Scale up of graphene production by liquid phase exfoliation

Lead Research Organisation: Imperial College London
Department Name: Chemical Engineering


Graphene has been a significant topic of discussion in the scientific community since its isolation and characterisation by Geim and Novezelov in 2004, resulting in the awarding of the Nobel Prize in Physics in 2010. It boasts properties far superior to 'common' materials; with its strength, thermal and electrical conductivity, flexibility, surface area and transparency making it a viable choice in a wide range of applications. Graphene comes in many forms, whether dispersed in a solvent or on a film of plastic, or with functional groups attached such as graphene oxide. The form required is dependent on the type of application, and dictates the production method required. Herein lies the main motivation for the project, as a low-cost method of production to bulk produce graphene is yet to be realised.
Graphene can be produced via bottom-up (BU) or top-down (TD) methods. BU involves producing graphene by using hydrocarbon reagents, by techniques such as chemical vapour deposition. TD involves the exfoliation of graphite into graphene through techniques such as sonication. The most common way graphene is produced for commercial applications is BU, as it currently offers a high degree of accuracy not achieved through TD techniques; however it suffers from a lack of ability to scale up.
Tour compared TD versus BU fabrication of graphene based electronics, and noted that the significant advantage to BU fabrication is the control of resolution, but utilising the graphene produced is difficult. He proposed that in the future there is some potential for combining the two techniques, by mass producing using TD methods, then removing defects such as oxygen functionality on the edges using BU techniques. Since the focus of the project is on the scale up of production utilising liquid phase exfoliation (LPE), a TD technique, this is the method that will be focused on for the remainder. It should be further noted that novel techniques in all branches of science should be sustainable and not rely on a depleting resource. TD techniques utilise the abundant resource graphite to produce a material that can replace many expensive, limited materials in several applications, for example the use of platinum in catalysts.
This project will focus on the use of a spinning tube design, which is still currently being manufactured. The rotation of the cylinders will generate areas of high shear stress, and at high enough rotation speeds, Taylor vortices will form, enhancing the exfoliation. Experimental work, coupled with numerical simulation will be used to analyse the stress fields formed, and compared to the graphene produced. Several options exist for the analysis of the graphene itself, including UV-vis and Raman spectroscopy, TEM and AFM. Due to the wide range of possibilities and analysis available it is necessary to focus on particular elements, with the main focus of the project on how the fluid dynamics inside the device effect the graphene produced.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 31/03/2022
1966368 Studentship EP/N509486/1 01/10/2017 30/06/2021 Usmaan Farooq
Description The overall aim of the project is to upscale graphene production via liquid phase exfoliation, a process in which graphite is exposed to high shear rates within a solvent. This means the graphite undergoes mechanisms such as peeling and fragmentation, breaking up into a few layer material which we designate few layer graphene. Using an innovative rig comprised of two concentric cylinders, the inner of which is rotating, high concentrations were achieved compared to literature values. Further investigation involved varying several parameters within the device, such as rotational speed and pump speed to analyse the effect. This was coupled with characterisation techniques such as high powered microscopes, and computational simulations to further investigate the mechanisms causing the break up of graphite. This required a broad range of skills as learning both the experimental methods and characterisation techniques were required, as well as OpenFoam, the software used to perform the computational simulations.

An element of the flow within the device involves the flow of liquid down the inner surface of a rotating cylinder. This flow has not been studied in detail, therefore it was decided to analyse it in depth via simulations. There was a wide range of findings, including the increased stability of the flow with an increase in rotation and the presence of angled waves due to rotation. Fast fourier transforms (FFT's) can be used to find the frequency of a signal, and these were used in a novel way to analyse the simulations, by deducing the wave frequency via 2D FFT's. Frequencies in both the axial and azimuthal directions of the cylinder were determined and found to vary with the imposed rotation. Linking back to the graphene production, the simulations can be used to determine the shear rates locally and globally, which help understand where exfoliation is taking place and to what extent.

The other key part of the rig is the outer section, the narrow gap between the inner and outer cylinder, where the phenomena Taylor-Couette flow occurs. Here is where high shear rates are achieved and most of the exfoliation happens. This has been simulated in detail using OpenFoam, with studies for the single phase case (just the solvent) and studies with particles, the latter of which has not been studied in detail previously. Simulating how the flow field behaves and how particles move within the field gives a better understanding of how exfoliation occurs and how it can be optimised.
Exploitation Route Since it has been shown high concentrations can be achieved in this lab scale setup of 1-2 litres, the main aim would be to scale up to pilot plant or industrial scale. This scale up would allow for further investigation into the quality and consistency of production on a larger scale, and potential for distribution of the graphene dispersion produced, which is particularly relevant in applications such as inkjet printing, whilst graphene can of course be used in a multitude of applications due to its extraordinary properties. In terms of the study into thin films on a rotating surface, the findings are applicable in both the area of nanomaterial production but also industrially for rotating falling film evaporators among others where the additional control over the flow gained by the imposed rotational may be beneficial.
Sectors Chemicals,Electronics,Energy,Environment,Transport