Despite improvements to air filtration technology in the aftermath of the COVID-19 pandemic, some of the smallest particles — those of automobile and factory emissions — can still make their way through less efficient, but common filters. An interdisciplinary team of researchers from Drexel University's College of Engineering have introduced a new way to improve textile-based filters by coating them with a type of two-dimensional nanomaterial called MXene.
Recently published in C Journal of Carbon Research , the team's research reports that a non-woven polyester textile — a low-cost material with low filtration efficiency — coated with a thin layer of MXene nanomaterial can turn it into a potent filter capable of pulling some of the finest nanoparticles from the air.
"It can be challenging for common filters to contend with particles less than 100 nanometers, which include those emitted by industrial processes and automobiles," said Michael Waring, PhD , a professor in Drexel's College of Engineering, and coauthor of the research. "Being able to augment a filter, through a simple coating process, to make it effective against these emissions is a significant development."
The researchers report that a polyester textile coated with a titanium carbide MXene can reach approximately 90% filtration efficiency for particles as small as 15-30 nanometers — the size of viruses and the finest dust particles — meaning that it could be effective as an augmentation process to air filters located in urban or industrial environments.
MXenes, a family of nanomaterials discovered by Drexel researchers in 2011 , have previously demonstrated proficiency in filtration applications, including water treatment , kidney dialysis , and hydrogen capture . The materials have also shown that they can enhance filters that remove airborne viruses in medical settings.
"With increasing manufacturing volume and decreasing price, MXenes are finding an increasing number of applications," said Yury Gogotsi, PhD, Distinguished University and Bach professor in the College of Engineering, who led the material's development and was among the researchers who discovered MXenes and founded MXene, Inc., a company that now manufactures them. "Particularly in the fields that require large amounts of material."
The latest discovery is a significant step in the exploration of the nanomaterials because it shows their capability to contend with some of the smallest particles in the air and that they can easily be integrated into a filter manufacturing process.
"Our ongoing research continues to reveal the potential of MXene coatings," Gogotsi said. "The fact that this highly conductive nanomaterial is also hydrophilic means that it can be dispersed in water to produce a coating that can easily be applied to virtually any substrate, including air filters. We are just scratching the surface of its capabilities."
In the processes of testing the MXene-coated filters, the team made an additional discovery, that pretreating the filters with magnesium salt assisted in the MXene coating process and improved the filter's performance by 25% — to achieve a maximum efficiency of about 90% for virus-size nanoparticles, which many common filters don't capture.
The addition of alkaline earth metal ions, such as magnesium, improved the MXene coating process. According to the researchers, this sort of chemical preparation further activates the surface of the MXene, which helps the material spread uniformly across the filter, creating a thicker coating and more complex channels through the material, which all contribute to better filtration capability.
The researchers tested untreated; MXene-coated; and MXene-coated and magnesium ion-treated filters in a vacuum-sealed chamber containing aerosolized sodium chloride (rock salt), and measured removal for particles ranging from 5.6 to 560 nanometers. The filters that had been MXene-coated and magnesium ion-treated performed significantly better than the other two at capturing particles of all sizes in the range, down to 15 nanometers.
In addition to their ability to improve filtration, MXenes are also highly conductive – a trait the researchers theorized could be leveraged to enable the filters to clean themselves. They tested the idea by applying an electric current to the MXene-coated filter, which raised its temperature to 100 degrees Celsius — enough to carefully burn off some particles and debris on the filter and restore its original filtration quality.
"Studies like this are encouraging for real-world application of MXenes in air filtration," said Prastuti Upadhyay, a Materials Science and Engineering undergraduate student in the College of Engineering, who was mentored by Drexel postdoctoral researcher Stefano Ippolito, PhD, and was the lead author of the paper. "But it should be noted that our air filters could still be improved by focusing on optimizing the MXene structure, pretreatment ions and the filter substrate. This leaves room for many exciting possibilities for this line of research."
