Scalable Wet Deposition of Zeolite Thin Film

• Main Authors: Pei-Sun Huang, 黃培舜
• Other Authors: Dun-Yen Kang
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/79w2ry

博士 === 國立臺灣大學 === 化學工程學研究所 === 106 === Zeolites are microporous materials with high crystallinity. Zeolite membranes and thin films can be used for catalytic reaction or separation processes in the chemical industry. Secondary growth is the most popular approach to the preparation of zeolite thin films and membranes; however, this process is time-consuming and is difficult for large-scale production. In this thesis, we proposed a scalable wet deposition method for preparing zeolite thin films. As a proof of concept, we implemented this method to fabricate zeolite thin films with two different zeolites: FAU and AEI. The first part of this thesis discusses, the fabrication of zeolite FAU thin films. Zeolite FAU suspensions are prepared at various pH values. Dynamic light scattering (DLS) was used to investigate the colloidal properties of the zeolite FAU suspensions. It was found that high pH value (pH = 13.5) destabilize the colloidal suspensions and results in high surface roughness of thin film. For the thin films formed from suspensions with high pH value, the zeolite FAU crystals transform into a dense phase. At relatively low pH value (pH = 12.5), the colloidal suspension is more stable. The thin film samples cast using this FAU suspension yields thin films with uniform morphology. We measured the dielectric constant of zeolite FAU thin film samples at various frequency. At high frequency (1000 kHz), thin films with a zeolite FAU structure exhibited dielectric constant as low as 2.1. In the second part of the study, we proposed a new approach to fabricating zeolite AEI thin films with high degree of crystal orientation via direct wet deposition. We deposit the colloidal suspensions that comprise aluminophosphate zeolite AEI on silicon wafer substrate. We combine the experimental and simulated 2D patterns of grazing-incidence wide-angle X-ray scattering (GIWAXS) to investigate the polycrystal orientation distribution in zeolite thin films. We elucidate the influence of crystal size, the deposition method, and substrate surface properties on the degree of preferred crystal orientation. Improved electrical properties and separation performance were observed for the zeolite thin films/membranes with high degree of preferred crystal orientation. Finally, we apply this method on the deposition of zeolite AEI thin films on a 6-inch silicon wafer to demonstrate the scalability of the proposed wet deposition technique.