【作者】 杨超；

【导师】 王焰新；

【作者基本信息】 中国地质大学 ， 环境科学与工程， 2012， 博士

【摘要】 全世界大约有20多个国家和地区都不同程度的存在因地下水中含氟浓度较高而导致的饮用水氟离子超标问题。饮用含氟水很容易引起氟中毒,世界卫生组织将饮用水中的氟离子浓度限定为1.0mg/l。在我国除上海、海南、台湾外,其他各个省市自治区都有不同程度的存在地方性氟中毒现象,有近7000万人的长期饮用含氟超标的饮用水。同时,沿用百年的常规净水工艺,即“絮凝—沉淀—过滤—消毒”,难以有效去除饮用水中氟离子(≤10ppm)。含氟水的有效去除关系到部分中西部和边远地区饮用水安全。因此,发展高效、低成本且无次生污染的实用净水脱氟技术,是保障饮用水安全亟需解决的关键问题。本论文针对我国含氟水的特点和深度净化处理的需求,设计合成介孔氧化硅、介孔氧化铝以及氧化硅-氧化镧介孔复合材料和多孔层状水滑石等特定结构与形貌的纳米吸附材料。探索其孔径大小及分布方式的调制规律：研究其在水中与氟离子的相互作用；探讨其吸附热动力学过程。揭示纳米吸附材料对氟离子的高效吸／脱附机理；阐明组分、介孔结构几何特性的变化对氟离子吸附特性的影响机制。其主要研究内容如下：1.利用介孔氧化硅MCM-41为模板成功制备出规则的六边柱状及圆柱状镧-硅复合介孔材料,其孔道直径约为4nm,比表面积约为800.40m2/g。在镧含量小于10%的范围内,随着材料中镧含量的增加,可实现有序介孔结构向蠕虫介孔结构的演化,显著调控材料的表面Zeta电位,从而提高其对水中氟离子的吸附。突破了具有表面负电荷特性的硅基介孔材料未能有效应用于无机阴离子吸附的难题。吸附试验研究表明：在微污染低浓度条件下(氟离子≤10ppm),镧-硅复合介孔材料表现出良好的快速去除水中氟离子的能力。氟离子初始浓度为5.72mg/时,60min内氟离子吸附量高达25.36mg/g。动力学研究表明吸附过程符合准二级动力学模型。2.介孔氧化铝的可控合成：采用P123聚醚为模板剂,以异丙醇铝为铝源,溶胶-凝胶合成出了高度有序介孔氧化铝,其比表面积为338m2/g,孔径约9nm,孔体积为0.88cm3/g。通过提高合成过程的煅烧温度可使介孔材料孔壁晶化,当温度达到850-C时,成功制备出晶态有序介孔γ-Al2O3,其比表面积为224.40m2/g,孔体积为0.664cm3/g。以硝酸铝和氯化铝为铝源,溶胶-凝胶合成出了球形蠕虫状介孔氧化铝,其比表面积分别为127.1m2/g和85.68m2/g,孔径约10nm和14nm,孔体积为0.33cm3/g和0.35.cm3/g。研究了不同铝源、煅烧温度等对介孔氧化铝的形貌、孔径大小、分布、孔道结构和晶体结构的演化规律。3.介孔氧化铝吸附氟离子性能研究：制备出的介孔氧化铝材料具有十分优异的氟离子快速吸附性能,吸附速率快(10min达到吸附平衡),吸附容量高。有序介孔氧化铝吸附容量高达115.41mg/g,蠕虫状介孔氧化铝吸附容量也高达96.18mg/g,为同等条件下传统的Y-Al2O3的几十倍,该数值远高于文献报道的铝系氟离子吸附材料。共存离子研究表明,晶化介孔氧化铝因其晶态结构的稳定性表现出良好的离子选择性和可重复利用性。在高氟离子浓度条件下,两种吸附剂的吸附热力学均符合弗里德里希模型。但在低浓度(氟离子≤10ppm)溶液中,吸附热力学符合朗格缪尔吸附模型。4.利用水热法合成均一、规整的六方片状镁铝层状水滑石(LDHs),其直径约为200～300nm,厚度为20nm。通过焙烧复原法验证了镁铝水滑石具有优异的“结构记忆”效应。重点研究了低浓度条件下(氟离子≤10mg/l)镁铝水滑石及焙烧水滑石的吸附性能,探讨了吸附时间、吸附剂的用量及溶液的pH值等对氟离子吸附量及去除率的影响；揭示了镁铝水滑石及其焙烧产物对氟离子吸附的热力学及动力学特性。再生实验表明纳米水滑石材料具有良好的重复使用性能。5.纳米吸附材料吸附氟离子的机理研究：经综合分析,我们认为纳米材料吸附氟离子经历三个过程：溶液中氟离子的扩散、氟离子在吸附剂表面吸附和氟离子与吸附剂活性基团的离子交换。并分别采用离子传输模型,吸附热动力学模型以及吸附剂表面的离子交换机理对其进行描述。同时,结合材料分析手段对镧-硅复合介孔材料、介孔氧化铝和镁铝水滑石吸附氟离子的机理进行了讨论。更多还原

【Abstract】 Today drinking water in more than20countries and regions worldwide has excessive fluoride concentration. The problem can easily cause fluoride toxicity in human, thus World Health Organization (WHO) sets the maximum concentration limit of fluoride ions in drinking water to1.0mg/l. In China, more than70million people are using drinking water with excessive fluoride concentration. Regional endemic fluoride toxicity has been reported in almost every province except Shanghai, Hainan and Taiwan. Therefore, removal of excessive fluoride ion in drinking water is critical to people’s health. However, conventional water purification technology, that is,"Flocculation—Precipitation—Filter—Disinfection", does not effectively remove fluoride ion in drinking water. So there is immediate need to develop new fluoride removal technology that is highly efficient, low-cost and pollution-free.This paper is specifically designed to meet the demand of deep purification treatment on drinking water with excessive fluoride concentration. A few nano-sized adsorption materials were synthesized to specific structure and surface topography, including mesoporous silica, mesoporous alumina Lanthanum oxide mesoporous compound and Porous layered double hydroxides. Different approaches to regulate micro-pore structure of those materials, such as pore size, pore distribution and surface site density, were explored. Interaction between mesoporous material and fluoride in aqueous solution was studied. Adsorption thermodynamics and kinetics process were analyzed. The mechanism of high efficient fluoride adsorption was discussed, and the relationship between micro-structure and fluoride adsorption property was investigated. The main contents of this paper are as follows:1. Regular six-edge columnar and cylindrical La-silicon composite mesoporous materials were synthesized using MCM-41as hard template. Pore size of the La-silicon composite was4nm and surface area was800.40m2/g. With the increase of lanthanum amount in the material, though always kept below10%, ordered mesoporous structure gradually evolved into worm-like mesoporous structure. Thus it was possible to adjust Zeta potential on the surface of the material significantly, which then improved fluoride adsorption capability of the material. So this work resolved the issue that silica mesoporous materials could not be effectively applied in inorganic anions adsorption. Sorption experiments indicated that La-silicon composite mesoporous materials had excellent adsorption property at low fluoride concentration (≤10mg/l). When initial fluoride concentration was5.72mg/l, fluoride adsorption capacity went up to25.36mg/g within60minutes. Kinetic data were well described by pseudo second-order model.2. Regulated synthesis of mesoporous alumina:Highly ordered mesoporous alumina was prepared using Aluminium isopropoxide as precursor and P123as template agent. Its surface area, pore size, and pore volume were338m/g,9nm and0.88cm3/g respectively. Mesoporous wall was crystallized in high temperature. When the temperature was raised to850℃, highly ordered crystalline mesoporous alumina was synthesized successfully, its surface area and pore volume were224.4m2/g and0.664cm3/g respectively. Two kinds of worm-like spherical mesoporous alumina were prepared by sol-gel method, using aluminum nitrate and aluminum chloride as precursor separately. The resulting surface area was127.1m/g and85.68m/g, pore size was10nm and14nm, pore volume was0.33cm/g and0.35cm/g respectively. In addition, study was done regarding the impact of synthesis conditions, such as precursor and temperature, on the morphology, pore size, pore distribution, and pore structure of mesoporous alumina. 3. Adsorption properties of mesoporous alumina:The synthesized mesoporous alumina demonstrated excellent adsorption capacity. The adsorption capacity of highly-ordered mesoporous alumina and worm-like mesoporous alumina was115.4mg/g and96.18mg/g respectively, about tens of times of traditional γ-Alumina adsorbent under the same condition. In addition, both types of mesoporous alumina had high adsorption rate (10min to reach equilibrium). Apparently highly-ordered mesoporous alumina had better adsorption capacity and adsorption rate than worm-like mesoporous alumina. Crystalline mesoporous alumina showed better co-existing anions resistance and regeneration property because of the stability of its crystal structure. The experimental data in high fluoride concentration were better described by Freundlich model, but Langmuir model fit better in low fluoride concentration (≤10ppm)4. Nano-sized Mg/Al-C03hydrotalcite-like compound (LDHs) was synthesized by hydrothermal synthesis method. The sample had uniform and thin hexagonal platelets with a mean lateral size as large as200～300nm and a thickness of about20nm. The XRD analysis indicated that LDHs had the so-called "memory effect" The adsorption experiments were performed with low initial fluoride ion concentration (≤10mg/L), The effect of adsorption time, adsorbent amount, solution’s pH value on adsorption capacity and fluoride ion removal rate were studied. Adsorption thermodynamics and kinetics property were also discussed. The regeneration results indicate that nano hydrotalcite-like compounds have good reusable nature.5. Analysis on fluoride adsorption mechanism of mesoporous material:After comprehensive analysis, three processes could used to describe the fluoride adsorption on nano materials:diffusion process, adsorption process, and ion exchange process. These processes can be explained by ion transport model, adsorption thermodynamic model and ion exchange mechanism respectively. According to the three models, the fluoride adsorption mechanism of La-silicon composite mesoporous material, mesoporous alumina, and Mg/Al hydrotalcite-like compound were discussed using material analysis method.更多还原