Title Page

Abstract

Contents

Chapter I. Introduction 12

1.1. Background of Covalent Organic Framework (COF) 12

1.1.1. Design principles of Covalent Organic Framework (COF) 15

1.2. Linkage types of Covalent Organic Framework 17

1.2.1. Boron-based linkage 18

1.2.2. Imine-based linkage 19

1.3. Synthesis method of Covalent Organic Framework 21

1.3.1. Solvothermal method 21

1.3.2. Ionothermal method 22

1.3.3. Microwave method 22

1.3.4. Light-promoted method 22

1.4. Two-dimensional Covalent Organic Framework film 24

1.4.1. Strategy for synthesizing 2D Covalent Organic Framework film: Top-down 25

1.4.2. Strategy for synthesizing 2D Covalent Organic Framework film: Bottom-up 27

1.5. Covalent Organic Framework as a sensor application 30

1.5.1. Color Changing Sensor (CCS) 30

1.5.2. Fluorescence Sensor 31

1.5.3. Chemiresistive Sensor 32

Chapter II. Materials and Methods 34

2.1. Synthesis of the two-dimensional TAPB-PDA COF film 34

2.1.1. Thickness controllability of TAPB-PDA COF film 36

2.1.2. Characterization of synthesized TAPB-PDA COF film 36

2.2. Fabrication of chemiresistive gas sensor device 37

2.3. Detection of targeted vapor with chemiresistive gas sensor device 38

Chapter III. Results and Discussion 39

3.1. Light-promoted TAPB-PDA COF film on the water surface 39

3.2. Chemiresistive gas sensor performance using TAPB-PDA COF film 45

Summary 49

References 50

Figure 1. Reaction diagram illustrating kinetical (green zone) and thermodynamical (red zone) pathways. △G‡ and △G stand for the activation energy and Gibbs free energy, respectively. 13

Figure 2. Crystallization process through "Error-Checking" and "Proof-Reading" using reversible reaction. 13

Figure 3. Schematic reaction of (a) COF-1 and (b) COF-5 synthesized using condensation reaction. 14

Figure 4. (a) linear COFs from linear building blocks. (b) hexagonal COFs from linear and trigonal building blocks. (c) tetragonal COFs from linear and tetragonal building blocks. (d) 3D COFs from linear and... 16

Figure 5. The scheme shows the post-functionalization of pore structure N3-COF-5 by "click"-reaction. R means different functional groups, and x% represents the content of N3-functionalized benzene diboronic acids. 16

Figure 6. Representative reactions that have been usually used for the construction of COFs. Bonding highlighted in red expresses the covalent bonds formed through these reversible reactions. 17

Figure 7. The schematic images for solvothermal method process. 1) Mixing the monomers; 2) Freezing; 3) lowing pressure; 4) Thawing; 5) sealing pyrex tube; 6) Heating; 7) extracting solid products. 18

Figure 8. (a) The equilibrium of acid-catalyzed imine-linkage formation. (b) The crystallinity of TAPB-PDA COF depending on the concentration of acetic acid (M) and water (M) in the synthesis condition (1:4... 20

Figure 9. Comparison of TAPB-PDA COFs using acetic acid-catalyzed and Lewis acid-catalyzed conditions. 20

Figure 10. PXRD patterns of solids from condensation reaction between zinc(II) 5,10,15,20-tetrakis(4-(dihydroxyboryl)phenyl) porphyrin and 1,2,4,5-tetra-hydroxybenzene depending on ratio of organic solvents. 21

Figure 11. Comparison of the time-dependent yield of COF-5 by using solvothermal method (black), UV-Hg lamp (orange), and UV-Xe lamp (blue). 23

Figure 12. Difference of morphology of COF-5 between UV light method and solvothermal method. Scanning Electron Microscopy images (a) th-COF, (b) Hg-UV-COF-5, and (c) Xe-UV-COF-5. 23

Figure 13. Schematic image of DaTp-COF chemically exfoliated by N-hexylmaleimide employing Diels-Alder reaction. 25

Figure 14. Schematic image of a formation of CONs from COFs (TpPa-1, TpPa-2, TpPa-NO2, TpPa-F4, TpBD, TpBD-(NO2)2, TpBD-Me2, and TpBD-(OMe)2) by using mechanical delamination. TEM and AFM... 26

Figure 15. (a) Schematic image of formed COF-5 film on graphene. (b) X-ray diffraction pattern of COF-5 precipitates showing randomly oriented COF-5 grains. (c) Grazing incidence XRD (GIXRD) data from COF-... 28

Figure 16. (a) AFM images of the surface of COF-5 film from flow condition (left) and static condition (right). Ra is 10.4 nm and 26.0 nm, respectively. (b) SEM images of the surface of COF-5 film from flow condition... 28

Figure 17. Schematic image and photograph describe synthesized COF films between the aqueous phase containing Sc(OTf)₃ and organic solution dissolving monomers. 29

Figure 18. (a) TAPB-TFP COF from TFP and TAPB monomers having irreversible tautomerization. (b) TAPB-PDA-OH COF from PDA-OH and TAPB building units which has potential for reversible tautomerization (c)... 30

Figure 19. (a) UV-Vis absorption spectra (black) and Fluorescence spectra (red) of TzDa COF in Ethyl acetate (b) Fluorescence spectra of TzDa COF in ethyl acetate having different water content. (c) Mechanism of water... 31

Figure 20. (a) Recovery and response curves of TXDBA-COF in desiccation and humidification condition (b) Repeated behavior of humidity sensor using TXDBA-COF. 32

Figure 21. (a) Ionic covalent organic framework (TpPa-SO₃ Na) (b) On/Off characteristics of humidity sensor using Ionic (TpPa-SO₃Na). 33

Figure 22. Comparison between polarity controlled and not controlled solvents on the water surface. Copper(II) phthalocyanine was added to solvents for identifying by naked eyes. 34

Figure 23. Schematic image of synthesizing TAPB-PDA COF film on the water surface via light irradiation. 35

Figure 24. Schematic image of fabricated chemiresistive gas sensor device. 37

Figure 25. Schematic images of lab-made chemiresistive gas sensor. 38

Figure 26. (a) Transferred TAPB-PDA COF film on SiO₂ substrate. (b) UV-Vis absorption spectrum of monomers (TAPB and PDA) solution. 39

Figure 27. (a) Fourier transform infrared (FT-IR) and (b) Raman spectroscopy analysis of TAPB (black), PDA (red), and TAPB-PDA COF film (blue). 40

Figure 28. Before and After washing TAPB-PDA COF films synthesized under lab-light and Xe lamp with 1,4-dioxane. 41

Figure 29. FT-IR spectrum of TAPB-PDA COF film synthesized under lab-light. 42

Figure 30. (a) UV-Vis absorption spectrum of TAPB-PDA COF film (b) Photoluminescence of TAPB-PDA COF film. 43

Figure 31. AFM images of TAPB-PDA COF film (left) loading low concentration of monomer solution (right) loading high concentration of monomer solution. 44

Figure 32. UV-Vis absorption spectrum of TAPB-PDA COF film. (red) thick film (black) thin film. 44

Figure 33. Photograph (left) and optic image (right) of the fabricated gas sensor device. 45

Figure 34. On-off switching behaviors for water, ethanol and acetone vapors in an empty device. (Voltage: 20V) 46

Figure 35. The time-dependent current corresponding to humidity. (Voltage: 20V) 46

Figure 36. I-V characteristics curve of TAPB-PDA COF device under vacuum condition. The voltage between two metal plates was applied in a range from -20V to 20V and the corresponding current was measured. 47

Figure 37. The time-dependent current measured until 70% of humidity. (Voltage: 20V) 47

Figure 38. Performance of chemiresistive gas sensor. IV curves of TAPB-PDA COF gas sensor device for (a) water, (b) ethanol, and (c) acetone. 48