Massive blooms of Sargassum can create serious environmental and economic problems when the seaweed accumulates along coastlines. A new study suggests that this troublesome marine biomass could instead become a useful resource for capturing carbon dioxide.
Researchers have developed a porous biochar from Sargassum tenerrimum that combines high CO2 adsorption capacity, rapid uptake, and strong regeneration stability. The key was modifying the seaweed with potassium hydroxide, or KOH, before converting it to biochar at a moderate temperature of 400 °C.
"Our results show that waste Sargassum can be transformed into a highly effective carbon adsorbent when its pore structure and surface chemistry are engineered together," said corresponding author Lina Liu of Nankai University. "The important point is not simply creating more pores. We also need to preserve the surface chemical groups that interact with CO2."
The study, published in Biochar X, examined how pyrolysis temperatures from 400 to 700 °C and different sequences of KOH modification affected the properties of Sargassum-derived biochar.
The best-performing material, called Sar-KOH, was produced by treating the raw seaweed with KOH before pyrolysis at 400 °C. It achieved a CO2 adsorption capacity of 120.5 mg per gram at 313 K, substantially higher than the untreated biochars tested in the study. After nine adsorption and regeneration cycles, the material retained 98.9% of its original capacity.
Microscopic and surface analyses helped explain the performance. KOH activation dramatically increased the biochar's specific surface area to 569.66 m²/g, compared with only 1.14 m²/g for untreated biochar produced at 400 °C. The resulting material contained a highly developed network of micropores, including abundant pores smaller than 0.7 nanometers.
These extremely small pores are particularly favorable for physically trapping CO2 molecules. At the same time, using the relatively moderate pyrolysis temperature of 400 °C helped preserve hydroxyl groups on the biochar surface. These groups can interact with CO2 through hydrogen bonding.
The researchers therefore identified a dual adsorption mechanism: micropores provide abundant sites for physical adsorption, while hydroxyl groups strengthen chemical interactions with CO2.
The sequence of treatment proved especially important. Applying KOH after the seaweed had already been converted to biochar produced a material with a CO2 capacity of only 40.0 mg/g. Treating the biomass before pyrolysis allowed KOH to interact more effectively with the carbon structure as it formed, creating a much more extensive porous network.
Sar-KOH also captured CO2 quickly, reaching adsorption equilibrium in approximately 11 minutes, compared with 26 to 28 minutes for untreated biochars.
Beyond carbon capture, the approach offers a potential route for making productive use of marine biomass associated with harmful macroalgal blooms. Instead of treating collected Sargassum solely as waste, it could serve as a renewable feedstock for carbon-based adsorbents.
The researchers note that additional work is still needed before practical deployment, including evaluating performance under realistic gas mixtures and optimizing material production and regeneration at larger scales.
By linking waste valorization with carbon capture, the study provides a strategy for designing sustainable adsorbents while addressing an increasingly visible marine biomass problem.
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Journal reference: 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
https://www.maxapress.com/article/doi/10.48130/bchax-0026-0019
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About the Journal:
Biochar X (e-ISSN: 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
