Synthesis And Applications Of W-silicalite-1 Zeolite Films

Zeolite films and membranes,owing to their precisely defined pore structure,a tunable composition and excellent stability,are particularly promising in applications as separation,catalysis,water treatment,corrosion protection and low-k materials.Of reported zeolite films,silicalite-1 zeolite films are of great interests due to their good stability as well as high hydrophobicity.At present,how to improve the separation performance of silicalite-1 zeolite films at a reduced preparation cost is an urgent problem in the actual application of silicalite-1 zeolite films.By introducing heteroatoms with different oxidation states and electronegativity,isomorphous substitution of silicon has been acting an important role in modifying the properties of zeolite films.In this thesis,starting with the improvement of separation performance and reduction of preparation cost,we prepared W-silicalite-1 zeolite films by introducing W into the synthesis solution.Centering on the preparation and applications of W-silicalite-1 zeolite films,the work was mainly carried out as follows:1.Randomly oriented silicalite-1 zeolite membranes were synthesized by the two-step growth method onα-Al₂O₃substrates and were applied to the pervaporation separation of 5 wt.%ethanol/water solution.The results by using multiple characterization techniques revealed that problems such as defects and poor hydrophobicity existed in the silicalite-1 zeolite membranes prepared under present conditions,which indicated the direction for the subsequent research work.2.The effects of W on the growth of zeolite crystals were investigated and the320 nm-thick and highly b-oriented W-silicalite-1 zeolite membranes with enhanced hydrophobicity were successfully synthesized by adjusting the W/Si ratio in the synthesis solution.3.Based on the above results,highly b-oriented W-silicalite-1 zeolite membranes with a thickness of 700 nm were synthesized onα-Al₂O₃substrates by the two-step growth method,which exhibited comparable performance for ethanol/water pervaporation.At 60°C,the W-silicalite-1 zeolite membrane showed a total flux of1.86 kg·m^-2·h^-1with a comparable separation factor of 21.4.W-silicalite-1 zeolite coated mesh films were also prepared on low-cost stainless steel mesh in the ultradilute synthesis solution by secondary growth and the zeolite coated mesh films showed hydrophobicity in air and superoleophobicity underwater,which were effective for the separation of various oil/water mixtures.The separation efficiency of the zeolite coated mesh films for dichloromethane/water,petroleum ether/water and hexane/water were all in excess of 94%and the water flux was as high as 105.71 L·m^-2·s^-1.Furthermore,the repeated experiment,stability behavior and the oil intrusion test demonstrated that the W-silicalite-1 zeolite coated mesh films possessed excellent mechanical and chemical stability under harsh environments.