Aza-crown-ether functionalized graphene oxide for gas sensing and cation trapping applications

Graphene oxide has been functionalized with 1-aza-15-crown-5 ether via chemical route synthesis. Modification of graphene oxide was achieved via nucleophilic attack where the amine groups of an aza-crown ether molecule can easily react with the epoxy sites of graphene oxide basal plane. Owing to the inherent two-dimensional character of graphene oxide, it resulted in large specific-surface material with strong affinity for charged chemical species. Such property was exploited for reversible and controlled interaction of adsorbed species, envisaging two possible applications of the functionalized graphene oxide. Thus, an easy-to-fabricate and high-sensitivity functionalized graphene oxide-based gas sensor was achieved. The sensing material proved to be highly stable and capable of selectively detecting humidity at room temperature over a wide range of concentrations. Moreover, the porous scaffold built by the functionalization, together with the well-known affinity of crown ethers to metal ions, allow the use of aza-crown ether functionalized graphene oxide for cation trapping application, e.g. pre-concentration of trace amount of metals or filter for water. Remarkable results in this field have been obtained with respect to some heavy-metal cations of environmental interest. We also demonstrated significant enhancement in performance versus pure graphene oxide in both tested applications. More generally, the functionalization approach we pursued appears to be quite flexible in the tested applications. In fact, with an appropriate selection of crown ethers with specific cage-like structure, functionalized graphene oxide allows the capture of any desired guest in order to prepare a wide range of other crown-ether-GO nanocomposites for different applications.