【作者】 杜丽；

【导师】 廖世军；

【作者基本信息】 华南理工大学 ， 应用化学， 2009， 博士

【摘要】 介孔材料以其高比表面积、结构排列有序、孔径大小均一、孔径可以在2～50 nm范围内连续调节等优点,以及这类材料在吸附、分离、催化、药物缓释等方面,甚至光、电、磁等领域的潜在应用前景而备受人们关注。目前广泛研究的硅基介孔材料由于骨架由氧化硅组成,仅仅具有少量的弱酸中心,基本不具备催化功能,不能充分发挥介孔材料结构的优越性。因此,通过向介孔孔壁上掺杂其他原子,或在材料表面修饰有机基团,赋予硅基介孔更好的吸附及催化性能已成为近年来介孔材料研究领域的热点课题。另一方面,通过使用多重模板剂的方式赋予介孔材料以特定的形貌,无论是从材料合成科学的角度,还是从材料应用的角度来看,均具有十分重要的意义。本文主要从实验和理论两个方面对新型的具有特殊形貌介孔材料和掺杂杂原子的介孔材料的制备与性能进行了研究。合成了系列掺杂介孔分子筛材料,以及具有球状、空心球状、叶片状等特殊形貌的介孔材料,考察了通过适当修饰和处理后的这些材料的催化、吸附、储氢、和控制释放性能。采用SEM/TEM、XRD、XPS等对这些材料进行了表征,获得了许多重要信息,并在此基础上提出了空心球状介孔材料的形成机理。通过一步合成法合成出了将一种新型的稀土金属钕掺杂的硅基介孔材料,非常重要的是,合成出的材料除了成功地实现了钕的掺杂外,还具有空心球状结构形貌。实验考察了反应时间、反应物中的硅钕比(nSi / nNd)以及模板剂的脱除方式对产物介孔结构的影响。XRD和XPS结果表明当nSi / nNd >10时,Nd可以很好地以三价形式替代硅原子嵌入到介孔材料骨架之中,钕掺杂介孔材料具有比表面积高、孔径分布均匀、良好的热和水热稳定性等重要特点。同时,钕掺杂介孔材料对于苯乙烯的催化氧化反应具有良好的催化性能。当硅钕摩尔比为20时,其苯乙烯转化率可达16.21 %,生成苯乙醛的选择性可达95.07 %。采用十二烷二胺(DADD)为主模板剂,聚乙烯吡咯烷酮(PVP)和三嵌段共聚物(F127)为助模板剂的双模板剂路线,我们成功地合成出了具有漂亮的树叶状及实心球状形貌的介孔材料。这些样品具有比表面积高,蠕虫孔道分布均匀、热稳定性高等特点。通过浸渍-氢气还原法将5 wt%的Pd负载到这类材料上制得一种高储氢量的储氢材料,发现这类材料具有优秀的储氢性能,在室温和氢压力为12 atm条件下,储氢量高达2.59 wt%,使得该材料可望成为一种有效的储氢材料。另外,采用十二胺(DDA)为主模板剂,PVP和F127为助模板剂分别合成出了具有空心球和棉花糖形貌的介孔材料。并在大量实验数据的基础上尝试提出了空心球形貌的形成机理,而且通过实验对机理进行了验证。选择不同分子量的具有不同链长的PVP聚合物为助模板剂制备得到不同大小的空心球介孔材料。当使用较长链长的PVP-30为助模板剂时,合成得到的粒径尺寸约为500 nm的空心球介孔材料。然而,使用短链长的PVP-10合成出的粒径尺寸明显下降到约为170 nm,结果表明空心球的尺寸可以通过PVP聚合物的链长进行调节控制。实验还考察了不同PVP浓度的影响,当PVP的浓度小于形成球状的临界胶束浓度时,空心球结构将逐渐消失。验证了我们提出的DDA为主模板剂形成介孔结构,PVP为助模板剂主导空心球结构的机理。空心球和棉花糖状的介孔材料均具有高比表面积、均匀孔径和大孔容,例如,空心球介孔材料的孔容高达1.77 cm3g-1,棉花糖状的介孔材料的比表面积高达1255 m2g-1。以两种材料为吸附剂,考察研究了样品储载客体分子香豆素480的储载能力,空心球介孔材料的储载量约是棉花糖状介孔材料储载量的3倍。从而说明空心球介孔材料是一种很好的储载客体分子的载体。最后,我们尝试通过引入一个纳米阀门在空心球介孔材料来制备一种新型的智能纳米储存材料,首先以DDA和PVP-10为双模板合成出了空心球和实心球介孔硅材料,然后将α-环糊精为阀门,三种不同链长的含苯胺基的有机硅烷链为“芯”的pH响应的纳米阀门安装在介孔材料上。该纳米阀门依靠的是α-环糊精和有机硅烷链之间的氢键结合作用。在中性条件下,α-环糊精与苯胺基链相互结合,大量的环状分子处在介孔的孔口处,因而客体分子被封闭在空心介孔硅材料中;而当pH≤5或6达到苯胺基中氨基得以质子化的pKa时,氨基被质子化带有正电荷,从而两者之间失去了相互结合作用力而分开,药物分子随之释放。实验考察了纳米阀门的药物释放在不同链长、不同pH值及不同介孔材料下的影响,实验表明短链纳米阀门比长链纳米阀门释放的量多,低pH值环境中释放的速率快,空心球中释放的量是实心球中释放量的2倍。因此可见,含有纳米阀门控制器的空心球介孔材料可望在药物缓释应用材料中担当一个重要角色。更多还原

【Abstract】 Mesoporous materials have attracted much more attention due to their advantages, such as high surface area, ordered arrangement, uniform pore structure, as well as their pore size could be adjusted in the range of 2 to 50 nm, and their potential application in the field of sorption, separation, catalysis, drug control-release, light, electricity and magnetism, etc. Due to the framework of the most current mesoporous materials is composed of SiO2, which only possess a little of weak acid centers, they are almost catalytic inactive. To make the silica based mesoporous materials possess catalytic active, embedding hetero atoms into the silica framework or modifying the framework of silicas with organic functional groups have been widely applied, and it is becoming one of the hottest topics in the field of mesoporous materials. Furthermore, synthesis of the mesoporous materials with special morphology by using multiple surfactants as co-templates is a novel attempt, it is a valuable attempt not only for improving the knowledge of materials science, but also for extending the application areas of mesoporous materials.The main topics of this dissertation are the preparation and characterization of the hetero atoms embedded mesoporous materials and the novel mesoporous silicas with special morphologies. A series of the metal embedded materials, and the mesoporous silicas with special morphologies, including solid sphere, hollow sphere, and leaf like shape, have been synthesized, their performances in catalysis, sorption, hydrogen storage, and medicine controlled release have been investigated, and some of the materials are modified by supporting precious metal or introducing functional groups. All the synthesized materials were characterized with SEM/TEM, XRD, XPS, et al, and some important information about the structure of materials has been obtained. Furthermore, a possible mechanism for the formation of hollow sphere structure also has been proposed.A new type of neodymium embedded mesoporous silica material has been synthesized successfully by a facile one-pot approach, it is important that the synthesized materials not only had the Nd incorporated into the framework of synthesized materials, but also exhibited a hollow sphere morphology. The effects of molar ratio of Si/Nd, synthesizing time and the removal method of templates have been investigated. Both XRD and XPS results confirmed the framework incorporation of Nd atoms into the framework of mesoporous silica when the molar ratio of Si / Nd is more than 10. It was found that the material showed high surface area, uniform pore size distribution, good thermal and hydrothermal stability. Meanwhile, it was also found that the Nd embedded hollow mesoporous silica material showed good catalytic activity and selectivity towards the oxidation of styrene. When the molar ratio of Si/Nd is 20, the conversion of styrene reached 16.21 %, and the selectivity of hyacinthin was high up to 95.07 %.By using 1, 12-diaminododecane (DADD) as main template, poly(vinylpyrrolidone) (PVP) and tri-block copolymer (F127) as co-templates, mesoporous silica with beautiful leaf-shape and solid sphere structures were successfully synthesized respectively. The mesoporous silicas showed high surface area, uniform pore wormlike pore structure and high thermal stability. By supporting 5 wt% Pd on the solid sphere mesoporous spheres with an impregnation-hydrogen reduction process, a high volume hydrogen storage material was prepared. It was found that the sample exhibited good hydrogen storage properties, the storage capacity was up to 2.59 wt% at room temperature and hydrogen pressure of 12atm, which might make it a promising hydrogen storage candidate material.Furthermore, a hollow sphere and cotton candy like mesoporous silica were synthesized by using DDA as main template, PVP and F127 as co-templates respectively. Based on the experimental results, a possible formation mechanism for hollow-sphere mesoporous morphology has been proposed. When the different molecular weight PVP with different chain length as co-template was applied, the different mesoporous materials were obtain. When long chain PVP-30 was used as co-template, the hollow sphere mesoporous silica with diameter of ca. 500 nm was synthesized; However, when short chain PVP-10 was used, the diameter was decreased to ca. 170 nm; indicating that the size of the hollow sphere was controlled by the chain length of the PVP polymers. In addition, the effect of PVP concentration was also investigated; it showed that the hollow sphere morphology will be disappeared when the concentration was lower than a critical value. It verified our proposed mechanism that the mesoporous structure might be dominated by main template DDA, and the morphology might be dominated by co-template PVP. Both hollow sphere and cotton candy like mesoporous silicas showed high surface area, uniform pore size, and large pore volume, e.g. the pore volume of the hollow sphere could be high up to 1.77 cm3g-1, and the surface area of the cotton candy like mesoporous silica could be 1255 m2g-1. The storage properties of the hollow sphere and the cotton candy like mesoporous silica were measured by loading Coumarin 480 dye molecules, the storage amount of hollow sphere is almost three times of that of the cotton candy like mesoporous silica, suggesting that the hollow sphere mesoporous silica with a large hollow space is a good guest molecule storage material.Finally, we attempted to prepare a novel type of intelligent nano storage materials by introducing a nanovalve into the hollow sphere materials, firstly the hollow sphere and solid sphere materials was synthesized by using DDA and PVP-10 as co-templates, then a pH value sensitive nanovalve was introduced on the mesoporous silica by using theα-cyclodextrin (α-CD) rings as capping agents and three different of anilino group linker molecules as stalks. The nanovalve’s work relied on the hydrogen bonding interaction betweenα-CD and the stalk. When theα-CD ring is complexed with the stalk at neutral pH, the bulky cyclic component is located near the pore openings, thereby blocking departure of cargo molecules that were loaded in the nanopores and hollow interior of the particle. Protonation of the nitrogen atoms at lower pH (≤5 or 6) causes the binding affinity to decrease, releasing theα-CD and allowing the cargo molecules to escape. The effect of different stalk lengths, pH conditions and different mesoporous silica on the release of fluorescent dye cargo molecules is measured, and the results showed that nanovalves functionalized with short linkers molecules can release more molecules than that with long linkers molecules, the release rate of cargo molecules would be faster at lower pH condition, hollow mesoporous silica can release as much as two times more cargo molecules than solid mesoporous silica. Therefore, the hollow sphere mesoporous silica with nanovalves will potentially play an important role in the application of drug delivery.更多还原