【作者】 蒋晓瑜；

【导师】 陈文哲；

【作者基本信息】 福州大学 ， 材料学， 2011， 博士

【摘要】 为了探索具有新型结构和潜在的高催化活性的功能纳米材料，本论文进行了两方面的研究工作，一是重点探索了钨簇多酸盐新结构的合成和结构表征，二是着重进行钴酸镧纳米材料的制备及电化学性能研究。论文第一部分以钨簇多酸作为研究对象，将有机物引入钨簇骨架，同时将稀土与钨簇通过适当的形式连接起来，通过溶液法成功合成了3个结构新颖的钨簇多酸盐化合物。化合物（I）[Na₂(C₈H₁₂N₂O₃)₄（C₂H₆SO）₄(W₆O₁₉)]_n是罕见的有机-钨簇结构，化合物（II）[（H₂O）Na（-DMSO）₃La（DMSO）₄(W₁₀O₃₂)]_n是首例(W₁₀O₃₂)₄单元的多维结构，又是首例W簇单元与稀土金属连成的2维结构，化合物（Ⅲ）[Na₁₀（H₂O）₁₈(H₂W₁₂O₄₂)]_n是十二钨酸盐的新型堆积方式，具有相当复杂的3维结构。第二部分着重进行钴酸镧纳米材料以及多元稀土系列钴酸盐的制备和电化学性能研究。运用热力学原理，在分子水平上研究分析了钴离子在柠檬酸溶胶凝胶法体系中的存在方式、柠檬酸作为多齿配体的最佳配位环境与配位方式，提出利用氨水改进柠檬酸溶胶凝胶法的新工艺并成功合成了钴酸镧，获得工艺控制简单，重现性优良的钴酸镧制备方法。系统地研究了合成条件、焙烧温度、稀土掺杂比例等对钴酸镧纳米材料及二元稀土钴酸盐相结构与形貌的影响。结果表明，控制凝胶形成的最佳条件，在600℃焙烧可获得纯钙钛矿相的LaCoO3纳米粉末，平均粒径为25.8nm，属于菱形结构。在600-900℃处理均不改变晶型，但随焙烧温度的提高，晶体尺寸增大。系列镧钕钴酸盐（La1-xNdxCoO3,x=0¹）研究发现，钕以不同掺杂比例均能与镧元素形成具有钙钛矿结构的镧钕钴酸盐。当x较小时具有菱形结构（LaCoO3为主），当x超过0.4时，转化为具有更高对称性的立方结构（NdCoO3为主）。进而系统合成了系列二元稀土钴酸盐（La1-xAxCoO3,A=Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Er）。除Ce以外的镧系元素均能与镧元素以1:1配比形成单相固溶体，所形成的二元稀土钴酸盐都具有钙钛矿结构，La与Ce以1:1配比不能形成钙钛矿结构，仅当Ce掺杂量少于10%时，形成的二元稀土钴酸盐具有钙钛矿结构。采用玻碳为基底将钴酸镧等纳米材料制成催化电极。系统地研究了钴酸镧及二元稀土钴酸盐纳米材料在碱性介质中的电化学行为。研究发现，600℃焙烧获得的钙钛矿结构钴酸镧具有最大的阳极电流，电催化活性最好。系列二元稀土钴酸盐的电化学活性研究发现，轻稀土钴酸盐比重稀土钴酸盐的电化学活性高，镧镨钴酸盐活性最高，而重镧系元素与镧组成的二元钴酸盐和镧铈二元钴酸盐基本没有催化活性。更进一步地，采用乙二醇还原法制备了载铂20%的复合材料Pt-LCO/C，并与Pt/C进行对比试验。发现铂在钴酸镧中的分散性比在纯纳米碳中好，获得铂金属颗粒仅2nm，且颗粒大小均匀。在碱性介质中对甲醇的电化学氧化行为测试中，Pt-LCO/C电极比Pt/C电极的扩散性更优，具有优良的电催化氧化甲醇的性能。采用微波辅助湿化学法也成功获得钙钛矿钴酸镧纳米材料，与溶胶凝胶法钴酸镧相比，微波法获得的纳米粒子粒径更小，比表面更大，电化学活性更高，但纯度不及溶胶凝胶法。更多还原

【Abstract】 In this dissertation, the synthesis and structures of Ployoxometalates （POMs） basedon tungsten-clusters, as well as the preparation and electrochemical properties oflanthanum cobaltite nano-particles were systematically investigated, for the purpose toexplore functional nanomaterials with a novel structure or potential catalytic activities.In the first part of the dissertation, POMs based on tungsten-clusters were chosen asresearch objects. Three POMs compounds based on tungsten-clusters with novel structureswere successfully achieved by traditional aqueous solution method, in which organicligands were introduced into framework of tungsten-clusters, and rare earth elements wereused as linkage. It should be noted here that, Compound （I）[Na₂(C₈H₁₂N₂O₃)₄（C₂H₆SO）₄(W₆O₁₉)]_nis a unusual2D organic-polyoxotungstate and a new example ofhexapolyoxotungstate units with a2-D structure. Compound （II）[（H₂O）Na（-DMSO）₃La（DMSO）₄(W₁₀O₃₂)]_nis the first example that the basic decapolyoxotungstates buildingblock linked up into multi-dimensional structure and the first polyoxotungsten compoundincorporating both rare transition metals and organic ligands with multi-dimension.Compound （Ⅲ）[Na₁₀（H₂O）₁₈(H₂W₁₂O₄₂)]_nis a new packing example of paradodeca-tungstate salt with simple composing but complicated3-D structure.In the second part of the dissertation, the preparation and electrochemical propertiesof lanthanum cobaltite nano-materials and rare transition metal cobaltites were studied.The existing types of Co ion and citric acid in the sol were analysed at molecule levelbased on thermodynamic principle. The coordination modes and the optimal coordinationenvironment of citric acid were also discussed. A new technological process, i.e. anammonium hydroxide improved citric acid sol-gel method, was drawn out and thenlanthanum cobaltites were successfully prepared. This process was stable with goodreproducibility for preparing cobaltite nano-particle.The effects of preparing condition, the calcination temperature and the rare transitionmetals doping on the phase structure and topography of lanthanum cobaltites and raretransition metal cobaltites were systematically studied. It comes to a conclusion that calcination temperature at600℃, using the new sol-gel technological process, gives outpure perfect perovskite structure LaCoO3nanomaterial with particle size25.8nm inrhombohedra symmetry. The LaCoO3particles are in perovskite structure when thecalcination temperature between600℃and900℃, but the particle size grows as thecalcination temperature rises. Then, a series of La and Nd cobaltites （La1-xNdxCoO3, x=0¹） were studied. The results show that perovskite phase can be formed at any ratio of Laand Nd, and rhombohedra structure （mainly LaCoO3） can be transformed into the cubicstructure （mainly NdCoO3） when x0.4. Further, the cobaltites La1-xAxCoO3（A=Ce, Pr,Nd, Sm, Eu, Gd, Tb, Dy, Er） were studied. The results show that La1-xAxCoO3cobaltitesalso possess a perovskite structure when x=0.5except La1-xCexCoO3, and theLa1-xCexCoO3has a perovskite structure only when x0.1.The cobaltites catalytic electrodes were fabricated with Nafion ion-exchange resin,and the electrochemical properties in alkaline solution were studied. It is found that thecatalytic electrode made by LaCoO3particles calcined at600℃has the highest anodecurrent, and the highest catalytic activities. Moreover, the electrochemical properties forseries of binary rare transition metals cobaltites La0.5A0.5CoO3were studies. It is found thatthe light rare earth lanthanum cobaltites show higher catalytic activities than heavy rareearth lanthanum cobaltites, and that the lanthanum cerium cobaltites or heavy raretransition metals lanthanum cobaltites show catalytic inactivities. Furthermore, thePt-LaCoO3/C and Pt/C catalyst （20wt.%Pt） were prepared by glycol reduction process.The results show that the catalyst of Pt-LaCoO3/C has advantageous of large surface area,excellent dispersion of Pt with particle size of ac.2nm, and finally show goodelectrocatalytic properties for alcohol electro-oxidation. The potential at anode currentpeak for methanol electro-oxidation on Pt-LaCoO3/C is lower than that on Pt/C electrode atthe same Pt loadings due to the higher dispersion Pt particles on LaCoO3/C.The perovskite lanthanum cobaltite was also successfully prepared by coprecipitationwith microwave irradiation to compare with the above research results. It has a smalleraverage particle size, higher BET surface area, higher electro-catalytic activities but lesspure in comparison with that prepared by sol-gel route.更多还原