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Synthesis and Characterisation of Graphene-Based Membranes
[Thesis]. Manchester, UK: The University of Manchester; 2017.
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University of ManchesterYu Young ShinDegree of Doctor of Philosophy (PhD)December 31 2016Synthesis and Characterisation of Graphene Based MembraneGraphene, often known as a wonder material due to its remarkable properties, is the thinnest membrane available to us. [1] In this project we have synthesised and characterised different types of graphene membranes and graphene-based membranes.Firstly, we have developed a simple fabrication technique to produce pressurised single-layer graphene membranes that can hold up to reversible strain of ~2%. The graphene balloons were investigated by Raman Spectroscopy: red shift of Raman peaks was observed with increasing strain, in good agreement with theoretical calculation. [2] Also, a characteristic broadening of the Raman peaks is observed beyond 1% strain, which has been attributed to nanoscale strain variations in the membranes.Another type of graphene-based membrane is prepared by assembling millions of tiny graphene flakes together into a laminate. Liquid-phase exfoliation is used to disperse graphene nanoflakes in a solution [3]; the dispersion is then deposited as a laminate by simple fabrication techniques such as drop casting. Because the properties of a graphene laminate strongly depend on the flake size and thickness distribution in the dispersion, it is important to be able to characterise LPE graphene. Here, we have developed a simple qualitative protocol based on Raman spectroscopy to characterise this materials. This protocol was first validated in two works, aimed at studying the enhancement of the yield of LPE graphene using two different stabilisers, n-octylbenzene and perchlorocoronene. We then applied our method to graphene/PIM-1 composite membrane. PIMs are a new class of polymers showing great potential in separation applications. An improvement in the performance of the membrane (e.g. permeability) is expected by adding graphene as a nanofiller. However, little is experimentally known about how the material disperses in PIM. Our results show that Raman spectroscopy is able to identify the presence of re-aggregated graphene-based materials in the composite. This is expected to produce strong changes in the mechanical properties and the physical ageing of the membrane.Lastly, we demonstrated fabrication of self-catalytic reactor membrane composed of graphitic carbon nitride (g-C3N4). Simple LPE and vacuum filtration techniques are employed, maximising the surface area and exposure of the active sites. The g-C3N4 membrane showed significantly enhanced catalytic performance compared to the bulk g-C3N4, achieving ~100% conversion efficiency for photo-degradation of several organic dyes. In conclusion, we investigated different types of graphene-based membranes, showing that LPE is simple technique with high versatility for different applications and Raman spectroscopy is a powerful technique for characterisation of graphene in all cases. References1. Geim, A.K. and K.S. Novoselov, The rise of graphene. Nature Materials, 2007. 6(3): p. 183-191.2. Ding, F., et al., Stretchable Graphene: A Close Look at Fundamental Parameters through Biaxial Straining. Nano Letters, 2010. 10(9): p. 3453-3458.3. Hernandez, Y., et al., High-yield production of graphene by liquid-phase exfoliation of graphite. Nat Nanotechnol, 2008. 3(9): p. 563-8.