Facile catalyst deposition using mist for fluidized-bed production of sub-millimeter-long carbon nanotubes

We developed a facile mist deposition method that yields nanometer-thick catalyst films on ceramic beads using aqueous solution of metal nitrates as a low cost catalyst precursor through two different strategies: (a) using a monolayer of a mixture of Fe(NO₃)₃ and Al(NO₃)₃ (Fe + Al) and (b) using a bilayer of Fe(NO₃)₃ on top of the mixture of Fe(NO₃)₃ and Al(NO₃)₃ (Fe/(Fe + Al)). In the fluidized bed, the catalyst precursor films were converted into Fe nanoparticles on an AlO_x layer by thermal annealing and CNTs were synthesized by chemical vapor deposition. The yield and specific surface area of the resulting CNTs were strongly influenced by the deposition methods. The bilayer deposition strategy showed an improved controllability in acquiring small catalyst particles at a high density, which obtained high yields of CNTs with large specific surface area. As a result, CNTs of 7.5 nm in diameter, triple-wall on average, and 0.6 mm in length were synthesized by employing the fluidized bed chemical vaper deposition technique, suggesting a new way for the high-yield production of long few-wall CNTs at reasonable cost.