【作者】 邹鲁；

【导师】 李峰；

【作者基本信息】 北京化工大学 ， 应用化学， 2008， 博士

【摘要】 尖晶石型复合金属氧化物作为一类重要的无机功能材料具有一系列重要特性,广泛应用于高温材料、半导体光电材料、磁性材料、生物和医学、传感器以及催化剂和催化剂载体等诸多领域。目前,制备该类尖晶石型复合金属氧化物材料的方法主要是传统的高温固相反应法,但由于该方法通常需要长时间的高温焙烧,产物特别容易团聚和烧结,整体均一性也较差,比表面积很小,严重地影响了该类材料的应用。水滑石（Layered Double Hydroxide,简写为LDHs）是一类具有特殊结构的层状材料,在高温焙烧条件下可以转化生成尖晶石型复合金属氧化物。由于LDHs存在着晶格能最低效应及晶格定位效应,层板中的金属离子和层间的阴离子以一定方式均匀分布,即在LDHs的每个结构单元中,其化学组成不变。因此,以LDHs作为前驱体可以在相对较低的焙烧温度和较短的焙烧时间下得到一系列组分可调、成分均匀、结构均匀的尖晶石型复合金属氧化物功能材料,从而大幅提高其物理化学性能。本论文利用水滑石层板离子的可调控性制备了一系列组成的LDHs材料,并提出了以LDHs为前驱体的自生成牺牲模板路线来设计合成一系列具有特殊结构的复合金属氧化物功能材料。如以ZnAl-LDHs和ZnCr-LDHs为前驱体在500℃下就得到了高比表面积介孔尖晶石型锌基复合金属氧化物（Znal₂O₄和ZnCr₂O₄）。将层板二价金属离子调变为镁,层板中引入钛后分别得到MgFe-LDHs和MgFeTi-LDHs,并以之为前驱体在700℃下得到了高比表面积介孔尖晶石型镁基复合金属氧化物（MgFe₂O₄和钛掺杂的MgFe₂O₄）。在上述水滑石前驱体焙烧过程中,生成的二价金属氧化物作为自生成牺牲模板对尖晶石纳米粒子具有分散和阻隔作用,从而抑制了尖晶石纳米粒子的生长,使其粒径较小,而在选择性溶蚀后留下了介孔结构;并且考察了水滑石前驱体中二价与三价金属离子摩尔比和焙烧温度的影响。当焙烧温度提高到900℃,以锌镓水滑石为前驱体得到了粒径为150nm的单晶态ZnGa₂O₄尖晶石发光材料。与传统高温固相反应法相比,该制备路线具有焙烧温度低,时间短,尖晶石生成程度高,粒径小且均匀等特点。在深入研究两种方法制得ZnGa₂O₄尖晶石的晶体结构、组成、表面结构、Ga³⁺配位环境、Ga-O键长等精细结构后,揭示出ZnGa₂O₄尖晶石光学能带宽度的差异来源于Ga-O键长的不同,Ga³⁺配位环境对其光致发光性能有较大影响,并运用晶体场理论成功解释了水滑石前驱体法制得ZnGa₂O₄尖晶石发紫外光的原因。以含镁水滑石为前驱体,通过改进工艺路线引入预焙烧和烧结成型等工艺步骤后制备了一系列大孔复合金属氧化物(MgAl₂O₄、MgFe₂O₄和In_2-xMg_xO₃)单块,详细研究了水滑石前驱体中二价与三价金属离子摩尔比和烧结温度对产物微结构以及组成的调控。对大孔MgAl₂O₄尖晶石单块表面硬脂酸修饰后,其表面实现了超疏水性能;而对大孔MgFe₂O₄尖晶石和In_2-xMg_xO₃单块,分别详细研究了其微结构以及组成的调变对磁学和光学性能的影响。水热法与溶剂热法作为一种软溶液工艺（SSP）和环境友好的制备技术常用于各种无机功能材料的合成。本论文以尿素水解均匀沉淀为基础,应用水热无模板绿色合成路线制备出高比表面积介孔ZnAl₂O₄和NiAl₂O₄尖晶石材料。该工艺路线包括水热条件下生成前驱体以及前驱体在焙烧过程中发生结构转变生成介孔尖晶石材料两个步骤,并提出了反应机理,详细研究了水热温度、尿素浓度以及焙烧温度等参数对前驱体和最终产物的组成和织构性能的影响。当水热体系中引入适量的不同类型的醇后,可在醇/水体系中实现溶剂热选择性一步合成具有晶态骨架的微/介孔ZnAl₂O₄尖晶石,详细研究了醇的类型以及加入量对最终产物的织构、组成和形貌等的影响。更多还原

【Abstract】 Spinel-type complex metal oxides are an important class of inorganic functional materials.They have found wide applications in areas such as high-temperature material,semiconductor,optoelectronic,magnetic material, biology,medicine,sensor,catalyst and catalyst support,because of their important structural and physicochemical properties.At present,the most commonly used route is the conventional solid-state reaction method which requires calcination of physical mixtures of precursors at considerably elevated temperatures for a long time.Therefore,the particles agglomerate and sinter during the calcination process,resulting in the nonuniform of the product and low surface area,which seriously affected their applications.Hydrotalcite-like compounds or layered double hydroxides（LDHs） belong to a large class of nature and synthetic anionic clays,in which the metal ions are bonded to hydroxyl groups to form two-dimensional brucite-like layers that are stacked together through electrostatic interactions between interlayer anions and positively charged layers.Within the layers,the cations are uniformly distributed on an atomic level without segregation of ’lakes’ of separate cations.Therefore,calcination of LDHs precursors at a lower temperature and shorter time can give spinel-type complex metal oxides with uniform composition and structure.However,these spinel-type complex metal oxides are always mixed with the oxide of the divalent metal.This reflects the fact that in LDHs,the ratio M^Ⅱ/M^Ⅲis typically in the range 2～4 whereas in a spinel the required ratio is M^Ⅱ/M^Ⅲ=0.5.This thesis describes the synthesis of serious LDHs materials and uses them as precursors to obtain spinel-type complex metal oxides with special structures.Based on this thought,we prepared ZnAl₂O₄ and ZnCr₂O₄ spinels with mesopore networks and unusually high specific surface areas using ZnAl-LDHs and ZnCr-LDHs as precursors.Similarly,after changing M^Ⅱto Mg and introducing Ti into the layer of LDHs precursor,we have prepared MgFe-LDHs and MgFeTi-LDHs,which are also used as precursors to obtain high specific surface area mesoporous MgFe₂O₄ and Ti-doped MgFe₂O₄ spinels.In above pathways,the large amount of highly dispersed M^ⅡO formed during the calcination of LDHs precursors,as self-generated sacrificial templates,have an obvious segregation and inhibition effect on the growth of spinel particles,and leaves porous structures after selective leaching.Besides, we investigated the influence of M^Ⅱ/M^Ⅲmolar ratio and calcination temperature on the structure and textural properties of products.Increasing the calcination temperature to 900℃,single-crystalline ZnGa₂O₄ spinel phosphor with average particle size of around 150 nm has been prepared from ZnGa-LDHs precursor.Compared with the traditional high-temperature solid-state reaction method,this synthetic approach involves a much lower calcination temperature and shorter calcination time,and the obtained ZnGa₂O₄ spinel particles are smaller and uniform.The X-ray crystal structure,composition,surface/near-surface chemical states,Ga³⁺coordination environment and Ga-O distance of ZnGa₂O₄ spinel products by two methods have been detailed investigated.It has been confirmed that that Ga³⁺ions locate not only on the octahedral sites but also on the tetrahedral sites in ZnGa₂O₄ spinel structure,and the Ga-O coordination environment has a great influence on the photoluminence of ZnGa₂O₄ phosphors.The increased band gap energy comes from the shortening of Ga-O bond length in the ZnGa₂O₄ spinel obtained by the precursor route.After further improvement of the LDHs precursor route with the introduction of pre-calcination and sintering process steps,complex metal oxide monoliths(MgAl₂O₄,MgFe₂O₄ and In_2-xMg_xO₃)with macropore frameworks have been obtained.The microstructures（morphologies,particle sizes,spacing among particles and compositions）of above macroporous monoliths have been finely tuned by changing precursor composition and sintering temperature of precursors.Further investigation shows that these as-prepared monoliths display promising surface super hydrophobicity for n-octadecanoic acid modified MgAl₂O₄ spinels,ferromagnetism for MgFe₂O₄ ferrites and semiconductor optical behaviors for Mg-doped In₂O₃,respectively. Hydrothermal and solvethermal syntheses are soft solution processes （SSP）and environment-friendly technology.They are commonly used for the preparation of various inorganic functional materials.Based on the urea hydrolysis homogeneous precipitation,high surface area mesoporous ZnAl₂O₄ and NiAl₂O₄ spinels with high thermal stability have been prepared via a facile template-free hydrothermal approach.After detailed characterization,it has been found that this strategy involves two-step reaction process,including the formation and structural transformation of precursor.By controlling the synthesis parameters such as reaction temperature,urea concentration,and calcination temperature,the structural and textural properties of mesoporous spinels can be regulated.However,after adding appropriate amount of different alcohols,crystallized micro/mesoporous Zn-Al complex oxides have been successfully prepared in a single step synthetic route without organic templates.In addition,the influence of alcohol types and adding amounts on the structure and textural properties of micro/mesoporous Zn-Al complex oxides have also been detailedly investigated.更多还原