Morphological control of rod- and fiberlike SBA-15 type mesoporous silica using water-soluble sodium silicate

Well-defined rodlike and fiberlike SBA-15 mesoporous silicas have been selectively synthesized from an aqueous reaction mixture consisting of a commercial sodium silicate solution, P123 triblock copolymer and HCl. The morphologies and physicochemical properties of the products were found to be greatly affected by the shearing stress exerted by cylindrical silicated-surfactant micelles in a flowing solution, referred to hereafter as "shearing flow". Monodispersed rodlike particles ca. 0.5-mum wide and ca. 1-2-mum long were formed under static reaction conditions, whereas continuous stirring of the reaction mixture led to the formation of fiberlike silicas with lengths of several hundred micrometers and a relatively uniform width of ca. 10 mum. The effects of the synthesis conditions, such as the initial ratio of the reactants, time, temperature, and the acid source, in addition to shearing flow, on particle morphologies were investigated. Fiberlike silicas of various lengths were obtained from a relatively wide range of synthesis conditions, while monodispersed rodlike silicas were prepared under very specific conditions. Each fiberlike product was found to be comprised of a bundle of fibers, with each fiber formed by the coupling of rodlike particles of almost identical size, irrespective of different synthesis conditions.