MIT researchers have come up with a new filtration material based on natural silk and cellulose that can remove a wide variety of the persistent ‘forever’ chemicals as also heavy metals. Its antimicrobial properties can also help keep the filters from fouling.
- By integrating cellulose into the silk-based fibrils that could be formed into a thin membrane, and then tuning the electrical charge of the cellulose, the researchers produced a material that was highly effective at removing contaminants in lab tests.
- The electrical charge of the cellulose gave it strong antimicrobial properties.
- This is a significant advantage since one of the primary causes of failure in filtration membranes is fouling by bacteria and fungi.
- The antimicrobial properties of this material would greatly help reduce that fouling issue.
The findings are described in the journal ACS Nano, in a paper by MIT postdoc Yilin Zhang, professor of civil and environmental engineering Benedetto Marelli, and four others from MIT.
THE HOW: It was serendipity at work as the team which was working on a way to make a labelling system to counter the spread of inferior counterfeit seeds, devised a way to process silk proteins into uniform nanoscale crystals, or ‘nanofibrils’, through an environmentally benign, water-based drop-casting method at room temperature.
- When initial attempts with silk nanofibrils did not work, the team tried with the abundantly available cellulose.
- Using a self-assembly method in which the silk fibroin protein is suspended in water and then templated into nanofibrils by inserting “seeds” of cellulose nanocrystals, caused the previously disordered silk molecules to line up together along the seeds, forming the basis of a hybrid material with distinct new properties.
PROOF OF PRINCIPLE: The new work serves as a proof of principle, and the team plans to continue working on improving the material, especially in terms of durability and availability of source materials.
- While the silk proteins used can be available as a byproduct of the silk textile industry, if this material were to be scaled up to address the global needs for water filtration, the supply might be insufficient.
- Also, alternative protein materials may turn out to perform the same function at lower cost.
- Initially, the material would likely be used as a point-of-use filter, something that could be attached to a kitchen faucet, and eventually scaled up to provide filtration for municipal water supplies. However, this only after testing demonstrates that this would not pose any risk of introducing any contamination into the water supply.
THE CONTEXT: A recent study by the US. Centers for Disease Control found that 98% of people tested had detectable levels of PFAS, a family of particularly long-lasting compounds also known as “forever chemicals,” in their bloodstream.
- PFAS chemicals are present in a wide range of products, including cosmetics, food packaging, water-resistant clothing, firefighting foams, and antistick coating for cookware.
- A recent study identified 57,000 sites contaminated by these chemicals in the US alone.
- The U.S. Environmental Protection Agency has estimated that PFAS remediation will cost $1.5 billion per year, in order to meet new regulations that call for limiting the compound to less than 7 parts per trillion in drinking water.
THE TEAM: The research team included MIT postdocs Hui Sun and Meng Li, graduate student Maxwell Kalinowski, and recent graduate Yunteng Cao PhD ’22, now a postdoc at Yale University.
- The work was supported by the US Office of Naval Research, the US National Science Foundation, and the Singapore-MIT Alliance for Research and Technology.
