By combining pre-oxidation with microwave activation, the researchers created abundant ultramicropores of 0.6–0.7 nm and CO₂-philic nitrogen sites, especially pyridinic and pyrrolic nitrogen. The optimized material achieved a CO₂ uptake of 4.72 mmol·g⁻¹ at 0 °C and 1 bar, and 3.33 mmol·g⁻¹ at 25 °C, while maintaining high CO₂/N₂ selectivity. This strategy offers a fast, energy-efficient and low-cost pathway for designing coal-derived adsorbents for future carbon capture applications.
Carbon dioxide capture is considered a key technology for reducing greenhouse gas emissions and supporting carbon neutrality goals. Carbon-based adsorbents have attracted broad attention because of their high surface area, chemical stability and tunable pore structures. In particular, nitrogen and oxygen doping can increase surface polarity and strengthen the interaction between carbon materials and CO₂ molecules. However, conventional furnace-based activation usually requires prolonged heating above 700 °C, which causes serious loss of nitrogen- and oxygen-containing groups and limits precise control over pore structure. These challenges highlight the need to develop faster, more controllable and more energy-efficient strategies for preparing high-performance porous carbon adsorbents.
A study (DOI:10.48130/scm-0026-0001) published in Sustainable Carbon Materials on 04 February 2026 by Xiaoxiao Meng’s & Wei Zhou’s team, Harbin Institute of Technology, reports that pre-oxidation-assisted microwave activation enables simultaneous regulation of pore architecture, heteroatom doping and CO₂ adsorption behavior in coal-derived activated carbon.
In this study, Ningdong coal was first demineralized to remove ash and inorganic impurities, producing a purified coal precursor. Part of the precursor was then pre-oxidized at 350 °C for 3 h in air to introduce oxygen-containing active sites. The researchers mixed the coal precursor with potassium hydroxide (KOH) and melamine, and then carried out microwave-assisted activation under nitrogen flow at 200, 250 or 300 W for only 10 min. The obtained activated carbons were washed, dried and compared with non-pre-oxidized controls. Multiple characterization methods were used to reveal how the structure evolved. Nitrogen adsorption–desorption analysis and scanning electron microscopy (SEM) showed that microwave activation produced a hierarchical pore network rich in micropores and ultramicropores. The optimized pre-oxidized sample, YYH-250W, displayed the most favorable pore structure, with a total pore volume of 0.55 cm³·g⁻¹. Raman spectroscopy, electron paramagnetic resonance (EPR), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) further showed that microwave irradiation increased structural defects and surface active sites, while pre-oxidation promoted nitrogen/oxygen co-doping. In the pre-oxidized series, nitrogen content increased from 7.36 at.% to 10.06 at.%, with enhanced pyridinic-N and pyrrolic-N species that act as electron-rich CO₂ adsorption sites. Adsorption tests confirmed the structural advantages. The YYH-250W sample delivered the highest CO₂ uptake, reaching 4.72 mmol·g⁻¹ at 0 °C and 3.33 mmol·g⁻¹ at 25 °C. All six samples showed CO₂/N₂ selectivity above 50, and the representative YYH-250W sample retained 97.6% adsorption efficiency after ten adsorption–desorption cycles. These results indicate that efficient CO₂ capture depends not only on surface area, but also on the combined optimization of ultramicropores, nitrogen/oxygen functional groups and surface polarity.
Overall, the study demonstrates that coupling pre-oxidation pretreatment with microwave activation can rapidly produce nitrogen/oxygen co-doped ultramicroporous coal-based activated carbons with strong CO₂ affinity, high selectivity and stable cycling performance. Compared with conventional thermal activation, the microwave route shortens the preparation process to 10 min and provides better control over both pore formation and heteroatom retention. The findings offer practical guidance for converting low-cost coal resources into functional carbon adsorbents and may support the development of scalable materials for carbon capture and separation technologies.
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References
DOI
10.48130/scm-0026-0001
Original Source URL
https://doi.org/10.48130/scm-0026-0001
Funding Information
This work was financially supported by the National Natural Science Foundation of China (Grant No. U21A2062).
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.