TECHNIQUE FOR DETERMINATION OF SURFACE FRACTAL DIMENSION AND MORPHOLOGY OF MESOPOROUS TITANIA USING DYNAMIC FLOW ADSORPTION AND ITS CHARACTERIZATION

ABSTRACT Received September 17, 2008Accepted March 3, 2009 . A technique to determine the surface fractal dimension of mesoporous Ti02 using a dynamic flow adsorption instrument is described. Fractal dimension is an additional technique to characterize surface morphology. Surface fractal dimension, a quantitative measurement of surface ruggedness, can be determined by adsorbing a homologous series of adsorbates onto an adsorbent sample of mesoporous Ti02. Titania wet gel prepared by hydrolysis of Ti-alkoxide was immersed in the flow of supercritical C02 at 60 °C and the solvent was extracted. Mesoporous Ti02 consists of anatase nano-particles, about 5nm in diameter, have been obtained. After calcination at 600. °C the average pore size of tM extracted gel, about 20nm in diameter, and the pore volume, about 0.35cm3i\u27, and the specific surface area, about 58 m2g\u271. Using the N2 adsorption isotherm, the surface fractal dimension, Os, has been estimated according to the Frenkel-Halsey-Hill (FHH) theory. The N2 adsorption isotherm for the as-extracted aerogel indicates the mesoporous structure.. Two linear regions are found for the FHH plot of the as-extracted aerogel. The estimated surface fractal dimensions are about 2.49 and 2.68. Both of the Os values indicate rather complex surface morphology. The TEM observation shows that there are amorphous and crystalline particles. Two values of Os may be attributed to these two kinds of particles. The two regions are in near length scales, and the smaller Os, Os =2.49, for the smaller region. This result indicates that there are two kinds of particles, probably amorphous and anatase particles as shown by the TEM observation