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Production and hydrogenation of graphene
[Thesis]. Manchester, UK: The University of Manchester; 2018.
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Abstract
Considerable research has been undertaken into graphene since its first isolation 14 years ago due to its intriguing combination of properties. One promising application for graphene is printable electronics due to its combination of dispersity, conductivity and transparency. However, the uptake of graphene in this area has been limited by a number of factors including scalable production of monolayer graphene dispersions and the ability to dope graphene to control its electronic structure. This dissertation seeks to address these challenges by investigating surfactant assisted liquid phase exfoliation of graphene and the reactivity of graphene on different substrates to hydrogen dopants. Fatty acids and aliphatic compounds were investigated as surfactants in the liquid phase exfoliation of graphene. Graphite was ultrasounded in organic dispersions of a surfactant and the resulting graphene was then isolated through centrifugation. These new surfactants were found to produce higher yields of monolayer graphene compared to pure solvents. In particular, CH3(CH2)28COOH in NMP was found to be highly effective with double the yield of graphene when compared to samples prepared in pure NMP and an increase in the relative percentage of monolayer graphene from 41% to 48%. Arachidic acid and 1-phenyloctane were also found to be successful surfactants when compared with samples prepared in pure NMP. Raman spectroscopy analysis of the flakes produced was found to qualitatively correlate with the established technique of HR-TEM analysis. The reactivity of graphene on Si, MoS2 and BN substrates was investigated though exposure of the flakes to hydrogen. The I(D)/I(G) Raman peak ratio was used to follow the degree of functionalisation. The hydrogenation reactivity was found to be highest on Si and MoS2 substrates, with relatively poor reactivity on h-BN. This difference in reactivity was attributed to the different strength of van der Waals forces between graphene and the different substrates.