Synthesis and characterisation of carbon nanotube modified anodised alumina membranes

Carbon nanotubes (CNTs) are considered as ideal model sorbent systems for studying the effect of pore size and surface characteristics on the sorption and transport properties of porous solids. In this study we synthesized CNTs on anodised alumina disks with pore sizes of 20, 100 and 200 nm. The disks were initially immersed into a nickel nitrate solution and purged with hydrogen at elevated temperatures in order to form metallic nickel nanoparticles. CNTs were thereinafter grown by CVD at 973 K using a mixture of acetylene and argon. When a nickel catalyst was involved, the CVD period adequate for CNT's growth was 15 min for all the templates. In absence of the catalyst the sufficient CVD duration was about 6 h for the 20 nm templates, while no CNT formation has been observed for the 100 and 200 nm templates during this period. Adsorption of n-hexane and relative permeability (RP) of the n-hexane/nitrogen system were applied to examine the resulting carbon nanotube membranes. Since the permeation of the non-condensable gas is governed by the Knudsen diffusion mechanism, a pore size distribution (PSD) was extracted directly from the derivative of the permeance curve against pore radii, after relating the latter with the equilibrium vapour pressure via the Kelvin equation and an accurate t-curve. These experiments were useful for the determination of the pore size distribution of the remaining open gaps of the developed membranes and gave an insight on the factors affecting the CNTs growth.