Chemical Modification Of Carbon Nanotubes Research Articles

Improvement the Flame Retardancy and Thermal Conductivity of Epoxy Composites via Melamine Polyphosphate-Modified Carbon Nanotubes.

Surface chemical modification of carbon nanotubes can enhance the compatibility with polymers and improve flame retardancy performances. In this work, the double bond active sites were constructed on the surface of carbon nanotubes modified by the γ-methacryloyloxypropyl trimethoxysilane (KH570). Glycidyl methacrylate (GMA) was further grafted onto the surface of carbon nanotubes via free radical polymerization. Finally, the flame retardant melamine polyphosphate (MPP) was bonded to the surface of carbon nanotubes by the ring-opening reaction. This modification process was proved to be achieved by infrared spectroscopy and thermogravimetric test. The carbon nanotubes modified by flame retardant were added into the epoxy matrix and cured to prepare flame retardant and thermal conductive composites. The flame retardancy of composites were studied by cone calorimetry, UL94 vertical combustion test and limiting oxygen index. The thermal conductivity of composites was characterized by laser thermal conductivity instrument. The results showed that when the addition amount of flame retardant MPP-modified carbon nanotubes in composites was 10 wt%, the flame retardant level of UL94 reached to V2, the limiting oxygen index increased from 25.1 of pure epoxy resin to 28.3, the PHRR of pure epoxy resin was reduced from 800 kW/m2 to 645 kW/m2 of composites and thermal conductivity of composites was enhanced from 0.21 W/m·K−1 of pure epoxy resin to 0.42 W/m·K−1 of the composites.

Theoretical and experimental study on the fluidity performance of hard-to-fluidize carbon nanotubes-based CO2 capture sorbents

Carbon nanotubes-based materials have been identified as promising sorbents for efficient CO2 capture in fluidized beds, suffering from insufficient contact with CO2 for the high-level CO2 capture capacity. This study focuses on promoting the fluidizability of hard-to-fluidize pure and synthesized silica-coated amine-functionalized carbon nanotubes. The novel synthesized sorbent presents a superior sorption capacity of about 25 times higher than pure carbon nanotubes during 5 consecutive adsorption/regeneration cycles. The low-cost fluidizable-SiO2 nanoparticles are used as assistant material to improve the fluidity of carbon nanotubes-based sorbents. Results reveal that a minimum amount of 7.5 and 5 wt% SiO2 nanoparticles are required to achieve an agglomerate particulate fluidization behavior for pure and synthesized carbon nanotubes, respectively. Pure carbon nanotubes + 7.5 wt% SiO2 and synthesized carbon nanotubes + 5 wt% SiO2 indicates an agglomerate particulate fluidization characteristic, including the high-level bed expansion ratio, low minimum fluidization velocity (1.5 and 1.6 cms−1), high Richardson—Zaki n index (5.2 and 5.3 > 5), and low Π value (83.2 and 84.8 < 100, respectively). Chemical modification of carbon nanotubes causes not only enhanced CO2 uptake capacity but also decreases the required amount of silica additive to reach a homogeneous fluidization behavior for synthesized carbon nanotubes sorbent.

Which is better? Experimental and simulation analyses of the chemical modification of carbon nanotubes to improve their dispersion in water

This work combines molecular dynamics with experimental results to explain the behavior of the two main functionalization alternatives of carbon nanotubes (acidification and silanization) when they are dispersed in water. It was observed that the presence of carboxyl and hydroxyl groups in the carbon nanotubes improves the interaction with the aqueous medium by 22% in comparison with the pristine and silanized material. This indicates that the process of acidifying carbon nanotubes to improve their dispersion in aqueous systems is preferable and it is not necessary to employ an additional silanization stage. Experimental studies show that the silanization process induces partial stability because of the positive charges on the surface material, whereas the acidified system is stable for up to 24 hours. On the one hand, pristine and silanized nanotubes show the formation and rupture of the agglomerates; on the other hand, the acidified system shows a behavior similar from that of water, since appropriate interactions occur between the nanotubes and the water molecules. Computational studies were used to evaluate the performance of the systems by calculating the diffusion coefficient and the potential energy of the system. The energy of the system relates to intermolecular interactions between the species involved; greater intermolecular forces guarantee a better integration of the nanotubes, since the forces do not represent an impediment either for the medium to flow or for the nanomaterial to diffuse within the medium. In addition, the distribution of the charge on the surface of the carbon nanotubes guarantees repulsion between them, improving colloidal stability.

Modifying Water Flow, Ion Selectivity, and Salt Rejection in Carbon Nanotubes via Surface Adsorption

Chemical modification of carbon nanotubes is seen as an attractive way to control the rapid flow of liquids, gases, and solutes through their interior. However, precise covalent modification of nan...

Density functional theory study of N-doping effect on the stability and activity of Pd/NCNT catalysts for heck reaction

Carbon nanomaterial-supported Pd nanoparticles (Pd/CNS) are easily prepared and effective heterogeneous catalysts for the Heck reaction. However, the drawbacks of poor stability and lower activities compared to homogeneous catalysts limit their use in industrial applications. Chemical modification of carbon nanotubes (CNTs) by heteroatom doping, has been shown to be an effective way to improve the activities and stabilities of Pd/CNT catalysts. Herein we aimed to understand the role of nitrogen-doped carbon nanotubes (NCNTs) in improving the activity and stability of supported Pd catalysts based on density functional theory (DFT) calculations. The adsorption energies of Pdn (n = 1–6) clusters were investigated for three different types of NCNTs containing graphitic-N (NNTS), pyridinic-N (NNTY), and pyrrolic-N (NNTL). The activities of Pd/NNTS, Pd/NNTY, and Pd/NNTL as catalysts for the Heck reaction were also studied. The calculations regarding the stability and energies of the various interactions revealed that N-doping the CNT structure had important influences on NCNT activity and stability. It was found that NNTL was the most suitable for loading of Pd to catalyze the Heck reaction. Our results showed that the geometry and electronic structures of the heteroatom-doped CNTs were vital for the stability and activities of the catalysts. This work shows that regulation of the distribution of N-structures in N-doped CNTs could effectively enhance the stability and activities of these catalysts.

Chemically Cross-Linked Carbon Nanotube Films Engineered to Control Neuronal Signaling.

In recent years, the use of free-standing carbon nanotube (CNT) films for neural tissue engineering has attracted tremendous attention. CNT films show large surface area and high electrical conductivity that combined with flexibility and biocompatibility may promote neuron growth and differentiation while stimulating neural activity. In addition, adhesion, survival, and growth of neurons can be modulated through chemical modification of CNTs. Axonal and synaptic signaling can also be positively tuned by these materials. Here we describe the ability of free-standing CNT films to influence neuronal activity. We demonstrate that the degree of cross-linking between the CNTs has a strong impact on the electrical conductivity of the substrate, which, in turn, regulates neural circuit outputs.

Evaluation of the pH influence on protein exclusion by restricted access carbon nanotubes coated with bovine serum albumin

This paper’s proposal was to study the pH influence on protein exclusion in restricted access carbon nanotubes (RACNT), obtained by chemical modification of carbon nanotubes (CNT) using concentrated acid oxidizing agent (HNO3—65 % v/v). Oxidized CNT were coated with a layer of bovine serum albumin (BSA), resulting in RACNT–BSA. The isoelectric points of CNT, oxidized CNT, RACNT–BSA, BSA, and cross-linked BSA were determined by potentiometric titration. Percolating the BSA solutions at a concentration of 3 μg mL−1, in a phosphate buffer at a pH range from 2.2 to 7.0, by RACNT–BSA inside SPE cartridges, we studied the interactions among them. Solubilized BSA adsorbed in the RACNT–BSA surface at a pH range near the Ip (3.5–5.2), while in the other studied pH ranges this did not occur, which is mainly governed by electrostatic phenomena.

Effect of carbon nanotube modification on poly (butylene terephthalate)-based composites

AbstractThe influence of the chemical modification of carbon nanotubes on the mechanical, thermal and electrical properties of poly(butylene terephthalate)-based composites was investigated. Polymer composites based on poly(butylene terephthalate) were obtained via in situ polymerisation or extrusion. Commercially available multi-walled carbon nanotubes (Nanocyl NC7000) at different loadings (mass %: 0.05, 0.25, 1, 2) were used as fillers. The functionalisation process took place under a chlorine atmosphere followed by a reaction with sodium hydroxide. The effect of carbon nanotube modification was analysed according to the changes in the polymer thermal and mechanical properties. An addition of modified carbon nanotubes in the amount of 0.05 mass % improved the mechanical properties of the composites in terms of both Young’s modulus and tensile strength by 5–10 % and 17–30 % compared with composites with unmodified carbon nanotubes and neat poly(butylene terephthalate), respectively. The in situ method of composite preparation was a more effective technique for enhancing the matrix–filler interactions, although a significantly lower amount of fillers were used than in the extrusion method.

Surface modification of materials to encourage beneficial biofilm formation

Biofilms are communities of sessile microorganisms that grow and produce extrapolymeric substances on an abiotic or biotic surface. Although biofilms are often associated with negative impacts, the role of beneficial biofilms is wide and include applications in bioremediation, wastewater treatment and microbial fuel cells. Microbial adhesion to a surface, which is highly dependent on the physicochemical properties of the cells and surfaces, is an essential step in biofilm formation. Surface modification therefore represents an important way to modulate microbial attachment and ultimately biofilm formation by microorganisms. In this review different surface modification processes such as organosilane surface modification, plasma treatment, and chemical modification of carbon nanotubes, electro-oxidation and covalent-immobilization with neutral red and methylene blue molecules are outlined. The effectiveness of these modifications and their industrial applications are also discussed. There is inadequate literature on surface modification as a process to enhance beneficial biofilm formation. These methods need to be safe, economically viable, scalable and environmental friendly and their potential to fulfil these criteria for many applications has yet to be determined.

Effect of different chemical modification of carbon nanotubes for the oxygen reduction reaction in alkaline media

The electrochemical reduction of oxygen on chemically modified multi-walled carbon nanotubes (CNTs) electrodes in 1M KOH solution has been studied using the rotating ring disc electrode (RDE). The surface modification of CNTs has been estimated by XPS and Raman spectroscopy. The effect of different oxygen functionalities on the surface of carbon nanotube for the oxygen reduction reaction (ORR) is considered in terms of the number of electrons (n) involved.Electrochemical studies indicate that in the case of the modification of CNTs with citric acid and diazonium salts the n values were close to two in the measured potential range, and the electrochemical reduction is limited to the production of peroxide as the final product. In the case of the modification of carbon nanotubes with peroxymonosulphuric acid, in the measured potential range, the n value is close to 4 indicating the four-electron pathway for the ORR. By correlating ORR measurements with the XPS analysis, we propose that the increase in electrocatalytic activity towards the ORR, for CNT can be attributed to the increase in C-O groups on the surface of CNTs after modification with peroxymonosulphuric acid.

Combination effect of physical drying with chemical characteristic of carbon nanotubes on through-thickness properties of carbon fiber/epoxy composites

The present work studied the combination effect of physical drying with chemical modification of carbon nanotubes (CNTs) on some through-thickness properties of carbon fiber/epoxy composites. Different drying methods of heat drying and freeze drying were utilized to affect CNT organization form in carbon fiber/CNTs preforms and composites: The adoption of heat-drying method made CNTs more inclined to form aggregates accompanied with randomly scattered CNTs, while continuous CNT networks could always be assembled when freeze drying method was employed. The formation mechanism of such CNT networks was discussed, and could be described as “freeze drying within confined space.” Chemical characteristic of CNTs was controlled by choosing different solutions of non-functionalized CNTs (NOCNTs) or hydroxyl-modified CNTs (OHCNTs). As a consequence, CNT networks modified composites, especially that with OHCNTs formed networks, displayed significantly better electrical performance than composites with CNT aggregates and scattered CNTs; NOCNT networks and scattered OHCNTs made the corresponding composites possess higher interlaminar shear strength (ILSS) value, whereas OHCNT networks impaired ILSS while enhancing flexural strength and modulus of composites.

Ring-opening reactions of epoxidized SWCNT with nucleophilic agents: a convenient way for sidewall functionalization

The rational chemical modification of carbon nanotubes (CNT) is crucial for their successful application in various areas of science and industry. In our approach, Birch reduction of single-walled carbon nanotubes (SWCNT) was followed by epoxidation with dimethyldioxirane (DMDO). Next, ring-opening reactions with thiosemicarbazide, p-phenylenediamine, aminosilica-coated magnetic nanoparticles, propargyl alcohol, 6-bromohexanoic acid, and ethyl potassium dithiocarbonate were performed, which resulted in a wide variety of functional groups being covalently anchored to the sidewalls of the nanotubes. Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible-near infrared spectroscopy (UV-Vis-NIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) were employed to confirm modifications and study the chemical composition of the obtained structures.

Electrical and Mechanical Properties as a Processing Condition in Polyvinylchloride Multi Walled Carbon Nanotube Composites

We investigated the electrical conductivity (sigma) and mechanical property of polyvinylchloride/carbon nanotube composites as a function of the CNT content and processing time during a solid-state process of high speed vibration mixing (HSVM) and high energy ball milling (HEBM). Both processes were suggested to avoid high temperatures, solvents, chemical modification of carbon nanotubes. In this study, the percolation threshold (phi(c)) for electrical conduction is about 1 wt% CNT with a sigma value of 0.21 S/m, and the electrical conductivity is higher value than that reported by other researchers from melt mixing process or obtained from the other solid-state processes. We found that the dispersion of CNTs and morphology change from CNT breaking are closely related to sigma. Especially, a large morphology change in the CNTs was occurred at the specific processing time, and a significant decrease in the electrical conductivity of polyvinylchloride/carbon nanotube composite occurred in this condition. A meaningful increase of electrical properties and mechanical property is observed in the sample with about 1-2 wt% CNT contents sintered at 200 degrees C after the milling for 20 min by HEBM process. Our study indicates the proper process condition required to improve sigma of PVC/CNT composites.

Progress on Cytotoxicity &lt;i&gt;In Vitro&lt;/i&gt; of Carbon Nanotubes

According to recent references, the progress on cytotoxicity in vitro of carbon nanotubes (CNTs) including the factors such as size , residual metal catalysts,and detection methods influencing cytotoxicity of CNTs are summarized. The results shown that residual metal catalysts must be removed as much as possible and ensure CNTs in some concentration range before using them.Biocompatibility of CNTs must be considered and chemical modification of CNTs to improve their use safety and advantages is indispensable.

Effect of Nitric Acid Concentration on Doping of Thin Film Single-walled Carbon Nanotubes for Electrode Application in Transparent, Flexible Dye Sensitized Solar Cells

ABSTRACTA simple method is proposed for the chemical modification of carbon nanotubes (CNT) thin film counter electrodes (CE) for the replacement of fluorine-doped tin oxide (FTO) and platinum catalyst (Pt) while retaining light transparency. In order to decrease the sheet resistance, CNT thin films underwent various concentrations (≤10 M) and durations of HNO3 treatment prior to cell fabrication, and the effect on thin film properties was analyzed. P-doping was observed, and the maximum change in work function was found to be +0.35 eV with 4 M HNO3. Optimum sheet resistance reduction (50%) and work function increment were achieved after 1 h treatment with 4 M HNO3. Changes in optical transmittances for all samples were negligible (± 5%). Pristine and HNO3 treated films on plastic substrates were tested as CE in flexible bifacial dye sensitized solar cells (DSSC). Most significant improvements in conversion efficiencies were obtained when CNT on plastic substrates were pretreated with 8 M HNO3 (from 1.18% to 1.40% under roomlight, from 0.19% to 0.26% under 1 Sun).

Preparation and Characterization of Disulfide Functionalized Multi-Walled Carbon Nanotubes for Biomedical Applications

To interact with different biologic systems for biomedical applications, chemical modification of carbon nanotubes is always a key step. Disulfide is sensitive to the reductive intracellular environment, and such stimulus-responsive covalent bonds were used to modify carbon nanotubes. After deprotection of N-tert-butoxycarbonyl (Boc) groups of the N-(tert-butyloxycarbonyl) cystamine modified multi-walled carbon nanotubes (MWNTs), positively charged ammonium (NH3 +) functionalized MWNTs (MWNTs-S-S-NH3 +) with disulfide linkages were obtained. Their surface functional groups and changes of morphologies were characterized by infrared (IR) spectroscope and transmission electron microscope (TEM), respectively. The weight percentage of the immobilized disulfide was estimated by thermogravimetric analysis (TGA). And their cytotoxicity in vitro on cultured human nasopharyngeal SUNE1 cells was evaluated. The biocompatibility of MWNTs was improved compared to that of MWNTs without functional groups.

Formylation of Single-Walled Carbon Nanotubes

We report an improved, elegant method for the covalent formylation of single-wall carbon nanotubes (SWNTs) via formyl transfer from N-formylpiperidine, which could potentially open the gateway for more versatile chemical modification of carbon nanotube (CNT) walls than is possible via other reported functionalisation methods. The formylation reaction does not inflict damage upon the pristine CNT structure, unlike the currently commonly used carboxylation route, and involves much fewer steps, and takes considerably less time, than most other reported routes. The modified SWNTs have been characterised by Raman spectroscopy, ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy and "covalent tagging" with derivatising groups followed by thermogravimetric analysis-mass spectroscopy (TGA-MS). UV-vis-NIR spectroscopy shows that there is only limited disruption of the intrinsic electronic structure of the SWNTs. This is confirmed from estimates of the extent of functionalisation from TGA-MS, which suggest that it may be as low as 2 atomic per cent.

New nitrene functionalizations onto sidewalls of carbon nanotubes and their spectroscopic analysis

The reactivity of p-toluenesulfonyl, methylsulfonyl and trimethylsilyl nitrene, derived from the corresponding azides, was studied towards single-walled carbon nanotubes (SWCNT) prepared by electric arc or HiPCO (High-pressure CO conversion) methods. The functionalized SWCNTs were analyzed by Raman, IR, and VIS/NIR spectroscopy. The spectroscopic results indicated that covalent modification of the SWCNTs was successful. While the IR measurements gave evidence of successful reaction in all studied cases, the Raman measurements indicated differences in the reactivity of the two tube types and between different nitrenes. VIS/NIR spectrum was measured for reaction with p-toluenesulfonyl azide and it indicated strong changes upon functionalization. In the reaction between p-toluenesulfonyl azide and SWCNTs, for tubes prepared by the electric arc method the Raman signal from the metallic tubes decreased while for HiPCO tubes an opposite effect was observed. For the reaction with p-toluenesulfonyl nitrene the changes in the Raman spectra induced by the reaction were substantial but for the other two nitrenes the changes were more modest. Therefore, control experiments were performed without heating the reactions mixtures and complementary IR analysis was performed for the samples. Based on the analysis, it can be concluded, that nitrenes provide a route for rich chemical modification of carbon nanotubes.

Chemistry of carbon nanotubes in biomedical applications

Carbon nanotubes (CNTs) have attracted great interdisciplinary interest due to their peculiar structural, mechanical and electronic properties. Applications of CNTs in biomedical research are being actively explored by many scientists worldwide. However, manipulation of CNTs is impeded by several problems, such as 1) formation of complex and entangled bundles; 2) very low solubility of CNTs in organic solvents and water; 3) inert properties of pristine CNTs under many chemical reaction conditions, etc. Chemical modification of CNTs has partly solved the above issues and is still one of the most effective means of manipulating and processing CNTs. Many bioapplications of CNTs rely on successful outer/inner surface functionalizations. This Feature Article is comprised of two main parts. In the first part, we briefly review the covalent surface chemistry for the CNT functionalization; in the second part, we focus on the biomedical applications of surface chemistry for CNTs, in particular, the chemistry for controlling biomedical functions and meanwhile lowering nanotoxicity of CNTs. We also analyze the underlying factors that led to the controversy in the previous experimental data of safety studies of CNTs.

Conducting Nanocomposites Derived from Poly(styrenesulfonate)-Functionalized MWCNT-PSS and PEDOT

We present a practical method for fabricating carbon nanotubes (CNTs) and conducting polymer nanocomposites with enhanced thermal stability. The conducting nanocomposites were prepared by chemical modification of CNTs with poly(styrenesulfonate) (PSS) followed by an in situ polymerization of 3,4-ethylenedioxythiophene in the presence of poly(styrenesulfonate)-functionalized multiwalled carbon nanotubes (MWCNT-PSS). Morphological analysis of the resulting CNT-PSS poly(3,4-ethylenedioxythiophene) (PEDOT) composites revealed the presence of PSS on the outer surface of the tubes with a core-shell structure and the association of PEDOT with the PSS bound to CNT. In comparison to the control PEDOT:PSS films, the composite film showed improved electrical properties along with high thermal stability, thus demonstrating its potential for application to robust optoelectronic devices.