(47b) Rapid Fabrication of Metal Organic Framework Thin Films Using Microwave-Induced Thermal Deposition

Nanoporous metal-organic frameworks (MOFs) have attracted considerable research interest due to their potential applications for hydrogen storage1, selective gas adsorption2,3 catalysis and enantioselective separation4. Metal-organic framework materials (MOF) generally consist of metal-oxygen polyhedera containing divalent (Zn2+, Cu2+)5 or trivalent (Al3+, Cr3+)6 metal cations interconnected with a variety of organic linker molecules, resulting in tailored nanoporous materials. With a judicious choice of organic linker groups, it is possible to fine-tune size, shape, and chemical functionality of the cavities and the internal surfaces2. This unique structural feature offers unprecedented opportunities in small-molecule separations as well as chiral separations and catalysis.7,8,9

While most of the previous works have focused on the discovery of new MOFs and their applications in powder form, there are only few studies on the preparation of MOF thin films on substrates.10,11 The highly inter-grown thin MOF films will find technologically important applications as gas separation membranes, chemical sensors, and nonlinear optical devices. However, it is yet to be shown that highly inter-grown continuous MOF films can be prepared.

In this work, we will present a novel method, microwave-induced thermal deposition (hereafter, MITD), to rapidly prepare MOF-5 seed layers on substrates under microwaves and to subsequently grow the seed layers into highly inter-grown continuous films.12 MITD is fundamentally different from the conventional microwave-assisted method for film preparation. MITD takes advantages of electron-phonon scattering (Joule heating) to rapidly increase kinetics of heterogeneous nucleation of MOF crystals on porous substrates coated with thin conductive layers. Therefore, our method does not depend on the properties of the substrates as long as a thin conductive layer can be deposited on the substrates. We will talk about the effect of microwave-induced Joule heating on the formation of MOF-5 seed crystal layers on the substrates coated with various conductive materials. The mechanical strength of MOF-5 thin film on the substrate will also be discussed. We will then present the selectively deposited MOF-5 patterns and the multi-layers of MOF-5 and silicalite-1 films on porous substrate. Finally, we will discuss a novel strategy to grow the MOF seed layers into well-intergrown continuous membranes and their performance for gas separations.

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11 S. Hermes, F. Schroder, R. Chelmowski et al., Journal of the American Chemical Society 127 (40), 13744 (2005).

12 Y. Yoo and H.-K. Jeong, Chemical Communications (DOI:10.1039/B800061A) (2008).