Graphite oxide as a polymer-like hydrophilic system with peculiar coordinating properties
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Graphite oxide as a polymer-like hydrophilic system with peculiar coordinating properties* E. A. Gushchina, E. A. Shilyaeva, and Yu. V. Novakovskaya Chemistry Department, M. V. Lomonosov Moscow State University, Build. 3, 1 Leninskie Gory, 119234 Moscow, Russian Federation. E-mail: [email protected] Structure-energetic and dynamic characteristics of graphite oxide model segments, as a basic element of which the C54 fragment of a carbon sheet was taken, and their hydration complexes involving a restricted number of water molecules are analyzed. The structure optimization and calculation of normal vibrations were performed at the density functional approximation with the B3LYP hybrid exchange-correlation functional with the basis that involves atomic functions of the 6-31G sets on the skeleton carbon atoms and terminal CH groups of the skeleton and of the 6-31G(d,p) sets on the atoms of all functional groups and water molecules. The ability of the hydroxyl groups of graphite oxide to initiate the reorganization of a three-dimensional H-bonded structure of water into the two-dimensional surface structure and to form very strong hydrogen bonds with water molecules providing their partial ionization was revealed. Key words: graphite oxide, hydration, hydrogen bonds, dissociation energy, spectral band peaks.
Graphite oxide (GO) is a layered material, which can hardly be named a compound, since the composition of the layers even in one sample differs (because of different accessibilities of surface regions to oxidants) and systems with different C : O ratios, i.e., with different degrees (depths) of oxidation of graphite, are formed when diverse synthesis procedures are used. Moreover, it cannot be excluded that even at the same oxidation depth both variations of the mutual arrangement of oxygen-containing groups on the graphite layer surface and in their relative amount are possible. On the one hand, all these factors complicate the experimental determination of the functional composition of this material and the development of a correct model of the structure (which is necessary for the reliable prediction of the properties of modification procedures). On the other hand, this gives rise to wide possibilities of modifying the properties due to diverse functional groups in various combinations. The irregular alternation of the prevailing oxidized (sp3 C) and remained non-oxidized (sp2 C) regions within one extended carbon sheet makes it possible to consider GO as a unique polymer containing functional groups of various chemical nature on a single strong (graphite) framework. The variation of the oxidation depth of the sample corresponds to changes in the combination and * Based on the materials of the International Conference "Chemistry of Organoelement Compounds and Polymers 2019" (November 18—22, 2019, Moscow, Russia).
density of arrangement of the oxygen-containing groups. The GO structure is also repeating in the direction perpendicular to the carbon sheet plane, since individual sheets having, on the average,
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