Microstructural and rheological investigation of upcycled metal-organic frameworks stabilized Pickering emulsions

A method for rheological measurements of air sensitive samples

The rheology of air or moisture sensitive liquids, gels, and glasses requires complicated rheometer-in-glovebox laboratory setups. Here, we demonstrate the use of a heavier-than-air cover gas, sulfur hexafluoride, and the design of a cover gas container that can attach to the lower geometry plate of any rheometer to carry out rheology experiments on air-sensitive liquids and soft solids. Rheological measurements of air-reactive ionic liquid trimethylsulfonium bromide-AlCl3, moisture sensitive titanium(IV) propoxide, and glycerin demonstrate the effectiveness of the cover-gas method for loading samples on acquiring correct temperature dependent viscosity data of the sample in the absence of reaction products.

Mechanistic Study of the Formation of Multicomponent Oxide Porous Microspheres (MICROSCAFS®) by Cryo-Scanning Electron Microscopy

Multicomponent oxide microspheres with interconnected macroporosity (MICROSCAFS®) are new materials with great potential as support materials for photocatalysis, optimized for real life applications and for other uses that are still being explored. They are obtained from an adapted sol-gel process combined with phase separation phenomena that occur within the water droplets of an emulsion. We present here a methodology based on cryogenic scanning electron microscopy (cryo-SEM) that allows, with minimal specimen preparation, the direct and in situ visualization of 'wet' alkoxide-derived microstructures, for the mechanistic study of the complex process of MICROSCAFS® generation. It is simultaneously combined with energy dispersive X-ray spectroscopy (EDS) to visualize phase separation phenomena and study the chemical elemental composition at specific regions of the sample and reaction times.

Development of protein-polyphenol particles to stabilize high internal phase Pickering emulsions by polyphenols' structure

Protein-polyphenol colloidal particles are promising stabilizers for high internal phase Pickering emulsions (HIPPEs). However, the relationship between the structure of the polyphenols and its ability to stabilize HIPPEs has not been studied thus far. In this study, bovine serum albumin (BSA)-polyphenols (B-P) complexes were prepared, and their ability to stabilize HIPPEs was investigated. The polyphenols were bound to BSA via non-covalent interactions. Optically isomeric polyphenols formed similar bonds with BSA, whereas a greater number of trihydroxybenzoyl groups or hydroxyl groups in the dihydroxyphenyl moieties of polyphenols increased the B-P interactions. Polyphenols also reduced the interfacial tension and enhanced the wettability at the oil-water interface. The HIPPE stabilized by BSA-tannic acid complex exhibited the highest stability among the B-P complexes and resisted demixing and aggregation during centrifugation. This study promotes the potential applications of polyphenol-protein colloidal particles-stabilized HIPPEs in the food industry.

Controlling polyHIPE Surface Properties by Tuning the Hydrophobicity of MOF Particles Stabilizing a Pickering Emulsion

Metal-organic frameworks (MOFs) show promise for the capture of greenhouse gases. To be used at a large scale in fixed-bed processes, their shaping under a hierarchical structure is mandatory and remains a major challenge, while keeping available their high specific surface area. For that purpose, we propose herein an original method based on the stabilization of a paraffin-in-water Pickering emulsion by a fluorinated Zr MOF (UiO-66(F4)) with polyHIPEs (polymers from high internal phase emulsions) strategy consisting of the polymerization of monomers in the external phase. After polymerization of the continuous phase and elimination of the paraffin, a hierarchically structured monolith is obtained with the UiO-66(F4) particles embedded in the polymer wall and covering the internal porosity. To avoid the pore blocking induced by the embedment of the MOF particles, our strategy was to modify their hydrophilic/hydrophobic balance with a controlled adsorption of hydrophobic molecules (perfluorooctanoic acid, PFOA) on the UiO-66(F4) particles. This will induce a displacement of the MOF position at the paraffin-water interface in the emulsion and then make the particles less embedded into the polymer wall. This leads to the formation of hierarchically structured monoliths integrating UiO-66(F4) particles with higher accessibility, maintaining their original properties and allowing their application in fixed-bed processes. This strategy was demonstrated by N₂ and CO₂ capture, and we believe that such original strategy could be applied to other MOF materials.