The growth of carbon nanotubes at the channel ends of the SAPO4-5 zeolite structures

The growth of carbon nanotubes (CNTs) were evidently observed, at the channel ends of the mesoporous SAPO4-5 zeolites. The Fe-catalyst SAPO4-5 crystallites prepared by the sol–gel method were employed to the thermal CVD process, at a temperature ∼650 °C for 30 min, using the mixture of acetylene and ammonia gases. The recorded SEM images show the formation of well aligned MWNTs at the channel ends of the crystallites. The analysis of HRTEM shows that, the outer diameter of CNTs varies in the range of 25–27 nm, whereas, the inner diameter varies in the range of 14–17 nm. The diameter of the CNTs was found to be varied marginally as compared to that of the channel diameter of the SAPO4-5 crystallite. Furthermore, the observed formation of CNTs, along the ab-plane, could either be originated at a depth from the channels or at the channel ends of the crystallites. Although the former is attributed to the precipitation of the Fe-catalyst in the channels, the later is thought to be due to the out diffusion and clustering of Fe-atoms near the channel ends of the crystallites. The recorded micro-Raman spectrum showed the small ratio of, I(D)/I(G), which suggest that, the synthesized tubes are of high quality with less amount of defects.