油水分離多孔膜的潤濕性質;Wetting Phenomena of Porous Films for Oil-water Separation

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Title:	油水分離多孔膜的潤濕性質;Wetting Phenomena of Porous Films for Oil-water Separation
Authors:	林政佑;Lin, Cheng-Yu
Contributors:	化學工程與材料工程學系
Keywords:	油水分離;奈米過濾膜;銅網;Oil-water Separation;Nanofiltration;Cu mesh
Date:	2017-06-15
Issue Date:	2017-10-27 12:54:56 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文使用簡易快速的方法，使氧化銅於低溫真空的環境下，還原成氧化亞銅的方式，製備超疏水銅網，並應用於油水分離。當表面成分還是氧化銅時，其為親水性材料，接觸角只有56.6度，水與油類皆會滲透濾網，無法達到油水分離之目的。而經過處理，表面成分變成氧化亞銅時，其為超疏水材料，接觸角上升至152.6度，油類仍可輕易滲透過去，水則不易滲透而滯留在濾網上，便能做到油水分離，並且分離效率能達到99%以上。另外，因為這樣的製備手段並不使用其他物質塗布，其耐用性甚高，於各式鹽類溶液、酸性、鹼性、界面活性劑溶液等環境下，仍可維持超高接觸角，達到油水分離之目的。最後，進一步得知，除了接觸角之外，若能適當縮小濾網的孔隙大小，並維持其高疏水性質，能提升其耐用性，於較高水壓環境下做到油水分離。而在工業中，也有部分狀況是採用奈米過濾膜（nanofiltration membrane）作為油水分離的材料，然而由於目前市售奈米過濾膜平均孔徑僅約1-10 nm，操作壓力通常需大於大氣壓力。本論文嘗試了解奈米過濾膜之潤濕性質，期望從潤濕性質的角度了解奈米過濾膜的其他性質，助於未來改善奈米過濾膜應用於廢水處理的效能。而在研究過程中意外發現，陶氏化學（Dow Chemical）所售的奈米過濾膜NF270，除了接觸角約20.8度，具有相當良好的親水性外，亦具有相當低接觸角遲滯的性質。2 μL的微小氣泡於微微傾斜（1.6度）、被浸潤在水相環境的NF270表面，能平順的滑移。因為NF270具有低接觸角遲滯的性質，氣泡於其表面上滑移時，並不會變形太多，維持著幾乎是圓球狀的樣子在滑移；如此觀察氣泡在界面活性劑溶液中的運動行為，即除去了形狀因素造成的影響。另外，奈米過濾膜在廢水處理中，亦被使用來阻絕特定鹽類離子滲透，達到硬水軟化的目的。一般來說，奈米過濾膜表面有些許帶有正或負電荷的官能基，以阻絕相同電性的離子。然而除了表面官能基、離子大小等因素會影響滲透結果之外，溶液中的鹽類離子種類也會互相競爭，影響滲透結果。在氯化鈉溶液中，發現氯離子較易滲透奈米過濾膜；然而在醋酸鈉溶液中，反而是鈉離子較易滲透。藉由量測奈米過濾膜兩端電位差並交互比對，便可知道離子的滲透程度。;In this study, a facile fabrication of superhydrophobic Cu mesh for oil-water separation is applied in a low-temperature vacuum environment. When the predominant composition of surface is CuO, it’s a hydrophilic substrate with contact angle 56o, and oil cannot be separated from water due to the penetration of both oil and water. After this facile fabrication, the composition of surface changes into Cu2O partially, and it becomes a superhydrophobic substrate with contact angle 152.6o. Oil-water separation can be achieved because oil penetrates the superhydrophobic mesh while water is repelled on the mesh. And the separation efficiency can be higher than 99%. In addition, there’s no chemicals coated on mesh in this fabrication, so the stability is pretty high. The mesh can be against various aqueous chemical drops such as salts, acid, base, and surfactant. Besides, if the pore size of a mesh is shrunk and a mesh remains hydrophobicity, the stability can be elevated and operated in an environment of higher intrusion pressure. Nanofiltration membranes sometimes are used as the material for oil-water separation. Due to the small pore size (1-10 nm), the operation pressure should be higher than atmospheric pressure. In order to improve the performance in future works, the wetting behavior of nanofiltration membrane (Dow FILMTEC™ NF270) is investigated in this study. The contact angle of NF270 produced by Dow Chemical is 20.8o which is hydrophilic, and also it has ultralow contact angle hysteresis. A small bubble (1.6 μL) can slide steadily on 2o-inclined NF270. Because of the ultralow contact angle hysteresis, a bubble doesn’t deform and move on the surface with spherical shape. Without the effect of shape, it becomes easier to observe bubble motion in surfactant solution. Besides, nanofiltration membranes are also used to reject specific salt ions for water softening. Generally, there’s positive or negative function group on a nanofiltration membrane to reject co-ions. However, besides the effects of function group and ion size, the ions in a solution also compete and the permeation ions varies. For NaCl solution, Cl- permeates NF270 more, while for CH3COONa solution, Na+ permeates NF270 more. By measuring the potential difference and comparing the correlation of various solutions, the ion permeation can be understood easily and straightforward.
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