Morphology Control And Photocatalytic Activity Of Rare Earth Doped 3D Multi-Layer Structures Of Cerium Oxide

Cerium is one of the most important rare earth elements due to its promising optical,magnetic and electrical performance,which is attributed to cerium's 4f orbital having unpaired electrons,and the fact that cerium can react with most of the elements to form multi-valence and multi-coordination compounds.Cerium dioxide,an important rare-earth oxide,has been extensively studied due to its significant fluorite-type structure,remarkable redox properties,photocatalytic activities and prominent oxygen storage and release capacity?OSC?via facile conversion between Ce4+ and Ce3+ oxidation states.In this thesis,we fabricated cerium dioxide with porous broom-like,hedgehog-like?octahedral + nanorods composite structure?and hollow sphere three dimensional hierarchical structure.Crystal nucleation and Ostwald ripening process synergy action formation mechanism of ceria three dimensional hierarchical structures was proposed based on scanning electron microscopy?SEM?and high resolution transmission electron microscopy?HR-TEM?observation.Structure information of products were studied carried on Raman spectral,X-ray diffractometer,UV-vis spectral and X-ray photoelectric spectrometer and set up the relationship between morphology and structure.Finally,the photocatalytic properties of products were discussed through the experiments of hydrogen temperature-programmed reduction?H₂-TPR?,oxygen temperature-programmed decomposition?O₂-TPD?and photocatalytic decomposition of acetaldehyde.Different morphology,structure and photocatalytic performance were discussed in detail.The following four parts were main content in my thesis:?1?CeO₂ with a Porous broom-like morphology was fabricated though hydrothermal reaction,using cerium nitrate hexahydrate as cerium resource and dihydrate trisodium citrate as morphology controller.Hydrothermal temperature,reaction time and different stoichiometric ratio were studied in detail in order to get the optima synthesis conditions and learnt the influence of experimental on the morphology.After that,we proposed the possible formation mechanism of porous broom-like morphology.H₂-TPR and photocatalytic decomposition of acetaldehyde were examined in the photocatalytic performance of CeO₂ with a porous broom-like morphology.?2?In order to improve the photocatalytic activities of ceria further,yttrium nitrate hexahydrate as a dopant was added into the system of ceria.After analysis the changes of crystal structure,we draw that the doped was successful.The optima doping concentration was founded after systematic H₂-TPR,O₂-TPD and photocatalytic decomposition of acetaldehyde experiments and gave a reasonable explanation on enhanced photocatalytic activities after Y-doped.?3?CeO₂ with a hedgehog-like?octahedral + nanorods composite structure?morphology was fabricated though hydrothermal reaction,using cerium nitrate hexahydrate as cerium resource,yttrium as dopant and Na₃PO₄ as morphology controller.Hydrothermal temperature,reaction time and different stoichiometric ratio were studied in detail in order to get the optima synthesis condition.The influence of photocatalytic activities and photocatalytic mechanism were present after evaluated the photocatalytic properties of products.?4?CeO₂ with a hollow sphere morphology was fabricated though hydrothermal reaction,using cerium nitrate hexahydrate as cerium resource,yttrium as dopant and polystyrene microsphere as soft template.The optima experiment condition was founded at the same time.The photocatalytic mechanism of rear earth doped ceria was proposed after evaluated the photocatalytic properties of products.