Jungkyu Choi

Microporous molecular sieve catalysts and adsorbents discriminate molecules on the basis of size and shape. Interest in molecular sieve films stems from their potential for energy-efficient membrane separations. However, grain boundary defects, formed in response to stresses induced by heat treatment, compromise their selectivity by creating nonselective transport pathways for permeating molecules. We show that rapid thermal processing can improve the separation performance of thick columnar fil

Oriented assembly of zeolite crystals on a porous support followed by secondary growth leads to continuous, thin, uniformly oriented zeolite films (see picture for a cross-sectional SEM image) of MFI with the 5.1×5.5-Å zigzag channels perpendicular to the support. These a-oriented films along with their previously reported b-oriented counterparts are the first set of thin molecular-sieve membranes with uniform but drastically different orientations. Molecular-sieve thin films are attracting rese

Chabazite (CHA)-type zeolites are promising for the separation of CO₂ from larger molecules, such as N₂ (relevant to postcombustion carbon capture) and CH₄ (relevant to natural gas/biogas upgrading). In particular, the pore size of CHA zeolites (0.37 × 0.42 nm²) can recognize slight molecular size differences between CO₂ (0.33 nm) and the larger N₂ (0.364 nm) or CH₄ (0.38 nm) molecules, thus allowing separation in favor

Continuous MFI-type zeolite membranes were fabricated on porous stainless steel tube supports by secondary (seeded) growth. The physical attachment of zeolite seed particles was initiated through sonication assistance on unmodified supports. Despite a sparse seed layer, a single hydrothermal growth step reliably led to c-/h0h-out-of-plane-oriented pure-silica MFI membranes. Rapid thermal processing was applied to as-synthesized membranes, extending the findings of a previous report on controllin

An oriented, hydrophobic membrane made of a decadodecasil 3 rhombohedral (DDR) zeolite (0.36 nm) could separate CO₂(0.33 nm) from larger N₂(0.364 nm) reliably.

The secondary growth methodology to form zeolite membranes has stringent requirements for homogeneous epitaxial intergrowth of the seed layer and limits the number of accessible high-quality zeolite membranes. Despite previous reports on hetero-epitaxial growth, high-performance zeolite membranes have yet to be reported using this approach. Here, the successful hetero-epitaxial growth of highly siliceous ZSM-58 (DDR-type zeolite) films from a SSZ-13 (CHA-type zeolite) seed layer is reported. The

It is quite challenging to avoid microdefect formation during hydrothermal growths and/or calcination processes, while manufacturing high-quality zeolite membranes in a reproducible manner. Even less than 1% of defects, which generally provide nonselective pathways, will considerably worsen the intrinsic, high molecular sieving-based separation performance of a continuous zeolite membrane. Herein, we propose a simple and reliable method for blocking defects using water-soluble dye molecules, whi