Separation of Graphene Quantum Dots by Polarity via Hydrophilic-Interaction Liquid Chromatography

Graphene quantum dots (GQDs) with pronounced emission in the visible and near-infrared regions are particularly promising nanomaterials for diagnostic imaging. Despite the relative simplicity of the top–down synthesis of graphene quantum dots via the oxidative degradation of reduced graphene oxide (hereafter termed RGQDs), it is evident that the product contains fractions with varying morphologies, functional groups, and polarities. To enhance the use of RGQD in applications requiring a high degree of monodispersity, it is necessary to separate RGQDs into fractions with distinct properties. In this work, hydrophilic-interaction chromatography was used to separate the RGQDs based on their polarity. Resulting two main fractions demonstrate similar optical and cell viability properties but differ in size, morphology, and types of functional groups as well as hydrophilic interactions. Specifically, more hydrophilic fraction 2 includes quasi-spherical highly functionalized RGQDs, while more hydrophobic fraction 1 is rich in graphene nanoribbons. This uncovers a simple and scalable synthetic route to the production of such nanoribbons. Application of chromatographic separation presented in this work is an innovative approach to synthesis and purification of graphene quantum dots and nanoribbons that not only enhances the purity of synthesized RGQDs but also enables the use of two fractions with different polarities for different goals in such applications as therapeutic delivery and optoelectronics.