Development and Application of Surface-active Graphene Quantum Dots

Abstract

Graphene quantum dots (GQDs), as one of derivatives of graphene, are essentially zero- dimensional for graphene. Their extremely small size endows them with more intriguing properties. Additionally, plenty of oxygen-containing groups are available on their surface or edges, which provide GQDs a great potential for surface modifications. Upon surface functionalization, the applications of GQDs nanoplates have been greatly enhanced in Pickering emulsification and fabrication of flame retardant polymer nanocomposites.

First of all, amphiphilic GQDs functionalized with dodecyl alkyl groups (C-GQDs) which are synthesized by a facile one-step method. The amphiphilicity could be acquired controllably and effectively, which make them used as Pickering emulsifier. The C-GQDs based Pickering emulsion could be obtained with a very low concentration, which could be utilized in a large-scale application considered about eco-friendly and cost-effective manner. Moreover, the pH-responsive properties of C-GQDs make these nanoplatelets recycled and reused in Pickering emulsion system. In order to improve the salt tolerance of GQDs as Pickering emulsifier, the GQDs was functionalized with zwitterionic structure (ZGQDs), which made them could be used under high ionic strength. Meanwhile, ZGQDs have the capacity to regulate molecular diffusion at interface, which made them have potential to be applied in controlled-release fields.

Furthermore, GQDs, as a type of carbon-based nanomaterials, have been widely used in fabricating polymer composites to improve the mechanical, thermal and flame retardant properties. C-GQDs, as a kind of stabilizer, could be used to fabricated PS nanocomposites which were coated with C-GQDs via an in-suit Pickering emulsion polymerization method The incorporation of C-GQDs onto the PS surface increased the thermal stability and flame retardancy of PS nanocomposites. Moreover, GQDs, as a kind of zero-dimensional nanomaterials, have potential to be used to functionalize two-dimensional materials to improve the interfacial affinity between nanoadditives and polymer matrix. Thus, we used C-GQDs to decorate montmorillonite (MMT) to fabricate nanohybrids CG@MMT. The as-prepared nanohybrids showed separated and flaked structure than unmodified MMT. The as-prepared polymer nanocomposites contained nanohybrids presented improved flame retardancy with well dispersion in PS matrix. In this work, this effective decorating method with zero-dimensional nanoparticles would provide possibilities for broadening the MMT applications.