| Summary: | 碩士 === 中山醫學大學 === 職業安全衛生學系碩士班 === 102 === Carbon molecular sieving membrane (CMSM) is generally supported on porous Al2O3 substrate to form asymmetric composite membrane to enhance its mechanical strength and separation performance. However, in our previously studies we have clearly demonstrated that the support layer can have significant effects on polymer segment arrangement and the interfacial adhesion between selective layer and substrate, which will result in defect formation and low separation performance. The adhesion mechanism between them is determined by the mechanical interlocking, chemical bonding and adsorption. Therefore, in this study, the TiO2 nano-network which containing hydroxyl groups was acting as intermediate layer to modify the interfacial adhesion. The particle size of TiO2 was controlled by adjusting the pH of the gel solution. Further, the effect of surface roughness of support and the viscosity of casting dope on the adhesion were also evaluated.
The results indicated that the pore structure of the substrate can be modified by TiO2 nano-network. The surface area and the total pore volume of substrate were increased, which is benefited for mechanical interlocking with polymer chain. Further, PEI chain was bonded by the Hydroxyl groups of the TiO2 to improve the chemical bonding. The mechanical strength of the TiO2-modified Al2O3 support was enhanced from 187.4 N to 215.9 compared to the original one.
The separation performance was observed strongly related with the pH of sol-gel solution, surface roughness and viscosity of dopes. When the pH value was low, the hydrolysis rate was increased to form fine TiO2 particle to penetrate into the voids of the substrate, which can improve the mechanical interlocking and selectivity, but loss some permeability. In addition, using polishing technology to modify the roughness of the intermediate layer, the gas permeability would be increased when the surface roughness was high. The irregular arrangement of polymer chains decrease the ultra-micropore and increase the d-spacing of membrane, so the selectivity will decrease.
At last, we change the polymer solution temperature to adjust the viscosity of dopes. The low viscosity of dopes will penetrate into the substrate to improve the mechanical interlocking, but the permeability will also decreased. When increasing the polymer solution temperature, the polymer chain was rigidified due to the high volatility of solvent. Therefore, the membrane became much dense. The d-spacing was decreased after carbonization and also resulted in low permeability.
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