三元共组装法合成有序介孔高分子—氧化物纳米复合材料及碳材料

【作者】 刘瑞丽；

【导师】 赵东元；

【作者基本信息】 复旦大学 ， 无机化学， 2007， 博士

【摘要】 介观结构材料的合成与组装是当前材料学、化学、物理学、生命科学等研究领域的热点。人们利用无机硅源、烷氧基硅、金属氯化物、有机金属氧化物或它们的混合物等为无机前驱体，采用不同的两亲分子为表面活性剂，通过有机—无机自组装已经合成出丰富多样的空间对称性的无机介孔材料；利用高分子为有机前驱体，两亲分子为表面活性剂，通过有机—有机自组装合成有机（碳）介观结构材料方法也蓬勃发展起来。在合成方面，已经不仅仅局限于单一组分与表面活性剂之间的组装，而是越来越注重将多种不同功能的构筑单元（如有机、无机与生物材料）整合在一起，通过与表面活性剂的多元协同共组装过程来构筑兼有多种优点于一体的有序纳米复合材料，从而扩展介孔材料在催化、能量存储／转化、磁等方面的应用。鉴于此，我们的工作将已经成熟的介孔无机材料的合成体引入到目前刚发展起来的介孔高分子材料的合成体系，通过溶剂挥发三元共组装法合成有序介孔高分子—无机氧化物纳米复合材料（如，高分子—氧化硅、高分子—氧化钛和高分子—氧化铝），经过高温处理后可以转化为相应的碳—氧化物纳米复合材料。同时，考察了其衍生物有序介孔碳材料在能量存储等方面的应用，以及碳—氧化钛在光催化方面的应用。论文的第二章，以三嵌段聚合物PEO-PPO-PEO（F127）为结构导向剂，水溶性A阶酚醛树脂（resol）为高分子前驱体和氧化硅寡聚体为无机前驱体，通过三元共组装一步法成功合成了有序介孔高分子-氧化硅和碳—氧化硅纳米复合材料。该过程具有简单、低廉、易操作的特点。所得到的复合材料具有“互穿”的骨架结构，且“均一”复合。复合材料中高分子／氧化硅和碳／氧化硅的比例可以从0到∞对进行调节。具有刚性特点的氧化硅的引入，有效地降低了高温处理过程中骨架的收缩。除去碳—氧化硅纳米复合材料中氧化硅组成之后，得到具有大的孔径（6.7 nm）和孔容（2.02 cm³／g）以及高比表面（2470 m²／g）的有序的介孔碳材料。同时，在合成复合材料的时候通过延长正硅酸乙酯的老化时间，最终可以得到双孔（2.6和5.8 nm）的有序介孔碳材料。所得到的有序介孔碳材料不仅具有大的孔径和高的比表面，同时具有互穿孔结构，这些优点将更有利于它的实际应用。同时，选用不同链段长度的三嵌段共聚物（PEO-PPO-PEO），以及含有更为疏水的PBO链段的PEO-PBO-PEO嵌段共聚物为模板，进行了其它介观结构有序介孔高分子—氧化硅和碳—氧化硅纳米复合材料合成的探索。论文的第三章，研究了所得到的具有大孔径和高的比表面积有序介孔碳材料（MP-C-46）在锂离子存储、双电层电容器等方面的应用。实验发现明显优越于通常得到的有序介孔碳（C-FDU-15）。在1M（C₂H₅）₄NBF₄／PC为电解质的有机体系中，碳MP-C-46表现出117F／g的电容，大于目前所报道的其它有序介孔碳材料。并且在很宽的电位区间（0～3V）、电流为200mV／s的情况下，仍表现出很好的平行四边形CV曲线。在锂离子存储方面，首次循环表现出了很高的电容1048mAh／g，且多次循环后仍具有良好的充／放电可逆容量。电化学结果表明，三元共组装法所得到的有序介孔碳材料在能量存储应用方面具有诱人的前景。论文的第四章，同样选用三嵌段聚合物PEO-PPO-PEO（F127）为结构导向剂，水溶性A阶酚醛树脂（resol）为高分子前驱体和四氯化钛寡聚体为无机前驱体，将三元共组装法和原位晶化技术结合起来，成功地合成了具有晶化骨架、高的热稳定性和高比表面的有序介孔碳—氧化钛纳米复合材料。复合材料中碳／氧化钛的比例可以在很宽范围内调节（以TiO₂的质量百分含量计算20-80wt％）。该复合材料将碳的高比表面和吸附性能等特点与氧化钛的光催化性能结合起来，以30C-70T1O₂的复合材料为例，在降解RheB的光催化方面表现出了良好的光降解性能。同时，该方法可以拓展到其它的碳—金属氧化物纳米复合材料的合成，如碳—氧化铝纳米复合材料。更多还原

【Abstract】 The synthesis and assembly of mesostructured materials represent an exciting direction in the research fields of materials science, chemistry, physics and life science. During the past decades, mesoporous inorganic materials with different mesostructures have been synthesized by organic-inorganic self-assembly, wherein Si（OR）₄, R_xSi（OR’）_4-x and MC1_x or their mixture are used as inorganic precursors and amphiphilic supramolecule is used as a template. Recently, mesoporous polymers （carbon） with open frameworks have been developed by organic-organic self-assembly of triblock copolymers with resols. However, up to now, the prepared materials are far from diversified in single compositions. More and more attention focuses on organizing muti-functional （organic, inorganic and biologic） building blocks into integrate nanocomposites, which have remarkable and complementary properties. Moreover, confined-space effects inside the nanospace of mesostructures would certainly modify the unique chemical behaviors. The research presented in this thesis is aimed to present a simple, low-costing and easily reproducible approach to prepare mesoporous nanocomposite, enriching the compositions and to take a further step to exploit their applications, such as electronics and magnetics and energy storage.This thesis is based on an "evaporation induced triconstituent co-assembly method", which was a combination of organic-inorganic self-assembly to ordered mesoporous silicates and organic-organic self-assembly to ordered mesoporous polymers. It consists of two parts: （1） Synthesis of ordered mesoporous carbon-silica and carbon-metal oxide nanocomposites by the evaporation induced triconstituent co-assembly method. And ordered mesoporous carbons can be derived with large pore size, pore volume and high surface area. （2） Studies on the applications of the resultant mesoporous carbons in energy storage and mesoporous carbon-titania nanocomposites in photocatalysis of RhB.In chapter 2, highly ordered mesoporous polymer-silica and carbon-silica nanocomposites with interpenetrating networks have been successfully synthesized by the evaporation-induced triconstituent co-assembly method, wherein soluble resol polymer is used as an organic precursor, prehydrolyzed TEOS is used as an inorganic precursor, and triblock copolymer F127 is used as a template. It is proposed for the first time that ordered mesoporous nanocomposites have "reinforced concrete"-structured frameworks. By adjusting the initial mass ratios of TEOS to resol, we determined the obtained nanocomposites possess continuous composition with the ratios ranging from zero to infinity for the two constituents that are "homogeneously" dispersed inside the pore walls. The presence of silicates in nanocomposites dramatically inhibits framework shrinkage during the calcination, resulting in highly ordered large-pore mesoporous carbon-silica nanocomposites. Combustion in air or etching in HF solution can remove carbon or silica from the carbonsilica nanocomposites and yield ordered mesoporous pure silica or carbon frameworks. The process generates plenty of small pores in carbon or/and silica pore walls. Ordered mesoporous carbons can then be obtained with large pore sizes of 6．7 nm, pore volumes of 2．0 cm³/g, and high surface areas of 2470 m²/g. The pore structures and textures can be controlled by varying the sizes and polymerization degrees of two constituent precursors. Accordingly, by simply tuning the aging time of TEOS, ordered mesoporous carbons with evident bimodal pores at 2．6 and 5．8 nm can be synthesized. Additionally, the synthesis of other topologies of mesostructured nanocomposites has been exploited by using other triblock copolymers, such as P123, F108andB50-6600．In chapter 3, the electrochemical behaviors of ordered mesoporous carbon MP-C-46 （based on chapter 2） in energy storage such as EDLC and lithium battery anode were investigated in detail in comparison with common carbon C-FDU-15, which was obtained by organic-organic self-assembly strategy without the presence of inorganic silicate precursor. In the organic electrolyte of 1 M （C₂H₅） ₄NBF₄/PC, this novel carbon shows a capacitance of 117 F/g, larger than that of other ordered mesoporous carbons that have been reported. The capacitor fabricated by this carbon material shows the rectangular-shape CV curves between 0～3 V over a wide range of scan rates up to 200 mV/s. And in lithium storage, a high specific capacity of about 1048 mAh/g was observed for this carbon at the first cycle. And the charge/discharge process remained at a high reversible capacity level with a good cycle performance. The results show the attractive capabilities of this carbon as a hopeful material in energy storage.In chapter 4, ordered mesoporous carbon-titania nanocomposites with crystalline framework were synthesized by the evaporation-induced triconstituent co-assembly followed by the in-situ crystallization technology. The composition of the nanocomposites can be controlled by adjusting the initial mass ratios of TiCl₄ to resol. The resultant materials possess not only high stability but also high BET surface area and uniform pore size distribution. Specifically, we demonstrate this method for ordered mesoporous crystalline carbon-metal oxides nanocomposites consisting of photocatalycally active nanocrystals and glass-like carbon with strong adsorption ability in the C-TiO₂ system, which show good performance in degradation of Rhodamine B. This approach could be applied to design many other ordered mesoporous crystalline M_xO_y-carbon nanocomposites with functional properties.更多还原