Chemistry of Graphene Oxide
Graphene oxide (GO) is used as a precursor during the production of graphene, a compound with unique properties currently being actively researched for photonic materials. GO has a heterogeneous nature and the surface contains various functional groups such as alcohols, epoxides, ketones, and carboxylic acid groups. One way of appending dyes, or chromophores, to GO is through group IV metal ions such as zirconium and hafnium that simultaneously bind a porphyrin and the GO. The bonding between the central metal of the chromophore and the oxygen molecules on the GO surface are observed by UV-Visible and fluorescence spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The bonding between the chromophore and the surface of the GO can potentially act as a building block in the production of innovative photonic devices such as flexible displays and solar energy harvesting materials. The potential to revolutionize these devices lies in the proper construction of these molecules so that maximum efficiency is achieved through maximum light absorption and emission. In this research we have used free base porphyrins to titrate and quantify the number of carboxylic acid groups on GO as a means to assess the number of this type of binding site for the group (IV) metalloporphyrins. From our data, the number is approximated to be between 2,000 and 6,000 carboxylic acid groups per square micron of GO. We have also tested new methods to exfoliate graphene from graphite using group IV metal ions and dye molecules under various conditions and found promising results using ZnPc, ZnPcF16, and ZrCl4. By performing these experiments, GO can be better characterized and understood, allowing for further research to occur in order to produce numerous advances in photonic devices.
Supported by NIH-RCMI grant numbers MD007599 (formerly RR003037) and NIDA grant R25DA032520