Inorganic Sol–Gel–Mediated Nanochannel Engineering of Graphene Oxide Membranes for Highly Perm-Selective Electrochemical Lithium Separation
- 주제(키워드) Sol-gel , Graphene , Membrane , Lithium
- 주제(DDC) 621.042
- 발행기관 아주대학교 일반대학원
- 지도교수 황종국
- 발행년도 2026
- 학위수여년월 2026. 2
- 학위명 박사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000035945
- 본문언어 한국어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
The growing demand for lithium, driven by the expansion of electric vehicles and renewable energy storage systems, necessitates sustainable and selective recovery technologies to supplement limited natural reserves. Electrochemical membrane separation has emerged as a promising pathway for lithium extraction from complex aqueous environments, offering minimal chemical usage with high energy efficiency. However, conventional polymeric ion-exchange membranes suffer from poor ion–ion selectivity, underscoring the need for precision-engineered nanostructured membranes. Graphene oxide (GO) membranes have attracted considerable attention owing to their well-defined nanochannels formed by the stacking of two-dimensional (2D) GO nanosheets. The interlayer spacing of GO membranes provides size-sieving pathways capable of distinguishing ions based on their hydrated diameters, thereby enabling high ion–ion selectivity. Despite these advantages, GO membranes face critical challenges. In aqueous environments, strong hydration of GO induces uncontrollable interlayer swelling, leading to deformation of membranes. Moreover, the interlayer spacing of GO is highly sensitive to external conditions, resulting in limited control over spacing stability and severe loss of ion–ion selectivity. Although various interlayer cross-linkers have been introduced to suppress swelling and modulate interlayer galleries, they frequently obstruct transport pathways or generate irregular pores, causing inherent permeability–selectivity trade-offs. These coupled challenges highlight the urgent need for GO membranes with structurally stable, precisely tunable, and highly selective nanochannels (chapter 1). The objective of the present study (Ph.D. thesis) is development of facile synthetic approaches that overcome the abovementioned challenges in GO membranes by utilizing inorganic sol-gel transition. To this end, we combine sol-gel chemistry, membrane engineering, and electrochemical lithium separation. Chapter 2 introduces the heteroatomic sol-reinforcing dot (HARD) strategy, in which amorphous aluminosilicate (AS) nanoparticles serve as inorganic crosslinkers within GO laminates. The AS network stabilizes the interlayer galleries, significantly suppressing water-induced swelling and enhancing mechanical robustness. The resulting AS/GO membranes exhibit superior Li⁺/Mn⁺ (M = Ni, Co, Mn, Fe) selectivity and long-term stability in redox-mediated electrodialysis, achieving a Li⁺ permeability of 2.0 mol m⁻² h⁻¹ and a Li⁺/Fe³⁺ selectivity of 42. Chapter 3 systematically investigates the influence of AS nanoparticle size (1–5 nm) on the interlayer configuration of reduced graphene oxide (rGO) membranes. The size of AS nanoparticle size not only affected the size of interlayer spacing, but also in-plane tortuosity and microstructural stability. The smallest-spacer membrane (AS-1 nm/rGO) delivers the optimal compromise between Li⁺ flux (~0.09 mol m⁻² h⁻¹), selectivity (25–33), and mechanical stability. Chapter 4 develops a vapor-induced pore expansion (VIP) approach to construct crosslinked and hierarchical rGO (CH-rGO) membranes featuring both ångström-scale selective channels and nanometer-scale transport highways. In this process, the cross-linked AS sol within interlayer generates vapor during thermal treatment, thereby inducing local interlayer expansion. The crosslinked interlayers contribute to achieving high ion selectivity, whereas the locally expanded regions facilitate rapid ion transport, leading to a synergistic balance between permeability and selectivity. Consequently, the CH-rGO membranes yield a fivefold enhancement in Li⁺ permeability compared to conventional rGO membranes, with exceptional selectivity (Li⁺/Ni²⁺ = 246, Li⁺/Co²⁺ = 390, Li⁺/Mn²⁺ = 447). Overall, this dissertation demonstrates that how conventional sol–gel chemistry provides a powerful design platform for constructing durable, high performance GO membranes for advancing electro-membrane lithium recovery processes. Besides, the synthesis methods in this study can be expanded to other research areas, which use 2D nanomaterial assemblies, such as water purification, energy storage system, and sensor.
more목차
Chapter 1. Introduction 1
1.1 Lithium Recovery from Waste Lithium Ion Batteries 1
1.1.1 Overview 1
1.1.2 Lithium Recovery from Primary Lithium Resource 4
1.1.3 Lithium Recovery from Secondary Lithium Resources 7
1.2 Membrane-based Lithium Recovery Processes 13
1.2.1 Pressure-driven Processes 19
1.2.2 Concentration-driven Processes 20
1.2.3 Electrochemical Processes 21
1.3 Graphene Oxide Membranes for Lithium Recovery 24
1.4 Inorganic Sol-Gel Processing 30
1.5 Aim and Scope of the Thesis 34
Chapter 2. Heteroatomic inorganic dots as structural reinforcers for swelling-resistant graphene oxide membranes in electrochemical lithium separation 37
2.1 Introduction 37
2.2 Experimental 42
2.2.1 Fabrication of AS/GO Membranes 42
2.2.2 Ideal Ion Permeation Experiments 43
2.2.3 Mixed Ion Separation using Redox-ED 45
2.2.4 Materials Characterization 48
2.3 Results and Discussion 50
2.3.1 Hybridization of AS sol and GO Nanosheets 50
2.3.2 Stability of AS/GO Membranes 55
2.3.3 Li+ Selective Transport of AS/GO Membrane 59
2.4 Conclusion 64
Chapter 3. Size-tunable amorphous inorganic crosslinkers for stable and selective reduced graphene oxide membranes in electrochemical lithium ion separation 65
3.1 Introduction 65
3.2 Experimental 70
3.2.1 Materials 70
3.2.2 Preparation of AS Nanoparticles with Controlled Sizes 70
3.2.3 Preparation of AS-x nm/rGO Membranes 72
3.2.4 Materials Characterizations 72
3.2.5 Measurement of Ion Transport Rate and Selectivity 74
3.2.6 Measurement of Relative Tortuosity 75
3.3 Results and Discussion 77
3.3.1 Synthesis and Characterization of AS Nanoparticles 77
3.3.2 Fabrication and Characterization of AS/rGO Membranes 81
3.3.3 Li+ Selective Permeation Across AS/rGO Membranes 89
3.4 Conclusion 97
Chapter 4. Hierarchical interlayer galleries in graphene oxide membranes via accelerated gel aging for lithium recovery 99
4.1 Introduction 99
4.2 Experimental Section 105
4.2.1 Materials 105
4.2.2 AS Sol Synthesis 105
4.2.3 Membrane Fabrication 106
4.2.4 Membrane Characterization 106
4.2.5 Measurement of Ion Transport Rate and Selectivity 108
4.2.6 Energy Barrier for Ion Transport through Membrane 110
4.3 Results and discussion 111
4.3.1 Fabrication of CH-rGO Membranes 111
4.3.2 Formation Mechanism of Hierarchical Spacing 120
4.3.3 Single Ion Li+/divalent Cation Perm-selectivity 134
4.3.4 Electrochemical Li+ Selective Separation Test 138
4.4 Conclusion 143
Chapter 5. Conclusion and future perspective 144
5.1 Conclusion 144
5.2 Future Perspectives 147
References 148
Abstract (국문 초록) 158
