Preparation and formation mechanism of nano-sized MnOx–CeO2 hollow spheres via a supercritical anti-solvent technique

Manganese and cerium composite oxide (MnOx–CeO2) hollow nanospheres were successfully prepared by precipitating manganese acetylacetonate and cerium acetylacetonate from their mixed methanol solution using supercritical carbon dioxide as an anti-solvent. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the precursor and as-prepared MnOx–CeO2. XRD analysis reveals the cubic fluorite structure of the MnOx–CeO2. HRTEM results indicate that the MnOx–CeO2 hollow spheres have an average diameter of about 50 nm, and a wall thickness of 10–20 nm. A new formation mechanism of these nano-sized hollow spheres has also been proposed based on the experimental results.