Periodic Precipitation of Zeolitic Imidazolate Frameworks in a Gelled Medium
Szabolcs Farkas, Máté Sándor Fonyi, Gábor Holló, Norbert Német, Nadia Valletti, Ákos Kukovecz, Gábor Schuszter, Federico Rossi, István Lagzi
Abstract
Formation of spatially periodic patterns is a ubiquitous process in nature and man-made systems. Periodic precipitation is the oldest type of pattern formation, in which the formed colloid particles are self-assembled into a sequence of spatially separated precipitation zones in solid hydrogels. Chemical systems exhibiting periodic precipitation mostly comprise oppositely charged inorganic ions. Here, we present a new sub-group of this phenomenon driven by the diffusion and reaction of several transition metal cations (Zn2+, Co2+, Cd2+, Cu2+, Fe2+, Mn2+, and Ni2+) with an organic linker (2-methylimidazole) producing periodic precipitation of zeolitic imidazolate frameworks. In some cases, the formed crystals reached the size of ∼50 μm showing that a gel matrix can provide optimal conditions for nucleation and crystal growth. We investigated the effect of the gel concentration and solvent composition on the morphology of the pattern. To support the experimental observations, we developed a reaction–diffusion model, which qualitatively describes the spatially periodic pattern formation.