Controlling covalent chemistry on graphene oxide

Graphene has attracted intensive research interest in many fields, owing to its remarkable physicochemical properties. Nevertheless, its low dispersibility in most organic solvents and in water, and its tendency to aggregate, prevent full exploitation of its properties. Graphene oxide (GO) is an alternative material that exhibits high dispersibility in polar solvents. GO contains abundant oxygen-containing groups, mainly epoxide and hydroxy groups, which can be further chemically derivatized. However, because of GO’s high reactivity, several reactions may occur simultaneously, often leading to uncontrolled GO derivatives. Moreover, because GO can be easily reduced, functionalization should be performed under mild conditions. In this Review, we discuss the chemical reactivity of GO and explore issues that hamper precise control of its functionalization, such as its instability, the lack of a well-defined chemical structure and the presence of impurities. We focus on strategies for the selective derivatization of the oxygenated groups and C=C bonds, along with the challenges for unambiguous characterization of the resulting structures. We briefly review applications of GO materials, relating their chemistry and nanostructure to desired physical properties and function, and chart future directions for improving the control of GO chemistry.