Synthesis and rheological properties of mesoporous nanocrystalline CeO2 via sol-gel process

Cubic-phase CeO2 with high surface area was prepared using sol-gel process. The effect of sol-gel parameters, viz. HCl:alkoxide and water:alkoxide molar ratios, indicated that the gelation time increased with acid concentration and the lowest gelation time was found at 55 water:alkoxide molar ratio. The XRD patterns of cerium dioxide at different calcination temperature (300-800degreesC) and times (1-7h) showed increasing crystallinity as a function of temperature and time, while the scanning electron microscope (SEM) micrographs showed the agglomeration of crystallites to form large particle cerium dioxide at higher calcination temperatures. The Brunauer-Emmett-Teller (BET) specific surface area increased with decreasing the HCl:alkoxide and water:alkoxide molar ratios, calcination temperature and time. The highest surface area was obtained at 0.8:1:55 HCl: alkoxide: water molar ratio and 400degreesC calcination for 1 h (180 m(2)/g). The viscoelastic properties of different HCl:alkoxide ratio solutions were studied using oscillatory shear. The fractal dimension determined from the frequency-scaling exponent of the modulus at the gel point indicated a dense critical gel structure at high HCl ratio and tight structure at low amount of acid. The get strength increased as a function of acid molar ratio and the 0.8 molar ratio gave the highest gel strength. (C) 2004 Elsevier B.V. All rights reserved.