Control of mesostructured silica particle morphology.pdfVIP

Control of mesostructured silica particle morphology Henry B. S. Chan,a Peter M. Budd*a and Timothy deV. Naylorb aDepartment of Chemistry, University of Manchester, Manchester, UK M13 9PL. E-mail: Peter.Budd@man.ac.uk bSmart Chemical Company Ltd., Unit 5, Blatchford Road, Horsham, W. Sussex, UK RH13 5QR Received 14th July 2000, Accepted 19th December 2000 First published as an Advance Article on the web 30th January 2001 The formation of mesostructured silica was investigated using acidic conditions with tetraethoxysilane (TEOS) as the silica precursor and cetyltrimethylammonium bromide (CTAB) as the structure directing agent. A synthesis mixture of composition 2.2TEOS : 1.1CTAB : 75HCl : 1000H2O gave a well ordered material exhibiting a range of particle shapes from extended rope-like structures of hexagonal cross-section to gyroid structures. Addition of monomethyltriethoxysilane (MTES) or tetrahydrofuran (THF) to the synthesis mixture gave rise to spherical particles. Studies of particle development showed initial growth of gel-like particles within which the mesostructure developed. A new model is proposed for the formation of mesostructured precipitates in which (1) growth of inorganic oligomers gives rise to a thermodynamically unstable mixture, (2) phase separation occurs giving droplets of a second liquid (or liquid crystal) phase rich in oligomer and surfactant, (3) the droplets are colloidally stabilized, (4) microphase separation occurs within the droplets, giving rise to a mesostructure and (5) further polymerization ?xes the mesostructure. Introduction Zeolites and other microporous materials, which have regular arrays of pores and channels with dimensions v2 nm, ?nd extensive use in catalysis and as ion exchangers and selective adsorbents. The challenge in recent years has been to extend the range of ordered nanoporous materials into the mesopore size range (2±10 nm) for application in separations and reactions involving large molecules, as chromatogra