Synthesis And Characterization Of Zeolite Beta Membranes And The Investigation Of Their Properties

Zeolite membrane is one of the developing inorganic membranes in recent years. Zeolite membrane with unique properties, such as uniform micropores, ion exchange, tunable-Si/Al, high temperature stability, solvent resistance, hydrophilicity-hydrophobicity, catalysis, and so on, which is an excellent membrane material to achieve separation and catalysis in molecule level have been widely used in separation, membrane reaction, catalysis, sensor, micro-electron areas. In a word, the zeolite membranes have particular superiorities in both separation and new-type areas. Therefore the research on zeolite membranes is greatly important, and needs further development.However, the prefect zeolite membranes are difficult to prepare as the growth of the zeolite crystals is a complex process and the growth of oriented zeolite crystal is difficult to control. The selectivity of the zeolite membrane is greatly reduced by the cracks, pinholes and inter-crystal gaps which exist in the incontinuous intergrowth of crystals of the membrane. Therefore, decreasing and eliminating the insufficiency of intergrowth of crystals are crucial to prepare the high quality zeolite membranes. On the other side, many efforts are focused on oriented zeolite membranes. The channels in the oriented zeolite membranes are identically directional and without blockages, so that the distance of transmission for molecules is diminished and the diffusion for molecules in the channels is speeded. Furthermore, oriented zeolite membranes are good host materials in host-guest chemistry by self-assembling or assembling of optic or electric-magnetic functional materials.Here we prepared (h0l) oriented high-silica zeolite Beta membrane by the secondary growth method on stainless steel net. Dealuminated zeolite Beta nanocrystals used as seeds were preliminary deposited on support, and then the seeded supports were vertically placed in autoclaves for hydrothermal synthesis. In addition, a synthesis growth method was improved to increase the quality of (h0l) oriented high-silica zeolite Beta membrane, and the surface of the zeolite Beta membrane was much more smooth, oriented and continuous. We also prepared (h0l) oriented high-silica zeolite Beta membranes on other supports such as, silicon wafer, glass, stainless steel slice,α-Al2O3 support, and these membranes were characterized by X-ray diffraction and scanning electron microscopy to determine their morphology and preferred orientation.Furthermore, (00l) and randomly oriented zeolite Beta membranes were also prepared by changing the composition of starting reaction gel and pH value on stainless steel net. It has many benefits using a stainless steel net as the support, such as large holes, high mechanical stability, excellent conductibility, chemical stability, and so on. The morphology and orientation of Beta crystals with different orientations could be changed with respect to the compositions of the reaction mixtures and synthesis conditions. A competitive growth model was proposed to explain the formation of oriented membranes. The continuous and defect-free zeolite Beta membrane with (h0l) orientation diminished the crack during calcination, exhibited higher pervaporation flux, and the (h0l) oriented high-silica zeolite Beta membrane will broaden its applications in separation.A new reaction mixture with the addition of n-propyl alcohol into the all-silica TEAOH-TEOS-HF-H2O gel was presented to prepare smooth and continuous pure-silica-zeolite Beta film on silicon wafer. n-Propyl alcohol was used to produce much homogeneous reaction mixture as well as accelerate the crystallization of Beta nanocrystals. In addition, by utilizing the secondary growth method the PSZ Beta film was much thinner and the synthesis time can further decrease to 36 h. After calcination, the PSZ Beta thin film showed good low-dielectric and mechanical strength properties.We also demonstrated that continuous and large-scale ITQ-16 and ITQ-17 films were successfully synthesized in the presence of Ge atoms and fluoride ions with TEAOH as organic structure directing agent on glass and stainless steel net. The proportion of polymorph C of the ITQ-16 film can be controlled by the addition of n-propyl alcohol into the synthesis gel. The n-propyl alcohol in the synthesis mixture has a stabilizing and buffering effect on the crystal growth. During the crystallization stage, a slow release of silicon, germanium and aluminum species into the gel is discussed to explain the purity control of the ITQ-16 film. X-ray diffraction and scanning electron microscopy were utilized to characterize the purity and the surface images of ITQ-16 and ITQ-17 films. Coumarin-151 was incorporated into the obtained ITQ-17 membranes by solvent diffusion method. The results of Emission microscopy, Uv-vis adsorption and emission spectrum indicated that the dye had assembled into the micropores of molecular sieve. The host/guest composite may be potentially apply in novel optical applications.