Manindu Weerasinghe, a Kansas State University doctoral candidate in chemistry, Sri Lanka, is studying materials that use light or darkness to purify air filled with toxins that are harmful to human health and the environment. Her research could one day lead to filters, humidifiers and other devices that can detoxify air in windowless rooms, manufacturing facilities and other indoor areas.
“Indoor pollutants can come from things like asbestos, markers and new carpet, and are very harmful in just small amounts,” Weerasinghe said. “A room like an office or a laboratory that may have few or no windows will have higher levels of indoor air pollutants than a room that has lots of windows. Also, if the room does not have good ventilation those levels would increase.”
For her research, Weerasinghe is testing and analyzing photocatalysts and dark catalysts — materials made by chemically bonding a metal to oxygen. Photocatalysts react to light while dark catalysts react to darkness. The photocatalysts being tested are made from chromium or vanadium with titanium. Cobalt is used for the dark catalysts. Finding which metal is most effective at combating pollutants is key.
Weerasinghe is also adding varying amounts of pure silica to each catalyst mixture. Silica is the substance used to make glass and ceramics and serves as an insulator in chemical reactions. Based on test results, adding silica improves a catalyst’s ability to remove air pollutants.
“Right now it’s not really clear why and how pure silica works so well, so that’s something I hope to also answer with more experiments,” she said. “Glass is not toxic and silica is very abundant and inexpensive, so it could be a very good material to use if this work moves from laboratory-scale production to an industrial-scale production.”
Once made, each photocatalyst and dark catalyst is tested in a chamber filled with air pollutants. Oxygen is added and the catalyst is exposed to light or darkness, triggering a chemical reaction that converts air pollutants in the chamber into smaller, less harmful levels of carbon dioxide over time. Although carbon dioxide is not the ideal byproduct, it is produced at such small levels that it presents fewer problems to health and the environment than the air pollutants, Weerasinghe said.
Of the photocatalysts, chromium photocatalysts reduce the most air pollutants. Although the work is still in its early stages, Weerasinghe is finding that the results are more complex. Tests using the cobalt dark catalysts show significant gains over the photocatalysts.
“In fact, the cobalt system is 10 times more active than the chromium system at degrading pollutants,” Weerasinghe said. “It’s also a rapid response system, meaning that about 10 minutes into the experiment the cobalt starts to react. This is something that wasn’t expected because these experiments are about using light. But the best results are coming from a system that doesn’t use light to react.”
In one instance, Weerasinghe tried to find the point at which the dark catalyst stopped reacting. After three days into the experiment no drop-off point could be found. She plans further studies to investigate this unexpected phenomenon.
Weerasinghe is writing about her findings with chromium photocatalysts and cobalt dark catalysts for future publications. Her adviser is Ken Klabunde, a university distinguished professor of chemistry who is considered a leader in turning chemistry into environment-friendly materials by the scientific community.