KAUST team develops carbon molecular membranes

According to postdoc Rifan Hardian, most polymer-based membranes exhibit poor chemical stability; they usually need additional chemical crosslinkers to improve their stability, which complicates their manufacture. Many membranes also tend to lose their performance as they swell and age and they may even break down to release trace contaminants.

Hardian and his KAUST colleagues Mahmoud A. Abdulhamid and Gyorgy Szekely claim to have overcome these drawbacks by creating a new kind of carbon molecular sieve (CMS) membrane that does not require additional crosslinkers.

The membrane is based on 6FDA-DMN, a polymer that can be formed into a flat, porous membrane with good thermal stability. Baking the polymer membrane at 400–600oC for several hours gradually burned off some of its chemical groups to leave a tough membrane made entirely of carbon. Electron microscope images showed that at the highest temperatures, this carbonisation process also shrank the membrane’s pores considerably.

After fine-tuning the conditions used to make the CMS membrane, the researchers tested its filtration abilities using solutions containing molecules of different sizes. The profile of molecules retained by the membrane, compared with those that passed through its pores, revealed how effective the membrane was at sieving different molecules.

The membranes prepared at 600oC performed best, holding back most of the smallest molecules while allowing solvent molecules to flow through. The team also found that the porous structure of the initial polymer was key to producing a CMS membrane with high solvent permeance.

“A combination of high rejection of small molecules and high solvent permeance indicate a better membrane performance,” Hardian said in a statement. “The membranes also exhibited exceptional stability in various organic solvents, including acid and base, for a long period.”

The researchers are now working to improve the membrane’s permeance and plan to incorporate various nanomaterials into the membrane to control its properties.

The team’s findings have been published in Applied Materials.

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