慢性肺阻塞病(COPD)為全球主要死因之一，患有嚴重COPD的患者無論病情是否惡化皆容易造成氣道阻塞，導致血液中二氧化碳 (CO2) 濃度升高並且引發急性呼吸衰竭。為了監測患者呼出氣體中的 CO2 濃度，非侵入性正壓呼吸器 (NIPV) 是主要且關鍵的療法。然而，NIPV具有低成本的優點，除此之外，與動脈採血等侵入式技術相比，它更為方便，例如不需要使用ICU設置重症監護室，也不須具備臨床技巧。
由於CO2的化學惰性，對其進行高靈敏度檢測是一項挑戰，已發表的文獻中只有少數材料可以有效地偵測 CO2。本研究將N 摻雜還原氧化石墨烯 (NrGO) 和聚乙烯亞胺 (PEI)逐層噴塗在由水熱法製成的 ZnO奈米棒 (ZNR)上，製備出可在在室溫下檢測CO2的PEI/NrGO/ZNR 感測器。由於垂直排列的 ZNR 擁有高縱橫比，可以防止 NrGO 和 PEI 的 3D 多孔氣體吸收層在噴塗過程中團聚。在室溫下 5% CO2與相對濕度13%的條件下，PEI/NrGO 和 PEI/NrGO/ZNR 感測器分別顯示 1.22% 和 8.63% 的感測靈敏度。 總體而言，PEI/NrGO/ZNR 奈米複合材料的感測靈敏度比 PEI/NrGO 高 7 倍以上，於 3、5、7、9 和 11% 的CO2氣體環境，PEI/NrGO/ZNR 感測器分別顯示 5.60%、8.63%、11.50%、14.14% 和 16.98% 的感測靈敏度，並具有出色的線性曲線擬合R2 = 0.9989。
PEI/NrGO/ZNR層狀奈米複合感測器的氣體感測機制可歸因於物理化學吸附過程，其中在富含胺的3D 網絡狀PEI/NrGO層上吸附的氣體分子，透過酸鹼反應和鹼催化水合作用分別產生氨基甲酸酯和碳酸。NrGO具有微孔和167.8 m2/g 的比表面積，有助於 CO2 的物理吸附。此外，於氣體脫附過程中加熱，可以在每次測試後完全恢復到起始電流。本研究製備的感測器在循環測試中表現出優異的穩定性和可重複性，因此可藉由非侵入式的方式監測患者呼氣中的 CO2濃度。

Chronic obstructive pulmonary disease (COPD) is the major cause of death worldwide. The patients with severe COPD with or without exacerbation tend to have airflow obstruction, which leads to increased levels of carbon dioxide (CO2) and subsequent hypercapnic respiratory failure. To monitor the CO2 level of the breath from patients, non-invasive positive pressure ventilation (NIPV) is a major and crucial therapeutic choice. However, NIPV provides advantages of low cost, and it is more convenient such as no requirement of ICU setting as well as it does not require airway skills as compared to invasive techniques like arterial blood sampling.
The chemical inertness of the CO2 makes it difficult to detect with great sensitivity, and only a few materials can do. In this work, we developed optimum layer by layer spray coatings of N-doped reduced graphene oxide (NrGO) and polyethylenimine (PEI) over hydrothermally produced ZnO nanorods (ZNR) to fabricate a PEI/NrGO/ZNR sensor for CO2 detection at ambient temperature (RT). The high aspect ratio of vertically aligned ZNR prevents the agglomeration of 3D porous gas absorbing layers of NrGO and PEI during spray coatings. In the presence of 5 vol% CO2 in air (13% relative humidity) at RT, the PEI/NrGO and PEI/NrGO/ZNR sensors show 1.22 and 8.63% responses, respectively. Overall, the sensing response of the PEI/NrGO/ZNR nanocomposite is more than seven times higher than that of PEI/NrGO. Upon exposure to 3, 5, 7, 9, and 11 vol% of CO2, the PEI/NrGO/ZNR sensor shows 5.60, 8.63, 11.50, 14.14, and 16.98% responses, respectively, with an excellent linear curve fitting of R2 = 0.9989. The gas sensing mechanism of the PEI/NrGO/ZNR layered nanocomposite sensor is a physicochemical adsorption process in which absorbed gas molecules on the 3D networked amine rich PEI/NrGO layers yielded carbamate and carbonic acids via standard acid-base and base-catalyzed hydration, respectively. The NrGO, possessing a specific surface area of 167.8 m2/g with ultra-micropores, aids the physisorption of CO2. Furthermore, full recovery to the base current can be achieved in each sensing cycle using a thermal-assisted recovery mechanism. Additionally, the sensors exhibit high stability and repeatability for sequentially tested operations, making them suitable for non-invasive CO2 monitoring in patients.

摘要 ii
ABSTRACT iv
ACKNOWLEDGEMENT vi
TABLE OF CONTENT viii
LIST OF FIGURES xi
LIST OF TABLES xiii
Chapter 1 1
1 Introduction 1
1.1 Overview 1
1.2 Research Motivation 4
1.3 Gas Sensor 8
1.4 Gas Sensing Property 10
1.5 Gas Sensor Technology 11
1.5.1 Metal Oxide Semiconductor 11
1.5.2 Conductive Polymer Composites 12
1.5.3 Carbon Nanomaterial 13
1.6 Previous work in our lab 14
Chapter 2 15
2 Literature Review 15
2.1 Zinc Oxide (ZnO) 15
2.1.1 Zinc Oxide Nano Crystal Structure 15
2.1.2 Zinc Oxide Nanorods 17
2.1.3 Synthesis Zinc Oxide Nanorod 17
2.2 Reduced Graphene Oxide 20
2.3 Polyethylenimine (PEI) 23
2.4 Gas Sensing Mechanism 24
Chapter 3 27
3 Experimental Procedure and Characterization Techniques 27
3.1 Sensor Fabrication 27
3.1.1 Electrode Fabrication Process 27
3.1.2 ZNR Hydrothermal Growth Process 29
3.1.3 Preparation of Graphene Oxide 30
3.1.4 Preparation of Nitrogen-Doped Reduced Graphene Oxide 31
3.1.5 Preparation of NrGO dispersion 31
3.1.6 Preparation of PEI dispersion 31
3.1.7 Sensing Layer Deposition: 31
3.2 Materials Analysis Instruments 32
3.3 Gas Sensing Measurement Setup and Process 33
Chapter 4 36
4 Result and Discussion 36
4.1 PEI/NrGO/ZNR 36
4.1.1 Scanning Electron Microscopy 36
4.1.2 Transmission Electron Microscopy 40
4.1.3 X-ray Diffraction Spectroscopy 40
4.1.4 Raman Spectroscopy 42
4.1.5 FTIR 43
4.1.6 Brunauer-Emmett-Teller 44
4.1.7 Thermogravimetric analysis 44
4.1.8 X-Ray Photo Electron Spectroscopy 46
4.1.9 Electrical Characterization 47
4.1.10 Sensing Performance Study 49
Chapter 5 55
5 Conclusions and Future Work 55
5.1 Conclusions 55
5.2 Future Work 56
References 58

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