The thermal exfoliation of graphite oxide (GO) is an efficient and easily scalable method in the production of graphene and graphene oxide-based materials. The theoretical surface area of pristine monolayer graphene is estimated to be as high as 2600 m2/g. Moreover, graphene electrical conductivity is approximately 1000 S/m. These properties offer great potential for graphene use in the fields of catalysis, selective membranes, sensors, and semiconductors if effectively converted into bulk materials with tuned properties. Graphene oxide suspension drying leads to face-to-face stacking of the individual flakes of graphene oxide and therefore, to the undetectable bulk GO surface area and porosity. The presence of oxygen groups in bulk GO hinders the delocalization of pi electrons as seen present in pristine graphene and therefore, reducing drastically GO electrical conductivity. To produce a GO-based material with various applicable properties, this work explores the thermal exfoliation of GO films with various thicknesses into reduced graphite oxide (rGO), via heating at various instrument-set heating rates and target temperatures. Drop-cast GO films exfoliated explosively in thermal reduction when the instrument-set heating rates were set to any heating rate above 100 K/min, similarly to bulk GO “cake.” The degree of exfoliation was independent to GO film thickness and the instrument-set heating rate (if above 100 K/min). The explosive exfoliation of GO films yielded porous rGO powder with fairly high surface area (~700 m2/g N2 BET). When exfoliated at low instrument-set heating rates 10 K/min, GO films with thickness less than 36 μm yielded free-standing and mechanically stable rGO films. Although this product rGO film has an undetectable specific surface area, it has relatively high electrical conductivity (~400 S/m). GO films thicker than 36 μm, also exfoliated at the heating rate 10 K/min, yielded rGO films with a modest surface area up to 171 m2/g. After a series of experiments of GO films of the same thickness, the threshold values of heating rate and target temperature that lead to explosive exfoliation of GO films was determined to be heating rates above 100 K/min and target temperatures above 150℃. Wrinkled and crumpled GO films showed thermal exfoliation behaviors similar to those of drop-cast films. At low instrument heating rate of 10K/min, the wrinkled rGO film products showed undetectable or very low surface area (1 m2/g). At any instrument-set heating rate 100 K/min and above, the wrinkled films exfoliated explosively resulting in rGO powder with surface area as high as 445 m2/g. GO film confined by a variety of materials (PDMS, borosilicate glass, paraffin wax coated paper, and aluminum foil) were thermally exfoliated and characterized. It was shown that at high instrument-set heating rates, the structural integrity of a film could be conserved when borosilicate glass was used. This straightforward method yields a flexible and free-standing rGO film with fairly high electrical conductivity (757 S/m) and some micro porosity (pore size < 1 nm) when probed with CO2 BET (971 m2/g).
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Citation
Kwon, Yongbeom,
"Towards Porous Reduced Graphite Oxide (rGO) Films via Thermal Exfoliation"
(2020).
Engineering Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/4aaz-e712
