Institute for Molecular Engineering pursues six water research projects

Steve Koppes
Associate News DirectorUniversity Communications

The Water Research Initiative of the Institute for Molecular Engineering has added a sixth research project to the original five that received funding last year.

The six projects are for research on new materials and methods to make clean water more accessible and less expensive. These seed projects involve physicists, chemists, geoscientists, environmentalists and molecular engineers working in collaborations involving scientists at the University of Chicago, Argonne National Laboratory and Ben-Gurion University of the Negev in Israel.

“The concept was to focus initially on scientific and technical matters: applying chemistry and nano-materials to issues pertaining to water purification and sustainability,” said Steven Sibener, initiative director and the Carl William Eisendrath Distinguished Service Professor in Chemistry and the James Franck Institute.

Scientists can engineer nano-materials—structures built from ensembles of molecules or atoms on a scale 10 to 50 times larger than that of single molecules—so that they can be “tuned” to meet the demands of a particular task. One such objective is water filtration.

Current filtration methods use membranes to remove salts and minerals from water. “But as a result of human activity, water is contaminated by harmful organic materials and micro-organisms and these are not removed by present membrane technology,” said Moshe Gottlieb, who heads the Ben-Gurion University arm of the initiative.

Mathematically modeling patterns

The newest project, involving Argonne and BGU, will benefit agriculture, green roofs, bioswales and engineered installations for storm water management. The project builds on the work of BGU scientists, who have developed a mathematical model that accurately represents patterns of plant and root growth under desert water conditions.

Project scientists aim to expand this model for application to environments that contain two major vegetation types, such as woody plants and trees, or shrubs and grasses. The BGU model was developed in Israel’s Negev Desert, but it might also prove useful in more temperate environments. Chicago’s green roofs, for example, also experience water scarcity.

“The city leads the country in developing green roofs, which are really good for mitigating storm water,” said M. Cristina Negri, an agronomist and environmental engineer at Argonne. Plants on green roofs need to adapt to suboptimal conditions because they live in thin soils, which are unable to retain much water during dry spells.

One of the original water research initiative projects uses a novel technique to make membranes that will not only filter harmful biological species from water, but also chemically cleanse it of toxins. Researchers grow a polymer film made of two materials. By manipulating the tendency of molecules to organize themselves into stable structures, the scientists get the film to “build itself” along the lines that they desire. The result is a web of specifically sized cylinders made of one component embedded in a matrix of another.

They expose this polymer to a third constituent that interacts only with the matrix, turning it into titanium dioxide. Finally, they remove the cylinders chemically, leaving a titanium dioxide mesh with cylindrical pores sized perfectly for the filtering job at hand. When modified slightly and exposed to light, titanium dioxide can break down toxic substances such as phenols. The resulting membrane is not only a physical filter, but a water purifier as well.

Another project also exploits catalytic reactions to create a high-efficiency purifier, this time on the surfaces of nano-structured membranes. A large fraction of the molecules in a nano-structure lie at the surface, where they can interact chemically with whatever is around them. The researchers are designing large-surface-area nano-membranes whose surfaces can catalyze reactions with toxins in water, breaking them down and rendering them harmless. These nano-membranes could be used, for example, to remove trace pharmaceuticals from the waste stream.

Clog-resistant filters

One of the biggest problems faced when filtering water is the colonies of microorganisms that grow on a filter’s surfaces. They form a tough, slimy film that clogs the membrane’s pores and make it useless. This means frequent and costly replacement. “Bio-fouling is one of these critical show-stopping issues,” Sibener said. Two of the seed projects explore ways of solving this problem.

The first aims to understand the structure of the microbial communities. The scientists will sequence the genomes of the biofilms and then study how they grow and interact with one another. And, crucially, they will see what happens to that growth when one changes the texture or the material of a membrane surface, providing a guide for developing membranes that are inherently resistant to bio-fouling.

The second group is creating and examining the properties of a series of polymer “brushes,” which can be used as membrane coatings. These are clusters of polymer chains in which one end of each chain is fixed to a surface—a membrane, for example—and the rest of the chain is free, creating a brush-like structure. When the “bristles” are dense, bacteria have a harder time penetrating the brush and growing on the membrane surface.

Before water can be used, purified or re-used, it has to be available in the first place. The final collaboration is developing an innovative method for tracking groundwater flow so that the size and characteristics of an aquifer can be evaluated and exploited in a sustainable way.

Scientists will use a laser device called ATTA-3 to count the number of krypton radio-isotopes: an inert noble gas, present in water samples taken from a series of wells. The concentration of krypton isotopes found in surface water decays when the water goes underground. Krypton’s rate of decay and its abundance in surface water are known. So, the concentration of isotopes in a well-water sample tells scientists how long the water has been underground. They can then determine the chronological connectivity from the oldest samples to younger ones, from well to well, making a map of the water flow in the aquifer.

These six projects were chosen from among the many proposals because of their inherent scientific excellence coupled with their tight focus on issues critical to developing water resources. But also, Sibener said, because they take advantage of the complementary strengths of the three participating institutions: “These projects all require a true partnership among the collaborating teams, allowing them to address critical issues that no single investigator has done or could do alone.”