【作者】 贺艳；

【导师】 崔学民；

【作者基本信息】 广西大学 ， 化学工艺， 2013， 博士

【摘要】 地质聚合物(Geopolymer)是一种由硅氧四面体和铝氧四面体聚合而成的具有非晶态或者准晶态的铝硅酸盐无机聚合物材料。由于其特殊的三维网络结构,地质聚合物具有强度高、耐腐蚀性、耐高温、施工性能优良等优点,它可广泛应用在建筑材料、冶金、固封核废料等领域。根据文献报道发现,地质聚合物网络凝胶体中有纳米晶体,而且地质聚合物的分子结构与沸石相似,因此研究地质聚合物与沸石分子筛的关系显得非常重要。偏高岭土与碱激发剂反应是制备和研究地质聚合物的经典体系,然而偏高岭土成分复杂,使得地质聚合物转化分子筛的反应机理非常复杂。本研究参照偏高岭土的组成,通过溶胶-凝胶法合成了与偏高岭土结构类似的高纯度的Al2O3-nSiO2粉体(n=1,2)。用合成的粉体制备了Na2O-Al2O3-2SiO2地质聚合物材料,利用SEM、HRTEM、XRD、FTIR、MAS NMR等测试手段,对Na2O-Al2O3-2SiO2地质聚合物及其原位转化的NaA分子筛的结构进行了研究；获得水热前后地质聚合物的组成与结构变化规律,并对地质聚合物转化成NaA分子筛的机理进行了初步研究；成功制备了致密的自支撑NaA分子筛膜,并探索该分子筛膜在海水淡化方面的应用。实验主要结论如下：(1)采用溶胶-凝胶法,制备了Al2O3-SiO2粉体和Al2O3-2SiO2粉体,通过纳米粒度分析仪(DTS)、SEM、XRD和MAS NMR等测试手段,考察Al2O3-SiO2粉体和Al2O3-2SiO2粉体的分子结构和碱激发活性。结果表明：Al2O3-SiO2粉体和Al2O3-2SiO2粉体均为无定形的高纯高活性粉体,具有类似偏高岭土的结构和性能,可以作为研究地质聚合物反应机理和制备NaA分子筛的理想前驱体材料。(2)根据NaA分子筛的理论配比设计地质聚合物体系的原料组成,考察了地聚合物材料的力学性能,以抗压强度为优化目标,研究了养护温度、养护时间、不同水玻璃模数、两种不同硅源的摩尔比对地质聚合物抗压强度的影响。确定了制备碱基地质聚合物最佳条件为：水玻璃模数为1.0,模数为1.0水玻璃中的硅与Al2O3-SiO2粉体中硅的摩尔比为1.0,养护温度为60℃,养护时间为6h。(3)主要研究了水热釜中水热母液的NaOH溶液浓度、水热母液的体积、水热时间、水热温度、不同水玻璃模数和不同硅源的摩尔比对地质聚合物转化成(?)aA分子筛结构和强度的影响,得出了地质聚合物原位转化NaA分子筛的最佳制备工艺：水热母液的NaOH溶液浓度为0mol/L,水热母液的体积为50ml,水热时间为6h,水热温度为90℃,水玻璃模数为1.0,水玻璃中硅源与Al2O3-SiO2粉体中硅源的摩尔比为1：1。(4)通过对Al2O3-SiO2粉体、Na2O-Al2O3-2SiO2地质聚合物和NaA分子筛的结构分析以及硅铝比和碱浓度等研究,发现Na2O-Al2O3-2SiO2地质聚合物与NaA分子筛晶体存在一个物质传递和结构遗传的关系,提出了以Al2O3-SiO2粉体和Na2SiO3溶液为原料的双硅源体系制备Na2O-Al2O3-2SiO2地质聚合物,再由Na2O-Al2O3-2SiO2地质聚合物转化NaA分子筛的反应机理。该反应机理分为解聚过程、缩聚过程和水热晶化过程。在解聚过程,Al2O3-SiO2粉体中Al-O键和Si-O键在OH-的作用下断裂形成[Al(OH)4]-和[OSi(OH)3]-,在解聚后期,[Al(OH)4]-和[OSi(OH)3]-反应生成五配位的铝硅酸盐中间体,这些带负电的中间体围绕钠离子经过缩聚反应形成初级凝胶；在缩聚过程中,[Al(OH)4]-和[OSi(OH)3]-在初始凝胶、固液界面和气孔周围的水合钠离子的水合层聚合形成以-Si-O-Al-O-为基本结构单元的聚合物凝胶,这些聚合物凝胶进一步形成了纳米有序结构,围绕这些纳米有序结构,硅氧四面体和铝氧四面体交替排列形成无定形的三维网络凝胶体。在水热晶化过程,Na2O-Al2O3-2SiO2地质聚合物中无定形三维网络凝胶体会以纳米有序结构(NaA晶核)为成核中心迅速转化为NaA分子筛晶体。(5)采用地质聚合物原位转化NaA分子筛的方法,成功制备了性能良好的自支撑NaA分子筛膜,对NaA分子筛膜的微观结构和分子结构进行了分析,探讨了在海化淡化方面的应用研究。结果表明：该方法制备的NaA分子筛膜表面致密、均匀,抗压强度达到57.6MPa,对于温度25℃,质量百分数为3.5%的NaCl溶液,随着膜厚从9.4m减少到2mm,水的通量从0.42增加至4.74kg·m-2·h-1。当膜厚超过9.4mm时,Na离子的截留率超过99.5%,而水的通量为0.42kg·m-2·h-1。随着渗透温度的增加,NaA分子筛膜在NaCl溶液中的水通量增加,当渗透温度为90℃时,膜厚为9.4mm NaA膜的水通量达到13.86kg·m-2·h-1。更多还原

【Abstract】 Geopolymer is a type of aluminosilicate inorganic polymer material consists of tetrahedral [AlO4] and [SiO4] units, which is of amorphous to semicrystalline. Geopolymer is of high strength, corrosion resistance, excellent thermostability and workability, due to its three-dimensional network structures, and is suitable for use in a wide range of areas including construction, refractory and immobilized nuclear waste applications. The literatures show that geopolymers contain some nanocrystallines, furthermore, the molecular structure of geopolymers is similar to that of zeolite. Therefore, it is very important to study the relationship between geopolymers and zeolites and the reaction mechanism of zeolites transforming from geopolymers.However, it is difficult to confirm the reaction mechanism of zeolites transforming from geopolymers because the chemical composition of metakaolin is very complex. High purity Al2O3-nSiO2powders (n=1,2) were synthesized by sol-gel method. The Na2O-2SiO2-Al2O3geopolymer materials were synthesized with synthetic powders. The structure of geopolymers and NaA zeolite transformed from these geopolymers were investigated by SEM、 HRTEM、XRD、FTIR and MAS NMR testing techniques. The composition and structure change rule of geopolymers and their hydrothermal products were obtained. The mechanism of NaA zeolites transformed from geopolymers was studied. The densification NaA membrane was successfully synthesized and used in desalination of seawater. The principal results are as follows:(1)Al2O3-SiO2powders and Al2O3-2SiO2powders were fabricated utilizing sol-gel method. Molecular structure and alkali-activated properties of these two powders were investigated by DTS、SEM、XRD and MAS NMR techniques. These results show that Al2O3-SiO2powders and Al2O3-2SiO2powders were amorphous and high reactivity powders. The properties and structure of these powders were similar to metakaolin. Al2O3-SiO2powders and Al2O3-2SiO2powders were ideal precursor materials used for the study of the reaction mechanism of geopolymerization and the preparation of NaA zeolites.(2)According to the theoretical proportion of NaA zeolite, the composition of raw materials of geopolymers was designed. The mechanical properties of geopolymers was studied. The optimum process parameters were determined by the compressive strength of the geopolymer products as the main criterion. The effects of curing temperature, curing time, different modulus of water glass and the molar ratios of two different Si sources on the compressive strength of geopolymers. The optimum process conditions of the preparation of geopolymers were determined as follows:the modulus of water glass was1.0; the molar ratios of the Si derived from sodium silicate(Na2O·SiO2) to the Si derived from Al2O3-SiO2powders was1:1; the curing temperature was60℃and curing time was6h.(3) The effects of the concentration of NaOH in hydrothermal mother liquid, the volume of hydrothermal liquid, hydrothermal time, hydrothermal temperature, different modulus of water glass and different molar ratios of Si source on the structure and strength of NaA zeolites converted from geopolymers. The optimum process conditions of the preparation of NaA zeolites derived from geopolymers are as flollows:the concentration of NaOH in hydrothermal mother liquid was0mol/L, the volume of hydrothermal mother liquid was50ml, the hydrothermal time was6h, the hydrothermal temperature was90℃, the modulus of water glass was1.0, the molar ratios of the Si derived from sodium silicate (Na2O·SiO2) to the Si derived from Al2O3-SiO2powders was1:1. (4) The structures of Al2O3-SiO2powders, Na2O-Al2O3-2SiO2geopolymers and NaA zeolite were analysed by HRTEM、SEM、FTIR、MAS NMR and BET techniques. Effects of the molar ratios of Si to Al and alkalinity on NaA zeolites derived from Na2O-Al2O3-2SiO2geopolymers. The relationship between Na2O-Al2O3-2SiO2geopolymers and NaA zeolites was mass transfer and genetic structure. Na2O-Al2O3-2SiO2geopolymers were synthesized by two silicon source system with Al2O3-SiO2powders and sodium silicate. Na2O-Al2O3-2SiO2geopolymers were converted into NaA zeolite after hydrothermal procedure. The reaction mechanism of NaA zeolites derived from geopolymers can be divided into depolymerization, condensation polymerization and hydrothermal crystallization processes. In depolymerization process, the Al-O and Si-O bonds derived from Al2O3-2SiO2powders were broken to form [Al(OH)4]-and [OSi(OH)3]-groups. The water glass contains a few polysilicate, except orthosilicates. In later stage of depolymerization process, pentacoordinate aluminosilicate intermidates were synthesized with [Al (OH)4]-and [OSi(OH)3]-groups, the pentacoordinate aluminosilicate intermidates formed the primary gel around Na+. In condensation polymerization process, the polycondensation of [Al(OH)4]-and [OSi(OH)3]-groups occurred to form polymer gels with the basic structure unit of-Si-O-Al-O-in the hydration layer of hydrated sodium ions which are located in initial gel, the interface between solid and liquid and pores. These gels converted into nano ordered structure. The amorphous three-dimensional network structures with tetrahedral [AlO4] and [SiO4] units generated around the nano ordered structure. In hydrothermal crystallization process, The amorphous three-dimensional network structures from Na2O-Al2O3-2SiO2geopolymers converted into NaA zeolite crystals.(5) Self-supporting NaA membrane was successfully synthesized by the method of NaA zeolite transformed from geopolymers. The microstructure and molecular structure of NaA membrane were analysed. It was investigated that the NaA membrane was used in desalination of seawater. These results show that the NaA membrane was densification uniformity, the compressive strength of NaA membrane was57.6MPa, in the NaCl solution with the mass percent of3.5%at the temperature of25℃,the water flux of NaA membrane increase from0.42to4.74kg·m-2·h-1with the film thichness of NaA membrane decreasing from9.4mm to2mm. The rejection rate of sodium ion was above99.5%, the water flux of NaA membrane was0.42kg·m-2·h-1, when the film thickness was9.4mm. The water flux of NaA membrane in NaCl solution increased with the decrease of pervaporation temperature. The water flux of NaA membrane with the film thickness of9.4mm, reached3.86kg·m-2·h-1at the pervaporation temperature of90℃.更多还原