Preparation of Stable Pickering Emulsions Stabilized with Concentrated Sols of Carbon Nitride and Graphene Oxide

A novel method has been proposed for preparing stable highly concentrated Pickering emulsions stabilized with 2D particles of carbon nitride (g-C3N4) and its mixtures with graphene oxide (GO) in a water/n-hexane system due to electrostatic interactions with zinc acetate (Zn(OAc)2). Optical microscopy and sedimentation stability analysis have been employed to determine optimal conditions for preparing emulsions with g-C3N4 concentrations up to 6 mg/mL. The formation of oil-in-water (o/w) emulsions stabilized with either g-C3N4 particles or GO/g-C3N4 binary dispersions has been confirmed by fluorescence microscopy using a water-soluble dye, fluorescein. Measurements of the ζ-potentials of g-C3N4 sols and emulsions stabilized with g-C3N4 have made it possible to determine the main stabilization mechanism of the highly concentrated Pickering emulsions. It has been found that acetate ions (CH3COO−) promote migration of negatively charged g-C3N4 particles from the aqueous phase to the interfaces, while zinc cations (Zn2+) are adsorbed on the g-C3N4 surface, thereby suppressing the mutual repulsion of the particles in the shells of emulsion droplets. During the formation of Pickering emulsions based on GO/g-C3N4 binary disperse systems, metal clusters contribute to the stabilization of emulsions due to coordination bonding between GO carboxyl groups and g-C3N4 particles. This mechanism provides efficient particle integration at the interfaces and prevents the highly concentrated Pickering emulsions from separation. The results obtained open up prospects for developing universal catalytic systems with controllable properties to be used for the degradation of organic pollutants and the synthesis of functional materials.