We investigated the effects of supercritical-CO2 treatment on the pore structure and consequent H2 adsorption behavior of single-walled carbon nanohorns (SWCNHs) and SWCNH aggregates. High-resolution transmission electron microscopy and adsorption characterization techniques were employed to elucidate the alterations in the SWCNH morphology and aggregate pore characteristics induced by supercritical-CO2 treatment. Our results confirm that supercritical-CO2 treatment reduces the interstitial pore surface area and volume of SWCNH aggregates, notably affecting the adsorption of N2 (77 K), CO2 (273 K), and H2 (77 K) gasses. The interstitial porosity strongly depends on the supercritical-CO2 pressure. Supercritical-CO2 treatment softens the individual SWCNHs and opens the core of SWCNH aggregates, producing a partially orientated structure with interstitial ultramicropores. These nanopores are formed by the diffusion and intercalation of CO2 molecules during treatment. An increase in the amount of H2 adsorbed per interstitial micropore of the supercritically modified SWCNHs was observed. Moreover, the increase in the number and volume of ultramicropores enable the selective adsorption of H2 and CO2 molecules. This study reveals that supercritical-CO2 treatment can modulate the pore structure of SWCNH aggregates and provides an effective strategy for tailoring the H2 adsorption properties of nanomaterials.

Effects of supercritical-CO2 treatment on the pore structure and H2 adsorptivity of single-walled carbon nanohorns
    Abstract
    1 Introduction
    2 Experimental
    3 Results and discussion
    4 Conclusions
    Acknowledgements 
    References

• Nam Ryeol Kim(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), Jeollabuk‑do, Wanju 55324, Republic of Korea, Department of Polymer Engineering, Graduated School and School of Polymer Science and Engineering, Chonnam National University, Gwangju 61186, Republic of Korea)
• Jae‑Hyung Wee(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), Jeollabuk‑do, Wanju 55324, Republic of Korea)
• Chang Hyo Kim(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), Jeollabuk‑do, Wanju 55324, Republic of Korea)
• Dong Young Kim(Convergence Research Division, Korea Carbon Industry Promotion Agency (KCARBON), Jeollabuk‑do, Jeonju 54852, Republic of Korea)
• Katsumi Kaneko(Research Initiative for Supra‑Materials, Shinshu University, Wakasato, Nagano 380‑8553, Japan)
• Cheol‑Min Yang(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), Jeollabuk‑do, Wanju 55324, Republic of Korea) Corresponding author