Preparation and Catalytic Activity of Co/CNTs Nanocomposites via Microwave Irradiation

Co nanoparticles supported on carbon nanotubes (CNTs) were prepared by microwave‐assisted heating of the hydrazine reduction in ethylene glycol (EG). The Co/CNT nanocomposites prepared by the microwave‐irradiation method (MIM‐Co/CNTs) were characterized by XRD, SEM, EDS, and BET. It was found that MIM‐Co/CNTs had compact coating, high cobalt loading, and large BET surface area. The obtained products for the thermal decomposition of ammonium perchlorate (AP) were investigated by DTA. The catalytic activity of MIM‐Co/CNTs was better than that of pure Co nanoparticles and Co/CNT nanocomposites by water‐bath method (WBM‐Co/CNTs). The addition of 5 wt.‐% MIM‐Co/CNTs decreased the high decomposition temperature of AP by 174.05 °C and increased the total DTA heat release by 0.799 kJ g⁻¹.     

Liquid-phase assisted spark-plasma sintering of SiC nanoceramics and their nanocomposites with carbon nanotubes

The appropriate conditions for liquid-phase assisted spark-plasma sintering (SPS) were identified for the fabrication of both SiC nanoceramics and their nanocomposites with carbon nanotubes (CNTs). A parametric study of the nanoceramics and nanocomposites with a given type of CNTs showed that the SPS temperature (as measured by the radial optical pyrometer) optimizing their densification, nanograin size, and mechanical properties is 1700 °C (soaking for a few minutes), below which there is incomplete densification, and above which there is obvious grain growth with no benefit in hardness or toughness in the case of the nanoceramics, and prejudicial to both properties in the case of the nanocomposites due to the CNT degradation. It was also shown that the nanocomposites have smaller nanograins than their nanoceramic counterparts, and are softer but tougher. Extension to nanocomposites with different types of CNTs confirmed these trends, and showed that the CNT features do not condition the densification, microstructure or mechanical properties of these nanocomposites.     

An Effective Strategy to Achieve Ultralow Electrical Percolation Threshold with CNTs Anchoring at the Interface of PVDF/PS Bi‐Continuous Structures to Form an Interfacial Conductive Layer

Conductive composites based on polymers and conductive nanofillers are widely studied as a promising material. The rational design of 3D conductive networks in composites is crucial to improve their electrical conductivity and reduce the dosage of nanofillers. Herein, poly(vinylidene fluoride) (PVDF) and polystyrene (PS) bi‐continuous structures with modified carbon nanotubes (CNTs) tailored to anchor at the interface are designed to achieve an ultralow electrical percolation threshold because of the formation of a thin interfacial conductive layer. In this work, the modification of CNTs with poly(methyl methacrylate) (PMMA), which contributes to the improvement of the compatibility between PVDF and CNTs, is effective to control the distribution of CNTs in composites. It promotes the migration of CNTs from the PS phase to the interface of PVDF and PS. Consequently, the interfacial conductive layer is formed at a low CNT content, and the electrical percolation threshold of PVDF/PS/CNTs‐PMMA nanocomposites is only 0.07 vol%, having a great decrease of about 50% compared with that of PVDF/PS/CNTs nanocomposites. Thus, it is demonstrated that the distribution of CNTs can be tailored to anchor at the interface by proper chemical modification to form an interfacial conductive layer and a decrease of percolation threshold can also be achieved.     

Functionalization of carbon nanomaterials for advanced polymer nanocomposites: A comparison study between CNT and graphene

The allotropes of carbon nanomaterials (carbon nanotubes, graphene) are the most unique and promising substances of the last decade. Due to their nanoscale diameter and high aspect ratio, a small amount of these nanomaterials can produce a dramatic improvement in the properties of their composite materials. Although carbon nanotubes (CNTs) and graphene exhibit numerous extraordinary properties, their reported commercialization is still limited due to their bundle and layer forming behavior. Functionalization of CNTs and graphene is essential for achieving their outstanding mechanical, electrical and biological functions and enhancing their dispersion in polymer matrices. A considerable portion of the recent publications on CNTs and graphene have focused on enhancing their dispersion and solubilization using covalent and non-covalent functionalization methods. This review article collectively introduces a variety of reactions (e.g. click chemistry, radical polymerization, electrochemical polymerization, dendritic polymers, block copolymers, etc.) for functionalization of CNTs and graphene and fabrication of their polymer nanocomposites. A critical comparison between CNTs and graphene has focused on the significance of different functionalization approaches on their composite properties. In particular, the mechanical, electrical, and thermal behaviors of functionalized nanomaterials as well as their importance in the preparation of advanced hybrid materials for structures, solar cells, fuel cells, supercapacitors, drug delivery, etc. have been discussed thoroughly.     

Robust and wear resistant in-situ carbon nanotube/Si3N4 nanocomposites with a high loading of nanotubes

Highly homogenous carbon nanotube (CNT)/silicon nitride (Si₃N₄) nanocomposites with high CNTs loadings, up to 22 vol.%, are developed through the in-situ synthesis of CNTs on the ceramic powders, and further densification using the spark plasma sintering technique. The CNTs dispersion degree, the composite density, and their properties, especially the tribological ones, are evaluated and compared with those obtained for nanocomposites processed by the ex-situ method based on the mixing of nanotubes and ceramic powders in a solvent media. Fully dense in-situ 12 vol.% CNTs nanocomposites are 87% and 65% more wear resistant than monolithic Si₃N₄ materials and ex-situ nanocomposites, respectively, in the latter case due to the higher nanotubes dispersion and better mechanical properties attained by the in-situ process. These new in-situ CNTs nanocomposites present multifunctionality and are promising for emerging applications, especially for gasoline direct injection systems.     

Role of single‐source‐precursor structure on microstructure and electromagnetic properties of CNTs‐SiCN nanocomposites

Novel single‐source‐precursors (SSPs), namely carbon nanotube modified poly (methylvinyl) silazane (CNTs‐HTT 1800), were synthesized via amidation reaction of poly (methylvinyl) silazane (HTT 1800) with carboxylic acid functionalized carbon nanotubes (CNTs‐COOH) at the assistance of ZnCl₂ catalyst, which was confirmed by means of Fourier transform infrared spectra (FT IR) and transmission electron microscopy (TEM). Besides, the TEM results unambiguously show the homogeneous distribution of the CNTs in the matrix of SSPs while serious aggregation of the CNTs in the matrix of physically‐blended‐precursor. Crack‐free monolithic silicon carbonitride modified by carbon nanotubes ceramic nanocomposites (CNTs‐SiCN) were prepared through pyrolysis of the obtained SSP green bodies at 1000°C. Due to the strong influence of polymer structure on the microstructure of final ceramics, the SSP‐derived CNTs‐SiCN nanocomposites clearly show the homogeneous distribution of the CNTs in the SiCN matrix while the physically‐blended‐precursor derived CNTs‐SiCN nanocomposites exhibit serious aggregation and entangling of the CNTs in the SiCN matrix. With the same CNT content in the feed, the SSP‐derived CNTs‐SiCN nanocomposites possess significant improvements of electromagnetic (EM) absorbing properties compared to those from physically‐blended‐precursors, due to the quality of the dispersion of CNTs in the ceramic matrices.     

Unique CNTs-chained Li4Ti5O12 nanoparticles as excellent high rate anode materials for Li-ion capacitors

Composite anode materials with a unique architecture of carbon nanotubes (CNTs)-chained spinel lithium titanate (Li₄Ti₅O₁₂, LTO) nanoparticles are prepared for lithium ion capacitors (LICs). The CNTs networks derived from commercial conductive slurry not only bring out a steric hindrance effect to restrict the growth of Li₄Ti₅O₁₂ particles but greatly enhance the electronic conductivity of the CNTs/LTO composites, both have contributed to the excellent rate capability and cycle stability. The capacity retention at 30 C (1 C = 175 mA g^?1) is as high as 89.7% of that at 0.2 C with a CNTs content of 11 wt%. Meanwhile, there is not any capacity degradation after 500 cycles at 5 C. The LIC assembled with activated carbon (AC) cathode and such a CNTs/LTO composite anode displays excellent energy storage properties, including a high energy density of 35 Wh kg^?1 at 7434 W kg^?1, and a high capacity retention of 87.8% after 2200 cycles at 1 A g^?1. These electrochemical performances outperform the reported data achieved on other LTO anode-based LICs. Considering the facile and scalable preparation process proposed herein, the CNTs/LTO composites can be very potential anode materials for hybrid capacitors towards high power-energy outputs.     

Hybrid polyvinyl alcohol/polyvinyl chloride nanocomposites reinforced with graphene-carbon nanotube for acid red environmental treatments

ABSTRACT

Hybrid polyvinyl alcohol and polyvinyl chloride/graphene and carbon nanotube nanocomposites PVA–PVC/Gr–CNTs_a-e were successfully synthesized by a solution-casting method. Mixed Gr–CNTs ratio (50%:50%) was prepared in 2, 5, 10, 15, and 20 wt% and added to the host polymers (PVA/PVC). The characterization tools for the fabricated nanocomposites show homogenous interaction between the fillers and PVA/PVC polymer matrix. A significant improvement in the thermal properties of the (PVA/PVC) matrix was observed by adding mixed fillers, even at low loadings of mixed Gr–CNTs on to the matrix. Scanning electron microscopy and transmission electron microscopy images of the prepared composites show a good dispersion of PVA–PVC and mixed Gr–CNTs and present core-shell morphology. Impressive improvement in the percentage of acid red removal using PVA–PVC/Gr–CNTs_a–e was achieved and improved with time, solution temperature, and composites mass. The process of removing acid red was described kinetically and thermodynamically. The pseudo-second-order kinetic model is the most appropriate kinetic model to describe the adsorption of acid red by PVA–PVC and PVA–PVC/Gr–CNTs_d nanocomposites from an aqueous solution. Our results offer a facile method for the removal of acid red from three types of water: red sea, tap water, and distilled water.     

Catalytic combustion synthesis of CNTs/MgO composite powders and the influences on the thermal shock resistance of low-carbon Al2O3–C refractories

Using MgC₂O₄, Mg powders as raw materials and Ni(NO₃)₂?6H₂O as a catalyst, CNTs/MgO composite powders were prepared by a catalytic combustion synthesis method. The CNTs/MgO composite powders were characterized by XRD, Raman spectroscopy, FESEM/EDS and HRTEM. The effects of catalyst content on the degree of graphitization and aspect ratio of the CNTs in composite powders were investigated. Moreover, the thermal shock resistance of low-carbon Al₂O₃–C refractories after adding the composite powder was investigated. The results indicated that the CNTs prepared with 1 wt% Ni(NO₃)₂?6H₂O addition had a higher degree of graphitization and aspect ratio. In particular, the aspect ratio could reach approximately 200. The growth mechanism of hollow bamboo-like CNTs in the composite powders was proven to be a V-L-S mechanism. The thermal shock resistance of Al₂O₃–C samples could be improved significantly after adding CNTs/MgO composite powders. In particular, compared with CM0, the residual strength ratio of Al₂O₃–C samples with added 2.5 wt% composite powders could be increased 63.9%.     

碳纳米管载PtPb、PtBi纳米催化剂对甲酸抗CO中毒的研究

混酸法预处理了载体碳纳米管（CNTs）,采用两步法制备PtPb/CNTs和PtB i/CNTs催化剂。以甲酸为研究对象,首次采用循环伏安法长时间连续性扫描的方法研究催化剂的抗CO中毒能力。研究发现,添加了Pb、B i金属后,增强了Pt/CNTs催化剂性能,如甲酸的起始氧化电位明显降低、氧化电流密度增大且抗毒性能增强。PtPb/CNTs、PtB i/CNTs催化甲酸的起始氧化电位都低于Pt/CNTs（0.099V）,依次为-0.108和-0.004V（Vs.Ag/AgC l）;在0.6V处,PtPb/CNTs、PtB i/CNTs催化氧化甲酸产生的电流密度都明显大于Pt/CNTs（0.79 mA/cm2）,依次为3.10和1.77mA/cm2;PtPb/CNTs、PtB i/CNTs催化剂的寿命依次为Pt/CNTs催化剂的4倍和5倍。本文主要进行燃料电池电催化剂材料的研究,对于制造新型电催化剂有一定的探索作用。     

Fabrication and toughening behavior of carbon nanotube (CNT) scaffold reinforced SiBCN ceramic composites with high CNT loading

Uniform dispersion, high loading and three-dimensional (3D) continuous network of carbon nanotube (CNT) are desired for high-performance nanocomposites to fully utilize the superior strength and toughness of CNTs. In this work, monolithic CNTs/SiBCN composites with high CNT loading (10 wt% and 20 wt%) were prepared from 3D scaffold-like CNT cottons and a liquid polyborosilazane (PBSZ) precursor through precursor infiltration and pyrolysis process. The 3D CNT scaffold in the nanocomposite can function as passive filler and gas path to ensure formation of monolithic bulks. Moreover, direct infiltration of PBSZ into the pores among CNT cotton can hinder agglomeration of CNTs and localize CNTs at the original sites, guarantee good alignment and high CNT concentration in the final nanocomposite. This highly concentrated 3D CNT reinforcement in the nanocomposite shows unique resistance to cracking under external stress related to the complex fracture behavior of CNT bundles during the cracking formation and extension process (including CNT bridging, aligning, pulling out and then breaking), which more favors for absorbing energies and enhance toughness of the ceramic composites.     

Dispersion of carbon nanotubes in ultrahigh‐molecular‐weight polyethylene by melt mixing dominated by elongation stress

A novel melt‐mixing method and corresponding mixer for polymer materials are reported. The effects of carbon nanotube (CNT) loading, rotation rate and mixing time on the morphology and properties of CNTs/ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposites were experimentally investigated in detail using the mixer. Homogeneous dispersion of CNTs in intractable UHMWPE is successfully realized without the aid of any additives or solvents. Differential scanning calorimetry results showed that the crystallinity increases 13.8% when 1 wt% of CNTs is added into the composites. The maximum crystallinity increased 13.5% and then decreased slightly with increasing rotation rate. The mixing time had little effect on crystallinity. Rheological tests reveal that the effect of CNT loading on the storage modulus/complex viscosity is a result of competition between the viscosity decrease due to the selective adsorption of UHMWPE onto CNT surfaces and the viscosity increase caused by the formation of an interconnected polymer–nanotube network. The storage modulus/complex viscosity decreased with increasing rotation rate/mixing time. This is a synergic result of the selective adsorption of the long molecular chains onto the CNT surface and their thermomechanical degradation. The results showed that the mixing process dominated by elongation stress is a simple, efficient green way to prepare CNTs/UHMWPE nanocomposites via melt mixing. © 2018 Society of Chemical Industry     

Controllable preparation of Ti/TiO2-NTs/PbO2–CNTs–MnO2 layered composite materials with excellent electrocatalytic activity for the OER in acidic media

High oxygen evolution overpotential and low corrosion resistance are the main challenges for oxygen evolution materials in acidic media. In this study, a novel composite material, Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂, with high oxygen evolution electrocatalytic activity was successfully prepared. First, TiO₂ nanotubes (TiO₂-NTs) were synthesized in situ on a Ti sheet via anodization and used as an intermediate layer. Subsequently, the adhesion and conductivity of the TiO₂-NTs layer were increased through additional anodization, annealing, and electrochemical reduction. Finally, PbO₂ was electrodeposited with a constant current in a lead acetate medium and doped with carbon nanotubes (CNTs) and MnO₂. The surface morphology, phase composition, and electrochemical performance of the composite materials were investigated. Notably, in an acidic electrolyte (150 g/L H₂SO₄), Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂ exhibited good stability (30 h) and a low oxygen evolution overpotential of 410 mV at 50 mA/cm², which is almost equivalent to that of precious metals (RuO₂ and IrO₂) and 499 mV lower than that of the industrial Pb–0.76 wt% Ag alloy. The outstanding performance is mainly attributed to the high aspect ratio of the TiO₂-NT structure, synergistic effects of the active particles, and inherently good electrochemical properties of the active particles. Therefore, this study provides a new synthetic route for oxygen evolution materials in acidic media.     

Synthesis of vinylferrocene and the ligand-exchange reaction between its copolymer and carbon nanotubes

To improve the dispersibility of carbon nanotubes (CNTs), poly(vinylferrocene-co-styrene) (poly (Vf-co-St)), was grafted onto the surface of CNTs by a ligand-exchange reaction. Poly(Vf-co-St) was obtained by a radical copolymerization reaction using styrene and vinylferrocene as the monomers. The vinylferrocene was synthesized from ferrocene via a Friedel-Crafts acylation. The molecular weight, molecular weight distribution, and amount of Vf in the poly(Vf-co-St) were 1.32 × 10⁴, 1.69 and 17.6% respectively. The degree of grafting of the copolymer onto the CNTs surface was calculated from thermogravimetric analysis and varied from 27.1% to 79.7%. The addition of the poly(Vf-co-St) greatly promoted the dispersibility of the modified CNTs in anhydrous alcohol. The electrical conductivity of composites prepared from the polymer-grafted CNTs and copolymer (acrylonitrile, 1,3-butadiene and styrene, ABS) strongly depended on the degree of grafting. These results show that the amount of polymer grafted onto the surface of CNTs can be controlled and that the electrical properties of composites prepared with these grafted polymers can be tuned.     

Electrical and thermal properties of carbon nanotubes/PMMA composites induced by low magnetic fields

Abstract

Ni particles supported on carbon nanotubes (CNTs) were dispersed in a polymethyl methacrylate (PMMA) matrix by solution blending and then cast onto an electrode to get composite films under low magnetic fields. The orientation of CNTs in the films was characterised by scanning electron microscope and optical microscope. Multimeter and high resistance meter were used to study the electrical behaviour of the nanocomposites. The glass transition temperature T _g of PMMA was determined by differential scanning calorimetry. The results show that the alignment of the CNTs dispersed in the PMMA was achieved under a low magnetic strength below 0·5 T. Because of the ferromagnetism of Ni particles, the magnetic alignment of CNTs susceptibly changed. The magnetic alignment units in this work were rod-like CNTs aggregates instead of single CNTs, which took part in the buildup of a specific CNTs network structure in PMMA matrix. The network structure played a key role in significantly improving electrical conductivity and T _g of the nanocomposites.     

Research progress on polymer-inorganic thermoelectric nanocomposite materials

A thermoelectric (TE) material is a material where a potential difference is generated as a result of a temperature difference or the corollary of this where a temperature difference is generated when a voltage is applied. These phenomena can be used to generate electricity and/or control temperature. Traditionally, thermoelectric materials are inorganic semiconductors which have been limited in their application by low efficiency and high cost. Since the 1990s, both theoretical and experimental studies have shown that low-dimensional TE materials, such as superlattices and nanowires, can enhance the value of the TE figure of merit (ZT) which is an indicator of TE thermodynamic efficiency. To date it has not been feasible to apply these materials in large-scale energy-conversion processes because of limitations in both their heat transfer efficiency and cost. When compared to inorganic materials, organic conducting polymers possess some unique features, such as low density, low cost, low thermal conductivity, easy synthesis and versatile processability and their use in preparing polymer-inorganic TE nanocomposites appears to have great potential for producing relatively low cost and high-performance TE materials. Recently, an increasing number of studies have reported on polymeric and polymer-inorganic TE nanocomposite materials. The purpose of this paper is to review the research progress on the conducting polymers and their corresponding TE nanocomposites. Its main focus is the TE nanocomposites based on conducting polymers such as polyaniline (PANI), polythiophene (PTH), poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), as well as other polymers such as polyacetylene (PA), polypyrrole (PPY), polycarbazoles (PC) and polyphenylenevinylene (PPV). Typically, polymer-inorganic TE nanocomposites are produced by physical mixing, solution mixing and in situ polymerization. The key factors that limit the use of these polymers and their polymer-inorganic TE nanocomposites as TE materials are their low ZT values. More recent developments designed to overcome the limitation including, for example, the use of carbon nanotubes and graphenes and the use of computational modelling to accelerate the selection of suitable pairs of conductive polymer and inorganic TE materials to achieve best possible nanocomposites are reviewed.     

High Oxygen‐Reduction‐Activity and Methanol‐Tolerance Cathode Catalyst Cu/PtFe/CNTs for Direct Methanol Fuel Cells

A novel nanocomposite Cu/PtFe/carbon nanotubes (CNTs) was designed, prepared and examined as a cathode catalyst for direct methanol fuel cells (DMFCs). The effects of Fe and Cu on oxygen reduction reaction (ORR) activity and methanol tolerance were investigated by varying their amounts or their configurations in the nanocomposite. The experimental results show that PtFe alloy on CNTs could not enhance methanol tolerance, but could improve the ORR activity. Cu was deposited on PtFe/CNTs to obtain better methanol tolerance. The optimum molar ratio of Cu/Pt/Fe in Cu/PtFe/CNTs is 2.1:1:0.7. After 500 cycles in 1 M HClO₄ solution, the Cu/PtFe/CNTs catalyst is fairly stable with 92% of its original ORR activity and 89.6% of its original electrochemical active surface areas (EAS) maintained.     

Preparation and biodegradation of clay composites of PLA

PurposePerspective applications of nanocomposites in biomedical applications are investigated in this work by producing intercalated dispersions of clays into a biodegradable polymer matrix. Poly(lactic acid) (PLA) was selected being produced from renewable resources and approved by the Food and Drug Administration for medical use.In order to improve PLA mechanical properties and to accelerate its degradation, different layered silicate nanoclays are added: montmorillonites and fluorohectorites, without or with organic modifiers. Preparation, characterization, mechanical properties and biodegradation in blood plasma are evaluated.ResultsNew biodegradable materials were obtained, with improved mechanical properties (Young modulus, Peak stress and Strain at break) and with increased degradation rate (weight loss and lactic acid release).     

可生物降解聚合物基纳米复合材料降解性能研究进展

可生物降解聚合物中的层状硅酸盐纳米复合材料,可极大提高其力学性能,但同时会影响到材料的降解速率。研究纳米填料对可生物降解聚合物降解速率的影响及降解机理的变化,可拓宽其应用领域。综述聚乳酸(PLA)、淀粉、聚己内酯(PCL)、纤维素、聚羟基烷脂肪酸酯(PHA)、聚琥珀酸丁二醇酯(PBS)等可生物降解聚合物基层状硅酸盐纳米复合材料制备及降解性能研究现状及进展。     

From carbon nanotube coatings to high‐performance polymer nanocomposites

Since their discovery at the beginning of the 1990s, carbon nanotubes (CNTs) have been the focus of considerable research by both academia and industry due to their remarkable and unique electronic and mechanical properties. Among numerous potential applications of CNTs, their use as reinforcing materials for polymers has recently received considerable attention since their exceptional mechanical properties, combined with their low density, offer tremendous opportunities for the development of fundamentally new material systems. However, the key challenge remains to reach a high level of nanoparticle dissociation (i.e. to break down the cohesion of aggregated CNTs) as well as a fine dispersion upon melt blending within the selected matrices. Therefore, this contribution aims at reviewing the exceptional efficiency of CNT coating by a thin layer of polymer as obtained by an in situ polymerization process catalysed directly from the nanofiller surface, known as the ‘polymerization‐filling technique’. This process allows for complete destructuring of the native filler aggregates. Interestingly enough, such surface‐coated carbon nanotubes can be added as ‘masterbatch’ in commercial polymeric matrices leading to the production of polymer nanocomposites displaying much better thermomechanical, flame retardant and electrical conductive properties even at very low filler loading. Copyright © 2007 Society of Chemical Industry