Amorphous structural models for graphene oxides

Carbon (Impact Factor: 6.16). 04/2012; 50(4):1690-1698. DOI: 10.1016/j.carbon.2011.12.014

ABSTRACT Based on the experimental observations, amorphous structural models of graphene oxides (GOs) were constructed and investigated by first-principles computations. Geometric structures, thermodynamic stabilities, and electron density of states of these amorphous GO models were examined and compared with the previously proposed ordered GO structures. The thermodynamically most favorable amorphous GO models always contain some locally ordered structures in the short range, due to a compromise of the formation of hydrogen bonds, the existence of dangling bonds, and the retention of the it bonds. Compared to the ordered counterparts, these amorphous GO structures possess good stability at low oxygen coverage. Varying the oxygen coverage and the ratio of epoxy and hydroxyl groups provides an efficient way to tune the electronic properties of the GO-based materials.

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Available from: Xingfa Gao, Feb 25, 2014
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    • "In order to represent the RGO structures, different amounts of epoxy (-O-) and hydroxyl (-OH) groups were randomly arranged to represent amorphous oxides, as proposed by Liu et al. [28]. In the present work we consider an amorphous oxide with low oxygen content and in the ratio of 2:1 between (OH:O) functional groups, which is within the [1.06:3.25] "
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    ABSTRACT: The present work performs a first-principles study of the lithiation of graphite oxides with low oxygen content, which resemble reduced graphite oxide materials. The chemical nature of the Li structure formed is analysed, leading to the conclusion that the nature of lithium binding in these materials is completely different from that observed in pristine graphite. The stability of the lithium structures formed under different loadings is studied, with the finding that the lithiation potentials predicted are within the ranges of the values observed experimentally.
    Electrochimica Acta 07/2014; 140:232-237. DOI:10.1016/j.electacta.2014.07.013 · 4.50 Impact Factor
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    • "This distance was a function of the O/C ratio. For GO structures different amounts of epoxy (eOe) and hydroxyl (eOH) groups were randomly arranged to represent amorphous oxides, as it was proposed by Liu et al. [17]. In this work we considered four different amorphous oxides, with a ratio of 2 between functional groups, which are within the "
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    ABSTRACT: By means of Density Functional Theory (DFT) calculations we investigated the optimal pore size for reduced graphite oxide (GOH) to favor hydrogen storage and to prevent oxygen interference. The interlayer distance of GOH is found to increase with oxygen content, given by the number of hydroxyl groups. Four types of GOHs were considered, with O/C ratio within a 0.09–0.38 range. In the case of the highest O/C ratio considered, 0.38, a spontaneous redox-reaction between hydroxyl groups delivering a water molecule and an epoxy group was found. Thus, GOHs with high O/C ratio are not recommended for hydrogen storage. In these materials the absorption energy values of hydrogen is in the range of −0.2 and −0.5 eV/molecule, that is within the values expected to allow an efficient storage. The best GOH for hydrogen storage was found to be that with a 0.09 O/C ratio since it has the largest void space and adequate absorption energy, −0.52 eV/molecule. On the other hand, oxygen absorption energy is lower in absolute value than that of hydrogen, which favors absorption of the latter, thus creating adequate conditions for its storage without oxygen interference.
    International Journal of Hydrogen Energy 03/2014; 39(9):4396–4403. DOI:10.1016/j.ijhydene.2013.12.206 · 2.93 Impact Factor
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    • "Epoxy and hydroxyl groups are established as two major oxygen-containing groups, whereas other groups, such as carbonyl and carboxyl, are established as minor groups [59] [60] [61] [62] [63] [64] [65] [66] [67] [68]. However, the GO structure cannot be clearly defined because of its amorphous character [67] and its different synthesis conditions. We used polycyclic aromatic hydrocarbons with four oxygencontaining groups (C 54 H 18 for epoxide and hydroxyl, C 37 H 14 for carbonyl, C 24 H 12 for carboxyl and hydroxyl group along the edges of GO, respectively) as the models for GO to explain the reaction mechanisms associated with GO reduction. "
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    ABSTRACT: We used density functional theory to study the reaction mechanisms of chemical reduction of graphene oxide (GO) by the sulfur-containing compounds HSO3− and H2SO3. We studied the reaction energy profiles for the following reactions: dehydroxylation of GO with one and two hydroxyl groups, de-epoxidation of GO with one or two epoxy groups and decarboxylation and decarbonylation of GO with carboxyl and carbonyl groups. We found that hydroxyl and epoxide groups could be easily reduced because of the lower energy barriers, whereas decarboxylation and decarbonylation reactions are not kinetically and thermodynamically easy because of the higher energy barriers. These reaction mechanisms at the atomistic level are not only supported by Chen’s experimental results [J. Phys. Chem. C 2010, 114, 19885], but are also beneficial for the development of new agents that could efficiently reduce GO.
    Carbon 02/2014; 67:146–155. DOI:10.1016/j.carbon.2013.09.073 · 6.16 Impact Factor
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