Surface Modification Of Carbon Nanotubes Research Articles

Carbon Nanotube (CNT) Foams As Sulfur Hosts for High Performance Lithium Sulfur Battery

The current Li-ion battery based on lithiation chemistry has a theoretical specific capacity of 372 mAh g-1. A battery chemistry beyond lithium ion vision is in urgent need to meet the ever-increasing energy storage demand. Lithium sulfur (Li-S) battery with a theoretical specific capacity of 1672 mAh g-1, is a promising candidate for next generation rechargeable lithium battery due to its high energy density, low raw material cost and environmental friendliness1. Despite these advantages, the current Li-S battery suffers from major problems including limited discharge capacity, poor cycle life and low coulombic efficiency, which severely hinder its commercialization. In this work, freestanding, three-dimensional macroporous carbon nanotube (CNT) foams were used as sulfur hosts. To synthesize CNT foams, poly(methyl methacrylate) (PMMA) microspheres were used as a template and Polyac-rylonitrile (PAN) was used as a precursor to create crosslinks among CNTs2,3. The sulfur was then infiltrated into the foam by melting diffusion method. The porosity and sulfur loading of the CNT/S composite can be easily tuned during synthesis. The as-obtained cathodes showed a stable electrochemical performance with an initial specific capacity varied from 1337 to 1016 mAh g-1 at 0.2 C under sulfur loading of 1-3 mg cm-1. The cell under sulfur loading of 2 mg cm-1 retained a capacity of 812 mAh g-1 after 100 cycles. The incomplete sulfur utilization and gradual capacity decay during cycles are mainly associated with the growth of insulating end product Li2Sx (x≤2) and the dissolution of soluble intermediate product Li2Sx (4≤x≤8). Several approaches to overcome the issues and further improve the electrochemical performance were studied, including surface modification of CNT for better polysulfide anchoring, optimizing cathode pore structure by mixing CNT with microporous carbon, applying an interlayer as an upper current collector and enforcing an all-solid-state reaction by partial recharging within the second discharge plateau. The results of these studies will be presented and discussed in the meeting. 1. A. Manthiram, Y. Fu, S. Chung, C. Zu, and Y. Su, Chem. Rev., 114, 11751–11787 (2014). 2. Y. Cui and M. Zhang, ACS Appl. Mater. Interfaces, 5, 8173–8178 (2013). 3. Y. Cui and M. Zhang, J. Mater. Chem. A, 1, 13984-13988 (2013).

Improving ORR activity of carbon nanotubes by hydrothermal carbon deposition method

Nitrogen doped carbons are an important family of materials with ideal activity for oxygen reduction reaction (ORR). It is always interesting to search functional carbons with high heteroatom contents and desirable structure for ORR. Within this study, the surface modification of carbon nanotubes (CNTs) via hydrothermal carbonization (HTC) technique in the presence of glucose and urea was reported, where the surface of CNTs is successfully coated by nitrogen containing hydrothermal carbon layers. The resulting composite combines both advantages of the outstanding electrical conductivity of CNTs and the effective ORR active sites provided by doped nitrogen in the HTC carbon layers. By controlling the ratio of glucose and urea, the nitrogen contents coated on the surface of CNTs can reach up to 1.7wt%. The resulting materials show outstanding electrochemical activity towards ORR in alkaline electrolyte, making it one of the valuable metal-free electrode materials and a competent alternative to the state-of-the-art Pt/C catalyst.

Photo-crosslinked thiol-ene based hybrid polymeric sensor for humidity detection

This study describes the preparation and characterization of new surface modified carbon nanotube particles (CNT) containing thiol-ene based hybrid polymers by photo-polymerization of pentaerythritol tetrakis, glyoxal bis(diallyl acetal), trimethylol propane triacrylate monomers and their usage for humidity sensing. CNT surface was photografted with polyethylene glycol acrylate (PEGA) to produce hydroxyl groups. Hydroxyl functionalized CNT/PEGAs were acrylated using isocyanatoethyl methacrylate (IEM) in order to improve the dispersion and interfacial interaction in composites. Furthermore, different amounts of gold nanoparticles containing compositions were also prepared. The humidity sensing properties of two samples were investigated by impedance measurements. The effects of CNT/Au modification, the applied potential bias and alternating current frequency on the electrical properties and the humidity sensitivity were determined. FCNT0 and FCNT5Au0.5 exhibit extremely high selectivity against humidity compare to various solvents; ethanol, acetone, methyl acetate and chloroform. FCNT0 has a reasonable good sensor performance for humidity measurements. It has high sensitivity, selectivity, stability, response/recovery and linear response properties in a full range of humidity measurements.

Acid surface modified carbon nanotube-filled fluoroelastomers aging test in oil-based drilling fluids

Acid surface–modified carbon nanotube (ACNT)-, carbon nanotube (CNT)-filled fluoroelastomer (FE), and unfilled-FE compounds were prepared (ACNT/FE, CNT/FE, and FE). The oil-based drilling (OBD) mud aging resistances of these elastomers were assessed by tests of weight gain, swelling, atomic force microscopy (AFM), and optical microscopy. The results show that for ACNT/FE-OBD (OBD mud tested ACNT/FE) and CNT/FE-OBD, there are no blisters, cracks, swellings, and deformed or uneven surfaces; however, for FE-OBD surfaces, these defects exist. ACNT/FE-OBD and CNT/FE-OBD have very low swelling, while for FE-OBD, the swelling is negative which indicates OBD chemical degradation of FE-OBD. All samples under study show low weight gain. AFM results show that roughness and average height of FE-OBD surface decreased considerably compared to that of FE. However, the changes in AFM results of ACNT/FE-OBD and CNT/FE-OBD compared to ACNT/FE and CNT/FE, respectively, are minor. ACNT/FE-OBD has a rougher surface with more average height and height variations compared to CNT/FE-OBD. Optical microscopy images show that the surface of FE-OBD is full of cracks but those of ACNT/FE-OBD and CNT/FE-OBD have no cracks. This study indicates that FE is not resistant to OBD, while ACNT/FE and CNT/FE are resistant to OBD.

Cheetah skin structure: A new approach for carbon-nano-patterning of carbon nanotubes

Selective localization and periodically patterning of polymer on surface of carbon nanotube (CNT) have been used as a practical approach for surface modification of CNT to overcome the poor solubility and processability of CNT in the different composites. Formation of carbon nanoparticle (CNP) on carbon nanotubes has been investigated in this research for the development of nanohybrid composites. Two distinct morphology of polyacrylonitrile (PAN) coated on CNT is observed. A novel approach to design a cheetah skin structure comprising of carbon-nano-patterning of carbon nanotubes is introduced. The cheetah skin structured CNT/CNP nanohybrid composite could lead to the development of the high-performance carbon based materials for high-tech applications in biotechnology, nano electronics and energy storage devices.

Formation mechanism of nano titanium carbide on multi-walled carbon nanotube and influence of the nanocarbides on the load-bearing contribution of the nanotubes inner-walls in aluminum-matrix composites

Carbon nanotubes (CNTs), generally do not completely impart their exceptional properties in aluminum-matrix composites because of the poor interfacial bonding between these nanofillers and the matrix. In the present study, surface modification of CNTs with nanocrystalline titanium carbide (TiC) was performed through a pressureless-spark plasma sintering. Mechanisms for the formation of nano TiC during the applied method were proposed. It was found that single nanocrystals of TiC were epitaxially grown on the surface of raw CNTs with the typical orientation relationship of TiC (200)//CNT (002) at the interface. The shapes of carbides were mostly nanolumps and nanoblocks relating to the reacted carbon sources. Different preferential nucleation sites for TiC, such as bamboo-like defects, radially unzipped sites were also investigated in details. Thermal stability of the modified-CNTs, analyzed by thermogravimetric analysis, showed a significant increment in thermal properties compared to raw CNTs. It was shown that TiC-modified CNT hybrid structure is helpful to improve the inner-wall bonding conditions, leading to the effective load transfer between the walls. It was revealed that compressive yield strength of Al-1.5 wt% modified-CNTs with the TiC:CNT mixing ratio of 4:2 is the highest compared with other composites with different amounts of CNTs.

Surfactant Assisted Stabilization of Carbon Nanotubes Synthesized by a Spray Pyrolysis Method

Surface modification of carbon nanotubes has been an interesting issue from a composites materials point of view. A nanotubes agglomeration has to be avoided to achieve a homogeneous dispersion in a composite matrix. In this research, we report on the synthesis of carbon nanotubes using a variant of the chemical vapor deposition technique known as spray pyrolysis method. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) studies showed that the synthesized products had an aligned structure with low purity degree, high content of catalyst particles, and a smaller amount of amorphous carbon. A secondary method was applied, which involves an acidic treatment that dissolves contaminant particles to enhance the purity of the nanotubes. Microstructural analysis, which includes XRD and SEM, indicates an effective reduction of impurities. Dispersion of the nanotubes was assessed using different surfactants, such as sodium dodecyl-sulfate (SDS) and ethylenediaminetetraacetic acid (EDTA). Finally, Raman spectroscopy, UV-Vis, and SEM techniques confirm that better results were obtained with EDTA. For EDTA and SDS surfactants, low concentrations of 0.3 mg/mL and 0.2 mg/mL were most efficient, respectively.

Energy mapping and surface energy heterogeneity profiles of surface-modified carbon nanotubes using IGC-SEA technique

Energy mapping and surface energy heterogeneity profiles of surface-modified carbon nanotubes using IGC-SEA technique

Efficient surface modification of carbon nanotubes for fabricating high performance CNT based hybrid nanostructures

Carbon nanotubes (CNTs) were chemically modified to achieve strong binding strength with the attached functional components as well as good dispersability and nanoparticle size-uniformity. An efficient multi-oxidation process was developed to create porous out layer with many nanoscale defects on the surface of CNTs for metallic nanoparticle close attachment and bond sufficient oxygen-containing groups, which assisted the dispersion of CNTs in the aqueous solution. The surface modified CNTs have advantages of strong binding capability, large surface area, high mechanical strength and good dispersability, which show great potential as building blocks for hybrid nanomaterials. Monodispersed silver nanoparticles with an average size of 3 nm were formed from inside the created nanoscale defects on the surface of CNTs without any obvious agglomerations. The fabricated hybrid exhibited much enhanced anti-bacterial performance compared to commercial silver nanoparticles due to the combined anti-bacterial effects of CNTs and silver nanoparticles. With these superior properties, the developed surface modification process could be widely used for improving the performances of many CNT based hybrid nanomaterials in diverse applications.

Assessing manganese nanostructures based carbon nanotubes composite for the highly sensitive determination of vitamin C in pharmaceutical formulation

This work is the first report describing the development of a novel three dimensional manganese nanostructures based carbon nanotubes (CNTs-Mn NPs) composite, for the determination of ascorbic acid (vitamin C) in pharmaceutical formulation. Carbon nanotubes (CNTs) were used as a conductive skeleton to anchor highly electrolytic manganese nanoparticles (Mn NPs), which were prepared by a hydrothermal method. Scanning electron microscopy and atomic force microscopy revealed the presence of Mn Nps of 20–25nm, anchored along the whole length of CNTs, in the form of patches having a diameter of 50–500nm. Fourier transform infrared spectroscopy confirmed the surface modification of CNTs by amine groups, whereas dynamic light scattering established the presence of positive charge on the prepared nanocomposite. The binding events were studied by monitoring cyclic voltammetry signals and the developed nanosensor exhibited highly sensitive response, demonstrating improved electrochemical activity towards ascorbic acid. Linear dependence of the peak current on the square root of scan rates (R2=0.9785), demonstrated that the oxidation of ascorbic acid by the designed nanostructures is a diffusion control mechanism. Furthermore, linear range was found to be 0.06–4.0×10−3M, and nanosensor displayed an excellent detection limit of 0.1µM (S/N=3). This developed nanosensor was successfully applied for the determination of vitamin C in pharmaceutical formulation. Besides, the results of the present study indicate that such a sensing platform may offer a different pathway to utilize manganese nanoparticles based CNTs composite for the determination of other bio-molecules as well.

Mechanical, electrical, and melt flow properties of polyurethane elastomer/surface-modified carbon nanotube composites

Carbon nanotube-reinforced polyurethane elastomer composites were prepared by melt-mixing. Nitric acid oxidation and silanization were applied to carbon nanotube surfaces to achieve better interfacial interactions with polyurethane elastomer. Tensile and hardness tests, differential scanning calorimetry, melt flow index test, dielectric measurements, and morphological studies of composites were reported. The best results were obtained for surface-modified carbon nanotubes containing composites with lower loading levels. Addition of carbon nanotubes leads to almost two-fold increase in strain and modulus compared to pristine polyurethane elastomer. Tensile strength of composites was also improved by inclusion of carbon nanotubes. However, strength values drop down with increasing carbon nanotube content. Shore hardness increased with the inclusion of modified carbon nanotube to polyurethane elastomer while pristine carbon nanotube caused remarkable decrease in hardness of polyurethane elastomer. Relatively higher melting points and slightly lower glass transition temperatures were observed for carbon nanotube-loaded composites compared to polyurethane elastomer because of plasticizing effect of carbon nanotube. Incorparation of carbon nanotube to polyurethane elastomer matrix caused reduction in melt flow index values due to formation of agglomarates, and n the contrary, surface modifications of carbon nanotube exhibited increase in melt flow index thanks to enhanced interfacial interactions between carbon nanotube and polyurethane elastomer. Significant increase in dielectric constant of composites was observed. Better dispersion of surface modified carbon nanotubes into polyurethane elastomer was also concluded from SEM micrographs of composites.

Epoxy nanocomposites with carbon nanotubes and montmorillonite: Mechanical properties and electrical insulation

Multiwalled carbon nanotubes have been widely used as mechanical reinforcement fillers for polymers during the past few decades. However, high electrical conductivity of raw multiwalled carbon nanotubes hampers their application in some fields demanding not only good mechanical properties and/or high thermal conductivity but also electrical insulation. In this research, carboxyl functionalized multiwalled carbon nanotubes and organically modified montmorillonite were introduced to prepare epoxy nanocomposites with anhydride as curing agent. The obtained epoxy nanocomposites possessed improved impact toughness, and the electrical insulation was maintained. Compared to the volume resistivity of the raw multiwalled carbon nanotubes (0.6 wt%)/epoxy nanocomposites, the volume resistivity of the organically modified montmorillonite/carboxyl functionalized multiwalled carbon nanotubes (0.6 wt%)/epoxy nanocomposites increased more than four order of magnitude. These excellent properties were attributed to the synergistic effect of carboxyl functionalized multiwalled carbon nanotubes and organically modified montmorillonite on toughening epoxy, as well as the suppression of electron transport by multiwalled carbon nanotubes surface modification and the organically modified montmorillonite layer in the multiwalled carbon nanotubes conductive network. The effects of adding nanofillers on the dielectric constant and dielectric loss values of epoxy nanocomposites were also studied. This work has demonstrated the feasibility of using multiwalled carbon nanotubes as mechanical reinforcement fillers, while simultaneously giving electrical insulation in the polymer nanocomposites.

Polymer brush synthesis on surface modified carbon nanotubes via in situ emulsion polymerization

In situ emulsion polymerization was employed for synthesizing carbon nanotube (CNT) composites in a colloidal system with poly(styrene) or PS to form nanostructured brush. CNTs were initially functionalized with oleic acid, followed by silanization with (3-aminopropyl) triethoxysilane to impart cross-linking properties. Styrene monomers were efficiently grafted to surface modified CNT via emulsion polymerization with variable CNT concentrations. FTIR analyses of the functionalized CNT and PS/CNT composites confirmed the bond formation and effectiveness of the developed experimental method. X-ray photoelectron spectroscopy confirmed the presence of the desired bonds and the composition of the composites. Structural properties of the composites characterized by TEM confirmed excellent deagglomeration and dispersion of CNTs in PS/CNT composite. Thermal characteristics from TGA and DSC data showed enhanced properties for the nanocomposites as a function of the CNT content. BET measurements indicated significant improvements in surface area and pore volume with enhancements in gas sorption for the polymer nanocomposites.

Study on novel poly (vinyl pyrrolidone) doped MWCNTs/polyrhodanine nanocomposites: Synthesis, characterization, and thermal performance

ABSTRACTIn this paper, poly (vinyl pyrrolidone) (PVP) doped multiwall carbon nanotubes (MWCNTs/polyrhodanine), were synthesized through one-step chemical oxidative polymerization of rhodanine monomers on the surface-modified carbon nanotubes. Characterization of MWCNTs/polyrhodanine was conducted by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and EDX spectrum analyses in which the results confirmed the successful formation of MWCNTs/polyrhodanine. In addition, to investigate the thermal properties of samples, thermogravimetric analysis (TGA) was employed, and results exhibited significant improvement in the nanocomposite thermal stability due to the addition of MWCNTs with reinforcement effect in polymer matrix.

Control of product nature and morphology by adjusting the hydrogen content in a continuous chemical vapor deposition process for carbon nanotube synthesis

Floating catalyst chemical vapor deposition (FCCVD) is commonly considered as one of the most attractive processes for the production of carbon nanotubes (CNTs). Understanding the phenomena occurring during the FCCVD synthesis of CNTs is critical to improve the process selectivity and scalability. The present work correlates information on gas chemistry and structural characteristics of the carbonaceous products, and show how both are strongly related to the hydrogen content in the reactor. Hydrogen plays different roles in the CNT growth process whose contributions depend on the synthesis conditions. Its presence induces an augmentation in carbon supply by promoting the decomposition of hydrocarbon vapors into more reactive byproducts, and by serving as an activation agent for the dissociation of physisorbed hydrocarbons on the surface of catalyst particles. However, high hydrogen content can induce catalytic hydrogenation of carbon and lead to surface modification of CNTs. Hydrogen also interferes with the decomposition of catalytic precursors, thus influencing the size and availability of catalyst nanoparticles. As a result, the mean and core diameters, crystallinity of the graphene walls, and length of CNTs are greatly influenced by the hydrogen flow, which offers the possibility to tune the CNT properties in a very simple, yet efficient way.

Surface-modified carbon nanotube coating on high-voltage LiNi0.5Mn1.5O4 cathodes for lithium ion batteries

Surface-modified carbon nanotubes were utilized as a coating for LiNi0.5Mn1.5O4 (LNMO) via a mechano-fusion method as a strategy to prevent unfavorable carbothermal reduction. Two types of carbon nanotubes were investigated as coating materials: carbon nanotubes (CNTs) and oxidized carbon nanotubes (OCNTs), which were prepared by a simple re-oxidation process. The samples coated with CNTs or OCNTs were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy, Raman spectroscopy, and elemental analyses. The OCNT-coated LNMO presented a highly enhanced discharge capacity retention (95.5%) and a coulombic efficiency of 99.9% after 80 cycles between 3.5 and 4.9 V (versus Li/Li+), whereas the CNT-coated LNMO exhibited poor retention of 47.2% and a coulombic efficiency of 95.3%. In addition, post-mortem XPS and electrochemical impedance spectroscopy (EIS) analysis proved that the OCNT coating improved the surface electrochemical stability and rate capability, whereas the CNT coating formed a thick resistive solid electrolyte interphase (SEI) film by accelerating the surface side reactions.

Nafion-based composite solid electrolytes containing carbon nanotubes

Nafion-based composite solid electrolytes containing multiwalled carbon nanotubes have been studied by impedance spectroscopy. The effect of carbon nanotube morphology on the proton conductivity of the composites has been estimated at low relative humidity. Surface modification of carbon nanotubes with acidic groups increases the proton conductivity.

"Patchy" Carbon Nanotubes as Efficient Compatibilizers for Polymer Blends.

Surface-modified carbon nanotubes (CNTs) have become well-established filler materials for polymer nanocomposites. However, in immiscible polymer blends, the CNT-coating is selective toward the more compatible phase, which suppresses their homogeneous distribution and limits harnessing the full potential of the filler. In this study, we show that multiwalled CNTs with a patchy polystyrene/poly(methyl methacrylate) (PS/PMMA) corona disperse equally well in both phases of an incompatible PS/PMMA polymer blend. Unlike polymer-grafted CNTs with a uniform corona, the patchy CNTs are able to adjust their corona structure to the blend phases by selective swelling/collapse of respective miscible/immiscible surface patches. Importantly, the high interfacial activity of patchy CNTs further causes a significant decrease in PMMA droplet size with increasing filler content. The combined effect of compatibilization and homogeneous distribution makes patchy CNTs interesting materials for polymer blend nanocomposites, where next to the compatibilization, a homogeneous filler distribution is important to gain the desired materials property (e.g., reinforcement).

Pulsed current field assisted surface modification of carbon nanotubes with nanocrystalline titanium carbide

Multiwalled carbon nanotubes (MWCNTs) were surface modified with titanium carbide (TiC) nanocrystalline particles by a novel pressureless spark plasma sintering method. The microstructure and properties of the nano-TiC modified MWCNTs were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, thermal gravity analysis and nanoindentation. Experimental results showed that the TiC nanoparticles were generated and grown epitaxially on the surface of MWCNTs by the pulsed current field assisted solid-state reaction between Ti and MWCNTs. The TiC nanoparticles were preferentially nucleated at defective sites of the nanotubes surfaces and grown along the [111] direction. Nano-TiC modified MWCNTs showed better oxidation resistance than that of the pure MWCNTs. Improvements of Young's modulus (31.18%) and nanohardness (62.74%) were achieved by doping of 1.0 wt.% TiC coated-MWCNTs into the aluminium matrix. The proposed modification strategy can be a versatile route for fabricating other nano-carbide coating on one dimensional nano-reinforcements.

Effects of multiwalled carbon nanotube surface modification and purification on bovine serum albumin binding and biological responses.

The potential diagnostic and therapeutic applications such as drug delivery of multi-walled carbon nanotubes (MWCNTs) are being increasingly explored due to their unique mechanical, chemical and biological properties. Carboxylation of MWCNTs has been widely used to improve the solubility in aqueous systems, and for further functionalization with biologically active moieties. Purity of carboxylated MWCNTs is of great importance in nanomedicine. An important consideration is that oxidation debris is generated during the process of carboxylation, which can be removed by base washing. We hypothesized that surface modification as well as further purification by debris removal may alter physicochemical properties of MWCNTs and their ability to bind proteins. In this study, we utilized pristine MWCNT carboxylated MWCNTs (F-MWCNTs) and base-washed carboxylated MWCNTs (BW-F-MWCNTs) to examine formation of a bovine serum albumin (BSA) protein corona and impact on biological responses. We found that carboxylation increased the capability of F-MWCNTs to bind BSA, and base washing further increased this binding by 41% implying that purification of F-MWCNTs is an important consideration in biological applications. The BSA protein corona decreased the hydrodynamic size of MWCNTs by nearly 50% because the coating improved colloidal behavior. The effect was significantly less pronounced for F-MWCNTs and BW-F-MWCNTs because they were highly dispersible to begin with. Functionalization increased cellular uptake by both rat aortic endothelial cells (RAEC) and macrophage-like murine cells (RAW264.7), while base washing showed results similar to the functionalized analog. Interestingly, BSA binding downregulated mRNA levels of interleukin-6 (IL-6) and heme oxygenase 1 (Hmox1) in RAEC cells but upregulated the expression of IL-6 and Hmox1 in RAW264.7 cells, indicating the dependence of cell types in biological responses to MWCNTs. Overall, our study demonstrated that surface modification as well as further purification impacted the interaction of MWCNTs with proteins and subsequent cellular responses. Interestingly, while the corona associated with the F-MWCNTs and BW-F-MWCNTs were significantly different, their respective cellular uptake and biological responses were similar. This implied that surface functionalization played a more important role than surface corona.