Massive blooms of Sargassum seaweed washing ashore can be transformed into a high-performance carbon-adsorption material, according to a 2026 study published in Biochar X. Researchers at Nankai University found that modifying waste Sargassum tenerrimum with potassium hydroxide (KOH) before moderate pyrolysis creates a porous biochar capable of capturing carbon dioxide efficiently while retaining nearly all its adsorption capacity after multiple reuse cycles.
Sargassum Biochar Production and KOH Activation
Transforming nuisance coastal seaweed into carbon-capture material requires precise chemical and thermal engineering, according to findings detailed in Biochar X. Researchers led by corresponding author Lina Liu of Nankai University demonstrated that raw Sargassum biomass modified with potassium hydroxide and heated to a moderate temperature of 400 °C produces an effective carbon adsorbent named Sar-KOH.
Pyrolysis thermally decomposes organic material in a limited-oxygen environment, yielding a carbon-rich solid while eliminating volatile components. The KOH treatment acts as a chemical activating agent. When applied to raw biomass before heating, the alkaline chemical interacts with the forming carbon framework to build a vast network of microscopic pores.
Did you know? Untreated Sargassum biochar produced at 400 °C has a specific surface area of just 1.14 square meters per gram. Activating the seaweed with KOH before pyrolysis expands that surface area to 569.66 square meters per gram.
Dual Adsorption Mechanism and Carbon Capture Capacity
The high-performance material achieves a carbon dioxide adsorption capacity of 120.5 milligrams per gram at 313 kelvin, substantially outperforming untreated seaweed biochars tested in the research, as reported in Biochar X. Microscopic analyses reveal that KOH activation creates abundant micropores smaller than 0.7 nanometers, which physically trap CO2 molecules through molecular confinement.
Simultaneously, the moderate 400 °C pyrolysis temperature preserves surface hydroxyl groups. These groups form hydrogen bonds with carbon dioxide, establishing a dual adsorption mechanism where micropores provide physical sites and hydroxyl groups strengthen chemical interactions. The treatment sequence is critical; applying KOH after pyrolysis yields a material with a carbon capture capacity of only 40.0 milligrams per gram.
Regeneration Stability and Rapid Gas Uptake
Practical deployment of carbon capture materials requires strong stability across repeated operational cycles. According to the study findings, Sar-KOH retains 98.9% of its original CO2 capture capacity after nine adsorption and regeneration cycles.
Furthermore, the material achieves adsorption equilibrium in approximately 11 minutes. This uptake speed compares favorably with untreated biochars evaluated in the study, which required 26 to 28 minutes to reach equilibrium. Additional work remains necessary to evaluate performance under realistic gas mixtures and to scale up production, according to the research team.
Pro Tip: Pre-treating biomass with chemical agents before thermal conversion allows the activating substance to shape the developing carbon matrix, maximizing internal pore volume compared to post-pyrolysis treatments.
Frequently Asked Questions
What is Sargassum biochar?
Sargassum biochar is a carbon-rich, porous material produced by thermally decomposing marine macroalgae under controlled, oxygen-limited conditions.
How does KOH modification improve carbon capture?
Potassium hydroxide acts as an activating agent that dramatically expands the material’s specific surface area and creates micropores smaller than 0.7 nanometers while preserving surface hydroxyl groups for chemical bonding.
What is the carbon dioxide capacity of Sar-KOH?
According to the Biochar X study, the optimized Sar-KOH material achieves a CO2 adsorption capacity of 120.5 milligrams per gram at 313 kelvin.
How durable is the seaweed-derived adsorbent?
The material retains 98.9% of its original capture capacity after nine adsorption and regeneration cycles.
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