Carbon Nanotubes and Graphene - Research and Applications

Multi-walled carbon nanotubes (MWNTs) were filled with long continuous Ag nanowires via a wet chemical method. The diameters of Ag nanowires were in the range of 10–20 nm, and lengths of 100–1500 nm. Microwave absorption and complex permittivity and permeability of MWNTs filled with Ag nanowires have been investigated in the range of 2–18 GHz, respectively. The reflection loss of the Ag nanowire filled MWNT/epoxy composites with the thickness of 1.0 ± 0.1 mm is below −10 dB in the range of 7.2–9.0 GHz, and the minimum value is −19.19 dB at 7.8 GHz. The microwave absorption of Ag nanowire filled MWNT/epoxy composites can be mainly attributed to the dielectric loss rather than magnetic loss. The absorption peak frequency of the MWNT/epoxy composites with thickness of 1 mm can be tuned by filling Ag nanowire into MWNTs.

Article to appear in Materials Science and Engineering: B (D.-L. Zhao et al., 2008)

The well-aligned carbon nanotube arrays (ACNTs) were used as supporting material and the γ-MnO2/ACNT electrode with high dispersion of γ-MnO2 has been prepared by electrochemically induced deposition method. The crystal structure and morphology of the γ-MnO2/ACNT electrode were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The capacitive properties of γ-MnO2/ACNT electrode were characterized by cyclic voltammetry and galvanostatic charge-discharge method. The specific capacitance of the γ-MnO2/ACNT electrode is as high as 784 F g-1 based on γ-MnO2 and 234 F g-1 based on γ-MnO2/ACNT composites in 0.1M Na2SO4 aqueous solution from 0 to 1 V when the charge-discharge current density is 1 mA cm-2. Additionally, the electrode shows excellent power characteristics, high electrochemical reversibility and excellent long-term charge-discharge cycle stability.

Large particle MCM-41 was synthesized using preshaped silica gel as the silica sources. The physical properties of MCM-41 samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and field emission scanning electron microscopy (FESEM). The sample showed highly ordered mesoporous structure and spherical morphology with particle sizes of 20-45 micrometers by pseudomorphic synthesis. The fluidization study shows that the large particle MCM-41 can be readily fluidized in the form of agglomerates and the exhibits both particulate and bubbling fluidization.

Co-Mo catalyst using large particle MCM-41 as support was successfully applied for the synthesis of single walled carbon nanotubes (SWCNTs) in a fluidized-bed reactor. The product was monitored by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), Raman and Fluorescence spectroscopy, which suggested the resulted semiconducting SWCNT possess the narrow (n,m) distribution. It is evidenced that the MCM-41 particles synthesized in this study will be promising for the application in fluidized-bed reactors. The results will broaden the application of MCM-41 as a heterogeneous catalyst in chemical reactions.
Source: X. Liu, H. Sun, Y. Chen, R. Lau, Y. Yang Chemical Engineering Journal (2008), article in press, doi:10.1016/j.cej.2008.04.035

A polyoxometallate (POM)-assisted method has been successfully developed to load well-dispersed Pt nanoparticles on CNTs. Polyoxometallate offers strong protection to Pt nanoparticles from aggregation due to the electrostatic repulsive interactions with the negatively charged PMo12 monolayer. At the same time, polyoxometallate may work as a “bridge”, facilitating the attachment of Pt nanoparticles on the surface of CNTs. Electrochemical testing results indicate that the presence of PMo12 can not only diminish the poisoning of Pt catalysts, but also enhances the electrocatalytic activity and long-term cycling stability of the catalyst. POM assisted synthesis appears to be a promising method to prepare well-dispersed Pt nanoparticles on CNTs.

Source: Electrochimica Acta (2008), article in press.

A simple, fast, reproducible and direct procedure was used for adsorption of Os(III)-complex as electron transfer mediator on glassy carbon electrode modified with SWCNTs. By immersing the glassy carbon electrode modified with immobilization of carbon nanotubes in Os-complex solution for less than 1 min a stable thin film of complex adsorbed on the surface of the electrode.

The glassy carbon electrode modified with thin film of CNTs/Os-complex showed a stable and reproducible electrochemical behavior, long stability, high electron transfer rate constant and excellent electrochemical reversibility. The Os(IV)/Os (III) redox couple immobilized on SWCNTs, can be used in electrocatalysis as electron transfer mediators to shuttle electrons between analytes and substrate electrodes.

The nanomolar concentration of selected analytes was determined amperometrically at the surface of this modified electrode. The prepared modified electrode can be used as a chronoamperometric detector for periodate, iodate and bromate determination in flow systems or chromatographic instruments. The modification procedure can be used for sensor and biosensor fabrication using other osmium derivatives as electron transfer.
Source: Analytica Chimica Acta (2008), article in press