Synthesis And Properties Of Novel Mesoporous And Macroporous Silicas

Mesoporous and macroporous materials have attracted widely attention in potential applications such as adsorption and separation, catalysis, electrochemistry, biological medicine, optical and electronic devices because of their high specific surface areas, regular structures and morphologies and controllable pore size. Many porous materials with different structures and morphologies have been reported in the last two decades. The synthesis and development of the mesoporous and macroporous materials with novel structures and morphologies are the hot research topics. However, the design and synthesis of templates are the key problems for the synthesis of such materials. Block copolymers have rich phase behavior in bulk and solution due to the different physical and chemical properties of the each block. The abundant mesoscopic structures can be obtained by the self-assembly of the block copolymers, and thus the block copolymers were used in the synthesis of inorganic mesoscopic materials. Mesoporous and macroporous materials with tunable pore size can be synthesized through the rational design of the block copolymers. Amphiphilic bola form surfactant that has high heat resistance and high stability in the interface of the gas-liquid and water is because of the characteristics of the structure that the hydrophilic parts are in the two ends and the hydrophobic part is in the middle. This provides a route for developing the functional materials by the self-assembly with inorganic source.The novel mesoporous and macroporous materials were synthesized through design and synthesis of the new type of the templates. Firstly, the novel macroporous silica photonic crystal was synthesized through the self-assembly of amphiphilic ABC triblock terpolymer in the good solvent and poor solvent mixtures, and the formation mechanism was studied. Secondly, the amino functional large-pore mesoporous silica was synthesized through the interaction between the hydrophilic group of the block copolymer and the co-structure directing agent, the large-pore mesoporous silicas with different morphologies and structures were synthesized through designing the different polymers. Finally, the earth-worm like lamellar mesoporous silica was synthesized by the self-assembly of novel bola form surfactant, the mesoporous silicon nanofibres were obtained through the megnesiothermic reduction and was used for the anode material of the lithium battery.Chapter 1. Review the background of the research and the related literature, put forward the research strategy.Chapter 2. Microphase-templated macroporous silica photonic crystal.A macroporous silica with complex azimuthally shifted hollow double diamond networks has been synthesised by the self-assembly of an amphiphilic ABC triblock terpolymer poly(tert-butylacrylate)-b-polystyrene-b-poly(ethylene oxide)(ASO) with the hydrophobic-hydrophobic-bydrophilic squence and silica source in a mixture of tetrahydrofuran and water. The structure of the macroporous silica consists of a porous system separated by two sets of hollow double-diamond frameworks shifted 0.25 c along <001> and adhered to each other crystallographically due to the loss of the mutual support in the unique synthesis, forming tetragonal lattice(space group I41/amd). Besides, this structure exhibits structural colour that ranged from violet to blue with a band gap in the visible wavelength range. Calculations demonstrate that this is a new type photonic structure with complete band gap. A core-shell multicontinuous microphase templating route was speculated for the formation of such unique macsroporous structure, in which common solvent tetrahydrofuran in hydrophobic shell and selective solvent water in hydrophilic core to enlarge each microphase sizes.Chapter 3. Synthesis of the mesoporous and macroporous silica by the self-assembly of the ABC triblock terpolymer and their phase transition mechanism. According to the self-consistent mean-field(SCMF) theory, it is predicated that the block copolymer phase will transform from body-centered cubic spheres(S), hexagonally packed cylinders(C) and bicontinuous gyroids(G), to lamellae(L) and further to inversed bicontinuous gyroids(G’), hexagonally packed cylinders(C’) and to body-centered cubic spheres(S’) with the increasing of the volume fraction. With increasing of the χN at a fixed volume fraction, the block copolymer phase will transform from body-centered cubic spheres(S and S’), hexagonally packed cylinders(C and C’) and bicontinuous gyroids(G and G’), to lamellae(L). In order to make clear the self-assembling behaviour of ASO, several ASO triblock terpolymers with different total and each polymerization degree of N and NA, NS,and different volume fraction of hydrophilic parts were synthesized. The mesoporous and macroporous silica with structures from face centered cubic spheres to two-dimensional hexagnol p6 mm and multi-continuous double diamond structures were synthesized with increasing volume fractions of the total hydrophobic parts. An inversed multi-continuous double-diamond structure was formed with a high χN at a high hydrophilic part volume fraction.Chapter 4. Synthesis of the large pore mesoporous silica by block copolymer with Co-structure directing agent method. Block copolymers contain PAA segment were designed and synthesized in this chapter, and the functional mesoporous silica was synthesized through the co-structure directing agent method. The PS-b-PAA is highly soluble in the good solvent, microphase separation occurs when the selective solvent water is added. The good solvent is mainly present in the hydrophobic PS regions of the aggregates to form large cavities, whereas water is driven out of the hydrophobic segments and mainly present in the hydrophilic PAA region, which can give rise microphase separation with the hydrophobic part(PS) in the core and the hydrophilic part(PAA) in the shell. Simultaneously, in hyrdophilic part, with the addition of 3-aminopropyltrimethoxysilane(APS) and tetraethylorthosilicate(TEOS), the alkoxysilane sites of APS are co-condensed with TEOS, to be assembled subsequently to form the silica framework. The trimethylene groups of the APS covalently tether the silicon atoms incorporated into the framework to the cationic ammonium groups. After the extraction of PS-b-PAA by ion exchange, the large-pore-mesoporous silica with amino group on the pore surface was finally obtained. The interaction between the PAA and the APS produces a uniform distribution of amino groups, and a regular array of the amino groups will be formed on the surface of the mesopores following the arrangement of the PS-b-PAA.Chapter 5. Synthesis of the mesoporous silica template by rigid bola-form surfactant for anode material of lithium ion battery. The rigid amphiphilic bolaform surfactant is soluble in quantity water to form the micelle with lamellar arrangement due to the rigid of the benzenone ring in the middle and the hydrophilic part on the both ends of the surfactant. The carboxylic acid and APS interact electrostatically each other, and the alkoxysilane sites of APS are co-condensed with TEOS, to be assembled subsequently to form the silica framework, and finally form the lamellar structure in the centre of the silica nanotube composite. Silica nanotubes were prepared by the calcination process of the as-synthesized composites at 550 oC for 6 h to remove the template, after the magnesiothermic reduction, silicon nanofibers were obtained by etching magnesium oxide. Finally, carbon-layer-coated silicon nanofibres(nf-Si@C) were obtained by chemical vapour deposition(CVD), which displayed a stable capacity of approximately 1141 mAh g-1 over 100 cycles at 0.2 C.