The contamination of water sources by chemicals used in today’s technology is a rapidly growing global problem. According to a recent study by the U.S. Centers for Disease Control, 98 percent of people tested had detectable levels of per- and polyfluoroalkyl substances (PFAS), a family of long-lasting compounds known as forever chemicals, in their bloodstream.
Researchers at MIT have developed a new filtration material that could offer a nature-based solution to this persistent contamination issue. The material, made from natural silk and cellulose, has the ability to effectively remove a wide variety of these persistent chemicals as well as heavy metals. Additionally, its antimicrobial properties can help prevent the filters from becoming fouled.
Contamination by PFAS and similar compounds is a significant issue, and current solutions may only partially resolve this problem efficiently or economically, according to MIT postdoc Yilin Zhang. That’s why the team developed a protein and cellulose-based natural solution.
Professor of civil and environmental engineering Benedetto Marelli noted that their filtration material was made possible by technology originally developed to create a labeling system to combat counterfeit seeds. His team found a way to process silk proteins into uniform nanoscale crystals, or “nanofibrils,” using an environmentally friendly, water-based drop-casting method at room temperature.
The research conducted by Zhang and the team suggests that the new nanofibrillar material they developed could potentially be quite effective at filtering contaminants. Initially, the silk nanofibrils alone didn’t yield the desired results, prompting the team to experiment with incorporating cellulose into the material.
By leveraging a self-assembly method involving the suspension of silk fibroin protein in water and the templating of nanofibrils with cellulose nanocrystals, the researchers were able to create a hybrid material with promising new properties. This integrated material, in the form of a thin membrane, demonstrated high effectiveness in removing contaminants during laboratory tests, particularly after the manipulation of the cellulose’s electrical charge.
The discovery that cellulose has strong antimicrobial properties due to its electrical charge is a game-changer in filtration technology. This advantage addresses a major issue of membrane fouling by bacteria and fungi, potentially revolutionizing water filtration.
“These materials can really compete with the current standard materials in water filtration when it comes to extracting metal ions and these emerging contaminants, and they can also outperform some of them currently,” Marelli says.
Lab tests have shown that this material outperforms the current standard materials, activated carbon, and granular activated carbon, by extracting significantly more contaminants from water.
The new breakthrough is just the beginning. While the initial results are promising, the team is committed to enhancing the material to improve its durability and ensure a sustainable source of materials. Although silk proteins are currently available as a byproduct of the silk textile industry, they recognize that scaling up production for global water filtration needs may present supply challenges. They are open to exploring alternative protein materials that could offer similar benefits at a lower cost.
Initially, the team’s focus will be on developing point-of-use filters that can be easily attached to kitchen faucets. As they refine the technology, the team aims to expand its application to municipal water supplies.
However, researchers are dedicated to conducting thorough testing to ensure that their filtration systems do not introduce any contamination into the water supply. One significant advantage of this new material is that both silk and cellulose are food-grade substances, minimizing the risk of contamination.
“Most of the normal materials available today are focusing on one class of contaminants or solving single problems,” Zhang says. “I think we are among the first to address all of these simultaneously.”
“What I love about this approach is that it uses only naturally grown materials like silk and cellulose to fight pollution,” says Hannes Schniepp, professor of applied science at the College of William and Mary, who was not associated with this work. “In competing approaches, synthetic materials are used — which usually require only more chemistry to fight some of the adverse outcomes that chemistry has produced. [This work] breaks this cycle! … If this can be mass-produced in an economically viable way, this could really have a major impact.”
Journal reference:
- Yilin Zhang, Hui Sun, Yunteng Cao, Maxwell J. Kalinowski, Meng Li, Benedetto Marelli. Directed Assembly of Proteinaceous–Polysaccharide Nanofibrils to Fabricate Membranes for Emerging Contaminant Remediation. ACS Nano, 2024; DOI: 10.1021/acsnano.4c07409