Controllable Preparation And Application Of Mesoporous Silica Microspheres

Mesoporous silica microspheres have been widely used in the fields of catalysis,adsorption,separation,energy conversion and environmental purification due to their high specific surface area,adjustable pore size and morphology.In the current literature reports,there are still many problems in the preparation of silica microspheres,such as complicated preparation process,severe aggregation of microspheres,poor sphericity and poor reproducibility.In view of the above problems,this work uses polyvinyl alcohol(PVA)as the sole additive and adopts a one-pot synthesis method to prepare mesoporous silica microspheres,including SBA-15 and "spheres-on-sphere".At the same time,using SBA-15 as a hard template and H2SO4 as a catalyst,using the inherent P123 carbonization inside the microspheres,a highly ordered meso can be successfully prepared without using an additional carbon source.This work will further promote the application of SBA-15 microspheres in different fields.(1)The first part of the thesis reports the preparation of SBA-15 microspheres using nonionic surfactant P123 as the template,the tetraethyl orthosilicate(TEOS)as the silicon source,and the PVA as the sole additive.The SBA-15 type microspheres can be successfully prepared by one-pot synthesis.The results show that:(a)The formation of microspheres depends on the synergy of the presence of PVA and the low temperature standing reaction process(the first step).(b)The temperature of the standstill step has a decisive influence on the particle size of the microspheres.As the standstill temperatures were increased from 24℃to 28℃,the average particle size of the SBA-15 microspheres decreased from 6.30 μm to 3.35 μm.(c)Taking the P60@26/35H100 sample obtained under the optimum conditions of the experiment as an example,the specific surface area,pore volume and particle sizes reach 824 m2·g-1,1.01 cm3·g-1 and 5.42 μm,respectively.(d)Mesoporous carbon microspheres C-P100@26/35H100-H2SO4 are highly ordered and contain two levels of mesopore sizes,2.5 nm and 5.9 nm,respectively.(2)The second part of the thesis reports the preparation spheres-on-sphere(SOS)type mesoporous silica microspheres using nonionic surfactant X as the template,tetraethyl orthosilicate(TEOS)as the silicon source,and the PVA as the sole additive.The one-pot synthesis method successfully produces SOS particle morphology.The experimental results show that:(a)the amount of PVA solution has a decisive influence on the particle size of the microspheres.As the mass of the PVA solution increases from 20 g to 50 g,the average particle size of the microspheres decreases from 5.85 μm to 3.83 μm.(b)The amount of PVA solution and H2SO4 is important for the number of small spheres supported on the SOS microspheres.(c)Taking the P50@26/35H140 sample obtained under the optimum conditions of the experiment as an example,the specific surface area,pore volume,particle size,pore size reach 886 m2·g-1,0.76 cm3·g-1,3.83μm and 5.8 μm,respectively.