Hydrothermal synthesis and mechanism of triangular prism-like monocrystalline CeO2 nanotubes via a facile template-free hydrothermal route

Monocrystalline CeO2 tablet-like nanostructures and triangular prism-like nanotubes were synthesized by thermal conversion of cerium carbonate hydroxide (CeOHCO3) precursors prepared by a simple template-free hydrothermal method using Ce(NO3)(3)center dot 6H(2)O as cerium source, CO(NH2)(2) as both precipitator and carbon source and polyvinylpyrrolidone (PVP) as surfactant. X-ray diffractometer (XRD) images inferred that the as-synthesized Ce(CO3)(OH) has a hexagonal structure, and the CeO2 obtained by calcining the Ce(CO3)(OH) at 500 degrees C for 5 h has a cubic fluorite structure. Scanning electron microscope (SEM) was employed to reveal the transformation from tablet-like to triangular prism-like structures, and then to triangular prism-like nanotubes with the increase of temperature from 120 up to 200 degrees C. Monocrystalline structure was revealed by high resolution transmission electron microscope (HRTEM) and select area electron diffraction (SAED) patterns. The thermal decomposition process of the as -synthesized Ce(CO3)(OH) was investigated by thermo-gravimetric differential thermal analysis (TG-DTA) apparatus, and the possible formation mechanism of CeO2 has been discussed. The spectral properties were characterized by Fourier transform infrared spectrum (FT-IR), Raman scattering, Photoluminescence (PL) spectra and UV-vis spectroscopy. There is a red-shifting in the band gap of the material compared to bulk one, which is mainly attributed to the influences of the Ce3+ ions, oxygen vacancies and the change of morphology. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.