新型二氧化硅囊泡材料的自组装及结构调控

【作者】 余美花；

【导师】 余承忠；

【作者基本信息】 复旦大学 ， 无机化学， 2008， 硕士

【摘要】 随着纳米技术的发展,新型多孔材料引起了研究者的极大兴趣,并在缓释、催化、分离等领域具有重要的应用价值。多孔材料往往通过模板方法来制备,其中作为模板剂的表面活性剂分子可以自组装为不同的超分子结构,例如囊泡和不同的液晶相结构。利用不同的液晶相为模板（liquid crystal templating,LCT）,可直接制备或者协同组装出有序介孔材料。Hubert等首先提出利用离子型表面活性剂形成有机囊泡作为模板（vesicle templating,VT）,进而制备无机氧化硅单层囊泡材料的方法。最近,我们利用商品化嵌段高分子PEO₂₀PPO₇₀PEO₂₀（PEO为聚环氧乙烷,PPO为聚环氧丙烷）为模板剂,在不加入有机共溶剂的条件下直接制备出大孔径、高孔容的无机单层囊泡材料,并提出了“协同囊泡模板”（cooperative vesicle templating,CVT）的机制。然而,相对目前大量利用LCT路线制备介孔材料的文献报道而言,通过CVT机制合成新型大孔材料的概念尚未得到更进一步的拓展。本论文在先前工作基础上,分别从无机前驱物和有机结构导向剂两方面进一步系统地考察了CVT方法在材料自组装及结构控制方面的详细机制,以拓展该路线的适用范围,并更深入地理解掌握LCT和CVT机制的区别和联系,以期制备出结构、形貌更丰富的新颖无机材料。我们发现在同一个模板体系中,仅仅通过硅源的改变就能实现囊泡或有序介孔结构的选择性合成。对于三嵌段聚合物B50-6600(EO₃₉BO₄₇EO₃₉,BO为聚环氧丁烷)或P85(EO₂₆PO₃₉EO₂₆)模板体系,在近中性的缓冲溶液体系中,保持其它合成参数完全一致的条件下,当正硅酸甲酯（tetramethyl orthosilicate,TMOS）作为硅源得到高度有序的介孔结构,然而利用正硅酸乙酯（tetraethyl orthosilicate,TEOS）作为前驱物则得到大孔径囊泡或泡沫结构。通过衰减全放射液体红外（ATR-FTIR）技术对B50-6600模板体系进行了硅物种演变的原位检测,并提出了“区分效应”机制对这一结果进行了合理解释。在此工作基础上,通过调节亲疏水体积比截然不同的表面活性剂B50-6600（EO39BO47EO39）和B20-3800（EO34BO11EO34）的比例或是带有不同烷氧基硅源TMOS和TEOS的比例,以及改变硅源和表面活性剂的摩尔比等方式,达到对CVT机制的精细调节,首次实现了二氧化硅囊泡材料形貌（空心球状、空心管状）、尺寸（25-100nm）和壁厚（5-25nm）的有效调控。LCT和CVT机制是一个相互竞争的过程,有效控制两种机制,对构造多级复杂结构的新颖材料具有非常重要意义。我们选择了分子量和疏水段较大的聚合物B50-6600为模板剂,在合适的反应条件下,找到了有机-无机复合球状胶束和囊泡状共存的体系点,最终得到新颖的覆盆子状多级二氧化硅空心球（hierarchical siliceous hollow spheres,HSHS）材料。通过考察反应时间及离子强度对材料结构的影响,提出了“胶体粒子”作用模型解释了覆盆子状HSHS新颖材料的形成过程。利用高分子聚合物EO₂₀PO₇₀EO₂₀（P123）作为有机导向剂,采用无机硅酸钠作为硅源,模拟硅藻的矿化过程,在偏酸性条件下,通过改变反应温度、反应物浓度,制备得到聚集的多层囊泡,椭圆状的单层泡沫,以及具有“话梅”形貌的带有海绵状墙壁的多层囊泡。在缓和的水溶液体系中制备得到具有多种复杂孔结构的二氧化硅材料。更多还原

【Abstract】 Novel porous materials have attracted much attention because of their significant applications in controlled release,catalyst supports,and separation.Generally,porous materials are fabricated by template approach.Surfactants can form different supra-molecular structures,such as vesicles and different liquid crystals.By using liquid crystal templating（LCT） or cooperative self-assembly,ordered mesoporous materials have been successfully synthesized.On the other hand,Hubert firstly reported the synthesis of unilamellar silica vesicles by directly coating the pre-formed unilamellar vesicles of ionic surfactants.Recently,by employing commercial triblock copolymer P123(EO₂₀PO₇₀EO₂₀,where EO is poly（ethylene oxide） and PO represents poly（propylene oxide）) as a template in the absence of organic cosolvents, unilamellar siliceous vesicles and nanofoams with large pore diameters and high pore volumes have been successfully synthesized.It is proposed that the siliceous vesicles are synthesized via a cooperative vesicle templating（CVT） approach.However, compared to thousands of documents on the study of ordered mesostructured materials via LCT approach,the general concept of fabricating vesicular materials possessing large pore diameters using CVT approach should be further investigated.In this thesis,we have systematically investigated the cooperative self-assembly of organic-inorganic vesicular structures from both the organic and inorganic parts.It is believed that the CVT mechanism can be generally applied to other systems. Moreover,through manipulating the LCT and CVT approaches,novel inorganic materials with various morphologies and hierarchical pore structures can be obtained.Firstly,we demonstrate that the vesicular or meso-structured inorganic-organic composites can be obtained selectively by just changing the silica source in one templating system.For triblock copolymers B50-6600(EO₃₉BO₄₇EO₃₉,where BO is poly（butylene oxide） either P85(EO₂₆PO₃₉EO₂₆) in a near neutral solution,when the other synthesis parameters are exactly the same,the use of tetramethyl orthosilicate （TMOS） as a silica source gives rise to highly ordered mesostructures,while the utilization of tetraethyl orthosilicate（TEOS） leads to vesicles or foams.And we utilized ATR-FTIR technology as an "in-situ" tool to monitor the hydrolysis and condensation of TMOS or TEOS in the B50-6600 templating system.On the basis of the study,we propose a "differentiating effect" in our synthesis approach to understand the influence of different silica source.Moreover,by varying the ratios of mixed block copolymers with different hydrophilic/hydrophobic moieties and/or mixed silica sources or changing the molar ratios of silica precursors and surfactant, siliceous vesicular structures with controlled shapes（such as hollow spheres,hollow tubes）,sizes（25-100 nm） and wall thickness（5-25 nm） have been successfully fabricated for the first time.When triblock copolymer B50-6600 with a large hydrophobic block and molecule weight is used as a template,by carefully adjusting the reaction conditions where both inorganic-organic composite vesicles and micelles are formed simultaneously in the solution,novel hierarchical siliceous hollow spheres（HSHS） materials with morphology similar to that of the raspberry has been obtained.Through studying the influence of reaction time and ionic strength on the self-assembled structure,we proposed a colloidal interaction model to understand the formation of HSHS structure.Commercial Pluronic triblock copolymer P123 is employed as a surfactant and Na₂SiO₃·9H2O as a silica source to synthesize siliceous materials at mild pH condition.By simply adjusting the reaction temperature and/or the concentrations of reactants,aggregated multilamellar vesicles,unilamellar nano-foams with a elliptical morphology,and labyrinth-like multilamellar vesicles with sponge-like walls have been successfully synthesized via a bioinspired approach.更多还原