Hydrothermally-induced morphological transformation of mesoporous MCM-41 silica

The effect of increasing the time allowed for hydrothermal crystallisation during high temperature (150 degreesC) synthesis of MCM-41 has been investi gated with respect to structural ordering and morphology. Increasing the cr ystallisation time, in an otherwise normal MCM-41 synthesis procedure under basic conditions, results in a change of morphology from sphere shaped par ticles to elongated or rope-like particles. At sufficiently long crystallis ation time, micrometre sized MCM-41 'ropes' made up of smaller silica nanot ubes or fibres are obtained. The morphological transformation appears to oc cur in stages and proceeds via shorter rod-like particles which may be obta ined at intermediate crystallisation time. The transformation is accompanie d by increase in pore size, pore wall thickening and greater silica condens ation. Tentative mechanisms for the morphology changes are proposed and dis cussed. (C) 2001 Elsevier Science B.V. All rights reserved.