Wiping Off Pollutants By Functionalized Mesoporous Molecular Sieves SBA-15from Aqueous Solution

Nanotechnology is a high-tech subjects. Because of its special feature, it has broadapplication prospects in environmental science. The use of nanotechnology andnano-materials to solve environmental pollution problems has become an inevitable trend ofresearch on environmental protection. With the rapid development of industrialization, waterpollution became more and more serious. The water pollution and the shortage of waterresources have become one of the important factors restricting economic development. Thus,the development of technology for water pollution control is the goal of environmentalworkers.In this thesis, the modified SBA-15molecular sieve is applied to the adsorptive study oforganic compounds and heavy metals from aqueous solutions and the study can providepractical and efficient method for the effective control of water pollution.1.Titania was incorporated into the mesopores of SBA-15by solid phase thermaldiffusion method, and the prepared （SBA-15）-TiO₂nanocomposite was characterized bypowder X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FT-IR）, nitrogenadsorption-desorption analyses, transmission electron microscopy （TEM） and scanningelectron microscopy （SEM）. The results showed that the frameworks of （SBA-15）-TiO₂andordered mesoporous structures of the SBA-15molecular sieve were kept well.2.The （SBA-15）-TiO₂was used to wipe off the methylene blue in water. The influenceof solution pH value on photo-catalytic activity. When the pH value of solution is8.2, the（SBA-15）-TiO₂has best catalytic effect on the degradation of the methylene blue. The（SBA-15）-TiO₂nanocomposite material which was prepared in this study has very highphoto-catalytic degradation effect on methylene blue. Methylene blue is completely degradedin10min under the function of the （SBA-15）-TiO₂catalyst, but it has not been completedafter60min under the function of the conventional nano-TiO₂. It shows that the catalyticefficiency of the （SBA-15）-TiO₂catalyst prepared in the present study is much better thanthat of the conventional nano-TiO₂.3.Nanoscale SBA-15molecular sieve was sand modified with ethylenediaminetetraacetic acid （EDTA） and thioglycolic acid （TGA）. The prepared materials werecharacterized by powder X-ray diffraction （XRD） and scanning electron microscopy （SEM）.The results showed that for the modified SBA-15, the frameworks and ordered mesoporousstructures of the SBA-15molecular sieve were kept well.4.The modified SBA-15was used as adsorbents to adsorb the heavy metal ions Cd²⁺,Cr⁶⁺, Hg²⁺and Pb²⁺in water body. The effects of pH, temperature and adsorptive time on the efficiency of adsorption were studied, and the optimum adsorptive conditions wereconfirmed. The results showed that the highest adsorptive efficiency of Cd²⁺, Cr⁶⁺and Pb²⁺can reach95.0%when the pH is4, temperature is35℃and adsorptive time is30min, andwhen the pH is5, temperature is35℃and adsorptive time is50min, the highest adsorptiveefficiency of Pb²⁺. When the pH is5, temperature is30℃and adsorptive time is50min, thehighest adsorptive efficiency of Hg²⁺can reach98.0%. The optimum adsorptive rate on Pb²⁺by the SBA-15modified by EDTA is better than that by SBA-15and the SBA-15modifiedby mercaptoacetic acid. The adsorptive capacity on Hg²⁺by the modified SBA-15is alsodifferent. The adsorptive capacity and intensity from strong to weak is the SBA-15modifiedby mercaptoacetic acid, the SBA-15modified by EDTA, SBA-15. This may be because theadsorption of Hg²⁺by SBA-15belong to ion exchange and physical adsorption. However, theSBA-15modified by mercaptoacetic acid can be used for treating the wastewater containingHg²⁺more effectively than the SBA-15because of the mercaptoacetic acid interaction withHg²⁺by the combination as well. The results showed that: Cd²⁺is absorbed quantitatively tothe SBA-15modified EDTA; absorption behavior is in accord with Langmuir adsorptionequation, which is due to monolayer adsorption, and the adsorption have ordered structure.5.The adsorption kinetics study shows that: the adsorption of Hg （II） and Cd （II） of theSH-SBA-15and EDTA-SBA-15with a false second-order kinetics model to describe theadsorption kinetics. The overall adsorption process rate is controlled by the speed of the fistand second stage. Adsorption isotherms show that: the SH-SBA-15for Hg （II） adsorption ofEDTA-SBA-15of Cd （II） the adsorption law in line with the Langmuir adsorption model,adsorption belongs to the monolayer adsorption, the uniformity and ordering of the surface ofSBA-15. ΔG0for negative adsorption is feasible and spontaneous. ΔH0for positiveadsorption process is endothermic, the adsorption heat value, indicating that the binding forcebetween Hg （II） with the SH-SBA-15, adsorption of Cd （II） EDTA-SBA-15are strong. ΔS0for a time when increased degree of confusion in the solid-liquid interface between theadsorbate and adsorbent. The higher temperature is conducive to chemical adsorption.Therefore, adsorption is an endothermic process and controlled mainly by chemicaladsorption.6. On the study of regeneration of adsorbent at room temperature, HCl was used tostudy the desorption of heavy metals in SBA-15. The effect of pH, temperature, and time ondesorption was studied, and the optimum desorption conditions were determined. The resultsshow that there is the best desorption effect of Cr⁶⁺and Cd²⁺when pH is1, temperature is35℃and adsorption time is4h, the desorption efficiency reached93.3%and98.2%. This studyshows that adsorbent SBA-15can be recycled. Meanwhile, this study provided research basis for the recycling of heavy metals, which greatly reduce the cost of water pollution control.The best desorption conditions on Pb²⁺by the SBA-15were confirmed. Its greatestdesorption ratio reached50%when the pH was2, temperature was35℃and desorptiontime was4h. The binding capacity between the SH-SBA-15with Hg（II） provide the newmethods for the selective management in wastewater treatment. The adsorptive experimentalresults showed that the optimum adsorbent was the SBA-15obtained by the modification ofthiolycollic acid. The desorption study of Cd（II）, Pb（II）, Cr（VI） and Hg（II） is determined onEDTA-SBA-15. The optimal adsorptive conditions were: pH=1, temp.25oC and theadsorptive time was4h. The experimental results indicated that the best desorbent was0.1mol/L HCl. The highest rate of desorption of75.05%could be reached at the desorption of4h, the highest desorption efficiency can reach94.2%,90.7%,92.3%,92.3%. TheThiol-modified SBA-15adsorbent was used for the removal of single and ternary metal ionssolutions of Cd（II）, Pb（II）, Cr（VI） and Hg（II）. The optimal adsorptive conditions were: pH=2,temp.25oC and the adsorptive time was4h. The experimental results indicated that the bestdesorbent was0.1mol/L HCl. The highest rate of desorption of75.05%could be reached atthe desorption of4h, the highest desorption efficiency can reach92.5%90.5%,86.2%,75.51%, the mercury ion desorption rate is the lowest of the four metal ions. There is a strongbinding force between SH-SBA-15and Hg（II）. The modified SBA-15was regenerated andfound to be suitable for reuse in successive adsorption-desorption cycles many times withoutsignificant loss in adsorption capacity.In this thesis, the new type of photocatalyst （SBA-15）-TiO₂was successfully prepared.The SBA-15can prevent the agglomeration of TiO₂very well in the photocatalytic process,and has been developed to increase the efficiency of the photocatalytic process of TiO₂.Meanwhile, the new adsorbents （EDTA-SBA-15and HS-SBA-15） for the treatment of heavymetals in waste water is superior to other adsorbent, and which can be renewable andsecondary use. Therefore, the modified SBA-15can be used as a quality of photocatalyst andadsorbent to remove pollutants from water, and has broad application prospects in thewastewater treatment.