Controlling the Size of CeO2 Nanoparticles in Ce(NO3)3 Thermolysis

Abstract

We have developed a technique for the synthesis of CeO₂ nanopowder with the use of a powdered cellulose (PC)/Ce(NO₃)₃/NaCl composite. It comprises the following steps: preparation of PC/Ce(NO₃)₃/NaCl, burnout of the cellulose template (600°C), and removal of the sodium chloride via washing with water. Using IR and UV spectroscopies, X-ray diffraction, and electron microscopy, we have assessed the effect of sodium chloride concentration in the parent composite on the physicochemical properties of the resulting CeO₂. The material prepared from PC/Ce(NO₃)₃/NaCl consisted of two types of CeO₂ particles: particles 15–40 nm in diameter (forming irregularly shaped structures) and particles 1.5–2.2 nm in diameter. These latter formed the surface of spherical aggregates ranging in size from 30 to 200 nm. Increasing the amount of NaCl in PC/Ce(NO₃)₃/NaCl has been shown to cause an increase in the fraction of spherical aggregates in the nanopowders. The size of the spherical aggregates and that of the particles aggregated on their surface are essentially independent of the amount of sodium chloride in the parent composite. The nanopowder prepared without sodium chloride (PC/Ce(NO₃)₃) consisted of only particles of the former type. In the material prepared from PC/Ce(NO₃)₃/NaCl, cerium dioxide was present in the form of cerianite and amorphous phase. A tendency has been found for the content of the amorphous phase in CeO₂ to increase as the amount of sodium chloride in PC/Ce(NO₃)₃/NaCl increases. If the parent composite was free of NaCl, no amorphous phase was formed. No Ce(III) has been detected in the material prepared from PC/Ce(NO₃)₃/NaCl, as distinct from that prepared from PC/Ce(NO₃)₃. Increasing the amount of sodium chloride in PC/Ce(NO₃)₃/NaCl increases the thickness of the hydroxyl–hydrate shell in the nanopowder. The carbon-containing impurities identified in the nanopowders have been shown to be the result of sorption from the ambient atmosphere. The catalytic activity of CeO₂ nanopowder for hydrogen peroxide decomposition as a model reaction rises in proportion to the increase in the amount of sodium chloride in the parent composite.