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Synthesis On Mesoporous Silica Nanomaterials And Carbon Dots

Posted on:2012-03-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z A QiaoFull Text:PDF
GTID:1101330332999408Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Synthesis of Mesoporous Silica Nanomaterials and Carbon DotsSince the discovery of MCM-41, mesoporous materials have received particular attention in many areas, such as catalysis, adsorption, separation, chemical sensors, bioscience and so on. Colloidal mesoporous silica nanomaterials have more potential for above applications because of their nano-scaled size, in particular for a variety of nanotechnological applications including biomedicine and biotechnology. Carbon dots (CDs) are interesting newcomers to the world of nanomaterials and are fascinating luminescent materials. CDs stand to have a huge impact in both health and environmental applications because of their potential to serve as nontoxic replacements to traditional heavy-metalbased quantum dots. Therefore, developing better synthetic routes for these two types of nanomaterials and more detailed fundamental studies of their properties have a level of urgency. In this thesis, systematic researches have been done on the synthesis, mechanism and application of mesoporous silica nanomaterials and CDs. Main research results during my Ph. D. study are described as follows.1. We have successfully prepared monodisperse and uniform mesoporous silica nanoparticles in mild synthesis conditions (pH 6-10). The particle size can be controlled from 25 nm to 200 nm by adding suitable additive agents (e.g. inorganic bases, amine, and alcohols) which affect the hydrolysis and condensation of silica species. The in situ pH measurement of synthesis system is introduced to investigate the formation process of mesoporous silica nanoparticles. Our results show that certain acid-base buffer capacity of the reaction mixture is essential for the formation of mesoporous silica nanoparticles in the TEOS-CTA+ system. The formation of nanoparticles is a typical sol-gel process of silica in the presence of surfactant. The combination and balance of hydrolysis and condensation processes of silica species determine the formation of nanoparticle. The size of nanoparticles is mainly determined by hydrolysis of silica species (controlled by the initial pH of the synthesis system), and the nucleation of nanoparticles is determined by the condensation of silica species. High quality nanoparticles result from the homogeneous growth of simultaneous nucleation. The nucleation and growth process of the nanoparticles can be extended into the self-assembly system of inorganic-surfactant and the formation of mesophase in aqueous media.2. A new class of silica cross-linked threadlike micelles has been successfully synthesized in the form of colloidal suspensions by using block copolymer P123 (EO20PO70EO20) as template, tetramethyl orthosilicate as silica source, and 3-aminopropyltriethoxysilane as stabilizing agent. The aggregation of threadlike hybrid micelles is suppressed by electrostatic repulsion from the positive–NH3+ on the surfaces of threadlike hybrid micelles in strong acidic media. The silica cross-linked threadlike micelle is the intermediate in the formation process of SBA-15. The threadlike hybrid micelles can be considered as the building unit of SBA-15. One hybrid micelles corresponds to the one channel in SBA-15. In the absence of APTES, the synthesis mixture gives a typical SBA-15 solid. Based on DLS and TEM results, we conclude that the spherical micelles evolve into threadlike micelles after introducing the silica source. Compared with P123 micelles, the threadlike hybrid micelles have significantly improved stability against dilution due to the presence of the cross-linked silica layer. Furthermore, the threadlike hybrid micelles are potential drug carrier and have a higher loading capacity and a slower release rate.3. By employing commercial activated carbons as carbon sources, we developed a simple and effective route to facilely prepare photoluminescent CDs. The carbon precusor preparation step is omitted. Our CD products are water-soluble, nanosized (4.5 nm), and multicolor photoluminescent. The quantum yield up to 0.126 is comparable to those for CDs prepared in the previous reports. In essence, the long range disordered structures of the carbon precursors for chemical oxidation method lead us to use activated carbons, a more general and low-cost carbon source with amorphous structure, to prepare photoluminescent CDs. Our preparation method presents a general and facile approach to produce photoluminescent CDs and can be carried out in large scale. Furthermore, these CDs showed excellent properties for bioimaging applications, such as high luminescence, easy penetration into live cells, remarkable photostability, and nontoxicity to cells.4. We explore a new strategy to synthesize highly luminescent CDs by pyrolysis of carbon nitride polymer at low temperature. The crued CDs could be effectively separated into two types of highly fluorescent CDs by cutoff membrane, with photoluminescent QYs as high as 0.415 and 0.328, which are comparable to those of the best commercial CdSe/ZnS QDs and brighter at the individual dot level (owing to the CDs being significantly higher in absorptivities). Moreover, the as-prepared two types of CDs exhibited size-dependent and wavelength-dependent photoluminescence in the violet to blue (380 nm470 nm) and blue to green ranges (425 nm510 nm), respectively.
Keywords/Search Tags:mesoporous silica nanoparticles, mechanism, cross-linked, micelle, drug delivery, carbon dots, multicolor photoluminescence
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