The structure of graphene oxide membranes in liquid water, ethanol and water -ethanol mixtures. ABSTRACT. Structure of graphene oxide (GO) membranes was studied in situ in liquid solvents using synchrotron radiation X-ray diffraction in a broad temperature interval. GO membranes are hydrated by water similarly to precursor graphite oxide powders but intercalation of alcohols is strongly hindered, which explains why the GO membranes are permeated by water and not by ethanol. Insertion of ethanol into the membrane structure is limited to only one monolayer in the whole studied temperature range, in contrast to precursor graphite oxide powders, which are intercalated with up to two ethanol monolayers (Brodie) and four ethanol monolayers (Hummers). As a result, GO membranes demonstrate absence of "negative thermal expansion" and phase transitions connected to insertion/de-insertion of alcohols upon temperature variations reported earlier for graphite oxide powders. Therefore, GO membranes are distinct type of material with unique solvation properties compared to parent graphite oxides even if they are composed by the same graphene oxide flakes.

A novel material, graphene nanoribbons encapsulated in single-walled carbon nanotubes (GNR@SWNT), was synthesized using confined polymerization and fusion of polycyclic aromatic hydrocarbon (PAH) molecules. Formation of the GNR is possible due to confinement effects provided by the one-dimensional space inside nanotubes, which helps to align coronene or perylene molecules edge to edge to achieve dimerization and oligomerization of the molecules into long nanoribbons. Almost 100% filling of SWNT with GNR is achieved while nanoribbon length is limited only by the length of the encapsulating nanotube. The PAH fusion reaction provides a very simple and easily scalable method to synthesize GNR@SWNT in macroscopic amounts. First-principle simulations indicate that encapsulation of the GNRs is energetically favorable and that the electronic structure of the encapsulated GNRs is the same as for the free-standing ones, pointing to possible applications of the GNR@SWNT structures in photonics and nanoelectronics.

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 Å upon a relative humidity (RH) increase in the range of 2 to ∼80%, and the immersion into liquid water increases the interlayer distance further by another 3 Å. 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.

Expansion under compression: The unit‐cell volume of graphite oxide pressurized in water media, continuously increases reaching a sharp maximum at ca. 1.3–1.5 GPa (see picture, squares). Expansion of the lattice to a maximum of about 28–30 % is because of gradual pressure‐induced water insertion into the interlayer space of graphite oxide. The effect is reversible (triangles), resulting in a unique “breathing” of the structure upon pressure variation.

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