Pollution-destroying lampshades on mission to provide cleaner air
17 August 2023
A new type of coating applied to lampshades transforms air pollutants into harmless compounds, paving the way for cleaner air.
Image: Minhyung Lee
The lampshades work with halogen and incandescent light bulbs, and the team is extending the technology so that it will also be compatible with LEDs.
The lampshades target volatile organic compounds (VOCs), which account for most indoor airborne pollutants, according to Hyoung-il Kim, PhD, the project’s principal investigator. These compounds include acetaldehyde and formaldehyde and are released by paints, cleaners, air fresheners, plastics, furniture, cooking and other sources.
“Although the concentration of VOCs in a home or office is low, people spend more than 90 percent of their time indoors, so the exposure adds up over time,” Kim says.
“Conventional methods to remove VOCs from indoor air rely on activated carbon or other types of filters, which have to be replaced periodically,” says Minhyung Lee, a graduate student in Kim’s lab at Yonsei University.
Other devices have been developed that break down VOCs with the help of thermocatalysts activated by high temperatures or with photocatalysts, which respond to light. But Kim notes that most of these units need a separate heater or an ultraviolet (UV) light source, which can produce unwanted byproducts.
His team wanted to take a simpler approach that would only require a visible light source that also produces heat – such as a halogen or incandescent bulb – and a lampshade coated with a thermocatalyst.
Halogen bulbs convert a mere 10 percent of the power they use into light, with the other 90 percent being transformed into heat, according to Lee. Incandescent bulbs are even worse, emitting five percent light and 95 percent heat. “That heat is typically wasted,” Kim says, “but we decided to use it to activate a thermocatalyst to decompose VOCs.”
In a paper published last autumn, the team reported that they had synthesised thermocatalysts made of titanium dioxide and a small amount of platinum.
The researchers coated the inside of an aluminium lampshade with the catalyst and placed the shade over a 100W halogen bulb in a test chamber containing air and acetaldehyde gas. Turning the lamp on heated the shade to temperatures up to about 120°C – warm enough to activate the catalysts and decompose acetaldehyde.
During this oxidation process, the VOC was initially converted into acetic acid, then into formic acid, and finally into carbon dioxide and water. Both of the acids are mild, and the amount of carbon dioxide released is harmless, Kim notes.
The researchers also found that formaldehyde can be decomposed under the same conditions and that the technique works with incandescent bulbs.
“This was the first demonstration to utilise waste heat from lamp sources,” Kim says. Most previous research projects, and even a couple of lamps on the market, have instead relied on light-activated photocatalysts to destroy indoor air pollution.
In its latest work, Kim’s group is turning to less expensive substitutes for platinum.
The team has already shown that these new iron- or copper-based catalysts can break down VOCs. In addition, copper is a disinfectant, so Kim anticipates that the copper catalyst could kill airborne microorganisms.
The scientists are now looking for ways to extend the pollution-destroying lampshade concept to LEDs, a fast-growing segment of the lighting market. Unlike halogen and incandescent bulbs, however, LEDs release too little heat to activate thermocatalysts.
So, Kim’s team is developing photocatalysts that are stimulated by the near-UV light emitted by LEDs, as well as other catalysts that transform part of the LEDs’ visible light output into heat.
“Our ultimate goal is to develop a hybrid catalyst that can utilise the full spectrum produced by light sources, including UV and visible light, as well as waste heat,” Kim says.