Crystal Growth of ZIF-8, ZIF-67, and Their Mixed-Metal Derivatives

TLDR: Doping ZIF-8 by Co(II) enhances the photodegradation of methylene blue dye under visible light irradiation in the absence of hydrogen peroxide, and using RDF, the formation of a solid-solution ZIF via the incorporation of Co( II) and Zn(II).

Abstract: A facile method to produce zeolitic imidazolate frameworks (ZIF-8, ZIF-67, and solid–solution ZIFs (mixed Co and Zn)) is reported. ZIF crystals are produced via a reaction–diffusion framework (RDF) by diffusing an outer solution at a relatively high concentration of the 2-methyl imidazole linker (HmIm) into an agar gel matrix containing the metal ions (zinc(II) and/or cobalt(II)) at room temperature. Accordingly, a propagating supersaturation wave, initiated at the interface between the outer solution and the gel matrix, leads to a precipitation front with a gradient of crystal sizes ranging between 100 nm and 55 μm along the reaction tube. While the precipitation fronts of ZIF-8 and ZIF-67 travel the same distance for the same initial conditions, ZIF-8 crystals therein are consistently smaller than the ZIF-67 crystals due to the disparity of their rate of nucleation and growth. The effects of the temperature, the concentration of the reagents, and the thickness of the gel matrix on the growth of the ZIF ...