Synthesis Of Mesoporous Molecular Sieves Using Coal Fly Ash And Its Application In The Organic Wastewater Treatment

Because of the shortage and the pollution of water resource, it is paid more attention by scientists to create effective methods of water treatment, including treating methylene blue and nitrobenzene, both of which are the main components of dyeing and the representative degradation-resistant hydrophobic organic compounds. Hence, researching the appropriate treatment methods of methylene blue and nitrobenzene is of significant in the field of environmental protection. So far, the method of photocatalytic degradation by nano-TiO₂ as the advantages of non-secondary-polluion and strong oxidation attracts widely attention. Moreover, the adsorption treatment using mesoporous molecular sieves with high specific surface area also a focus of concern because this method is relatively simple and efficient and the adsorption time is comparatively short. Those two methods both are worth developing and using on a large scale.Compared with the silicon source in traditional mesoporous molecular sieves, fly ash used in our research is cheaper and more available. Fly ash as the silicon source not only broadens the scope of optional silicon sources, but also achieves the effective utilization of the solid industrial wastes. Our main research contents are in the following.1. We used the fly ash obtained from a thermal power plant ?Shijingshan, Beijing? as the key material and the alkali-melting process to produce silicon. Then we used the CTAB as template and used the hydrothermal method to compound the MCM-41 in alkaline medium. Finally, in acid medium the SBA-15 mesoporous molecular sieves were obtained by hydrothermal method using P123 as template. Alkali-melting-hydrothermal method is relatively convenient in producing mesoporous molecular with stable structure. We also investigated the effect of mole ratios of Si/CTAB and Si/P123, pH, temperature, and crystallization time and crystallization temperature to the ordering of the mesoporous molecular sieves.2. We used the post-synthesized sol-gel method to obtain TiO₂/MCM-41 composites, in which MCM-41 could control the particle size of nano-TiO₂ effectively and improve decentrality of it. Therefore the photocatalytic efficiency could be enhanced. We used the obtained TiO₂/MCM-41 composites to photocatalyze and degrade methylene blue in simulated sunlight. In this research we observed that the best capacity of TiO₂ is 60 wt% and the photocatalytic efficiency increased with the temperature and the pH. After recycling four times, the removal rate of the composites is 91.64% of that of new composites. Because of the sunlight as light source, the TiO₂/MCM-41 composites can be used more widely and have large utility value.3. In order to improve the hydrophobicity of SBA-15, we modified the methyl of it and research the adsorption to the persistent organic pollutant which, in our experiments, is nitrobenzene. It was observed that if the concentration of nitrobenzene was 8?mol/L, the best concentration of CH₃-SBA-15 is 2.5 g/L. Furthermore, the adsorption and removal rate drcreased with the increasing of the temperature and the best value of pH was 5.