Summary We report that the decoration of metallic single-walled carbon nanotube (m-SWCNT) networks with cobalt(II) oxide (CoO) can improve the electrical conductivity of the networks. To measure the electrical conductivity, we prepared m-SWCNT networks between the source and drain electrodes of field-effect transistors (FETs). Then, the amount of CoO nanoparticles (NPs) used for decoration was controlled by treating the FETs with different volumes of a solution containing Co(NO3)2•6H2O. Atomic force microscopy imaging showed that CoO NPs were intensively deposited on the intertubular junction of the m-SWCNT networks. X-ray photoelectron spectroscopy confirmed that the oxidation state of the Co element on m-SWCNT was CoO. Raman spectra revealed that heavy decoration of CoO increased the D-band intensity of the m-SWCNT, indicating that the CoO NPs disordered the sp2 hybridized carbon atoms of the m-SWCNT via decoration. The electrical conductivity of the m-SWCNT networks was enhanced up to 28 times after decoration, and this was attributed to the CoO NPs connecting the m-SWCNTs at junctions of the networks.
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Summary: Graphene-based energy storage devices, such as supercapacitors and lithium ion batteries have triggered substantial research interests due to the remarkable physical and chemical properties. However, the restacking due to intensive π–π interactions dramatically decreases the specific surface area, leading to the poor energy storage performance. In addition, the electrical conductivity of commonly reduced graphene oxide (G) is several orders of magnitude lower than pristine graphene due to the incomplete reduction and the presence of numerous defects. Here, we report a doubl enhanced strategy to improve the energy storage performance of G through pristine CNTs directly dispersed by GO and subsequent multicomponent surface self-assembly coating of ordered mesoporous carbon. The resulted graphene–CNT ordered mesoporous carbon ternary hybrids (GCMCs) possess an ordered, interconnected mesostructure, a high specific surface area of 1411 m2 g−1, large mesopores of 4.3 nm, and good conductivity. With their tailored architecture, the GCMCs-based supercapacitor shows high specific capacitance (2.4–16.5 times higher than G) and excellent cycle along with 100 % capacitance after 1000 cycles. Additionally, lithium ion battery anodes made of these GCMCs have exhibited a high reversible capacity of 903 mAh g−1 at 0.1 A g−1 after 100 cycles, which is 3.9 times higher than that of G.
Citation: Ashok Kumar Sundramoorthy †, Sara Mesgari †, Jing Wang †, Raj Kumar ‡, Mahasin Alam Sk. †, Siew Hooi Yeap †, Qing Zhang ‡, Siu Kwan Sze §, Kok Hwa Lim *†, and Mary B. Chan-Park *†, Journal of the Americal Chemical Society, 2013, 135 (15), pp. 5569 – 5581.
Summary: Semiconducting single-walled carbon nanotubes (s-SWNTs) have emerged as a promising class of electronic materials, but the metallic (m)-SWNTs present in all as-synthesized nanotube samples must be removed for many applications. A high selectivity and high yield separation method has remained elusive. A separation process based on selective chemistry appears to be an attractive route since it is usually relatively simple, but more effective chemicals are needed. Here we demonstrate the first example of a new class of dual selective compounds based on polycyclic aromatic azo compounds, specifically Direct Blue 71 (I), for high-purity separation of s-SWNTs at high yield. Highly enriched (93% purity) s-SWNTs are produced through the simple process of standing arc-discharge SWNTs with I followed by centrifugation. The s-SWNTs total yield is up to 41%, the highest yet reported for a solution-based separation technique that demonstrates applicability in actual transistors. 91% of transistor devices fabricated with these s-SWNTs exhibited on/off ratios of 103 to 105 with the best devices showing mobility as high as 21.8 cm2/V s with on/off ratio of 104. Raman and X-ray photoelectron spectroscopic shifts and ultraviolet–visible–near-infrared (UV–vis–NIR) show that I preferentially complexes with s-SWNTs and preferentially suspends them. Preferential reaction of naphthyl radicals (generated from I with ultrasonication) with m-SWNTs is confirmed by changes in the D-band in the Raman spectroscopy, matrix-assisted desorption–ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and molecular simulation results. The high selectivity of I stems from its unique dual action as both a selective dispersion agent and the generator of radicals which preferentially attack unwanted metallic species.
Summary: The ultraviolet optical properties of semiconducting-enriched and metallic-enriched single-walled carbon nanotube (semi-enriched and m-enriched SWCNT) networks were studied using spectroscopic ellipsometry. According to calculated energy loss function, the energy loss peak assigned to the maximum intensity of π-plasmon energy was found to increase from 4.5 eV to 5.0 eV as SWCNT network composition was changed from m-SWCNT enriched to semi-SWCNT enriched. These results clearly demonstrate that the dielectric response in the 4–6 eV range is sensitive to changes in the surrounding dielectric environment depending on the semi-/m-SWCNT content. Therefore, the spectral shift of this energy loss is attributed to the enhanced electron confinement by the presence of the surface plasmon due to a small amount of m-SWCNT, which is an important phenomenon at the SWCNT network.
Summary: An improved layer-by-layer vacuum filtration method was adopted for the fabrication of single-walled carbon nanotube (SWCNT) films aiming at a series of SWCNT films with controllable thickness and density. The electrical transport properties of the multilayered SWCNT films have been investigated. With the constant film density, the decrease of the layer number of the SWCNT film results in an increase of the temperature coefficient of resistance (TCR). SWCNT film with 95% metallic nanotubes has shown a lower TCR than that of the SWCNT films with a low percentage of metallic nanotubes. The effect of thermal annealing and subsequent acid (HNO3) treatment on the electrical properties of the SWCNT films has also been investigated.
Summary: Surfactants are routinely used in the production of graphene and additionally in their solubilisation with the aim of reducing the likelihood of coalescing. We demonstrate that surfactants, which are an inherent property of graphene, are a major contribution to the electrochemical performance. Using well characterised commercially available graphene we demonstrate that the surfactant may be detrimental in electrochemical processes, for example in the electrochemical oxidation of NADH, used prolifically as the basis of over 300 biosensors, and in the electrochemical oxidation of acetaminophen, an analgesic and antipyretic drug which requires routine monitoring in a plethora of areas. The use of control experiments in the form of surfactant modified carbon electrodes is particularly encouraged in de-convoluting the origin of the electrochemical response of graphene modified electrodes.
Summary: We compare electrochemical response of single-, few-, and multilayer graphene sheets and conclude that there is no significant difference between them. Therefore, there is no need for single-layer graphene sheets for electrochemical applications because multilayer graphene provides equal voltammetric performance.
Summary: The noncovalent functionalization of single-walled carbon nanotubes (SWNTs) is important in the development of advanced materials and nanoelectronic sensors and devices. A cobalt-terpyridine transition metal complex with pendant pyrene moieties has been shown to successfully functionalize SWNTs via noncovalent π−π stacking interactions. Cyclic voltammetry at SWNT coated platinum electrodes has been utilized to investigate the process of surface modification and provides conclusive evidence of robust surface functionalization. The electrochemical methodology for examining surface functionalization of SWNTs described herein is generalizable to any redox-active system and provides a simple and powerful means for in situ examination of processes occurring at the surface of nanostructured materials.