Tiny and tunable: Porous crystals excel at recognizing molecules

BUFFALO, N.Y. — Porous crystals called COFs function like a sieve, allowing tiny molecules to pass through their holes while blocking others.

Because of this ability, COFs – covalent organic frameworks – could greatly reduce energy consumption and operational costs associated with industrial gas separation. They could also make more effective sensors and catalysts.

Before this can happen, however, researchers find a way to make COF pores both uniform and small enough to distinguish molecules that are roughly one ten-billionth of a meter. In other words, incredibly small.

A study from University at Buffalo researchers and colleagues at the University of Colorado at Boulder and the National Renewable Energy Laboratory, published June 28 in the journal Science, describes a significant advancement in this field.

Researchers report using oxyborate – a compound made of oxygen and boron atoms – to create a series of ionic covalent organic frameworks, or ICOFs, with pores small enough to differentiate molecules in methane, nitrogen, oxygen, carbon dioxide and hydrogen.

“The ICOFs we developed are both rigid and flexible. This is made possible by thermoregulatory oscillations of these ICOFs at different temperatures,” says co-lead author Miao Yu, SUNY Empire Innovation Professor in the UB Department of Chemical and Biological Engineering.

The materials differentiate molecules by very precisely controlled and tunable pores, through which molecules enter the inside of COFs and stick to the surface for storage. 

While more work must be done to commercialize the technology, perhaps the most practical use of the ICOFs involves them being “glued” together in pellet form, says Yu, who is a core faculty member of the UB RENEW Institute. Packed in an adsorption bed, the pellets could separate gas mixtures such as nitrogen and oxygen.

The work was supported with funds from the University at Buffalo, the Department of Energy and the National Science Foundation.