Yale University researchers have tapped into a plant-derived material to effectively purify water.
Researchers in the lab of Professor Chinedum Osuji in collaboration with Professor Menachem Elimelech have developed a highly ordered and aligned nanoporous polymer material, based on natural fatty acids derived from vegetable oils. This is thought to more effectively purify water than current petroleum-based membrane materials.
“The structure you get is highly selective because the size of the pores is very well-defined, while the fact that the pores are aligned ensures extremely efficient operation,” Osuji, an associate professor of chemical & environmental engineering, said in a statement.
According to the study, the researchers directed self-assembly by using physical confinement and magnetic fields to provide a vertical alignment of the columnar nanostructures in large area thin films.
Due to the selective nature of the material, it has potential for nanofiltration applications to held rid water of contaminants including textile dyes and pharmaceuticals.
While membrane-based technologies have benefits in water purification, current technologies hamper the technologies true ability to purify water.
“They have low selectivity,” Xunda Feng, a postdoctoral associate in Osuji’s lab and co-author of the paper, said in a statement. “They are also fabricated entirely from petroleum-based materials.”
Producing polymers from renewable or sustainably-derived materials has been difficult in the past because of environmental issues.
However, the researchers used molecular templating—where a single molecule acts as a guide for molecules of fatty acids to self-assemble into hexagonally packed columns— to create the new material.
The template can be removed to yield nanopores because the fatty acid molecules do not physically bond to the guiding molecule.
The self-assembly process defines the precise size of the nanopore, while the chemical nature of the nanopore walls is defined intrinsically by the fatty acid or by simple chemical modifications performed after forming the membrane.
The researchers tested the membranes in adsorption experiments to examine how readily molecules of different sizes and different charge could enter the pores.
They observed that just a small difference of 0.4 nm resulted in a change from complete admittance to near-complete rejections of molecules. The membranes also displayed a complete rejection of negatively charged molecules regardless of their size.
“These novel membranes can selectively transport water and desired molecules but reject unwanted ones, in a manner that is superior to current commercially available membranes,” Gilad Kaufman, a contributor to the project and a Ph.D. candidate in Osuji’s lab, said in a statement.
The synthesis of the template molecule is also low-cost and scalable, and additional membranes can be produced by the template molecule that is eventually removed from the polymer membrane.
According to Osuji, the next step will be to make large films and examine their selectivity in pressure-driven flow to examine which molecules go through and which ones do not. The researchers will also explore other potential uses including high-density nanopattern transfer for the semiconductor industry.
The study was published in ACS Nano.
