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1.
This study presents a versatile and scalable strategy of ‘oxidation controlled exfoliation’ of rGO nanosheets synthesized from both Hummers and modified Hummers method. A co-relation between degree of oxidation of graphite oxide (GO) sheets and exfoliation of resulting synthesized rGO nanosheets has been successfully developed which in turn reflects in various properties of rGO sheets. The extent of exfoliation of rGO sheets has been well analyzed by XRD, SEM, BET and TEM techniques. Moreover, the quantitative analysis of degree of oxidation of GO has been estimated from FTIR spectra using quotient law method. The variations in number of rGO layers, defect density and sp2 domain size have been investigated in detail by Raman spectroscopic technique. Both qualitative-quantitative analysis of rGO nanosheets have been discussed from their SAED pattern and HR-TEM images. The optical characterization of GO and corresponding rGO nanosheets has been studied in detail by UV- Vis spectroscopic technique.  相似文献   

2.
Abstract

This work studies the application of supercritical-phase exfoliation method to produce 100% yield of high-quality graphene. This simple and cost-effective method utilizes supercritical carbon dioxide and ultrasonication to produce pure and defect-free mono-, few- and multi-layer graphene sheets. The process parameters such as pressure, sonication time, sonication amplitude and the amount of starting graphite were examined. The production of defect-free single-, few- and multi-layer graphene sheets was confirmed using atomic force microscopy and Raman spectroscopy. The Fourier-transform infrared spectroscopy confirms that our method does not cause any oxidation to the synthesized graphene. The conductivity of the best yield graphene sample has been tested by four-point probe method and high electrical conductivity of 8.5?×?104 S/m was recorded. The synthesized graphene can be used in many applications such as supercapacitors, batteries, composites and conductive inks.  相似文献   

3.
Electrostatic deposition of graphene   总被引:2,自引:0,他引:2  
Loose graphene sheets, one to a few atomic layers thick, are often observed on freshly cleaved HOPG surfaces. A straightforward technique using electrostatic attraction is demonstrated to transfer these graphene sheets to a selected substrate. Sheets from one to 22?layers thick have been transferred by this method. One sheet after initial deposition is measured by atomic force microscopy to be only an atomic layer thick (~0.35?nm). A few weeks later, this height is seen to increase to ~0.8?nm. Raman spectroscopy of a single layer sheet shows the emergence of an intense D band which dramatically decreases as the number of layers in the sheet increase. The intense D band in monolayer graphene is attributed to the graphene conforming to the roughness of the substrate. The disruption of the C-C bonds within the single graphene layer could also contribute to this intense D band as evidenced by the emergence of a new band at 1620?cm(-1).  相似文献   

4.
A short-time and low-cost synthesis route was used to produce large lateral size (from 2 to 15 μm) from monolayers to few layers of graphene by a two-step process of electrochemical exfoliation with a deep eutectic solvent in a mixture with water that can be reused, and ultrasonic bath. The graphene was characterized by SEM, TEM, AFM, Raman and electrochemical activity. During the electrochemical exfoliation, high expanded graphene particles were obtained and these were dispersed in a mixture of water with 5%wt ethylene glycol by an ultrasonic bath in order to complete the exfoliation process. An enhancement of the electrical conductivity of these dispersions was obtained with the increase of graphene concentration, 0.38 mg/mL, which best result was achieved with 30 wt% water and a DC voltage of 10 V. It was possible to add a conductive layer to a glass substrate with the graphene obtained and Tyndall effect was observed.  相似文献   

5.
We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single-layered graphene sheets being tens of microns wide in lateral dimensions is assessed by complementary probes including spatially resolved micro-Raman spectroscopy, atomic force microscopy and electrostatic force microscopy. This versatile method opens the way for deposition of graphene on any substrates, including flexible ones.  相似文献   

6.
We demonstrate a synthesis of graphene layers on graphene templates prepared by the mechanical exfoliation of graphite crystals using a developed chemical vapor deposition (CVD) apparatus that has a furnace with three temperature zones and can regulate the temperatures separately in each zone. This results in individual control over the decomposition reaction of the carbon feedstock and the growth of graphene layers by activated carbon species. CVD growth using multi-temperature zones provides wider temperature windows appropriate to grow graphene layers. We observed that graphene layers proceed by a layer-by-layer growth mode using an optical microscopy, an atomic force microscopy, and Raman spectroscopy. This result suggests that a graphene growth technique using the CVD apparatus is a potential approach for making graphene sheets with precise control of the layer numbers.  相似文献   

7.
利用高压均质液相剥离法,以鳞片石墨为原料,水为介质,制备高浓度石墨烯水分散液。采用紫外可见光谱研究表明活性剂浓度、高压均质压力和循环次数对石墨烯水分散液浓度C_G的影响。通过拉曼光谱、扫描电镜、透射电镜、激光粒度仪分析水分散液中石墨烯的结构和形貌。结果表明:通过调节各工艺参数,获得了浓度为324.3mg·L-1的石墨烯水分散液,所得浓度是超声液相剥离法的10倍;石墨烯水分散液中石墨烯缺陷少、厚度薄、片径大,具有良好的品质;将所得石墨烯分散液制备石墨烯自支撑膜,其电导率可达3.2×10~4S·m-1。  相似文献   

8.
Graphene has superior electrical conductivity than graphite and other allotropes of carbon because of its high surface area and chemical tolerance. Electrochemically processed graphene sheets were obtained through the reduction of graphene oxide from hydrazine hydrate. The prepared samples were heated to different temperatures such as 673 and 873 K. X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM), Raman spectra and conductivity measurements were made for as-prepared and heat-treated graphene samples. XRD pattern of graphene shows a sharp and intensive peak centred at a diffraction angle (2θ) of 26·350. FTIR spectra of as-prepared and heated graphene were used to confirm the oxidation of graphite. TEM results indicated that the defect density and number of layers of graphene sheets were varied with heating temperature. The hexagonal sheet morphology and purity of as-prepared and heat treated samples were confirmed by SEM–EDX and Raman spectroscopy. The conductivity measurements revealed that the conductivity of graphene was decreased with an increase in heating temperature. The present study explains that graphene with enhanced functional properties can be achieved from the as-prepared sample.  相似文献   

9.
Large-scale production of high-quality graphene is very critical for practical applications of graphene materials and devices. Exfoliation of graphite in an aqueous solution of surfactants is one of the most promising approaches to produce graphene. In this study, a novel anionic surfactant [sulfonated used engine oil (SUEO)], which was prepared from used engine oil, was employed to exfoliate the graphite nanoplatelets into graphene sheets in an aqueous solution under sonication to form a stable dispersion. The efficiency of SUEO for exfoliating and dispersing graphene was investigated and compared with that of traditional surfactants, such as sodium dodecyl sulfate, sodium dodecyl benzene sulfate, cetyl trimethyl ammonium bromide, and polyvinylpyrrolidone. Result showed that the graphene dispersion with excellent stability had a higher concentration (0.477 mg/mL) than others at 0.5 g/L optimal SUEO dosage in 4 h sonication time. The superior performance of SUEO can be attributed to its special molecular structures, whose hydrophobic moieties contain cycloalkanes/aromatics with different molecular weights and/or side chain –R with different lengths. Structural diversities are very helpful to the “jigsaw-puzzle” process on the graphene surface, where the total interfacial energy of the mixture system was minimized. Microscopic (SEM, TEM, and AFM) and spectroscopic (XRD, XPS, and Raman) measurements revealed that the dispersion consisted of few-layer graphene sheets with lower levels of defects or oxidation. This study presents a new class of dispersing agents for graphene that assists in the exfoliation process in water with high concentration and the stabilization of the graphene sheets against reaggregation.  相似文献   

10.
An easy method of producing graphene sheets with high quality from mesocarbon microbeads (MCMBs) is demonstrated using oxidation, rapid expansion and ultrasonic treatment. Single layer graphene sheets have been successfully prepared from MCMBs through thermal exfoliation. The structure of the graphene sheets was investigated by scanning and transmission electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. MCMBs expanded mainly along the c-axis and formed worm-like ellipses from the original regular spherules. Exfoliation continued with the fragmentation of the pieces and produced delamination of the graphene sheets. MCMBs can be an excellent starting material for producing high quality graphene sheets with high yields, becoming an attractive raw material for industrial up-scale.  相似文献   

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