The Influence of Water in the Vapor‐Assisted Conversion Synthesis of UiO‐67 MOF Thin Films

Abstract

Water is known to play an important role for the crystallization and stability of Zr‐based metal‐organic frameworks (MOFs). This work investigates its effect on the vapor‐assisted conversion (VAC) synthesis of UiO‐67 MOF thin films on Au‐coated Si substrates. We demonstrate the equilibration processes taking place during the VAC procedure, confirming the gradual equilibration of all solutions upon heating. The presence of water affects the vapor phase composition but does not significantly impact the acetic acid equilibration rate. However, the preparation of UiO‐67 thin films by VAC is highly sensitive to the water content in the reaction. Some water is required for the formation of the zirconium clusters, but excessive water in the reaction vial yields poorly crystalline materials. Atmospheric water that is taken up by the vapor source can be sufficient to reduce crystallinity dramatically. This complication can be partially overcome by increasing the amount of acetic acid in the vapor source.

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“…Through a sequence of procedures including sealing, heating, cooling, and washing, the MOF film with tuned thickness, low roughness, and homogeneous distribution can be synthesized on various substrates, such as gold, silicon, indium tin oxide (ITO), and quartz. 117–121 Many factors, such as precursor volume, modulator and building block concentrations, reaction temperature/time, and water content can affect the film growth. 117,118,121 The use of a large precursor volume can result in the formation of thick MOF films.…”

“…117–121 Many factors, such as precursor volume, modulator and building block concentrations, reaction temperature/time, and water content can affect the film growth. 117,118,121 The use of a large precursor volume can result in the formation of thick MOF films. 117,118 By increasing the concentration of modulator, it is possible to enhance film orientation and crystallinity by retarding nucleation.…”

“…117,118 Additionally, the water content has a significant impact on the sensitivity of certain Zr-based MOFs, such as UiO-67. 121 Optimal water levels are crucial for the formation of Zr clusters, while excessive amounts result in poor crystallinity. 121 Therefore, careful adjustment of these factors can further optimize the quality of the film.…”

“…121 Optimal water levels are crucial for the formation of Zr clusters, while excessive amounts result in poor crystallinity. 121 Therefore, careful adjustment of these factors can further optimize the quality of the film. However, this method also demands a relatively high level of professional expertise from researchers, posing a certain degree of challenge to those lacking experience in materials preparation.…”