The novel COF aerogel. Photo: Jeff Fitlow/Rice University.
The novel COF aerogel. Photo: Jeff Fitlow/Rice University.

Researchers at Rice University have developed a simple chemical process for creating light and highly absorbent aerogels that can take a beating. They discovered that covalent organic frameworks (COFs), crystal structures with strong molecular bonds, can form a porous aerogel for use as a custom membrane in batteries or other devices or as an absorbent to remove pollutants from the environment.

Conventional COFs are usually powders. Chemical and biomolecular engineer Rafael Verduzco, graduate students Dongyang Zhu and Yifan Zhu and their colleagues at Rice's Brown School of Engineering have come up with a way to synthesize COF aerogels in any form and at any size, limited only by the reaction chamber.

The process, which they report in a paper in Chemistry of Materials, involves mixing together COF monomers, a solvent and a catalyst at 80°C (176°F) to produce a uniform gel. Washing and drying the gel to remove the solvent leaves behind the scaffold-like aerogel with pores between 20µm and 100µm.

"The big advantage of polymers is that you can dissolve them in a solvent, you can spray coat, spin coat and dip coat them, and they're easy and cheap to work with," Verduzco explained. "But COFs are not. They're an insoluble powder and hard to do anything with, but they are really promising for applications because you can design or engineer them almost any way you want on the molecular level. They're like Lego blocks and you can pick the molecular shapes, sizes and characteristics you'd like to include in the final material.

"We were looking for ways to make COFs easier to work with, more like polymers, and we found that under particular reaction conditions they would form a gel. When you extract the solvent, you get this very light foam, or aerogel."

According to Verduzco, COF aerogels could become a valuable addition to industrial absorbents now in use for remediation because their porous structures can be customized.

The researchers formulated six aerogels and found that their remediation properties with various dyes, oils and gold nanoparticles were far better and faster than COF powders. In a test with iodine vapor, a product of nuclear fission, the aerogel absorbed 7.7 grams of iodine per gram of aerogel, significantly better than a COF powder of the same material.

The aerogels could also be washed and reused at least 10 times without deforming. "They're pretty soft but you can squish them by hand and they spring back," Verduzco said.

He sees even greater potential for COFs as membranes to separate components in advanced batteries, the subject of a recent review paper in Advanced Functional Materials by many of the same researchers.

The COF aerogel could also mimic biological membranes. "Nobody's figured out how to efficiently separate a mixture of ions or molecules that are about the same size and shape, but with this class of materials, we can precisely control the pore sizes and shapes," Verduzco said.

"Biological membranes separate ions of the same size and charge through small changes in pore functionality that preferentially bind one ion or the other. I think we can start to make synthetic materials that have similar properties."

The lab is now developing a library of COF aerogels to test in applications. "There's really a lot to explore here," Verduzco said.

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.