μ-Tiles and mortar approach: A simple technique for the facile fabrication of continuous b-oriented MFI silicalite-1 thin films

Here we report a simple method, what we call a μ-tiles and mortar method, to grow highly b-oriented MFI thin films on substrates in a facile manner. The method involves three main steps: (1) rapidly assembling b-oriented MFI micro-crystal layers on porous substrates using manual assembly (i.e., direct assembly by rubbing crystals on functionalized surfaces), (2) passivating the flat crystal faces by sputtering a thin gold/palladium layer to prevent the nucleation and growth of crystals along the out-of-plane direction while allowing the growth of crystals along the in-plane direction, and followed by (3) filling the gaps between the MFI micro-crystals by allowing the crystals to grow only in the plane while preventing the out-of-plane growth of the crystals. It is shown that the key to the successful fabrication of oriented MFI thin films is to promote the in-plane (i.e., parallel to the support) growth of oriented zeolite tiles on substrates during the secondary growth step so as to eliminate the intercrystal gaps and generate a continuous film while preventing the out-of-plane (i.e., perpendicular to the support) growth and nucleation of mis-oriented grains. Using the μ-tiles and mortar method, we have demonstrated that continuous b-oriented MFI thin films can be readily made with controllable microstructure such as membrane thickness, size of single crystal domain, and density of grain boundary. We have also made, for the first time, MFI thin films that have preferentially oriented crystal grains with randomly oriented grain boundary structure. The method reported here has potentials to address some of the current engineering challenges for practical applications of zeolite membranes by enabling the fabrication of oriented zeolite membranes in a simple manner.