Facilitated transport membranes use reversible chemical reactions to selectively transport molecules. However, the same reaction that enhances CO₂ uptake can also limit its diffusion. We use CO₂-reactive polymer membranes as a model system to understand how carrier chemistry controls this balance.
How does covalent bonding affect transport?
In amine-functionalized membranes, CO₂ forms a carbamate covalently bound to the polymer. For the reacted CO₂ to move between amine sites, the C–N bond must repeatedly break and reform. The resulting activation barrier can severely restrict CO₂ permeation.
Can a noncovalent pathway accelerate diffusion?
We replace amine carriers with amidines, which convert CO₂ to bicarbonate under hydrated conditions. Bicarbonate interacts electrostatically with the polymer but is not covalently attached, allowing it to move more freely between carrier sites.
Our goal is to establish how carrier chemistry, reaction pathways, and binding mechanisms determine the activation energy of reactive diffusion. These insights will guide the design of faster and more efficient facilitated transport membranes.
Hydrogen-rich gas streams often contain acid-gas impurities such as CO₂ and H₂S. We design facilitated-transport membranes with sterically hindered (“bulky”) amine carriers that selectively remove H₂S while limiting competing reactions with CO₂.
How does steric hindrance control acid-gas selectivity?
Unhindered amines react readily with both H₂S and CO₂. By increasing the steric bulk around the amine, we suppress carbamate formation with CO₂ while preserving rapid, reversible acid–base interactions with H₂S.
Can bulky carriers overcome the permeability–selectivity tradeoff?
We investigate how carrier structure and local polymer environment influence H₂S permeability and H₂S/CO₂ selectivity. The goal is to maintain rapid H₂S transport without sacrificing molecular discrimination.
Our goal is to establish molecular design principles for highly selective acid-gas carriers. These insights will guide the development of efficient membranes for removing H₂S from hydrogen-rich syngas and other industrial gas streams.
Macrocycles provide well-defined cavities and localized interaction sites that can introduce molecular precision into polymer membranes. We use macrocycle-containing selective layers to address two fundamental questions:
How does cavity size control transport?
We investigate whether macrocycle dimensions can produce effective steric sieving between species of different sizes.
How do molecular interactions control diffusion?
We examine how interaction strength influences selective uptake, residence time, and mobility. Stronger interactions may enhance selectivity but slow diffusion, whereas weaker interactions may accelerate transport while reducing selectivity.
Our goal is to establish how cavity size and interaction strength work together—and to identify the optimal balance between selectivity and rapid transport. These design principles will guide membranes for challenging applications such as ion sieving and olefin/paraffin separation.
Solid sorbents, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and related materials, are generally synthesized as fine particles. Practical applications, however, require these particles to be assembled into structured sorbents that provide efficient transport, mechanical stability, and compatibility with scalable modules.
How can sorbent particles be transformed into flexible, porous structures?
We disperse sorbent particles in a dissolved polymer and process the resulting suspension through nonsolvent-induced phase inversion. This process immobilizes the particles within a highly porous polymer scaffold while preserving access to their active surfaces.
Why use a polymer scaffold?
The interconnected pores promote rapid mass and heat transfer between the embedded sorbent particles and the bulk gas stream. Unlike conventional rigid monoliths, the resulting scaffold remains flexible and can be incorporated into modules with adaptable form factors, including plate-and-frame and spiral-wound configurations.
Our goal is to develop scalable structured sorbents that combine high sorbent loading, rapid transport, and flexible module design. Potential applications include direct air capture, atmospheric water harvesting, volatile organic compound removal, and desiccant-based drying.