A team of scientists from Tufts University School of Engineering has developed new, biology-inspired filtering technology that could help fight a drinking water-related disease that affects tens of millions of people around the world and potentially improve environmental remediation, industrial and chemical production, and mining, among other processes.
Reporting in the Proceedings of the National Academy of Sciences, the researchers demonstrated that their new polymer membranes can separate fluoride from chloride and other ions – electrically charged atoms – with twice the selectivity of that reported by previous studies. other methods. They say applying the technology could prevent fluoride toxicity in water supplies where the element occurs naturally at levels too high for human consumption.
It is well known that adding fluoride to a water supply can reduce the incidence of tooth decay, including cavities. What is less known is that some groundwater supplies have natural levels of fluoride so high that they can lead to serious health problems. Prolonged exposure to excess fluoride can cause fluorosis, a condition that can actually weaken teeth, calcify tendons and ligaments, and lead to bone deformities. The World Health Organization estimates that excessive levels of fluoride in drinking water have caused tens of millions of cases of dental and skeletal fluorosis worldwide.
The ability to remove fluoride with a relatively inexpensive membrane filter could protect communities from fluorosis without requiring the use of high-pressure filtration or having to completely remove all components and then remineralize drinking water.
“The potential for ion-selective membranes to reduce excess fluoride in drinking water supplies is very encouraging,” said Ayse Asatekin, associate professor of chemical and biological engineering in the School of Engineering. “But the technology’s potential utility extends beyond drinking water to other challenges. The method we used to manufacture the membranes is easy to scale up for industrial applications. And because implementation as a filter can also be relatively simple, inexpensive, and environmentally sustainable, it could have many applications for improving agricultural water supply, cleaning up chemical waste, and improving chemical production. .
For example, theoretically, the process could improve yields from limited geological reserves of lithium for sustainable production of lithium batteries or uranium needed for nuclear power generation, Asatekin said.
In developing the design of the synthetic membranes, the Asatekin team drew inspiration from biology. Cell membranes are remarkably selective in allowing passage of ions into and out of the cell, and they can even regulate the internal and external concentrations of ions and molecules with great precision.
Biological ion channels create a more selective environment for the passage of these small ions by lining the channels with functional chemical groups that have different sizes and charges and different affinity for water. The interaction between passing ions and these groups is forced by the nanoscale dimensions of the channel pores, and the passing rate is affected by the strength or weakness of the interactions.
The filtration membranes created by the Asatekin team were designed by coating a zwitterionic polymer – a polymer in which molecular groups contain positive and negative charges tightly bound to their surface – onto a porous support, creating membranes with channels narrower than one nanometer surrounded by both water repellent and plus and minus charged chemical groups. As with biological channels, the very small pore size forces the ions to interact with the charged and water-repellent groups in the pores, allowing some ions to pass through much faster than others. In the current study, the polymer composition was designed to target the selection of fluoride over chloride. By changing the composition of the zwitterionic polymer, it should be possible to target the selection of different ions, according to the researchers.
Most current membrane filters separate molecules by significant differences in particle or molecule size and charge, but have difficulty distinguishing single atom ions from each other due to their small size and when their charges electrics are almost identical.
In contrast, the Tufts researchers’ membranes are able to separate ions that differ by only a fraction of their atomic diameter, even when their electrical charges are nearly identical.
ZwitterCo, a Cambridge-based company that helped fund this work, will explore scaling up the manufacture of ion separation membranes to test their application in an industrial setting.