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Title Page

ABSTRACT

Contents

Ⅰ. INTRODUCTION 12

Ⅱ. EXPERIMENTAL METHODS 15

2.1. Materials 15

2.2. Measurements 16

2.3. Syntheses 17

2.3.1. Synthesis of 4,6-dioxido-1,3-benzenedicarboxylate (H₄m-DOBDC) 17

2.3.2. Synthesis of DGIST-12 19

2.4. Sr²⁺ adsorption kinetics test 19

2.5. Sr²⁺ adsorption isotherm test 20

2.6. Sr²⁺ adsorption capacity test at different pH values 21

2.7. Sr²⁺ adsorption selectivity test 21

2.8. Solid-liquid ratio test 22

2.9. Desorption test with various conditions 23

Ⅲ. RESULTS AND DISCUSSIONS 24

3.1. Characterization of DGIST-12 24

3.2. Sr²⁺ adsorption kinetics test 32

3.3. Sr²⁺ adsorption isotherm test 38

3.4. Sr²⁺ adsorption selectivity test 45

3.5. Solid-liquid ratio test 49

3.6. Adsorption mechanism studies 51

3.7. Water stability and retention of Sr²⁺ adsorption capacity of DGIST-12 56

3.8. Desorption test with various conditions 58

Ⅵ. CONCLUSION 61

References 62

요약문 66

List of Tables

Table 1. Selected distances (Å) of possible hydrogen bonding sites for DGIST-12. 28

Table 2. Crystal structure refinement data for DGIST-12. 31

Table 3. Sr²⁺ concentration (Cₜ) and amount of adsorbed Sr²⁺ (q) at different times in kinetics experiments. 35

Table 4. Parameters of the kinetic models for the adsorption of Sr²⁺. 36

Table 5. Sr²⁺ concentration (Cₜ), amount of adsorbed Sr²⁺ (q) and removal efficiency at the different times in kinetics experiments using a low concentration Sr²⁺ solution. 37

Table 6. Equilibrium concentration of Sr²⁺ (Ce) and amount of adsorbed Sr²⁺ (q) at different initial concentrations(C₀). 41

Table 7. Parameters of the isotherm models for the adsorption of Sr²⁺. 42

Table 8. Equilibrium time and maximum capacity for Sr²⁺ adsorption using different MOF-based adsorbents. 44

List of Figures

Figure 1. ¹H-NMR spectrum of H₄m-DOBDC. 18

Figure 2. Microscope image of DGIST-12. A scale bar is 60 μm. 27

Figure 3. FE-SEM images of DGIST-12. 27

Figure 4. (a) Synthesis scheme of DGIST-12 and the crystal structure of DGIST-12 viewed along c-axis and the In₈ cluster. (b) Schematic illustration of Sr²⁺ exchange with [NH₂Me₂]⁺ in DGIST-12. Color code: Light purple,... 28

Figure 5. N₂ adsorption-desorption isotherms of DGIST-12 activated at different temperatures from 25 °C to 180 °C. 29

Figure 6. Simulated PXRD pattern of DGIST-12 and PXRD patterns of DGIST-12 as-synthesized and soaked in various organic solutions. The dried crystals were soaked in each organic solvent for 1 day. 29

Figure 7. Simulated PXRD pattern of DGIST-12 and PXRD patterns of DGIST-12 as-synthesized and soaked in various pH solutions. The dried crystals were soaked in each pH solution for 1 day. 30

Figure 8. Sr²⁺ adsorption kinetics of DGIST-12. 34

Figure 9. Pseudo-first-order plot for the Sr²⁺ adsorption on DGIST-12. 34

Figure 10. Pseudo-second-order plot for the Sr²⁺ adsorption on DGIST-12. 35

Figure 11. Sr²⁺ removal efficiency of DGIST-12 at different contact times in a low concentration Sr²⁺ solution. 36

Figure 12. Sr²⁺ adsorption isotherm of DGIST-12. 40

Figure 13. Linear fitting plots by the Langmuir isotherm model for the Sr²⁺ adsorption on DGIST-12. 40

Figure 14. Linear fitting plots by the Freundlich isotherm model for the Sr²⁺ adsorption on DGIST-12. 41

Figure 15. Sr²⁺ adsorption capacity of DGIST-12 in various pH solutions. 42

Figure 16. Simulated PXRD pattern of DGIST-12 and PXRD patterns of DGIST-12 after Sr²⁺ adsorption at pH 3, 7, and 11. 43

Figure 17. Sr²⁺ removal efficiencies of DGIST-12 in presence of competing ions, Na⁺, K⁺, Cs⁺, Mg²⁺, and Ca²⁺. 47

Figure 18. Sr²⁺ removal efficiencies of DGIST-12 in presence of competing ions, Co²⁺, Ni²⁺, Mn²⁺, Cd²⁺, and Zn²⁺. 47

Figure 19. Sr²⁺ removal efficiencies of DGIST-12 at different Na⁺/Sr²⁺ ratios. 48

Figure 20. (a) Sr²⁺ adsorption capacity and removal efficiency of DGIST-12 at different solid-liquid ratios with 100 ppm Sr²⁺ solution. (b) Sr²⁺ adsorption capacity of DGIST-12 at different solid-liquid ratios with 200 ppm Sr²⁺ solution. 50

Figure 21. FT-IR spectra of DGIST-12 before (black) and after (red) Sr²⁺ adsorption. 52

Figure 22. EDX spectrum of pristine DGIST-12. 52

Figure 23. EDX spectrum of DGIST-12 after Sr²⁺ adsorption. 53

Figure 24. Elemental mapping image of DGIST-12 before (a) and after (b) Sr²⁺ adsorption, showing the distribution of In, Sr, and N. 53

Figure 25. Sr 3d XPS spectra of DGIST-12 before (a) and after (b) Sr²⁺ adsorption. N 1s XPS spectra of DGIST-12 before (c) and after (d) Sr²⁺ adsorption. 54

Figure 26. TGA curves of DGIST-12 before (black) and after (red) Sr²⁺ adsorption. 55

Figure 27. Sr²⁺ uptake capacity for DGIST-12 as a function of the number of water washing cycles. 57

Figure 28. Sr²⁺ uptake retention of DGIST-12 as a function of the number of water washing cycles. 57

Figure 29. Sr²⁺ uptake retention of DGIST-12 after desorption process using various concentrations of NH₄NO₃ solutions. 59

Figure 30. Sr²⁺ uptake retention of DGIST-12 after desorption process using various concentrations of (a) KCl solutions and (b) NaCl solutions. 59

Figure 31. Sr²⁺ uptake retention of DGIST-12 after desorption process using 1 M HNO₃ solution. 60

초록보기

 방사성 스트론튬 (90Sr)은 반감기가 길고 (t1/2 ＝ 28.8 년) β- 붕괴 (분해 에너지 ＝ 0.546 MeV)로 인해 위험한 방사성 오염물질 중 하나로 알려져 있다. 현재까지 다양한 방법이 개발되어 방사성 폐수에서 방사성 스트론튬을 제거하는 데 사용되고 있다. 그 중 이온교환법은 높은 흡착 용량과 쉬운 사용법, 그리고 적은 운용비용으로 인해 유망한 전략으로 간주된다. 본 연구에서는 In3+와 m-DOBDC4- (4,6-dioxido-1,3-benzenedicarboxylate)로 구성된 물에 안정한 음이온성 금속-유기 구조체 (metal-organic framework)인 DGIST-12 를 합성하였고 이를 이용하여 방사성 스트론튬의 효과적인 흡착제로 사용하기 위한 연구를 진행했다. DGIST-12 는 높은 다공성을 가지고 있으며 음전하를 띈 In8 - 옥소 클러스터로 인한 반대 전하 양이온인 다이메틸암모늄 이온이 스트론튬과 효과적으로 교환될 수 있다. DGIST-12 의 스트론튬 최대 흡착 용량은 20 분 이내에 도달하며 pH 4-11 의 넓은 범위에서 흡착 용량을 유지한다. 중요한 점은 DGIST-12 가 다양한 경쟁 양이온 존재 시에도 스트론튬을 선택적으로 흡착한다는 것이다. 본 연구는 효율적이고 선택적인 방사성 오염물질 제거를 위한 새로운 흡착제 설계의 잠재력을 입증한다.

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