【作者】 李成超；

【导师】 王太宏；

【作者基本信息】 湖南大学 ， 材料科学与工程， 2013， 博士

【摘要】 多孔材料是90年代初迅速兴起的一类新型结构材料,具有较大的比表面积、良好的均匀透过性、比强度高、重量轻、隔音、隔热、渗透性好等优点,使其具有其它材料难以取代的优异性质,成为跨学科研究的重点之一。以往的研究主要集中于探索新的多孔材料合成方法及其应用研究,经过近20年的发展,硅基与非硅基有序多孔材料的合成已经相当成熟。目前,研究者们的注意力开始转移到形貌可控、组成可控以及多孔性可控的多孔材料合成。纳米材料的出现以及纳米科技的发展为多孔胶体材料的合成与应用提供了新的契机。与传统模板法合成的块体多孔材料相比,多孔胶体材料具有更好的分散性,特别是在催化反应中,传质过程更快、更高效。前驱体法是一种制备多孔材料的有效方法。近年来在制备多孔材料的研究中引起了人们的广泛关注。前驱体法的优势在于可以通过合成参数的调节,控制前驱体的颗粒大小、形貌、分散性等,从而制备出满足各种应用需求的多孔胶体材料。基于此,本论文研究了几种基于前驱体的多孔材料制备路线,通过XRD、SEM、TEM、 HRTEM、BET、XPS、TGA等材料表征方法,对前驱体的可控合成以及转化合成多孔胶体材料的可行性进行了系统研究,并对其在相关领域的潜在应用进行了探索,本论文主要开展了以下几方面的研究工作：(1)在第2章中,发展了一种基于配位化学的单组分/多组分稀土胶体球的制备路线。该方法具有普适性,适用于任何稀土元素。由于稀土元素具有类似的配位化学性质,在该体系中,每种稀土元素具有几乎一样的配位化学行为,当加入两种或多种稀土硝酸盐,就能制备出多组分的固溶体胶体球,组分之间的摩尔比率任意可调,并且元素mapping测试表明每种组分在单个胶体球上分布非常均匀。更重要的是,所制备的多组分胶体球继承了稀土元素特有的磁学及发光性质,它们的荧光性质能够通过调节掺杂离子的种类及浓度而变化。在此基础之上,进一步系统研究了热解转化制备单组分/多组分稀土氧化物胶体球的可行性,研究表明制备的氧化物固溶体球仍然具有单分散性,且元素分布均一。以上研究不但为多组分稀土材料的制备提供了新思路,并且所开发的多组分稀土固溶体胶体球在固体电解质,催化,荧光材料等领域具有很大的研究与应用价值。(2)在第3章中,建立了一种简易的、间接的制备路线合成多孔稀土基胶体球。由于不同稀土元素化合物溶度积常数(ksp)及生长速度的不同,利用阴离子直接沉淀法制备多孔多组分的稀土基胶体球几乎难以实现。本研究发展的方法绕开了不同稀土元素化合物的本质差异(溶度积、饱和浓度和生长速度),利用了它们的共性-配位化学性质。首先,将不同的稀土离子用配位剂沉淀,然后利用水热辅助的离子交换方法,通过控制试验参数,转化合成了一系列多孔单组分／多组分稀土氧化物,稀土氟化物,稀土磷酸盐胶体球。该合成路线实现了对产物的微观形貌、多孔性、元素组成与分布的多重控制。(3)在第4章中,以有机醇盐为前驱体,开发出了一种一般性的多孔胶体球制备方法。该合成路线主要利用了有机醇盐易水解的特点,首先在丙酮中通过反溶剂作用制备出有机醇盐胶体球,然后将所制得的醇盐前驱体在水热条件下原位水解,形成多孔结构,所得产物不但保持了球形形貌,具有好的分散性,并且具有大的比表面积。将制备的这些胶体球应用到催化反应中,催化活性大大提高,与迄今报道的最好结果相比,反应速度提高了一倍以上。(4)在第5章建立了一种基于碳酸盐体系的多孔胶体颗粒制备路线。首先利用溶剂热体系,控制制备出不同形貌的具有单分散性的碳酸钴胶体颗粒前驱体,并系统研究了合成条件对产物形貌的影响,总结出其内在的生长机制。然后将所得产物热转化制备出多孔氧化钴胶体颗粒。结果表明,所得产物保持了前驱体均一的微观形貌。氮气吸附测试表明所制备的颗粒具有大的比表面积,将其应用于乙醇与一氧化碳气体传感器,展现出了非常好的灵敏度和响应速度。(5)在第6章中发展了一种基于配位聚合物的多孔过渡金属氧化物纳米线的合成体系。在水热条件下控制合成了3d过渡金属配合物纳米线,并且对该反应体系进行了系统研究,探索了各反应参数如前驱体盐、温度以及溶剂比率与形貌之间的关系。通过在空气中热分解这些配合物,能够简单的制备出它们对应的多孔氧化物纳米线。这些产物不但保留了原有的纳米线形貌,并且由于有机组分分解留下大量孔洞。多孔结构和大比表面积使得这些3d过渡金属氧化物在催化,能源储存等方面具有非常大的应用前景。将制备的多孔过渡金属氧化物材料用作锂离子电池负极材料时,表现出了极好的充放电循环性能。更多还原

【Abstract】 The porous materials, as a new class of structural materials, have received considerable attention since1990s, due to their large specific surface area, and good uniformity through strength, light weight, good sound and heat insulation, permeability, etc. These porous materials possess a lot of promising properties, which are different from their solid counterparts. The emergence of nanomaterials as well as the development of nano techno logy provides a new opportunity for the development and application of porous materials. Compared with the conventional bulk porous materials synthesized by templates, nanoscaled porous materials have better dispersibility. They are emerging as promising materials for broad applications in enzyme immobilization, adsorption, energy storage, drug delievery, CO2capture and catalysis, and can also serve as fundamental building blocks for complex structures. As supports for catalysts, monodisperse porous spheres inherit the merits of the large specific surface area of their large bulk counterparts and high dispersibility of tiny nanoscale particles in a liquid medium. Therefore, they will be able to well mediate the conflicts between short diffusion path, high catalytic activity, and facile recyclable separation after use. Furthermore, the specific pore structures in porous spheres have been used to immobilize functional molecules and nanoparticles to tailor the material properties or as templates for the synthesis of namomaterials replicas. In this regards, extensive research efforts have focused on the synthesis of diverse porous spheres during the past few years. In particular, research in the synthesis of porous nonsiliceous spheres has seen tremendous growth, which extensively broadened the scope of porous sphere materials. However, development of a low-cost, simple synthesis process for porous nanomaterials is still a great challenge in present study. In this dissertation, we explore sveral precursor-based synthetic routes for the controllable preparation of porous nanomaterials prepared with different morphologies. More details ae summarized below:(1) In chapter2, we have devised in this work a general synthetic strategy for preparation of single-and multicomponent rare-earth coordination polymer colloidal spheres (RE-CPCSs). This strategy is based on an integration of coordination chemistry and antisolvent effect for synchronized precipitation. Highly monodisperse RE-CPCSs with homogeneous mixing of RE elements, which are not readily attainable by any existing methods, have been successfully prepared for the first time. In addition, the type and molar ratio of these colloidal spheres can be adjusted easily in accordance to the variety and dosage of precursor salts. The molar ratio of RE elements in as-prepared colloidal spheres shows a linear relationship to that of starting reactants. Furthermore, the RE based core/shell colloidal spheres can be facilely prepared by introducing other metal salts (beyond lanthanide elements) owing to their different coordination chemistry and precipitation behavior. By adjusting concentrations of the ionic activators, luminescent properties can be tuned accordingly. Furthermore, the RE-CPCSs can be transformed to monodisperse lanthanide oxide spheres via simple heat treatment. We believe that the present synthetic strategy provides a viable route to prepare other lanthanide containing colloidal spheres that have enormous potential for future applications as optoelectronic devices, catalysts, gas sensors and solar cells.(2) In chapter3, we demonstrate a novel indirect synthetic route to prepare monodisperse porous multicomponent rare earth (RE) based colloidal sphere with uniform size and tunable compositions using RE-CPCSs as precursors. For the multicomponent system, the essential differences of lanthanides in solubility product constant (Ksp), saturated concentration and growth rate, make it almost impossible to synthesize multicomponent RE-based colloidal sphere with controlled morphology and porosity. Generally, the Ksp value of a lanthanide precipitation decreases with decreased ionic radius of the RE ions, following the lanthanide contraction law. Since the colloidal spheres are formed via nucle at ion/growth processes, nucleation can only takes place when the degree of supersaturation (S, given below) reaches the critical supersaturation. It thus can be inferred from that stable nuclei of RE ions with small ionic radii are easier to be formed compared to those with larger ionic radii. This conclusion has also been demonstrated by Matijevic’s experimental results, in which the light lanthanides tend to precipitate in a way different from those heavier ones in terms of morphology of the resultant particles during the direct precipitation process. However, the indirect synthetic strategy is based on the integration of coordination chemistry precipitation of RE ions and subsequent ion-exchange process so as to steer clear of obstacle from differences in solubility product constant.(3) In chapter4, we develop a low-cost reaction protocol to synthesize highly effective mesoporous Nb2O5-based solid acid catalysts with additional morphological control. In the synthesis, the monodisperse glycolated niobium oxide spheres (GNOS) were prepared by a simple antisolvent precipitation approach, and subsequently converted to mesoporous niobium oxide spheres (MNOS) with large surface area of312m2·g-1by hydrothermal treatment. The obtained mesoporous MNOS were further functionalized with sulfate anions at different temperatures or incorporated with tungstophosphoric acid (TPA) to obtain recyclable solid acid catalysts. The antisolvent acetone used in obtaining GNOS can be completely recovered at a high purity. Our MNOS-based catalysts have shown remarkable performance in a wide range of acid-catalyzed reactions such as Friedel-Crafts alkylation, esterification and hydrolysis of acetates. Because they are monodisperse spheres with diameters in submicrometer regime, the catalysts can be easily separated and reused.(4) In chapter5, we report a polyo1process for controlled growth of cobalt carbonate (COCO3). A preparative investigation on morphogenesis of COCO3crystals has been carried out, and three types of highly uniform COCO3products (i.e., peanut-like, capsule-like, and rhombus crystals) in the submicrometer region have been synthesized at200℃under batch conditions. Uniform particles of tricobalt tetroxide (CO3O4) have also been obtained at300℃from the COCO3submicrometer crystals after thermal transformation in laboratory air. The CO3O4powder products possess mesoporosity and essentially preserve the pristine morphologies of their respective solid precursors. Due to high crystal uniformity and specific surface areas in the range of140-149m2/g, the mesoporous CO3O4exhibits enhanced performances for ethanol and carbon monoxide sensing.(5) In chapter6, transition metal-based coordination polymer nanowires were synthesized using nitrilotriacetic acid (NA) as a chelating agent by a one-step hydrothermal approach. In the synthesis, transition metal ions were bonded with amino or carboxyl groups of NA to form one-dimension polymer nanowires, which can be confirmed by FTIR and TGA results. Our experimental results show that the morphologies of polymer nanowires greatly depend on the precursor salts, ratios between deionized water and isopropyl acohol. The probable molecular formula and growth mechanism have been proposed. After heat treatment, the cobalt ion-based coordination polymer nanowires can be converted into porous transition metal oxide nanowires, which completely preserved the nanowire-like morphology. When used as anodes in lithium-ion batteries, the obtained porous nanowires exhibited a high reversible capacity of810mAhg-1and stable cyclic retention at30th cycle. The good electrochemical performance could be attributed to the porous nanostructure, which provides pathways for easy accessibility of electrolytes and fast transportation of lithium ions.更多还原