Growth of nanostructured polycrystalline cerium oxide through a solvothermal precipitation using near-supercritical fluids.

Well-crystallized cerium dioxide with cubic phase were formed and self-assembly grown to nanofibers or nanosheets via a solvothermal precipitation from near-supercritical fluids without any help of metal catalysts or capping agents. The self-assembly attachment process without any preferred or selective orientation dominated the growth of the polycrystalline nanofibers or nanosheets consisting of grains of approximately 3 nm to which are formed by the coalescence of the single crystalline cerium oxide seeds. The growth is attributed to be driven by phase separation due to partial compatibility between ethyl alcohol and supercritical carbon dioxide fluid during the precipitation reaction, not by different surface energies or defects. With increasing temperature, the nanofibers with a weblike network structure were formed and then fused to large spherical particles. As a result, the polycrystalline fibers or sheets consisting of pure cerium dioxide phase were produced by the solvothermal reaction with an aid of the supercritical carbon dioxide from the alcoholic metal salt solution.