New insights in the chemical functionalization of graphene oxide by thiol-ene Michael addition reaction

Abstract Graphene oxide (GO) is a carbon material with wide chemistry, and its functionalization represents the main challenge to develop multi-functional materials for different applications. Besides to epoxide and carboxyl groups, the alkenes that arise during the graphite oxidation seem to provide an excellent approach for developing selective reactions. In specific, α,β-unsaturated acids can be functionalized by thiol-ene Michael addition (TEMA) using base catalysts. However, when base catalysts are used, the thiol-epoxide ring opening reaction (TEROR) has been considered as the predominant and unique reaction. Therefore, there is a need to understand the reactivity of the GO when TEMA and TEROR take place from a qualitative and quantitative point of view. Herein, we studied the functionalization of GO and reduced graphene oxide (RGO) with cysteamine (CA) using different base catalysts. XPS results revealed that despite the thermal reduction of GO, the functionalization was possible confirming the coupling reaction between the CA and α,β-unsaturated acids of RGO by TEMA. In addition, a quantitative analysis was conducted via fluorescent labelling corroborating that TEMA produced more CA molecules bonded to GO than TEROR.