The journal Biochar recently published the work of Harn Wei Kua, who investigated how the internal architecture of biochar affects its ability to function as a carbon negative material. Biochar is essentially a form of charcoalCharcoal is a black, brittle, and porous material produced by heating wood or other organic substances in a low-oxygen environment. It is primarily used as a fuel source for cooking and heating.   More produced by heating organic waste such as teak wood sawdust in an oxygen free environment. While it is well known that the smallest pores in the material do most of the heavy lifting in terms of holding gas, this new research takes a closer look at the larger mesopores and macropores. Traditionally, these larger openings were thought to be mere passive tunnels that directed gas toward the smaller storage sites. However, this study reveals that their role is much more active and complex than previously assumed.

The research indicates that the roughness of these larger pore surfaces plays a vital role in slowing down carbon dioxide molecules as they travel through the material. When these molecules are slowed by the uneven surface geometry, they become more susceptible to weak physical attractions known as Van der Waals forces, which pull them from the gas stream and bind them to the sorbent. By using advanced mathematical modeling, the study found that the structural complexity of these pores, often measured as a fractal dimension, is a strong indicator of how well the material will perform. This suggests that engineers can optimize carbon capture not just by making more small holes, but by managing the texture and volume of the larger ones.

One of the most striking findings involves how high temperatures during the production process change the biochar at a microscopic level. As the pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperature increases from 300 to 1000 degrees Celsius, the total volume of the pores increases, but the total surface area actually decreases because the pores begin to merge and expand. Interestingly, when the temperature hits around 700 degrees Celsius, the internal walls of the biochar begin to develop in-foldings or tiny flakes. These structural changes can act as roadblocks, physically impeding the flow of gas into the interior of the material. This explains why the ability of gas to permeate through the biochar does not always improve simply because the material has more holes.

The study employed a sophisticated approach to measure these effects, using mercury intrusion and carbon dioxide adsorption data to validate new formulas for surface complexity. These new models proved to be more physically realistic than older versions, which often produced impossible results when applied to such geometrically complex materials. By analyzing the samples with scanning electron microscopy, the researcher was able to visualize these in-foldings and confirm why certain samples performed differently than expected. For instance, while biochar produced at 1000 degrees Celsius had the highest overall capture rate, it was the careful balance of pore volume and 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 that best predicted its success.

Ultimately, this research provides a clearer roadmap for designing better carbon filters. By understanding that the larger pores are active participants in the capture process, scientists can now look for mechanical or chemical ways to keep these pathways open and rough. The ability to accurately predict capture capacity using structural data means that different types of organic waste can be screened and processed more efficiently. This moves us a step closer to using common wood waste as a high tech tool for cleaning the atmosphere, turning a byproduct of the timber industry into a powerful weapon against global warming.

Source: Kua, H. W. (2026). Ascertaining the role of mesopores and macropores in capturing carbon dioxide in multi-hierarchical biochar sorbent: a theoretical and experimental approach. Biochar, 8(1), 33.