Self-Assembly of Metal-Organic Frameworks in Pickering Emulsions Stabilized with Graphene Oxide

Metal-organic frameworks (MOFs) integrated with inorganic colloidal carriers compose a new class of functional hybrid materials possessing properties useful for a number of applications, in particular, selective sorption and (photo)catalysis. A new method has been developed for the synthesis of porous composites consisting of graphene oxide and MOF crystallites based on porphyrins. Graphene oxide serves simultaneously as a protective matrix for MOF and an emulsifier providing the assembly of immiscible components, which have different solubilities, in Pickering emulsions. Zinc acetate plays the role of a metal cluster, which immobilizes MOF crystallites on graphene oxide surface and participates in the MOF synthesis as a secondary structural block. This combination of the components makes it possible to avoid a chemical modification of graphene oxide during the assembly of the composite material. This strategy has been employed to obtain two series of model supramolecular composites based on zinc meso-tetra(4-pyridyl)porphyrinate and zinc meso-di(4-pyridyl)-di(4-carboxyphenyl)pophyrinate and study the relation between their structure, morphology, and properties. The developed colloid-chemical method makes it possible to simplify the synthesis of supramolecular composite materials and may be adapted to different combinations of inorganic matrices and MOFs.