How rice waste has been turned into a powerful indoor air cleaner

Researchers have developed a novel, low-cost air purifying material from rice husk ash, a byproduct generated by burning the protective shells of rice grains at high temperatures.

The composite can double the adsorption of formaldehyde gas, a volatile organic compound (VOC) classified as a human carcinogen, which off-gasses from common household items such as plywood, paints and textiles, posing chronic respiratory and cancer risks, especially to children.

Scientists at the University of Science in Ho Chi Minh City started with rice husk ash, a plentiful by-product of the rice industry. Through a simple activation process using sodium hydroxide and ultrasonic treatment they created a highly porous activated biochar.

They coated this porous sponge with a special polymer that acts like millions of microscopic chemical ‘hooks’ called amines.

It is these amine groups that are the key to the material’s success. They chemically react with and capture formaldehyde molecules. While the PEI coating slightly reduced the material’s overall surface area, the powerful chemical grab of the hooks makes the material far more effective at capturing formaldehyde than a simple physical filter would be.

The PEI-modified biochar exhibited a maximum formaldehyde adsorption capacity of 256 mg/g, double that of the unmodified biochar (128 mg/g). The adsorption process was also faster.

‘We wanted to create a solution that was as sustainable as it was effective,’ say the lead researchers. ‘By using rice husk ash and a low-energy ultrasonic treatment, we avoided the high-temperature calcination usually required in manufacturing. The result is a material that is cheaper to make and much kinder to the environment.’

The research highlights a compelling circular economy approach, transforming an agricultural waste product into a valuable tool for public health. The synthesis method is simpler, more energy-efficient, and more sustainable than many existing techniques for creating activated carbons.

While the study marks a significant proof-of-concept under controlled laboratory conditions, the authors acknowledge next steps are needed, including testing under real-world variables like humidity, temperature, and mixed gas environments, as well as evaluating the material’s long-term stability and regeneration potential.

The full research can be read here.