title: Spontaneous organization of uniform CeO2 nanoflowers by 3D oriented attachment in hot surfactant solutions monitored with an in situ electrical conductance technique.
abstract: Uniform CeO(2) nanoflowers were synthesized by rapid thermolysis of (NH(4))(2)Ce(NO(3))(6) in oleic acid (OA)/oleylamine (OM), by a unique 3D oriented-attachment mechanism. CeO(2) nanoflowers with controlled shape (cubic, four-petaled, and starlike) and tunable size (10-40 nm) were obtained by adjusting the reaction conditions including solvent composition, precursor concentration, reaction temperature, and reaction time. The nanoflower growth mechanism was investigated by in situ electrical conductance measurements, transmission electron microscopy, and UV/Vis spectroscopy. The CeO(2) nanoflowers are likely formed in two major steps, that is, initial formation of ceria cluster particles capped with various ligands (e.g., OA, OM, and NO(3) (-)) via hydrolysis of (NH(4))(2)Ce(NO(3))(6) at temperatures in the range 140-220 degrees C, and subsequent spontaneous organization of the primary particles into nanoflowers by 3D oriented attachment, due to a rapid decrease in surface ligand coverage caused by sudden decomposition of the precursor at temperatures above 220 degrees C in a strong redox reaction. After calcination at 400 degrees C for 4 h the 33.8 nm CeO(2) nanoflowers have a specific surface area as large as 156 m(2) g(-1) with high porosity, and they are highly active for conversion of CO to CO(2) in the low temperature range of 200-400 degrees C. The present approach has also been extended to the preparation of other transition metal oxide (CoO, NiO, and CuO(x)) nanoflowers.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint Laboratory in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing, China.
authors.forename: Huan-Ping
authors.initials: HP
authors.lastname: Zhou
authors.forename: Ya-Wen
authors.initials: YW
authors.lastname: Zhang
authors.forename: Hao-Xin
authors.initials: HX
authors.lastname: Mai
authors.forename: Xiao
authors.initials: X
authors.lastname: Sun
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
authors.forename: Wei-Guo
authors.initials: WG
authors.lastname: Song
authors.forename: Chun-Hua
authors.initials: CH
authors.lastname: Yan
mesh_terms: D002384:Catalysis; D002563:Cerium / Q000737:chemistry*; D004553:Electric Conductivity; D046529:Microscopy, Electron, Transmission; D049329:Nanostructures; D013501:Surface-Active Agents / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D013501:Surface-Active Agents; D002563:Cerium; C030583:ceric oxide