Ceria sols were synthesized by a forced hydrolysis method using cerium sulphate or cerium nitrate as precursors. High-resolution TEM was used to determine the microstructure and particle size of CeO2. A polycrystalline structure of ceria sols with crystallite sizes of 4.4 and 8.6 nm was obtained. The particles had a well-defined polyhedral shape. Direct bandgaps for ceria nanoparticles were 2.80 and 3.31 eV, respectively. The isoelectric point, pH(iep), of ceria sols in KNO3 solutions was investigated. The isoelectric point of ceria was found to be pH(iep) = 7.6 +/- 0.2. The obtained results indicate that the isoelectric point in the presence of SO42- ions shifts to lower pH value. The particle size of ceria increases with pH, reaching the maximum value at pH(iep) as the result of agglomeration. (C) 2014 Elsevier B.V. All rights reserved.