Synthesis And Characterizations Of Several Functional Composites Based On Mesoporous Structure

Since the Mobil scientists first reported the synthesis of highly ordered M41S seriesof mesoporous silicate molecular sieve in1992, mesoporous materials with regularpore structure, high specific surface area and pore volume, uniform and adjustablepore size have been greatly concerned by the international physics, chemistry andmaterials academia. So far, the study on the synthesis of mesoporous materials hasachieved fruitful results. However, compared with the results achieved in thesynthesis of mesoporous materials, in the application areas of progress is slow. In thisthesis, the main line of mesoporous materials, different materials and methods havebeen adopted to synthesize functional composite materials with a mesoporousstructure and their application value on the field of humidity sensor, sewage treatment,photocatalysis have also been studied. Our researches make contribute to realizelarge-scale industrial application of mesoporous materialsIn the second chapter, mesoporous silicon-based materials SBA-15was used ashost materials to mix with K₂CO3to form K₂CO3/SBA-15composites by solid-phasegrinding and solution infiltration two different ways. Firstly, mesoporous SBA-15powders with two-dimensional hexagonal ordered structure, high thermal stabilitywere synthesized by hydrothermal method. In the solid-phase grinding process,different amount of K₂CO3was selected to mix with1g SBA-15by grinding with amortar, and finally formed K₂CO3/SBA-15composites through the calcination process.Compared with pure SBA-15, the sensitivity to humidity of K₂CO3/SBA-15wassignificantly improved. The optimal mixing ratio was1g SBA-15added0.8g K₂CO3. The composite formed by this ratio showed good humidity sensitive characteristics.However, in the calcination process, the mesoporous structure completely collapsed.Analysis on the humidity sensitivity mechanism of0.8g K₂CO3/SBA-15sample, webelieve the reason is that there are easily dissociatve potassium salts existed in thiscomposite. In solution infiltration method, different amount of K₂CO3was dissolvedin aqueous solution, and then mixed with1g SBA-15respectively, finally driedovernight to form K₂CO3/SBA-15composites. The composites obtained by thismethod have highly ordered mesoporous structure, and the optimal loading ratio is1gSBA-15added0.16g K₂CO3. Ordered pore structure, high specific surface area andpore volume created by this composite can adsorb lots of water molecule, acceleratethe transmission of the particles, which play a crucial role to improve the sensitivity ofthe material towards humidity.View on the research of the last chapter, we found that mesoporous structure hasgreat help to improve the sensitivity of materials to humidity. In the third chapter, weadopted the synchronous self-assembly techniques loading metal oxides on the SiO₂matrix to form the mesoporous wall by one-pot synthesis. This method is that whenthe surfactant molecules formed micelles in solution, synchronously adding siliconsource and metal oxide precursor by continuous stirring make the silicon source andprecursor evenly attach to the surface of the micelles. Finally, mesoporous structureformed by calcining process, and SiO₂and metal oxide mixed evenly to form porewall. We have chosen two different metal oxides, ZnO and Fe₂O3in this chapter. Theexperimental results show that this method not only operates easily, but also can formhighly ordered mesoporous structure after calcinations. Analysis on thehumid-sensitivity properties of two materials, we found that pure ZnO or Fe₂O3arenot sensitive to humidity, when loading two metal oxides to the pore walls, thehumidity sensitivity significantly improved. For amorphous ZnO-SiO₂composites,the best ratio is Zn/Si=1:1, and for highly crystallization Fe₂O3/SiO₂composites, thebest ratio is Fe/Si=0.5:1. For their humidity sensing mechanism, we were also doing adetailed study.We composed different types of materials with SiO₂in order to prepare newhumidity-sensitive materials, which broaden the ideas in the application ofmesoporous materials on the humidity sensor. Magnetic materials due to they can be easily removed from the reaction system byan external magnetic field have been highly concerned by many researchers.Functional materials composed with magnetic materials, which both havefunctionality and magnetism, can greatly increase the practicability of materials. Thefourth chapter, we first prepared Fe₃O₄microspheres, in which sodium citrate wasadded. Our aim is to graft hydrophilic group"–COOH" to the surface of magneticcore, showing a good dispersibility in polar solvents such as water or ethanol in orderto facilitate subsequent coating. The second step, the entity SiO₂coated on the surfaceof the magnetic core to form the monodisperse Fe₃O₄@SiO₂core-shell structure. Thethird step, CTAB as pore formed template, TEOS as silica source, by adjusting theratio of CTAB and TEOS, mesoporous SiO₂shell coated on the surface ofFe₃O₄@SiO₂microspheres to form Fe₃O₄@SiO₂@meso-SiO₂composites withflower-like morphology. This composite has monodisperse core-shell structure, largespecific surface area and pore volume, which has strong adsorption towards the heavymetal ions of Pb₂₊,Cd₂₊in industrial wastewater. Otherwise, the strong magnetismthis composite has makes great help for recovery and recycling from externalmagnetic fields. Therefore, this material can be used as a good adsorbent in sewagetreatment.TiO₂is an important semiconductor material. Due to its abundant source,non-toxicity, having a wide band gap and good photocatalytic activity in the nearultraviolet region, light and chemical corrosion resisted, TiO₂is widely used inphotocatalysis. Among them, mesoporous TiO₂due to the high surface area,developed pore structure causes the reaction active centers increased. Narrow anduniform pore size distribution is also beneficial for molecular to diffuse and reach thereactivity centers. Therefore, compared with non-porous TiO₂, mesoporous TiO₂has ahigher photocatalytic activity. The fifth chapter of this thesis continued the research ofthe fourth chapter, Mesoporous TiO₂shell was chosen to coat on the surface of Fe₃O₄microspheres。As direct coating will produce a photodissolution phenomenon in orderto reduce the photocatalytic activity of TiO₂,we still select the entity SiO₂as aninterlayer to prepare Fe₃O₄@SiO₂@meso-TiO₂composite. This composite both hasthe structure characteristics of mesoporous TiO₂and magnetic properties of Fe₃O₄. Inaddition, TiO₂shell exists as crystalline anatase phase. In the experiments on the degradation of Rhodamine B (RhB) under UV light, compared with non-porousFe3O4@SiO₂@TiO₂, Fe3O4@SiO₂@meso-TiO₂composite showed higherphotocatalytic activity. Excellent properties make this composite expected to be anew-type photocatalyst in the treatment of industrial wastewater.In Chapter4and5, combined with today's hot of magnetic recovery, differentmesoporous materials were coated on the surface of the magnetic core to preparemagnetic nanocomposites with mesoporous structure, which not only increase theusefulness of functional materials, but also make a step toward the practicalapplication for mesoporous materials.In this thesis, by using different materials, different synthesis methods, several newfunctional composites based on mesoporous structure have been prepared. Our aim isto utilize the features of the ordered mesoporous structure to expand practicalapplication fields of mesoporous materials, so as to achieve the purpose of materialsserved application.