Preparation Of Mesoporous Silica Microspheres By Micro - Silica Fume And Their Adsorption Properties Of Pb ^{2 +}

In recent years, water heavy metal pollution incidents become frequent in China, there are a lot of methods to treat the heavy metal pollution, and the adsorption method is a very promising method for heavy metal pollution treatment. Mesoporous silica has large specific surface area and rich surface functional groups, so it is an effective adsorbent for the removal of heavy metal ions. However, mesoporous silica has not yet been able to used as adsorbent on a large scale, One of the important reasons is that the limitation of silica source, template agent and synthesis methods, it is resulted in high preparation cost. On the other hand, silica fume (SF) is the byproduct of industrial silicon and ferrosilicon generation process, the amorphous silica content reaches85%. It is still extensive industrial by-products currently and acted as industrial waste for a long time, it’s direct emission and amass result in waste of resources, environmental pollution and other multiple problems. The study combined backgrounds of mesoporous silica and silica fume industry with the seriousness situation of water heavy metal pollution, using silica fume as raw materials to prepare high efficiency Pb2+absorption agent.This thesis studied the new process route of preparing mesoporous silica by using silica fume as silica resource, adsorbent with different adsorptive properties were successfully prepared, and monodisperse mesoporous silica microspheres with spherical regular, narrow particle size distribution were also successfully prepared finally. The structure and morphology of samples were quantitatively investigated by zata potential and particle size analyzer, N2sorption isotherms, XRD, SEM and TEM.The whole process could be divided into three steps. Firstly, using silica fume prepare nanometer silica sol; Secondly, using polymerization-induced colloid aggregation (PICA) approach prepared disordered porous silica microspheres(PSM); Finally, disordered porous silica microspheres (PSM) could be transformed into ordered mesoporous silica microspheres(MSM) by pseudomorphic transformation, optimizing the process parameters of each process respectively, then using it to the adsorption of Pb2+. This thesis mainly included the following aspects.1. Preparation of Silica Sol from silica fumeAdhesive nanometer silica sol were synthesized using the pretreated and acid leached silica fume as silica resource. The factors that affected the silica particle size were discussed, such as H2O/SiO2molar ratio, titration temperature, pH value and surfactants. The optimal parameters of synthesis condition were listed as follow H2O/SiO2molar ratio was260, titration temperature was room temperature, pH value was2, The average particle size of the silica sol prepared as83.2nm.2. Preparation of disordered Porous Silica Microspheres(PSM) by PICA method from Silica SolMonodisperse porous silica microspheres with spherical regular, narrow particle size distribution were also successfully prepared by PICA method using Silica Sol as raw materials. The factors that affected the morphology of PSM were discussed, such as the sol silica content, the polymerization temperature, polymerization time, pH value, the molar ratio of urea/formaldehyde, urea-formaldehyde concentration, ethanol content. The optimal parameters of synthesis condition were listed as follow:the sol silica content of silica sol was7.5%, the polymerization temperature was30℃, polymerization time was1h, pH value was1, the molar ratio of urea/formaldehyde was1.0:1.5, urea-formaldehyde concentration was0.8g of urea and1.5ml formaldehyde in every40ml system. The mechanisms of synthesizing PSM were also discussed. The prepared PSM particle size was about1.8microns, specific surface area was190.705m2/g, entrance was0.390cm3/g, the average pore size was6.711nm.Adsorption properties of PSM for Pb2+were discussed, The factors that influence absorption efficiency of PSM was also been studied, such as the PSM dosage, solution pH value, adsorption time, the initial concentration of Pb2+. The adsorption isotherm and adsorption kinetics of PSM have been analyzed. The results showed that he biggest adsorption capacity of Pb2+in PSM was36.71mg/g.the adsorption process was accorded with the Langmuir adsorption isotherm equation and the secondary dynamic model3. Preparation of ordered mesoporous Silica Microspheres(MSM) by pseudomorphic transformation from PSMMonodisperse ordered mesoporous silica microspheres with spherical regular and narrow particle size distribution were also successfully prepared by pseudomorphic transformation. The6factors that affected the process of pseudomorphic transformation were discussed. Such as temperature, time, NaOH dosage, water dosage, CTAB amount and cosurfactant. The optimal parameters of synthesis condition were listed as follow: Material ratio of SiO2:NaOH:CTAB:H2O=1:0.3:0.3:200, in the hydrothermal reaction ax in140℃for10h. We also discussed the principles of pseudomorphic transformation. The specific surface area of MSM could be greatly improved compared with PSM, pore size distribution range became more narrows, after the pseudomorphic transformation. The specific surface of MSN was711.950m2/g, the entrance was0.126cm3/g, the average pore size was3.265nm.The absorption ability of MSN to the heavy metal of Pb2+was studied, the results showed that the biggest adsorption capacity of Pb2+was38.91mg/g, the adsorption process was accorded with the Langmuir adsorption isotherm equation and the secondary dynamic modelThe CTAB/SiO2composite microspheres (C-MSM) synthesized with pseudomorphic transformation were used as adsorbent for Pb2+, it’s adsorption isotherm and adsorption kinetics have been analyzed, the results show that CTAB can significantly improve the material adsorption capacity. The biggest adsorption capacity of Pb2+in C-MSM was increaced to66.67mg/g.