Preparation of Mesoscale and Macroscale Silica Nanotubes Using a Sugar-Appended Azonaphthol Gelator Assembly

Sugar-appended azonaphthol derivatives 1 possessing an aromatic hydroxyl group and 2 possessing the n-butanoyloxy group were synthesized and proved to be capable of gelating water/ethanol mixtures. Gels formed by gelator 1 displayed different morphologies depending on the gelator concentration. The aqueous gel formed by 3.0 wt % of 1 consisted of crystalline fibers with thicknesses ranging from 400 to 600 nm, whereas at lower a concentration of gelator 1 (0.1 wt %) the gel consisted of a three-dimensional network of fibers with thicknesses of 20 to 30 nm. These gels were subjected to the sol-gel polymerization process, using tetraethoxysilane (TEOS). Interestingly, the obtained silica consisted of nanotubular structures with inner diameters of 20-25 nm and 450-600 nm using two different gels of 1, respectively. These results prove that the diameter size of silica nanotubes can be controlled by varying the gelator concentration.