Purification and characterization of double-wall carbon nanotubes synthesized by catalytic chemical vapor deposition on mesoporous silica

Differentiation of Bone Mesenchymal Stem Cells Into Vascular Endothelial Cell-Like Cells Using Functionalized Single-Walled Carbon Nanotubes

Carbon nanotubes (CNTs) are a promising bioactive scaffold for bone regeneration because of their superior mechanical and biological properties. Vascularization is crucial in bone tissue engineering, and insufficient vascularization is a long-standing problem in tissue-engineered scaffolds. However, the effect of CNTs on vascularization is still minimal. In the current study, pristine single-walled carbon nanotubes (SWNTs) were purified to prepare different ratios of SWNTs/EDC composites, and their surface morphology and physicochemical properties of SWNTs/EDC were studied. Furthermore, the effect of SWNTs/EDC on vascularization was investigated by inducing the differentiation of bone mesenchymal stem cells (BMSCs) into vascular endothelial cell-like cells (VEC-like cells). Results showed that SWNTs/EDC composite was successfully prepared, and EDC was embedded in the SWNTs matrix and uniformly distributed throughout the composites. The AFM, FTIR spectra, and Raman results confirmed the formation of SWNTs/EDC composites. Besides, the surface topography of the SWNTs/EDC composites presents a rough surface, which may positively affect cell function. In vitro cell culture revealed that SWNTs and SWNTs/EDC composites exhibited excellent biocompatibility and bioactivity. The SWNTs/EDC composite at mass/volume ratios 1:10 had the best enhancement of proliferation and differentiation of BMSCs. Moreover, after culture with SWNTs/EDC composite, approximately 78.3% ± 4.2% of cultured cells are double-positive for FITC-UEA-1 and DiI-Ac-LDL double staining. Additionally, the RNA expression of representative endothelial cell markers VEGF, VEGF-R2, CD31, and vWF in the SWNTs/EDC composite group was significantly higher than those in the control and SWNTs group. With the limitation of our study, the results suggested that SWNTs/EDC composite can promote BMSCs differentiation into VEC-like cells and positively affect angiogenesis and bone regeneration.

Photochemical evidence of electronic interwall communication in double-wall carbon nanotubes

Single- and double-wall carbon nanotubes (CNTs) having dimethylanilino (DMA) units covalently attached to the external graphene wall have been prepared by the reaction of the dimethylaminophenylnitronium ion with the corresponding CNT. The samples have been characterized by Raman and XPS spectroscopies, thermogravimetry, and high-resolution transmission electron microscopy in which the integrity of the single or double wall of the CNT and the percentage of substitution (one dimethylanilino group every 45 carbons of the wall for the single- and double-wall samples) has been determined. Nanosecond laser flash photolysis has shown the generation of transients that has been derived from the charge transfer between the dimethylanilino (as the electron donor) to the CNT graphene wall (as the electron acceptor). Importantly, the lifetime of the double-wall CNT is much shorter than that monitored for the single-wall CNT. Shorter-lived transients were also observed for the pentyl-esterified functionalized double-wall CNT with respect to the single-wall analogue in the presence of hole (CH(3)OH) and electron quenchers (O(2), N(2)O), which has led to the conclusion that the inner, intact graphene wall that is present in double-wall CNT increases the charge mobility significantly, favoring charge recombination processes. Considering the importance that charge mobility has in microelectronics, our finding suggests that double-wall CNT or two-layer graphene may be more appropriate to develop devices needing fast charge mobility.

Precise control of the number of walls formed during carbon nanotube growth using chemical vapor deposition

We demonstrate a one-step approach for selecting the number of walls formed during carbon nanotube (CNT) growth by catalytic decomposition of CH(4) over Fe-Mo/MgO catalysts. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), thermal gravimetric analysis (TGA) and Raman spectroscopy analyses indicate that high purity single-walled, double-walled and triple-walled carbon nanotubes can be synthesized by tuning the Fe:Mo atomic ratio of catalysts. The results reveal that the concentration of Mo in the catalyst plays an important role in the size of catalyst particles and in the deposition rate of carbon atoms during CNT growth. Thus, the wall numbers of CNTs can be controlled precisely.

Highly conductive carbon nanotube buckypapers with improved doping stability via conjugational cross-linking

Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200 S cm( - 1), which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300 h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220 MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc.

The synthesis of silica nanotubes through chlorosilanization of single wall carbon nanotubes

We demonstrate that single wall carbon nanotubes (SWCNTs) can be coated by a layer of silica through the reaction between chlorosilane and acid-treated SWCNTs. The presence of carboxylic acid groups in the SWCNTs provides the active sites where chlorosilane can be anchored to form the silica coating. Silica nanotubes with diameters ranging from 5 to 23 nm were synthesized after the calcination of silica coated SWCNTs at 900 degrees C in air. It was found that the presence of SWCNT templates and carboxylic acid groups on the SWCNTs' surface is essential to the formation of silica nanotubes. Furthermore, the dependence of the inner diameters of the silica nanotubes on the diameters of bundled or isolated SWCNTs was observed. This novel technique can be applied to the synthesis of other oxide nanotubes if a precursor such as TiCl(4) or ZrCl(4) is used.

Oxidative purification of carbon nanotubes and its impact on catalytic performance in oxidative dehydrogenation reactions

Oxidative purification with mild diluted HNO3 followed by NaOH washing lowers the amount of amorphous carbon attached to multiwalled carbon nanotubes (CNTs). The graphitic structure improves remarkably by further annealing in argon at elevated temperatures, that is, 1173, 1573, and 1973 K. The influence of the purification treatment on the catalytic activity of the CNTs is investigated for the oxidative dehydrogenation (ODH) of ethylbenzene and propane as probe reactions. All samples tend to approach an appropriately ordered structure and Raman analysis of the used samples displays a D/G band ratio of 0.95-1.42. Oxygen functionalities are partly removed by the annealing treatment and can be rebuilt to some extent by oxygen molecules in the ODH reactant flow. The presence of amorphous carbon is detrimental to the catalytic performance as it allows for unwanted functional groups occurring in parallel with the formation of the selective (di)ketonic active sites.

Advances in engineering of diameter and distribution of the number of walls of carbon nanotubes in alcohol CVD

A detailed study on the influence of the substrate loading (relative to the catalyst content) and supply pressure of the feedstock on the diameter and distribution of the number of walls in carbon nanotubes in alcohol chemical vapor deposition (CVD) is presented. Here we show how one can modify the technique for the bulk formation of high quality desired nanotube types: single-walled, double-walled or multi-walled CNTs. The influence of the concentration of the catalysts with respect to the substrate concentration was examined to select the optimal conditions in terms of the sample quality. Resonance Raman spectroscopy and high resolution transmission electron microscopy have been applied to characterize the samples.

Room temperature purification of few-walled carbon nanotubes with high yield

Purification of high-quality few-walled carbon nanotubes (fWNTs) was developed by slow but selective oxidation in hydrogen peroxide (H(2)O(2)) at room temperature. The purity, nanotubes' structure, and thermal stability of purified fWNTs were characterized by transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis (TGA), respectively. The results showed that fWNTs could be selectively purified by prolonging the stirring time in 30 wt % H(2)O(2) solution. Highly purified fWNTs were obtained, having a high G/D ratio in Raman spectra and good thermal stability indicating the good quality of the purified fWNTs. The approach provides a simple low cost method for purification that also has higher nanotube yield than other purification methods.

Synthesis of uniform double-walled carbon nanotubes using iron disilicide as catalyst

The preparation of carbon nanotube (CNT) materials with high purity is critical for many potential applications. These materials not only need to be free of carbonaceous impurities but also have uniform diameters. Within the CNT family, double-walled carbon nanotubes (DWNTs), as the simplest member of multiwalled carbon nanotubes, have demonstrated good potential in many bulk applications. However, the synthesis of DWNTs with uniform diameter and high purity is still a challenge. Here, a method to prepare high-purity DWNTs using iron disilicide (FeSi2) as catalyst is demonstrated. Over 90% of CNTs in the sample were DWNTs with a narrow diameter distribution in the range of 4-5 nm. An additional advantage of using FeSi2 as catalyst is to simplify the process to prepare suitable catalyst because commercially available FeSi2 can be used directly without any further treatment.

Enhanced Photoluminescence from Very Thin Double-Wall Carbon Nanotubes Synthesized by the Zeolite-CCVD Method

Photoluminescence (PL) from purified (>90%) double-wall carbon nanotubes (DWNTs), which have been synthesized by zeolite catalyst-supported chemical vapor deposition (zeolite-CCVD), of very small diameters (0.8-nm average inner tube) is reported. The PL contour mappings for various ratios (1-90%) of double- versus single-wall carbon nanotubes by thermal oxidation have enabled us to unambiguously identify the chirality of inner tubes for the DWNTs synthesized. After the extensive high-temperature oxidation at 700 degrees C, high-purity (>90%) DWNTs of approximately 0.8 nm inner diameter are obtained, and most of these correspond to the DWNTs having inner tubes with chiralities of (7,5), (7,6), and (9,4).

Size-selective growth of double-walled carbon nanotube forests from engineered iron catalysts

We have succeeded in synthesizing vertically aligned doubled-walled carbon nanotube (DWNT) forests with heights of up to 2.2 mm by water-assisted chemical vapour deposition (CVD). We achieved 85% selectivity of DWNTs through a semi-empirical analysis of the relationships between the tube type and mean diameter and between the mean diameter and the film thickness of sputtered Fe, which was used here as a catalyst. Accordingly, catalysts were engineered for optimum DWNT selectivity by precisely controlling the Fe film thickness. The high efficiency of water-assisted CVD enabled the synthesis of nearly catalyst-free DWNT forests with a carbon purity of 99.95%, which could be templated into organized structures from lithographically patterned catalyst islands.