In a landmark study published in Biochar X, lead author Yuanling Li and a team of researchers developed an advanced solid adsorbent using macroalgal bloom waste from Sargassum tenerrimum. Harmful macroalgal blooms threaten marine ecosystems globally and create immense volumes of unwanted organic waste. Simultaneously, hard-to-abate industrial sectors require low-cost, scalable solid adsorbents to capture atmospheric carbon dioxide without competing for terrestrial agricultural residues. To address these twin environmental challenges, the research team established a chemical tailoring method that optimizes both the internal pore architecture and surface functional chemistry of seaweed-derived biochar. By systematically evaluating pyrolysis temperatures ranging from 400 to 700 degrees Celsius alongside different chemical activation sequences, the authors demonstrated a sustainable route for turning invasive marine biomass into high-performance carbon capture media.

The primary breakthrough of the study stems from discovering the precise synergy between moderate thermal treatment and the timing of potassium hydroxide activation. Biomass pyrolyzed at higher temperatures typically loses essential oxygen-containing surface functional groups due to thermal decomposition. Conversely, lower temperatures without chemical modification produce dense carbon structures with negligible surface area. By mixing raw Sargassum biomass with potassium hydroxide prior to heating at 400 degrees Celsius, the resulting material, designated Sar-KOH, developed a vast specific surface area of 569.66 square meters per gram. Gas physisorption measurements revealed a dense network of ultra-micropores with pore widths narrower than 0.7 nanometers. These narrow pores generate overlapping adsorption potential fields that physically trap carbon dioxide molecules with exceptional efficiency.

In addition to developing structural 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, the moderate 400-degree process preserved a high concentration of basic surface functional groups. Fourier-transform infrared and X-ray photoelectron spectroscopy confirmed that Sar-KOH retained abundant surface hydroxyl groups, which act as weak basic sites. These hydroxyl groups engage in dipole interactions and hydrogen bonding with carbon dioxide, providing a weak chemical attraction that complements physical adsorption. As a result, Sar-KOH achieved a maximum carbon dioxide capture capacity of 120.5 milligrams per gram at 40 degrees Celsius, outperforming biochars modified after carbonization as well as unmodified algal samples. Kinetic testing showed that the material reached adsorption equilibrium in approximately eleven minutes, driven by favorable surface reaction rates.

Beyond raw performance, the engineered biochar demonstrated outstanding durability and climate benefits in practical evaluation scenarios. Across nine consecutive thermal regeneration cycles using a nitrogen purge at 120 degrees Celsius, Sar-KOH lost only 1.1 percent of its initial uptake capacity, retaining 98.9 percent of its functionality. Temperature-programmed desorption confirmed that the mild heating required for full regeneration keeps energy demands low compared to liquid amine scrubbers. A cradle-to-regeneration life cycle assessment further revealed that, accounting for biomass collection, thermal processing, and eighteen operational cycles, the system maintains a net negative global warming potential. The net climate benefit translates to 0.29 kilograms of carbon dioxide equivalent permanently sequestered per kilogram captured, establishing Sargassum biochar as a viable candidate for circular carbon management.

Source: Li, Y., Wang, T., Zhu, J., Duan, S., & Liu, L. (2026). Tailoring the porosity and surface chemistry of Sargassum biochar for enhanced CO2 capture. Biochar X, 2026, e021.