Activated carbon fibers (ACFs) are highly efficient adsorbents for liquid and gaseous phases due to their tunable porosity, high surface area, and rapid adsorption kinetics. While polyacrylonitrile (PAN)-based ACFs are widely studied, the fundamental mechanisms governing nitrogen transformation and porosity evolution during chemical activation remain poorly understood. This study examines the structural, mechanical, chemical, and textural modifications in nitrogen-rich PAN-derived CFs during KOH activation, utilizing nitrogen contents and functionalities as indicators of the activation process. ACFs and crushed ACFs were prepared from pure PAN fibers by stabilization, carbonization, and KOH activation with different ratios at 600–900 °C. Aggressive activation conditions drastically reduced the nitrogen content and selectively decomposed specific nitrogen functionalities: pyridinic N diminished sharply, graphitic N remained comparatively stable, and pyrrolic N and pyridone species collapsed at higher temperatures. Structural and textural analyses revealed a correlation between increased disorder and lattice change, leading to the formation of a more uniform porous network in the crushed samples. However, this enhanced porosity came at the cost of mechanical integrity, as shown by reduced tensile strength and modulus. This study clarifies the relationship between activation parameters and the final properties of PAN-ACFs, providing a foundation for the optimized synthesis of these materials.

Evolution of nitrogen functionalities in PAN-based carbon fiber during KOH activation to understand the formation of pore structure
    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials and sample preparation
        2.2 Characterization
    3 Results and discussion
        3.1 Structural and mechanical characteristics
        3.2 Chemical analysis
        3.3 Textural characteristics
        3.4 KOH activation mechanisms of PAN-based CFs by tracing nitrogen functional groups
    4 Conclusion
    References

• Sungho Lee(RAMP Convergence Research Center, Korea Institute of Science and Technology, 92 Chudong-ro Bongdong-eup, Wanju-gun, Jeonbuk 55324, Republic of Korea, Department of Nano Material Engineering, KIST School, University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea) Corresponding author
• Sora Lee(RAMP Convergence Research Center, Korea Institute of Science and Technology, 92 Chudong-ro Bongdong-eup, Wanju-gun, Jeonbuk 55324, Republic of Korea)
• Nang Kong Kham Hlaine(RAMP Convergence Research Center, Korea Institute of Science and Technology, 92 Chudong-ro Bongdong-eup, Wanju-gun, Jeonbuk 55324, Republic of Korea, Department of Chemistry, Jeonbuk National University, 567 Baekje-ro, Deokjin-gu, Jeonju-si, Jeonbuk 54896, Republic of Korea)
• Kyoungsoo Kim(Department of Chemistry, Jeonbuk National University, 567 Baekje-ro, Deokjin-gu, Jeonju-si, Jeonbuk 54896, Republic of Korea)
• May Zaw Win(Graduate School of Energy Science and Technology, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea)
• Kwang Bok Yi(Department of Chemical Engineering Education, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea)