Aerogel, a futuristic-sounding lightweight solid sometimes referred to as "frozen smoke," could one day mop up oil spills like one this week in the Irish Sea and filter wastewater because of its super-absorbent, sponge-like qualities.
Nanogel, a branded aerogel made of modified, water-repellent silica, soaked up oil faster and in greater quantities than other materials that are typically used in wastewater filtration, according to a study in the latest issue of the biweekly journal Industrial & Engineering Chemistry Research. Boston-based Cabot Corp., which makes Nanogel, helped pay for the research and supplied the product.
"We think aerogels are much better than other sorbents, like activated carbon and vermiculite, that have been tried," co-author Bob Pfeffer, a professor of chemical engineering at Arizona State University (A.S.U.), tells ScientificAmerican.com. "We think the aerogels are much more efficient." Sawdust, peat sorb, bentonite, organoclay, reed canary grass and flax or hemp fiber also have been used as filters, but whether aerogel would turn out to be a more or less expensive material would depend on its manufacturing cost and whether it could be reused.
Aerogel attracts oil, toluene and other organic compounds that end up in wastewater from industrial plants. Its potential as a cleaning product comes from its properties of adsorption (as molecules stick to the aerogel's surface) and absorption (as its pores suck molecules into the gel's interior). Aerogel has enormous surface area and can hold up to seven times its weight. (You can get a good sense of aerogel from this episode of KQED Quest Lab.) If it's not reused, it would be thrown out.
Scientists from A.S.U., Shell and the New Jersey Institute of Technology tested the product by exposing a column of Nanogel beads to a mix of water and soybean oil to mimic the sort of filtration that goes on at wastewater treatment plants. The next step is to run the process continuously to see if it would work on a larger scale in wastewater treatment facilities.
Pfeffer's group isn’t studying the use of aerogels for oil spill cleanups, "though that clearly is an application for this because aerogels are such great absorbers," he says. Because they're so lightweight, "they'd absorb the oil before they would sink. Other sorbents would sink to the bottom before they'd absorb the oil." Previous research has shown that another aerogel was able to filter up to 14 times its weight in an oil–water mixture.
Aerogel was discovered in the 1930s and today is used to insulate both spacesuits, snowsuits and industrial pipelines. We've got more on the history of aerogel, among the strangest of solids.
A 0.07-ounce (two-gram) block of aerogel supports a 5.5-pound (2.5-kilogram) brick/NASA JPL via Wikimedia Commons