Tailorable Synthesis of Highly Oxidized Graphene Oxides via an Environmentally-Friendly Electrochemical Process

Abstract

Graphene oxide (GO) is an attractive alternative to graphene for many applications due to its captivating optical, chemical, and electrical characteristics. In this work, GO powders with a different amount of surface groups were synthesized from graphite via an electrochemical two-stage process. Many synthesis conditions were tried to maximize the oxidation level, and comprehensive characterization of the resulting samples was carried out via elemental analysis, microscopies (TEM, SEM, AFM), X-ray diffraction, FT-IR and Raman spectroscopies as well as electrical resistance measurements. SEM and TEM images corroborate that the electrochemical process used herein preserves the integrity of the graphene flakes, enabling to obtain large, uniform and well exfoliated GO sheets. The GOs display a wide range of C/O ratios, determined by the voltage and time of each stage as well as the electrolyte concentration, and an unprecedented minimum C/O value was obtained for the optimal conditions. FT-IR evidences strong intermolecular interactions between neighbouring oxygenated groups. The intensity ratio of D/G bands in the Raman spectra is high for samples prepared using concentrated H2SO4 as an electrolyte, indicative of many defects. Furthermore, these GOs exhibit smaller interlayer spacing than that expected according to their oxygen content, which suggests predominant oxidation on the flake edges. Results point out that the electrical resistance is conditioned mostly by the interlayer distance and not simply by the C/O ratio. The tuning of the oxidation level is useful for the design of GOs with tailorable structural, electrical, optical, mechanical, and thermal properties.

Antibacterial Action of Nanoparticle Loaded Nanocomposites Based on Graphene and Its Derivatives: A Mini-Review

“…Hence, the nanomaterial-bacteria interactions are conditioned by the type of graphene-based nanomaterial. Further, depending on the synthesis process, the number of oxygenated groups including hydroxyl, ketone, epoxy, ether, and carboxylic acid will vary, resulting in C/O ratios ranging from 0.43 [22] to 25.3 [31]. The degree of hydrophilicity plays a crucial role in antibacterial activity.…”

“…Electrochemical reduction is also possible, and does not require chemical reagents. The reduction is exclusively driven by the electron exchange between GO and the electrodes in a conventional electrochemical cell [22].…”

Graphene Oxides Derivatives Prepared by an Electrochemical Approach: Correlation between Structure and Properties

“…Analogous curvatures and surface folds have been previously reported for GO functionalized with amines [ 38 ], ascribed to increased number of regular hydrogen bonds between the amine moieties. Thus, EGO 14 presents a low C/O ratio ( Table 1 ), that is, a high oxidation level, likely with a very high content of carboxylic acid groups [ 37 ], preferentially located at the sheet edges, which are able to interact via hydrogen bonding. Such surface wrinkling could be a crucial advantage for use in catalytic reactions, due to the higher accessibility of the catalytic sites.…”

“…The synthesized EGOs were collected by filtration, washed with water, purified via centrifugation at 2500 rpm, and ultrasonicated for 30 min at a power of 140 W, leading to well-dispersed EGO. A more detailed description of the synthesis procedure is given in [ 37 ]. The nomenclature of the EGO samples and the experimental conditions for their synthesis are collected in Table 1 .…”

“…In a previous study [ 37 ], we reported a novel, straightforward, green, and inexpensive two-stage approach for the synthesis of electrochemically exfoliated graphene oxides (EGOs) that allows to finely control the level of GO oxidation and exfoliation by carefully modifying the synthesis conditions. A broad range of experimental conditions were tested to optimize the synthesis route in order to attain homogeneous EGOs that preserved the integrity of the graphene flakes at a good yield.…”