Potassium-enhanced biochar unlocks new pathway to remove harmful nitrogen dioxide from air
image: Density functional theory study on the microscopic mechanism of NO2 adsorption and reduction by potassium-doped biochar: the key role of the active sites
Credit: Tong Hao, Qian Zhou, Jinyuan Jiang, Haoyang Song, Yiting Pan & Dongni Shi
Air pollution caused by nitrogen dioxide is a growing global health concern, but new research suggests that a simple modification to biochar could significantly improve its ability to capture and neutralize this harmful gas.
“We found that adding potassium fundamentally changes how biochar interacts with nitrogen dioxide at the molecular level, making the reaction faster and more efficient,” said the study’s corresponding author.
Nitrogen dioxide, a key component of air pollution from vehicles and industrial emissions, contributes to respiratory disease and the formation of fine particulate matter and ground-level ozone. The World Health Organization recently tightened its recommended exposure limits, highlighting the urgent need for better control technologies.
Biochar, a carbon-rich material produced from biomass, has emerged as a promising low-cost option for capturing pollutants. Its porous structure and abundant surface sites allow it to adsorb gases, but the detailed reaction mechanisms have remained unclear. In this study, researchers used advanced computational modeling to uncover how potassium improves biochar’s performance.
Using density functional theory, the team simulated how nitrogen dioxide molecules interact with biochar surfaces at the atomic level. Their results show that two nitrogen dioxide molecules are sequentially adsorbed and then converted into less harmful products, including nitric oxide and carbon dioxide. The process involves several key steps, including bond breaking, molecular rearrangement, and gas release.
The addition of potassium plays a crucial role in accelerating these reactions. It lowers the energy barriers required for breaking nitrogen oxygen bonds and promotes the release of reaction products. As a result, the overall reaction becomes both thermodynamically more favorable and kinetically faster.
Importantly, the researchers found that potassium’s effect depends strongly on distance. Its influence extends only within a nanoscale range of about 0.6 nanometers. Within this range, potassium enhances adsorption and reaction rates, but beyond it, the effect diminishes. This finding provides new insight into how active sites on biochar surfaces should be designed and distributed.
The study also reveals that the structure of the biochar surface matters. Edges with certain atomic configurations, such as zigzag structures, show stronger adsorption and higher reactivity compared to other configurations. These structural differences influence how nitrogen dioxide molecules bind, react, and ultimately transform into other compounds.
Beyond improving adsorption, the presence of potassium increases both the maximum achievable reaction rate and the overall efficiency of pollutant removal. This suggests that carefully engineered biochar materials could be tailored for high-performance air purification applications.
By combining detailed molecular simulations with thermodynamic and kinetic analysis, the research provides a clearer picture of how biochar works at the smallest scales. These insights can guide the development of next-generation materials for controlling air pollution.
As cities continue to struggle with rising nitrogen dioxide levels, such advances could offer practical and scalable solutions. Modified biochar, derived from abundant biomass resources, may become an important tool in reducing emissions and improving air quality.
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Journal Reference: Hao, T., Zhou, Q., Jiang, J. et al. Density functional theory study on the microscopic mechanism of NO2 adsorption and reduction by potassium-doped biochar: the key role of the active sites. Biochar 7, 67 (2025).
https://doi.org/10.1007/s42773-025-00449-z
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.