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 investigated with respect to structural ordering and morphology. Increasing the crystallisation time, in an otherwise normal MCM-41 synthesis procedure under basic conditions, results in a change of morphology from sphere shaped particles to elongated or rope-like particles. At sufficiently long crystallisation time, micrometre sized MCM-41 'ropes' made up of smaller silica nanotubes or fibres are obtained. The morphological transformation appears to occur in stages and proceeds via shorter rod-like particles which may be obtained at intermediate crystallisation time. The transformation is accompanied by increase in pore size, pore wall thickening and greater silica condensation. Tentative mechanisms for the morphology changes are proposed and discussed. (C) 2001 Elsevier Science B.V. All rights reserved.