X-ray fluorescence as a method of monitoring metal catalyst content during the purification of carbon nanotubes

There have been several studies that suggest that catalyst metals in carbon nanotubes (CNTs) may pose a health threat. As there are many potential applications of CNTs in medicine, it is important to be able to quantitatively determine the amount of metal catalyst contained in a CNT sample. The relative catalyst content of carbon nanotube samples synthesized via arc-discharge has been determined at various stages of the purification process using X-ray fluorescence (XRF) analysis. Purification was achieved by immersing samples in heated nitric acid. The intensities of the nickel K_α X-rays were studied to determine the relative catalyst content in the samples. Scanning electron microscopy (SEM) images of purified nanotubes have been compared to the images of a sample that has been irradiated by 0-15 keV bremsstrahlung in order to determine if the XRF analysis of the nanotubes is in any way destructive. No obvious structural defects were observed as the result of irradiation.     

Low‐Temperature Growth of Carbon Nanotubes Catalyzed by Sodium‐Based Ingredients

Synthesis of low‐dimensional carbon nanomaterials such as carbon nanotubes (CNTs) is a key driver for achieving advances in energy storage, computing, and multifunctional composites, among other applications. Here, we report high‐yield thermal chemical vapor deposition (CVD) synthesis of CNTs catalyzed by reagent‐grade common sodium‐containing compounds, including NaCl, NaHCO₃, Na₂CO₃, and NaOH, found in table salt, baking soda, and detergents, respectively. Coupled with an oxidative dehydrogenation reaction to crack acetylene at reduced temperatures, Na‐based nanoparticles have been observed to catalyze CNT growth at temperatures below 400 °C. Ex situ and in situ transmission electron microscopy (TEM) reveal unique CNT morphologies and growth characteristics, including a vaporizing Na catalyst phenomenon that we leverage to create CNTs without residual catalyst particles for applications that require metal‐free CNTs. Na is shown to synthesize CNTs on numerous substrates, and as the first alkali group metal catalyst demonstrated for CNT growth, holds great promise for expanding the understanding of nanocarbon synthesis.     

Thermal stability evolution of carbon nanotubes caused by liquid oxidation

Carbon nanotubes (CNTs) grown by chemical vapor decomposition of ethylene on alumina- and silica-supported Fe–Co bimetallic catalysts were examined before and after purification encompassing chemical oxidation treatment in 3 M NaOH and 3 M HNO₃ solutions, sequentially. Thermal properties were investigated and correlated with structural changes followed by TEM, X-ray diffraction and Raman spectroscopy characterization. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were employed simultaneously in the regime of TPO and TPH, in diluted flow of either O₂ or H₂. TG revealed almost complete burning of both refined CNT samples in diluted O₂, indicating the efficiency of the purification method used to remove the catalyst remains. However, different trends and significant magnitudes of changes in the heat of combustion demonstrate changes in CNTs stability after purification as a function of the catalyst support type. This is the consequence of changes in carbon type, CNTs order degree and morphology, as well as the degree of functionalization, which have their own effects on the CNTs thermal stability.     

Floating catalyst CVD synthesis of carbon nanotubes from CpFe(CO)2X (X = Me, I): Poisoning effects of I

Multiwalled carbon nanotubes (MWCNTs), carbon fibers (CFs) and carbon spheres (CSs) were synthesized by an injection chemical vapour deposition (CVD) method using toluene solutions of CpFe(CO)₂Me as catalyst. The effect of pyrolysis temperature (800-1000 °C), catalyst concentration (5 and 10 wt% in toluene) and solution injection rate (0.2 and 0.8 ml/min) on the type and yield of carbonaceous product synthesized was investigated. The carbonaceous materials were characterized by transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and Raman spectroscopy. The use of CpFe(CO)₂I as catalyst generated only carbon fibres and balls (wide range of conditions). Studies involving the addition of I₂ to catalyst solutions confirmed the poisoning effect of I on CNT production.     

Synthesis and Catalytic Studies of Uniform Os &; Os–Pd Nanoparticles Supported on MWNTs

Os and Os–Pd nanoparticles supported on multi-walled carbon nanotubes were prepared by vacuum pyrolysis at 573 K using the [Os₃CO₁₀(NCMe)₂] and [Pd(acac)₂] as precursors. The nanoparticles prepared showed a narrow size distribution (Os: 1.8 nm; Os–Pd: 4.3 nm) and were decorated evenly on the surface of the nanotubes. By controlling the metal-to-nanotube ratio, Os nanotubes were prepared using the carbon nanotubes as a template. The catalysis of Os–Pd nanoparticles towards CVD carbon nanotube synthesis was studied. Dedicated to Professor Gunther Schmid on the occasion of his 70th birthday.     

Selected-area growth of carbon nanotubes by the combination of focused ion beam and chemical vapor deposition techniques.

In this article, we report a technique for growing carbon nanotubes in a more controllable fashion, which enables us to synthesize nanotubes directly in various forms of designed patterns. This nanofabrication process is based on a combination of focused ion beam (FIB) and chemical vapor deposition (CVD) techniques. In this process, arrays of conductive patterns were first deposited on silicon substrates by directing a gaseous compound (C(9)H(16)Pt) via the capillary needle-sized nozzles within a FIB system. The substrates were then coated with catalyst and further modified by the FIB to localize the position of the catalyst. Finally, the growth of carbon nanotubes on the designed substrates was carried out by CVD of hydrocarbon gases. This fabrication technique has the advantage of positioning carbon nanotubes in selected locations. This may open up opportunities for the direct synthesis of carbon nanotubes onto almost any substrate material, thus allowing fabrication of carbon nanotube-based devices.     

Determination of metformin based on amplification of its voltammetric response by a combination of molecular wire and carbon nanotubes

Molecular wires containing copper(II) (CuMW), in the form of the coordination polymer (Cu(II)₄(bpp)₄(maa)₈(H₂O)₂).2H₂O (bpp=1,3-bis(4-pyridyl)propane, maa=2-methylacrylic acid), and multiwalled carbon nanotubes (CNT) have been combined to prepare a paste electrode (CuMW/CNT/PE). The voltammetric response of the CuMW/CNT/PE to metformin (MET) was significantly greater than that of electrodes prepared from other materials, because of both the surface effect of CuMW and CNT and coordination of MET with the Cu(II) ion in the CuMW. A novel voltammetric method for determination of MET is proposed. In pH 7.2 Britton–Robinson buffer, using single sweep voltammetry, the second-order derivative peak current for oxidation of MET at 0.97 V (relative to SCE) increased linearly with MET concentration in the range 9.0 × 10⁻⁷–5.0 × 10⁻⁵ mol L⁻¹ and the detection limit was 6.5 × 10⁻⁷ mol L⁻¹. Figure When a combination of molecular wires containing copper(II) (CuMW) and multiwalled carbon nanotubes (CNT) was used to prepare a paste electrode (CuMW/CNT/PE) the voltammetric response to metformin (curve c) was significantly higher than that at a carbon/PE (curve a) or a CNT/PE (curve b), because of the amplification effect of CNT and CuMW. A novel voltammetric method is proposed for determination of MET     

Adsorption properties of carbon nanotubes depending on the temperature of their synthesis and subsequent treatment

A correlation between the temperature of the synthesis of carbon nanotubes (CNT) by method of catalytic pyrolysis from ethanol on a nickel catalyst and their ability for the modification of oxidation under various conditions and also their adsorption capacity to a number of metal ions is demonstrated. The study of infrared spectra in correlation with the total acidity of the CNT synthesized and modified under various conditions has shown that the samples synthesized at 400°C possess the maximum ability for modification. This can be explained by the higher deficiency of their structures at low synthesis temperatures. Adsorption isotherms of silver, copper, lead, cadmium, zinc, iron, and magnesium ions under batch and dynamic modes were studied, depending on pH and element concentration in the solution. It was found that CNT synthesized at 400°C and treated with conc. HNO₃ in an autoclave at 110–120°C possess the maximum adsorption capacity of all the studied elements, which exceeds the capacity of active coal, traditionally used for these purposes, by several times. The attained adsorption capacity is 5–10 times higher than that reported in the literature for carbon nanotubes in relation to the same elements. Prospects of using CNT as collectors for the preconcentration of trace impurities in spectroscopic methods of analysis are considered.     

Synthesis of carbon nanotubes using scrap tyre rubber as carbon source

Carbon nanotubes(CNTs) were successfully synthesized through chemical vapor deposition(CVD) method over cobalt catalysts using scrap tyre rubber as carbon source.The CNTs as produced were investigated by means of X-ray diffraction, thermogravimetric analysis,scanning electron microscope,transmission electron microscopy and Raman spectrum techniques.It was found that the obtained carbon material mainly existed in the form of CNTs.     

Purification of Single-walled Carbon Nanotubes Grown by a Chemical Vapour Deposition (CVD) Method

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Critical aspects related to processing of carbon nanotube/unsaturated thermoset polyester nanocomposites

Carbon nanotubes (CNTs) have outstanding mechanical, thermal and electrical properties. As a result, particular interest has been recently given in exploiting these properties by incorporating carbon nanotubes into some form of matrix. Although unsaturated polyesters with styrene have widespread use in the industrial applications, surprisingly there is no study in the literature about CNT/thermoset polyester nanocomposite systems. In the present paper, we underline some important issues and limitations during the processing of unsaturated polyester resins with different types of carbon nanotubes. In that manner, 3-roll mill and sonication techniques were comparatively evaluated to process nanocomposites made of CNTs with and without amine (NH₂) functional groups and polyesters. It was found that styrene evaporation from the polyester resin system was a critical issue for nanocomposite processing. Rheological behaviour of the suspensions containing CNTs and tensile strengths of their resulting nanocomposites were characterized. CNT/polyester suspensions exhibited a shear thinning behaviour, while polyester resin blends act as a Newtonian fluid. It was also found that nanotubes with amine functional groups have better tensile strength, as compared to those with untreated CNTs. Transmission electron microscopy (TEM) was also employed to reveal the degree of dispersion of CNTs in the matrix.     

CVD synthesis of spiral carbon nanotubes over asymmetric catalytic particles

The influence of asymmetric catalytic particles prepared by various methods was investigated on the growth of spiral carbon nanotubes using the CVD method. Asymmetric particles were prepared by either milling or crystallization from oversaturated solution onto the surface of catalyst support or catalyst impregnation at pH 8–9. As-prepared catalysts were tested in the decomposition of acetylene. Carbon deposit, thus carbon nanotubes and spirals were observed by transmission electron microscopy the activity was characterized by carbon yield.     

Direct growth of aligned multiwalled carbon nanotubes on treated stainless steel substrates

Growth of aligned carbon nanotubes (CNTs) on electrically conductive substrates is promising for many applications; however, the lack of complete understanding of the substrate effects on CNT growth poses a lot of technical challenges. Here, we report the direct growth of aligned multiwalled nanotubes (MWNTs) on chemically treated stainless steel (Type 304) using a chemical vapor deposition (CVD) process. A detailed X-ray photoelectron spectroscopy (XPS) analysis has been carried out for the various treated samples in order to better understand the correlation between the surface properties of the substrates and the MWNT growth. The XPS studies revealed that the CNTs prefer to grow on the enriched surface of iron oxides obtained by the chemical treatment rather than on the passive chromium oxide films present on the surface of the as-received stainless steel substrates. The density and alignment of the MWNTs could therefore be controlled by tuning the ratio of the iron oxides to chromium oxides through the chemical treatment on the stainless steel surfaces. On the basis of this method, selective growth of CNT patterns on stainless steel has also been demonstrated.     

Carbon nanotube arrays supported manganese oxide and its application in electrochemical capacitors

Manganese oxide (MnO_x) has been coated on carbon nanotubes (CNTs) and fabricated as the electrodes for electrochemical capacitors (ECs) by cathodic electrodeposition. In the process, randomly oriented CNT arrays are grown directly onto the Ti/Si substrates by chemical vapor deposition method. Potentiostatic method has been utilized for cathodic electrodeposition of MnO_x onto the surface of CNTs while immersed in KMnO₄ solution. The highly porosity and fibrous microstructure of the as-prepared MnO_x/CNT electrode is beneficial for the electrolyte access to the active material, whereas CNTs provide improved electronic conductivity. Electrochemical investigations show that the increase in the loading mass of MnO_x results in a significant reduction in the specific capacitances (SCs) of the MnO_x/CNT electrodes. The MnO_x/CNT electrode with MnO_x loading mass of 50 μg shows a high SC of 400 F g⁻¹ with good long cycle stability at a current density of 10 A g⁻¹, suggesting its potential application in ECs.     

CVD法制备单壁碳纳米管的纯化与表征

针对CVD法合成的单壁碳纳米管的特点提出了较为有效的纯化方法，并对纯化后碳管的存在形式进行了表征.结果表明,CVD法制备的单壁碳纳米管中所含的载体和催化剂绝大部分可以通过盐酸除去.在表面活性剂溶液中超声分散碳纳米管,可以使管与无定形碳及石墨状碎片进行有效的剥离.空气加热氧化法和稀硝酸回流法可有效地去除碳杂质,稀硝酸回流可以在纯化的同时对管的末端及侧壁进行功能化.     

Oxide-driven carbon nanotube growth in supported catalyst CVD

Detailed HREM studies on carbon nanotubes (CNTs) synthesized via chemical vapor deposition (CVD) using nanoengineered Fe particles on oxide supports show capped tops and open-ended roots. We demonstrate that the pristine catalyst particle dictates the CNT diameter and number of walls at nucleation. The consecutive inward formation of concentric graphene caps during nucleation constricts and elongates the catalyst particle within the tube core. Continued growth stems from the oxide support.     

Carbon nanotube supported single phospholipid bilayer

Single bilayer membranes of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were formed on micron thin-films of hydrophilized carbon nanotubes (CNT) by fusion of small unilamellar vesicles. The structure of the membrane was investigated using neutron reflectivity (NR). The underlying thin film of CNT was formed by chemical vapor deposition (CVD) in the presence of Fe catalyst, followed by reaction with 5 M nitric acid to render the film hydrophilic. We demonstrate that this platform lends support to homogeneous and continuous bilayer membranes that have promising applications in the fields of biomaterials, biosensors, and biophysics.     

电位质子滴定与NEXAFS和XPS表征功能化多壁碳纳米管比较(英文)

Since the discovery of carbon nanotubes (CNT), this material has been recognized as an attractive catalyst support. CNT must be functionalized before use as a catalyst support and typically this involves oxidation. However, the functional group distribution on the CNT is very complex mixture of groups and varies with oxidation agent used. Here a simple acid-base titration is introduced to characterize the oxygen functionalized CNT. By comparing characterization with near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for both at the C and O K-edges, it can be demonstrated that potentiometric proton titration can be a fast and quantitative analysis for Brnsted acid functional groups on CNT.     

CVD synthesis of nitrogen doped carbon nanotubes using ferrocene/aniline mixtures

Nitrogen doped carbon nanotubes (N-CNTs) have been synthesized by the chemical vapour deposition (CVD) floating catalyst method using either 4-ferrocenylaniline or mixtures of varying concentrations of ferrocene/aniline together with toluene as added carbon source. The N-CNTs produced are less stable (thermal gravimetric analysis measurements), less graphitic and more disordered (transmission electron microscope measurements) than their undoped counterparts. The ratio of the Raman D- and G-band intensities increase with the nitrogen concentration used during the CNT growth. Furthermore, the transmission electron microscope (TEM) studies reveal that the CNTs are multi-walled (MW), and that the diameters of the N-MWCNTs can be controlled by systematically varying the concentrations of the nitrogen source. The TEM analysis also revealed that when ferrocenylaniline and ferrocene/aniline reactions are compared at similar Fe/N ratios, higher N doping levels are achieved (ca. 2-5×) when ferrocenylaniline is the catalyst.     

Voltammetric detection of synthetic water-soluble phenolic antioxidants using carbon nanotube based electrodes

Glassy carbon electrodes (GCE) modified with carbon nanotubes (CNT) have been created for detection of phenolic compounds—one of the important group of antioxidants in life sciences. The surface of electrode has been characterized by atomic force microscopy. The presence of CNT leads to an at least 20-fold increase in the surface roughness of the electrode. The CNT layer displays closely intertwined vermicular structures with high degree of homogeneity at CNT suspension concentration of 0.2–0.5 mg L⁻¹. Synthetic water-soluble antioxidants (hydroquinone, catechol, pyrogallol, and their derivatives) are electrochemically active on bare GCE and CNT-modified GCE in phosphate buffer solution pH 7.4. Effect of substitutes in molecular structure of phenolic antioxidants has been evaluated. In several cases, oxidation at CNT-modified GCE occurs at potentials that are less positive by 100–200 mV in comparison to bare GCE. The electrodes were studied with respect to their capability of phenols voltammetric sensing. CNT-modified GCE display an enlarged linear range in the calibration graphs and lower detection limits. Voltammetric method for determination of hydroquinone, catechol, pyrogallol, and their derivatives has been developed.