Effect of oxidation treatment of multi-walled carbon nanotubes on the adsorption of pentachlorophenol from aqueous solution: Kinetics study

Multi-walled carbon nanotubes (MWCNTs) were oxidized using different oxidizing agents and the produced oxidized MWCNTs were characterized using different techniques. IR measurements showed the presence of carboxylic acid function groups especially for the MWCNTs oxidized with nitric acid and hydrogen peroxide. The adsorption of pentachlorophenol (PCP) to pristine and oxidized multi-walled carbon nanotubes (MWCNTs) has been studied. The results showed that the oxidation of the MWCNTs decreased their abilities to adsorb PCP compared with the pristine MWCNTs. The adsorption was studied kinetically and the results showed that the adsorption process occurs in two different steps. The first step involves the transfer of PCP to the surface of the oxidized MWCNTs, which was very fast due to the diffusion of PCP from the liquid phase to the solid phase. This step followed by a second slower step of adsorption could be due to intra-particle diffusion.     

Dissolution of MWCNTs by using polyoxadiazoles,and highly effective reinforcement of their composite films

Nonmodified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) nanocomposites are successfully prepared by a facile solution route. The pristine MWCNTs are dispersed in a sPOD solution, and the mixtures are fabricated into thin films by solution casting. The homogeneous dispersion of nanotubes in the composites is confirmed by transmission electron microscopy. The mechanical properties, thermal stability, and electrical conductivity are investigated. Tensile strength, elongation at break, and tensile energy to break are shown to increase by more than 28, 45, and 73%, respectively, by incorporating up to 1.0 wt % pristine MWCNTs. The experimental values for sPOD/MWCNTs composite stiffness are compared with Halpin‐Tsai and modified Halpin‐Tsai predictions. The storage modulus is found to increase up to 10% at low CNT loading. The composite films, which have an outstanding thermal stability, show an increase of up to 57 °C in the initial degradation temperature. The addition of 1.0 wt % MWCNTs increases the electrical conductivity of the sPOD matrix by two orders of magnitude. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

二氧化锡填充多壁碳纳米管材料的制备及电化学性能

用硝酸氧化法处理多壁碳纳米管(MWCNTs), 使得MWCNTs端口打开, 长度变短, 表面得到改性. 通过二氯化锡与硝酸银反应, 过滤后的溶液在浓硝酸环境中, Sn2+在毛细作用下扩散进入碳纳米管管腔, 吸附、成核并在热处理作用下沉积, 从而制备出SnO2/MWCNTs纳米复合材料. XRD和TEM测试表明, 部分SnO2填充到MWCNTs管腔, 形成不连续的纳米颗粒. 电化学测试表明, SnO2填充的MWCNTs可以结合两者的优势, 使得复合材料的循环性能和比容量均有所改善.     

Voltammetric study on pristine and nitrogen-doped multi-walled carbon nanotubes decorated with gold nanoparticles

Films consisting of pristine multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped MWCNTs (N-MWCNTs) were fabricated by means of chemical vapor deposition and chemically decorated with gold nanoparticles (AuNPs). Optical microscopy and image analysis reveal that the deposited AuNPs have diameters of 50–200 nm and 100–400 nm, respectively. The AuNP-modified films of MWCNTs and of N-MWCNTs were initially investigated with respect to their response to the ferro/ferricyanide redox system. The N-MWCNTs/AuNPs exhibit lower detection limit (0.345 μM) for this redox system compared to that of MWCNTs/AuNPs (0.902 μM). This is probably due to the presence of nitrogen that appears to enhance the electrocatalytic activity of MWCNTs. The findings demonstrate that the electrochemical responses of both films are distinctly enhanced upon deposition of AuNPs on their surfaces. The detection limits of MWCNTs/AuNPs and N-MWCNTs/AuNPs systems are lower by about 43 % and 27 %, respectively, compared to films not modified with AuNPs. The electrocatalytic activity of the films towards the oxidation of ascorbic acid (AA), uric acid (UA), and dopamine (DA) was studied. The findings reveal that N-MWCNTs/AuNPs represent a powerful analytical tool that enables simultaneous analysis of AA, UA, and DA in a single experiment.

Modification of multi-walled carbon nanotubes by microwave digestion method as electrocatalyst supports for direct methanol fuel cell applications

Multi-walled carbon nanotubes (MWCNTs) which were directly synthesized on carbon cloth were modified by a microwave digestion method in 5 M HNO₃ for supporting Pt nanoparticles. The characterizations of modified CNTs were carried out by TEM, XPS, FTIR and Raman spectroscopy. The HRTEM image shows the caps of MWCNTs are opened after modifying by microwave digestion method. The open-end and undamaged MWCNTs can provide a larger surface area for supporting more catalysts. Furthermore, the methanol electrocatalytic oxidation of microwave digestion treated Pt/MWCNTs electrode shows higher current density than pristine and nitric acid-treated MWCNTs from cyclic voltammograms. This can be an effective and undamaged method for modifying CNTs.     

Purification and dispersibility of multi-walled carbon nanotubes in aqueous solution

In this paper, the pristine multi-walled carbon nanotubes (P-MWCNTs) were purified either by the high temperature treatment (HT-MWCNTs) or by concentrated acid treatment (CA-MWCNTs). The HT-MWCNTs were prepared by heating at 500°C, while the CA-MWCNTs were treated by the mixture of concentrated nitric and sulfuric acids taken in a volume ratio of 3: 1. Ultrasonic processing and surfactants were utilized to achieve homogenous MWCNTs suspensions. The HT-MWCNTs and CA-MWCNTs were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). Among these three MWCNTs, the prepared homogeneously dispersed MWCNTs suspensions were characterized by UV–Vis absorbency and transmission electron microscopy (TEM). Finally, the dispersion mechanism was discussed. The results showed that both high temperature treatment and concentrated acid treatment can be used for purification of the P-MWCNTs, removing the amorphous carbon and other impurities. In these suspensions, the purified MWCNTs showed a better dispersibility in aqueous solution. The high temperature treatment was a kind of physical purification treatment method and it just burned the amorphous carbon away and strengthened the structure of MWCNTs, while the concentrated acid treatment was a chemical purification treatment method and this chemical treatment method grafted more effective groups to improve the dispersibility of MWCNTs.     

Influence of modification of MWCNTs on the structure and performance of MWCNT‐Poly(MMA‐AM) hybrid membranes

Hybrid membranes containing multi‐walled carbon nanotubes (MWCNTs) were initially prepared to separate benzene/cyclohexane mixtures. Subsequently, MWCNT surfaces were chemically modified using two methods to change the surface polarity of the MWCNTs and improve the distribution thereof in Poly(methylmethacrylate) (PMMA). This change consequently enhanced the separation performance of hybrid membranes with MWCNTs. Raman spectroscopy was used to characterize the structure of the pristine MWCNTs and the modified MWCNTs. The morphology and distribution of the MWCNTs in PMMA were investigated by transmission electron microscopy. The results showed that the addition of MWCNTs clearly improved the separation performance of the hybrid membranes. Surface modification introduced polar groups onto the MWCNT surface, which significantly improved the distribution of MWCNTs in the PMMA membranes and the performance of hybrid membranes. MWCNTs with higher surface polarity also increased the amount of MWCNTs distributed homogeneously in PMMA. Aminated MWCNTs (MWCNT‐NH₂) showed the highest surface polarity. Thus, the content of MWCNT‐NH₂ well distributed in PMMA was the highest among the three types of MWCNTs. The highest separation factor for the hybrid membranes with 1.0 wt% MWCNT‐NH₂ was about seven times that of membranes containing pristine MWCNTs. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface functionalizing effect of fillers on the tribological properties of MWCNT reinforcement HSGFs/phenolic laminate composites under water lubrication

Multi‐wall carbon nanotubes (MWCNTs) and high strength glass fabrics (HSGFs) were modified by polydopamine and polyethyleneimine, respectively. The aim is to improve the friction and wear performance of the synthesized laminate composites in water environment. In this work, polydopamine was used to improve the dispersibility of MWCNTs in phenolic resin matrix, and polyethyleneimine was utilized to enhance the wettability and reactivity of HSGFs. The modified results showed that the dispersibility of MWCNTs treated by polydopamine in water had a distinct improvement in comparison with that of the pristine MWCNTs. Furthermore, it can be clearly observed that good dispersibility can improve the friction and wear performance of the laminate composites. After functionalizing HSGFs by polyethyleneimine, the laminate composites exhibited excellent interfacial bonding, also greatly enhancing the friction and wear properties of the composites.     

Revealing the Effect of Surface Composition on Multiwalled Carbon Nanotubes Supported Pt-Fe Alloy Electrocatalysts for Methanol Oxidation Performance

The designs of efficient and inexpensive Pt-based catalysts for methanol oxidation reaction (MOR) are essential to boost the commercialization of direct methanol fuel cells. Here, the highly catalytic performance PtFe alloys supported on multiwalled carbon nanotubes (MWCNTs) decorating nitrogen-doped carbon (NC) have been successfully prepared via co-engineering of the surface composition and electronic structure. The Pt₁Fe₃@NC/MWCNTs catalyst with moderate Fe³⁺ feeding content (0.86 mA/mg_Pt) exhibits 2.26-fold enhancement in MOR mass activity compared to pristine Pt/C catalyst (0.38 mA/mg_Pt). Furthermore, the CO oxidation initial potential of Pt₁Fe₃@NC/MWCNTs catalyst is lower relative to Pt/C catalyst (0.71 V and 0.80 V). Benefited from the optimal surface compositions, the anti-corrosion ability of MWCNT, strong electron interaction between PtFe alloys and MWCNTs and the N-doped carbon (NC) layer, the Pt₁Fe₃@NC/MWCNTs catalyst presents an improved MOR performance and anti-CO poisoning ability. This study would open up new perspective for designing efficient electrocatalysts for the DMFCs field.     

氢氧化镍/多壁碳纳米管复合材料的溶剂热法制备及电容性能

采用溶剂热法制备了氢氧化镍/多壁碳纳米管[Ni(OH)2/MWCNTs]复合纳米材料;借助X射线衍射仪和透射电镜分析了产物的结构和形貌,利用循环伏安测试测定了复合材料的电容特性.结果表明:片状β-Ni(OH)2较好地附着在MWCNTs上;复合样品的循环伏安行为明显有别于空白样品Ni(OH)2,峰电流较高.这表明引入MWCNTs可改善Ni(OH)2的电化学性能.与此同时,当MWCNTs的质量分数为10%时,相应的Ni(OH)2/MWCNTs复合物的氧化还原峰电位差最小,循环可逆性最佳.     

Enhanced Electron Transfer Properties of Carbon Spheres Chains via Electrochemical Functionalization

Electrochemical functionalization via electrochemical oxidation in nitric acid of various concentrations (0.1 M, 0.2 M and 2 M) was employed to enrich the surface of carbon sphere chains (CSCs) with some useful physico‐chemical properties such as hydrophilicity, oxygen functionalities and electron transfer properties. The functionalization process in 2 M HNO₃ solution led to the creation of an original hybrid material made of carbon sphere chains‐carbon nanobuds. This material displayed a prominent response towards the electrocatalytic oxidation of ferrocyanide with a peak current three times and twice superior to those delivered by pristine CSC and multiwalled carbon nanotubes (MWCNTs) electrodes, respectively.     

Multi-walled carbon nanotubes as the gas chromatographic stationary phase: role of their functionalization in the analysis of aliphatic alcohols and esters

Presented hereafter is the novel application of differently functionalized multi-walled carbon nanotubes (f-MWCNTs) as stationary phases for the GC separation of C(1)-C(5) alcohols and esters. Low-cost packed columns, easily prepared in laboratory, were used with satisfactory results. Depending on the functional groups introduced on the pristine MWCNTs, remarkably different behaviours have been observed, thus indicating that derivatization is a key factor to achieve optimal resolution. The best performance was shown by the 2,2'-(ethylenedioxy)diethylamine derivatized MWCNTs, allowing the separation of alcohol isomers, for this reason chosen for the investigation of fermentation by-products in distilled spirits. The degree of derivatization has been assessed for each packing material by thermogravimetric analysis (TGA). A computational study has been performed to correlate the physico-chemical properties of alcohol probes with the retention behaviour.     

The cytotoxicity of oxidized multi-walled carbon nanotubes on macrophages

Carbon nanotubes (CNTs) have been developed for medical and biotechnological applications in the past decades. Their widespread applications make it important to understand their potential hazards to human and the environment. In this study, the possible toxicological effects of the oxidized multi-walled carbon nanotubes (O-MWCNTs) were assessed on RAW 264.7 macrophages in vitro. Several toxicological endpoints, such as cell viability, the release of LDH and IL-8, GSH/GSSG ratio, intracellular calcium concentration and ultrastructural changes in cell morphology, were carried out. The results showed that O-MWCNTs had very limited effects on oxidative stress, cellular toxicity and apoptosis. Transmission electron microscope clearly demonstrates RAW 264.7 macrophages engulfed plenty of O-MWCNTs, and some of them resided in the cytoplasm, while the morphology was not altered by O-MWCNTs. As the control, the pristine MWCNTs (p-MWCNTs) show higher cytotoxicity than O-MWCNTs, damaging cell viability and inducing cell apoptosis. All these toxicological data are of benefit to more wide applications of O-MWCNTs in the future.     

Supramolecular Assemblies of Nucleoside Functionalized Carbon Nanotubes: Synthesis,Film Preparation,and Properties

Nucleoside‐functionalized multi‐walled carbon nanotubes ( N‐MWCNTs ) were synthesized and characterized. A self‐organization process using hydrogen bonding interactions was then used for the fabrication of self‐assembled N‐MWCNTs films free of stabilizing agents, polymers, or surfactants. Membranes were produced by using a simple water‐dispersion‐based vacuum‐filtration method. Hydrogen‐bond recognition was confirmed by analysis with IR spectroscopy and TEM images. Restoration of the electronic conduction properties in the N‐MWCNTs membranes was performed by removing the organic portion by thermal treatment under an argon atmosphere to give d‐N‐MWCNTs . Electrical conductivity and thermal gravimetric analysis (TGA) measurements confirmed the efficiency of the annealing process. Finally, oxidative biodegradation of the films N‐MWCNTs and d‐N‐MWCNTs was performed by using horseradish peroxidase (HRP) and low concentrations of H₂O₂. Our results confirm that functional groups play an important role in the biodegradation of CNT by HRP: N‐MWCNTs films were completely biodegraded, whereas for d‐N‐MWCNTs films no degradation was observed, showing that the pristine CNT undergoes minimal enzyme‐catalyzed oxidation This novel methodology offers a straightforward supramolecular strategy for the construction of conductive and biodegradable carbon nanotube films.     

The influence of edge-plane defects and oxygen-containing surface groups on the voltammetry of acid-treated, annealed and “super-annealed” multiwalled carbon nanotubes

The role of edge-plane-like defects at the open ends of multiwalled carbon nanotubes (MWCNTs) and at hole defects in the tube walls is explored using cyclic voltammetry with two charged redox probes, namely potassium ferrocyanide and hexaamineruthenium(III) chloride in unbuffered aqueous solutions, and one neutral redox probe, norepinephrine, in pH 5.7 buffer. Further, the presence of oxygen-containing functional groups (such as phenol, quinonyl and carboxyl groups), which decorate the edge-plane defect sites on the voltammetric response of the MWCNTs, is also explored. To this end, three different pre-treatments were performed on the pristine MWCNTs made using the arc-discharge method (arc-MWCNTs). These were (a) arc-MWCNTs were subjected to acid oxidation to form acid-MWCNTs—open-ended MWCNTs also possessing numerous hole defects revealing a large number of edge-plane-like sites heavily decorated with surface functional groups; (b) acid-MWCNTs, which were subsequently vacuum-annealed at 900 °C to remove the functional groups but leaving the many undecorated edge-plane-like sites exposed (ann-MWCNTs); (c) ann-MWCNTs, which were subjected to a further vacuum “super-annealing” stage at 1,750 °C (sup-MWCNTs), which caused the hole defects to close and also closed the tube ends, thereby, restoring the original, pristine, almost edge-plane defect-free MWCNTs structure. The results of the voltammetric characterisation of the acid-, ann- and sup-MWCNTs provide further evidence that edge-plane-like sites are the electroactive sites on MWCNTs. The presence of oxygen-containing surface groups is found to inhibit the rate of electron transfer at these sites under the conditions used herein. Finally, the two charged, “standard” redox probes used were found to undergo strong interactions with the oxygen-containing surface groups present. Thus, we advise caution when using these redox probes to attempt to voltammetrically characterise MWCNTs, and by extension, graphitic carbon surfaces.     

The adsorption of resorcinol from water using multi-walled carbon nanotubes

Adsorption of resorcinol and other phenolic derivatives on pristine multi-walled carbon nanotubes (MWCNTs) and HNO₃ treated MWCNTs has been investigated in attempt to explore the possibility to use MWCNTs as efficient adsorbents for pollutants. MWCNTs showed higher adsorption ability in a rather wide pH range of 4–8 for resorcinol, while decreased uptake capacity was found for acid-treated MWCNTs. Other phenolic derivatives such as phenol, catechol, hydroquinone and pyrogallol were employed to study the influence of the number and position of hydroxyl groups on the adsorption capacity. The amounts adsorbed by MWCNTs increased with the increasing number of hydroxyl. The substitution of phenol with a hydroxyl in meta-position leads to a much higher absorption ability than substitution in ortho- or para-position, which suggested that MWCNTs possess a great potential in removal of resorcinol from water, as well as the other phenolic derivatives.     

A determination method of pristine multiwall carbon nanotubes in rat lungs after intratracheal instillation exposure by combustive oxidation-nondispersive infrared analysis

This paper describes a method for determination of multiwall carbon nanotubes (MWCNTs) in rat lungs after intratracheal instillation exposure. The MWCNTs were quantitatively decomposed to CO₂ by combustive oxidation and were then determined by non-dispersive infrared analysis. Samples were pretreated by acid digestion, muffle ashing and in situ preheating to remove interferences due to coexisting biological carbon from the lung tissue sample, while preserving the MWCNTs as in its their original form. The preservation was confirmed by transmission electron microscopic observation of the pretreated samples of exposed lung tissues and by the fact that the recoveries of MWCNTs spiked to the lung tissues were close to 100%. The detection limit for MWCNTs obtained by the proposed method was 0.30 μg and the repeatability as expressed by the relative standard deviation was 5.6% (n = 4). The method was sufficiently sensitive and precise to apply to real samples of rat lung to investigate the in vivo persistence of intratracheally instilled MWCNTs. To our knowledge, this is the first report of this type of sample pretreatment and direct determination of pristine MWCNTs without modification or tagging. Conventional indirect methods use tagging with other compounds or metal impurities in the CNTs for detection, and the detachment of these tags can increase uncertainties in the determination of the CNTs. The tags can also change how the CNTs persist in vivo, which can lead to an incorrect understanding of the persistence of pristine CNTs in vivo.     

Studying of antifungal activity of functionalized multiwalled carbon nanotubes by microwave‐assisted technique

In this paper, we reinforced the antifungal activity of multi‐walled carbon nanotubes (MWCNTs) using an effective technique. Covalent functionalization of MWCNTs was performed by lysine and arginine under microwave radiation. To prove functionalization phenomenon, the grafted chemical groups on the surfaces of MWCNTs were analyzed by Fourier transform infrared and Raman spectroscopy. Antifungal activities of functionalized MWCNTs as well as pristine MWCNTs were tested against different fungal species based on minimal inhibitory concentration (MIC) and radial diffusion assay. MIC results showed that the antifungal activity of MWCNTs‐lysine, in comparison to pristine MWCNTs against fungi, including Aspergillus niger, Aspergillus fumigatus, Candidate albicans, Penicillium chrysogenum, Saccharomyces cerevisiae, Fusarium culmorum, Microsporum canis, Trichophyton mentagrophytes, Trichophyton rubrum and Penicillium lilacinum were increased 1.92, 2.36, 2.35, 1.3, 1.5, 1.1, 2.54, 1.23, 1.42 and 2.1 times, respectively. Similarly, the antifungal activity of MWCNTs‐arginine was increased 1.98, 2.40, 2.55, 1.8, 1.9, 1.7, 2.64, 1.36, 2.1 and 2.55 times, respectively. On the basis of the results of this study, it is clearly indicated that covalent groups of lysine and arginine could improve the antifungal activity of MWCNTs. Copyright © 2012 John Wiley & Sons, Ltd.     

MWCNT Decorated Rich N-Doped Porous Carbon with Tunable Porosity for CO2 Capture

Designing of porous carbon system for CO₂ uptake has attracted a plenty of interest due to the ever-increasing concerns about climate change and global warming. Herein, a novel N rich porous carbon is prepared by in-situ chemical oxidation polyaniline (PANI) on a surface of multi-walled carbon nanotubes (MWCNTs), and then activated with KOH. The porosity of such carbon materials can be tuned by rational introduction of MWCNTs, adjusting the amount of KOH, and controlling the pyrolysis temperature. The obtained M/P-0.1-600-2 adsorbent possesses a high surface area of 1017 m² g⁻¹ and a high N content of 3.11 at%. Such M/P-0.1-600-2 adsorbent delivers an enhanced CO₂ capture capability of 2.63 mmol g⁻¹ at 298.15 K and five bars, which is 14 times higher than that of pristine MWCNTs (0.18 mmol g⁻¹). In addition, such M/P-0.1-600-2 adsorbent performs with a good stability, with almost no decay in a successive five adsorption-desorption cycles.