Synthesis of micro-mesoporous TiO2 materials assembled via cationic surfactants:: Morphology, thermal stability and surface acidity characteristics

Nano-structured titanium dioxide materials were synthesized hydrothermally (TiCl4, 353 K, 5 days) via assembling through cationic surfactants in particular cetyltrimethylammonium bromide (CTAB) and cetylpyridinum bromide (CPB). The bulk chemical and phase compositions, crystalline structure, particle morphology, thermal stability and surface texturing were determined by means of X-ray powder diffractometry (XRD), Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal analyses (DTA/TGA) and N-2 sorptiometry. The acidity of synthesized materials was studied by FTIR spectroscopy of adsorbed pyridine as a probe molecule. The results revealed that the crystallites size of all materials lie in the range of 10.1-18.2 nm and organized in a morphological structure that change from nano-sized spheres to cotton fibrils shape. Surfaces thereon exposed were found to assume high specific areas (240418 m(2) g(-1)) and micro-mesoporous surfaces with pore size in the range 23.2-43.7 A. Rutile phase was only produced for all TiO2 materials assembled by cationic surfactants following heating up to 623 K. The transformation of rutile to anatase TiO2 was coincided with the developed interaction between vanadia and titania assembled by CPB template. The V in the resulting vanado-titanate was entirely incorporated in TiO2 structure. The as-synthesized phases of either rutile or anatase were maintained after calcining at 973 K exhibiting a significant thermal stability. Pyridine adsorption at RT indicated the involvement of acid-base site pair on all TiO2 assembled by cationic templates where that prepared by conventional method only exposed Lewis and Bronsted acid sites with a higher tendency to the latter comparatively. (C) 2007 Published by Elsevier Inc.