近年來，含油廢水的處理是一個越來越受重視的議題，從民生廢水、石化工業甚至船隻的漏油事件均可窺見其重要性。然而現今的技術大部分仍受限於分離效率、高成本、二次汙染等問題。矽藻土為矽藻類的化石殘骸於水底沉積，經自然環境作用而形成的非金屬礦物，是一種具有成本低廉、容易取得及親水特性的天然多孔材料。此研究運用矽藻土作為原料，並搭配冷凍鑄造法，藉由調控降溫速率及固含量合成一具多階層孔洞的薄片。其於水中展現了對多種油類與有機溶劑的超疏油性，並具有高油水分離效率、高水通量、無二次汙染等優點。此方法亦相對穩定，對油類具有高侵入壓力、在經歷多個分離週期後仍能維持其效能，並可於嚴苛的環境，如:酸、鹼、鹽水環境下使用。綜上所述，我們利用一個成本低廉、環保又相對簡易的方法合成具有高油水分離效果、穩定性及耐久性的多孔材料，期待未來能應用於含油廢水的處理上。

Recently, separation of oil from oily wastewater has caught much attention due to the increased oil pollution caused by our daily life, industrial wastes, and offshore oil spills. However, conventional techniques still have limitations to date, including low efficiency, high cost, and second contamination. Diatom is a silica-based phytoplankton that can be found abundantly in aqueous environment, and it produces almost 25% of the oxygen we breathe. After the death of diatom, the silica-based cell wall remains and forms a fossilized material known as diatomite. Owing to its water-absorbing and porous nature, diatomite becomes a potential candidate for oil/water separation. In this study, we utilized diatomite as raw material to fabricate a hierarchically porous plate via the freeze-casting technique. After purification, the nanostructure of diatom could be well-preserved, and aligned hierarchical micro-sized channels and nano-sized pores were successfully synthesized through the optimized cooling rate and water content. The hierarchically porous plate displays both superhydrophilicity and underwater superoleophobicity evaluated by various oils, such as soybean oil, hexane, dodecane and n-hexadecane. Additionally, our work demonstrates superior oil/water separation efficiency, high water permeance, and high oil intrusion pressure. Moreover, the as-synthesized plate shows low adhesion to oil underwater that the oil can be washed away easily by water flushing, and maintained good durability even after several separation cycles. Finally, the plate exhibits excellent environmental stability under harsh environments, including strong acid, base, saturated sodium chloride solution, and hot water. To recapitulate, we synthesized a cost-effective, eco-friendly, and robust diatomite-based porous plate by freeze casting method which showed superior oil/water separation performance, reliability and stability. With these advantages, it has potential to be further applied in the separation of large amount of oily waste water and is suitable for long-term applications.

中文摘要 i
Abstract ii
List of Tables viii
Figure Caption ix
Chapter 1. Introduction 1
1.1 Background 1
1.1.1 Oil/Water Separation 1
1.1.2 Freeze Casting 2
1.2 Motivations and Goals 3
Chapter 2. Literature Review 7
2.1 Wetting on Solid Surfaces 7
2.1.1 Wettability in Air 7
2.1.2 Wenzel and Cassie-Baxter Equations 8
2.1.3 Underwater Wettability of Oil 9
2.2 Recent Development on Super-wettability for Oil/Water Separation 13
2.2.1 Oil/Water Separation by SHBOI Materials 13
2.2.2 Oil/Water Separation by UWSOB Materials 15
2.3 Diatomaceous Earth 21
2.3.1 Introduction 21
2.3.2 Potential Applications 22
2.4 Freeze Casting 25
2.4.1 Theoretical Background 25
2.4.2 Processing Principles 27
2.4.3 History and Recent Development on Freeze Casting 30
2.4.4 Previous Research on the Diatomaceous Earth Scaffold Synthesized by Freeze Casting 32
Chapter 3. Experimental Methods 43
3.1 Diatomaceous Earth Scaffold Preparation 43
3.1.1 Preparation of the Slurry 43
3.1.2 Controlled Solidification of the Slurry 44
3.1.3 Sublimation of the Solvent 45
3.1.4 Sintering of the Green Body 45
3.2 Characterizations and Measurements 49
3.2.1 Surface Characterization 49
3.2.2 Oil/Water Separation 51
3.2.3 Stability and Durability Test 53
Chapter 4. Results and Discussion 58
4.1 Freeze-casted Diatomaceous Earth Scaffolds 58
4.1.1 Surface Morphology and Microstructure 58
4.1.2 Wettability Measured in Air 62
4.1.3 Wettability Measured Underwater 64
4.2 Oil/Water Separation Performance 77
4.2.1 Separation Efficiency 77
4.2.2 Water Flux Measurement 78
4.2.3 Intrusion Pressure Measurement 81
4.2.4 Stability under Harsh Environments 83
4.2.5 Durability and Anti-fouling Property 84
Chapter 5. Conclusions 98
References 100

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