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Alkylamine-Driven Chemical Modulation of MOF Structure Evolution and Molecular Transport

알킬아민 기반 화학적 모듈레이션을 통한 MOF 구조 진화 및 분자 수송 제어

  • 남기진 (서강대학교 일반대학원)

초록(요약문)

Against the backdrop of increasing energy demand and growing climate concerns, the separation of light olefins from their corresponding paraffins remains one of the most energy-intensive industrial processes because it still relies predominantly on cryogenic distillation. The challenge originates from the nearly identical kinetic diameters and physicochemical properties of olefin/paraffin pairs, necessitating molecular-level control over transport pathways for energy-efficient separation. Zeolitic imidazolate frameworks （ZIFs）, with their crystalline porosity and chemically tunable framework structures, provide a promising platform for membrane-based molecular sieving. However, their practical implementation remains limited by insufficient control over framework evolution, poor compatibility with polymer matrices, non-selective interfacial defects at high filler loadings, and the lack of effective strategies for controlling crystalline-to-glassy structural transformation. This thesis demonstrates that alkylamine chemistry serves as a versatile platform for directing MOF structure evolution across multiple hierarchical levels—from multivariate ligand incorporation and defect engineering to crystal–glass transformation—thereby enabling systematic regulation of molecular transport in composite membranes. First, alkylamine-assisted synthesis under strongly basic conditions enables controlled incorporation of mixed imidazolate ligands into multivariate ZIF-8 （SZIF-8）, promoting tailored pore architectures, controlled defect formation, and improved compatibility with polyimide （PI） matrices. The resulting mixed-matrix membranes （MMMs） suppress non- selective interfacial transport pathways while optimizing molecular diffusion through framework-level pore engineering, achieving an 85% increase in C2H4/C2H6 selectivity compared with the pristine PI membrane. The alkylamine-driven modulation strategy is subsequently extended to Co-based ZIFs through controlled Co–alkylamine defect engineering. The generated defect structures simultaneously tailor microporosity, pore aperture, framework rigidity, surface chemistry, and filler–polymer interfacial adhesion, resulting in improved water stability and highly uniform filler dispersion even at elevated filler loadings. Consequently, the optimized MMM exhibits a 387% increase in C3H6 permeability together with a 90% improvement in C3H6/C3H8 selectivity relative to the neat polymer membrane, demonstrating the effectiveness of defect-mediated molecular transport regulations. Finally, alkylamine-modulated ZIFs are transformed into crystal– glass composite membranes through acid-induced framework disruption followed by thermal hot pressing. This controlled structural evolution enables simultaneous regeneration of crystalline domains within a glassy matrix, providing precise control over effective transport pathways through crystal–glass interface engineering. By suppressing non-selective defects while maintaining molecular sieving characteristics, the resulting crystal–glass membrane achieves outstanding C2H4/C2H6 selectivity of 14.9 with preferential C2H4 transport. Overall, this thesis establishes alkylamine modulation as a unified chemical strategy for directing MOF structure evolution across crystalline, defect-engineered, and crystal–glass architectures. By integrating framework-level structural control with interfacial engineering, this work provides a versatile design platform for regulating molecular transport in MOF-derived composite membranes. The findings not only advance the fundamental understanding of structure–transport relationships in MOF membranes but also provide practical design principles for next-generation energy-efficient membrane technologies for olefin/paraffin separations.

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목차

Acknowledgements 7
Abstract 8
CHAPTER 1 19
1.1 Olefin/Paraffin Separation Processing 20
1.2 Fundamental Principles of MOF-Based Gas Separation 25
1.3 Classification of MOF-Based Platforms for Membrane Gas Separation 27
1.3.1 MOF membranes 27
1.3.2 Mixed Matrix Membranes 28
1.3.3 Glass Membranes 29
1.4 Research objectives 30
CHAPTER 2 39
2.1 Principles of Membrane Gas Transport 40
2.2 Gas Transport Mechanism in Membranes 40
2.3 Permeation 42
2.4 Sorption 42
2.5 Diffusion 44
2.6 Current Challenges in Membrane-Based Olefin/Paraffin Separation 47
2.6.1 MOF-based Membranes 47
2.6.2 Zeolitic imidazolate frameworks 48
CHAPTER 3 54
3.1 Introduction 55
3.2 Experimental 56
3.2.1 Materials 56
3.2.2 Synthesis of DZIF-8 and SZIF-8s 56
3.2.3 Fabrication of SZIF-8 MMMs 57
3.2.4 Characterization 57
3.2.5 Gas Transport for PSZIF-8 MMMs 58
3.3 Results and Discussion 59
3.3.1 Zn-Dim Coordination Induced Synthesis Mechanism 59
3.3.2 Effect of Zn-Dim Coordination in SZIF-8s 63
3.3.3 Zn-Dim Coordination Induced SZIF-8 MMMs 67
3.3.4 Gas Transport for PSZIF-8 MMMs 68
3.4 Conclusions 72
CHAPTER 4 77
4.1 Introduction 78
4.2 Experiential Section 80
4.2.1 Materials 80
4.2.2 Synthesis of Defect-Engineered ZIF-67s 81
4.2.3 Fabrication of Dense Membranes 81
4.2.4 Supplementary Characterizations 82
4.2.5 Gas Transport Characterization of MMMs 83
4.2.6 Computational Work 84
4.3 Results and Discussion 84
4.3.1 Modulating Co-AA Defects of ZIF-67 84
4.3.2 Identifying Co-AA Defects of ZIF-67 Derivatives 88
4.3.3 Structural and Textural Impact of Co-AA Defects in ZIF-67 91
4.3.4 Structural Characterization of Various ZIF-67 Derivative MMMs 100
4.3.5 Gas Transport Characterization for Membranes 103
4.4 Conclusions 109
CHAPTER 5 116
5.1 Introduction 117
5.2 Experimental Section 119
5.2.1 Materials 119
5.2.2 Synthesis of ZIF-8 119
5.2.3 Synthesis of Alkylamine-Modulated ZIF-8s （AZIF-8s） 120
5.2.4 Formic Acid-Treated AZIFs （FAZIFs） 120
5.2.5 Fabrication of scgZIF-8 and scgAZIF-8 Membranes 121
5.2.6 Supplementary Characterization 121
5.2.7 Apparent Porosity Recovery of scgAZIF-8 Membranes- 122
5.2.8 Gas Transport Characterization of Membranes 123
5.3 Results and Discussion 124
5.3.1 Design Principle of Alkylamine-Modulated scgAZIF-8 Membranes 124
5.3.2 Characterization of FA-Induced Melt Processability in ZIFs 125
5.3.3 Hot-Pressing-Induced Recrystallization of scgAZIF-8 Membranes 132
5.3.4 Alkylamine-Directed Pore-Structure Modulation 142
5.3.5 Gas Transport Characterization of scgZIF Membranes 147
5.4 Conclusions 149
CHAPTER 6 155
6.1 Summary and Conclusions 156
6.2 Future Perspectives 159

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