A simple chemical process developed at Rice University creates lightweight, highly absorbent aerogels that can be beaten.
Covalent Organic Frames (COFs), crystal structures with strong molecular bonds, can form a porous airgel for use as a custom membrane in batteries or other devices or as an absorbent to remove pollutants from the environment.
Conventional COFs are generally powders. Chemical and biomolecular engineer Rafael Verduzco, lead authors and graduate students of Rice Dongyang Zhu and Yifan Zhu and their colleagues at the Brown School of Engineering in Rice have discovered a way to synthesize COF aerogels that can be made under n ‘ Any shape and size, limited only by the reaction chamber.
The process reported in the Materials Chemistry of the American Chemical Society uses COF monomers, a solvent and a catalyst. When mixed and heated to 80 degrees Celsius (176 degrees Fahrenheit), they become a uniform gel. Washing and drying the gel to remove the solvent leaves behind the scaffold-shaped airgel with pores between 20 and 100 microns.
“The big advantage of polymers is that you can dissolve them in a solvent, you can spray, spin, and dip coat them, and they’re easy and inexpensive to work with,” Verduzco said. “But COFs aren’t. It’s an insoluble powder that’s hard to do anything with, but they really show promise for applications because you can design or design them almost however you want at the level. Molecular They are like Lego blocks and you can choose the molecular shapes, sizes and characteristics you want to include in the final material.
“We were looking for ways to make COFs easier to use, like polymers, and we found that under particular reaction conditions they would form a gel,” he said. “When you pull out the solvent, you get this very light foam, or airgel.”
Verduzco said COF aerogels could be a valuable addition to industrial absorbents currently used for sanitation, as their porous structures can be customized.
The lab formulated six aerogels and found that their sanitizing properties with various dyes, oils, and gold nanoparticles were much better and faster than COF powders. In a test with vapor of iodine, a product of nuclear fission, the airgel absorbed 7.7 grams of iodine per gram of airgel, significantly better than a COF powder of the same material.
The researchers found that aerogels could be washed and reused at least 10 times without warping. “They’re pretty soft but you can crush them by hand and they bounce back,” Verduzco said.
He sees even greater potential for COFs as membranes to separate advanced battery components, the subject of a recent review article edited by Dongyang Zhu in Advanced Functional Materials.
They could also mimic biological membranes. “No one has figured out how to effectively separate a mixture of ions or molecules that are roughly the same size and shape, but with this class of materials we can precisely control the size and shape of the pores.” , said Verduzco.
“Biological membranes separate ions of the same size and charge themselves by small changes in the functionality of the pores that preferentially bind to one ion or the other,” he said. “I think we can start making synthetic materials that have similar properties.”
The laboratory is developing a library of COF airgels to be tested in applications. “There really is a lot to explore here,” Verduzco said.
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