Enhancing hydrophilic properties of spherical C(sp2)-hybridized carbon nanostructures through the targeted oxidation of their outer layer

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Oxidation processes affect the structural integrity of carbon nanostructure (CN), leading to changes its physico-chemical properties, as a result of oxidation of sp 2 -hybridized carbon atoms, and formation of appropriate functional groups, further determining the surface properties of CNs. This work used several oxidation methods to develop effective procedures for the selective modification of the carbon nano-onion (CNO). Hydrogen peroxide, urea hydrogen peroxide complex, acetic chloride or anhydride, and trifluoroacetic acid were used as the primary reagents in various configurations for the functionalization of CNOs, which resulted in the formation of oxygen-containing groups, mainly carbonyls, phenolic, carboxyl, ethers, and esters. The dispersion of functionalized CNOs was tested in a series of protic, aprotic polar, and nonpolar solvents that were used to determine the Hansen Solubility Parameters. The dispersion of oxidized CNOs was determined experimentally in water, by designating the zeta potential of dispersed CNOs and their diameters using dynamic light scattering. The formation of oxygen-containing groups ensures high dispersion of CNs in polar solvents and provides high stability in water for more than two months. It is the first work describing such effective methods of functionalizing spherical nanostructures containing C(sp 2 )-hybridized carbon atoms, where the dispersion stability in water is so significant.