Synthesis and characterization of hybrid organic/inorganic nanotubes of the imogolite type and their behaviour towards methane adsorption

Abstract

Imogolite-like nanotubes have been synthesised in which SiCH₃ groups have been introduced in place of the SiOH groups that naturally occur at the inner surface of imogolite, an alumino-silicate with formula (OH)₃Al₂O₃SiOH, forming nanotubes with inner and outer diameter of 1.0 and 2.0 nm, respectively. The new nanotubular material, composition (OH)₃Al₂O₃SiCH₃, has both larger pores and higher specific surface area than unmodified imogolite: it forms as hollow cylinders 3.0 nm wide and several microns long, with a specific surface area of ca. 800 m² g⁻¹ and intriguing surface properties, due to hydrophobic groups inside the nanotubes and hydrophilic Al(OH)Al groups at their outer surface. Adsorption of methane at 30 °C has been studied in the pressure range between 5 and 35 bar on both the new material and unmodified imogolite: it resulted that the new material adsorption capacity is about 2.5 times larger than that of imogolite, in agreement with both its larger pore volume and the presence of a methylated surface. On account of these properties and of its novelty, the studied material has several potential technical applications, e.g. in the fields of gas chromatography and gas separation.