Surface and textural properties of network-modified silica as a function of transition metal dopant zirconium

Abstract

Surface and textural properties of Zr-doped silica [xZrO2-(100 - x)SiO2] have been investigated as a function of zirconium content in the range of x = 5 to 50 (mol % Zr) via heating their respective xerogels (prepared with a novel sol-gel route developed recently) in air at 500 °C for 4 h. Nitrogen adsorption-desorption investigations (BET/BJH) on the 500 °C-heated samples show a maximum specific surface area of 484 m2g-1 at x = 20, and a minimum of 105 m2g-1 at x = 50. With increase of zirconium content, porosity of the Zr-doped silica can be tuned conveniently from the mesoporous (100 Å) to the microporous (≤ 20 Å) region with unimodal (or nearly unimodal) pore size distributions. Material issues such as thermal reactions, oxide mixing level and formation mechanisms have also been investigated with FTIR, XRD, DTA/TGA, and XPS methods. It is found that silica networks have been significantly modified with the introduction of zirconium, and crystallization of ZrO2 in the doped silica occurs only at 903-953 °C. Moreover, surface analysis shows that there is no appreciable element enrichment in the surface region, whereas significant changes in binding energies of Zr 3d, Si 2p, and O 1s have been detected. The above observations are indications that a good mixing has been attained.