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Vortex fluidic exfoliation of graphite and boron nitride.

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TLDR
Graphite is exfoliated into graphene by shearing vortex fluidic films of N-methyl-pyrrolidone (NMP) as a controlled process for preparing oxide free graphene, and for exfoliating the corresponding boron nitride sheets.
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This article is published in Chemical Communications.The article was published on 2012-03-19 and is currently open access. It has received 263 citations till now. The article focuses on the topics: Boron nitride & Graphene.

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A review on mechanical exfoliation for the scalable production of graphene

TL;DR: In this paper, the authors highlight the recent progress on mechanical exfoliation for graphene production during the last decade, focusing on the widely used sonication method with the latest insight into sonication-induced defects, newly explored ball milling method, the fluid dynamics method that has emerged in the last three years, and the innovative supercritical fluid method.
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Advances in 2D boron nitride nanostructures: nanosheets, nanoribbons, nanomeshes, and hybrids with graphene

TL;DR: The structural basics, spectroscopic signatures, and physical properties of the 2D BN nanostructures are discussed and various top-down and bottom-up preparation methodologies are reviewed in detail.
Journal ArticleDOI

Nano boron nitride flatland.

TL;DR: A comprehensive review of the structural characteristics and synthetic routes of BN monolayers, multilayers, nanomeshes, nanowaves, nanoflakes, nanosheets and nanoribbons is presented.
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Computational Screening of 2D Materials for Photocatalysis

TL;DR: A computational screening approach is reviewed to rapidly and efficiently discover more 2D materials that possess properties suitable for solar water splitting and discusses future research directions and needed method developments for the computational design and optimization of 2D material for photocatalysis.
References
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Journal ArticleDOI

Electric Field Effect in Atomically Thin Carbon Films

TL;DR: Monocrystalline graphitic films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands and they exhibit a strong ambipolar electric field effect.
Journal ArticleDOI

Processable aqueous dispersions of graphene nanosheets

TL;DR: It is reported that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization, making it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.
Journal ArticleDOI

Structural defects in graphene

TL;DR: In this article, the present knowledge about point and line defects in graphene are reviewed and particular emphasis is put on the unique ability of graphene to reconstruct its lattice around intrinsic defects, leading to interesting effects and potential applications.
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Frequently Asked Questions (12)
Q1. What is the mechanism of the exfoliation of graphene sheets?

The displacement of single layers of graphene or BN relative to each other suggests that the exfoliation involves a slippage process, 55 which is consistent with the limited directional aspect of the van der Waals interactions between two sheets. 

For the contact of two graphene sheets, the binding energy per in-contact atom can be estimated as about ½ that for 80 bulk graphite. 

The 20 shearing involves vortex fluidics in a rapidly rotating tube, and is an alternative and tunable energy source for the exfoliation process with potentially minimal damage of the graphene. 

Sonication induced exfoliation of graphite, and other laminar materials, occurs in NMP2,3,11 which has similar surface tension 25 relative to graphene, and acts as a stabilising surfactant to avoid reassembling/restacking of the graphene. 

In the fluid environment, however, any graphene-90 graphene contact lost due to shearing away from perfect overlap is replaced by graphene-fluid contact so the restoring force is F0 = (σgg− σgf ) L which is presumably much weaker since, for this solvent, σgg ∼ σgf. 

if the slipped graphene stack ends up adhering to the wall of the tube, further surface energies will come into play. 

Clearly the angle and speed affects the shearing/exfoliation, although there would be an upper limit of 60 the speed where the centrifugal force accelerates the flat graphite flakes and any generated graphene to the surface of the tube, possibly minimising the extent of exfoliation. 

This suggests that stacks that were initially very strongly sheared may later come to equilibrium in the stationary fluid at a degree of overlap that is relatively independent of the initial degree of shearing induced by the shearing flow. 

In vacuo, only σgg is present, resulting 85 in a relatively strong, approximately constant slippage force F0 = σgg L parallel to the sheets, tending to pull ‘slipped’ graphene sheets back into full registry (maximum overlap area). 

9,10 Developing facile methods for accessing viable 15 quantities of graphene devoid of such defects, and also of chemical degradation, is therefore important in advancing the myriad of applications of graphene. 

such a slippage process would require the individual sheets to be partially lifted from the surface of the bulk material at some point to provide the necessary lateral force to start the slippage, Figure 60 1(c). 

Height profile measurements using atomic force microscopy (AFM), Figure 2c and 2d, were close to 1 nm, in accordance with mono-layer 10 graphene sheets.