**Graphene‐Based Materials Functionalization with Natural Polymeric Biomolecules**

Edgar Jimenez‐Cervantes Amieva, Juventino López‐Barroso, Ana Laura Martínez‐Hernández and Carlos Velasco‐Santos

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/64001

#### **Abstract**

The use of 2D nanocarbon materials as scaffolds for the functionalization with different molecules has been rising as a result of their outstanding properties. This chapter describes the synthesis of graphene and its derivatives, particularly graphene oxide (GO) and reduced graphene oxide (rGO). Both GO and rGO represent a tunable alternative for applications with biomolecules due to the oxygenated moieties, which allow interactions in a either covalent or non‐covalent way. From here, other dis‐ cussed topics are the biofunctionalization with keratin (KE) and chitosan (CS). The non‐ covalent functionalization is based primarily on secondary interactions such as van der Waals forces, electrostatics interactions, or π–π stacking formed between KE or CS with graphenic materials. On the other hand, covalent functionalization with KE and CS is mainly based on the reaction among the functional groups present in those biomole‐ cules and the graphenic materials. As a result of the functionalization, different applications have been proposed for these novel materials, which are reviewed in order to offer an overview about the possible fields of application of 2D nanocarbon materials. In a nutshell, the objective of this work is as follows: first, overhaul different aspects about the synthesis of graphene chemically obtained, and second, make a review of different approaches in the functionalization of 2D carbon materials with specific biomolecules.

**Keywords:** graphene oxide, reduced graphene oxide, reduction, functionalization, co‐ valent, non‐covalent, chitosan, keratin

© 2016 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.

#### **1. Introduction**

Carbon is one of the most interesting elements of nature and is one of the primary constitu‐ ents for the formation of all organic matter. Its capacity to bind to itself in different ways makes carbon a very versatile element, giving rise to a series of structures called allotropes. Some of these carbon forms have attracted great interest in the past few decades due to their small size, in the scale of nanometers, and their very particular shape or dimensionality, which directly affect their chemical and physical properties. Among these carbon nanostructures, graphene (GE) has become an outstanding material presenting a unique set of "superlative" properties such as mechanical, electrical, thermal and electronic characteristics, enlisted in many reports [1–4].

Graphene is the name of a single layer of carbon atoms arranged in a two‐dimensional (2D) crystalline hexagonal lattice, due to the sp<sup>2</sup> hybridization of carbon. Thus, graphene has strong in‐plane σ bonds, responsible for its high mechanical strength and flexibility, and it also has weak out‐of‐plane π bonds responsible for its thermal carrying, electrical charge, and trans‐ parency, and graphene is also impermeable. Nevertheless, all these properties are only observed in a single defect‐free graphene layer, which is costly to produce in a scalable degree. Alternatively, there are other ways to produce graphene with relative ease, such as the chemical phase exfoliation of graphite oxide. This method yields the synthesis of graphene oxide (GO), a highly oxidized version of graphene. The subsequent reduction in the oxygen content brings a partial restoration to graphenic state, producing reduced graphene oxide (rGO) or chemically converted graphene (CCG) (**Figure 1a**). These graphene‐based materials

**Figure 1.** (a) Schematic chemical structures of graphene, graphene oxide, and reduced graphene oxide. (b) Route of graphite to reduce graphene oxide.

are considered as a functionalization of a graphene sheet, because of the presence of oxygen species [5].

Even when GO and rGO have a lower set of properties compared with those of GE, they can be improved through an additional functionalization among others with organic and different bio‐molecules. Since the presence of oxygen groups is greater in GO, its reactivity is higher compared with rGO, and thus, graphene oxide is more suitable to be functionalized through covalent interactions. On the other hand, even when rGO retain some oxygen sites, its partial graphitic surface makes it adequate for a non‐covalent functionalization. In this manner, tailored‐made properties can be successfully achieved giving rise to a wide range of potential applications.

In this manner, GO and rGO have been modified with all kind of biomolecule groups, such as nucleic acids, proteins and peptides, antibodies, enzymes, polysaccharides and amino acids, for applications related to biological/biomedical fields which require a good degree of compatibility, adherence, or biocide characteristics. Long‐chain biopolymers containing amino groups, such as keratin (a protein) and chitosan (a polysaccharide), show an excellent covalent linkage with GO, and a good adsorption on rGO (keratin), and they could function either increasing the bacterial adhesion or inhibiting the bacterial growth. This chapter focuses in the study and insight of the interactions between amine‐containing biopolymers through covalent and non‐covalent interactions with GO and rGO. The details of synthesis of graphene oxide and reduction are reviewed and discussed; a brief discussion involving the different types of functionalization is mentioned; finally, some researches related to functionalization of biomolecules on graphenic materials along with their diverse potential uses is also discussed.
