A team of researchers has announced a breakthrough in carbon dioxide (CO2) capture technology, unveiling a novel biochar material synthesized from corn straw using a microwave-assisted, two-step chemical activation strategy. This innovative approach, published in Sustainable Carbon Materials, promises a low-cost, scalable solution for addressing global greenhouse gas emissions and advancing climate change mitigation efforts.
As atmospheric CO2 levels continue to rise, reaching 422.5 ppm globally in 2024, the urgent need for effective capture and sequestration technologies has become more apparent. Traditionally, methods such as amine scrubbing have been employed to remove CO2 from industrial flue gases but suffer from high energy demands, chemical degradation, and expensive equipment maintenance. In contrast, solid-phase adsorbents like activated carbon and biochar have emerged as promising alternatives, offering greater stability and economic viability.
Biochar, a porous carbon-rich material produced by thermochemically converting biomass waste, is particularly attractive for its environmental benefits. Its production is carbon-negative, meaning it naturally sequesters atmospheric carbon during manufacture. However, performance limitations related to pore structure and adsorption kinetics have prevented biochar from matching the efficiency of conventional activated carbons.
In this study, scientists developed a unique two-step activation protocol combining preliminary phosphoric acid activation with potassium hydroxide etching, all driven by microwave pyrolysis. The process allows precise control over the material's mesopore proportion, which is crucial for balancing CO2 adsorption capacity and kinetic efficiency. By optimizing the ratio of phosphoric acid to biomass during synthesis, the research team demonstrated that their biochar, labeled PKBC-3, achieved a remarkably high specific surface area of 3,038.92 square meters per gram and a micropore volume of 1.089 cubic centimeters per gram.
Crucially, PKBC-3 reached a maximum CO2 adsorption capacity of 3.434 millimoles per gram at room temperature and standard atmospheric pressure—placing it among the top performers compared to other biomass-derived adsorbents. Furthermore, dynamic breakthrough experiments revealed that when the mesopore proportion was carefully tuned to around 40 percent, the material achieved rapid adsorption kinetics with a dynamic capacity of 3.02 millimoles per gram. This optimal mesopore design enabled CO2 molecules to swiftly diffuse into micropore sites for effective capture.
The authors say their findings resolve a long-standing trade-off in biochar design. Traditionally, increasing micropore volume improved total adsorption capacity but hindered mass transfer rates, while boosting mesopore volume enhanced kinetics but risked reducing overall capacity. By establishing a threshold for the ideal mesopore proportion, the research provides new criteria for engineering biochars that unite high capacity with efficient kinetics.
"Our approach allows for the targeted construction of hierarchical porous networks within biochar, maximizing both capacity and performance," the authors explained. "This strategy holds significant promise for industrial applications in carbon capture and climate mitigation."
The team plans to further scale up their process for industrial flue gas treatment and investigate surface modifications to boost selectivity for CO2 over other gases. The work was supported by the National Natural Science Foundation of China and the Heilongjiang Provincial Key Research and Development Program.
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Journal reference: Qiu T, Cao W, Xie K, Ahmad F, Zhao W, et al. 2025. CO2 capture performances of H3PO4/KOH activated microwave pyrolyzed porous biochar. Sustainable Carbon Materials 1: e004 https://www.maxapress.com/article/doi/10.48130/scm-0025-0004
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About Sustainable Carbon Materials :
Sustainable Carbon Materials is a multidisciplinary platform for communicating advances in fundamental and applied research on carbon-based materials. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon materials around the world to deliver findings from this rapidly expanding field of science. It is a peer-reviewed, open-access journal that publishes review, original research, invited review, rapid report, perspective, commentary and correspondence papers.
