Engineers at the University of South Carolina (USC) have developed an ultra-thin, ultra-selective membrane that could greatly advance the purification of gas mixtures.
According to a press release, the membrane is just two nanometers thick and selects its molecules based on size. For example, helium and hydrogen pass through with ease while oxygen, nitrogen, carbon dioxide, methane and carbon monoxide sift though at a much slower rate.
"The hydrogen kinetic diameter is 0.289 nm, and carbon dioxide is 0.33 nm. The difference in size is very small, only 0.04 nm, but the difference in permeation is quite large," said lead researcher Miao Yu, a chemical engineer in USC's College of Engineering and Computing. "The membrane behaves like a sieve. Bigger molecules cannot go through, but smaller molecules can."
The research team was able to create the membrane efficiently as well, crafting it on the surface of a porous aluminum oxide support. Creating something with virtually no weak spots on a molecular scale is no small feat. Miao said this difficulty has resulted in many previous microporous membranes to be as thick as 20 nanometers, "and usually thicker."
The new development could have a large potential effect on several laboratories. Efficient separation of carbon dioxide from gaseous mixtures is a high research priority, given the raised concern with greenhouse gasses.
Also likely of interest to other labs will be its ability to solicit hydrogen from gas mixtures. Because of its integral use in energy systems like fuel cells, isolating it from other gasses, or purifying it, will be a sought-after commodity.
Another possibility, Miao noted, was with the purification of water. The sieve's molecular dimensions are on par with the size of water, making it possible for the membrane to filter copious amounts of tainted water.
"Having membranes so thin is a big advantage in separation technology," Miao said. "It represents a completely new type of membrane in the separation sciences."
