Preparation Of Nano-oxides By Malate Sol-gel Method And The Research On Property

Nano-metal oxides are one kind of very useful nanomaterials. Because of the quantum size effect, small size effect, surface effect and macro-quantum tunnel effect, it's property is obviously superior to the counterpart bulk materials. In this dissertation, the research situation of the nano-magnesia, nano-nickel oxide and nano-ceria are introduced, and the classification, theory, advantage and drawback of the sol-gel method are analyzed. Using Mg, Ni, Ce as the delegate of mainly group element, transition metal element and rare earth element respectively, the corresponding nano-metal oxides were prepared by sol-gel method. The structure and composition of the as-prepared nano-oxides were characterized. And the reactive condition was improved and optimized. Their some application was analyzed.The magnesium oxide nanocrystallites were prepared by sol-gel method, using malic acid and magnesium nitrate as raw materials. On different prepared conditions, the particle size can change from 7nm to 20nm. FI-IR,TG-DTA,XRD and TEM were used to investigate the composition, decomposition processing of the gel and the phase of the gel and sample, the morphology, particle size and particulate distribution of the sample. The influence of ratio of the raw materials, calcined temperature and time ,the initial pH value and the amount of ethanol on the particle size and morphology of the sample was analyzed. The results show that the mole ratio of Mg²⁺ to malic acid being 1:1.5 ,calcined temperature at 500～700°C,calcined time for 3h,the initial pH value being 3-7 and the volume ratio of ethanol to water being 1:4 were best condition. The production of the nano-magnesia may be related with the exist of ammonium nitrate, and it was used to decrease the particle size and agglomeration. UV-Vis Spectra show that UV-shielding capacity of the nanosized magnesium oxide was superior to normal magnesium oxide. Doped Eu²⁺ can obviously increase the UV-shielding capacity of the nanosized magnesium oxide, and the reason was analyzed.NiO nanoparticles have been successfully prepared by calcining malate gel, using basic nickel carbonate (BNC) and malic acid as the raw materials and H₂O as the solvent. The reaction was studied by TG-DTA, XRD and FT-IR. The particle size and morphology of NiO nanoparticles was characterized by TEM. The results show that nickel malate could be formed by the reaction of BNC and malic acid. the gel was composed of nickel malate and residual malic acid. the precursor can translate into NiO nanoparticles completely at 400°C under the air, and the as-prepared sample has cubic crystal structure with about 14 nm of average diameter by the Scherrer formula. The NiO calcined at 400°C for 1 h was of narrow particle size distribution, weak agglomeration and small particle size. The particle size of NiO increased with the increasing of temperature. With the increase of malic acid, the degree of the agglomeration was increased. the particle size decreased with the increase of the solvent. With the increase of the calcined time, the particle size increased gradually and no obvious agglomeration was found. Compared with other methods, the developed method is simple and the raw materials was inexpensive, so that it has potential for further scale-up application in industry. Furthermore, the reason for the metallic nickel formation in the course of the preparation was explained.The nanocrystalline ceria powders have been synthesized by the combustion technique, using malic acid as the reductant (fuel) and cerium nitrate as the oxidant. The auto-combustion (at about 220°C) of the precursor containing cerium nitrate and malic acid resulted in loose nanoceria powders. The precursor and as-burnt powders were investigated with infrared (IR) spectra, thermal analysis, X-ray diffraction and transmission electron microscopy. The experiments showed that the particle size is uniform. The influence of the molar ratio of malic acid to cerium nitrate (M/C value) was investigated. As M/C values are decreased from 3 to 1, the combustion rate is increased significantly, and the crystallite size is increased from 8.5 nm to 24.7 nm. The combustion reaction mechanism was analyzed with IR spectra and thermal analysis techniques. The UV-shielding capacity of the as-burnt ceria is superior to bulk ceria. The absorption of the as-burnt ceria in UV field is related with the molar ratio of the raw materials. The influence of the as-burnt ceria on the thermal decomposition of ammonium perchlorate (AP) were investigated and compared with bulk ceria. The results show that the as-burnt ceria has high catalytic activity on the thermal decompostion of AP. The end temperature of decomposition of AP reduce 46 °C, and the higher temperature decomposition reduce 48°C. The decomposing rate of AP is enhanced. The catalytic behavior of the as-burnt ceria is superior to bulk ceria. The catalytic mechanism of ceria was analyzed.