Single-walled carbon nanotubes prepared in small AlPO4-5 and CoAPO-5 molecular sieves by low-temperature hydrocracking

Abstract

Single-walled carbon nanotubes (SWNTs) were prepared in the channels of small AlPO4-5 and cobalt-incorporated AlPO4-5 (CoAPO-5) crystals (4–6 μm in diameter and 10–30 μm in length), by hydrocracking at 350 °C. The effects of Co content in the precursor gel and carbon density of the structure-directing agent on the resulting SWNTs were investigated. The results of high-resolution transmission electron microscopy and polarized Raman scattering indicated that SWNTs formed in the channels of AlPO4-5 and CoAPO-5 crystals, after hydrocracking for 10 h at 350 °C. The SWNTs were 0.4 nm in diameter, and possessed well-defined symmetry. When the Co/Al ratio of the precursor gel was 0.075, the relative intensity ratio of Raman D to G band (ID/IG) was 0.286, and the weight loss (500–700 °C) of the SWNTs formed in CoAPO-5 was 3.27 wt%. This Co/Al ratio yielded the lowest obtained ID/IG value and the highest weight loss of SWNTs, which indicated the lowest amorphous carbon density and the highest SWNT quantity. The density and quantity of SWNTs in the AlPO4-5 crystals increased when the structure-directing agent was changed from triethylamine to tripropylamine, because of the higher carbon content of the latter's unit cell. Low-temperature hydrocracking can be used to prepare SWNTs in the channels of AlPO4-5 and CoAPO-5 crystals, even for small low-quality crystals.