Biochar is widely studied as a low cost material that can remove carbon dioxide from the atmosphere. Scientists have long believed that only the smallest pores in biochar play the main role in capturing carbon dioxide molecules. A new study now challenges this assumption by showing that larger pores may contribute more actively to carbon capture than previously thought.
The research, published in the journal Biochar, examines how different pore structures in biochar affect its ability to capture carbon dioxide. The study combines theoretical modeling with experimental measurements to analyze the behavior of micropores, mesopores, and macropores in biochar produced at different temperatures.
Biochar is a carbon rich material produced when biomass such as wood waste is heated in a low oxygen environment. Because the carbon contained in the original biomass becomes stabilized in the solid material, biochar has been considered a potentially carbon negative material. When used as a sorbent that captures additional carbon dioxide, its climate benefits may increase further.
Most previous studies have assumed that micropores, which are extremely small pores less than about one nanometer in diameter, are responsible for most carbon dioxide adsorption. Larger pores, known as mesopores and macropores, have generally been considered passive channels that allow gas molecules to move toward the smaller pores.
The new research revisits this idea by developing improved mathematical models to describe the complex surfaces inside biochar pores. The study analyzes sawdust feedstock and biochar samples produced at temperatures ranging from 300 to 1000 degrees Celsius. The researchers measured pore properties using techniques including mercury intrusion porosimetry and carbon dioxide adsorption experiments.
"Our findings show that the larger pores in biochar are not merely passageways," said the study's author. "Their geometry and internal surface roughness can directly influence how carbon dioxide molecules interact with the material."
The results show that carbon dioxide capture increases significantly with higher pyrolysis temperatures. Biochar produced at 1000 degrees Celsius captured up to about 3.82 millimoles of carbon dioxide per gram of sorbent, compared with about 1.26 millimoles per gram for biochar produced at 300 degrees Celsius.
The study also found strong correlations between carbon dioxide capture and several pore related properties, including micropore volume, micropore surface area, and fractal surface geometry. While micropores remain the dominant adsorption sites, the structure and roughness of mesopores and macropores also influence the process.
Microscopic imaging revealed that high temperature biochar develops complex pore surfaces with folds and irregular structures. These features can slow the movement of carbon dioxide molecules inside the material, increasing the chance that the molecules are captured through physical adsorption forces.
"Our work suggests that optimizing the full pore hierarchy of biochar could improve its performance as a carbon capture material," the author said. "Designing biochar with the right combination of micropores, mesopores, and macropores may allow us to develop more efficient and affordable sorbents."
Beyond improving carbon capture technologies, the findings may also help guide future design of porous materials used in environmental remediation, energy systems, and gas separation.
As countries seek scalable solutions to reduce atmospheric carbon dioxide, materials derived from biomass waste such as biochar could play an important role. By revealing how the internal structure of biochar affects carbon capture, the study provides new insights into how these materials can be engineered for greater climate benefits.
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Journal Reference: Kua, H.W. Ascertaining the role of mesopores and macropores in capturing carbon dioxide in multi-hierarchical biochar sorbent: a theoretical and experimental approach. Biochar 8, 33 (2026).
https://doi.org/10.1007/s42773-025-00549-w
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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.
