Enhanced Self–Assembly and Spontaneous Separation for Ultrathin, Air‒Floating Graphene Macrofilms and their Application in Ultrasensitive In‐Site Growth Sensors

Self-assembled graphene films at air-liquid interface have great potential for multiple applications. However, the large size and ultrathin thickness for graphene-based films are hardly achieved simultaneously because of poor assembly ability of graphene oxide (GO) and cautious film transfer process (FTP). Herein, the ethanol-based binary solution with supramolecular clusters and weak polarity is introduced to enhance the assembly performance of GO. In this regime, GO film is formed within 52 s, and its formation temperature can be as low as -20 °C. More importantly, the attractive force between the formed GO film and this binary solution is 62% lower than that between GO film and traditional aqueous solution. On this basis, for the first time a spontaneous separation of the self-assembled GO film from solution is reported, and the air‒floating graphene films (AGFs) with nanoscale thickness and centimeter-scale diameter are prepared without FTP. By means of this separation behavior, the in situ growth AGFs sensors are fabricated, and they express fast response and ultrahigh sensitivity to imperceptible change in temperature and disturbances that are hardly recognized by common sensors. Therefore, a new accessible strategy is demonstrated to prepare ultrathin graphene macrofilms, which can be the excellent candidates for multifunctional, ultrasensitive sensors.