Waste heat from lights could remove indoor pollutants

A team of Korean researchers has found a way to remove indoor pollutants by tapping into waste heat from lamplights.

They’ve made a coating for lampshades which can remove volatile organic compounds (VOCs) from the air and turn them into harmless by-products.

The coating currently only works with halogen lights and other bulbs which produce a lot of excess heat, but the researchers are hoping to tune it to more efficient LEDs soon.

VOCs are small, carbon-containing substances like acetaldehyde and formaldehyde, which are emitted by paints, plastics, cooking, and other household 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,” says Dr Hyoung-il Kim, a researcher at Yonsei University, South Korea.

“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.

Kim and colleagues have been investigating catalysts which can trigger a chemical reaction that turns VOCs into CO₂. Because concentrations of VOCs are low indoors, the amount of CO₂ made is so low as to be harmless – on par with the amount humans exhale.

Chemical reactions typically need some energy to work. The team has been investigating thermocatalysts, which use heat to trigger the reaction.

They’ve developed a catalyst made mostly from titanium dioxide (a white pigment used in toothpastes, foods, sunscreen and paints) and tiny amounts of the precious metal platinum.

This catalyst can reduce a high concentration of VOCs at room temperature, but it performed better when coating the inside of a halogen lampshade.

Excess heat from the lamp heated the shade to 120°C, making the catalyst capable of removing even low levels of VOCs.

The researchers are now looking to make the reaction work with cheaper metals than platinum, like iron and copper.

They’re also looking into photocatalysts, which use light instead of heat to trigger reactions, to allow them to work with LEDs.

LEDs are an increasingly popular lighting source, because they don’t waste most of their energy as heat – but that means they also don’t produce the temperatures needed for this catalyst to work.

Using light instead of heat to catalyse the reaction would solve that problem.

“Our ultimate goal is to develop a hybrid catalyst that can utilize the full spectrum produced by light sources, including UV and visible light, as well as waste heat,” says Kim.

The researchers have presented their work at the Fall 2023 meeting of the American Chemical Society.