Gas-Induced Reversible Dispersion/Aggregation of Graphene

The low dispersibility of graphene in water, given its hydrophobic nature, is considered a serious problem that limits its use. Here, we describe a method to stably disperse graphene using a dispersant containing a tertiary amine and a pyrene group. The dispersant modifies the graphene surface via pi-pi stacking, allowing it to be dispersed in water. The dispersant undergoes a hydrophobic-hydrophilic transition upon being stimulated by CO2 and N-2, exhibiting a faster response (reaction time of 1.5 min) and lower recovery temperature (40 degrees C) than those of compounds with amidine-like structures. We found that the graphene modified by this gas-sensitive dispersant exhibited reversible dispersion/aggregation behavior upon the bubbling/removal of CO2. The proposed method is a simple one for the reversible dispersion/aggregation of graphene by stimulating it with a gas and should be suitable for fabricating sensors, drug-delivery systems, "smart" surfaces, and switching devices.