The Preparation And Characterization Of Mesoporous Montmorillonite And Its Applications In Support

The siliceous mesopore has thermal stability and hydrothermal stability in air and oxygen containing water vapor. However, it lost its mesoporous structure after being heated in boiling water and aqueous solutions. The collapse of porous structure was attributed to the amorphous porous wall and hydrolysis of silicate by water molecule. So thermal stability and hydrothermal stability of mesoporous sieve is a problem to be settled. The pillared clay is a kind of mineral materials with two-dimensional pore, which is formed the polymer inorganic cation or organic ions (molecules) into the interlayer of clay minerals. Its unique structure makes it have a large surface area, adjustable pillared spacing, high surface activity and thermal stability properties. It has a wide range of applications in catalysis, optical functional materials, sewage treatment, antimicrobial materials, pharmaceuticals, nanocomposites, nuclear waste disposal areas and so on. Current major research was focus on preparation and application of pillared microporous montmorillonite. But its narrow pore, limits their development. For a greater potential research of pillared mesoporous montmorillonite is still in the exploratory stage.In recent years, people have been committed to finding an efficient and inexpensive photocatalytic material which has good photochemical activity of photocatalytic, while the nano-technology of the photocatalysis is the presime to ensure the performence. However, extremely small particles lead to shortcomings of difficult recovery. Therefore, in practice, the catalyst loading can form a strong binding between support and photocatalyst. It not only solved the proberlem of recovery, but also the big surface area of the support dispersed the catalyst evenly, inhibited the growth of grain, increased the surface area and adsorption of reactants. It played an important role to accelerate the accumulation and transfer of reactants. Therefore, the research and development of new support with high efficiency have become an important thing.In this paper, mesoporous material was hydrothermally synthesized with montmorillonite and TEOS as the silicon precursor and CTAB as template. The samples were characterized by XRD, FT-IR, TG-DTA, nitrogen adsorption–desorption isotherms, SEM and TEM. The experimental results showed that layers of montmorillonite were present as smaller porous wall. On the basis of gallery-templated synthesis, we expanded the scope of application of the mechanism and found proposed mechanism for the formation of mesoporous montmorillonite. The reaction system is divided into two environments: interlayer and outer-layer, 2.9 nm excellent performance pores formed between layers, and 3.9 nm pores which have amorphous wall formed outside the layer.In order to obtain interlayer mesopore which had better stability,the montmorillonite materials were pretreated. The pretreatment included grinding and alkali activation. Based on the experiments, grinding can be divided into two stages. In a relatively short time, grinding mainly effected on reducing the size and stripping the layer of montmorillonite. While, long time grinding will destroy the structure of montmorillonite. Moderate grinding increases the dispersion of montmorillonite layers, expands the layer spacing and improves the specific surface area, interlayer cation exchange capacity and zeta potential. It is conducive to the synthesis of mesoporous montmorillonite. So the optimum grinding time was determined to be 1 hour in experimental condition. Moderate grinding can make the mesopore form easily in interlayer, which promotes the formation of pillared structure and improves the hydrothermal stability of the samples. The activation of NaOH makes Ca-montmorillonite change into Na-montmorillonite which has more excellent performance and it benefits to the formation of interlayer small pore with size of 2.9 nm in process of the mesoporous montmorillonite synthesis. It further improved the performance of synthesized products. The optimum alkali activation process was that 24.5 ml 4.5 wt% montmorillonite was added in 5ml 10% NaOH solution and activated for 2 hours at room temperature.In addition to the studies of the pretreatment conditions of montmorillonite, this paper investigated the effects of pH of synthesis system, quaternary ammonium template chain length and the crystallization conditions on the pillared mesoporous montmorillonite. Changes in pH value of reaction system affect not only the hydrolysis of TEOS but also the stability of eta potential of montmorillonite. The lower pH (≦ 8.5) benefitted synthesis of bigger pore and higher pH (>8.5) benefitted to synthesis of smaller pore. The pH value of 10 is the best reaction conditions, and the pH in the small-scale fluctuations was not seriously affecting the stability of montmorillonite within the synthesis process of mesoporous. Template carbon chain can control the pore size of mesoporous montmorillonite. When the chain increased two carbon atoms length, the diameter of pore increased about 0.4nm. X-ray low angle diffraction showed that these pores were formed in the montmorillonite interlayer, so it had a good hydrothermal stability. Using different template can control the pore size of mesoporous montmorillonite. Crystallization temperature and time of synthesis system are also the important conditions, which could affect the synthesis of pillared mesoporous montmorillonite. Experimental results showed that best crystallization condition for synthesis of mesoporous montmorillonite was 2 day room temperature crystallization. Large surface area, high thermal and hydrothermal stability of pillared mesoporous montmorillonite are the idea material to work as a support.ZnO/SnO₂ was loaded on of the mesoporous montmorillonite with high surface area. When loading amount was small, catalyst didn't form crystal because of high dispersion of photocatalysis. Only high loading amount can form a crystal and Zn2SnO4 was inhibited by loading, enhancing photocatalytic effect. When the loading amount was 80% and the calcined temperature was 700oC, the sample had the best photocatalytic properties and showed good repeatability. We achieved the purpose with a small number of support which can immobilize and improve the photocatalytic effectly. Photo-degradation reaction rate of loaded photocatalyst was far exceeds that of the unloaded photocatalyst and the photocatalyst loaded on montmorillonite. The crystalline pore wall of mesoporous montmorillonite combined with the photocatalys, and their interface effects increase the effective bandgap of the loaded semiconductor, leading to the higher electron/hole separation and hence photocatalytic activityies than that on MCM-41.Additionally, TiO₂ was loaded on montmorillonite, mesoporous montmorillonite and MCM-41 by Sol-gel method. Support limits the grain growth and aggregation of TiO₂. After loading on mesoporous montmorillonite, the composite surface area was still high. In composite catalyst the support still maintained the intact and clear pore structure, and promoted the mass transfer process of the catalytic reaction. Due to the small grain size of TiO₂, the photo-degradation reaction rate of TiO₂ on the pore material far exceeded that unloaded TiO₂ and that on montmorillonite. The crystal pore wall of mesoporous montmorillonite made photocatalytic activity of TiO₂ on it better than that on MCM-41, and better hydrothermal stability leads to good reusability.