| Summary: | 碩士 === 雲林科技大學 === 化學工程與材料工程研究所 === 96 === The pH-switchable ion selective membranes were fabricated by coating a self-assembled monolayer (SAM) of 3-aminopropyltrimethoxysilane (APS) or 3-glycidoxypropyl-trimeyhoxysilane (GOPS) on nanoporous anodic aluminum oxide membrane (AAOM), followed by grafting a SAM of glutamic acids (Glu). They were then used to perform the diffusion experiments of single amino acid- L-tyrosine.
First, the measurements of contact angle (CA)、attenuated total reflection infrared (ATR)、scanning electron microscopy (SEM) were used to characterize the nanoporous AAOM surface before and after surface modification. Using the CA measurements, the optimal formation times and the CA values were 3 hrs and 54° for an APS-SAM and 2 hrs and 63° for a GOPS-SAM, respectively. In the ATR measurement, the characteristics peaks of asymmetric (va) and symmetric (vs) C-H stretching bands were exhibited at 2936、2840 cm-1 for the APS-SAM, and 2937、2870 cm-1 for the GOPS-SAM, respectively, which revealed that the silane-SAMs were well functionalized. In the SEM measurement, it confirmed that the pores were not clogged after the surface modification. Then, the amounts of available amine and epoxy groups present on the membrane surface were quantified from the reaction with the amine group of PABA. The results show that the amount of amine group was 0.002379 mmole/g for the APS-SAM and the amount of epoxy group was 0.002886 mmole/g for the GOPS-SAM. Also, the further grafting of the Glu-SAM was confirmed by the CA measurement.
The membrane surface charge was characterized by the electroosmotic (EO) flow measurement. The results show that the bare AAO, APS coating, and APS-Glu coating membranes presented positive surface charge, while the H2O2 pretreatment and GOPS-Glu coating membranes had negative surface charge. The pH-switchable characteristic of the modified membrane was demonstrated by the effect of solution pH on the EO flow rate. Among the above modified membranes, the APS coating membrane had the most significant pH effect, and the GOPS-Glu membrane followed. It confirmed that silane coating on AAOM followed by glutamic acid attachment was a useful way to increase the surface charge of membrane.
In the diffusion experiment of L-tyrosine, the unmodified AAO and H2O2 pretreatment membranes had no pH effect on the flux. However, there had a significant pH effect on the flux for the modified membranes, due to the repulsive force formed between L-tyrosine and the membrane with the same charge. The results show that the APS coating membrane had low flux at low pH, but the GOPS-Glu coating membrane had low flux at high pH. Again, it proved that silane coating on AAOM followed by glutamic acid attachment was a useful way to fabricate pH-switchable ion selective membranes.
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