preprints.org > materials science > surfaces, coatings & films > doi: 10.20944/preprints202303.0152.v1

Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 7 March 2023 / Approved: 8 March 2023 / Online: 8 March 2023 (08:57:06 CET)

Zeolitic imidazolate frameworks (ZIFs) have potential for various gas and ion separations due to their well-defined pore structure and relatively easy fabrication process compared to other metal-organic frameworks. As a result, many reports have focused on preparing polycrystalline and continuous ZIF layers on porous supports. In this study, we investigated how humidity and chamber temperature influence the structure of a ZIF-8 layer prepared by the hydrothermal method. We controlled the chamber temperature (ranging from 50 °C to 70 °C) and relative humidity (ranging from 20 % to 100 %) using a thermos-hygrostat chamber. We found that as the chamber temperature increased, ZIF-8 preferentially grew into particles rather than forming a continuous polycrystalline layer. By measuring the temperature of the reacting solution based on chamber humidity, we discovered that the heating rate of the reacting solution varied with humidity, even at the same chamber temperature. At higher humidity, thermal energy transfer was accelerated as water vapor delivered more energy to the reacting solution. Therefore, a continuous ZIF-8 layer could be formed more easily at low humidity ranges (ranging from 20 % to 40 %), while micron ZIF-8 particles were synthesized at a high heating rate. Our findings suggest that controlling the heating rate of the reacting solution is critical to preparing a continuous ZIF-8 layer, particularly for future scale-up of ZIF-8 membranes.

Zeolitic imidazolate framework; Membrane; Nucleation; Relative humidity; Solution heating rate

MATERIALS SCIENCE, Surfaces, Coatings & Films