The lampshades target volatile organic compounds (VOCs), which account for most indoor airborne pollutants, including acetaldehyde and formaldehyde. These compounds are released by paints, cleaners, air fresheners, plastics, furniture and cooking.
The invention works with halogen and incandescent light bulbs, and the team is extending the technology so it will also be compatible with LEDs, the researchers said.
"Although the concentration of VOCs in a home or office is low, people spend more than 90 per cent of their time indoors, so the exposure adds up over time," said Hyoung-il Kim, the project's principal investigator.
In the past, conventional methods to remove VOCs from indoor air have relied on activated carbon or other filters, which have to be replaced periodically.
Other devices have also broken down VOCs with the help of thermocatalysts activated by high temperatures or with photocatalysts, which respond to light. However, most of these units need a separate heater or an ultraviolet (UV) light source, which can produce unwanted by-products.
Instead, the researchers wanted to develop a device that would only require a visible light source that also produces heat – such as a halogen or an incandescent bulb – and a lampshade coated with a thermocatalyst.
A lampshade coated with a catalyst uses heat from an incandescent bulb to destroy indoor air pollution. / Minhyung Lee
Image credit: Minhyung Lee
Halogen bulbs convert a mere 10 per cent of the power they use into light, with the other 90 per cent being transformed into heat. Incandescent bulbs emit 5 per cent light and 95 per cent heat.
"That heat is typically wasted," Kim says, "but we decided to use it to activate a thermocatalyst to decompose VOCs."
The researchers coated the inside of an aluminium lampshade with the catalyst made of titanium dioxide and a small amount of platinum. They then placed the shade over a 100-watt halogen bulb in a test chamber containing air and acetaldehyde gas.
The team turned the light on, heating the shade to temperatures up to about 250°F – 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.
"This was the first demonstration to utilise waste heat from lamp sources," Kim said.
In its latest work, Kim's group is turning to less expensive substitutes for platinum, such as new iron- or copper-based catalysts. They are also looking for ways to extend the pollution-destroying lampshade concept to LEDs, a fast-growing segment of the lighting market.
However, since LEDs release too little heat to activate thermocatalysts, Kim's team is developing photocatalysts that are stimulated by the near-UV light emitted by LEDs, or that can transform it 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.
Earlier this month, a law came into force banning the manufacture and sale of incandescent bulbs in the US, with companies that violate the ban facing a maximum penalty of $542 (£427) per bulb.
