Chemical vapor infiltration tailored hierarchical porous CNTs/C composite spheres fabricated by freeze casting and their adsorption properties

Abstract

Carbon nanotubes (CNTs) are one of the most promising candidates as adsorbents in many fields due to their unique structural characteristics. In this paper, hierarchical porous CNTs/carbon (CNTs/C) composite spheres were prepared and their strength and adsorption of vitamin B12 (VB₁₂) were investigated. The initial porous CNT spheres were fabricated by freeze casting followed by freeze drying. Afterwards, the primary porous CNT spheres were further reinforced and tailored by chemical vapor infiltration (CVI) and steam activation. Consequently, the composite CNTs/C spheres with hierarchical porous structure and high strength were successfully fabricated. SEM and polarized light microscopy observations showed that, in addition to macro-sized radial through-pores in the spheres, many micro-sized pores were distributed uniformly in the wall of the radial tunnel-like through-pores. Mercury porosimetry and BET tests indicated that the width of the radial lamellar channels was about 5–15 μm, and the average diameter of the mesopores was about 3.8 nm. Adsorption of VB₁₂ for these hierarchical porous CNTs/C spheres could reach 51.48 mg g⁻¹, which is about 3.7 and 3.4 times those of traditional activated carbon beads and macroporous resin beads, respectively.