A simple room-temperature synthesis of mesoporous silica rods with tunable size and porosity

The morphology and textural characteristics of mesoporous silicas formed in the modified Stöber media with reactant ratios of 1TEOS:19.9EtOH:xH₂O:10.4NH₃·H₂O: 0.3CTAB (x = 0~2,973) have been investigated by SEM, small angle XRD, and N₂-sorption measurements. The results show that when the reaction mixture is simply diluted with water, a series of morphologically different silicas are formed in the order of: microspheres → irregular particles → rectangular rods → round nanorods. The microspheres are formed when the water ratio ranges from 0 to 124, whereas nanorods are dominant in the products when the water ratios are larger than 372. It is demonstrated that the size of the nanorods decreases with the increase of water. Except the sample synthesized without water, all the other samples are mesoporous. The mesopores in the nanorods become larger, but more and more disordered with increasing the amounts of water. Based on the experimental results, the mechanism of the morphological transformations is proposed. Finally, the dye adsorption behavior of the nanospheres and the nanorods was tested and compared.