Engineering linker defects in functionalized UiO-66 MOF nanoparticles for oil-in-water Pickering emulsion stabilization

Abstract

Designing metal–organic framework (MOF)-based solid nanoparticles to stabilize Pickering emulsions by fine-tuning their hydrophobicity and lipophobicity is vital for essential applications and fundamental understanding. We demonstrate in situ grafting of palmitic acid in UiO-66 MOF through its linker defects. Our designed and activated nanoparticles (denoted as UP′) stabilized the Pickering emulsions of n-heptane-in-water. Furthermore, we showed how UP′ stabilized emulsion droplets disperse in media by covering each tiny droplet with a nanoscale layer made of UP′. To support our claim, we carried out the freeze-drying process to remove the liquid part from the emulsion, leaving behind the solid shell-like microstructures that we further characterized through several microscopic techniques. The stable n-heptane-in-water emulsion was confirmed by dilution (drop test), conductivity, zeta potential, and theoretical surface electrostatic potential measurements. Rheological studies indicate that the Pickering emulsions of n-heptane-in-water stabilized by UP′ are much more resistant to deformation and flow imparting higher (mechanical) stability and shelf-life. Pickering emulsions stabilized by UP′ emerged as a versatile way to design smart functional materials of UiO-66 through engineering linker defects that may have potential applications in interfacial catalysis, dye or contaminant separation, etc.