【作者】 闫静宜；

【导师】 沈玉华；

【作者基本信息】 安徽大学 ， 无机化学， 2011， 硕士

【摘要】 类水滑石化合物又称为层状双金属氢氧化物(Layered Double Hydroxides,简称LDHs),是一类具有特殊结构的层状材料。它独特的结构有利于多种功能性离子的引入,扩大了此类材料的应用范围,尤其是其作为催化剂和催化剂前体的应用更引起人们的普遍关注。而过渡金属因为特殊的电子结构排布使其在催化、发光、磁性材料等领域都具有广泛的应用。因此本论文提出利用LDHs的结构特征,以过渡金属作为构成层板的元素,研究其在催化降解有机染料方面的应用并引进磁性材料制备核壳式结构可循环利用的Fe3O4@SiO2@(Co/Cr)-LDH光催化材料。论文的主要内容可以分为三个部分：1.以较为活泼的铁系元素二价钴和三价铬、铁作为构成LDH的层板结构的金属离子,以NaOH和Na2CO3为沉淀剂,晶化温度60℃,晶化时间24小时下合成出层状结构完整的类水滑石Co/Cr-LDH和Co/Fe-LDH。对所制得的纳米类水滑石材料进行了形貌、微观结构、比表面等表征。探讨了纳米水滑石可能的反应机制。结果表明,产物为晶相单一的类水滑石,层间阴离子为CO32-,具有较高的比表面积。以具有偶氮结构的甲基橙溶液为模拟染料污水,以样品对甲基橙的光催化降解率为指标,在模拟太阳光下考察制备出的LDHs的光催化活性,取得了较满意的效果。对催化反应进行动力学研究确定催化反应为一级动力学反应。2.以磁性Fe3O4负载层状双羟基金属氢氧化物Co/Cr-LDH,复合物将催化性与磁性联合,利于其回收再利用。本实验采用溶剂热方法制备的磁性纳米Fe3O4为基体,再以硅酸乙酯为原料,通过水解的方法在其表面生成了一层SiO2壳层以保护Fe3O4粒子。采用溶剂热法,水热180℃保持8小时后成功将Co/Cr-LDH沉积包覆在Fe3O4@SiO2核表面形成Fe3O4@SiO2@(Co/Cr)-LDH磁性复合光催化材料。对合成样品的形貌和结构进行扫描电镜(SEM),透射电镜,X射线衍射(XRD),红外(FT-IR)等表征。结果表明,样品为球形,LDH包覆完全。样品的磁性测试表明复合物对外加磁场有强响应性。在模拟太阳光下,Fe3O4@SiO2@(Co/Cr)-LDH对甲基橙的降解显示了良好的光催化活性,并且该催化剂回收利用了四次后降解率依然可以达到百分之八十。3.复合金属氧化物具有比表面积大、活性元素分布均匀、金属离子还原条件温和的优点,可应用于许多酸碱催化和氧化还原催化过程。本章在碱性条件下通过化学共沉淀法制备层状双羟基金属氢氧化物Ni/Cr-LDH.在合适的温度下,焙烧LDHs分解生成复合金属氧化物。通过SEM, XRD, FT-IR, BET(比表面)等测试方法对Ni/Cr-LDH及其热解过程中产物的形貌、微观结构、晶型及性能等进行分析。结果表明,热分解过程比较复杂,复合氧化物的性质与前体以及焙烧温度有关。用甲基橙的降解反应作为光催化的模型反应,在模拟太阳光下对比研究Ni/Cr-LDH及其焙烧物的光催化活性,并对光催化反应进行动力学研究。结果表明,这些样品的催化性能与其结构及组成有关,其中二元复合金属氧化物Ni(Cr)O表现出相对较好的光催化活性,组分间的协同效应得到发挥。更多还原

【Abstract】 Layered double hydroxides (LDHs) have attracted extensive attention because of its structures and properties. The layered structure of LDHs makes it possible for many functional ions to be incorporated and the uniform dispersion of metal-organic anions in interlayer galleries or metal cations in layers extends the applications of layered materials to a wide variety of fields, especially as the catalyst and catalyst precursor. Meanwhile the electronic structure of transition metal offers many advantages in the areas of optical, magnetic and catalytic materials. Therefore, my dissertation aims to introduce transition metal as constituting elements to the layer board to synthesize LDHs with special structure and study the photocatalytic degradation application of organic dyes and we also prepared Fe3O4@SiO2@(Co/Cr)-LDH shell magnetic nanocomposites. The main research content can be divided into three parts:1. In this chapter, the transition metals cobalt, ferrum and chromium were introduced to synthesize the LDHs at pH=9-10, aging temperature of 60℃and aging time of 24 hours by coprecipitation using NaOH and Na2CO3 as the precipitator. The structure, surface morphology, specific surface area and preparation mechanism of the resulting sample were investigated. The result indicated that the crystalling phase of the product was single and the specific surface area was large, CO32- was the unique ion in the interlayer of LDHs. A solution of methyl orange with azo was used as simulated dye wastewater to study photocatalytic activity of LDHs on degradation of methyl orange at room temperature under visible light irradiation. The rate of photocatalysis degradation can be expressed in first-order kinetics model. The result was satisfactory and LDHs have potential as new type visible catalysts.2. The nanomaterial combines both catalytic capability and high separation efficiency, making it an ideal support for recoverable anionic functional materials. Herein, magnetic Fe3O4 crystalline nanoparticles were synthesized using a solvent-thermal method. By using the hydrolysis of tetraethyl orthosilicate, a silica-coated magnetite core was prepared following a sol-gel process. After that, Fe3O4@SiO2@(Co/Cr)-LDH shell nanocomposites deposited from a layered double hydroxide at aging temperature of 180℃and aging time of 8 hours by solvent-thermal method. Nanoparticle morphology and structure were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopic (FT-IR) techniques. Their magnetic saturation values were determined using a vibration sample magnetometer. The result indicated a typical layer by layer structure with a magnetite core, a silica layer in the middle layer, and an LDH shell nano structure in the outer layer can be clearly observed. The obtained product possesses high magnetization values and superparamagnetic property which provides a convenient means to remove nanoparticles from solution. A solution of methyl orange as the simulated dye wastewater, we investigate the photocatalytic activity of composite nanomaterial on degradation of methyl orange under visible light irradiation. The results indicated that the nanocomposites had perfect photocatalytic degradation activity of methyl orange. Remarkably, the photocatalyst still kept the decomposition efficiency up to 80% even after being used for four times.3. A co-precipitation method was used for the preparation of nanometer-size Ni/Cr-LDH particles. The LDHs were facile to be decomposed when heated and obtained the complex oxides. Because of their typical characteristics such as big specific surface area, even distribution of catalytic active cites and mild reduction condition of metallic cations, the complex oxides will have fine application prospects in some acid-base catalysis or redox catalysis reactions. The physicochemical performances of the LDHs and complex oxides were characterized by using the modern instrumentals of SEM, XRD, FT-IR and BET techniques. The thermal decomposition procedure is complicated and the properties of complex oxides are mainly determined by the composition of the precursor and calcination temperatures of thermal decomposition process. We investigated the photocatalytic activity of Ni/Cr-LDH and complex oxides on degradation of methyl orange under visible light irradiation. The mechanisms and the kinetics of photocatalysis degradation of methyl orange were also discussed and the degradation data were fitted to the pseudo first-order kinetic model. Attributed to the synergistic effect of the components, the complex oxide Ni(Cr)O showed the preferable catalytic performance. It is shown that the differences in catalytic performances of these samples are related to the structure and composition of the catalysts.更多还原