(84d) Controlling Interfaces in Mixed-Matrix Membranes by Solvothermal Deposition of Inorganic Nanostructures On Zeolite Crystals

Gas separation membranes with high performance can be made by incorporation of zeolite molecular sieves in polymeric membranes. Although these ?mixed matrix? membranes are prepared by phase inversion methods widely used for polymeric membrane fabrication, defects can be formed at the interface between zeolites and polymers due to their poor compatibility. Since non-selective permeation through these defects gives rise to poor separation performance, the nanoscale enhancement of adhesion between zeolite and polymer is a critical issue. Many studies have focused on organic functionalization of the zeolite surface, but the results were often unsatisfactory in terms of enhancing the performance of the membrane. Meanwhile, it was recently reported that zeolites with nanostructured inorganic surfaces, made via a halide/Grignard route showed excellent adhesion in mixed matrix membranes leading to high separation selectivities. However, this method utilizes a complicated procedure, unstable reactants, and has only been applied on aluminosilicate surfaces thus far.

Here we present a simpler, more general, high-yield solvothermal process for nanostructure deposition on zeolite surfaces. In this study, pure-silica MFI and aluminosilicate LTA crystals of various sizes were prepared and then treated by a solvothermal process to deposit Mg(OH)2 nanostructures on the surface in a controlled manner. For comparison, the previous treatment methods utilizing methylmagnesium bromide (Grignard reagent) were also performed. SEM characterization showed that the smooth surfaces of the zeolite crystals were altered to roughened surfaces by the formation of nanostructures on the zeolite surfaces after the treatments. The degree of surface roughness was quantified by external surface area measurements, and the solvothermal-treated particles showed significantly higher roughness than Grignard treated particles. N2 physisorption and CO2 sorption measurements revealed that micropore volume reduction of the zeolite by the surface treatment was marginal or negligible. Mixed matrix membranes were prepared using polyetherimide (Ultem 1000) as the polymer matrix. SEM observation and gas permeation measurements revealed that zeolite particles coated with Mg(OH)2 nanostructures were uniformly distributed in the polymer and exhibited significantly enhanced zeolite-polymer adhesion.