Scientists have developed an air purifier that is charged by sunlight and indoor LED lights, potentially offering an inexpensive, lower-maintenance alternative to standard filtration systems that protect users from pollutants and airborne diseases. The study, publishing September 25 in the Cell Press journal Chem, demonstrates that the air filter maintained 99% of its maximum filtration efficiency after a month of use and 95% for the following 2 months. In the future, the filter could be used in reusable versions of the N95 masks worn throughout the COVID-19 pandemic.
"The light-charged system offers a sustainable and customizable approach for particle capture, effectively overcoming the challenges of poor filtration stability and clogging commonly observed in conventional filters," says author Jihong Yu of Jilin University in Changchun, China.
Most commercial air filters use a high-voltage electrical field called "corona discharge" to imbue airborne particles with static electric charges, which they then use to pull the particles from the air to purify an indoor environment. However, these systems require external power sources, limiting their applications. While some alternatives exist that don't require wall plugs, such as triboelectric filters that capture fine dust, pollen, and bacteria, these have their own limitations, such as the need for synthetic materials and the fact that their charge degrades over time.
To overcome these issues, Yu and colleagues took a different approach to air filtration, developing a light-charged system by outfitting a polypropylene membrane with a coating that responds to light and heat, generating continuous on-site surface charge. To test the device, the researchers exposed it to sodium chloride and soot particles measuring about 0.3 micrometers in size at humidities spanning 20% to 90%.
The device "demonstrates broad applicability in areas such as indoor air protection, dust removal, health and hygiene, and biological apparatus," says Yu, noting that it could be incorporated into face masks similar to N95 masks.
When the device becomes saturated with particles captured from the air, it can be flushed with water. Then, its surface electrostatic field is restored through light activation. The team found that even low-energy light sources such as indoor LEDs or overcast sunlight could generate enough power to sufficiently charge it for N95- and N99-level filtration efficiency. This simple process allows the filter to be reused through hundreds of filtration cycles with virtually no maintenance, say the authors.
The study demonstrates the device's potential for real-world applications, say the authors, who have developed prototypes for facemasks, outdoor screens, and biological apparatuses that use the filter. However, Yu notes that the filter's self-cleaning process could be further improved, and more research will be needed to assess how easily the filtration system can be mass produced and integrated with other products.
"Promoting the light-charged air filtration system for real-world use is one of our future plans," Yu says. "Meanwhile, we would like to focus on proposing air purification pathways under extreme environments."
