Indrek Külaots is using garbage to make the world a cleaner place.
Untold tons of plant matter are discarded in the United States every day. Much of this biomass — farm waste, sawdust, wood scraps, household yard waste — is trucked off to landfills. As it rots, it produces carbon dioxide and methane, greenhouse gases that contribute to global warming.
“My research focuses on trying to make better use of this bio-waste material,” said Külaots, lecturer in engineering. He has found a way to turn this trash into sorbent material than can sop up industrial pollutants.
Using a simple technique called pyrolysis — the same process used to make charcoal — plant waste can be broken down into what’s called bio-char. “This char product has relatively high surface area and is also highly porous,” Külaots said. “We can use those pores as workers for pollutant capture.”
He has patented a method of using modified bio-char to absorb elemental mercury. Bio-char could one day be used as a cost-effective way to scrub mercury from power plant vapor emissions, replacing expensive activated carbon filters. Bio-char sorbents also show promise for cleaning up other pollutants like arsenic, cadmium, and lead, Külaots says.
Külaots’ interest in environmental engineering began in his native Estonia. After earning his master’s degree in mechanical engineering at the Tallinn Technical University, he worked on a project to recycle fly ash, a byproduct produced by the burning of oil shale. His work on that subject caught the eye of Eric Suuberg, an engineering professor at Brown. Suuberg thought Külaots’ work could be applied to fly ash created by the burning of coal, which is a major concern in the United States
“He saw my work and said, ‘Why don’t you apply?’” Külaots said. “So I came to Brown as a Ph.D. student and I never left.”
After earning a master’s degree in applied mathematics in 2000 and a Ph.D. in chemical engineering in 2001, Külaots stayed at Brown as a senior research engineer. In 2009, he was awarded a joint position as lecturer and research engineer. This year he joins the faculty as a lecturer.
In addition to teaching classes in chemical, mechanical, and environmental engineering, he’s expanding his research program to include a hot topic in the material sciences world: graphene.
Graphene is a one-atom-thick sheet of carbon, with vast surface area. It began getting notoriety a few years ago and quickly gained a reputation as a miracle material. Its electrical properties make it a likely successor of silicon in microprocessors. It also holds promise as a way to store gases like hydrogen for use in fuel cells, and it can catalyze chemical reactions.
But for all its miraculousness, graphene has a problem. The sheets have a tendency to get stuck together in stacks when processed, which decreases this vast surface area on each sheet. Think of two sheets of paper stapled at all four corners. It’s not possible to write on the back of the first page or the front of the second because those surfaces are stuck together.
“My research is how to interrupt this stacking,” Külaots said. “How can we get something in the middle so we can actually use the inner layer space as well?”
He’s developing tiny carbon columns to do the job.
“It’s just a pillar, like in ancient Rome,” he said. “But when you’re working at the nanoscale it’s not that easy.” Despite the difficulty, Külaots has had success using his pillars to recover some of this lost space, and recently presented his work at one of the world’s top conferences on carbon materials.
“These pillared graphene and graphene oxide systems have a great potential in the fields of gas storage, separation, and catalysis, if properly converted into bulk materials,” he said.
Such is the fast-paced world of engineering: Even before graphene makes it out of the lab and into production, Külaots is thinking of ways to make it better.