"Particularly" Interesting Research
Particles—of all kinds of substances—are everywhere: in the air we breathe, the food we eat, the machines we use...and, of course, on that shelf we haven't dusted in months. What you might not know is that there is a lot of science behind many of those particles, and an entire field of research dedicated to them.
In the Department of Chemical and Biomolecular engineering, the
Good Particles, Bad Particles
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A high resolution transmission electron microscopy (HRTEM) image of a Ni-CeO2 nanoparticle. |
Why research particles at all? The answer becomes easier to understand when you look beyond that dusty shelf. Since particles are almost everywhere and in or on almost everything, they effect the environment in which we live and the products we use, for better or for worse. "Bad particles" contribute to our allergies and air pollution, sabotage some types of manufacturing (for example, computer chips), and are sometimes poisonous, even fatal (as in the case of anthrax)! On the other hand, "good particles" might be used in life-saving medications, paint, biosensors (to detect bad particles), healthy soil, cosmetics, manufacturing of consumer products, and to improve fuel efficiency. Both good and bad particles may occur naturally, be engineered for a specific purpose, or exist as a byproduct of another process. Because of this wide variety, particle research is an interdisciplinary science, and engineers who specialize in it have career opportunities in many different fields.
Particles and Fuel
Small particle-based catalysts show potential in the development of fuel cells, which generate power from hydrogen and oxygen more efficiently and with less pollution than internal combustion engines. In this scenario, particles (often metal, like platinum) within the fuel cell facilitate the reaction of hydrogen gas (H2) and oxygen, resulting in an output of electrons (which provide the energy) and water
To address this problem, the P2OWDER Group is searching for ways to extract hydrogen from existing fuels with established distribution networks. Once again, particle catalysts play a key role: The hydrocarbons in a fuel, such as diesel or jet fuel, are broken down using processes such as partial oxidation or steam reformation. Next, a process called a water gas shift reaction is used to lower the amount of the carbon monoxide (CO) and make more hydrogen. In the reaction, the group's particle catalyst both "lends" an oxygen atom to CO, creating less harmful carbon dioxide gas (CO2), and "borrows" an atom of oxygen from water molecules, transforming them into hydrogen gas. The group's catalyst has the advantage of being less expensive than platinum-based catalysts currently used in fuel cell research, and its manufacture via an aerosol process is simple and easily scaled to produce larger amounts.
Particles and the Body
Particle science also has the potential to enhance medical procedures. Iron particles, for example, could be coated with substances designed to form bonds with specific types of cells. When released in the body, the particles will travel to their intended target. A MRI (Magnetic Resonance Imaging) device would detect the iron particles, producing an image showing doctors where they have gone, and, as a result, where the targeted cells are.
Professor Ehrman is also using particle science to conduct fundamental studies that could eventually lead to better pulmonary delivery of vaccines. Inhaled vaccines can be as effective as shots, but produce far less medical waste and reduce the risk of transmitting bloodborne illnesses.
Particles in the Environment
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ChBE graduate student and P2OWDER Group member Patricia Castellanos presents her work on Maryland's air quality. |
The group also works with "the bad side of particles." In one project, P2OWDER is assisting the Maryland Department of Environment, developing possible future emissions control scenarios that will bring Maryland closer to attainment of the National Ambient Air Quality Standards. P2OWDER Group researchers use emissions and chemical transport modeling to understand the physics and dynamics of ozone and aerosol formation and transport in an attempt to develop better ways to reduce these pollutants.
Students involved with this project also measure air quality. Working in collaboration with a group from the University's Atmospheric Sciences Department, P2OWDER takes measurements of gas phase pollutants and aerosols from an airplane as part of an on-going project to document and understand Maryland's air quality.
Building A Better Particle
The P2OWDER Group produces its particles from the atomic level up, until they have created products at a nano- or micron-scale for specific applications. Processes for making particles can be loosely classified as "wet" or "dry". Particles formed in a "wet" process come from a solution, while those formed in a "dry" process come from gas. Most of the group's particles are formed in flame reactions: the source material (called a precursor) is vaporized in a flame, then reacts with oxygen and condenses to form oxide particles. Multiple materials can be combined in this way.
At the center of the group's lab is the flame aerosol reactor where the reactions take place. Precursor material, droplets or vapor suspended in a gas, is fed into its chamber, where it vaporizes and reacts in a methane flame. The change in temperature downstream of the flame pushes the resulting particles toward a thermophoretic particle collector, a piece of aluminum that is kept cool by circulating water through it. The particles are strongly attracted to its cool surface, a phenomenon known as thermophoresis, from which the collector takes its name. Once the reaction is over and the flame is turned off, the particles can be collected by scraping them off the aluminum.
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In the photo above, the precursor solution contains copper, which, when atomized by a nebulizer and exposed to the flame in the reactor, causes it to turn green. |
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The methane-nitrogen-oxygen gas mix used to create the collector's slit flame is premixed—it doesn't need anything from the surrounding atmosphere (or any air, for that matter) to exist. Researchers can adjust the mix, and therefore the flame, to get exactly the temperature they want. Control over the flame is important: it creates a uniform environment in which the reactions occur, and allows control over particle size. Particles are smaller when formed at lower temperatures, and larger at higher ones.
For an overview of the particle-creation process, please see our sidebar, "Particle Production."
Learn More
Increasingly, thinking small—very small—is leading to big impacts on the way we live. Particle research is one way nanotechnology has the potential to make a difference in our health, environment, and quality of consumer goods. To learn more about Dr. Ehrman’s current research and recent publications:
Visit the P2OWDER Group website »
Meet Dr. Ehrman »
