A newly created polymer could improve water treatment through its ability to trap contaminants more effectively.
Cornell University researchers say this porous material absorbs pollutants at rates of up to 200 times more efficiently than conventional water purification technologies such as those based on activated carbon. The polymer is a form of cyclodextrin, a cornstarch derivative typically used in air fresheners.
The new polymer is shaped like a cup, which gives it more surface area to capture toxins. Two grams of beta-cyclodextrin has a surface area equivalent to half an NBA basketball court.
The polymer is related to the odor-trapping cyclodextrin material found in the odor-neutralizing spray Febreze. Its shape and porosity give this form of cyclodextrin an adsorption rate from 15 to 200 times greater than activated carbon or other, non-porous forms of cyclodextrin.
Will Dichtel, associate professor of chemistry and chemical biology at Cornell University, explained:
What we did is make the first high-surface-area material made of cyclodextrin, combining some of the advantages of the activated carbon with the inherent advantages of the cyclodextrin. […] When you combine the best features of those two materials, you get a material that’s even better than either class. These materials will remove pollutants in seconds, as the water flows by, so there’s a potential for really low-energy, flow-through water purification, which is a big deal.
Cyclodextrin, on which the polymer is based, is a sugar molecule. This material also includes a six carbon ring material called tetrafluoroterephthalonitrile. These compounds are heated in a solution of potassium carbonate and tetrahydrofuran — a solvent used as an adhesive or sealant. This process creates the porous, 3-D lattice material.
New Polymer’s Advantages
The researchers tested the efficacy of the material’s contaminant removal capability with a complex mixture of organic micropollutants including BPA. Prototype filtration systems using the porous beta-cyclodextrin were tested at “environmentally relevant” lower concentrations that might be found in real-world settings. The material was found to be suitable for use in future rapid, flow-through water treatment methods.
It also performed better than several types of activated carbon and two nonporous cyclodextrin polymers. While conventional materials took roughly 30 minutes to reach their maximum adsorption capacity, the new polymers reached 95 percent of capacity in 10 seconds.
This cyclodextrin material is recyclable, which will be another advantage as it moves into commercial production and use. While activated carbon requires a high-intensity heat treatment to be regenerated, the cyclodextrin-based filtering medium can be easily cleaned at room temperature with either methanol or ethanol. After this procedure, the researchers say there was no change in the material’s performance.
The material is also inexpensive to make. The researchers expect that once the manufacturing process is refined, costs may drop as low as $5-25 per kilogram. This would make beta-cyclodextrin-based filtering media roughly half the cost of charcoal filters.
Scalable Water Treatment
Dichtel said the team is now preparing to integrate the polymer into a scalable water treatment system. The aim is to ultimately manufacture the material at an industrial scale.
Susan Richardson, an environmental chemist at the University of South Carolina in Columbia who was not involved in the study, told Science:
This was pretty exciting. […] It looks very promising. I can’t see a downside yet.
The work was supported by the National Science Foundation through the Center for Sustainable Polymers. The researchers, whose task is to discover high-performance materials from sustainable, non-petroleum sources, come from Cornell, the University of Minnesota, and the University of California, Berkeley.
Ongoing work to determine water purification applications for this polymer will be partially funded through the five-year, $650,000 award Dichtel received as a 2015 MacArthur Foundation Fellowship winner.
Cornell University has filed a provisional patent application for the new cyclodextrin polymers.
The full results — “Rapid Removal of Organic Micropollutants From Water by a Porous Beta-Cyclodextrin Polymer” — were published in the journal Nature.
Image courtesy Cornell University.