**Modifications**

Provisional chapter

## **Green Routes for Graphene Oxide Reduction and Self-Assembled Graphene Oxide Micro- and Nanostructures Production** Green Routes for Graphene Oxide Reduction and Self-Assembled Graphene Oxide Micro- and Nanostructures

Rebeca Ortega-Amaya, Yasuhiro Matsumoto , Esteban Díaz-Torres, Claudio Davet Gutierrez-Lazos, Manuel Alejandro Pérez-Guzmán and Mauricio Ortega-López Rebeca Ortega-Amaya, Yasuhiro Matsumoto, Esteban Díaz-Torres, Claudio Davet Gutierrez-Lazos, Manuel Alejandro Pérez-Guzmán and

Additional information is available at the end of the chapter Mauricio Ortega-López Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67403

#### Abstract

Production

Graphene-derived materials are currently studied because of their actual and projected applications. Among them, graphene oxide (GO) promises for outstanding applications as it can be prepared at large scale by simple, scalable, and low-cost techniques. The existent chemical methods based on the graphite exfoliation (phase solution and Hummers based) produce highly functionalized graphene, i.e., GO-like materials that converts into reduced GO (rGO) after a reduction treatment. The present work presents the current scenario on the GO green reduction methods, on the development of hierarchical carbon-based structures by the self-assembly of GO sheets at interfaces, and on rGObased hybrid nanocomposites. It is worth noting that, to date, the production and application of graphene-related materials are the fastest-growing research areas.

Keywords: graphene oxide, reduced graphene oxide, green reduction, metal, composites, self-assemble

### 1. Introduction

Graphene, one-atom thick layer of densely packed carbon atoms into a honeycomb crystal lattice, is considered the key building block of graphite, carbon nanotubes, and fullerenes [1]. It is of current interest due to its remarkable physical and chemical properties, which makes it

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

useful for theoretical studies for several technological applications. Current applications of graphene include flexible electronics, batteries, and so on [2]. Diverse methods have been proposed to produce high-quality single and few layer graphene films. Among them, graphite micromechanical cleavage, chemical vapor deposition, and graphitization of SiC have been the most utilized methods [3]. Although these methods produce high-quality graphene in a controlled way, they suffer from mass production scaling.

In the past years, graphene-derived materials, such as graphene oxide (GO), graphane (the hydrogenated version of graphene), graphene fluoride, and so on [4, 5] have been paid special interest because of their potential applications. Particularly, GO and its reduced version, reducedgraphene oxide (rGO), have emerged as a technologically important material by its their own right [6].

GO is mainly prepared through chemical methods and therefore achieves unique and useful physiochemical properties to prepare a variety of functional materials for a range of advanced applications, such as rGO self-assembled microstructures [7, 8] and, rGO-based composites with inorganic nanoparticles (metals, semiconductors, metal oxides). These GO-derived materials have successfully been tested in the technological areas of nanomedicine, electronics, environmental remediation, energy conversion, and others [7–9].

The chemical methods to prepare single-layer GO use graphite as the raw material, which is exfoliated either using strong oxidants in aqueous medium (based on Hummers' method) or using organic solvents (based on the solution-phase technique), among others [10]. During the graphite oxidation process, oxidative species intercalate into graphite galleries provoking the partial disruption of the graphene sp<sup>2</sup> -hybridization and the covalent attachment of oxygenrich species. This results on the weakening of the interlayer attractive force, so that single-layer GO sheets are easily obtained upon application of low power sonication in water [8].

From a structural point of view, GO is considered as a graphene sheet comprising in-plane undisturbed π-conjugated domains, and functionalized ones with covalently attached hydroxyl and epoxy groups, and additional carboxyl and carbonyl groups located at the sheet edge [11]. This chemical structure gives GO an amphiphilic character and then makes it dispersible in polar or nonpolar solvents [12]. This amphiphilic character preserves in rGO because it is obtained after the partial remotion of these functional groups by a reduction process.

Interestingly, rich oxygenated groups attached to the graphene structure makes GO and rGO highly hydrophilic and susceptible for further functionalization. Therefore, pristine or reduced GO can conveniently be functionalized to facilitate the interfacial interaction between GO and other materials including polymers, metal oxides, and inorganic nanoparticles to form GObased composite materials, or to link the sheets together and then lead to macroscopic GObased materials [13, 14].

Due to its multiple applications, GO is produced at an industrial level. Nowadays, worldwide research groups are looking for ways to find cost-effective and environment-friendly methods for graphene-derived materials' mass production. These include electrochemical, mechanical, and chemical exfoliation of graphite [15]. In general, these methods produce GO-like materials, i.e., functionalized graphene, and they may be further processed to produce rGO with multiple functionalities. To date, the phase solution graphite exfoliation-based methods have demonstrated their high versatility to fabricate bulk amounts of graphene-derived materials at relatively low cost [16].

There are diverse methods for GO reduction, such as thermal reduction, chemical reduction using toxic or green reductive reagents, and multistep reduction (either by combining chemical and thermal processes or by combining green and toxic reducers to get an effective reduction). Dangerous and toxic reagents such as hydrazine, oxalic acid, sodium hydrosulfite, and sodium borohydride were reported to reduce GO efficiently. On the other hand, GO environmentfriendly reduction routes include flash photo reduction, hydrothermal dehydration, solvothermal reduction, catalytic reduction, and photocatalytic reduction. Furthermore, green reductants have also been essayed including vitamin C, alcohols, bovine serum albumin, gingseng, bacteriorhodopsin, bacteria, and polyphenols (present in green tea and caffeic acid, among others) [17, 18].

This work presents an overview on the environmental-friendly methods to reduce GO and produce GO-based nanocomposites. A survey of their applications is also presented.

In addition, we present the mechanistic aspects on GO-based nanocomposites, as well as those associated in the formation of GO nano- and microstructures by self-assembly process.
