Showing papers on "Carbon nanotube published in 2012"

KOH activation of carbon-based materials for energy storage

Abstract: Because of their availability, adjustable microstructure, varieties of forms, and large specific surface area, porous carbon materials are of increasing interest for use in hydrogen storage adsorbents and electrode materials in supercapacitors and lithium–sulfur cells from the viewpoint of social sustainability and environmental friendliness. Therefore, much effort has been made to synthesize and tailor the microstructures of porous carbon materials via various activation procedures (physical and chemical activation). In particular, the chemical activation of various carbon sources using KOH as the activating reagent is very promising because of its lower activation temperature and higher yields, and well-defined micropore size distribution and ultrahigh specific surface area up to 3000 m2 g−1 of the resulting porous carbons. In this feature article, we will cover recent research progress since 2007 on the synthesis of KOH-activated carbons for hydrogen and electrical energy storage (supercapacitors and lithium–sulfur batteries). The textural properties and surface chemistry of KOH-activated carbons depend on not only the synthesis parameters, but also different carbon sources employed including fossil/biomass-derived materials, synthetic organic polymers, and various nanostructured carbons (e.g. carbon nanotubes, carbon nanofibers, carbon aerogels, carbide-derived carbons, graphene, etc.). Following the introduction to KOH activation mechanisms and processing technologies, the characteristics and performance of KOH-activated carbons as well as their relationships are summarized and discussed through the extensive analysis of the literature based on different energy storage systems.

Sulfur-doped graphene as an efficient metal-free cathode catalyst for oxygen reduction.

Abstract: Tailoring the electronic arrangement of graphene by doping is a practical strategy for producing significantly improved materials for the oxygen-reduction reaction (ORR) in fuel cells (FCs). Recent studies have proven that the carbon materials doped with the elements, which have the larger (N) or smaller (P, B) electronegative atoms than carbon such as N-doped carbon nanotubes (CNTs), P-doped graphite layers and B-doped CNTs, have also shown pronounced catalytic activity. Herein, we find that the graphenes doped with the elements, which have the similar electronegativity with carbon such as sulfur and selenium, can also exhibit better catalytic activity than the commercial Pt/C in alkaline media, indicating that these doped graphenes hold great potential for a substitute for Pt-based catalysts in FCs. The experimental results are believed to be significant because they not only give further insight into the ORR mechanism of these metal-free doped carbon materials, but also open a way to fabricate other ne...

Past achievements and future challenges in the development of optically transparent electrodes

Abstract: Increasing demand for raw materials means that alternatives to indium-tin oxide are desired for optically transparent electrode applications. Carbon nanotube, metal nanowire networks and regular metal grids have been investigated as possible options. In this review, these materials and recently rediscovered graphene are compared with the usual transparent conductive oxides.

An oxygen reduction electrocatalyst based on carbon nanotube–graphene complexes

Abstract: Oxygen reduction reaction catalysts based on precious metals such as platinum or its alloys are routinely used in fuel cells because of their high activity. Carbon-supported materials containing metals such as iron or cobalt as well as nitrogen impurities have been proposed to increase scalability and reduce costs, but these alternatives usually suffer from low activity and/or gradual deactivation during use. Here, we show that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions. Under a unique oxidation condition, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes. The graphene sheets contain extremely small amounts of irons originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst, as revealed by atomic-scale microscopy and electron energy loss spectroscopy. Whereas the graphene sheets formed from the unzipped part of the outer wall of the nanotubes are responsible for the catalytic activity, the inner walls remain intact and retain their electrical conductivity, which facilitates charge transport during electrocatalysis.

Three-Dimensional Nitrogen and Boron Co-doped Graphene for High-Performance All-Solid-State Supercapacitors

Abstract: carbide-derived carbon, [ 12 ] carbon nanotubes (CNTs), [ 14–17 ] and graphene, [ 6 , 7 , 10 , 18 , 19 ] possess notable features including high surface area, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as thinfi lm electrode materials for ASSSs. However, the fabrication of ASSSs generally involves complex solution processing, highpressure pressing, high-temperature sintering, and sputtering techniques. [ 11 , 12 , 14–17 ] Moreover, polymer binders and conductive additives are required to enhance the adhesion between electrode materials and substrates as well as to improve the conductivity of the electrode, which unavoidably leads to decreased energy density of the devices. [ 6 , 20 ] Therefore, several challenges remain in developing ASSSs, such as to: i) explore high-performance electrode materials, ii) enhance the interfacial compatibility between electrode and solid-state electrolyte, and iii) simplify the device fabrication process. Graphene aerogels (GAs) represent a new class of ultralight and porous carbon materials that are associated with high

Biomimetic superelastic graphene-based cellular monoliths

Abstract: Many applications proposed for graphene require multiple sheets be assembled into a monolithic structure. The ability to maintain structural integrity upon large deformation is essential to ensure a macroscopic material which functions reliably. However, it has remained a great challenge to achieve high elasticity in three-dimensional graphene networks. Here we report that the marriage of graphene chemistry with ice physics can lead to the formation of ultralight and superelastic graphene-based cellular monoliths. Mimicking the hierarchical structure of natural cork, the resulting materials can sustain their structural integrity under a load of >50,000 times their own weight and can rapidly recover from >80% compression. The unique biomimetic hierarchical structure also provides this new class of elastomers with exceptionally high energy absorption capability and good electrical conductivity. The successful synthesis of such fascinating materials paves the way to explore the application of graphene in a self-supporting, structurally adaptive and 3D macroscopic form.

Spherical Ordered Mesoporous Carbon Nanoparticles with High Porosity for Lithium–Sulfur Batteries

Abstract: Rechargeable lithium–sulfur (Li–S) batteries are attracting increasing attention due to their high theoretical specific energy density, which is 3 to 5 times higher than that of Li-ion batteries based on intercalation chemistry. Since the electronic conductivity of sulfur is extremely low, conductive carbon materials with high accessible porosity to “wire” and contain the sulfur are an essential component of the positive electrode. During the past decades, attempts have been made to fabricate C/S composites using carbon black, activated carbons (ACs), and carbon nanotubes (CNTs). Although improvements resulted, the cathodes suffered from inhomogeneous contact between the active material and the electronic conductors. A major step forward in fabricating a uniform C/S composite was reported in 2009. Some of us employed CMK-3, an ordered mesoporous carbon (OMC) featuring high specific surface area and large pore volume as a scaffold. As much as 70 wt% sulfur was incorporated into the uniform 3–4 nm mesopores, and the cells exhibited reversible capacities up to 1350 mAhg , albeit at moderate rates. Inspired by this, another OMC, a bulk bimodal mesoporous carbon (BMC-1) was investigated as a Li-S cathode. The favorable pore dimensions and large pore volume greatly improved the rate performance. An electrode with 40 wt% S showed a high initial discharge capacity of 1135 mAhg 1 at a current rate of 1 C (defined as discharge/ charge in one hour). However, similar to other reports, the capacity is sensitive to the sulfur ratio, dropping to 718 mAhg 1 at a sulfur content of 60 wt%. These results suggest that the texture of the mesoporous carbon could be further enhanced. Recently, Archer et al. reported nanoscale hollow porous C/S spheres prepared through vapor infusion. These materials displayed good cyclability and capacity at a C/5 rate, illustrating the advantages of nanosized porous carbon in the sulfur cathodes. Here we report the synthesis of unique nanoscale spherical OMCs with extremely high bimodal porosities. The particles were investigated as a cathode material and sulfur host in Li–S batteries where they showed high initial discharge capacity and good cyclability without sacrificing rate capability. Unlike bulk porous carbons, these carbon– sulfur sphere electrodes did not display significant capacity fading with the increase of sulfur content in the cathodes. We show that the nanoscale morphology of these materials is of key importance for ensuring very efficient use of the sulfur content even at high cycling rates. Morphology control is a central issue in OMC synthesis. There are numerous examples of mesoporous bulk materials obtained either by hard-templating or soft-templating, including thin films, membranes or free fibers. Most syntheses use evaporation-induced self-assembly (EISA) followed by thermal treatment for template-removal and carbonization. It is a challenge to either create solution-based OMC nanoparticle syntheses or to adapt the established EISA methods to nanoparticles. Only few examples of OMC nanoparticles have been reported so far which are mostly unsuitable for applications in Li–S cells due to low pore volume and/or surface area. Approaches include templating with PMMA colloidal crystals or mesoporous silica nanoparticles, aerosol-assisted synthesis, ultrasonic emulsification or hydrothermal synthesis. Ordered arrays of fused mesoporous carbon spheres were reported by Liu et al. using a macroporous silica as template. Recently Lei et al. reported the synthesis of 65 nm mesoporous carbon nanospheres, with both 2.7 nm mesopores and high textural porosity (surface area of 2400 mg ). These showed promising supercapacitor properties. Our spherical OMC nanoparticles of 300 nm in diameter, prepared by a novel method, can be dispersed in water by sonification to form stable colloidal suspensions. The spherical mesoporous carbon nanoparticles were obtained in a twostep casting process. An opal structure of PMMA spheres was cast with a silica precursor solution to form a silica inverse opal. The inverse opal was then used as template for a triconstituent precursor solution containing resol as the carbon precursor, tetraethylorthosilicate (TEOS) as the silica precursor and the block copolymer Pluronic F127 as a structure-directing agent. Carbonization was followed by etching of the silica template and the silica in the carbon/silica nanocomposite, resulting in the formation of OMC with hierarchical porosity. Through the presence of silica in the [*] J. Schuster, B. Mandlmeier, Prof. Dr. T. Bein Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU), Butenandtstrasse 5–13 (Gerhard Ertl Building), 81377 Munich (Germany) E-mail: tbein@cup.uni-muenchen.de Homepage: http://bein.cup.uni-muenchen.de G. He, T. Yim, K. T. Lee, Prof. Dr. L. F. Nazar Department of Chemistry, University of Waterloo 200 University Avenue West, Waterloo, Ontario N2L 3G1 (Canada) E-mail: lfnazar@uwaterloo.ca [] These authors contributed equally to this work.

Inkjet-printed graphene electronics.

Abstract: We demonstrate inkjet printing as a viable method for large-area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to ∼95 cm2 V–1 s–1, as well as transparent and conductive patterns, with ∼80% transmittance and ∼30 kΩ/□ sheet resistance. This paves the way to all-printed, flexible, and transparent graphene devices on arbitrary substrates.

Highly Stretchable and Highly Conductive Metal Electrode by Very Long Metal Nanowire Percolation Network

Abstract: A highly stretchable metal electrode is developed via the solution-processing of very long (>100 μm) metallic nanowires and subsequent percolation network formation via low-temperature nanowelding. The stretchable metal electrode from very long metal nanowires demonstrated high electrical conductivity (~9 ohm sq(-1) ) and mechanical compliance (strain > 460%) at the same time. This method is expected to overcome the performance limitation of the current stretchable electronics such as graphene, carbon nanotubes, and buckled nanoribbons.

Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide.

Abstract: The high rate of electron/hole pair recombination reduces the quantum yield of the processes with TiO2 and represents its major drawback. Adding a co-adsorbent increases the photocatalytic efficiency of TiO2. In order to hybridize the photocatalytic activity of TiO2 with the adsorptivity of carbon nanotube, a composite of multi-walled carbon nanotubes and titanium dioxide (MWCNT/TiO2) has been synthesized. The composite was characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared absorption spectroscopy (FTIR), and diffuse reflectance UV–vis spectroscopy. The catalytic activity of this composite material was investigated by application of the composite for the degradation of methyl orange. It was observed that the composite exhibits enhanced photocatalytic activity compared with TiO2. The enhancement in photocatalytic performance of the MWCNT/TiO2 composite is explained in terms of recombination of photogenerated electron–hole pairs. In addition, MWCNT acts as a dispersing agent preventing TiO2 from agglomerating activity during the catalytic process, providing a high catalytically active surface area. This work adds to the global discussion of how CNTs can enhance the efficiency of catalysts.

Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials

Abstract: We found that an optimized mixture of graphene and multilayer graphene - produced by the high-yield inexpensive liquid-phase-exfoliation technique - can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300 % in the graphene-based polymer at the filler loading fraction f =10 vol. %. It was determined that a relatively high concentration of single-layer and bilayer graphene flakes (~10-15%) present simultaneously with thicker multilayers of large lateral size (~ 1 micrometer) were essential for the observed unusual K enhancement. The thermal conductivity of a commercial thermal grease was increased from an initial value of ~5.8 W/mK to K=14 W/mK at the small loading f=2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene - multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene - matrix interface.

Ferroferric Oxide/Multiwalled Carbon Nanotube vs Polyaniline/Ferroferric Oxide/Multiwalled Carbon Nanotube Multiheterostructures for Highly Effective Microwave Absorption

Abstract: Light-weight nanocomposites filled with carbon nanotubes (CNTs) are developed for their significant potentials in electromagnetic shielding and attenuation for wide applications in electronics, communication devices, and specific parts in aircrafts and vehicles. Specifically, the introduction of a second phase into/onto CNTs for achieving CNT-based heterostructures has been widely pursued due to the enhancement in either dielectric loss or magnetic loss. In this work, ferroferric oxide (Fe(3)O(4)) was selected as the phase in multiwalled carbon nanotube (MWCNT)-based composites for enhancing magnetic properties to obtain improved electromagnetic attenuation. A direct comparison between the two-phase heterostructures (Fe(3)O(4)/MWCNTs) and polyaniline (PANI) coated Fe(3)O(4)/MWCNTs, namely, three-phase heterostructures (PANI/Fe(3)O(4)/MWCNTs), was made to investigate the interface influences of Fe(3)O(4) and PANI on the complex permittivity and permeability separately. Compared to PANI/Fe(3)O(4)/MWCNTs, Fe(3)O(4)/MWCNTs exhibited enhanced magnetic properties coupled with increased dielectric properties. Interfaces between MWCNTs and heterostructures were found to play a role in the corresponding properties. The evaluation of microwave absorption of their wax composites was carried out, and the comparison between Fe(3)O(4)/MWCNTs and PANI/Fe(3)O(4)/MWCNTs with respect to highly efficient microwave absorption and effective absorption bandwidth was discussed.

Micro-Supercapacitors Based on Interdigital Electrodes of Reduced Graphene Oxide and Carbon Nanotube Composites with Ultrahigh Power Handling Performance

Abstract: A novel method for fabricating micro-patterned interdigitated electrodes based on reduced graphene oxide (rGO) and carbon nanotube (CNT) composites for ultra-high power handling micro-supercapacitor application is reported. The binder-free microelectrodes were developed by combining electrostatic spray deposition (ESD) and photolithography lift-off methods. Without typically used thermal or chemical reduction, GO sheets are readily reduced to rGO during the ESD deposition. Electrochemical measurements show that the in-plane interdigital design of the microelectrodes is effective in increasing accessibility of electrolyte ions in-between stacked rGO sheets through an electro-activation process. Addition of CNTs results in reduced restacking of rGO sheets and improved energy and power density. Cyclic voltammetry (CV) measurements show that the specific capacitance of the micro-supercapacitor based on rGO–CNT composites is 6.1 mF cm−2 at 0.01 V s−1. At a very high scan rate of 50 V s−1, a specific capacitance of 2.8 mF cm−2 (stack capacitance of 3.1 F cm−3) is recorded, which is an unprecedented performance for supercapacitors. The addition of CNT, electrolyte-accessible and binder-free microelectrodes, as well as an interdigitated in-plane design result in a high-frequency response of the micro-supercapacitors with resistive-capacitive time constants as low as 4.8 ms. These characteristics suggest that interdigitated rGO–CNT composite electrodes are promising for on-chip energy storage application with high power demands.

Assembling carbon-coated α-Fe2O3 hollow nanohorns on the CNT backbone for superior lithium storage capability

Abstract: Novel hierarchical nanostructures composed of carbon coated α-Fe2O3 hollow nanohorns on carbon nanotube (CNT) backbones have been constructed by direct growth and thermal transformation of β-FeOOH nanospindles on CNTs, followed by carbon nanocoating. When evaluated as a potential anode material for lithium-ion batteries, such hierarchical structures exhibit superior lithium storage capabilities by virtue of their advantageous structural features.

Oxygen Reduction Electrocatalyst Based on Strongly Coupled Cobalt Oxide Nanocrystals and Carbon Nanotubes

Abstract: Electrocatalyst for oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and energy-intensive industries. The design and synthesis of highly active ORR catalysts with strong durability at low cost is extremely desirable but remains challenging. Here, we used a simple two-step method to synthesize cobalt oxide/carbon nanotube (CNT) strongly coupled hybrid as efficient ORR catalyst by directly growing nanocrystals on oxidized multiwalled CNTs. The mildly oxidized CNTs provided functional groups on the outer walls to nucleate and anchor nanocrystals, while retaining intact inner walls for highly conducting network. Cobalt oxide was in the form of CoO due to a gas-phase annealing step in NH3. The resulting CoO/nitrogen-doped CNT (NCNT) hybrid showed high ORR current density that outperformed Co3O4/graphene hybrid and commercial Pt/C catalyst at medium overpotential, mainly through a 4e reduction pathway. The metal oxide/carbon nanotube hybrid was found to be advantageous o...

Sub-10 nm carbon nanotube transistor.

Abstract: Although carbon nanotube (CNT) transistors have been promoted for years as a replacement for silicon technology, there is limited theoretical work and no experimental reports on how nanotubes will perform at sub-10 nm channel lengths. In this manuscript, we demonstrate the first sub-10 nm CNT transistor, which is shown to outperform the best competing silicon devices with more than four times the diameter-normalized current density (2.41 mA/μm) at a low operating voltage of 0.5 V. The nanotube transistor exhibits an impressively small inverse subthreshold slope of 94 mV/decade-nearly half of the value expected from a previous theoretical study. Numerical simulations show the critical role of the metal-CNT contacts in determining the performance of sub-10 nm channel length transistors, signifying the need for more accurate theoretical modeling of transport between the metal and nanotube. The superior low-voltage performance of the sub-10 nm CNT transistor proves the viability of nanotubes for consideration in future aggressively scaled transistor technologies.

Very long Ag nanowire synthesis and its application in a highly transparent, conductive and flexible metal electrode touch panel

Abstract: The future electronics will be soft, flexible and even stretchable to be more human friendly in the form of wearable computers. However, conventional electronic materials are usually brittle. Recently, carbon based materials are intensively investigated as a good candidate for flexible electronics but with limited mechanical and electrical performances. Metal is still the best material for electronics with great electrical properties but with poor transparency and mechanical performance. Here we present a simple approach to develop a synthesis method for very long metallic nanowires and apply them as new types of high performance flexible and transparent metal conductors as an alternative to carbon nanotubes, graphene and short nanowire based flexible transparent conductors and indium tin oxide based brittle transparent conductors. We found that very long metallic nanowire network conductors combined with a low temperature laser nano-welding process enabled superior transparent flexible conductors with high transmittance and high electrical conductivity. Further, we demonstrated highly flexible metal conductor LED circuits and transparent touch panels. The highly flexible and transparent metal conductors can be mounted on any non-planar surfaces and applied for various opto-electronics and ultimately for future wearable electronics.

Carbon-based nanostructured materials and their composites as supercapacitor electrodes

Abstract: This critical review provides an overview of current research on carbon-based nanostructured materials and their composites for use as supercapacitor electrodes. Particular emphasis has been directed towards basic principles of supercapacitors and various factors affecting their performance. The focus of the review is the detailed discussion regarding the performance and stability of carbon-based materials and their composites. Pseudo-active species, such as, conducting polymer/metal oxide have been found to exhibit pseudo-capacitive behavior and carbon-based materials demonstrate electrical double layer capacitance. Carbon-based materials, such as, graphene, carbon nanotubes, and carbon nanofibers, provide high surface area for the deposition of conducting polymer/metal oxide that facilitates the efficient ion diffusion phenomenon and contribute towards higher specific capacitance of the carbon based composite materials with excellent cyclic stability. However, further scope of research still exists from the view point of developing high energy supercapacitor devices in a cost effective and simple way. This review will be of value to researchers and emerging scientists dealing with or interested in carbon chemistry.

Amphiphilic Egg-Derived Carbon Dots: Rapid Plasma Fabrication, Pyrolysis Process, and Multicolor Printing Patterns

Abstract: Carbon-based photoluminescent nanoparticles have recently received increased interest, owing to their favorable optical properties along with their biocompatibility and low toxicity. Such nascent nanomaterials, the so-called carbon dots (CDs or C-dots), are a promising alternative to more toxic metal-based semiconductor quantum dots (QDs) for applications such as bioimaging. Recent advances in the synthesis of CDs allow them to be formed from fine carbon structures (like graphene and multi-wall carbon nanotubes) by topdown methods, or from chemical precursors (like ammonium citrate and ethylenediaminetetraacetic acid) by bottom-up approaches. Typically, these CDs require surface oxidation and/or further passivation to emit fluorescence, which also makes them hydrophilic. Alternatively, some one-step strategies to fabricate surface-passivated CDs have also been shown. We reported a one-step synthesis of multicolor CDs from pyrolysis of epoxy-enriched polystyrene photonic crystals and their potential for use in light-emitting diodes. Herein, we present a simple and rapid strategy to fabricate CDs from cheap and natural carbon sources and further extend their application as printing “inks”. The fluorescent CDs developed herein have the following notable characteristics: 1) one-step generation in minutes from low-cost, natural, edible chicken eggs by plasma-induced pyrolysis; 2) good amphiphilicity with high solubility in a broad range of aqueous and organic solvents; 3) resistance to acids and bases; 4) versatile applications as fluorescent carbon inks for luminescent patterns. Figure 1 shows the fabrication of egg-derived fluorescent CDs and their application as “inks” for luminescent patterns using inkjet or silk-screen printing. We chose chicken eggs as the starting material to maintain low toxicity and affordability of the final product. Low-temperature plasma with highenergy, inherently charged particles (electrons or cations) and excited neutral species was used to create an active chemical environment for the synthesis of the nanostructures. As shown in Figure 1, the egg was separated into egg white and egg yolk, using an egg-separator, prior to use. A glass dish filled with egg white or yolk was placed between two quartz slides (height= 1.5 cm) of the plasma generator. Subsequently, intense and uniform plasma beams generated from the upper electrode (voltage= 50 V, current= 2.4 A) irradiated the egg samples for 3 min to yield dark black products, referred to as CDpew and CDpey for the plasma-treated egg white and yolk, respectively. The yield of CDs from the egg sample was calculated to be approximately 5.96%. Elemental analysis showed an increase in the carbon content of the products (62.42% for CDpey and 56.75% for CDpew) in comparison to that of the starting material (57.55% for egg yolk and 43.50% for egg white), implying carbonization occurs during the plasma treatment (Supporting Information, Table S1). Significantly, solutions of CDpew and CDpey display bright blue fluorescence under UV light (lex= 302 nm). Figure 2 shows high-resolution transmission electron microscope (HRTEM) images of the CDs. CDpey had uniform dispersion without apparent aggregation and a mean particle diameter (Dp) of 2.15 nm (Figure 2a and Figure S2). Detectable rings in the selected-area electron-diffraction (SAED) pattern revealed the crystalline structure of CDpey (Figure 2a inset). Well-resolved lattice fringes with an interplanar spacing of 0.208 nm were observed (Figure 2b), which is close to the (100) facet of graphite. On the other hand, CDpew was well distributed (Dp= 3.39 nm) and appeared Figure 1. Digital photographs of plasma-induced fabrication of eggderived CDs and their application as fluorescent carbon inks. Egg white or yolk, after a few minutes of plasma treatment under ambient conditions, were transformed into well-defined CDs with bright blue emission under UV light. The CD solutions can also be used as inks for making luminescent patterns by inkjet or silk-screen printing.

Synergistic effects from graphene and carbon nanotubes enable flexible and robust electrodes for high-performance supercapacitors.

Abstract: Flexible and lightweight energy storage systems have received tremendous interest recently due to their potential applications in wearable electronics, roll-up displays, and other devices. To manufacture such systems, flexible electrodes with desired mechanical and electrochemical properties are critical. Herein we present a novel method to fabricate conductive, highly flexible, and robust film supercapacitor electrodes based on graphene/MnO2/CNTs nanocomposites. The synergistic effects from graphene, CNTs, and MnO2 deliver outstanding mechanical properties (tensile strength of 48 MPa) and superior electrochemical activity that were not achieved by any of these components alone. These flexible electrodes allow highly active material loading (71 wt % MnO2), areal density (8.80 mg/cm2), and high specific capacitance (372 F/g) with excellent rate capability for supercapacitors without the need of current collectors and binders. The film can also be wound around 0.5 mm diameter rods for fabricating full cells...

Reduced graphene oxide for catalytic oxidation of aqueous organic pollutants.

Abstract: We discovered that chemically reduced graphene oxide, with an ID/IG >1.4 (defective to graphite) can effectively activate peroxymonosulfate (PMS) to produce active sulfate radicals. The produced sulfate radicals (SO4•—) are powerful oxidizing species with a high oxidative potential (2.5–3.1 vs 2.7 V of hydroxyl radicals), and can effectively decompose various aqueous contaminants. Graphene demonstrated a higher activity than several carbon allotropes, such as activated carbon (AC), graphite powder (GP), graphene oxide (GO), and multiwall carbon nanotube (MWCNT). Kinetic study of graphene catalyzed activation of PMS was carried out. It was shown that graphene catalysis is superior to that on transition metal oxide (Co3O4) in degradation of phenol, 2,4-dichlorophenol (DCP) and a dye (methylene blue, MB) in water, therefore providing a novel strategy for environmental remediation.

In vivo NIR fluorescence imaging, biodistribution, and toxicology of photoluminescent carbon dots produced from carbon nanotubes and graphite.

Abstract: Oxidization of carbon nanotubes by a mixed acid has been utilized as a standard method to functionalize carbon nanomaterials for years. Here, the products obtained from carbon nanotubes and graphite after a mixed-acid treatment are carefully studied. Nearly identical carbon dot (Cdot) products with diameters of 3-4 nm are produced using this approach from a variety of carbon starting materials, including single-walled carbon nanotubes, multiwalled carbon nanotubes, and graphite. These Cdots exhibit strong yellow fluorescence under UV irradiation and shifted emission peaks as the excitation wavelength is changed. In vivo fluorescence imaging with Cdots is then demonstrated in mouse experiments, by using varied excitation wavelengths including some in the near-infrared (NIR) region. Furthermore, in vivo biodistribution and toxicology of those Cdots in mice over different periods of time are studied; no noticeable signs of toxicity for Cdots to the treated animals are discovered. This work provides a facile method to synthesize Cdots as safe non-heavy-metal-containing fluorescent nanoprobes, promising for applications in biomedical imaging.

Strong, Conductive, Lightweight, Neat Graphene Aerogel Fibers with Aligned Pores

Abstract: Liquid crystals of anisotropic colloids are of great significance in the preparation of their ordered macroscopic materials, for example, in the cases of carbon nanotubes and graphene. Here, we report a facile and scalable spinning process to prepare neat “core–shell” structured graphene aerogel fibers and three-dimensional cylinders with aligned pores from the flowing liquid crystalline graphene oxide (GO) gels. The uniform alignment of graphene sheets, inheriting the lamellar orders from GO liquid crystals, offers the porous fibers high specific tensile strength (188 kN m kg–1) and the porous cylinders high compression modulus (3.3 MPa). The porous graphene fibers have high specific surface area up to 884 m2 g–1 due to their interconnected pores and exhibit fine electrical conductivity (2.6 × 103 to 4.9 × 103 S m–1) in the wide temperature range of 5–300 K. The decreasing conductivity with decreasing temperature illustrates a typical semiconducting behavior, and the 3D interconnected network of 2D graph...

Nitrogen-doped graphene foams as metal-free counter electrodes in high-performance dye-sensitized solar cells.

Abstract: Owing to their low-cost production, simple fabrication, and high energy conversion efficiency, dye-sensitized solar cells (DSSCs) have attracted much attention since Oregan and Gr tzel s seminal report in 1991. A typical DSSC device consists of a dye-adsorbed TiO2 photoanode, counter electrode, and iodide electrolyte. The counter (cathode) electrode plays a key role in regulating the DSSC device performance by catalyzing the reduction of the iodide–triiodide redox species used as a mediator to regenerate the sensitizer after electron injection. The ideal counter electrode material should possess a low sheet resistance, high reduction catalytic activity, good chemical stability, and low production costs. Because of its excellent electrocatalytic activity for the iodine reduction, high conductivity, and good chemical stability, platinum has been widely used as a counter electrode in DSSCs. However, the high costs of Pt and its limited reserves in nature have been a major concern for the energy community. Recently, much effort has been made to reduce or replace Pt-based electrodes in DSSCs. In particular, carbon black, carbon nanoparticles, carbon nanotubes, and graphene nanosheets have been studied as the counter electrode in DSSCs. However, their electrical conductivities and reduction catalytic activities still cannot match up to those of platinum. To improve the device performance for DSSCs with a carbon-based counter electrode, it is important to balance its electrical conductivity and the electrocatalytic activity. Since the electrocatalytic activity of graphene for the triiodide reduction often increases with increasing number of defect sites (e.g., oxygen-containing functional groups in reduced graphene oxide), a perfect graphene sheet may have a low charge-transfer resistance (Rct), but a limited number of active sites for catalyzing the triiodide reduction. Unlike chemical functionalization of graphene to introduce electrocatalytic active sites by damaging the conjugated structure in the graphitic basal plan with a concomitant decrease in the electrical conductivity, doping the carbon network with heteroatoms (e.g., N, B, and P) can introduce electrocatalytic active sites with a minimized change of the conjugation length. Furthermore, heteroatom doping has also been demonstrated to enhance the electrical conductivity and surface hydrophilicity to facilitate charge-transfer and electrolyte–electrode interactions, respectively, and even impart electrocatalytic activities. Indeed, our recent articles, along with articles of others, on nitrogen doping of carbon nanotubes and graphene have clearly shown that nitrogen-doped carbon nanomaterials can act as metal-free electrodes to show even higher electrocatalytic activities, better long-term operation stability, and more tolerance to crossover/poisoning effects relative to a platinum electrode used for oxygen reduction in fuel cells. The newly discovered electrocatalytic reduction activities, together with the doping-enhanced electrical conductivities and surface hydrophilicity, made N-doped carbon nanomaterials ideal as low-cost, but very effective, counter electrodes in DSSCs. To our best knowledge, however, the possibility for N-doped carbon nanomaterials to be used as metal-free electrocatalysts at the counter electrode for triiodide reduction in DSSCs has not been exploited. In the present study, we prepared three-dimensional (3D) N-doped graphene foams (N-GFs) with a nitrogen content as high as 7.6% by annealing the freeze-dried graphene oxide foams (GOFs) in ammonia, and used the resultant 3D N-GFs supported by fluorine-doped tin oxide (FTO) glass substrates as the counter electrode in DSSCs. We found that the resultant DSSCs with the foamlike N-doped graphene counter electrode showed a power conversion efficiency as high as 7.07%, a value which is among the highest efficiencies reported for DSSCs with a metal-free carbon-based counter electrode and is comparable to that of DSSCs with a Pt counter electrode (7.44%) constructed under the same condition. The observed superb performance of DSSCs with the newly developed 3D N-GF metal-free counter electrode can be attributed to the heteroatom doping-induced high [*] Dr. Y. Xue, Dr. H. Chen, Dr. J. Qu, Prof. L. Dai Institute of Advanced Materials for Nano-Bio Applications, School of Ophthalmology and Optometry, Wenzhou Medical College 270 Xueyuan Xi Road, Wenzhou, Zhejiang 325027 (China) E-mail: jia.qu@163.com

Dispersion of Carbon Nanotubes: Mixing, Sonication, Stabilization, and Composite Properties

Abstract: Advances in functionality and reliability of carbon nanotube (CNT) composite materials require careful formulation of processing methods to ultimately realize the desired properties. To date, controlled dispersion of CNTs in a solution or a composite matrix remains a challenge, due to the strong van der Waals binding energies associated with the CNT aggregates. There is also insufficiently defined correlation between the microstructure and the physical properties of the composite. Here, we offer a review of the dispersion processes of pristine (non-covalently functionalized) CNTs in a solvent or a polymer solution. We summarize and adapt relevant theoretical analysis to guide the dispersion design and selection, from the processes of mixing/sonication, to the application of surfactants for stabilization, to the final testing of composite properties. The same approaches are expected to be also applicable to the fabrication of other composite materials involving homogeneously dispersed nanoparticles.