Brodie vs Hummers graphite oxides for preparation of multi-layered materials

Abstract

Graphite oxides synthesized by one and two step Brodie oxidation (BGO) andHummers (HGO) methods were analysed by a variety of characterization methods in order to evaluate the reasons behind the difference in their properties. It is found that the Brodie method results in a higher relative amount of hydroxyl groups and a more homogeneous overall distribution of functional groups over the planar surface of the graphene oxide flakes. The higher number of carbonyl and carboxyl groups in HGO, detected by several methods, including XPS, NMR and FTIR, unavoidably results in defects of the graphene "skeleton", holes and overall disruption of the carbon-carbon bond network, stronger deviation from planar flake shape and poor ordering of the graphene oxide layers. It is also suggested that functional groups in HGO are less homogeneously distributed over the flake surface, forming some nanometer-sized graphene areas. The presence of differently oxidized areas on the GO surface results in inhomogeneous solvation and hydration of HGO and effects of inter-and intrastratification. The proposed interpretation of the data explains the higher mechanical strength of multi-layered BGO membranes/papers, which are also less affected by humidity changes, thus providing an example of a membrane property superior to that of HGO.

Graphite oxide swelling in molten sugar alcohols and their aqueous solutions

“…[60] Nearly the same d(001) of 9.93 Å and 9.96 Å are found for BGO intercalated with xylitol and sorbitol, Next set of experiments was performed using in situ synchrotron radiation XRD recorded during the heating of BGO mixed with xylitol or sorbitol. The first heating cycle was performed up to 400 K to verify the structure of BGO in molten sugar alcohol and keeping temperature below the point when thermal deoxygenation of GO could be expected (~>130 0 C, [60]), Figure 2a. Analysis of XRD data shows that the same phase with d(001) ~ 9.9 Å is formed in molten sugar alcohols.…”

“…Detailed characterization of precursor graphite oxides used in this study (BGO and HGO) was performed in our earlier study [60]. Both materials showed similar oxidation degree (C/O=2.7 and C/O=2.6 respectively) but rather different vapour sorption properties, thermal stability (revealed by TGA), certain difference in FTIR and NMR spectra.…”

“…Detailed characterization of these materials using XRD, FTIR, TGA and some other methods were presented in our previous publications. [30,40,44,48,56] The ref [56] provides characterization of the same materials as those which are used here for study of sugar alcohol intercalation. XRD data were recorded using in house diffractometers Siemens D5000…”

Engineering 3D Graphene-Based Materials: State of the Art and Perspectives

“…Flakes obtained from direct exfoliation of graphite (e.g., by liquid phase exfoliation [6,7]) have more regular structure and better conductive properties, and are therefore more suitable for electronics applications, but are also more expensive and difficult to obtain and handle. Therefore, for the 3D scaffold building, usually, the process starts from the oxidation of graphite to graphite oxide, e.g., by Hummer's method [38], followed by exfoliation-reduction either thermally [39], leading to Thermal Exfoliate Graphite Oxide (TEGO), or using microwaves, leading to Microwave Exfoliate Graphite Oxide (MEGO) [40,41], resulting in materials with SSA usually not exceeding 800 m 2 /gr [42,43]. Samples can be subject to additional treatments, such as further reduction, or chemical activation (e.g., with KOH), which modify the edges with the result of increasing the porosity to specific pore volume (SPV) greater than 2 cm 3 /g [30,44] and improving the SSA up or exceeding the graphene limit (2630 m 2 /g).…”

Toward Large-Scale Production of Oxidized Graphene

“…At a low degree of oxidation, hydroxyl groups can chemically turn into epoxide groups and vice versa, allowing for the use of GO for specific technological applications [24]. In addition, the GO structure reveals a mixed sp 2 −sp 3 hybridization as a direct consequence of the degree of oxidation acquired during the oxidation process [26] (see, e.g., Brodie [27], Staudenmaier [28], Hummer [29], Marcano [30], and Chen [31]). Hummer et al reported the method most used nowadays: the oxidation of graphite is realized by treatment with KMnO 4 and NaNO 3 in concentrated H 2 SO 4 .…”