近年來由於溫室效應逐漸加劇，因此如何降低大氣中的二氧化碳濃度成為大眾所關心的議題，碳捕捉(Carbon capture)也逐漸成為熱門的研究議題。然而現今技術多半受限於分離效率不佳、再生能力低落等問題。沸石為一種天然的孔洞材料，其奈米等級的孔洞使其擁有極大的表面積，常被使用於過濾或催化劑，其中鈉沸石13X尤其具有較佳的二氧化碳吸附能力，本實驗採用鈉沸石13X為原料，並搭配冷凍鑄造法(Freeze Casting)合成單一方向性的孔洞材料，使氣體容易擴散進入內部以增進吸附效率。由於沸石粉末需要聯結劑(Binder)才能形成強度足夠的塊材，因此本實驗利用膨潤土以及聚乙烯醇做為聯結劑，利用燒結以及醚化的方法增進其機械性質。吸附結果顯示經冷凍鑄造法合成的孔洞材料不論在吸附量以及氣體擴散係數方面皆能與傳統的沸石球顆粒相匹敵。綜上所述，我們利用沸石的天然孔洞以及冷凍鑄造法，成功合成出多階層的孔洞材料，期待未來能應用於碳捕捉上。

Carbon capture has become a popular issue recently due to global warming. Adsorption of carbon dioxide from the atmosphere is also catching attention from public. However, technique to date still suffers from low gas separation efficiency and regeneration difficulties. Zeolite is natural microporous material that is often used as filter or catalyst. One of the members in the zeolite family called sodium 13X has ability to adsorb carbon dioxide from the atmosphere. Owing to this characteristic, it is chosen as the raw material in this study. Freeze casting method is utilized to synthesize hierarchical micro-sized channel and nano-sized pores through optimized cooling rate and water content. These unidirectional channels allow gas to flow to the interior of the scaffold and enhance adsorption efficiency. Furthermore, binders are necessary in order to provide enough mechanical strength. Bentonite/Poly Vinyl Alcohol are selected as inorganic/organic binder and sintering/etherification process are conducted to elevate compressive strength. The thermogravimetric analysis indicates that the total amount of adsorption is 3 mmol/g and the diffusivity is 10-15~10-16 m2/s. Both results are competitive to the zeolite pellet that is commonly seen. To summarize, hierarchical porous scaffold with unidirectional channels can be successfully synthesized by freeze casting. The total amount of adsorption and diffusivity are both comparable to the zeolite beads that are normally used.

致謝 i
中文摘要 ii
Abstract iii
Contents iv
List of Table vii
Figure Caption viii
Chapter 1. Introduction 1
1.1 Background 1
1.1.1 Carbon capture 1
1.1.2 Freeze casting 2
1.2 Motivation and Goals 3
Chapter 2. Literature review 5
2.1 CO2 Adsorption 5
2.2 Zeolite 13X 12
2.3 Freeze casting 14
2.3.1 Theory 14
2.3.2 Processing Principles 16
2.3.3 History and Recent Development on Freeze Casting 19
Chapter 3. Experimental Methods 46
3.1 Synthesis of Zeolite Scaffold 46
3.1.1 Preparation of Slurry 46
3.1.2 Controlled Solidification of the Slurry 46
3.1.3 Sublimation of the Solvent 47
3.1.4 Sintering of the Green Body 47
3.2 Synthesis of Zeolite/PVA Composite Scaffolds 48
3.4 Characterization and Measurement 49
3.4.1 Structural and Elemental Analysis 49
3.4.2 Compressive Mechanical Testing 49
3.4.3 TGA Analysis 50
3.4.4 BET Analysis 50
3.4.5 Mercury Intrusion 50
Chapter 4. Results and Discussions 55
4.1 Optimization of slurry preparation 55
4.2 Elemental Analysis and Structural Characterization 56
4.2.1 Crystallinity 56
4.2.2 Microstructural Characterization 57
4.3 Compressive Mechanical Properties 60
4.4 Adsorption Efficiency of Carbon Dioxide 62
4.4.1 Time Dependent Carbon Dioxide Adsorption 62
4.4.2 Carbon Dioxide Adsorption Isotherm 64
Chapter 5. Conclusions 87
Reference 89

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