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Efficient Preparation And Properties Of Silica Aerogel Based On Gel Emulsion Template Method

Posted on:2017-08-30Degree:MasterType:Thesis
Country:ChinaCandidate:Y Y ZhangFull Text:PDF
GTID:2351330512470404Subject:Applied Chemistry
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Aerogels, which can be acted as the lightest solid material, open interesting opportunities for traditional applications in catalytic supports, adsorption, separation, sensor, biological medicine, and space special material materials, etc. owing to their low bulk densities, large pore volumes, high specific surface areas, and low thermal conductivities. To realize the above-mentioned various applications, aerogels in general ought to be prepared both easily and economically by mainly avoiding laborious drying methods, and to be possessed the good mechanical properties by conquering its fragility by nature. Significant efforts, therefore, have also been made to develop various methods/strategies for optimization of drying procedure and efficient improvement of mechanical performance. In comparison to recently significant accomplishment of reinforcement of aerogels by usage of doping, cross-linking, and adjusting the porous structures, there is no big breakthrough in the drying technique just because the simpler and cheaper alternative drying technique, which is effectively avoided the serious shrinkage and cracking due to the high capillary during the evaporation of the liquid in the pores, is not put forward as yet up to date. As a result, the unscaleable and expensive superficial drying is still main drying approach in order to obtain the aerogel monoliths possessing the ultra-low apparent density. Furthermore, the solvent exchange approach can't completely eliminate shrinkage occurred during APD, commonly yields the aerogel-like monoliths with the bulk higher bulk density of 0.g/cm3. Obviously, to develop a very convenient, economic and environmentally preparation for aerogels is very important for the real applications.On the basis of progress and topical issues of aerogel field, the gel-emulsion templated strategy is developed for preparation for silica aerogel monoliths. Construction of rigid and hydrophobic interfacial film by designing and synthesizing the novel stabilizer is to be used for successful preparation of the ordered meso-pores silica aerogel monoliths with ultra-low apparent density by using solvent-exchange free the ambient-pressure dying. Furthermore, p-cyclodextrin (?-CD) was grafted onto the surface of porous structures in silica aerogel monolith. By taking the advantages of a hydrophobic internal cavity and a hydrophilic external surface of ?-CD, the organic pollutants in the aqueous phase is to be efficiently adsorbed by using ?-CD modified silica aerogel monolith. Specifically, the major work was done in the following two aspects:In the first part of the thesis, a series of monolithic silica aerogels were prepared via one-step sol-gel reaction in the continuous phase of a specially designed stabilizer (Chol-OH)-based W/O gel emulsions, of which the oil phase is one of the silica precursors, organosilanes, employed, followed by solvent exchange free APD process. The gel emulsions as prepared showed remarkable stability that makes the hydrolysis and condensation of the organosilanes occur without damage of the template, a basis for the obtaining of the final porous silica monoliths. The chemical nature, the densities of the monolithic silica aerogels could be largely tuned via simple variation of the precursor and the water content in the gel emulsions. In this way, monolithic silica aerogels from super-hydrophobic (water contact angle larger than 150°) to extreme hydrophilic (water contact angle lower than 25°) and that with a density as low as 0.026 g/cm3 could be prepared. In addition, the internal structures of the aerogels can also be tuned by alternating the reaction rate of the sol-gel process. As confirmed by morphological studies, the as prepared monolithic silica aerogels possess highly porous inter-connected structures, and the macro-pore walls of the materials are composed of highly ordered meso-pore (?25 nm) structures. To our lucky, the aerogels as obtained are mechanically stable and could be cut into any shapes required. Their thermal conductivities at ambient pressure, humidity, and temperature (32?) could be 18% lower than that of the reference air (24.4 mW/(mK)). It is to be believed that we open the new route to large-scale, low-cost, and low energy consumption preparation of silica.In the second part of the thesis, renewable ?-cyclodextrin (?-CD) was grafted onto the surface of porous structures in silica aerogel monolith based on the first work. Because ?-Cyclodextrin (?-CD) having a special conic structure containing a hydrophobic internal cavity and a hydrophilic external surface, therefore AM-NH-CD shows an exceptional ability to adsorption and separation of organic pollutants from the contaminated water. As-prepared AM-NH-CD was characterized through FT-IR, water contact angle and TGA measurements. SEM images show that the modification process did not affect the macro/micro-structures of silica aerogel monoliths. In the water treatment, AM-NH-CD can efficiently adsorb 1-Naphthylamine (0.030 mmol/L) from contaminated water. However, compared with results in the literature, the adsorption efficiency and the adsorption capacity of AM-NH-CD in this work is not good. Through TGA tests of silica aerogel materials at the different stages of synthesis, it is be found that the lower grafting percent of ?-CD caused the poor adsorption performance of organic pollutant in the aqueous phase. Clearly, efficient preparation of functioned silica aerogel monoliths is the pivotal important for realization of real applications. Nevertheless, this work still lays a solid foundation for the purification of water containing organic pollutant.
Keywords/Search Tags:Monolithic silica aerogels, Ambient-pressure drying, Solvent exchange free, Gel-emulsion template, Adsorption of organic pollutants in aqueous phase
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