奈米二氧化鈦(TiO2)/聚醚碸(PES)超過濾薄膜之製備及抗汙效果研究

Nano-titania (TiO2)/polyethersulfone (PES) ultrafiltration membrane preparation and antifouling capability analyses

林建德(Jian-De Lin)

指導教授 ： 鄭廖平

淡江大學/工學院/化學工程與材料工程學系碩士班/碩士(2018年)

https://doi.org/10.6846/TKU.2018.00810

摘要

本研究在製膜液中導入自行合成之奈米二氧化鈦(titania, TiO2)溶膠及聚乙烯吡咯烷酮(PVP)兩種添加劑，藉由前者之親水性改善PES薄膜易結垢之缺失，及後者之造孔功能，使孔隙交穿連通，製備出PES/TiO2複合薄膜(俗稱mixed matrix membrane, MMM)，依PVP添加量不同，將薄膜分為P0、P1.5以及P5三系列，每系列薄膜中各含不同濃度TiO2。TiO2是採用溶膠-凝膠法合成，其粒徑大小約為2-3 nm，並且為了讓TiO2能充分分散在製膜液中，不論調配製膜液或合成TiO2皆以二甲基乙醯胺(DMAc)作為溶劑；所製得薄膜皆呈現非對稱結構，表面為皮層，內部則由手指狀巨孔及不規則大型巨孔所構成，隨著PVP添加量增加，上下表面孔洞逐漸變大，使得純水通量隨之增加，而不規則大型孔洞逐漸轉化為手指狀巨孔；改變TiO2添加量時，會使得薄膜表孔洞尺吋呈先增後降趨勢，使得純水通量亦呈相同趨勢，薄膜之孔隙度約為80~88%，上表面接觸角則會隨著TiO2的添加而逐漸下降，抗張強度隨著PVP添加量提高，逐漸下降，這是由於上下表面孔洞變大所造成，然而當固定PVP添加量時，抗張強度則會隨著TiO2的添加，呈先增後降趨勢。PVP在薄膜的殘留量是由NMR分析取得，結果顯示約90% PVP於成膜過程中已被移除，殘留量僅佔膜重1~2%。熱性質方面，由TGA與DSC分析可知隨著TiO2的添加，薄膜熱穩定性隨之提升，最大裂解溫度可提升約5C，玻璃轉換溫度約提升10C。將薄膜進行BSA過濾時，發現P0及P1.5系列之移除率皆可達99%，而P5只有約93%，至於純水通量及回復率則隨著TiO2的添加呈現先增後降趨勢，原因是TiO2可提高表面親水性，進而減少BSA和薄膜表面的疏水性吸附，但過量添加會導致TiO2團聚而降低其效能。利用PEG測試薄膜之截留分子量，發現P0系列約為270~350 kDa、P1.5系列約為325~510 kDa、P5系列約為450~850 kDa，此現象與純水通量以及孔洞大小數據互相呼應。

關鍵字

溶膠凝膠法 ； 聚醚碸 ； 二氧化鈦 ； 超過濾 ； 抗汙 ； 截留分子量

並列摘要

In this research, we introduce TiO2 sol (synthesized via the sol-gel procedure) and polyvinylpyrrolidone (PVP) into the casting dope for polyethersulfone (PES)/TiO2 composite membrane formation. The former additive is used to enhance the hydrophilicity, whereas the latter functions as a pore former to engender pore-pore interconnection. Prepared membranes (termed mixed matrix membrane, MMM) can be divided into 3 series: P0, P1.5 and P5, according to the amount of added PVP. Each series consists of several membranes with TiO2 contents. To disperse TiO2 finely (on the scale of 2-3 nm) in the casting dope, the sol-gel process incorporates DMAc as the solvent, same as that used for preparation of the casting dopes. All membranes show the asymmetric structure with a dense surface (skin) and a porous cross section composed of finger-liked macrovoids and large irregular macrovoids. With the increase of added PVP, the pores on the top and bottom surfaces increase, resulting in an increase of the pure water flux, while the irregular large macrovoids gradually transform into finger-liked macrovoids. Changing the amount of added TiO2, the surface pore size of the membrane is found to increase first and then decrease; the pure water flux follows the same trend. The porosity of the membrane is about 80-88%, and the contact angle of the top surface gradually decreases with the addition of TiO2. The tensile strength decreases with the increase of added amount of PVP, which is attributed to the larger pores of the top and bottom surfaces. However, when the added PVP is fixed, the tensile strength increases first and then decreases with the addition of TiO2. The amount of PVP resided in the membrane has been determined by NMR analysis. The results show that about 90% of the PVP is removed during the membrane formation process and the residual amount only accounts for 1-2% of the membrane weight. Thermal properties based on TGA and DSC analysis show that the thermal stability of the membrane increases with the TiO2 content: an increase of 5C on the maximum thermal degradation temperature and 10C of the glass transition temperature. The BSA filtration experiments show that the rejection ratio of the P0 and P1.5 series are both 99% and yet it is only about 93% for the P5 series. As to the pure water flux and the recovery ratio, both increase first and then decrease with the TiO2 content. The reason is that TiO2 can increase the hydrophilicity of the membrane surface and thus reduces the hydrophobic adsorption of BSA on the surface. However, excessive amount of TiO2 can cause agglomeration of TiO2, which in turn lead to decrease of its antifouling efficiency. PEG is used to determine the molecular weight cut-off (MWCO) of the membranes. For the P0 series, the MWCO is about 270-350 kDa, for the P1.5 series, it is about 325-510 kDa, and for the P5 series, it is about 450-850 kDa. These results are consistent with the pure water flux and the pore size data.

並列關鍵字

sol-gel method ； polyethersulfone ； TiO2 ； ultrafiltration ； antifouling capability ； molecular weight cut-off

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