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Graphene Quantum Dots (GQDs) are of interest to the biomedical community due to their unique fluorescence properties, which may be advantageous for biology and medicine. Advantages of this graphene nanomaterial over fluorescent dyes for biomedical imaging include bright emission, easy surface modification, biocompatibility, and anticipated low toxicity. We hypothesize that GQDs with desirable fluorescence properties which can be used for effective biomedical imaging (such as near infrared emission) may be synthesized from cheap carbon sources. Here, we show that these fluorescent GQDs are fabricated in a facile wet chemistry route using activated charcoal as the starting material. The GQDs were characterized with AFM, TEM, FTIR, PL spectroscopy, Raman spectroscopy and animal imaging techniques. The particles were visible in animals indicating their potential for biomedical imaging. The GQDs exhibited excitation that spanned the UV and visible ranges and emission that spanned the visible and near infrared ranges. The GQDs were an average of 4 nm in height, crystalline, from 1 to 60 nm in size. The GQDs were consistent with the presence of graphene and the following functional groups: C-O, C-H, C=C, and CO2H. In conclusion, GQDs with favorable photophysical properties can be produced from affordable and widely available raw materials for imaging and other biomedical application purposes.
The junction resistance control of conducting networks is a crucial factor for high performance of the network-structured conducting film. Here, we show that silver nanowire (AgNW) networks can be stabilized by using single-walled carbon nanotubes (SWCNTs) which were functionalized with 2-ureido-4[1H]pyrimidinone (UHP) moieties. UHP-modified SWCNTs allowed us to fabricate AgNW suspension containing SWCNTs without adding additional dispersant molecules. The stabilization of AgNW networks was achieved by minimizing the joule heating at the NW-NW junction assisted by in-situ interconnection with the work function modulated SWCNTs. We propose that the electrical transportation pathway was modulated by the SWCNTs through the SWCNT-AgNW junctions, which results in a relatively lower junction resistance than the NW-NW junction in the network film.
The mechanism for the precipitation of multilayer graphene was investigated with respect to the use of an Al2O3 barrier layer and Au capping layer. The Al2O3 barrier layer suppresses the dissolution of carbon into the catalyst, especially at low temperature, and assists a decrease in the density of graphene nuclei. On the other hand, the Au capping layer is beneficial to weaken the strong binding between the catalyst and the graphene carbon atoms, and enhances the surface migration of precipitated carbon adatoms. A combination of the Al2O3 barrier layer and Au capping layer is useful for the synthesis of high-quality graphene with large grains. On a sample with both layers annealed for 60 min, the area of 5-layer graphene islands is as large as 10 μm, and covers 60% of the entire surface. The Raman D/G band intensity ratio of 0.024 indicates the precipitated graphene is high quality.
Electrochemical Double Layer Capacitors, EDLC, using Cobalt sulfide- Graphene (CoSG) composite electrodes, were fabricated and the storage process was studied. CoSG composite was prepared by a simple chemical route. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Field Emission Scanning Electron microscopy (FESEM) were used to characterized the as prepared composites which indicated formation of Co S phase. Solutions of perfluorosulfonic acid and Polyvinylidene Fluoride (PVDF) were used as electrode binding material. The storage capacitance of the composites were studied in 1M KCl and 6M KOH electrolytes using standard electrochemical techniques like cyclic voltammetry, CV, electrochemical impedance spectroscopy, EIS, and discharge profiles. The capacitance was estimated for various binder concentrations for both the electrolytes. The concentration of perflurosulfonic acid binder of 0.8 wt% and PVDF of 0.04 wt% showed optimized specific capacitances of 657.8 F/gm and 1418.8 F/g, respectively. Some of the problems in storage density in activated carbon, like varying micro or meso pores, poor ion mobility due to varying pore distribution, low electrical conductivity, can be overcome by using Graphene and composites of Graphene. Graphene in various structural nomenclatures have been used by different groups for charge storage. Optimization of the electrode structure in terms of blend percentage, binder content and interface character in the frequency and time domain provides insights to the double layer interface structure.
This work reports the efficient structural restoration of defective graphene oxide (GO) to a crystalline graphene by an ultrahigh temperature process at around 1800 °C achieved by a solar furnace. The GO samples were treated at high temperature by irradiating concentrated sunlight and focusing it on the sample under an inert nitrogen environment at atmospheric and reduced pressure. The structural restoration of GO was analyzed by Raman spectra, and the features of their D- and 2D-bands were remarkably improved at ultrahigh temperatures. The restoration was induced not by a photochemical reaction but dominantly by a thermally stimulated reaction. The process under reduced pressure gives rise to significantly better features in the Raman spectra than that of the atmospheric condition. This tendency shows that a trace amount of impurities contained in pure nitrogen gas are not negligible and attack the GO surfaces to induce considerable defects. These results indicate the superiority of the ultrahigh temperature process at reduced pressure for efficient GO restoration and the formation of highly crystalline graphene.
Controlled amounts of colloidal Au nanoparticles (NPs), electrochemically pre-synthesized, were directly deposited on MWCNTs sensor devices by electrophoresis. Pristine and Au-functionalized MWCNT networked films were tested as active layers in resistive gas sensors for detection of pollutant gases. Au-modified CNT-chemiresistor demonstrated higher sensitivity to NO2 detecting up to sub-ppm level compared to pristine one. The investigation of the cross-sensitivity towards other pollutant gases revealed the decrease of the sensitivity to NO2 with the increase of Au content, and, on the other side, the increase of that to H2S; therefore the fine tune of the metal loading on CNTs has allowed to control not only the gas sensitivity but also the selectivity towards a specific gaseous analyte. Finally, the sensing properties of Au-decorated CNT sensor seem to be promising in environmental and automotive gas sensing applications, based on low power consumption and moderate operating temperature.
One-dimensional carbon nanomaterials (1-DCNMs), as one of the most promising one-dimension nanomaterials due to its unique microstructure, peculiar chemical, mechanical, thermal, and electronic properties, have long been considered as an important building block to construct micro-nano-electrics and devices. The growth controllability in direction, morphology and microstructure may provide a straightforward platform for fabricating high performance 1-DCNMs-based devices. Recently, electric and magnetic fields have emerged as key techniques to control the 1-DCNMs' growth direction, morphology and microstructure. In this paper, we focus explicitly on the 1-DCNMs preparations with assistance of a magnetic field, and the main problems that should be solved in the future are also discussed.
Carbon films deposited by filtered cathodic vacuum arc have been used to form high quality Schottky diodes on p-Si. Energetic deposition with an applied substrate bias of -1 kV and with a substrate temperature of 100 °C has produced carbon diodes with rectification ratios of ∼ 3 × 106, saturation currents of ∼0.02 nA and ideality factors close to unity (n = 1.05). Simulations were used to estimate the effective work function and the thickness of an interfacial mixed (C/SiO2) layer from the current/voltage characteristics of the diodes.
Nano-graphite oxide has been synthesized from graphite flakes using modified Hummer’s method. Fourier transform infrared (FT-IR) data, x-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed functionalization of the synthesised nano-graphitic platelets with oxygenated bonds. Using thermal embedding technique for the fabrication of self-assembled films, electrodes of nano-graphite oxide have been fabricated for enzyme free detection of cholesterol electrochemically. The electrodes provided a linear response for the enzyme less detection in the range of 50mg/dl to 500mg/dl with a correlation coefﬁcient, R, of 0.99784 and sensitivity of 1.0587 µA/mg.
A novel approach for synthesis of few layer graphene films on SiC has been developed which uses halogen based inductively coupled-reactive ion etching (ICP-RIE) and rapid thermal annealing (RTA) in atmospheric pressure argon. These films have been characterized using x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Surface characterization by XPS reveals the presence of defects similar to those observed for graphene oxide (GO) but at a much lower levels that those observed for GO. As in the case for GO, the defect density could be further reduced by chemical methods which improved carbon to defect ratio based on XPS analyses. Raman spectroscopy showed the presence of D, G and 2D peaks at 1330 cm-1, 1599 cm-1 and 2671 cm-1, respectively, which is comparable with similar graphene films formed by thermal annealing of SiC. The full widths at half max (FWHM) for these peaks was, however, comparable to those observed for GO. Electrical characterization of these graphene films using collinear four point probe measurements showed the electrical resistivity of these films is consistent with the observed values for few layer exfoliated graphene. Gas sensor structures were fabricated using lithography free methods, and initial gas response studies were performed for H2.