Controllable pore structures of pure and sub-millimeter-long carbon nanotubes

We report the controllable pore structures of pure (>99.5 wt%) and sub-millimeter-long single-walled and few-walled (triple-walled on average) carbon nanotubes (SWCNTs and FWCNTs, respectively) synthesized via fluidized-bed chemical vapor deposition. The pore structures and adsorption properties of the CNTs were characterized using N₂ adsorption analysis at 77 K. A significant advantage of the synthesized vertically-aligned SWCNTs (diameter range: 2–4 nm) and FWCNTs (diameter range: 4–8 nm) arrays, having small bundle structures, is that the guest molecules can easily access the external surfaces of the CNTs, leading to high specific surface areas (SSAs; 903 and 337 m² g⁻¹, respectively) and pore volumes (2.56 and 2.05 mL g⁻¹, respectively). Interestingly, following sonication, the SSAs of the SWCNTs and FWCNTs increased by 36% and 41%, respectively. Additionally, after mixed acid (HNO₃/H₂SO₄) treatment, the SSAs of the SWCNTs and FWCNTs increased by 34% and 120%, respectively, which are attributed to the corresponding increases in the micropore and mesopore SSAs. These results suggest that CNT networks with controllable pore structures can be fabricated by altering the diameter distribution and alignment degree of the CNTs, thus highlighting the potential of our approach to develop cost-effective CNT-based structures for applications such as high-performance energy storage materials.