CVD-zirconia on fumed silica and silica gel

Two series of CVD-zirconia/silica samples were synthesised on the basis of silica gel Si-60 and fumed silica A-380 as substrates using zirconium tetrachloride chemisorbed then hydrolysed heated. The reaction cycles were repeated up to four times. Structural and adsorption characteristics of zirconia/silicas were investigated using X-ray diffraction (XRD), nitrogen adsorption-desorption, infrared (IR) and ultraviolet/visible (UV-vis) spectroscopies and quantum chemical methods. A tetragonal lattice gives the main contribution to zirconia crystallites. The size of these crystallites depends not only on the number of the reaction cycles (ir) but also on the type of a silica matrix. The zirconia crystallite size grows on zirconia deposition onto fumed silica with increasing ir, but it is near the same for zirconia/silica gel in consequence of a restricted size of pores of Si-60. The fumed silica substrate inhibits change of phase of zirconia on heating to a greater extent than the silica gel substrate. Motives of several crystalline lattices of zirconia were found after sample calcination at high temperatures. UV-vis and IR spectra of adsorbed probe compounds ((dimethylamino)azobenzene (DMAAB) and pyridine (Py)) suggest that CVD-zirconia/silica surface is characterized by several types of acidic sites.