Properties of ceria nanoparticles with surface modified by acidic groups
The effect of the precursor and surface modification by sulfate and phosphate groups on the properties of cerium oxide was studied. The obtained materials were characterized by infrared (IR) and Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), thermogravimetric analysis (TGA) with the gas phase composition analysis, Brunauer–Emmett–Teller (BET) method, and impedance spectroscopy. The significant fraction of Се3+ ions at the surface of cerium oxide particles obtained from Ce(NO3)3 promotes the formation of double sodium cerium sulfate and cerium phosphate upon treatment with solutions of sodium hydrogen sulfate and sodium dihydrogen phosphate, respectively. The modification of ceria surface by sulfate groups leads to a decrease in specific surface area and water content of the obtained materials, as well as to a significant decrease in their proton conductivity. CeO2 samples prepared from cerium ammonium nitrate have a significantly smaller particle size and higher conductivity. Its value for cerium oxide modified with phosphate groups increases up to 3.5 × 10−4 S/cm at 65 °C. The effect of hydration degree as well as Ce^3+ content on the cerium oxides properties is discussed.