The Synthesis,Structure And Their Catalytic Properties Of Doped Rare-earth Zirconates

Nowadays,the preparation of novel nanometer-scale and submicron materials is one of the most popular topics in the research fields of material science.The research objects contain the pyrochlore type of rare-earth zirconates Ln2Zr2O7?Ln = La,Nd,Sm,Eu,Dy,Er?,with high conductivity,high chemical stability and high catalytic activity.With the green synthesis methods,nano particles in small size and with high dispersibility were obtained under relatively mild conditions.The soft-chemistry method in the preparation process of pyrochlore type of rare-earth zirconates was used in this dissertation.The doped nano-materials based on Ln2Zr2O7 were obtained and their structures,morphologies and photocatalytic properties were studied.The main contents are as follows.Salt-assistant Gly self-propagating combustion method?SGCM?was used to prepare Ln2Zr2O7?Ln = La,Nd,Sm,Eu,Dy,Er?series nano-crystals at a relatively low temperature.The impact of Ln on the crystal structure of Ln2Zr2O7 was systematically analyzed.The reaction mechanism was also studied.The results indicated that the products prepared by SGCM had little reunion and had uniform distribution of particle size.The average size of particle was around 30 nm.The photocatalytic properties of Ln2Zr2O7 series products obtained by SGCM was systematically analyzed and it was found that all of the products had nice photocatalytic activities and the type of Ln had a strong effect on the catalytic activity of Ln2Zr2O7.The photocatalytic activities ranked in the decreasing sequence of Dy2Zr2O7>Nd2Zr2O7>Er2Zr2O7>Sm2Zr2O7>La2Zr2O7.With the increase of atomic number,the change of the photocatalytic activity of nanocrystals was consistent with the change of the magnetic moment of the rare earth metal cations Ln3+.This indicated that the photocatalytic activity of the rare earth metal cations was also due to the 4f electron structure.The preparation and the photocatalytic activities of La_2-xLn_xZr₂O₇ series with La partially substituted by other Ln were systematically studied.SGCM was used to prepare La2-x LnxZr2O7 series nano-crystals?Ln3+= La3+,Nd3+,Sm3+,Eu3+,Dy3+,Er3+?.The results showed La-site could be partially substituted by other lanthanides Ln without changing the crystal form.In fact,Ln came into the crystal lattice of Ln2Zr2O7 instead of La,and the product was single-crystalline-phase solid solution.The products La_2-xLn_xZr₂O₇ had high dispersibility and uniform distribution of particle size.The average size of the particles was 20 nm?40 nm.The fluorescent properties and the photocatalytic activities of the products were also investigated.With SGCM,the compounds of Ln_2-xM_xZr₂O₇ series with Ln substituted by some transition metals were synthetized and single-crystalline-phase solid solution were obtained.The results showed Ln3+ could be partially substituted by M3+ without changing the crystal form.The products were single-crystalline-phase pyrochlore type solid solution.The particles prepared by SGCM were uniformly distributed,and had regular shape and high dispersibility.Their photocatalytic activities were studied,and it was found that Ln_2-xM_xZr₂O₇ series had good catalytic activities.The compounds La_2-xLn_xZr₂O₇ and Ln_2-xM_xZr₂O₇ were obtained by SGCM and their catalytic activities on the thermal decomposition of ammonium perchlorate?AP?were studied.The catalysis of Ln_2-xM_xZr₂O₇ on AP with the method of differential scanning calorimetry/thermogravimetry-mass spectrometry?DSC/TG-MS?was also studied.The results showed that Ln_2-xM_xZr₂O₇ had strong catalytic effect on AP.The addition of two percent of Ln_2-xM_xZr₂O₇ brought down the decomposition temperature of AP and increased the amount of decomposition heat release.Ln_2-xM_xZr₂O₇ worked most effectively as nano-catalyst.Compared with pure metallic oxide,doped pyrochlore type nano particles all had better catalytic performances on AP.The fluorite type cubic nano crystal Dy2-xCoxCe2O7 was prepared by using a salt-assistant solution combustion method.The raw materials were Dysprosium Nitrate,Cobalt Nitrate and Cerium Nitrate;the combustion agent was Glycine and the reaction inert salt was KCl.By changing the nGlycine/nM value,the amount of salt and the calcination temperature,the particle diameter of the nano-crystals was controlled and fluorite type cubic nano-crystal Dy2-xCoxCe2O7 was obtained.Dy3+ could be partially substituted by Co3+,without changing the crystal form.The product was single-crystalline-phase fluorite solid solution.The obtained nano-particles had good dispersion and the particle size was approximately 18nm.The catalytic properties of Dy1.9Co0.1Ce2O7 on AP were characterized by DSC/TG-MS.The results showed that Dy1.9Co0.1Ce2O7 had relatively high catalytic activity on AP.The addition of two percent of Dy1.9Co0.1Ce2O7 made the decomposition temperature of AP drop by almost 120?.The released decomposition reaction heat increased from 453.11 J/g to 1337.68 J/g.The results indicated that the catalytic effect of nano Cobalt-doped Dysprosium Cerium Oxide on the thermal decomposition of AP was better than that of the nano metal oxides and Dysprosium Cerium Oxide without being doped prepared under the same conditions.