Divided into single-wall and multi-wall carbon nanotubes, these nanomaterials show notable electrical and thermal conductivity, as well as tensile strength. They can be found in many material science applications, especially in the fields of electronics, optics, and composite materials. Microwave synthesis, SAXS, and x-ray diffraction are three important methods for research in this field. Anton Paar has decades of experience providing technology in all three areas – and we are happy to share it with you to help you advance your research. Below, you find a study about investigation of the size and internal structure of carbon nanotubes with SAXS, in-situ X-ray diffraction studies to investigate the synthesis of graphitic nanofibers, and several examples of microwave synthesis where nanocomposites for batteries and bioactive nanocomposites were generated.
Olivine-type lithium phosphates are of considerable interest in energy storage research. Their structural and electrochemical properties can be easily modified by various dopants and different synthesis methods. Here, a facile microwave-assisted hydrothermal method has been elaborated with subsequent infusion of the as-prepared nanoparticles with multiwalled carbon nanotubes.
In a beaker, lithium hydroxide, dissolved in 10 mL water, was mixed under vigorous stirring together with ammonium dihydrogen phosphate and phosphoric acid in 10 mL water. Then 10 mL aqueous solutions of manganese and iron sulfate together with acetic acid were added and the mixture was evenly distributed to four 80 mL quartz vessels. The reaction vessels were placed in the rotor, which was closed with the lid and subjected to microwave irradiation at constant 400 W.
After cooling, the product was repeatedly centrifuged and washed with acetone and water. After drying at 70 °C overnight, the powder was sintered at 600 °C for 6 h under an Ar/H2 atmosphere (95:5).
Finally, the dried nanopowder was mixed in an 80 mL quartz vessel with commercially available carbon nanotubes under sonication and again subjected to microwave irradiation at constant 400 W.
The olivine-type nanoparticles are directly obtained from in-situ-generated LiFePO4 and LiMnPO4 precursors. In an additional microwave-assisted dry-media approach, the nanomaterial was functionalized with carbon nanotubes. The infusion with carbon nanotubes resulted in enhanced electrochemical performance and good cycling performance compared to the pristine lithium phosphate.
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S. Sifuba et al., J. Nanotechnol. 2021, 6532348
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Novel approaches for anticancer therapy emphasize sonodynamic therapy utilizing specific porphyrin scaffolds which are excited by inertial acoustic cavitation. This leads to cell death via the production of reactive oxygen. The development and investigation of suitable nanosystems for cancer treatment involve the modification of single-wall carbon nanotubes (SWCNTs). Microwave irradiation facilitates the solvothermal process to introduce the porphyrin moiety.
A G10 vial was charged with the single-wall carbon nanotubes and the porphyrin (2 wt equivalents). The solvent was added and the vial was subjected to microwave irradiation.
After cooling, the product was repeatedly centrifuged and washed with DMF and DCM and finally dried at 100 °C for 2 days.
Different substituted porphyrins were prepared according to literature conditions and were covalently linked onto the carbon support with this general procedure.
SWCNTs can be efficiently modified by covalently grafted porphyrin moieties. The obtained compounds were fully characterized by FTIR, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. The resulting nanohybrids require activation by ultrasonic irradiation to become biologically active. Upon such sonodynamic applications, colon cancer cells can be effectively killed with higher selectivity and efficiency than conventional polymeric core shell nanoparticles.
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F. Bosca et al., RSC Adv. 2020, 10, 21736-21744
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Sodium-oxygen batteries are potential alternatives to the widely used lithium-ion batteries, especially in the context of electromobility. The degradation process of the electrochemically formed Na2O in these devices is being intensively investigated. Here, modified carbon nanotubes are used as catalysts to elucidate the effect on these electrochemical systems. Microwave heating facilitates the in situ oxidative formation of ruthenium oxide nanoparticles which are directly dispersed on the surface of the carbon nanotubes.
In a beaker, commercially available carbon nanotubes were dispersed in water and sonicated for 30 min. The ruthenium salt was added and the mixture was kept under vigorous stirring for another 30 min. Then the mixture was transferred to a G30 vial and subjected to microwave irradiation for 30 min.
After cooling, the product was repeatedly centrifuged and washed with water and ethanol and dried at 60 °C overnight. The nanocomposite was annealed at 150 °C for 1 h before being used for electrode preparation.
The annealed nanocomposite was used to prepare an appropriate cathode on nickel foam for corresponding battery measurements. The dispersion of the ruthenium dioxide on the carbon nanotubes led to improved electrochemical processing due to a smooth formation of a sodium oxide film in the active battery. This increased the electrolyte-electrode contact area for better performance in the oxygen evolving reactions. However, further investigations are required to substantially improve the performance of sodium-oxygen batteries.
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M. F. Tovini et al., J. Phys. Chem. C 2018, 122, 19678-19686
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Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. They are composed of one (single-walled CNT) or several (multi-walled CNT) layers of carbon with a graphitic structure wrapped around a hollow core. Both the dimensions of this core and the wall are in the range of nanometers, while the overall length of the tubes is typically much longer. Composites of CNTs dispersed in matrix materials (e. g. polymers) show very interesting and at the same time novel properties. This makes them potentially useful in many fields, such as materials science, electronics, optics and others. Small-angle X-ray scattering (SAXS) is sensitive to electron-density variations within an inhomogeneous (core-shell type) nanomaterial. Therefore, the internal structure of such materials can be determined by measuring the SAXS pattern and calculating the electron-density profile of the material’s cross-section. For CNTs this means that both the diameter of the core and the thickness of the graphitic shell wrapped around it can be determined.
A composite material comprising multi-walled carbon nanotubes dispersed in a thermoplastic elastomer (urethane based) was measured using the Anton Paar SAXSpace small- and wide-angle X-ray scattering system. For background subtraction the empty elastomer (without CNTs) was used. After subtracting the polymer scattering from the total signal, the scattering curve of the CNTs was obtained (Figure 1). From this, the pair-distance distribution function (PDDF) was calculated by applying the Indirect Fourier Transformation (IFT) technique [1]. This function was further converted, i.e. "deconvoluted" into the radial electron-density profile (Figure 2) using program DECON [1].
When evaluating the electron-density profile of the studied CNTs, the diameter of the hollow core can be directly read from the profile: it is found to be 4 nm in total (see Figure 3). The thickness of the wall scales with the number of layers that are wrapped around this core. In this study, the wall thickness was found to be 5.5 nm. With a typical wall-to-wall distance of 0.34 nm, this relates to 16 layers on average, which are wrapped around the core of an individual CNT.
Figure 1: Background-subtracted scattering curve (red) and corresponding fit (blue) obtained by GIFT
Figure 2: Radial electron density profile calculated with DECON
Figure 3: Schematic drawing of the studied carbon nanotubes
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Nanostructured carbon materials can be used for various applications (e.g., as catalyst supports or in Li-ion-batteries), but are also of major interest as media for hydrogen storage. Nanostructured carbon materials can be produced by different procedures, among them catalytic chemical vapor deposition (CCVD).
In-situ X-ray diffraction (XRD) studies can be used to investigate the CCVD synthesis of graphitic nanofibers (GNF) and their potential as hydrogen storage materials. The behavior of the synthesized fibers during high temperature activation and during the adsorption/desorption of hydrogen can also be investigated by XRD.
An NiO/CuO catalyst (Ni:Cu=98:2 weight%) was first formed in an H2/N2-gas stream at 350 °C (reducing conditions). The reduction of NiO to metallic Nickel was completed after 2 hours. The catalyst was diluted with silicon to contain the formation of the graphitic nanofibers. Silicon was also used as an internal calibration standard. After catalyst formation, the graphitic nanofibers were prepared by CCVD in an atmosphere of C2H4/H2/N2 at 600 °C.
In-situ X-ray diffraction studies were performed on a laboratory powder X-ray diffractometer with environmental conditions controlled by the XRK 900 Reactor Chamber from Anton Paar. The XRD investigations were carried out in the angular range between 15 and 65° 2θ at temperatures up to 900 °C and pressures of up to 5 bar.
With the XRK 900 Reactor Chamber, in-situ X-ray diffraction studies of catalysts as well as of graphitic nanofibers were successfully performed. After CCVD preparation of the nanofibers, they were treated with hydrogen at 5 bar and 600 °C.
The amount of hydrogen adsorbed on the fibers was found to be approx. 1 wt%. The hydrogen storage leads to an increase of the d002 lattice distance of 0.03 Å due to hydrogen incorporation between the graphite layers. The lattice expansion could only be observed when the synthesized fibers were not exposed to air.
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