Versatile self-assembled graphene oxide membranes obtained under ambient conditions by using a water-ethanol suspension

Nowadays there is a special interest in synthesising well-controlled self-generated graphene oxide (GO) membranes by scalable, cheap, mild and non-toxic synthesis pathways without negatively affecting their remarkable properties. Keeping this in mind, in this study we report a low cost and scalable pathway that can be used for preparing free-standing GO membranes by a self-assembly process under ambient conditions at an air-liquid interface of an isopycnic sorted GO water-ethanol fraction. The precursor GO suspension used for the preparation of this membrane-forming fraction is obtained by subjecting graphite to a more active-protected oxidative exfoliation, in which non-toxic and non-hazardous gases are generated. To improve the exfoliation and to obtain the isopycnic separation of well-defined GO fractions, ultrasonication and centrifugation are used. The prepared self-assembled GO membranes with controllable thickness are strong enough to be harvested in a simple way. The tunability of the morphological, structural and optical properties of the membranes is obtained by varying the self-assembly time. A structural model for the membrane formation via the self-assembly process is also proposed. Since during the self-assembly process mild conditions and non-toxic components are used, this method can be successfully applied in specific areas like the fabrication of biohybrid platforms or environmentally friendly devices.