碳量子點對醋酸纖維素薄膜成膜機制之影響

Effect of carbon quantum dots on the cellulose acetate membrane formation mechanism

楊鴻禮(Hong-Li Yang)

指導教授 ： 李魁然 ； 蔡惠安

中原大學/工學院/化學工程研究所/碩士(2020年)

https://doi.org/10.6840/cycu202000458

摘要

水資源日漸匱乏以及環保意識抬頭，人們因節約資源和成本低廉之原因，逐漸倚重薄膜分離程序。而薄膜分離程序中，薄膜為分離程序之核心，因此本研究以薄膜成膜時之成膜機制為主軸，藉由成膜機制探討以控制薄膜之孔洞，進而改變薄膜之分離效能、耐用性及成本。本實驗選用低成本並具高度親水性之碳量子點 (carbon quantum dots, CQDs)，以濕式相轉換法製備醋酸纖維素(cellulose acetate, CA)/CQDs混成薄膜，探討CA濃度及CQDs添加量對薄膜成膜機制之影響。研究結果發現，隨著CA濃度增加，高分子溶液之黏度上升，成膜時巨型孔洞被抑制，但是光學顯微鏡觀察以及光穿透實驗結果顯示，相分離速率並未隨之下降。然於CA/NMP/H2O的熱力學三相圖中觀察發現，其相分離行為主要由相分離所需固含量所影響，因此CA濃度改變之成膜機制受成膜熱力學所主導。
在CQDs添加之研究發現，隨著CQDs濃度增加，CA高分子溶液之黏度上升。由光學顯微鏡觀察以及光穿透實驗結果顯示，相分離速率與水於鑄膜液中的擴散係數隨CQDs添加量之增加而下降，顯示CQDs添加會影響CA薄膜成膜時之成膜動力學。由相圖觀察發現，添加CQDs後，系統之相分離區變大，並以FTIR-microscopy觀察結果發現，表層之相分離行為受到persuade water layer所影響，使表層產生較快之相分離，但薄膜較深層處之成膜行為則受到黏度之影響，因此CQDs添加之表層成膜由成膜熱力學所主導，而薄膜內部則由動力學所主導。
在超過濾測試結果發現，添加CQDs系統之CA薄膜，其親水性及水通量皆高於未添加之CA薄膜，達到731.89 ± 68.27 LMH之純水通量及160.65 ± 20.86 LMH之BSA水溶液測試通量。並於BSA吸附測試證明，CQDs具備減少BSA吸附之能力。而在乾/濕式法所製備之薄膜，以溶劑揮發時間10 min添加1,000 ppm CQDs 之CA薄膜分離效能最佳，達到59.98 ± 19.97 LMH及91.47 ± 5.83 %之BSA截留率。並由antifouling測試發現，添加CQDs系統之CA薄膜擁有較高之通量回復率以及可逆結垢，而不可逆結垢則較小，證明添加CQDs之CA薄膜具備antifouling之能力。

關鍵字

碳量子點 ； 成膜機制 ； 抗結垢

並列摘要

The aim of this work is focus on membrane formation, which control pore of membrane for improving membrane performance, lifetime and cost. In this study, cellulose acetate (CA) membranes fabricated by phase inversion method in N-methyl-pyrrolidone (NMP) using a range of procedures were blended with carbon quantum dots (CQDs) in a range of concentrations from 0~3,000 ppm. The effects of CA concentration, CQDs addition on membrane formation mechanism were investigated. The results show that the viscosity of polymer solution increased and the macrovoids of CA membrane suppressed as increasing CA concentration. While, at the observation of optical microscopy and results of light transmission experiment, no further decrease in phase separation rate was observed. However, the observation of ternary phase diagram of CA/NMP/H2O for thermodynamic shows that the phase separation behavior was mainly affect by the amount of polymer content, resulting in membrane formation of different CA concentrations was dominated by membrane thermodynamic.
The observation of CQDs addition was found that viscosity of polymer solution increase with increase CQDs concentration. As CQDs concentration increases, Phase separation rate and water diffusion coefficient in dope increases accordingly for the observation of optical microscopy and results of light transmission experiment. It was found that, CQDs addition affects the membrane kinetic of CA membrane during formation. The addition of CQDs is effective in increasing demixing gap for phase diagram. Furthermore, the observation of ternary phase diagram of CA/NMP+CQDs/H2O for thermodynamic shows that the phase separation behavior at top layer was mainly affect by the persuade water layer, causing faster phase separation at top layer, but slower formation behavior at deep layer effect caused by viscosity. Given the above observations, membrane formation of different CQDs addition was dominated by membrane thermodynamic at top layer and membrane kinetic at deep layer.
The observation of ultrafiltration test was found that, the hydrophilicity and water flux of CA/CQDs membrane were significantly improved compared to CA membrane while the pure water flux and BSA flux were further increased to 731.89 ± 68.27 LMH and 160.65 ± 20.86 LMH. However, CA membrane with 10 min-1000 ppm CQDs exhibited best performance in comparison with other membranes which prepared by dry/wet method. The resultant increase in BSA flux and rejection to 59.98±19.97 LMH and 91.47±5.83%. The CA/CQDs membranes have higher flux recovery ratio, reversible fouling ratio and lower irreversible ratio were proved its antifouling ability, which is supported by observation from antifouling test.

並列關鍵字

carbon quantum dots ； membrane formation ； antifouling

參考文獻

[1] H. Kaur, V.K. Bulasara, R.K. Gupta, Influence of pH and temperature of dip-coating solution on the properties of cellulose acetate-ceramic composite membrane for ultrafiltration, Carbohydrate Polymers, 195 (2018) 613-621.

[2] K.H. Youm, A.G. Fane, D.E. Wiley, Effects of natural convection instability on membrane performance in dead-end and cross-flow ultrafiltration, Journal of Membrane Science, 116 (1996) 229-241.

[3] M.H. Al-Malack, G. Anderson, Crossflow microfiltration with dynamic membranes, Water Research, 31 (1997) 1969-1979.

[4] A.Y. Kirschner, Y.H. Cheng, D.R. Paul, R.W. Field, B.D. Freeman, Fouling mechanisms in constant flux crossflow ultrafiltration, Journal of Membrane Science, 574 (2019) 65-75.

[5] C.F. Wan, T.S. Chung, Techno-economic evaluation of various RO+PRO and RO+FO integrated processes, Applied Energy, 212 (2018) 1038-1050.