In a newly published paper in the journal Carbon Research, Thanh Luu Huynh and a team of scientists explore a greener path to tackling indoor air pollution by turning agricultural leftovers into high-performance filters. Formaldehyde, a common indoor pollutant found in everything from furniture to paints, poses significant health risks, but traditional methods to remove it are often expensive or energy-intensive. The researchers utilized rice husk ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More, an abundant waste product from industrial boilers in Vietnam, as the foundation for their new material. By applying a specialized treatment involving sodium hydroxide and ultrasound, they created an activated biochar with a massive internal surface area, providing ample space for pollutants to be trapped.

The most significant finding of the study involves the functionalization of this biochar with a polymer called polyethyleneimine. This modification adds a dense layer of amine groups to the surface of the carbon, which chemically bonds with formaldehyde molecules. While standard activated biochar relies mostly on physical trapping, this new composite uses a dual-action approach. The scientists found that this chemical “handshake” between the filter and the gas allows for a much faster and more thorough cleaning process. In laboratory tests, the modified material reached its maximum capacity at 256 milligrams per gram, outperforming many existing bio-based filters while maintaining a simpler production route.

Beyond just the performance metrics, the research highlights a shift toward circular economy principles. Unlike traditional activated carbons that require extreme heat during a process called calcination, this method operates at much lower temperatures, significantly reducing the carbon footprint of the manufacturing process. The team used advanced imaging and chemical analysis to confirm that the polymer was successfully embedded within the porous structure of the biochar without clogging the essential pathways needed for air to flow through. This balance of high porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More and active chemical sites makes the material a prime candidate for future use in household air purifiers.

The success of this rice husk-based filter suggests that the future of air purification may lie in the clever reuse of waste. By proving that low-cost materials can match or exceed the performance of more expensive synthetic alternatives, the study opens the door for more accessible indoor air quality management. The researchers concluded that their method is not only efficient but also economically viable for large-scale use. As the world spends more time in enclosed spaces, sustainable innovations like this provide a vital layer of protection against the invisible chemicals that often linger in our homes.

Source: Huynh, T. L., Dao, B. T. T., Le, M. T., Doan, K. A. T., Nguyen, T. D., Le, H. N., & Ha-Thuc, C.-N. (2026). Polyethyleneimine-modified activated biochar derived from rice husk ash: material development and preliminary formaldehyde adsorption study. Carbon Research, 5, Article 5.