Direct Observation of Carbon Nitride-Stabilized Pickering Emulsions

Pickering emulsions are emulsions stabilized by solid particles located at surfaces/interfaces of liquid droplets that have promising applications for drug delivery and in nanomaterials synthesis. Direct observation of Pickering emulsions can be challenging. Normally, cryoelectron microscopy needs to be used to better understand these types of emulsion systems, but cryofreezing these emulsions may cause them to lose their original morphologies. In this work, we demonstrate that graphitic carbon nitride (g-C₃N₄) can stabilize oil-in-water (o/w) emulsions, with hexane illustrated as a typical oil phase. The g-C₃N₄-stabilized emulsions can act as an excellent platform for in situ study of emulsifying behavior from the mechanical point of view. Owing to its large lateral size and blue, stable fluorescence, the locations and motions of the g-C₃N₄ stabilizer can be finely in situ monitored by light microscopy, fluorescence microscopy, and confocal microscopy. Accordingly, we illustrate two stabilizing configurations of the g-C₃N₄ particles with respect to the emulsion droplets under static conditions. Further, we demonstrate the capability to manipulate emulsion droplets and investigate their response to external forces. We perform real-time observations of the g-C₃N₄ particles and the emulsion droplets that move in the continuous phase and study their adsorption kinetics toward each other. Finally, the π-π interaction between the stabilizer and aromatic liquid phase (e.g., toluene) is considered and studied as an influencing factor on emulsifying behavior.