Solubilization and Dispersion of Carbon Allotropes in Water and Non-aqueous Solvents

Available methods for solubilization and dispersion of several carbon allotropes (with the exception of dispersions in polymers) in organic solvents and water are reviewed. Main attention is paid to graphite, graphene, fullerenes, nanoonions, nanodiamonds, carbon nanotubes, and carbon nanodots. The techniques to increase the "solubility" of carbon allotropes include chemical functionalization of the carbon surface (covalent and non-covalent functionalization, oxidation via ozonation, insertion of electron-withdrawing atoms (fluorination), polymer grafting, swelling and biomolecule treatments, use of molecular "wedges" for intercalation, thermal reduction, etc.). The combination of functionalization with the use of surfactants, ultrasound, laser ablation, milling, microwave expansion, hydrothermal methods, and other treatments leads to better results. The possibility of dispersion and the size of the formed particles depend on a series of factors, in particular the nature of the solvent, its viscosity and hydrogen-bond donation ability, dispersion interactions, pi-pi stacking between the carbon surface and reagents, and the nature of the surfactants, among others.