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Three dimensional (3D) of CeO2 nanostructures such as convex lens-like, hollow triangular prism, broccolilike, grapelike CeO2 have been successfully synthesized by cerium carbonate hydroxide (CeOHCO3) precursors, which were prepared by a hydrolysis process followed by a facile hydrothermal method without using any template or surfactant. The influence of urea amount on CeO2 nanostructures was discussed. The synthesizing mechanism and the morphological evolution of CeOHCO3 and CeO2 were proposed. The CeO2 samples were examined by XRD, SEM, TEM, UV–Vis, PL, and Raman scattering. The UV–Vis absorption spectrum of the CeO2 samples showed that the band gap energy (Eg) in rang of 2.6–2.9 eV, which is lower than that of bulk ceria.

Gear-like CeO 2 microstructures have been successfully synthesized by a CTAB (cetyltrimethyl ammonium bromide)-assisted hydrothermal method using Ce(NO 3 ) 3 ·6H 2 O as the cerium source and ammonium hydrogen carbonate as the precipitator. X-ray diffraction (XRD) inferred that the synthesized CeO 2 microstructures exhibited a fluorite cubic structure. A scanning electron microscope (SEM) revealed that the CeO 2 microstructures have a gear-like microstructure. X-ray photoelectron spectroscopy (XPS) and the Raman spectroscopy reflected the existence of the oxygen vacancies and Ce 3+ ions in the bowknot-like CeO 2 microstructures. The synthesized CeO 2 shows excellent room temperature optical properties, which is likely associated with Ce 3+ ions and oxygen vacancies in the gear-like CeO 2 samples.

CeO 2 nanopoles have been successfully synthesized by a hydrothermal method using CeC l3 ·7H 2 O as cerium source, NaOH as mineralizer, and ethylenediamine as complexant. The pole-like nano-CeO 2 was examined by XRD, TEM, XPS, UV–vis, PL, and Raman scattering. The results show that the crystallinity of the nanopoles is not so good, and the main valence of cerium is +4. The estimated direct band gaps are 3.014, 3.099, 2.931, and 2.927 eV for the samples synthesized within 2, 18, 50, and 100 h, respectively. These band gaps are smaller than bulk CeO 2 , oxygen vacancies and Ce 3+ ions result in an effective red shifting of the band gap. The visible luminescence exhibits similar emission peaks of room temperature photoluminescence and the emission intensity increases with the increase of concentration of oxygen vacancies and Ce 3+ ions.

Monocrystal CeO2 nanopoles of 15–25 nm in diameter and 300–900 nm or more in length were synthesized within 100 h using hydrothermal method with CeCl3·7H2O as cerium source, NaOH as mineralizer, and ethylenediamine as complexant. The results of XRD and SADE analysis indicate that the as-synthesized CeO2 samples have the fluorite structure. The band gaps of CeO2 samples are 0.08–0.38 eV smaller than that of bulk CeO2. X-ray photoelectron spectroscopy shows that the concentration of Ce3+ is higher than 20% for CeO2 samples. All the as-synthesized CeO2 samples exhibit the room temperature ferromagnetism (RTFM), and the saturation magnetization (Ms) gradually increases with the increase of Eg up to 2.92 eV and then decreases with Eg increasing more. The highest Ms of 0.167 emu/g is obtained from the CeO2 nanopoles synthesized within 100 h. The RTFM mechanism of CeO2 nanopoles has been proposed which can be mainly attributed to the influence of oxygen vacancies and Ce3+ ions.

Morphology control of CeO 2 nanostructures was achieved by using ethanol/water mixtures with varied volume ratios from 0:1 to 1:0 in a facile hydrothermal process with CeCl 3 ⋅7H 2 O as cerium source and N 2 H 4 ⋅H 2 O as mineralizer. It was found that the increase of ethanol/water ratio resulted in the morphology change from thin nanorods to short-thick nanorods, and then to nanoparticles, which is mainly attributed to the influences of hydrocarbon chains, dielectric constant, and viscosity of the solution on the thermodynamics of the reaction system and kinetics of nucleation. Various characterization techniques have been used to study the CeO 2 nanostructures, including XRD, XPS, SEM, HRTEM, Raman, and PL spectra. Photoluminescence spectra of the CeO 2 nanoparticals exhibited an unique UV–violet–blue emission which is likely associated with the defect states existing extensively between Ce 4f and O 2p bands, better crystallinity of the sample, and higher concentration of Ce 3+ ions in sample.

The hexagonal rotor-like cerium carbonate hydroxide (CeCO3OH) and CeO2 nanostructures were successfully synthesised via a facile hydrothermal method using Ce(NO3)3 · 6H2O as the cerium resource, HNO3 additive to form an acidic solution, CO(NH2)2 as both precipitator and carbon source and polyvinylpyrrolidone as surfactant. Characterisation techniques using an X-ray diffractometer, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, thermogravimetric differential thermal analysis apparatus and UV–vis absorption spectrum have been used for studying the roles of Ce(NO3)3 · 6H2O and HNO3. It was found that the amount of Ce(NO3)3 · 6H2O has an obvious effect on the morphology of the as-synthesised CeCO3OH and CeO2 nanostructures, whereas HNO3 has a significant influence on the crystalline phase. CeO2 has a higher UV absorption than as-synthesised CeCO3OH, which is likely associated with the charge-transition between Ce3+ and Ce4+.

The novel carbon- or chromium-doped TiOXphotocatalysts with different oxygen defects were synthesized by mechanochemical technique and heating process. The samples were characterized by X-ray diffraction, UV-vis spectrophotometer, and fluorescence spectrometer. Carbon and chromium species were incorporated into TiOXcrystal matrix. The mass fraction of Ti7O13in TiOXphotocatalysts could be tunable through carbon or chromium doping. The mass fraction of Ti7O13could be an indication of the degree of oxygen defects (the concentration of Ti3+) in the TiOX. The degree of oxygen defects increased for carbon doping, while the degree of oxygen defects decreased for chromium doping. The photocatalytic activity measurement results showed that photodegradation rate of methyl orange reached the maximum value with mass fraction of Ti7O13of about 66.93%, but the photodegradation rate decreased when mass fraction of Ti7O13is raised further. In addition, the origin of absorption in the visible spectral range for carbon-doped TiOXas well as the effect of band gap on photocatalytic activity has also been discussed in this paper.

Bowknot-like CeO 2 microstructures have been successfully synthesized by a CTAB (cetyltrimethyl ammonium bromide)-assisted hydrothermal method using Ce(NO 3 ) 3 ·6H 2 O as cerium source and urea as mineralizer. X-ray diffraction (XRD) inferred that the synthesized CeO 2 microstructures exhibited a fluorite cubic structure. A scanning electron microscope (SEM) revealed that the CeO 2 microstructures have a bowknot-like microstructure. X-ray photoelectron spectroscopy (XPS) and the Raman spectroscopy reflected the existence of the oxygen vacancies and Ce 3+ ions in the bowknot-like CeO 2 microstructures. Magnetization measurements exhibited room temperature ferromagnetism (RTFM) with a saturation magnetization ( M s ) of 3.97×10 −3 emu/g and coercivity ( H c ) of 200 Oe, which is likely associated with Ce 3+ ions and oxygen vacancies in the bowknot-like CeO 2 samples.

CeO 2 nanopoles have been successfully synthesized by a hydrothermal method using CeCl 3 ·7H 2 O as cerium, NaOH as mineralizer, and ethylenediamine as complexant. X-ray diffraction (XRD) and selective area electron diffraction (SAED) infered that the as-synthesized CeO 2 nanopoles exhibited a fluorite cubic structure and monocrystalline phase. Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CeO 2 have pole-like nanostructures. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy reflected the existence of the oxygen vacancies and Ce 3+ ions in the CeO 2 nanopoles. Magnetization measurements exhibited room temperature ferromagnetism (RTFM) with saturation magnetization ( Ms ) of 0.167 emu/g, and coercivity ( H C ) of 165 Oe, which is likely associated with Ce 3+ ions and oxygen vacancies in the CeO 2 nanopoles.

CeO 2 nanopolyhedra and square-like nanoparticles were selectively synthesized by a novel hydrothermal synthesis process with the aid of different surfactants, using Ce(NO 3 ) 3 ⋅ 6H 2 O as cerium resource and N 2 H 4 ⋅ H 2 O as mineralizer. The products were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. CeO 2 nanopolyhedra were prepared using polyvinyl pyrrolidone as surfactant, while square-like CeO 2 nanoparticles were prepared using ethylenediamine as surfactant. The possible morphology-selective synthetic mechanism was investigated. X-ray photoelectron spectroscopy measurement revealed that the main valence of cerium irons in the nanopolyhedra was tetravalent, and the subordinate was trivalent which results in formation of oxygen vacancies.

Ceria (CeO2) nanoparticles were successfully synthesised by a novel hydrothermal synthesis process using Ce(NO3)3·6H2O as cerium source and hydrazine hydrate (N2H4·H2O) as mineraliser. The crystal phases, surface morphology and optical properties of CeO2 nanoparticles were characterised by X-ray diffraction, scanning electron microscope, UV-vis spectrophotometer and fluorescence spectrometer. The particle size (ranging from 10 to 20 nm) decreases with the increase of N2H4·H2O from 2 to 8 ml and its mechanism has been proposed and can be mainly attributed to the effect of N2H4·H2O on OH− ionic concentration in the solution. The lattice parameter (∼0.54 nm) decreases with the increase of the crystallite size that can be attributed to both lattice relaxation and valence effect of Ce ions. The absorbance in UV light region increases with the increases of N2H4·H2O from 2 up to 6 ml and then decreases when the dosage of N2H4·H2O is 8 ml. The bandgap energy increases from 3.13 to 3.23 eV with the increases of N2H4·H2O from 2 up to 6 ml because of electrostatic potential effect and then decreases to 2.97 eV when the dosages of N2H4·H2O is 8 ml. The emission intensity increases with the increase of N2H4·H2O from 2 ml up to 6 ml and then unobviously decreases when dosage of N2H4·H2O is 8 ml.