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

Abstract

A primitive cubic lattice composed of 1,000 atoms has 488 surface sites. By definition, every atom in a strictly two-dimensional single-layer lattice composes its surface. These surface atoms are the ones that undergo chemical interactions with the surrounding medium, thereby defining the functionalities of the nanostructure. As such, one of the most important morphological properties of nano-objects is the extremely large specific surface area that enhances their levels of reactivity. Here, we introduce an optical spectroscopy method to measure the surface area concentration, ρA, of mass-produced graphene nanoflakes in liquid dispersions. The information is accessed from the quenching of the fluorescence signal from the dye molecules dispersed in the medium. We found that the quantum efficiency of the fluorescence signal decays exponentially with the concentration of graphene’s surface area, the decay rate being independent of the degree of exfoliation. If the mass concentration ρ is known by other means, the specific surface area can be extracted from the ratio ρA/ρ. The measurements can be performed directly in liquid suspensions of nanoflakes, being highly applicable to the quality control of mass-produced two-dimensional nanomaterials, especially by means of mechanically assisted liquid-phase exfoliation.

Advancing Evidence-Based Data Interpretation in UV–Vis and Fluorescence Analysis for Nanomaterials: An Analytical Chemistry Perspective

“…It is a common observation that addition of nanomaterials to fluorophore-containing solutions modifies (enhances or reduces) sample fluorescence. − However, the influence of absorption and scattering on the fluorescence signal has often been overlooked or insufficiently addressed. − The failure to correct the absorption inner filter effect (IFE) typically results in an underestimation of the sample’s true fluorescence intensity or an overestimation of nanoparticle-induced fluorescence quenching. Since the impact of scattering on sample fluorescence intensity is usually small, correcting only the sample IFE caused by sample absorption is usually adequate for most applications.…”