Preparation And Investigation On Properties Of The Functional Mesoporous Materials With Different Morphologies

Since the pioneering reports by Mobil scientists, mesoporous materia ls with highlyordered pore structure, uniform pore size, large pore volume and high specia l surfacearea have attracted considerable attention. It is very important to design themorphologies of mesoporous materia ls for desired applica tions in catalysis, adsorption,separations and sensors. Recent studies have demonstrated mesoporous materia ls canbe prepared in the form of monoliths, films, spheres, fibers, tubes and so on. Inpractica l applica tion, the mesoporous materia ls with different morphologies haveexhibited a wide variety of useage: mesoporous films can be used for membraneseparation and gas sensing; mesoporous spheres may be applied to a stationary phase inhigh-performance liq uid chromatography; mesoporous fibers or tubes possess goodoptica l or electrical conductivity. For the sake of future development in functiona l andeconomic mesoporous materia ls, it is significa nt, in theory as well as in practice, tofabricate mesoporous materia ls with controllable morphologies and explore therelationship between the morphology and the property of mesoporous materialsprepared.The thesis put stress upon the fabrication of mesoporous materia ls with controllablemorphologies. Severa l types of mesoporous materials with different morphologies(films, fibers), various components (silica, carbon) and distinct properties (optical, electrical) have successfully been prepared by combining the concepts of sol-gelchemistry and supra molecular self-assembly and utilizing the methods ofelectrospinning, hard template-ind uced reverse replication and in situ doping orencapsulation. A variety of characteriza tion can be applied to investigate detailed ly theproperties of the functiona l mesoporous materials. Large number of experimental datahave revea led the effects of encapsulating concentration of guests on the properties ofthe materia ls and the relation between experimental conditions in preparation and themorphologies of the materia ls.Firstly, a dye-doped mesoporous silica films supported by stainless steel nets havebeen fabricated during the traditiona l sol-gel process through combination of themethods of in situ synthesis and dip-coating. For the optica lly active materia ls dopedby various concentration dye, we have studied their morphologies, mesostructures andoptica l properties of ultraviolet adsorption, fluorescence luminescence and laserluminescence in detail. Experimental data have shown that not only the optica lly activemateria ls process well-refined macroscopic homogeneity and ordered mesoscopicregularity, but also the optica l properties of them are certain functions of concentrationof dye. According to laser luminescence characteriza tion, it can be proved that theoptica lly active materia ls with the particular concentration displa yed the specificperforma nce of distributed feedback laser (DFB laser), namely, the gain narrowing ofbands over threshold energy and the occurring of superlinear dependence. A series ofcontrast experiments have indica ted that the grids of stainless steel nets used forsupporting the optica lly active films are capable of serving as the laser resonators inwhich light can be fed back and revea l amplified spontaneous emission (ASE).Additiona lly, we have confirmed that the aperture of grids is also an important factor ofthe optica l performa nce of the materia ls. So the promising results are a great leapforward toward new solid state laser system with properties tunable over a wide range.Secondly, mesoporous silica fibers have been prepared by electrospinning. We havefocused our mind on controlling the morphologies of electrospun fibers by adjustingexperimental conditions of electrospinning, and have genera lized some conclusionsfrom experimental evidence. In order to make further investigation into the effects of experimental conditions of electrospinning on the morphologies of electrospun fibers,a series of contrast experiments have been conducted as following: 1. Adjustment in thequantities of viscosifier PVP. Experimental results have shown that well-refinedelectrospun fibers are impossible to be formed until the quantities of PVP reach certainconcentration. Then, the dia meter of electrospun fibers has thickened with an increaseof concentration of PVP. 2. Adjustment in supply voltage. Experimental data haveindica ted that well-proportioned electrospun fibers have been made when supplyvoltages exceed a critica l value. The dia meter of electrospun fibers increase as supplyvoltages increase and the morphology of them will become inferior if the supplyvoltages are much too high. 3. Adjustment in flow rate. Experimental evidence suggestthat the faster the flow rate, the faster the electrospinning, the more the electrospunfibers during the same period, and the thicker the dia meter of electrospun fibers. It isunfavorable for generating uniform electrospun fibers in case of too fast or too slowflow rate. 4. Adjustment in dista nce between the positive and nega tive termina l. As thedista nce between the positive and nega tive termina l increase, the electric field strengthdecrease, and the dia meter of electrospun fibers become thin. On the other hand,various concentration dyes have been doped in the electrospun fibers by in situsynthesis, and the properties of ultraviolet adsorption and fluorescence luminescence ofthe dye-doped materia ls have been studied systematica lly.Thirdly, a series of highly ordered mesoporous carbon nanofibers have beenprepared by combining the advantage of the confined channels of anode aluminamembranes with the facile one-step synthesis method of mesoporous carbons. Then,the mesoporous carbon nanofibers with hexa gona l structure have been functiona lizedby a noncova lent method under mild condition. The noncova lent functiona liza tion notonly avoids direct dama ge to carriers caused by the violent H2O2 oxidation method, butalso leads to a high density and homogeneous distribution of surface functiona l groups.Pt nanoparticles have been encapsulated in mesoporous carbon nanofibers usingethylene glycol reduction method preparing fibrous Pt catalysts. Ethylene glycol playroles in both solvent and reducing agent during the whole reduction process. Themethanol electrocatalytic performa nce of the Pt catalysts have been investigated by cyclic voltammetry (CV). Experimental data have proved that highly effective Ptcatalysts have been obtained as Pt nanoparticles were encapsulated in mesoporouscarbon nanofibers by mea ns of mild functiona liza tion and have exhibited excellentmethanol ele ctrocatalytic activity. Through comparing the electrochemica l propertiesamong a series of Pt catalysts, we have also researched the influence of experimentalcondition on preparation of catalysts in detail.In conclusion, severa l kinds of mesoporous materia ls with various morphologieshave been prepared using the combined methods of sol-gel, electrospinning, hardtemplate-ind uced reverse replication and doping or encapsula tion. According to theexperimental evidence based upon characterization of properties of them, it can beconfirmed that the functiona l materia ls have integrated the advantages of hosts inmorphologies and structures with the excellence of guests in functiona lities and haverevea led good optica l and electrical performa nce. Therefore, it is expected that thefunctiona l mesoporous materials with different morphologies will be applied into moredoma ins in the future, such as catalysis, adsorption, separation and biosensors.