Massive blooms of Sargassum are usually treated as a coastal crisis. When the floating seaweed washes ashore in enormous quantities, it can smother beaches, disrupt tourism and fisheries, release unpleasant odors as it decomposes, and create costly disposal challenges for coastal communities. Now, researchers have proposed a strikingly different fate for this troublesome marine biomass: transforming it into a high-performance material capable of capturing carbon dioxide. In a new experimental study, scientists converted Sargassum tenerrimum into a porous biochar whose structure and surface chemistry were carefully engineered to attract and hold CO₂ molecules.
The material’s performance depended on a deceptively simple combination of chemical treatment and controlled heating. Researchers first modified the raw seaweed with potassium hydroxide, commonly known as KOH, and then converted it into biochar through pyrolysis at 400 °C. Pyrolysis thermally decomposes organic material in a limited-oxygen environment, producing a carbon-rich solid while driving off many volatile components. The KOH treatment acted as a chemical activating agent, helping create a highly developed network of microscopic pores as the seaweed’s natural organic structure was transformed into carbon. The resulting adsorbent combined high CO₂ capacity with rapid uptake and remarkable resistance to repeated regeneration.
The best-performing sample, named Sar-KOH, captured 120.5 milligrams of carbon dioxide per gram of material at 313 kelvin. That result was substantially higher than the capacities measured for untreated Sargassum-derived biochars in the same study. More importantly, the material did not quickly lose its effectiveness after use. Following nine adsorption and regeneration cycles, Sar-KOH retained 98.9 percent of its original CO₂-capture capacity. Such stability is essential for practical carbon-capture systems, because an adsorbent must be used repeatedly rather than discarded after a single exposure to gas.
The researchers attribute the unusually strong performance to the interaction of two features: a large internal surface area and chemically active groups retained on the carbon surface. KOH activation increased the specific surface area of the 400 °C biochar to 569.66 square meters per gram, compared with only 1.14 square meters per gram for untreated biochar produced at the same temperature. This dramatic difference means that the activated material offers vastly more internal space where gas molecules can accumulate. Its pore network was especially rich in micropores, including many narrower than 0.7 nanometers, dimensions that are highly favorable for concentrating CO₂ through physical adsorption.
Pores of this scale can capture carbon dioxide through confinement and surface interactions. As CO₂ molecules enter the tiny channels, they experience attractive forces from the surrounding carbon walls, allowing them to accumulate without requiring a permanent chemical reaction. Yet the researchers found that pore volume alone could not explain Sar-KOH’s performance. Heating the biomass too aggressively can create or enlarge pores while simultaneously removing oxygen-containing functional groups from the surface. In the Sargassum biochar, the moderate 400 °C pyrolysis temperature helped preserve hydroxyl groups, which can interact with CO₂ through hydrogen bonding. The result was a dual adsorption mechanism: micropores supplied abundant physical adsorption sites, while hydroxyl groups strengthened the material’s chemical affinity for the gas.
This balance helps explain why the production sequence mattered so much. When KOH was applied after the seaweed had already been converted into biochar, the resulting material captured only 40.0 milligrams of CO₂ per gram. By contrast, treating the raw biomass before pyrolysis allowed the alkaline chemical to interact with the organic components while the carbon framework was forming. That process produced a more extensive and better-connected porous architecture. It also enabled the researchers to preserve a more favorable surface chemistry, demonstrating that the timing of activation can be just as important as the chemical used for activation.
Sar-KOH was not only effective but also fast. The material reached adsorption equilibrium in approximately 11 minutes, while the untreated biochars required between 26 and 28 minutes under the tested conditions. Rapid uptake could be valuable in systems where gas streams move continuously and adsorbents have only a short time to interact with the target molecules. After saturation, the captured CO₂ can be released during regeneration, allowing the material to be reused. The study’s high retention after nine cycles suggests that the carbon framework remains structurally stable during repeated adsorption and desorption, although much longer testing will be needed to determine how the material performs over industrially relevant lifetimes.
The findings also highlight the potential of turning a marine-waste problem into a resource for climate technology. The worldwide accumulation of Sargassum has generated interest in applications ranging from fertilizers and animal-feed ingredients to biofuels and carbon materials. Converting the seaweed into an adsorbent could offer an additional route for managing collected biomass while producing a material for emissions-control technologies. However, the approach is not yet ready to solve large-scale carbon emissions. The researchers emphasize that future work must examine how Sar-KOH behaves in realistic gas mixtures containing water vapor and other contaminants, rather than in controlled laboratory conditions. Production costs, KOH recovery, energy use, transport of wet seaweed, and regeneration requirements will also determine whether the process can compete with established commercial adsorbents.
The study, published in Biochar X, offers a broader design lesson for next-generation carbon-capture materials. Creating more pores is not necessarily enough; the most effective adsorbents may be those that combine carefully tuned pore dimensions with surface groups capable of selectively interacting with CO₂. By linking chemical activation, moderate-temperature pyrolysis and biomass waste valorization, the researchers developed a material that addresses both a coastal pollution challenge and the search for inexpensive carbon-capture technologies. Their results suggest that unwanted Sargassum blooms could become more than a symbol of environmental disruption: under the right chemical and thermal conditions, they may serve as a renewable feedstock for capturing one of the most important greenhouse gases.
Subject of Research:
Sargassum-derived biochar for carbon dioxide capture
Article Title:
Tailoring the porosity and surface chemistry of Sargassum biochar for enhanced CO₂ capture
News Publication Date:
27-Jul-2026
Web References:
https://doi.org/10.48130/bchax-0026-0019
https://www.maxapress.com/bchax
References:
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 2: e021. DOI: 10.48130/bchax-0026-0019
Image Credits:
Yuanling Li, Tao Wang, Jinyu Zhu, Siyu Duan and Lina Liu
Keywords:
Sargassum tenerrimum, biochar, carbon dioxide capture, CO₂ adsorption, potassium hydroxide activation, pyrolysis, micropores, hydroxyl groups, adsorption, carbon capture, marine biomass, waste valorization
