| Design and synthesis of suitable photochemical sensors which can selectively recognize natural organic anions and neutral molecules is a challenging task. Over the past decade the appearance of mesoporous materials for researchers provided a new way of thinking. Researchers have combined the concept of supramolecular chemistry and structural characters of the mesoporous materials, modified the channels of mesoporous materials by mimicking enzyme recognition pattern, and developed a new class of organic-inorganic hybrid silicon-based mesoporous materials which has improved recognition abilities towards natural organic anions and neutral molecules, compared to the conventional sensors.On the basis of our group results on supramolecular chemistry and molecular recognition studies, we began to synthesize new organic inorganic hybrid mesoporous materials in recent years on the purpose of selective recognition of biologically active species by photochemical sensing. MCM-41was selected as the framework of mesoporous materials in this thesis, which was grafted with simple organic molecules. After its structural characterization, the molecular recognition studies were performed. Through these efforts, we not only get familiar with the synthesis and characterization of inorganic-organic hybrid mesoporous materials, but also have some preliminary understanding on the structure-function relationship of the hybrid materials. On this basis, we chose the medium chain fatty acids as target. The medium chain fatty acids do have an important role in life, but so far no research on photochemical sensing of a medium-chain fatty acids has been uncovered. We synthesized hybrid mesoporous materials with multiple recognition sites with multi-group synergies on the ground of structural characters of medium-chain fatty acids. The material exhibited high selectivity of fluorescent recognition to medium-chain fatty acids in aqueous medium. The correlation between structure and recognition function of this hybrid mesoporous material may provide new ideas for design, synthesis and application of more fluorescent sensors of organic-inorganic hybrid material.The thesis is divided into five chapters, the specific content of each chapter is as follows:The first chapter is the introduction of the thesis. This chapter firstly introduces some basic knowledge of the mesoporous inorganic materials, organic-inorganic hybrid mesoporous materials and photochemical sensing; then domestic and international progress of organic-inorganic hybrid mesoporous materials in photochemical sensing and adsorption separation were reviewed; finally, the design philosophy and main research contents of this thesis were also described.The second chapter introduces a new organic-inorganic hybrid mesoporous material:the synthesis and structural characterization of N-methyl piperazine functionalized MCM-41(S2). Firstly, ordered hexagonal mesoporous silicon MCM-41was chosen as inorganic carrier. Then, y-(2,3-epoxy propoxy) propyl group was covalently linked to the inner channels of MCM-41to give the silylated MCM-41(S1). After that, hybrid mesoporous material S2was obtained through the ring-opening reaction of N-methyl piperazine and epoxy group. The synthesized MCM-41, S1and S2were characterized by nitrogen absorption-desorption, X-ray powder diffraction, scanning and transmission electron microscopy, infrared spectroscopy, solid state29Si NMR spectroscopy, TGA and elemental analysis. The results showed that structural parameters of MCM-41are consistent with the literature. y-(2,3-epoxypropoxy) propyl and methyl piperazine has successfully been covalently binded to the inner channels of the MCM-41without the destruction of long-range ordered structure of the mesoporous material. The load of ?-(2,3-epoxypropoxy) propyl and methyl piperazine for S1and S2were0.99and0.82mmol/g, respectively. The maximum pore size distribution (nm) for MCM-41. S1and S2, were2.92,2.66and2.29, respectively; The cumulative pore volume (cm3/g) were0.83,0.49and0.23, respectively. BET specific surface areas (m2/g) were995,693and377, respectively. High loading of organic groups S1and S2suggest that the chose organic functional approach is simple and effective. Comparison of the structure parameters of MCM-41, S1and S2indicates a certain degree of congestion in the S2channel.The third chapter introduces the adsorption properties of S2towards copper ions, and discusses the relationship between the channel structure and adsorption properties. Within the channel of S2, the organic functionalities contain one secondary hydroxyl and two tertiary amino groups. We expected that S2should be a good copper ion adsorbent based on the strong coordination between copper ions and amine, and the probably synergistic effects of two tertiary aminos in N-methylpiperazinyl. The results showed that the single copper ion adsorption capacity Qm is consistent with reported values of silicon-based nano-tubes functionalized with tertiary amines, which implies two tertiary aminos in N-methyl piperazinyl failed to synergistically chelate. This result is in accord with the S2channel congestion conclusions in the former chapter. The proposed reason is that space congestion limits the chair to boat flipping which goes against the complex of copper ions.In chapter four, we investigated the recognition ability of MCM-41-T (without the removal of the template) towards fatty acids of different chain length by utilizing competitive substitution method, which exploits the structure and property difference between phenols and fatty acids. First we get MCM-41-T-p-NP by adsorption of nitrophenol (p-NP) with MCM-41-T, and then replace nitrophenol in MCM-41-T-p-NP by fatty acid of a certain chain length. Nitrophenol removal rate is calculated by mass concentration of replaced nitrophenol. The results showed that the ability to substitute p-nitrophenol in MCM-41-Tp-NP is highly related to the chain length of fatty acids. Short chain (3,4,5carbon atoms) acids can only replace a small amount of nitrophenol. The removal rates increase rapidly with C6-C8acids, and increase more rapidly from nonanoic acid, reach its maximum at dodecanoic acid. Then removal rates with tridecanoic and tetradecanoic acids decrease slightly, and decrease further for hexadecanoic and octadecanoic acids. In a series of fatty acids with different chain length, lauric acid demonstrated the strongest ability to replace the nitrophenol. Through comparing of hydrophobicity and pKa value of various fatty acids, we can get the conclusion that the recognition ability of MCM-41-T is depending on the chain length (hydrophobicity) of the fatty acids. The inner diameter of MCM-41-T channel also affects the removal rate. It is likely to cause congestion when the long fatty acids (C16, C18) are absorbed into the hydrophobic layer of the MCM-41-T channels, resulting in the decrease of nitrophenol removal rate. The above finding could potentially be used to discriminate fatty acids of different chain length and remove fatty acids contaminants in environment. Also it provided a good foundation for further research on the recognition of medium chain fatty acids.The fifth chapter described the design, synthesis and photochemical sensing of the first organic-inorganic hybrid mesoporous material S3which exhibited high selectivity of fluorescent recognition of medium-chain fatty acids in aqueous medium. We discussed the relationship of structure and sensing performance, and analyzed the factors that led to high selectivity of fluorescence enhancement. The work took a different strategy from the literature in the construction of biomimetic "active cavity", that is a pre-designed "recognition center"with multiple interaction sites, N-butyl-4-piperazine-1,8-naphthalimide (3) to selectively recognize medium chain fatty acids with fluorescent response. And the "recognition center"was connected to the inner channel of S1through ring-opening reaction with epoxy propoxy to obtain S3. The connection of3with mesoporous materials was confirmed by infrared spectroscopy and elemental analysis. The reservation of the hexagonal nano-ordered structure of mesoporous materials was proved by X-ray powder diffraction, low-temperature nitrogen adsorption and desorption, scanning and transmission electron microscopy and other evidence. The loading of3in S3is0.13mmol/g; maximum pore diameter distribution is2.60nm; cumulative pore volume is0.40cm3/g; BET specific surface area is660m2/g. S3demonstrated a strong selective fluorescent recognition towards the medium chain fatty acid containing C8-C12carbon atoms with or without the presence of interfering agent benzoic acid, which is the first fluorescent chemical sensor for identification of medium chain fatty acids in aqueous medium. The crucial factor causing high selectivity of S3with fluorescence enhancement is the "recognition center" N-butyl-4-piperazine-1,8-naphthalimide (3) with multiple recognition sites. On the other hand, Once it was binded to the channel, due to its bige size, steric hindrance prevented more molecules involved in the reaction, and resulted in a low load rate and a large amount of unreacted3-glycidoxypropyl, thus a loose channel with relatively hydrophobic microenvironment was formed. As comparison with the short chain carboxylic acid and long chain fatty acids, the relatively hydrophobic environment is more likely for medium chain fatty acid to enter the channel. And the steric interaction in the channel also prevented long chain fatty acids from entering. By comparing the load of organic group and pore structure parameters of the MCM-41, S1, S2and S3, we analyzed the relationship between the structures of organic functional groups and the molecular recognition behaviors of S2and S3. |
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