Catalyst-coated lampshades work as indoor air purifiers

South Korean scientists have designed catalyst-coated lampshades that work with halogen and incandescent light bulbs to transform indoor air pollutants into harmless compounds. The researchers presented their results at ACS Fall 2023, the August meeting of the American Chemical Society (ACS).

The lampshades target volatile organic compounds (VOCs), which account for most indoor airborne pollutants. 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% of their time indoors, so the exposure adds up over time,” noted Dr Hyoung-il Kim, the project’s principal investigator.

“Conventional methods to remove VOCs from indoor air rely on activated carbon or other types of filters, which have to be replaced periodically,” added Minhyung Lee, a graduate student in Kim’s lab at Yonsei University. And while other devices can break down VOCs with the help of thermocatalysts activated by high temperatures or photocatalysts activated by light, most of these units need a separate heater or an ultraviolet (UV) light source, which can produce unwanted by-products.

Kim’s 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% of the power they use into light, with the other 90% being transformed into heat, while incandescent bulbs emit 5% light and 95% heat.

“That heat is typically wasted, but we decided to use it to activate a thermocatalyst to decompose VOCs,” Kim said.

The researchers previously reported that they had synthesised thermocatalysts made of titanium dioxide and a small amount of platinum. The team coated the inside of an aluminium lampshade with the catalyst and placed the shade over a 100 W halogen bulb in a test chamber containing air and acetaldehyde gas.

Turning the lamp on heated the shade to temperatures up to around 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. 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 said.

Kim’s group is now turning to less expensive substitutes for platinum, having already shown that their new iron- or copper-based catalysts can break down VOCs. In addition, copper is a disinfectant, so Kim anticipates that a copper catalyst could kill airborne microorganisms.

The scientists are now looking for ways to extend their 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 said.

Image caption: A lampshade coated with a catalyst uses heat from an incandescent bulb to destroy indoor air pollution. Image credit: Minhyung Lee.