Research Of Hydrothermal Synthesis And Performance For CeO₂Nanomaterials

As a broad-spectrum and inexpensive rare earth oxide, cerium oxide (CeO2) has a wide range of applications at fluorescent materials, mechanical aspects of polishing, fuel cells and photocatalysis because of its unique optical properties, the oxygen storage capacity, a high strength mechanical polishing, the ability to cycle between Ce3+and Ce4+. Studies have shown that the property of CeO2was affected by the topography, lattice constant, particle size and defects.CeO2nanomaterials were synthesized by hydrothermal method. X-ray diffraction (XRD, XD-3) was used to analyse the crystalline phase of the product; transmission electron microscopy (TEM, JEM-2100) and scanning electron microscope (SEM, S-4800) were used to analyse morphological of the product; ultraviolet-visible-near-infrared spectrophotometer (UV-VIS-NIR, U-4100) was used to measure the absorption spectra of the samples; fluorescence spectrophotometer (PL, F-4500) was used to measure luminescence spectra, excitation wavelength X=290nm; comprehensive physical measurement system (PPM, SPPMS EC-Ⅱ (9T)) was used to measure the hysteresis loop; confocal laser microscopy Raman spectrometer (Raman, inVia-Reflex) was used to measure the Raman spectra, excitation wavelength X,=532nm; X-ray photoelectron spectroscopy (XPS, ESCALAB250) was used to measure the surface composition and to analyse surface elements chemical state of the product. The main contents of research are as follows:1. CeO2nanorods were synthesized by hydrothermal method using CeCl3·7H2O as cerium source, hydrazine hydrate as precipitant, ethylenediamine as complexing agent, using different dosage of ethylenediamine to prepare four different samples. The band gap increases and then decreases with the increase of ethylenediamine. The band gap occurs great red-shift with the ethylenediamine dosage of6mL. The intensity of fluorescence gets maximum with the ethylenediamine dosage of5mL.2. Monocrystal CeO2nanorods of15-25nm in diameter and300-900nm or more in length were synthesized within100h by hydrothermal method using CeCl3·7H2O as cerium source, NaOH as mineralizer, and ethylenediamine as complexant. The results of XRD and SADE analysis indicate that the as-synthesized CeO2samples have the fluorite structure. The band gaps of CeO2samples are0.08-0.38eV smaller than that of bulk CeO2. X-ray Photoelectron Spectroscopy shows that the concentration of Ce3+is higher than20%for CeO2samples. All the as-synthesized CeO2samples exhibit the room temperature ferromagnetism (RTFM), and the saturation magnetization (Ms) gradually increases with the increase of Eg up to2.92eV and then decreases with Eg increasing more. The highest Ms of0.167emu/g is obtained from the CeO2nanorods synthesized within100h. The RTFM mechanism of CeO2nanorods has been proposed which can be mainly attributed to the influence of oxygen vacancies and Ce3+ions.3. In this paper, four undoped CeO2nanoparticles was prepared by hydrothermal method, the induced magnetism and magnetization in CeO2was found to increase with the increase of oxygen vacancies according to the analysis results. At the same time, CeO2cell atomic configurations were established according product structure to reveal the origin of ferromagnetic by theory research. Density-functional calculation shows that oxygen vacancies in CeO2cause spin polarization of4f electrons for Ce ions and net magnetic moment of CeO2samples. The research finding may help to develop CeO2nanostructures with controlled magnetic properties for practical applications.