Liquid Exfoliation Of Graphene Research Articles

Exploring the Role of Molecular Intercalants in Electrochemical Production of Graphene-Based 2D Materials

Since the discovery of graphene, two-dimensional (2D) materials have gained extensive attention due to the unique material properties from their reduced dimensionality. Numerous techniques have been thoroughly investigated for the fabrication of graphene-based 2D materials. Among them, electrochemical synthesis is one of the most promising approaches for the large-scale production of 2D materials with tunable properties [1-3]. Especially, intercalation of various ions/molecules electrochemically driven in between the graphene sheets plays the key role in the synthesis of single or few-layer 2D materials. However, the influence of molecular intercalants is still poorly understood.In this work, we studied different types of intercalants (i.e., ClO4 -, PF6 -, BF4-, HSO4 -) and explored the inserting process of molecular anions in-between the weekly-bonded layered materials driven by electrochemistry. Combining the cyclic voltammetry, XRD, Raman and density functional theory computation modeling, we can monitor the intercalation behavior of different anions and evaluate the contribution of intercalants in the high-yield production of graphene by electrochemical exfoliation. By optimizing the use of certain molecular intercalants, high exfoliation yield (>80 %) of graphene nanosheets with moderate oxidation damage and good electrochemical stability was achieved assisted by electrochemical exfoliation. Our study provides new insights into the electrochemical production of graphene-based 2D materials and suggests that the introduction of molecular intercalants is a promising tool for the controlled synthesis of layered 2D materials.Reference:(1) Xia, Z. Y.; Pezzini, S.; Treossi, E.; Giambastiani, G.; Corticelli, F.; Morandi, V.; Zanelli, A.; Bellani, V.; Palermo, V. The Exfoliation of Graphene in Liquids by Electrochemical, Chemical, and Sonication-Assisted Techniques: A Nanoscale Study. Advanced Functional Materials 2013, 23 (37), 4684-4693. DOI: 10.1002/adfm.201203686.(2) Xia, Z. Y.; Maccaferri, G.; Zanardi, C.; Christian, M.; Ortolani, L.; Morandi, V.; Bellani, V.; Kovtun, A.; Dell'Elce, S.; Candini, A.; et al. Dispersion Stability and Surface Morphology Study of Electrochemically Exfoliated Bilayer Graphene Oxide. Journal of Physical Chemistry C 2019, 123 (24), 15122-15130. DOI: 10.1021/acs.jpcc.9b03395.(3) Cao, J. Y.; He, P.; Mohammed, M. A.; Zhao, X.; Young, R. J.; Derby, B.; Kinloch, I. A.; Dryfe, R. A. W. Two-Step Electrochemical Intercalation and Oxidation of Graphite for the Mass Production of Graphene Oxide. Journal of the American Chemical Society 2017, 139 (48), 17446-17456. DOI: 10.1021/jacs.7b08515.

Fully desktop fabricated flexible graphene electrocorticography (ECoG) arrays

Objective: Flexible Electrocorticography (ECoG) electrode arrays that conform to the cortical surface and record surface field potentials from multiple brain regions provide unique insights into how computations occurring in distributed brain regions mediate behavior. Specialized microfabrication methods are required to produce flexible ECoG devices with high-density electrode arrays. However, these fabrication methods are challenging for scientists without access to cleanroom fabrication equipment. Results: Here we present a fully desktop fabricated flexible graphene ECoG array. First, we synthesized a stable, conductive ink via liquid exfoliation of Graphene in Cyrene. Next, we established a stencil-printing process for patterning the graphene ink via laser-cut stencils on flexible polyimide substrates. Benchtop tests indicate that the graphene electrodes have good conductivity of ∼1.1 × 103 S cm−1, flexibility to maintain their electrical connection under static bending, and electrochemical stability in a 15 d accelerated corrosion test. Chronically implanted graphene ECoG devices remain fully functional for up to 180 d, with average in vivo impedances of 24.72 ± 95.23 kΩ at 1 kHz. The ECoG device can measure spontaneous surface field potentials from mice under awake and anesthetized states and sensory stimulus-evoked responses. Significance: The stencil-printing fabrication process can be used to create Graphene ECoG devices with customized electrode layouts within 24 h using commonly available laboratory equipment.

The effect of surfactants and their concentration on the liquid exfoliation of graphene

We investigated the effect of surfactants and their concentration on the final graphene concentration via the liquid-phase exfoliation method. Ionic surfactant and non-ionic surfactant have different mechanisms in the exfoliation process.

Graphene: The Exfoliation of Graphene in Liquids by Electrochemical, Chemical, and Sonication‐Assisted Techniques: A Nanoscale Study (Adv. Funct. Mater. 37/2013)

A graphite ‘flower’ is produced by V. Palermo and co-workers in order to study the production and exfoliation mechanism of soluble of graphene and graphene oxide nanosheets due to chemical etching, electrochemical treatment, or sonication in organic solvents of bulk graphite. In the background of the back cover image, the same material is visualized by electron microscopy. The exfoliation process and roughening of the flat graphite substrate upon exfoliation is directly visualized at the nanoscale on page 4684.

Liquid Exfoliation of Layered Materials

Background Since at least 400 C.E., when the Mayans first used layered clays to make dyes, people have been harnessing the properties of layered materials. This gradually developed into scientific research, leading to the elucidation of the laminar structure of layered materials, detailed understanding of their properties, and eventually experiments to exfoliate or delaminate them into individual, atomically thin nanosheets. This culminated in the discovery of graphene, resulting in a new explosion of interest in two-dimensional materials. Layered materials consist of two-dimensional platelets weakly stacked to form three-dimensional structures. The archetypal example is graphite, which consists of stacked graphene monolayers. However, there are many others: from MoS 2 and layered clays to more exotic examples such as MoO 3 , GaTe, and Bi 2 Se 3 . These materials display a wide range of electronic, optical, mechanical, and electrochemical properties. Over the past decade, a number of methods have been developed to exfoliate layered materials in order to produce monolayer nanosheets. Such exfoliation creates extremely high-aspect-ratio nanosheets with enormous surface area, which are ideal for applications that require surface activity. More importantly, however, the two-dimensional confinement of electrons upon exfoliation leads to unprecedented optical and electrical properties. Advances An important advance has been the discovery that layered crystals can be exfoliated in liquids. There are a number of methods to do this that involve oxidation, ion intercalation/exchange, or surface passivation by solvents. However, all result in liquid dispersions containing large quantities of nanosheets. This brings considerable advantages: Liquid exfoliation allows the formation of thin films and composites, is potentially scaleable, and may facilitate processing by using standard technologies such as reel-to-reel manufacturing. Although much work has focused on liquid exfoliation of graphene, such processes have also been demonstrated for a host of other materials, including MoS 2 and related structures, layered oxides, and clays. The resultant liquid dispersions have been formed into films, hybrids, and composites for a range of applications. Outlook There is little doubt that the main advances are in the future. Multifunctional composites based on metal and polymer matrices will be developed that will result in enhanced mechanical, electrical, and barrier properties. Applications in energy generation and storage will abound, with layered materials appearing as electrodes or active elements in devices such as displays, solar cells, and batteries. Particularly important will be the use of MoS 2 for water splitting and metal oxides as hydrogen evolution catalysts. In addition, two-dimensional materials will find important roles in printed electronics as dielectrics, optoelectronic devices, and transistors. To achieve this, much needs to be done. Production rates need to be increased dramatically, the degree of exfoliation improved, and methods to control nanosheet properties developed. The range of layered materials that can be exfoliated must be expanded, even as methods for chemical modification must be developed. Success in these areas will lead to a family of materials that will dominate nanomaterials science in the 21st century.

The Exfoliation of Graphene in Liquids by Electrochemical, Chemical, and Sonication‐Assisted Techniques: A Nanoscale Study

AbstractThe different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation and electrochemical oxidation are compared. The exfoliation process and roughening of a flat graphite substrate is directly visualized at the nanoscale by scanning probe and electron microscopy. The etching damage in graphite and the properties of the exfoliated sheets are compared by Raman spectroscopy and X‐ray diffraction analysis. The results show the trade‐off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non‐covalent exfoliation and preservation of graphene properties on a molecular scale.