MIT’s new silk-cellulose water filter blocks stubborn forever chemicals, metals

Water contamination is a pressing global issue, with harmful chemicals like PFAS, or “forever chemicals,” posing a significant threat to our health and environment. These persistent compounds have been found in everything from drinking water to cosmetics, and their widespread presence is a cause for concern.

A recent study from the U.S. Centers for Disease Control (CDC) highlight the pervasive presence of PFAS in the bloodstream of 98% of people tested.

These persistent chemicals are notoriously difficult to remove from water sources, posing significant health and environmental risks. However, a team of researchers at the Massachusetts Institute of Technology (MIT) has developed a promising new filtration material that could offer a natural solution to this stubborn problem.

The material, made from natural silk and cellulose, has shown impressive results in removing PFAS and heavy metals from water. Additionally, it possesses antimicrobial properties that prevent the filters from becoming fouled over time.

This innovation could potentially revolutionize water filtration technology, providing a more sustainable and effective approach to tackling water contamination.

A new approach to filtration: Silk and cellulose

The research was led by MIT postdoctoral researcher Yilin Zhang, Professor Benedetto Marelli from the Department of Civil and Environmental Engineering, and four other MIT researchers. Their study addresses the widespread contamination of water sources by PFAS , which are commonly found in products like cosmetics, food packaging, water-resistant clothing, firefighting foams, and non-stick cookware.

In the U.S. alone, a recent study identified 57,000 sites contaminated by PFAS. The U.S. Environmental Protection Agency (EPA) estimates that cleaning up this contamination to meet new regulations will be expensive. To keep PFAS levels below 7 parts per trillion in drinking water, the cost is expected to reach $1.5 billion every year.

“Contamination by PFAS and similar compounds is actually a very big deal, and current solutions may only partially resolve this problem very efficiently or economically,” says Zhang. “That’s why we came up with this protein and cellulose-based, fully natural solution.”

The idea for the filtration material originated somewhat by chance. Professor Marelli’s group initially developed the technology for a completely different purpose. They were creating a labeling system to combat counterfeit seeds, which are often of inferior quality.

They devised a method for processing silk proteins into uniform nanoscale crystals, or “nanofibrils,” using an environmentally friendly, water-based drop-casting method at room temperature.

Zhang then proposed that these silk nanofibrils could be useful for filtering contaminants from water. However, their initial attempts with just the silk nanofibrils didn’t work. The team decided to add cellulose, a material that is widely available from agricultural wood pulp waste. By combining silk and cellulose and using a method that aligns the silk molecules into nanofibrils, they created a hybrid material with unique properties perfect for water filtration.

Advantages and future applications

The integration of cellulose into the silk-based nanofibrils made the material highly effective at removing contaminants in lab tests. It also gave the material strong antimicrobial properties. This is a significant advantage, as one of the main challenges in filtration technology is membrane fouling caused by bacteria and fungi. The antimicrobial properties of this new material could greatly reduce this issue, making the filters more durable and reliable.

“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 explains in the press release.

In laboratory tests, the material was able to extract significantly more contaminants from water than the widely used standard materials, such as activated carbon or granular activated carbon.

While this research serves as proof of concept, the team plans to continue refining the material, particularly in terms of durability and the availability of source materials.

Although the silk proteins used can be sourced as a byproduct of the silk textile industry, scaling up production to meet global water filtration needs may require alternative protein materials that could perform the same function at a lower cost.

Initially, the material is likely to be used as a point-of-use filter, potentially attached to a kitchen faucet. Over time, it could be scaled up to provide filtration for municipal water supplies, but only after thorough testing ensures that it does not introduce any new contaminants into the water supply. However, one significant advantage of this material is that both silk and cellulose are considered food-grade substances, making any contamination unlikely.

“Most of the normal materials available today are focusing on one class of contaminants or solving single problems,” Zhang notes in the press release. “I think we are among the first to address all of these simultaneously.”

The promise of a sustainable solution

The innovation has drawn praise from other experts in the field. Hannes Schniepp, a professor of applied science at the College of William and Mary, who was not involved in the research, commended the approach.

“What I love about this approach is that it is using only naturally grown materials like silk and cellulose to fight pollution,” Schniepp says.

“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.”

The findings of this research were published in the journal ACS Nano .