Properties and applications of materials based on graphite oxide

Sammanfattning: Graphite oxide (GO) is a hydrophilic, layered material prepared by oxidation of graphite. In the first part of this thesis, we studied materials produced from GO by intercalation and functionalization. The second part of the thesis was focused on supercapacitor applications of high surface area carbons prepared from GO using chemical activation. A detailed study of acetylated GO (AcGO) was performed to verify structure and properties of this material. Reports from 1960’s suggested that AcGO has “pillared” structure. Our analysis showed that the AcGO demonstrates expanded structure due to acetylation but exhibits negligible specific surface area and should not be considered as a pillared material. Pillared reduced GO (prGO) was prepared by applying mild annealing to GO material pillared with tetrapod-shaped amine molecules. PrGO showed relatively high surface area due to remaining pillaring molecules in the structure. The prGO is hydrophobic and exhibits 100x improved conductivity compared to precursor. PrGO is one of few true pillared structures reported in literature so far, and the first ever prepared starting from pillared GO.We also investigated the sorption of common dyes, methylene blue (MB), rose bengal (RB) and crystal violet (CV), by multilayered graphene oxide materials. We found that MB dissolved in ethanol intercalates the GO structure, as evidenced by significant expansion of inter-layer distance, and increase in weight due to sorption. In contrast to MB, GO is not easily intercalated by CV and RB dyes. We believe that the flat MB molecule shape allows easier insertion between GO layers compared to twisted and non-flat CV and RB molecules. Our results suggest that penetration into GO inter-layers depends not only on the size of molecules, but also on the shape.Temperature dependent study of structures formed by Brodie GO (BGO) in liquid alkyl alcohols was performed for a set starting from undecyl alcohol (no. of C=11) and up to behenyl alcohol (no. of C=22). We found that BGO exhibits strong swelling in all molten alcohols in this set. Heating just above the melting point of alcohol results in expansion of inter-layer distance of GO due to intercalation of two layers of alcohol molecules in orientation perpendicular to graphene oxide planes (α-phase). Further heating of α-phase results in incongruent melting and formation of new phase with significantly smaller inter-layer distance and amount of intercalated alcohol (β-phase). The transition from α-to β-phase is distinctly different compared to swelling transitions previously observed for BGO in smaller alcohols (no. of C<10). A more detailed study of the BGO-C16 system revealed that β-phase has structure with alcohol molecules forming layers mostly in parallel to graphene oxide orientation.In the second part of this thesis we studied activated reduced GO (a-rGO) as electrode material in supercapacitors. A-rGO is a high surface material (~3000 m2g-1) obtained by KOH activation of rGO. We developed formulations for stable aqueous dispersions of a-rGO optimized for preparation of electrodes by semi-industrial spray-gun deposition. The electrodes prepared by spray deposition showed energy storage parameters only slightly lower compared to lab scale blade-deposited electrodes. Spray-gun deposition might provide significant advantage for industry over conventional methods to prepare electrodes from a-rGO. We also applied KOH activation procedure, optimized for producing high surface area a-rGO, to biochar prepared from pine cones. Using this cost free “waste” picked up in Umeå region forest we produced high quality activated carbon very similar to a-rGO in terms of structure, pore size and surface area. Overall, the energy storage parameters of electrodes prepared using the activated carbon from pine cones were on the same level as a-rGO electrodes, which are produced by a lot more complex and expensive chemical treatments.