Chemically modified graphene can be a platform to investigate noncovalent interactions (electrostatic forces, van der Waals forces, pi-pi stacking, etc.) with potential technological applications. In this presentation, I will briefly review chemical methods to isolate and form graphene with a focus on the highly versatile graphene oxide, which is derived from graphite. For graphene oxide sheets suspended in water, the balance between repulsive electrostatic and attractive van der Waals forces can be mediated by pH. In the presence of an electric field, these interactions can be directed to produce multilayered films with vastly different surface wetting characteristics.
Graphene oxide can be simultaneously reduced to graphene and functionalized with groups such as amines via solvothermal reactions. We have found that a simple hydrothermal reaction with ammonia can be used to accomplish both. The evolution of the structure and surface charge can be observed in accordance with the reaction time. The newly introduced basic groups in this nitrogen-doped graphene (NDG) shift its isoelectric point to higher pH values. Thus, interesting assemblies could be formed in a range of moderate pH values.
The widely tunable surface charge and graphitic character of these graphene materials suggest they may be useful in some unconventional settings. I will discuss applications in catalysis and encapsulation on the basis of controlling electrostatic and pi-pi stacking interactions in these graphene materials.
Saad A. Hasan is a researcher at Uppsala University in Sweden. His research focuses on the chemical modification of graphene coupled with their assembly and use as templates. Saad is also developing a joint project with partners in the United States to study the biomolecule interactions of oxygen- and nitrogen-functionalized graphenes. He completed his PhD in 2010 at Vanderbilt University (Nashville, USA).