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Spontaneous Organization of Uniform CeO 2 Nanoflowers by 3D Oriented Attachment in Hot Surfactant Solutions Monitored with an In Situ Electrical Conductance Technique
Author(s) -
Zhou HuanPing,
Zhang YaWen,
Mai HaoXin,
Sun Xiao,
Liu Qiang,
Song WeiGuo,
Yan ChunHua
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701348
Subject(s) - nanoflower , oleylamine , calcination , materials science , chemical engineering , thermal decomposition , specific surface area , nanocrystal , nanotechnology , catalysis , chemistry , nanostructure , organic chemistry , engineering
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 °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 °C in a strong redox reaction. After calcination at 400 °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 °C. The present approach has also been extended to the preparation of other transition metal oxide (CoO, NiO, and CuO x ) nanoflowers.