**5. Graphene and graphene-oxide**

#### **5.1 Graphene**

Since 2004, the Nobel Prize winning material, graphene is taken as one of the most wonderful achievements in the field of science and technology [7, 12]. Graphene is an atomically-thin (0.35 nm in thickness), it is a two-dimensional sheet with a honeycomb structure made up of sp2 hybridization carbon atoms which are linked together with strong sigma keys [7]. Graphene has unique properties that make it a core of scientific research that many of them can be transformed into practical [5, 7–9]. These valuable properties includes (1) a highly specific surface area [5, 7], as reported by Zhu et al. [13]; specific surface area (SSA) values of carbon materials obtained from GO have been well below 2630 m2 /g, but the specific surface area of common active carbon is only 1500 m<sup>2</sup> /g [12].

It has also a remarkable elasticity and mechanical strength; atomic force microscopy (AFM) measures the performance of freestanding monolayer graphene membrane based on Nano indentations; the result showed it has a breaking strength of 42 N·m−1 and a Young's modulus of TPa 1.0. even if graphene is an extremely strong material, still an external mechanical load can change the electronic properties of graphene thus, it is possible to affect its field emission performance. Graphene's capability to absorb pressure can also be affected by different degrees of axial compression. The varying sizes of buckling stress and strain are measured using a cantilever beam. When graphene is used as a membrane material, it can provide a stronger support force and adjustable sheet spacing. Therefore, the mechanical strength and controllability of the membrane can be improved. Graphene also exhibited excellent molecular barrier abilities and superior thermal and electrical conductivity [8–11]. Frequently, graphene and its derivatives are used in super capacitor, fuel cells, capacitive deionization, desalination, and others [13]. Different literature also reported graphene derivatives which can be integrated with other materials such as inorganic nanostructures, organic crystal, polymers, organic framework, biological materials, and carbon nanotubes to improve specific properties of the materials (Yi [11]).

### **5.2 Graphene-oxide (GO)**

The structure of GO similar to graphene but it also contains hydroxyl (–OH), alkoxy (C–O–C), carbonyl (C=O), carboxylic acid (–COOH), and other oxygenbased functional groups. GO has a non-stoichiometric general formula of the type CxHyOz. See **Figure 4** it is a suitable nanoparticle to improve the hydrophobicity of the membrane. The functional groups making it more dispersed in the polymeric solution. That means, if it is incorporated in the membranes, it can be improve properties for water purification. GO-incorporated membranes consist of a high mechanical strength and thermal stability [11]. The GO-incorporated membrane can enhance water transport even in low-pressure applications [14].

The most important property of GO nano-sheets is antifouling during operation due to negative charge and high hydrophobicity [7, 11]. It is believed that the GO-incorporated membranes have improved fouling resistance by reducing surface roughness and increasing hydrophilicity [7]. The GO-incorporated membrane shows high water permeability in various applications such as NF, RO, FO, and PRO processes [11]. Although the benefits of GO has been reported many, the material is still

**Figure 4.** *Depicted generic chemical and physical structures of graphene-based materials.*

*Graphene Oxide-Based Membranes as Water Separation: Materials, Preparation… DOI: http://dx.doi.org/10.5772/intechopen.105371*

expensive and is relatively difficult to manufacture at a larger capacity. Therefore, the manufacture of the material expected to well develop to decrease the cost and complication of manufacturing [11, 12].
