Emmanuel P. Giannelis, Materials Science and Engineering, spends his days working with microscopic nanoparticles, but his view of what these tiny systems can do is as big as the world. “The biggest challenges we are facing right now, and that we can address technologically, focus on energy production and water purification, and their impact on the environment,” says Giannelis. “To produce energy, you must consume water. To purify water, you must consume energy. If you have a solution for one, you can find the solution for the other.”
The Unique and Amazing Properties of Nanoparticles
Giannelis is looking for the solutions to these problems in the unusual and amazing properties of nanoparticles. Roughly the size of large molecules, nanoparticles have a high surface-to-volume ratio, which means more atoms are on the surface of the particle than are inside. The atoms on the surface behave differently from those on the inside—in essence they are positioned to be more aware of outside stimulus and to react to it. This is in contrast to traditional materials, which have the bulk of their atoms on the inside. Because nanoparticles have so many surface atoms, they can have distinctive properties as well as unique behaviors when exposed to electrical or magnetic fields.
Giannelis’ research group consists of undergraduates, graduate students, and postdocs who have worked for years to synthesize nanoparticles that differ from those produced by other researchers. The Giannelis lab’s nanoparticles are hybrids, made up of organic and inorganic parts. They are also permanently charged, with positive and negative ions that attract each other and bind the particles together, giving them the ability to flow like liquids. Giannelis is putting these special properties to work in a number of innovative ways centering on carbon dioxide capture, water purification, and energy storage.
The Sponge, a Hybrid Nanoparticle for CO2 Capture
Capturing carbon dioxide before it goes into the atmosphere is an especially pressing problem given the current concerns with global warming (caused in part by CO2). Giannelis has investigated ways to clean the exhaust from power plants, especially coal-burning ones, which are high in CO2 emissions. His lab has developed a hybrid nanoparticle he calls a “sponge.” The particle has an inorganic wall of silica with a highly porous surface, combined with organic molecules of carbon-trapping amine. The amine molecules saturate the surface of the silica and chemically bond with it, creating a stable particle. The sponge nanomaterial can be used to line special exhaust pipes at power plants to catch the CO2 that is present in the exhaust from a plant. When the sponges are completely saturated with the gas, the capturing process can be reversed through controlled heating and the CO2 is released into a holding tank for future use in another industrial application. The sponge nanomaterial is then ready to capture more carbon dioxide.
“When CO2 initially comes out in the power plant’s exhaust, it is diluted gas,” says Giannelis. “It’s mixed with water and other things, and it’s not usable for industrial purposes. But after capture by our sponges, it’s 100 percent pure carbon dioxide. So not only do we prevent the CO2 from going into the Earth’s atmosphere, but we capture it in such a way that it is readily usable again.”
The researchers have scaled up the sponge nanomaterial so it can be produced in relatively large amounts, and recently they received a grant for $150,000 from New York State to demonstrate the material industrially and to distribute it to several potential customers. In addition, as part of the “Living Laboratory” initiative, they hope to have an opportunity to put the sponges to work in a real-life test by retrofitting the power plant at Cornell.
Along with the carbon dioxide capture technology, Giannelis has been looking at the other side of the energy equation: water purification. Working with Menachem Elimelech, Professor of Chemical Engineering at Yale University, Giannelis and his team have added their charged nanoparticles to membranes used in existing water purification applications. The nanoparticles make the surface of the membranes more hydrophilic, or water-liking.
More than any other, the electrolyte nanomaterial clearly demonstrates the benefit of hybrid architecture.
“Normally water purification membranes become clogged with microorganisms,” says Giannelis. “As the deposits build up, you have to use more and more energy to push the water through the membranes. Eventually they become completely clogged, and you have to stop the process to clean them. With our nanomaterial, that cleaning step is not as intensive. Because the membranes are hydrophilic, the microorganisms just wash right off.” Ease of cleaning means money is saved, as well as energy, while water is purified to the benefit of the environment: a perfect example of the energy-water-environment nexus Giannelis wants to address.
In his quest to solve problems associated with energy, Giannelis has also turned his attention to renewable energy sources like solar and wind power. “The sun doesn’t always shine and the wind doesn’t always blow,” he says, “so we have to store the energy at production to use later when it can’t be produced. That’s why batteries are crucial.”
While batteries have been around for almost two centuries and have gone through many improvements over the years, they still have one major flaw: the electrolyte that allows ions to move from one electrode to another within the battery, and to thus produce electricity, is flammable. Giannelis has eliminated the danger of fire by changing the composition of the electrolyte, which is traditionally 100 percent organic. His new electrolyte membrane incorporates hybrid nanoparticles that have an organic material’s ability to conduct ions and an inorganic material’s resistance to fire.
“Our nanomaterial allows the ions to move back and forth and produce electricity,” he says. “But you can hold a blow torch near it, and it won’t catch fire.” Perhaps more than any other, the electrolyte nanomaterial clearly demonstrates the benefit of hybrid architecture. “It gives us the best of both worlds,” Giannelis says with satisfaction.