Beyond the size: Assessing the influence of synthesis parameters on ZIF-8 monolith degradation in aqueous environments

This article reports the room-temperature synthesis of ZIF-8 monoliths, systematically varying synthesis parameters while maintaining a constant metal:ligand ratio of 1:7.9. The washing procedure, aging time, centrifugal speed, precursor concentration, solvent type, ammonia concentration, and metal salt were changed to investigate their effect on the water stability of the resulting monolith. The synthesised monoliths were characterised by optical microscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and N<inf>2</inf> gas adsorption, while the precursor nanocrystallites were analysed by scanning electron microscopy (SEM). Water stability was evaluated by immersing monolithic pieces in Mili-Q water for 24 h, followed by UV-Vis spectroscopy to track linker release and inductive coupled plasma optical emission spectroscopy (ICP-OES) to quantify metal ion leaching. The use of Zn(CH<inf>3</inf>COO)<inf>2</inf>, along with the washing procedure, are the most important parameters for improving water stability and enhancing the phase purity, textural properties and transparency of the monolith. Other parameters contributing to these characteristics are centrifugal speeds exceeding 4200 rpm, concentrated synthesis, and partial replacement of methanol for aqueous ammonia. Based on this comprehensive analysis, a refined synthesis protocol was formed, yielding a more water-stable ZIF-8 monolith. However, despite its improved stability, the monolith was unable to adsorb rhodamine B from aqueous solutions as the dye's size far exceeds the pore window of ZIF-8, limiting adsorption to the external surface.

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DDC Class

541.39: Chemic Dynamics, Statics and Equilibrium; Affinity

620.11: Engineering Materials

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EXC 3120 - BlueMat - Wassergesteuerte Materialien

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https://creativecommons.org/licenses/by/4.0/

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publishedVersion

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