Ultrasonic exfoliation of graphene in water: A key parameter study (original) (raw)
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Graphene Synthesis by Ultrasound Energy Assisted Exfoliation of Graphite in Various Solvents
Liquid Phase Exfoliation (LPE) method has been gaining increasing interest by academic and industrial researchers due to its simplicity, low-cost, and scalability. High intensity ultrasound energy was exploited to transform graphite to graphene in the solvents of dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), and perchloric acid (PA) without any surfactants or ionic liquids. The crystal structure, number of layers, particle size, and morphology of the synthesized graphene samples were characterized by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Ultraviolet visible (UV–vis) spectroscopy, Dynamic Light Scattering (DLS), and Transmission Electron Microscopy (TEM). XRD and AFM analyses indicated that G-DMSO and G-DMF have few layers and G-PA has multilayers. The layer numbers of G-DMSO, G-DMF, and G-PA were determined as 9, 10, and 21, respectively. By DLS analysis, the particle sizes of graphene samples were estimated in a few micrometers. TEM analyses showed that...
Graphene Synthesis via Exfoliation of Graphite by Ultrasonication
Graphene has newly grabbed the attention of many researchers and scholars for it's huge range of properties, mainly high surface area is the most innovative field of research. High surface area property has a great significance for its demand in almost all applications in addition to supercapacitors. Accordingly, an attempt here is accomplished to create the graphene by sonication method using ODCB solvent. Different characterization techniques are mentioned in support of the work accomplished and it is found that the interlayer distance between graphite layers increases with increasing duration of sonication process. In XRD result, it can be found that first peak at 2θ of 26.4 degree disappears and a distinguishable peak at 11.3 degree with inter graphite layer spacing in close value with 0.78 nm in association with some other diffraction peaks appear. SEM images very nicely represent homogeneous graphene film with particle size varying from 42 to 150 nm. UV-VIS absorption spectra suggests that the peak absorption in graphene decreases with high wavelengths. At 210 nm, a peak can be noticed and one more peak around 226 nm with a little bit less intensity of absorption peak can be observed in UV-VIS spectra. The details offered by SEM, XRD and UV-VIS throughputs are also mentioned. It is quoted that upon sonication the distance between graphite layers increases, thereby originating graphene. Thus it can be concluded that the graphene with enormous extraordinary properties (including Super capacitor) can be synthesized following the sonication method using organic solvents. Long hour processing via sonicator leads to formation of homogenous dispersion of graphene in case of ODCB. For thorough exfoliation of graphite, the sonication should be maintained with a very dilute system in order to reduce the importance of the graphene sheets recombination process.
Langmuir
Among the most reliable techniques for exfoliation of two-dimensional (2D) layered materials, sonication-assisted liquid-phase exfoliation (LPE) is considered as a cost-effective and straightforward method for preparing graphene and its 2D inorganic counterparts at reasonable sizes and acceptable levels of defects. Although there were rapid advances in this field, the effect and outcome of the sonication frequency are poorly understood and often ignored, resulting in a low exfoliation efficiency. Here, we demonstrate that simple mild bath sonication at a higher frequency and low power positively contributes to the thickness, size, and quality of the final exfoliated products. We show that monolayer graphene flakes can be directly exfoliated from graphite using ethanol as a solvent by increasing the frequency of the bath sonication from 37 to 80 kHz. The statistical analysis shows that ∼77% of the measured graphene flakes have a thickness below three layers with an average lateral size of 13 μm. We demonstrate that this approach works for digenite (Cu 9 S 5) and silver sulfide (Ag 2 S), thus indicating that this exfoliation technique can be applied to other inorganic 2D materials to obtain highquality few-layered flakes. This simple and effective method facilitates the formation of monolayer/few layers of graphene and transition metal chalcogenides for a wide range of applications.
Advancement in liquid exfoliation of graphite through simultaneously oxidizing and ultrasonicating
J. Mater. Chem. A, 2014
Layered crystals, once exfoliated in liquids, create nanosheets with large surface area and likely generate electron band gaps. The current liquid exfoliation of graphite is performed by either oxidation, ultrasonication or the oxidation followed by ultrasonication; these methods are respectable but have limitations in general: the oxidation actually produces graphene oxide while the sonication is timeconsuming with a low yield. In this paper we report a highly effective yet simple approach for the fabrication of high-quality graphene; the approach consists of simultaneously oxidizing and ultrasonicating graphite for merely 60 min, followed by washing and filtration. Exfoliation was markedly promoted by the simultaneous treatment, where 80% of the sheets comprise single or few layers with lateral dimensions ranging 50 nm to over 100 nm; their carbon to oxygen ratio is at 8.85; the ratio of Raman D-to G-band intensity is as low as 0.211; and the sheets can be stably dispersed in acetone for at least 48 hours and they have an electrical conductivity over 600 S cm À1 . A thin graphene film made by casting exhibited a sheet resistance of $1000 U square À1 with 80% transparency at 550 nm. Fig. 6 Statistics and AFM micrographs and height profiles of graphene sheets made by oxidi-sonication for 20 min (a1-3), 40 min (b1-3) and 60 min (c1-3).
Ultrasound exfoliation of inorganic analogues of graphene
Nanoscale research letters, 2014
High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.
Managing the degree of exfoliation and number of graphene layers using probe sonication approach
Fullerenes, Nanotubes and Carbon Nanostructures, 2017
We have demonstrated a fast, versatile and scalable approach to synthesize high quality few layer graphene sheets with low defect ratio and high crystallinity produced from exfoliation of graphite flakes in DMF by using probe sonication. The effect of sonication time on degree of exfoliation and number of graphene layers has been fully investigated. The degree of exfoliation of graphene sheets as a function of sonication time has been successfully analyzed by XRD, UV-Vis spectroscopy, TEM and BET studies. The morphological changes at different sonication times have also been observed by SEM. A structural and defect characterization of graphene sheets has been discussed in detail by Raman spectroscopic technique. The shift in position of 2D Raman band and its deconvolution provided information about formation of multi to few layer graphene sheets with sonication. Moreover, Raman results are highly consistent with TEM studies as per number of graphene layers is concerned.
Liquid Exfoliation of Defect-Free Graphene
Accounts of Chemical Research, 2013
Due to its unprecedented physical properties, graphene has generated huge interest over the last 7 years. Graphene is generally fabricated in one of two ways: as very high quality sheets produced in limited quantities by micromechanical cleavage or vapour growth, or a rather defective, graphenelike material, graphene oxide, produced in large quantities. However, a growing number of applications would profit from the availability of a method to produce high quality graphene in large quantities. This Account describes recent work to develop such a processing route inspired by previous theoretical and experimental studies on the solvent-dispersion of carbon nanotubes. That work had shown that nanotubes could be effectively dispersed in solvents whose surface energy matched that of the nanotubes. We describe the application of the same approach to the exfoliation of graphite to give graphene in a range of solvents. When graphite powder is exposed to ultrasonication in the presence of a suitable solvent, the powder fragments into nanosheets, which are stabilized against aggregation by the solvent. The enthalpy of mixing is minimized for solvents with surface energies close to that of graphene (~68 mJ/m 2). The exfoliated nanosheets are free of defects and oxides and can be produced in large quantities. Once solvent exfoliation is possible, the process can be optimized and the nanosheets can be separated by size. The use of surfactants can also stabilize exfoliated graphene in water, where the zeta potential of the surfactant-coated graphene nanosheets controls the dispersed concentration. Liquid exfoliated graphene can be used for a range of applications: graphene dispersions as optical limiters, films of graphene flakes as transparent conductors or sensors, and exfoliated graphene as a mechanical reinforcement for polymer-based composites. Finally, we have extended this process to exfoliate other layered compounds such as BN and MoS 2. Such materials will be important in a range of applications from thermoelectrics to battery electrodes. This liquid exfoliation technique can be applied to a wide range of materials and has the potential to be scaled up into an industrial process. We believe the coming decade will see an explosion in the applications involving liquid exfoliated two dimensional materials.
Facile synthesis of graphene by ultrasonic-assisted electrochemical exfoliation of graphite
Materials Today: Proceedings, 2020
Graphene, a 2-dimensional form of carbon, attracted significant attention in a wide range of applications such as energy storage, power generation, chemical sensors, composite materials owing to its unmatched physical and chemical properties. In this study, graphene powder was synthesized by ultrasonic-assisted electrochemical exfoliation of the graphite electrode from acidic bath. An external ultrasonic bath (ultrasonic frequency of 40 kHz and ultrasonic power of 180 W) was employed to provide ultrasonic assistance during the electrochemical exfoliation process. The synthesized graphene powder was characterized with FTIR spectroscopy, Raman spectroscopy, XRD, and SEM techniques to study the chemical, microstructural and morphological properties. FTIR spectrum exhibited the CO and O-H functional groups and the C=C stretching of the hexagonal ring of graphene. Raman spectrum showed two sharp peaks for I D and I G bands at 1350cmAˋ1and1350 cm À1 and 1350cmAˋ1and1580 cm À1 , respectively. The XRD results revealed the polycrystalline nature of graphene powder. The SEM results showed various sizes and shapes of graphene powder. Our proposed method shows huge potentials for facile synthesis of graphene powder on a large scale.