Measuring the Surface Area Concentration and Specific Surface Area of Mass-Produced Graphene Nanoflakes via Fluorescence Quenching

A primitive cubic lattice composed of 1,000 atoms has488 surfacesites. By definition, every atom in a strictly two-dimensional single-layerlattice composes its surface. These surface atoms are the ones thatundergo chemical interactions with the surrounding medium, therebydefining the functionalities of the nanostructure. As such, one ofthe most important morphological properties of nano-objects is theextremely large specific surface area that enhances their levels ofreactivity. Here, we introduce an optical spectroscopy method to measurethe surface area concentration, & rho;(A), of mass-producedgraphene nanoflakes in liquid dispersions. The information is accessedfrom the quenching of the fluorescence signal from the dye moleculesdispersed in the medium. We found that the quantum efficiency of thefluorescence signal decays exponentially with the concentration ofgraphene's surface area, the decay rate being independent ofthe degree of exfoliation. If the mass concentration & rho; is knownby other means, the specific surface area can be extracted from theratio & rho;(A)/& rho;. The measurements can be performeddirectly in liquid suspensions of nanoflakes, being highly applicableto the quality control of mass-produced two-dimensional nanomaterials,especially by means of mechanically assisted liquid-phase exfoliation.