How MXenes Can Improve Air Filtration

Andrew Corselli

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 has introduced a new way to improve textile-based filters by coating them with a type of two-dimensional nanomaterial called MXene.

Recently featured 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 Co-Author Michael Waring, Ph.D., Professor in Drexel’s College of Engineering. “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 percent 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, Ph.D., 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.

Here is an exclusive Tech Briefs interview, edited for length and clarity, with Gogotsi.

Tech Briefs: What was the biggest technical challenge you faced while developing this air filter coating method?

Gogotsi: We didn't know whether it would work. So, we worked with Michael Waring, who is an expert in filtration in air conditioning, to bring our new materials, MXenes, to real systems. Identifying what filter needs improvement; identifying how we can get a filter to capture mid-sized particles: viruses, bacteria, and small dust, as those are difficult to capture. And to also demonstrate that MXenes, with their charged surfaces — highly polar surfaces — are able to attract those particles and prevent their penetration through the filter.

Tech Briefs: Can you please explain in simple terms how it works?

Gogotsi: Basically, you take a regular filter — like in your air conditioning system — and spray MXene particles on the surface. They stick to the surface of the filter and create sticky patches. They don't really close much of the filter; so, air flow continues. But, they create sticky patches where there is a much stronger interaction with those particles. We use salt as a model system, but potentially it can be anything within this range. We can significantly improve the performance.

Tech Briefs: Do you have plans for further research, work, etc.? And, if not, what are your next steps?

Gogotsi: We do. MXenes are still very new materials, and, initially when they were discovered at Drexel, we looked into very special applications — electromagnetic interference filters, optical filters, sensors, others — which required a small amount of material and which would tolerate expensive materials. But, now that the material is becoming more common, we can look into everyday applications. We're looking into, for example, thermal installation of a wall with a very thin MXene like a paint on the walls that can significantly drop the temperature, minimize heat losses from homes, making a very efficient thermal insulation. And we started to look into ways we can also improve filtration.

Prastuti Upadhyay is a brilliant undergraduate student, and has been working on MXenes for at least two years. We looked at what the application would be for a type of gel that she made with MXenes. The idea was trying it on filters to see if it works. Now, we demonstrated it works, proof of concept. So, what you do next — optimization — capturing particles of different sizes, smaller and larger. Optimizing airflow and efficiency, getting it beyond 95 percent. I think those would be the next steps. We also have tried just one MXene. We don't know how the surface chemistry of this material or the particle size of the MXene affects the behavior. So, beyond the proof of concept, there are all these parametric optimization studies we need to do.

And again, air filtration systems are used in different situations. Some of them may be expensive and very important. For example, hospitals where there may be dangerous bacteria; spaceships; and some of them are installed in our homes where pretty much efficiency is important, but cost is the key factor. So, we’ll probably first look into those types of filters that need to be for special applications and will be more cost-tolerant at the same time.

There is one more thing that is important: MXenes are conductive, they're like graphene but more conductive. What that means is that we can clean this filter. By applying an electrical potential, we can either burn whatever is on the surface or kill bacteria viruses and ensure that the filter is safe after use. Those are special applications, which conventional filters cannot do. We will start with the unique properties of MXenes to target some of those applications.

Tech Briefs: Those are all the questions I have. Is there anything else you'd like to add that I didn't touch upon?

Gogotsi: One thing that I've been stressing is it's a great to see undergraduate students really pushing the limits of knowledge. My previous undergraduate student last year went to study for a Ph.D. at the University of Chicago. She discovered a couple of new MXenes! There was another undergraduate student who discovered an entire sub-family of MXenes. And now we have a student who has for the first time, explored new applications of MXenes.

So, it shows that science can be done not only by Ph.D.s. This is a great opportunity to see students go from the early stages inspired by science to push the limits of our knowledge in science and engineering.