| 1. |
- Lin, Hu, et al.
(författare)
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Rapid aging of bilayer graphene oxide
- 2022
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:48, s. 20658-20667
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Tidskriftsartikel (refereegranskat)abstract
- Atomic force microscopy (AFM) imaging was used to study swelling of individual bilayer graphene oxide (GO) flakes in water and ethanol vapors. We found that within 5 days after sample deposition the swelling of bilayered Hummers GO (HGO) in ethanol vapors disappears nearly completely, whereas the swelling in water remains not affected. Swelling can therefore be used as a sensitive indicator of rapid aging of bilayered HGO, which occurs both in air and under inert gas. The surprising ability of 5-days-aged bilayered HGO to swell in water but not in ethanol fits to the effects observed in μm-thick GO membranes after several years of aging. Remarkably, bilayered Brodie GO (BGO) maintains swelling in ethanol after storing it under the same conditions as HGO. Moreover, we demonstrate that AFM can be used to detect hole defects in individual GO sheets. The BGO bilayer swelling in ethanol vapors starts either on the flake edges or in very few points, forming ∼2 Å height fronts, which propagate slowly within interlayer spaces in all directions. The increase of the average distance between HGO sheets occurs simultaneously all over the flake, demonstrating a high abundance of hole defects. Our results imply that the permeation path length in HGO membranes must be significantly shorter compared to BGO, which is important to take into account in the modeling of membrane permeation.
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| 2. |
- Rezania, B., et al.
(författare)
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Hydration of bilayered graphene oxide
- 2014
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 14:7, s. 3993-3998
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Tidskriftsartikel (refereegranskat)abstract
- The hydration of graphene oxide (GO) membranes is the key to understand their remarkable selectivity in permeation of water molecules and humidity-dependent gas separation. We investigated the hydration of single GO layers as a function of humidity using scanning force microscopy, and we determined the single interlayer distance from the step height of a single GO layer on top of one or two GO layers. This interlayer distance grows gradually by approximately 1 A upon a relative humidity (RH) increase in the range of 2 to similar to 80% and the immersion into liquid water increases the interlayer distance further by another 3 A. The gradual expansion of the single interlayer distance is in good agreement with the averaged distance measured by X-ray diffraction on multilayered graphite oxides, which is commonly explained with an interstratification model. However, our experimental design excludes effects connected to interstratification. Instead we determine directly if insertion of water into GO occurs strictly by monolayers or the thickness of GO layers changes gradually. We find that hydration with up to 80% RH is a continuous process of incorporation of water molecules into single GO layers, while liquid water inserts as monolayers. The similarity of hydration for our bilayer and previously reported multilayered materials implies GO few and even bilayers to be suitable for selective water transport.
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| 3. |
- Talyzin, Alexandr, et al.
(författare)
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Delamination of graphite oxide in a liquid upon cooling
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:29, s. 12625-12630
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Tidskriftsartikel (refereegranskat)abstract
- Graphite oxide (GO) in liquid acetonitrile undergoes a transition from an ordered phase around ambient temperature to a gel-like disordered phase at temperatures below 260 K, as demonstrated by in situ X-ray diffraction. The stacking order of GO layers is restored below the freezing point of acetonitrile (199 K). The reversible swelling transition between a stacked crystalline phase and an amorphous delaminated state observed upon cooling provides an unusual example of increased structural disorder at lower temperatures. The formation of the gel-like phase is attributed to the thermo-responsive conformational change of individual GO flakes induced by stronger solvation. Scanning force microscopy demonstrates that GO flakes deposited onto a solid substrate from acetonitrile dispersions at a temperature below 260 K exhibit corrugations and wrinkling which are not observed for the flakes deposited at ambient temperature. The thermo-responsive transition between the delaminated and stacked phases reported here can be used for sonication-free dispersion of graphene oxide, micro-container applications, or the preparation of new composite materials.
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