Defective carbon nanotubes with stone-wales defect arrays

Presented herein are the structural and electronic properties of defective (n, n) carbon nanotubes (CNTs) (n = 3, 4, 5, 6) and of a defective graphene sheet, obtained form first-principles calculations of their electronic band strucutres. CNTs are newly discovered nanostructures with promising electronic and structural properties desired for nanoscale device applications. To enhance their functionality, various methods, such as ion implantation and ion irradiation, have been suggested for the manipulation of single-wall CNTs (SWNTs). In this study, periodic Stone-Wales defect arrays were considered. Defective (n, n) CNTs and a defective graphene sheet were analyzed in terms of their geometries and defect formation energies. In particular, the defective (5, 5) CNT was compared with the C60 fullerene and the perfect (5, 5) CNT in polygon structures and total energies. The electronic band structures via first-principles calculations were also analyzed. A significant difference was found between the electronic band structures determined via first-principles calculations and those determined with the use of a one-parameter tight-binding model.     

New procedure for preparation of highly stable and well separated carbon nanotubes in an aqueous modified polyacrylonitrile

Carbon nanotubes (CNTs) due to their nonreactive surface can not effectively disperse in polymeric matrix. Efficient exploitation of CNTs properties to improve material performance is generally related to the degree of dispersion, saturation by the matrix and interfacial adhesion. In order to obtain a suitable dispersion, the CNTs usually need treatment before they can be utilized. In this work, an easy procedure for preparation a stable dispersion of well separated and individual CNTs in an aqueous polymeric solution by using of Gum Arabic (GA) and modified polymer has been described. The applied polymer was a modified water soluble acrylonitrile polymer. The modification was carried out through functionalizing polyacrylonitrile by 2‐aminoethanol. Individual dispersion of the CNTs in the aqueous GA solution after two month can be observed. By incorporating the modified polyacrylonitrile to the solution, the stability of the individual CNTs dispersion several times was increased in such a way that after six month, the CNTs were still kept at their individual positions. According to the suggested mechanism of dispersion, hydrogen bonds between GA/CNTs and the modified polyacrylonitrile chains can be formed that increasing the dispersion ability. The effects of salts and temperature on dispersion ability of GA were also studied.     

Significant improvement in static and dynamic mechanical properties of graphene oxide–carbon nanotube acrylonitrile butadiene styrene hybrid composites

Herein, hybridization of graphene nanosheets and carbon nanotubes (CNTs) has been made to solve the problem of restacking of graphene nanosheets and agglomeration of CNTs. The multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (RGO) and graphene oxide–carbon nanotubes (GCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites have been prepared using micro-twin-screw extruder. The effect of these reinforcements on static and dynamic mechanical properties of composites is studied. The ultimate tensile strength and elastic modulus for 7 wt.% GCNT–ABS composites show enhancement of 26.1 and 71.3% over pure ABS matrix, respectively. Various parameters such as coefficient “C” factor (the ratio of storage modulus of the composite to polymer in glassy and rubbery regions), degree of entanglement, crosslink density and adhesion factor have been calculated to analyze the interaction between fillers and polymer matrix. The 3-D hybrid structure of GCNTs overcomes the associated problem of CNTs agglomeration and graphene restacking. GCNT hybrid composites show higher dispersion as well as effectiveness for increased filler amount as compared to RGO and MWCNTs based composites. GCNTs prove its superiority over MWCNTs and RGO by showing a synergistic effect in the glass transition temperature and storage modulus. Raman spectroscopy and scanning electron microscopy are used to confirm the interaction and distribution of the filler and matrix, respectively.     

Hybrid network structure and thermal conductive properties in poly(vinylidene fluoride) composites based on carbon nanotubes and graphene nanoplatelets

A small quantity of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were introduced into the poly(vinylidene fluoride) (PVDF)/GNP and PVDF/CNT composites, respectively, to prepare the corresponding ternary PVDF/CNT/GNP and PVDF/GNP/CNT composites. The results demonstrated that adding CNTs into the PVDF/GNP composites greatly promoted the formation of the hybrid network structure of fillers. This was much different from the scenario that adding GNPs into the PVDF/CNT composites. GNPs and CNTs exhibited excellent nucleation effects for the crystallization of PVDF matrix; however, the variation of the PVDF crystallinity was small. Adding CNTs into the PVDF/GNP composites greatly enhanced the electrical conductivity of the PVDF/CNT/GNP composites. This was also different from the scenario of the PVDF/GNP/CNT composites. Furthermore, the PVDF/CNT/GNP composites exhibit higher thermal conductivity and higher synergistic efficiency compared with the PVDF/GNP/CNT composites. The conductive mechanisms and the synergistic effects of the ternary composites were then analyzed.     

A Novel Multiscale Reinforcement by In-Situ Growing Carbon Nanotubes on Graphene Oxide Grafted Carbon Fibers and Its Reinforced Carbon/Carbon Composites with Improved Tensile Properties

In-situ growing carbon nanotubes(CNTs)directly on carbon?bers(CFs)always lead to a degraded tensile strength of CFs and then a poor?ber-dominated mechanical property of carbon/carbon composites(C/Cs).To solve this issue,here,a novel carbon?ber-based multiscale reinforcement is reported.To synthesize it,carbon?bers(CFs)have been?rst grafted by graphene oxide(GO),and then carbon nanotubes(CNTs)have been in-situ grown on GO-grafted CFs by catalytic chemical vapor deposition.Characterizations on this novel reinforcement show that GO grafting cannot only nondestructively improve the surface chemical activity of CFs but also protect CFs against the high-temperature corrosion of metal catalyst during CNT growth,which maintains their tensile properties.Tensile property tests for unidirectional C/Cs with different preforms show that this novel reinforcement can endow C/C with improved tensile properties,32% and 87%higher than that of pure C/C and C/C only doped with in-situ grown CNTs.This work would open up a possibility to fabricate multiscale C/Cs with excellent global performance.     

Thermal behavior of functionalized conventional polyaniline with hydrothermally synthesized graphene/carbon nanotubes

Abstract

Conventional polyaniline (PANI) was mixed as a binder polymer matrix with carbonous materials. Hydrothermal technique was utilized to fabricate a nanocomposite of graphene (G)/carbon nanotubes (CNTs). The morphological features and quality of the synthesized PANI, G/CNTs, and their mixtures were investigated. Scanning electron microscopy (SEM) images confirm the formation of wide area graphene sheets with folds around the edges. In addition, the hydrothermally fabricated G/CNTs exhibited a uniform distribution with partial agglomeration. However, adding their mixture to PANI generated a mesh like porous morphology which demonstrates an enhancement in surface area and providing 3D conduction network. Moreover, Raman spectra confirm the quality of the synthesized samples. The generated disorder and defects within the structure, and the ratio of quinoid ring (Q) to benzenoid (B) ring in the fabricated samples were depicted. In addition, the enhancement in thermal parameters and reversing the thermo-electric carrier type into N-type after doping were attributed to the generated facile conduction paths of G/CNTs.     

The Regulating Role of Carbon Nanotubes and Graphene in Lithium‐Ion and Lithium–Sulfur Batteries

The ever‐increasing demands for batteries with high energy densities to power the portable electronics with increased power consumption and to advance vehicle electrification and grid energy storage have propelled lithium battery technology to a position of tremendous importance. Carbon nanotubes (CNTs) and graphene, known with many appealing properties, are investigated intensely for improving the performance of lithium‐ion (Li‐ion) and lithium–sulfur (Li–S) batteries. However, a general and objective understanding of their actual role in Li‐ion and Li–S batteries is lacking. It is recognized that CNTs and graphene are not appropriate active lithium storage materials, but are more like a regulator: they do not electrochemically react with lithium ions and electrons, but serve to regulate the lithium storage behavior of a specific electroactive material and increase the range of applications of a lithium battery. First, metrics for the evaluation of lithium batteries are discussed, based on which the regulating role of CNTs and graphene in Li‐ion and Li–S batteries is comprehensively considered from fundamental electrochemical reactions to electrode structure and integral cell design. Finally, perspectives on how CNTs and graphene can further contribute to the development of lithium batteries are presented.     

新型纳米碳基吸波复合材料的研究进展

新型碳纳米材料(如石墨烯、碳纳米管)因独特的微观结构及优异的介电性能,在电磁屏蔽及吸波领域受到了广泛关注。结合国内外研究情况,综述了碳基聚合物、碳基金属以及多元碳基吸波复合材料制备及性能的最新研究进展,并展望了新型碳纳米材料在吸波材料中应用的发展方向。     

Deformation and fracture in graphene nanosheets

Graphene nanosheets (GNSs) are flake-like materials composed of few-layer graphene sheets. GNSs are similar to multi-walled carbon nanotubes (CNTs) in graphene structures and in layer numbers. However, GNSs and CNTs behave very differently in deformation and fracture. In this study, natural graphite flakes were employed to make expanded graphite (EG), which is composed of partially connected GNSs. Both sonication and three-roll milling were used to separate the GNSs and to disperse them into an epoxy resin. By compacting EG, the GNSs inside were compressed and deformed. By breaking the GNS/epoxy composite, most GNSs on the cracked surfaces were fractured. Both SEM and TEM have been used for microscopic observations. The micrographs revealed that folding and wrinkling are the major modes of deformation, while tearing and peeling are the dominant modes of fracture. These modes are virtually non-existent in CNTs. The factors to cause the different behavior are discussed.     

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.     

Functional microspheres of graphene quantum dots

Graphene-quantum-dot microspheres (GQDSs) have been prepared by assembly of graphene quantum dots (GQDs) via a water-in-oil (W/O) emulsion technique without the addition of any surfactants. Although made of quantum-sized graphene dots, the as-formed GQDSs are solid and remain intact after slight ultrasonication. The versatile W/O emulsion method allows the in?situ intercalation of functional nanocomponents into the GQDSs for specific applications. As exemplified by the Fe(3)O(4)-containing GQDSs, Fe(3)O(4)-GQDSs exhibit a large magnetic response. Furthermore, the embedded Fe(3)O(4) nanoparticles in GQDSs can act as the catalysts for the growth of carbon nanotubes (CNTs), which opens the opportunities for fabricating new complex structures of CNTs surrounding GQDSs by simple chemical vapor deposition.     

CNTs/PBO复合材料的合成及性能

利用原位液晶聚合制备了碳纳米管(CNTs)/PBO复合材料,并利用取样对比分析、热重分析和纤维的强力测定对原位液晶聚合及材料的耐热和拉伸性能进行了研究。与同等条件下PBO控制聚合取样对比分析表明:碳纳米管表面活性基团会影响聚合,减少碳纳米管的加入量或推迟其加入的时间可以改善CNTs/PBO原位聚合状况。研究表明:CNTs/PBO复合材料保持了PBO的优异耐高温性能。纤维拉伸性能与同条件下PBO纤维相比提高40％~70％。      

碳纳米管在水泥基复合材料中的分散方法研究进展

碳纳米管(CNTs)作为性能优越的新型纳米材料被广泛用于增强基体材料,但是其易团聚且难以分散,使得实现其在基体材料中的均匀分散成为研究的重点。详细介绍了CNTs在增强水泥基复合材料研究中的分散方法与分散机理,并比较了各种分散方法的优缺点。重点论述了超声时间、酸处理时间、表面活性剂种类与掺量等因素对CNTs分散效果的影响,并讨论了评价CNTs分散效果的表征方法。将CNTs均匀分散到水泥基体中,可以显著提高复合材料的各项力学性能。     

Effect of a multiscale reinforcement by carbon fiber surface treatment with graphene oxide/carbon nanotubes on the mechanical properties of reinforced carbon/carbon composites

An effective carbon fiber/graphene oxide/carbon nanotubes (CF-GO-CNTs) multiscale reinforcement was prepared by co-grafting carbon nanotubes (CNTs) and graphene oxide (GO) onto the carbon fiber surface. The effects of surface modification on the properties of carbon fiber (CF) and the resulting composites was investigated systematically. The GO and CNTs were chemically grafted on the carbon fiber surface as a uniform coating, which could significantly increase the polar functional groups and surface energy of carbon fiber. In addition, the GO and CNTs co-grafted on the carbon fiber surface could improve interlaminar shear strength of the resulting composites by 48.12% and the interfacial shear strength of the resulting composites by 83.39%. The presence of GO and CNTs could significantly enhance both the area and wettability of fiber surface, leading to great increase in the mechanical properties of GO/CNTs/carbon fiber reinforced composites.     

Ni (OH)2-碳纳米管-还原氧化石墨烯复合材料的制备及电化学性能

利用简单易行的一步水热法制备了Ni（OH）₂-碳纳米管-还原氧化石墨烯（Ni（OH）₂-CNTs-RGO）三元复合材料,研究了不同水热反应温度对三元复合材料性能的影响。采用XRD、FTIR、Raman、X射线光电子能谱（XPS）、SEM及TEM对Ni（OH）₂-CNTs-RGO复合材料的结构和表面微观形貌进行表征。利用循环伏安（CV）、电化学交流阻抗（EIS）和恒电流充放电测试了复合电极材料的电化学性能。研究结果表明,当反应温度为120℃时,所制备的Ni（OH）₂-CNTs-RGO复合材料具有大的比表面积和三维网状结构,复合材料中六角形的β-Ni（OH）₂纳米片和CNTs均匀分散在RGO片层表面,有效阻止了RGO的团聚。Ni（OH）₂-CNTs-RGO复合电极材料在充电倍率为0.2 C时,放电比容量达到362.8 mAh/g,5 C时放电比容量为286.2 mAh/g,仍大于Ni（OH）₂在0.2 C时的放电比容量,表明CNTs与RGO的协同作用有效提高了电极材料的导电性和活性物质的利用率,最终提升了Ni（OH）₂-CNTs-RGO复合材料的倍率性能。     

碳纳米管/羟基磷灰石复合材料的制备及表征

以含钴介孔分子筛为催化剂、乙醇为碳源, 采用CVD法制备碳纳米管(CNTs)。通过原位合成法制备一系列不同碳纳米管含量的碳纳米管/羟基磷灰石(CNTs/HA)复合材料。分别采用XRD、FTIR、TEM、N₂吸附-脱附和Raman光谱等分析手段, 对所合成CNTs/HA复合材料的晶相、结构、形貌和比表面积等进行了表征。同时研究了碳纳米管的添加量对所合成CNTs/HA复合材料形貌的影响。XRD与Raman结果表明, 所得CNTs/HA复合粉体中仅有CNTs与HA两种物相, 纯度较高, 结晶度较好; TEM结果显示, CNTs/HA复合材料中CNTs表面均匀包裹着一层纳米级的针状HA晶粒, 两者形成了较强的界面结合, 且当CNTs与HA的质量比为3:17时, CNTs与HA形成最佳结合状态; N₂吸附-脱附表征结果表明, 与HA的比表面积相比, CNTs/HA复合材料具有较高比表面积。