矽量子點/聚醯胺/聚醚碸中空纖維膜的製備與應用於奈米過濾之研究

Study on Preparation of Silicon Quantum Dots/Polyamide/ Polyethersulfone Hollow Fiber Membrane for Nanofiltration

張智翔(Chih-Hsiang Chang)

指導教授 ： 李魁然

共同指導教授 ： 蔡惠安(Hui-an Tsai)

中原大學/工學院/化學工程研究所/碩士(2021年)

https://doi.org/10.6840/cycu202100641

摘要

隨著全球人口增加和經濟的高速發展，水資源缺乏與廢水問題越來越嚴重，而在廢水處理技術中，奈米過濾 (nanofiltration, NF)膜可以有效處理廢水，甚至可回收廢水中的多價重金屬離子。相較於平板膜，中空纖維膜可以提供更高的比表面積，使單位體積模組具高的有效作用面積，可提升單位時間的廢水處理量。本研究合成兩種含矽之矽量子點 (silicon quantum dots, SiQDs)，分別為具有胺官能基團的矽量子點 (NSiQDs)和兼具胺及羥基官能基團的矽量子點 (NOSiQDs)。由於合成之矽量子點具有胺基團，可以與醯氯單體產生反應，形成聚醯胺 (polyamide, PA)。因此本研究以合成之SiQDs作為水相單體，並與均苯三甲醯氯 (trimesoyl chloride, TMC)在聚醚碸(polyethersulfone, PES)中空纖維膜的管腔內部進行界面聚合反應，以製備PA /PES超薄複合(thin-film composite, TFC)中空纖維奈米過濾薄膜。在奈米過濾效能測試以及光穿透實驗中發現，以NSiQD及NOSiQDs量子點作為界面聚合反應之水相溶液單體，其聚合反應的速率較使用哌嗪 (piperazine, PIP)做水相單體來得慢，且較慢的反應速率導致的低交聯程度對分離效能有直接的影響。本研究同時選定親水性較佳的NOSiQDs與PIP以定比例混合，作為界面聚合時的水相溶液，期望改善PA/PES中空纖維奈米過濾複合薄膜的二價鹽截留率較低的問題。
在NOSiQDs/PIP水相溶液混合比例的實驗中發現，NOSiQDs與PIP之間形成的氫鍵可以有效幫助提升與TMC的聚合程度，藉此提升PA/PES複合中空纖維膜的二價鹽截留率，但隨著NOSiQDs/PIP混合水相溶液中NOSiQDs比例提升，因羥基比例的提升又會使聚合程度下降，形成較鬆散的聚合層，混合水相溶液的最佳單體混合比例為50/50 NOSiQDs/PIP。

本研究結果顯示，在相同水相混合比例SiQDs/PIP=50/50，且同樣聚合條件下，由於 NOSiQDS/PIP的TFC膜比NSiQDs/PIP的TFC膜具有更多的羥基可提供高親水性，因此製備之PA/PES複合中空纖維膜具有更高的滲透水通量，在4 bar的操作壓力下，兩條件所製備之TFC膜其純水通量分別為58.3414.26 LMH及36.955.73 LMH。而50NOSiQDs/50PIP製備的TFC中空纖維膜與PIP-TMC製備的TFC中空纖維膜相比，50NOSiQDs/50PIP製備的TFC中空纖維膜其二價鹽硫酸鈉的截留率比PIP-TMC製備的TFC中空纖維膜高出16%，分別約為96%與80%。儘管混合水相溶液製備的TFC中空纖維膜的滲透通量略微下降，本研究依舊提供了有效的方法提升奈米過濾二價鹽截留率。

關鍵字

矽量子點 ； 奈米過濾 ； 中空纖維膜 ； 界面聚合

並列摘要

With the rapid development of population and economy, wastewater problems have become more serious. In the wastewater treatment, nanofiltration (NF) membrane can effectively recover multivalent heavy metal ions. Compared with flat-sheet membranes, hollow fiber membranes can provide a higher area per unit volume module. In this study, hydrophilic silicon quantum dots (NSiQDs) with amine groups and silicon quantum dots (NOSiQDs) with both amine and hydroxyl groups were synthesized. Due to the amine groups in SiQDs, it can react with acyl chloride to form a polyamide (PA) layer. The SiQDs were used as the aqueous monomers and reacted with trimesoyl chloride (TMC) through interfacial polymerization on the lumen of the PES hollow fiber membrane to fabricate PA/PES thin-film composite (TFC) hollow fiber membrane for nanofiltration. In the performance test and light transmission experiment of NSiQD and NOSiQDs quantum dots, it was found that the polymerization rate of NSiQD and NOSiQDs quantum dots was slower than that of PIP as the aqueous monomer. The slower reaction rate results in a low crosslink degree. Thus, in this study, NOSiQDs quantum dots with better hydrophilicity and PIP were selected and mixed in a fixed ratio as the aqueous solution, hoping to improve the problem of lower divalent salt rejection.
In the experiment of the mixing ratio of NOSiQDs/PIP, hydrogen bonds were formed between NOSiQDs and PIP that can effectively help to increase the degree of polymerization, thereby increasing the rejection rate of divalent salts. However, as the ratio of NOSiQDs increases and the ratio of PIP decreases, the increase in the ratio of hydroxyl groups reduced the degree of polymerization and formed a loose selective layer. The best mixing ratio is 50 NOSiQDs/50 PIP.
The results of this study show that under the same water mixing ratio and the same polymerization conditions, the TFC membrane of NOSiQDS/PIP has higher hydrophilicity provided by more hydroxyl groups than NSiQDs/PIP resulting with higher permeable water flux. The conditional pure water fluxes were 58.34±14.26 LMH and 36.95±5.73 LMH at 4 bar operation pressure, respectively. Compared with the PIP/TMC prepared TFC hollow fiber membrane, the rejection of divalent salt of 50 NOSiQDs/50 PIP prepared TFC hollow fiber membrane was higher than 16%, which was 80% and ≒96%, respectively. However, even though the permeation flux slightly decreased, this study still provides an effective method to increase the rejection rate of divalent salt.

並列關鍵字

silicon quantum dots ； nanofiltration ； hollow fiber membrane ； interfacial polymerization

參考文獻

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