Unusual infrared-absorption mechanism in thermally reduced graphene oxide

Abstract

Infrared absorption of atomic and molecular vibrations in solids can be affected by electronic contributions through non-adiabatic interactions, such as the Fano effect. Typically, the infrared-absorption lineshapes are modified, or infrared-forbidden modes are detectable as a modulation of the electronic absorption. In contrast to such known phenomena, we report here the observation of a giant-infrared-absorption band in reduced graphene oxide, arising from the coupling of electronic states to the asymmetric stretch mode of a yet-unreported structure, consisting of oxygen atoms aggregated at the edges of defects. Free electrons are induced by the displacement of the oxygen atoms, leading to a strong infrared absorption that is in phase with the phonon mode. This new phenomenon is only possible when all other oxygen-containing chemical species, including hydroxyl, carboxyl, epoxide and ketonic functional groups, are removed from the region adjacent to the edges, that is, clean graphene patches are present.

Role of the synthesis route on the properties of hybrid LDH-graphene as basic catalysts

“…6A) of parent GO revealed peaks at 865 and 1038 cm -1 respectively attributed to the asymmetric bending and stretching of C-O-C vibrations, of the epoxy group. 18,19 The peak observed at ~1730 cm -1 is due to the C=O stretching from carboxylic acid and carbonyl moieties. 19 The peaks at ~3350 cm -1 (broad, with a shoulder at ~3165 cm -1 ) and 1624 cm -1 can be assigned to O-H stretching and H-O-H bending of adsorbed water molecules, respectively.…”

“…18,19 The peak observed at ~1730 cm -1 is due to the C=O stretching from carboxylic acid and carbonyl moieties. 19 The peaks at ~3350 cm -1 (broad, with a shoulder at ~3165 cm -1 ) and 1624 cm -1 can be assigned to O-H stretching and H-O-H bending of adsorbed water molecules, respectively. At a first glance, once the HT is present in the composite, the bands relative to the oxidized surface of GO disappeared (confirming GO reduction by hydrothermal treatment) and those corresponding to HT rose with its increasing amount.…”

“…[18][19][20][21][22][23][24][25][26][27][28][29] A slighter influence of the drying and synthesis methods than at low HT loading on the hybrids' catalytic performance was observed, the catalysts submitted to freeze drying presenting the higher DAA yields. Of particular interest is the case of the hybrid catalyst prepared by coprecipitation and freeze dried (HT/rGO-10CFD) which showed the best performance with an average DAA amount of 102.7 mmol/gHTc; that is a specific activity (based on the weight of HT present in the hybrid catalyst) about 2.5 times higher than that of HTc.…”

Reparameterization of the REBO-CHO potential for graphene oxide molecular dynamics simulations

“…The chemical structure of GO has only recently been revealed 28 , but diverse applications were already considered in flexible electronics 29 , in battery electrodes 30 and as a paper-like composite material 31,32 . We can also expect that graphene produced from graphene oxide through chemical 27 or thermal reduction of oxygen 33 , may partly but not fully inherit the superior thermal conductivity of pristine graphene 34 . The possible oxygen residue on graphene may has strong influence on its thermal conductivity, and this can be studied through equilibrium molecular dynamics simulation 25 as long as an accurate and computation efficient carbon oxygen many body potential is available for GO.…”

“…REBO potential formalism meets this requirement. Recent theoretical studies of GO were performed using both Density Functional Theory (DFT) 33,[35][36][37] and ReaxFF 38,39 , but there is no application of the REBO or AIREBO potential to GO. Ni et al 3 have recently extended the second generation of REBO potential 2 to simulate hydrocarbon-oxide molecules.…”