Researchers at the Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts, have designed a way to sustainably remove micropollutants from water using zwitterionic hydrogels to capture both organic and inorganic micropollutants with minimal operational complexity.
Derived from the German word “zwitter,” meaning “hybrid,” “zwitterionic” molecules are those with an equal number of positive and negative charges. Because many inorganic and some organic micropollutants are themselves charged, Patrick Doyle, a professor in the MIT Department of Engineering and his team have been investigating how to deploy zwitterionic molecules to capture micropollutants in water.
In the past, zwitterionic molecules have been used as coatings on membranes for water treatment because of their non-fouling properties. However, in the Doyle group’s system, zwitterionic molecules form the scaffold material, or backbone within the hydrogel — a porous three-dimensional network of polymer chains that contains a significant amount of water.
“Zwitterionic molecules have very strong attraction to water compared to other materials used to make hydrogels or polymers,” said Devashish Gokhale, a PhD student in Doyle’s lab.
According to a press release from MIT, tests show the hydrogels can eliminate six chemically diverse micropollutants at least 10 times faster compared to the traditionally used commercial activated carbon. The system is also compatible with a diverse set of materials, making it multifunctional.
Micropollutants can bind to many different sites within the hydrogel platform: organic micropollutants bind to the micelles or surfactants while inorganic micropollutants bind to the zwitterionic molecules. Micelles, surfactants, zwitterionic molecules, and other chelating agents can be swapped to essentially tune the system with different functionalities based on water being treated.
This kind of “plug-and-play” doesn’t require a change in the design or synthesis of the hydrogel platform, and doesn’t take away from existing functionality. In this way, the zwitterionic-based system can rapidly remove multiple contaminants at lower concentrations in a single step, without the need for large, industrial units or capital expenditure.
The particles also can be regenerated and used repeatedly. Soaking the particles in an ethanol bath removes the micropollutants, allowing indefinite use without loss of efficacy. When activated carbon is used for water treatment, the activated carbon itself becomes contaminated with micropollutants and must be treated as toxic chemical waste and disposed of in special landfills.
Their work was published in Nature Water. Doyle’s group is now pursuing commercialization of the platform for both at-home use and industrial-scale applications.