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Ordered mesoporous structure and pore controlled synthesis and electrochemical and bio- separation

Author: ChenDeHong
Tutor: ZhaoDongYuan
School: Fudan University
Course: Inorganic Chemistry
Keywords: mesoporous template silica electrical double-layered capacitor (EDLC) phosphopeptides enrichment
CLC: TB321
Type: PhD thesis
Year: 2006
Downloads: 1269
Quote: 3
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Abstract

As a kind of porous inorganic materials with the pore size between 2-50 nm, mesoporous molecular sieves might find a lot of applications in the fields of catalysis, adsorption, sensor and so on, because of their highly ordered pore structures and very large specific surface areas. Since the first report about M41S mesoporous materials by the scientists at Mobil Research and Development Corporation, researchers around the world have prepared thousands of mesoporous materials with different compositions, new pore systems and novel properties based on supermolecule assembly concept. However, rationally controlling the mesoporous materials at micro-, meso- and macro-scale and giving some ideas of structure-property-function relationships is still a urgent challenge for the scientists all over the world in this field. When above-mentioned problem can be really solved and the design of goal-materials based on their application can also be realized, the promising commercial utility of mesoporous materials is expected to come into being finally. Thus, to exploit the controlling methods for mesoporous materials on micro-, meso- and macro-scale would be the main task in this field in the future.This thesis divides into two major parts: in the first part, the control on the mesostructures of silica materials templated by using anionic-nonionic mixed surfactants is described. Nitrogen-containing carbon microspheres with very large pore size and iron oxide microspheres with well-crystallized structures have been prepared by using a facile polymerization-induced colloids aggregation method in the second part, and their potential applications in the fields of high-power electrical double layer capacitor （EDLC） and selective enrichment of phosphopeptides are respectively characterization.Two kinds of surfactants including cationic ones and nonionic block copolymers are mainly used for the preparation of mesoporous materials in previous reports, which are respectively represented by the synthesis of M41S or SBA-n series materials. However,the cationic surfactants are usually expensive, which will hamper the practical application of resulting mesoporous materials because of their relatively higher costs. In view of the facts that both anionic and nonionic surfactants are very cheap and have been widely used in industrial fields in the processing of their various formulations, research on the synthesis of mesoporous materials templated by anionic-nonionic mixed surfactants may not only be theoretically important, but also provide more options for economical and large-scale productions of mesoporous materials with controllable structures.In chapter 2, mesoporous silica with Iα （?）d structure has been successfully prepared by using mixed surfactants of commercially available nonionic block copolymer P123 (EO₂₀PO₇₀EO₂₀) and anionic sodium dodecyl sulfate （SDS） or sodium dodecyl benzene sulfonate （SDBS） as structure-directing agents through an acid-catalyzed silica sol-gel process. The products have highly ordered bicontinuous cubic mesostructure with large surface area （～ 770 m²/g）, pore volume （～ 1.5 cm³/g） and uniform pore size （～ 10 nm）. The results based on the 950 ℃ high temperature treatment indicate that resultant template-free mesoporous silica products have excellently thermal stability. Morphologies of the resultant materials can further be controlled by adding inorganic salt （such as Na₂SO₄） into the mixed surfactants system and coral- and petaline-like mesoporous silicas with continuous skeletons have been prepared. Effects of preparation parameters on the formation of the mesostructure have been extensively investigated and optimum conditions for resulting mesoporous materials are given.Based on the work of chapter 2, another special sodium dioctyl sulfosuccinate （AOT） anionic surfactant has been chosen to mix with nonionic F127 block copolymers for the preparation of mesoporous materials. A successive mesophase transformation induced by AOT molecules has been demonstrated to fabricate four kinds of large pore mesoporous silica materials in a triblock copolymer F127 surfactant assembly system. The transformation of the highly ordered mesostructures from face-centered cubic （spacegroup Fm（3）m） to body-centered Im（?）m then towards two-deminsional （2-D） hexagonalp6m and eventual to cubic bicontinuous Ia （?）d symmetries has been achieved by tuningthe amount of AOT and 1,3,5-trimethylbenzene （TMB）. These mesoporous silica structures have highly ordered regularity in large domains and possess high surface areas, large pore volumes and uniform pore sizes. The understanding of blend-surfactant assemble mechanism will lead to a more rational approach for economical and large-scale production of mesoporous materials with controllable structures.Supermolecule assembly methodology is valuable to prepare mesoporous materials. However, this process encounters limitations when the sol-gel process of some inorganic components could not be efficiently controlled. In chapter 4 and 5, a polymerization-induced colloids aggregation method has been used to synthesis nitrogen-containing carbon microspheres with very large pore size and iron oxide microspheres with well-crystallized structures, and their potential applications in the fields of high-power electrical double layer capacitor and selective enrichment of phosphopeptides are respectively characterization.In chapter 4, a kind of graphitized mesoporous carbon spheres （MCS） materials containing in-frame incorporated nitrogen have been successfully prepared by using low-cost melamine-formaldehyde resin （MF） as the precursor. The as-prepared MCS materials simultaneously possess the following characteristics: high specific surface areas （1460 m²/g） for charge storage, large pore size （31.0 nm） to facilitate the ion diffusion with a high speed, suitable quantity of nitrogen （6.34 wt%） on the surface of the materials to enhance its wettability by the electrolyte and fairly good graphitized carbon nanostructures to reduce the electrode resistance. The electrochemical performances based on the cyclic voltammetry （CV） analysis and galvanostatic charge/discharge measurements indicate that as-prepared MCS materials present much better specific capacitance and rate capability as the electrode for EDLC than the most popularly applied activated carbon when constantly charged/discharged over a wide loading current range （1-50 A/g）. In addition, the precursors used in this simple process are commerciallyavailable low cost chemicals, which will be favourable in the preparation of MCS on a large scale.A facile polymerization-induced colloids aggregation method has been used to synthesis iron oxide microspheres with well-crystallized structures in chapter 5, and their potential application in the field of selective enrichment of phosphopeptides from complex sample are also conducted by using MALDI-TOF-MS method. The resulting iron oxide materials are monodisperse microspheres with the diameter ca. 3 μm, and their pore sizes are as large as 48 nm. The results based on the MALDI-TOF-MS analysis suggest that resulting iron oxide microspheres has a high selectivity to enrich both mono-and multi-phosphopeptides from tryptic digest of complex proteins, and the coverage of phosphopeptides for tryptic digest of commercial casein proteins amounts to 93%, indicating a better selective enrichment ability than previous reported materials. In addition, the process of concentrating phosphopeptides is hugely simplified by using mesoporous iron oxide spheres as compared with the well-known IMAC method. In consideration of the preparation process for mesoporous iron oxide microspheres is very simple and low-cost, the resulting mesoporous iron oxide spheres are expected to have potential application in the isolation of phosphopeptides prior to MS analysis.

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