| As a most important rare-earth oxide, cerium oxide (CeO2) has been widely applied in fluorescent materials, fuel cells, photocatalysis and magneticmaterials because of its unique physicochemical properties and crystal structure. Many studies have indicated that the properties of nanoscale CeO2 materials were influenced by the morpholopy, particle size, lattice parameter and crystal defects.CeO2 nanomaterials have been prepared by a simple hydrothermal method. X-ray diffraction was used to test and analysis phase composition of products. Scanning electron microscope and transmission electron microscopy were used to measure morphology and particle size of samples. Surface composition and surface element chemical state of CeO2 samples were measured by X-ray photoelectron spectroscopy. Raman spectra of samples were measured by a Raman spectrometer using a laser with 532 nm excitation. Ultraviolet-visible-near-infrared spectrophotometer was used to measure the absorption spectra of the samples, from which energy bands of the samples can be calculated. Comprehensive physical measurement system was used to measure magnetic properties of the samples. The main contents of research are as follows:1. Bowknot-like CeO2 microstructures have been successfully synthesized by a CTAB (cetyltrimethylammonium bromide)-assisted hydrothermal method using Ce(NO3)3-6H2O as cerium source and urea as mineralizer. X-ray diffraction (XRD) inferred that the synthesized CeO2 microstructures exhibited afluorite cubic structure and no second phase is detected. XPS and Raman analysis indicated that there are a lot of Cesl and oxygen vacancies at the surface of samples. Magnetization measurements exhibited room temperature ferro magnet ism (RTFM). which is likely associated with Ce" ions in the bowk not-like CeO? samples2. The different morphologies CeO2 microstructures have been successfully synthesized bv a CTAB-assisted hvdrothermal method using Ce(NO3)3·6H2O as cerium source and NH4HCO3 as mineralizer. XRD indicated that all the samples are pure CeO2 powder. The XPS revealed that a lot of Ce3+appeared at the surface of CeO2 products and with the dosages of NH4HCO3 increase, the concentration of Ce3+ will be decreased. And their energy bands (Eg) are smaller than that of bulk CeO2. All the synthesized CeO2 samples exhibited the room temperature ferromagnetism (RTFM), and with the increse of Eg and lattice pare meter, the saturation magnetization (Ms) decrease gradually, but with the decrease of concentration of Ce3+, the Ms also decreases. The RTFM mechanism of CeO2 nanomaterials have been proposed, which can be mainly attributed to the influence of Ce3+ions, and the more Ce3+, its Ms will be better.3. Co-doped CeO2 nanorods of 10-30 nm in diameter and 200-500 nm or more in length have been synthesized by a simple co-precipitation method. The results of XRD analysis indicated that the synthesized CeO2 samples have the fluorite structure and no second phase is detected. X-ray photoelectron spectroscopy and Raman spectra showed that Ce4+and Ce3+ions coexist at the surface of non-doped CeO2 nanorods. The magnetic measurements displayed that Co-doped CeO2 nanorods exhibited stronger ferromagnetism at room temperature, and while the dosage of Co ions increases, the ferromagnetism increases more. It can be concluded that the magnetic properties of CeO2 nanomaterials can be associated with the presence of Ce3+and Co2+, which leads to the change of spin and orbital angular momentum. As a result, the ferromagnetism will be generated. |
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