Graphene oxide synthesis using modified Tour method

Abstract

Graphene oxide (GO) colloidal solution has been synthesised by the modified Tour method, in which the pH of the reaction medium has been increased to 2.0-2.2 at the final stage of graphite oxidation by adding NaOH solution. The solid-phase graphene oxide consists of multilayered graphene particles with a thickness of about 7.5 nm (9-10 layers of graphene) and an average size of about 7.7 nm. Reduced graphene oxide (rGO) has been prepared by hydrazine and microwave reduction. A comparative study of the structure, morphology, and electrical transport properties of rGO samples obtained by various methods has been carried out using XRD, SAXS, Raman spectroscopy, low-temperature nitrogen adsorption, and impedance spectroscopy. Structural analysis has shown the presence of two fractions of plate-like rGO particles for each reduction method, which consist of 4-6 layers of graphene in stacks and have a lateral size in the range of 7.1-7.6 nm. The BET specific surface area of the microwave-reduced rGO was higher than that of the chemically reduced one (296 and 237 m 2 g −1 respectively). The frequency dependence (10 −2 -10 5 Hz) of the AC conductivity of the GO and rGO samples has been analysed in the temperature range of 25 °C-175 °C. For the GO sample, the proton exchange conductivity mechanism dominates. A Drude-like response of electrical conductivity at frequencies above 10 3 Hz with transition to Johnscher's law response at 175 °C has been observed for rGO samples obtained using both chemical and microwave routes. Changes in activation energies and relaxation times have been interpreted using a model of a thermally activated frequency-dependent electron hopping mechanism between randomly coupled conducting sp 2 rGO packages separated by disordered sp 3 rGO regions with correspondingly higher resistivity.

Functional groups in graphene oxide

“…Graphene oxide is an atomically thin, two-dimensional material chemically exfoliated from graphite oxide via different approaches developed by Brodie, 30 Staudenmaier, 31 Hofmann, 31 Hummers 30,31 and Tour. 32 For better knowledge of the chemical and structural variations of GO exfoliated via different historical synthetic routes, the interested readers are referred to the review paper published in 2009. 33 The fundamental chemistry is that the GO sheet mainly contains sp 2 carbons (CQC), epoxy/hydroxyls (C-O), carbonyl (CQO) and carboxylates (O-CQO).…”

Structural and electrical properties of sulfur-doped graphene oxide/graphite oxide composite

“…Parameters of the NDR effect observed for the graphene oxide/graphite oxide composite material The electrical conductivity of the obtained graphene oxide/graphite oxide composite material is the result of a complex mutual influence of both mechanisms. The first is an electronic hopping between partially oxidized graphite particles forming a randomly distributed grid, and the second is a protonic mechanism of charge transport according to the Grotthuss mechanism [16]. Based on the synthesis conditions, it can be assumed that GO fragments are located between graphite oxide particles, and water molecules are embedded between graphene stacking layers [5].…”

Solution combustion synthesized NiFe2O4 / reduced graphene oxide composite nanomaterials: morphology and electrical conductivity

“…Complex oxide/rGO composite materials were obtained under the same experimental conditions by one-pot synthesis, when a colloidal solution of graphene oxide was added to the metal salt mixture before the fuel agents. Colloidal graphene oxide was prepared according to the modified Marcano-Tour protocol [7]. Both pure ferrite (T0 sample) and NiFe2O4 / rGO composites (mass ratio of spinel and rGO phases was 3:1 (T1 sample) and 3:2 (T2 sample), respectively) were obtained.…”