Liquid‐Phase Quasi‐Epitaxial Growth of Highly Stable, Monolithic UiO‐66‐NH₂ MOF thin Films on Solid Substrates

Abstract

High quality, monolithic UiO-66-NH 2 thin films on diverse solid substrates have been prepared via a low temperature liquid phase epitaxy method. The achievement of continuous films with low defect densities and great stability against high temperatures and hot water is proven, clearly outperforming other reported types of MOF thin films.Metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) represent a class of highly functional solid materials assembled from metal or metal/oxo nodes and di-or higher-topic organic linkers, [1,2] that continue to receive enormous attention. Due to their modular composition and the ability to access large number of topologies, [3] a huge number of different types of these porous materials, covering a broad spectrum of functionalities, has become available. In addition, combination of different types of Hetero-MOFs fabricated by employing heteroepitaxy via layer-by-layer procedures [4] allows the integration of several different functionalities in these materials, including electrical conductivity, [5] optical upconversion, [6] luminescent properties, and the ability to modulate electrical properties upon illumination with light. [7] For numerous usages of MOFs, the commonly isolated powder-form, consisting of μm-sized particles, is well suited, e. g. for gas storage [8] and water treatment applications. [9]

Stability of Monolithic MOF Thin Films in Acidic and Alkaline Aqueous Media

“…Furthermore, Pan et al [ 42 ] explored a pure aqueous synthesis route for ZIF-8 and reported excelling stability of the material in boiling water and methanol. Considering ZIF-8 SURMOFs like the ones explored in this work, a previous work [ 16 ] showed that the films lost their crystallinity after being immersed in boiling water for 1 h and SEM images revealed a complete detachment of the film from the substrate. Moreover, Sheng et al [ 44 ] explored the effect of varying Zn salts on the hydrothermal stability of ZIF-8 and observed significant degradation in the material after 10 days with the exception of the ZIF-8 derived from Zn acetate.…”

“…Lin et al [ 49 ] reported also high stability of the material in water and in fluoride-containing solution. Continuing with water scenarios, a previous work explored the stability of UiO-66-NH 2 SURMOF films in boiling water [ 16 ]. The results showed that for these MOF thin films the crystallinity and the adhesion to the substrate was unchanged after immersion for one hour.…”

“…UiO-66-NH 2 SURMOF samples were synthesized using the previously reported method [ 16 ]. First, Au-coated silicon wafers were functionalized using a 1 mM ethanolic solution of 11-Mercapto-1-undecanol (MUD, Sigma Aldrich, Darmstadt, Germany).…”

“…Previous works have shown that high-quality, crack/pinhole-free homogeneous MOF thin films can be obtained by careful optimization of the concentration, immersion times, and temperatures of the reactant solutions. For a growing number of MOF materials, appropriate layer by layer (LBL) synthesis conditions yielding high-quality SURMOFs have been developed, including HKUST-1 [14], ZIF-8 [15], and UiO-66-NH 2 [16]. Such MOF thin films have been characterized using a wide range of techniques and have been also successfully used to fabricate devices for diverse applications delivering high-performance results [13].…”

SURMOF Devices Based on Heteroepitaxial Architectures with White‐Light Emission and Luminescent Thermal‐Dependent Performance

“…[ 37 ] Over the last two decades, Wöll and colleagues have implemented the LPE technique for building SURMOFs for many applications, employing conventional MOFs such as ZIFs, IRMOF‐n, MIL‐n or HKUST‐1, and recently UiO‐NH 2 ‐66. [ 27,44,45 ] Briefly, a pretreated quartz or silicon substrate was placed in a reactor at 55 °C (which is 10 °C lower than in our previous report). [ 37 ] Thereafter, the substrate was immersed in ethanolic solution of either Ln(NO 3 ) 3 or H 3 BTC alternatingly.…”