A newly developed filtration material could offer a nature-inspired way to tackle water pollution from PFAS chemicals. This innovative material, made from natural silk and cellulose, has the capability to filter out a wide range of these persistent chemicals along with heavy metals, and it also features antimicrobial properties that can help prevent the filters from becoming clogged.
The global issue of water pollution caused by chemicals present in modern technology is escalating. A recent study by the U.S. Centers for Disease Control indicated that 98% of individuals tested showed detectable levels of PFAS chemicals, commonly referred to as forever chemicals, in their bloodstreams.
Researchers at MIT have developed a new filtration material that might serve as a natural solution to this ongoing contamination challenge. Utilizing natural silk and cellulose, this material effectively eliminates a variety of these stubborn chemicals and heavy metals. Furthermore, its antimicrobial qualities help maintain filter efficiency by preventing fouling.
The research results were published in the journal ACS Nano, in a paper co-authored by MIT postdoctoral researcher Yilin Zhang, civil and environmental engineering professor Benedetto Marelli, along with four other MIT contributors.
PFAS chemicals can be found in numerous products, including cosmetics, food packaging, water-repellent clothing, firefighting foams, and non-stick coatings for cookware. A recent survey revealed approximately 57,000 sites contaminated with these chemicals in the United States alone. The U.S. Environmental Protection Agency estimates that cleaning up PFAS could cost around $1.5 billion annually to comply with new regulations that limit these compounds to less than 7 parts per trillion in drinking water.
Pest contamination by PFAS and similar substances “is a significant issue, and existing solutions may only partially address this problem effectively or economically,” Zhang explains. “This has driven us to create a fully natural solution based on proteins and cellulose,” he adds.
Marelli shares that “we stumbled upon this project by coincidence.” The original technology that enabled the creation of the filtration material originated in his team’s effort to develop a counterfeit seed labeling system, aimed at combating inferior seed quality. They devised a method to transform silk proteins into uniform nanoscale crystals, or “nanofibrils,” using a sustainable, water-based drop-casting technique conducted at room temperature.
Zhang proposed that this new nanofibrillar material might effectively filter contaminants, but the initial trials with silk nanofibrils alone fell short. The team then decided to incorporate cellulose, a readily available material derived from agricultural wood pulp waste. By utilizing a self-assembly approach where silk fibroin protein is suspended in water and combined with “seeds” of cellulose nanocrystals, the previously chaotic silk molecules align with the seeds, forming the foundation of a novel hybrid material with unique characteristics.
By blending cellulose into the silk fibrils, which can be shaped into a thin membrane and adjusting the electrical charge of the cellulose, the researchers created a highly efficient material for contaminant removal in laboratory evaluations.
The team discovered that the cellulose’s electrical charge also endowed it with strong antimicrobial properties. This is a crucial benefit, as the most common cause of filtration membrane failure is bacterial and fungal fouling. The researchers believe the antimicrobial features of this material will significantly mitigate the fouling problem.
“These materials can truly compete with current filtration standards when it comes to extracting metal ions and emerging contaminants, even exceeding some existing options,” Marelli notes. In laboratory experiments, their materials extracted contaminants from water at rates significantly higher than those achieved by common filtration materials like activated carbon.
While this research serves as proof of concept, Marelli indicates that the team intends to enhance the material further, particularly regarding its durability and the availability of raw materials. Although silk proteins can be sourced from the silk textile industry, scaling this solution to meet global water filtration demands might be challenging due to potential supply limitations. Additionally, alternative protein sources might offer the same benefits at lower costs.
Initially, the material is expected to function as a point-of-use filter that can be installed on kitchen faucets, Zhang mentions. In the future, it may be expanded for use in municipal water supply systems, but only after thorough testing ensures that introducing it will not contaminate the water supply. An advantage of this material is that both silk and cellulose are considered food-safe substances, reducing the risk of further contamination.
“Most available materials today tend to focus on addressing only one type of contaminant or singular issues,” Zhang states. “We believe we are among the first to tackle multiple challenges simultaneously.”
The team of researchers included MIT postdocs Hui Sun and Meng Li, graduate student Maxwell Kalinowski, and recent graduate Yunteng Cao, PhD ’22, who is now a postdoc at Yale. This research was supported by the Office of Naval Research, the National Science Foundation, and the Singapore-MIT Alliance for Research and Technology.
