Control of graphene aerogel self-assembly in strongly acidic solution via solution polarity tuning

Abstract

In view of their advantages (plasticity, low density, adjustable pore size, high porosity of >99.9%), three-dimensional graphene aerogels (GAs) are widely used for energy storage and adsorption separation, which has inspired the development and optimization of the corresponding synthetic techniques. In particular, self-assembly in the liquid phase features the benefits of tunability and sustainability and is viewed as a promising strategy of GA synthesis. During hydrothermal GA preparation, hydrophilic graphene oxide (GO) gradually turns lipophilic upon reduction, and the resulting phase transition separation and polarity change induce self-assembly into an aerogel. However, the effect of solution polarity on the structure or state of dispersed GO nanosheets, which affects the final property-determining process of automatic assembly, is still unclear. Herein, we prepared a series of GAs by hydrothermal reduction of unwashed GO with vitamin C in liquid-phase systems of different polarity and investigated the effects of polarity on the self-assembly process and aerogel properties using a range of instrumental techniques. The results showed that GO reduction is slowed down in weakly polar systems and further demonstrated that the shape of partially reduced graphene oxide (rGO) flakes depends on solution polarity. Flaky, layered, and stacked rGO particles obtained in strongly polar media self-assembled into anisotropic gully aerogels that were brittle and almost completely inelastic. Conversely, in weakly polar media, the prepared rGO sheets were twisted, which increased the number of contact points and modes between sheets and resulted in self-assembly into uniform-pore-structure honeycomb aerogels that showed good elasticity and could be repeatedly compressed.