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<p>Polyacrylonitrile (PAN)-based activated carbon fibers are renowned for their exceptional adsorption properties, with precise pore structure control being critical for enhancing adsorption selectivity. This study, for the first time, employs high-intensity synchrotron radiation small-angle X-ray scattering (SAXS) to investigate the carbonization and activation processes of PAN-based pre-oxidized fibers under a carbon dioxide (CO<sub>2</sub>) atmosphere, quantitatively characterizing pore structure evolution from the nanometer to mesoscopic scale. During the carbonization stage, the pore long and short axes reached their maximum and minimum values at 550&#xa0;°C and 400&#xa0;°C, respectively. The activation process was found to proceed in distinct stages. In the early stage, the proportion of micropores (approximately 1.4&#xa0;nm) reached its maximum of 86.9% at 70&#xa0;min of activation, which is ideal for size-selective applications. However, subsequent adsorption tests with p-nitrophenol (PNP) and methylene blue (MB) revealed that maximum adsorption capacity occurred at a much later activation time (~ 210&#xa0;min), a point corresponding to the highest total accessible surface area before structural collapse. Over-activation beyond this point led to a drastic loss in performance. This study provides a quantitative understanding of pore formation and evolution, demonstrating how activation time can be precisely controlled to optimize for either adsorption selectivity or total capacity, thus offering a crucial foundation for designing fit-for-purpose materials.</p>

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In-situ SAXS study on pore structure evolution during carbon dioxide activation of PAN-based pre-oxidized fibers

  • 期刊论文

  • 发表日期：

    2025年9月4日

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  • Zhuang Li,
  • Guiquan Guo,
  • Zhihong Li,
  • Yanjun Gong,
  • Lili Dong,
  • Dongfeng Li

摘要

Polyacrylonitrile (PAN)-based activated carbon fibers are renowned for their exceptional adsorption properties, with precise pore structure control being critical for enhancing adsorption selectivity. This study, for the first time, employs high-intensity synchrotron radiation small-angle X-ray scattering (SAXS) to investigate the carbonization and activation processes of PAN-based pre-oxidized fibers under a carbon dioxide (CO2) atmosphere, quantitatively characterizing pore structure evolution from the nanometer to mesoscopic scale. During the carbonization stage, the pore long and short axes reached their maximum and minimum values at 550 °C and 400 °C, respectively. The activation process was found to proceed in distinct stages. In the early stage, the proportion of micropores (approximately 1.4 nm) reached its maximum of 86.9% at 70 min of activation, which is ideal for size-selective applications. However, subsequent adsorption tests with p-nitrophenol (PNP) and methylene blue (MB) revealed that maximum adsorption capacity occurred at a much later activation time (~ 210 min), a point corresponding to the highest total accessible surface area before structural collapse. Over-activation beyond this point led to a drastic loss in performance. This study provides a quantitative understanding of pore formation and evolution, demonstrating how activation time can be precisely controlled to optimize for either adsorption selectivity or total capacity, thus offering a crucial foundation for designing fit-for-purpose materials.