Synthesis Of Silica Mesoporous Materials By Using Nonionic Surfactant As Template Under Mildly Acidity Conditions

Ordered mesoporous materials have been receiving wide attention since it was first reported in1992because of their tunable pore size, high surface area as well as potential applications in the fields of catalysis, separation and adsorption, assemble of novel function materials, biology and medicine, ect. Presently, a variety of the ordered mesoporous silica materials have been successfully synthesized. However, it is still difficult to prepare the mesoporous materials on large-scale for its high cost and rigorous synthesis conditions. For example, SBA-16was usually synthesized under strong acidity conditions. In this thesis, we synthesized the ordered silica mesoporous materials with nonionic triblock copolymer (F108, F127and P104) as the templates through a two-step pathway under mildly acidic conditions. The dependence of the morphology and internal structure on synthetic conditions was also studied, and the hexagonal platelet silica materials SBA-15with cheap domestic P104as the template was prepared. Moreover, a new lamellar mesoporous silica material with higher thermal was firstly synthesized using industrial reagent nonionic surfactant PEG6000DS as the template in nonaqueous system. All of these studies can not only lead to the low cost production of mesoporous silica materials for practical applications, but also be helpful to investigate the mechanism of formation for the mesoporous silica materials. This thesis is arranged as the following:In chapter2and3, two kinds of well-ordered mesoporous silica materials with cubic cage-like mesostructures were synthesized by using triblock copolymer F108and F127with high EO/PO ratios as templates without the addition of inorganic slat via a novel two-step pathway above the isoelectric point of silica. Because the concentration of templates in these systems are as low as1.0wt.%, it will be much helpful for the industrialization of such mesoporous materials for their lower cost and environmentally friendly characteristics. When F108was used as the template, a novel SBA-16-type mesoporous silica materials with Im3m cubic mesostructure were synthesized under mildly acidic conditions (pH=2.15～4.50). The analytical results reveal that the prepared SBA-16-type mesoporous silica materials have a uniform pore diameter (3.37-4.24nm) and pore wall (8.84～10.2nm), and belong to the small-pored and thick-walled mesoporous silica materials. When F127was used as the template, the well-ordered Fm3m cubic mesostructured mesoporous silica materials were synthesized under mildly acidic conditions (pH=2.20～4.10). The prepared Fm3m mesoporous materials at pH=2.20exhibit a macron-sized spherical morphology with uniform size of3μ,m, which may be used as a stationary to separate large biomolecule in high-performance liquid chromatography.In chapter4, the highly ordered mesoporous silica materials were synthesized by templating with a nonionic triblock copolymer P104via two-step pathway in mildly acidic conditions. It was found that a mesostructure transformation was induced by acidity from the SBA-15type2-dimentional (2D) hexagonal channel mesostructure (pH=1.51～2.67) to the MSU-X type with3-dimentional (3D) worm-like mesostructure (pH=3.93～4.56) under the same synthetic system. The results show that various silica mesoporous materials can be synthesized by adjusting the interaction between organic micelles and inorganic species in one system. This new discovery based on the two-step synthesis may be possible to be applied to investigate the formation mechanism of mesostructure for mesoporous silica. Moreover, the success opens up a new route to synthesis of MSU-type silica mesoporous materials with concentration of template as low as1.0wt.%.In chapter5, the evaluation on the dependence of the morphology on synthetic conditions demonstrated that, for SBA-15mesoporous silica synthesized by templating P104via the one-step or two-step pathway under strongly or mildly acidic conditions, the morphology is strongly dependent on the reaction temperatures, the concentration of inorganic salt and the acid species, and the short column-shaped particles, the well-defined hexagonal platelets, the spheres can be obtained through adjusting these synthetic parameters. By adjusting these parameters, the similar interaction between organic micelles and inorganic species in different reactant systems can be obtained, which may results in the similar final morphology. In addition, the ordered and cubic mesoporous silica materials with dodecahedron shape (4-6μm) were synthesized by using F108as template under a moderately acidic condition of0.5M HCl solution.In chapter6, SBA-15mesoporous silca with uniform equilateral hexagonal tablet crystal morphology was synthesized by using domestic P104as the template with the addition of K2SO4. The cost for synthesis of this SBA-15with hexagonal tablet morphology may be much lower because of its cheaper domestic P104.In chapter7, a new lamellar mesoporous silica material with higher hydrothermal stability was firstly synthesized using industrial reagent nonionic surfactant PEG6000DS as the template in nonaqueous system through S0I0route. This method will not only extend the preparative area of mesoporous materials, but also provide a convenient and cheap pathway for pareparaing ordered mesoporous films with lamellar structure.