Fabrication of Thin Metal-Organic Framework MOF Films on Metal-Ion-crosslinked GO-modified Supports
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Fabrication of Thin Metal-Organic Framework MOF Films on Metal-Ion-crosslinked GOmodified Supports Julius Choi1, Hyuk Taek Kwon2, and Hae-Kwon Jeong*2,3 1 Department of Biological and Agricultural Engineering, Texas A&M University, College Station, TX 77843-2117, United States. 2 Artie McFerrin Department of Chemical Engineering and 3Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843-3122, United States. * Corresponding author, email address: [email protected] ABSTRACT Thin films of metal-organic frameworks (MOFs) have shown promising for applications such as gas separation, gas storage, optoelectronics or sensing. However, synthesis of polycrystalline MOF films and membranes depends largely on the surface properties of supports, limiting the availability of common supports. It is, therefore, highly desirable to develop ways to modify the surface properties of common supports for the preferred heterogeneous nucleation of the MOFs. Here, we demonstrated that graphene-oxide (GO) can be exploited to readily modify the surface properties of common supports, thereby leading to well inter-grown polycrystalline MOF films. A prototypical zeolitic-imidazolate framework ZIF-8 was chosen as a model MOF system. The stabilization of GO layers with divalent metal ions was found a key step to synthesize well inter-grown ZIF-8 films. The effect of divalent metal ions on the stability of GO layers and the quality of the resulting ZIF-8 films were systematically investigated. Finally, the single gas permeation behaviors of the ZIF-8 films grown on GO-modified supports were tested. INTRODUCTION Metal-organic frameworks (MOFs), a new class of crystalline nanoporous materials formed by the assembly of metal ions and organic ligands, have attracted a great deal of interest primarily due to their exceptionally high surface areas/pore volumes as well as tunable pores/cavities with a judicious choice of organic linkers [1]. In particular, zeolitic-imidazolate frameworks (ZIFs), a subclass of MOFs, consisting of zinc or cobalt metal centers and imidazolate-derived linkers, have attracted tremendous attentions due to their relatively high chemical/thermal stabilities, their ultra-microporosities, and high surface area when compared to other MOF materials [2]. For example, thin films of a prototypical ZIF-8 constructed from zinc and 2-methylimidzolate have shown great promises as high-performance sensors and highly selective membranes [1,2]. The applications of MOF materials such as in optical, sensing, and membrane-based separation applications often require the facile formation of MOF thin films on supports of choice [1,3]. However, synthesis of polycrystalline MOF films on supports (either porous or nonporous) requires preferential nucleation of MOF crystals on supports. As such, there are only a handful of supports used for continuous polycrystalline MOF films and membranes including a few oxides and polymers [1-4]. One strategy to improve the heterogeneous nucleation of MOFs on supports is to
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