This is the fifth episode of Dean Aaron Bobick’s new podcast: Engineering the Future.
How can nanoparticles be leveraged as aerosols and what applications exist?
From Washington University in St. Louis' McKelvey School of Engineering, I'm your host, Dean Aaron Bobick, and this is Engineering the Future, where we explore pressing problems of today, in which engineering discovery, innovation, and education can provide solutions for tomorrow. Welcome to our final episode of our four-part series on nanoparticles. In the last episode, ee discussed some of the medical applications of using engineered nanoparticles in both therapeutics and diagnostics. In this our last episode, we'll discuss some other innovative uses of these engineered nanoparticles in a variety of industrial applications. So talking with Hong Chen, she mentioned working with our colleague, Professor Pratim Biswas, who works in our energy, environment and chemical engineering department. And Pratim has been providing her with the nanoparticles that she takes advantage of in her work. But Pratim has done much work that uses nanoparticles in a variety of ways, so I thought I could close out by chatting with him just a little bit to understand what he does. So joining us is Pratim Biswas, who's the Lucy and Stanley Lopata professor in the EECE department. Pratim, thanks for joining us.
So Pratim, I got to start with-- so I've only been here now a couple of years, and people affectionately refer to you as Professor Aerosols. You're all about aerosols. And I didn't know a lot about aerosols. It has something to do with basically spraying stuff, but you use aerosols to produce these nanoparticles. Now, that's different than Srikanth. We talked to Srikanth Singamaneni about using chemistry to do it. So can you briefly just describe what are aerosols, and how do you use those to produce nanoparticles?
Yeah. Aerosols are basically small particles suspended in some gaseous medium. And the way we sort of utilize this, it's a fascinating field which deals with the formation of these small particles, their growth, their transport, how they move around, and then ultimately, even their deposition. So we utilize these principles to intentionally produce materials from the gas phase. So we start with the molecular state and then can assemble these things into clusters and then particles. And obviously, as these are wanted or good particles, as we refer to, we can tune the functionality for specific applications.
So those of us that are-- most of our understanding of aerosols has to do with spray cans, basically there, there's a liquid and there's a gas under pressure, and that forces the liquid through some sort of a nozzle. And that nozzle, because of the way the pressure interacts there, causes this liquid to essentially produce airborne particles.
Now, I guess what you guys do must be a little more sophisticated than that.
Correct. Yeah. So here, we are actually starting with some precursor chemicals in the vapor state or what we refer to as the molecular state.
So we have something that's already gaseous. It's vapor.
Yes, it's gaseous. They could react because chemical reactions could be driven rapidly in this state. And then we can produce a material that is desired.
So Srikanth and Hong Chen have already talked about using these particles in medical domains, but I know that you've used them for many other types of applications where you've engineered these particles to be good for those applications. What are some of your more interesting ones?
So I'll pick the first one in the energy sector. We, of course, talk a lot about the solar energy. But if you look around, there are very few individuals or institutions, organizations that have solar panels on their roof. Primarily because of the cost. We still make solar panels with the same technology that we make cell phones with. So aerosol techniques are ideally suited to produce photovoltaic materials and then ultimately devices, which can become solar panels.
Previously, we've talked a little bit about nanoparticles, about some of their properties, or that they've got tremendous amount of surface area as a function of their volume, and that gives them interesting reactivity. We've talked about how it interacts with light in unusual ways. What about nanoparticles makes them useful as photovoltaic materials?
So there are couple of fold of reasons for this. One is the ability to obtain a certain composition that is desired, which has these, in some case, optimal properties of, let's say, let's just pick light harvesting. So I can tune the composition. I would work with theorists who would tell this is a desired composition. Using aerosol techniques, I can readily make a host of materials in the lab now, and then prove that these are good light harvesting materials.
So from a theory perspective, you can say something about what the nature of a material should be.
What does that mean, the nature of the material? You talk about the material properties. What properties are we getting at that matter?
So for solar cells, it's multiple properties. One is, of course, the light harvesting capability. Most of the semiconducting oxides might be harvesting off the visible band, sunlight that comes down to us. We want to tune the material so it can readily absorb visible light, as we call it.
And I presume you also have to control the shape and size of particles.
You could end up being sensitive to light frequencies that you want because, for example, they're very plentiful in the daytime.
Correct. So it's both the composition, the shape, the structure, and things like that. So a host of properties.
Oh, cool. So what's another application for which you found that nanoparticles can be brought to bear?
Right. So another fabulous area is actually moving these nanoparticles around. You heard from our colleagues, Hong Chen, that we can use these to deliver into the human body and target delivery at a certain organ, a certain region of the human body. We come from the Midwest here. There's wide-based agriculture here. And if you look at the fertilizers that are used, less than 30% of the chemicals are picked up by the plants. And there's a added problem. The run into the environment has run off and create all problems on water bodies. Instead, if I could prepare a nanocomposite that can be readily picked up by the roots, number one, at a certain rate that the plant wants to pick it up, or I could also deliver it as a spray through the leaves. The leaves have gas exchange. They have stomata, which are hundred micrometers as thick as our hair, openings for gas exchange. If I make it the right size, I can deliver it through that very efficiently.
So maybe at the end of the day, fertilizer's just chemistry. It's a matter of providing the right molecules to the plant. And what you're saying is instead of dumping them in aggregate and then hoping it goes up, I guess, through the water, that we can do it through the air, essentially, through the pores - I'll call them pores, even though they're not exactly pores - in the plants themselves. And this is where, again, having nano technology available, so you can make the chemistry that you want to be in the shape and size that you want, would give for efficient delivery.
Correct. That's correct. And farmers have been using this now as test or field trials. And they're very excited about this product because they have to use a lot less, saves the money. So the benefit of this nanoparticle technology is directly to the consumer. In this case, the farm.
Well, that's great. I mean, I think when we think of nanotechnology, we tend to think of very high-tech kinds of things. And I think one of the trends that people are unaware of is how high tech has permeated agriculture.
And this is one example of doing that. Well, Pratim, don't want to keep you any longer. Thank you so much for joining us. We've learned a lot about nanoparticles. I will say it's from you that I learned about the difference between the good and the bad and the ugly particles. And I hope by now that our audience has too. So thanks for joining us.
Yeah. Thank you. I enjoyed it. [music]
So that concludes our four-part series on nanoparticles. We learned something about what these particles are, how they are formed, and most importantly, why they have special properties. The fact that they have very little mass for the amount of surface area makes them highly reactive and is part of why some particles are so harmful to human health when in the atmosphere. But their small size makes them interact with light in unique ways. This, in turn, allows us to use them for interesting applications, ranging from medical diagnostics to solar panel materials. As Spock would say, fascinating. Well, thanks for joining us. This is Dean Aaron Bobick at Washington University in st. Louis, and this is Engineering the Future. [music]
The McKelvey School of Engineering at Washington University in St. Louis promotes independent inquiry and education with an emphasis on scientific excellence, innovation and collaboration without boundaries. McKelvey Engineering has top-ranked research and graduate programs across departments, particularly in biomedical engineering, environmental engineering and computing, and has one of the most selective undergraduate programs in the country. With 140 full-time faculty, 1,387 undergraduate students, 1,448 graduate students and 21,000 living alumni, we are working to solve some of society’s greatest challenges; to prepare students to become leaders and innovate throughout their careers; and to be a catalyst of economic development for the St. Louis region and beyond.