Bioinspired Filter Captures Carbon

One research team’s efforts to find such materials has yielded a high-surface-area capture membrane inspired by one of nature’s most efficient gas exchangers: a bird’s lungs. The work, by Aaron P. Esser-Kahn of the University of California, Irvine, and colleagues, was reported yesterday at the American Chemical Society national meeting in Indianapolis.

To fly, birds need a lot of energy, so they’ve evolved intricate structures in their lungs to rapidly exchange CO₂ for oxygen. “We wanted to be able to match what nature can create,” Esser-Kahn said in a session sponsored by the Division of Polymeric Materials: Science & Engineering.

The chemist and his team produced their bird-lung mimics by stretching polylactic acid fibers of two different diameters between a pair of brass plates. They then filled polydimethylsiloxane into a mold around them. After the PDMS set, the team heated the assembly in vacuum to degrade the tightly packed fibers and leave behind microchannels of two sizes.

When the researchers filled the small-diameter channels with MEA and flowed CO₂ through the larger ones, they observed the gas diffuse through the walls of the polymer structure and react with MEA. Surprisingly, Esser-Kahn told the audience, the greenhouse gas transferred most rapidly when the channels were packed into a not-found-in-nature “double square” pattern, rather than a dodecagonal or hexagonal pattern that more closely simulates a bird’s airways.

The Esser-Kahn group’s membrane production method may enable the manufacture of high-surface-area three-dimensional architectures not accessible via standard approaches, says Abraham Duncan Stroock, a chemical engineer at Cornell University. This “newsworthy” work, he adds, “has taken seriously the challenge of recreating the extraordinary rates of mass transfer that are seen in the vascular systems of animals.”

With these preliminary results in hand, Esser-Kahn’s team will next try to optimize the porosity of its filters and filter material, which can break down over time with exposure to MEA.