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The Challenge of Water Contamination and an Innovative Solution

The issue of water contamination due to chemicals prevalent in modern technology has escalated into a significant global concern. A recent investigation by the U.S. Centers for Disease Control has revealed that an alarming 98 percent of individuals tested showed detectable levels of PFAS, commonly referred to as “forever chemicals,” in their bloodstream. These compounds are notorious for their persistence in the environment and human body.

In response to this crisis, researchers at MIT have developed a groundbreaking filtration material that may offer a nature-inspired remedy to this contamination challenge. This innovative material, synthesized from natural silk and cellulose, has demonstrated the capability to eliminate a wide range of these enduring chemicals, as well as heavy metals. Notably, its antimicrobial properties also help prevent the filters from becoming fouled.

The details of this research are published in the journal ACS Nano, authored by MIT postdoctoral researcher Yilin Zhang, civil and environmental engineering professor Benedetto Marelli, and several other collaborators from MIT.

Understanding PFAS Contamination

PFAS (per- and polyfluoroalkyl substances) are ubiquitous in numerous consumer products, ranging from cosmetics and food packaging to waterproof clothing and firefighting foams. A concerning study identified approximately 57,000 contaminated sites across the United States. The U.S. Environmental Protection Agency (EPA) has projected that remediation efforts for PFAS may incur costs of around $1.5 billion annually, particularly in light of new regulations that aim to restrict these harmful compounds in drinking water to less than 7 parts per trillion.

Zhang emphasizes the severity of PFAS-related contamination, stating, “This is actually a very big deal, and existing solutions may only address this issue partially and not in a cost-effective manner. That’s why we devised this fully natural solution based on protein and cellulose.”

The Genesis of the Filtration Technology

Interestingly, as Marelli explains, the team’s journey began serendipitously. The initial technology that paved the way for this filtration material emerged from efforts to create a labeling system aimed at fighting the issue of counterfeit seeds, which often turn out to be substandard. The team had successfully engineered a method to process silk proteins into uniform nanoscale crystals, or nanofibrils, using a water-based drop-casting technique at room temperature, considered environmentally friendly.

While Zhang initially proposed that their nanofibrillar material could be effective in filtering contaminants, early attempts using silk nanofibrils alone proved inadequate. The solution came in the form of integrating cellulose, a widely available material sourced from agricultural wood pulp waste. In their process, the silk fibroin protein was suspended in water and templated into nanofibrils using cellulose nanocrystals as “seeds.” This innovative method caused the disordered silk molecules to align, creating a hybrid material with entirely new properties.

Enhancing Filtration Effectiveness

By incorporating cellulose into the silk-based fibrils to form a thin membrane, and by tweaking the electrical charge of the cellulose, the researchers achieved a high level of efficacy in contaminant removal during laboratory tests.

The cellulose’s charge also imparted significant antimicrobial properties, addressing one of the major challenges in water filtration: fouling caused by bacteria and fungi. According to researchers, the antimicrobial attributes of their material could significantly lessen fouling, thereby improving its longevity and efficiency as a filtration system.

“Our materials can truly rival current standard filtration materials when it comes to extracting metal ions and emerging contaminants, and they may even surpass some of the existing options,” asserts Marelli. Laboratory trials have shown that their materials extracted exponentially more pollutants from water than conventional filtration alternatives like activated carbon.

Future Prospects and Considerations

While this research serves as proof of concept, Marelli indicates that ongoing efforts will focus on enhancing the material’s durability and sourcing. Although silk proteins can be derived as a byproduct of the silk industry, scaling the material for widespread water filtration applications could face supply challenges. Researchers are also exploring alternative proteins that could potentially offer similar benefits at reduced costs.

Initially, the team envisions this filtration material being employed as a point-of-use system, such as a filter that attaches to kitchen faucets. Over time, with adequate testing to ensure safety, it could be expanded to serve municipal water supplies. One notable advantage is that both silk and cellulose are food-grade substances, reducing the likelihood of introducing new contaminants.

“Most current materials tend to focus on a single category of contaminants or problems,” emphasizes Zhang. “We believe we are among the first to tackle multiple challenges simultaneously.”

This research collaboration included MIT postdocs Hui Sun and Meng Li, graduate student Maxwell Kalinowski, and recent PhD graduate Yunteng Cao, who is now a postdoctoral researcher at Yale. The project received support from the Office of Naval Research, the National Science Foundation, and the Singapore-MIT Alliance for Research and Technology.

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