Bottom‐up synthesis, dispersion and properties of rectangular‐shaped graphene quantum dots

Carbon nanomaterials have attracted the attention of the scientific community for more than 30 years, first with fullerene and nanotubes and now with graphene and graphene related materials. Graphene quantum dots can be synthesized following the top-down or the bottom-up approach. The first used harsh chemical and/or physical treatments of graphitic materials to obtain nanoparticles, while the second is based on the synthesis of polycyclic aromatic hydrocarbons exhibiting various sizes and shapes that are perfectly controlled. However, the limited solubility of carbon materials prevents the synthesis of nanoparticles containing more than few hundreds of sp2 carbon atoms. Here we report on a family of rectangular-shaped graphene nanoparticles containing up to 162 sp2 carbon atoms. These particles are not functionalized on their periphery in order to keep the maximum similarity with pure graphene nanoparticles. Sodium deoxycholate surfactant was choosen to study their dispersion and their optical properties and the electronic structure of the particles were studied using Density Functional Theory. We observe that the larger particles (GQD 3 and GQD 4) present a slightly better dispensability than the smaller ones, probably because the larger GQDs can accommodate more surfactant molecules on each side, which helps to stabilize their dispersion in water.