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Rare Earth Alkoxides And Rare Earth Oxide Mesoporous Materials Synthesis And Characterization

Posted on:2004-11-19Degree:MasterType:Thesis
Country:ChinaCandidate:J H LiuFull Text:PDF
GTID:2191360125470074Subject:Materials science
Abstract/Summary:PDF Full Text Request
The rare earth(La, Pr, Nd, Sm) alkoxides were synthesized in the condition of alkaline earth alkoxides as the providers of alkoxy, anhydrous rare earth acetates as the raw materials. In addition, some work about the preparation of rare earth nano-metal oxides were carried out by taking the rare earth methoxides as materials. The effect to rate of production of the reaction active of different alkaline earth, the reaction efficiency of different low-carbon alcohols and reaction time were investigated. The rare earth mesostructured materials were prepared by taking the non-surfactants triethylamine and polyethylene glycol as the structure-directing agents. The thermal stability of mesoporous structure, the effect to the mesoporous structure of polyethylene glycol molecular weight and the additive quantum of triethylamine were investigated. The results showed that it is feasible to synthesis the rare earth alkoxide by taking the alkaline earth alkoxides as the providers of alkoxy. IR spectra results show that there appears the characteristic absorb band of the bond C-O-Ln of rare earth methoxides, rear earth ethoxides and rear earth isopropoxides respectively at around 1035cm-1, 1050 cm-1, 1160 cm-1 and 1130 cm-1. The characteristic absorb bands of rare earth ions arisen in the Uv-vis spectra confirm farther the samples are rare earth alkoxides. The alkaline earth calcium presents higher reaction activity comparing to magnesium. The yields of rare earth alkoxides present descending trend as the carbon number increase of the alkoxy alcohol. As increasing of reaction time, the yields of rare earth alkoxides rise gradually, i.e. methoxides> ethoxides> isopropoxides. The nanometer neodymium oxide, which was made from the rare earth neodymium methoxide, presented global shape distribution and the particle size was around 50nm.The XRD results showed that the pore wall presend cubic fluorite structure in the mesoporous CeO2 powders prepared. HRTEM results revealed that the pores presented ordered pore array with pore size around 5nm. Surface areas in excess of 200m2/g are obtained after dried at room temperature. The pore distribution of the sample prepared using the non-surfactant template approaches indicated there exist some micropore in the pore structure. The TEA played the key role in the formation of mesostructured CeO2 and the additive PEG reduces the number of micropore in the pore system. After calcined in different temperatures, the micropore amount decreased and the mesopore distribution became broad with the most probable pore size around 8nm. PEG can improve the thermal stability of the mesoporous CeO2. The BET surface area of the samples air-dried decreased with the increasing of PEG molecular weight.
Keywords/Search Tags:rare earth alkoxide, alkaline earth alkoxide, rare earth mesoporous material, triethylamine, polyethylene glycol
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