TECHNOLOGY UPDATE
A technology that fabricates clean air from oxygen With the goal of creating pollutioncleaning fabric coatings, an Emory University scientist has found a way to destroy toxic chemicals commonly found in indoor air using little more than oxygen from that air. Indoor air pollution is a top human health risk, according to EPA's Science Advisory Board. EPA studies indicate that indoor levels of many air pollutants may be 2-5 times, and occasionally more than 100 times, higher than outdoor levels. The problem is exacerbated by reduced ventilation in energy-efficient buildings, for their tight seals inadvertently trap emissions from synthetic building materials and furnishings, personal care products, pesticides, and household cleaners, according to EPA's Indoor Environments Web site. Comprehensive federal regulations covering indoor air quality do not exist, according to a spokesperson for EPA's Indoor Environments Division. Inspired by the green ideal of mimicking the reactions found in nature, Craig Hill, the Goodrich C. White professor of chemistry at Emory University, and industrial collaborators set out to find a way to activate the conversion of airborne oxygen into highly reactive forms capable of destroying some key indoor pollutants, without causing more pollution in the process. These chemical species include hydrogen peroxide (H202) and the hydroxyl radical (OH), as well as the catalyst itself. Together, they are "where all the action is in nature," as Hill put it when he described his research at the Third Annual Green Chemistry and Engineering Conference in Washington, D.C., in July. Reactions based on these chemicals occur continuously—at this very moment, oxygen radicals are aging the skin of everyone reading this article—but the conversion of oxygen to the © 1999 American Chemical Society
A new chemical coating for fabrics like curtains has the potential to clean airborne pollutants like formaldehyde from indoor air.
more reactive forms takes place very slowly, he explained. By using combinatorial evaluation methods, Hill found catalysts that were capable of speeding up this conversion. All of the candidate catalysts are from an enormously variable group known as polyoxometalates (POMs), large molecules containing metals like silicon, tungsten, gold, and silver. Hill's candidates are intrinsically stable, as well as being inexpensive, easy to synthesize, and nontoxic, he said. The POMs that Hill seeks to patent are able to remove airborne toxins at temperatures, pressures, and humidity levels commonly found indoors. The catalysts target several toxins, including two that the Occupational Safety and Health Administration (OSHA) consider to be major indoor air pollutants: formaldehyde and hydrogen sulfide. Both are components of cigarette smoke. Hydrogen sulfide is an eye irritant that usually ends up in indoor air as a byproduct of chemical reactions, according to OSHA. Formaldehyde is a suspected carcinogen that is released by a number of building products, including the pressboard used to make flooring, shelving, cabinets, and furniture. Wrinkle-free fabric finishes used on draperies and clothing are also a major source of formaldehyde, according to the U.S.
Consumer Product Safety Commission (CPSC), as are a number of cosmetics, paints, and coatings. Exposure to more than 0.1 part per million of formaldehyde can cause flulike symptoms, which include watery eyes; runny nose; burning sensations in the eyes, nose, and throat; headaches; and fatigue, according to CPSC literature. The only kind of indoor air cleaners capable of targeting such gaseous pollutants contain sorbent materials like activated carbon or alumina. Hill believes that his discovery could be applied to drapery, upholstery, carpeting, and even clothing. The market prospects for such a fabric coating could be quite good, according to John Turner, senior chemist at Cotton, Inc., a research organization for the cotton industry, although he noted that the coating's dermatologic properties would have to be evaluated to make sure that its activity did not irritate the skin. Chemists at the University of California-Davis have devised a fabric coating technology capable of repelling pesticides using a chlorinated chemical, but Hill's process has the potential for a much broader market. Japanese consumers already spend the equivalent of $4 billion on what are called selfdeodorizing fabrics reputed to remove fish and tobacco smoke smells from room air, Hill said. Products based on similar principles are also popular in Germany, Turner said. Hill has succeeded in getting the POM catalyst to adhere to cotton fabric, but has had less success with nylon, to date. He is still trying to attack the problem of removing the chemicals that build up on the fabric. He is funding the research with grants from the Army Research Office and TDA Research in Wheat Ridge, Colo., a chemical and engineering research firm specializing in catalysis and advanced materials. —KELLYN S. BETTS
SEPTEMBER 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 3 5 9 A
