Carbon/Metal Oxide Nanocomposites for Energy and Environmental Applications : A Strategy of Energy Storage and Clean Water = 탄소·금속산화물 나노복합재의 에너지 저장및 환경적 활용방법

국문 초록 (Abstract)

본 논문은 금속 산화물과 탄소 기반 복합재를 슈퍼 커패시터와 광촉매 분야에 도입하여
합성, 특성화 및 응용에 대해 조사하였으며, 수퍼 캐퍼시터는 최근 몇 년간 급속 에너지
저장에 대한 수요가 급증함에 따라 급속 충방전 사이클이 용이하여 기존 배터리 기술의
대안으로 각광받고 있다. 또한, 이 연구는 고성능 에너지 저장 시스템의 개발과 환경
개선 기술의 향상이라는 두 가지 글로벌 과제를 해결하는 데 큰 가능성을 가지고 있는
재료에 대해 연구하고 있다. 수질 오염과 같은 환경 문제는 해결 방안이 절실히 요구되고
있으며, 이를 위해서는 빛을 이용하여 주변을 효과적으로 정화할 수 있는 보다 발전된
물질이 요구된다. 본 논문의 목표는 첫째, 개선된 전기 전도도, 용량 성능 및 광촉매 효율이 높은 탄소 기반 재료를 금속 산화물에 적용하는 이점을 확인하고자 한다. 둘째,
실제 적용을 위해 재료의 동작을 제어하는 기본 메커니즘에 대해 자세히 설명하고자
한다. 이러한 맥락에서 금속산화물과 탄소계 물질의 통합이 중추적인 역할을 할 수 있을
것으로 판단 되며, 본 논문에서는 금속산화물과 탄소계 복합재의 합성을 통하여 그
구조를 파악하고 전기화학적 에너지 저장 및 광 촉매 열화에 대한 성능을 검증했다.
첫 번째 연구에서, SnO2-rGO 나노 복합물의 추출물을 환원제로 사용하는 수열 합성을
소개한다. 이 나노 복합물은 뛰어난 광 촉매 효율을 나타내며 60 분 이내에 메틸렌 블루
염료의 98% 분해가 가능하다. 또한, 구조적으로 안정성이 뛰어나 환경 정화에 큰 도움을
줄 수 있다. 296 F g
-1 의 높은 비용량을 나타내는 rGO 의 전도성을 활용한다면 SnO2-rGO
나노 복합물을 슈퍼 커패시터에 도입하여 높은 효율 가치를 나타낼 수 있다.
두 번째 연구에서는 마이크로웨이브 보조 방법을 사용하여 합성된 새로운 β-MnO2 및
CNTs 복합체를 슈퍼 커패시터 전극에 도입했다. 이 복합물은 263.8 F g-1 의 특정 용량과
5,000 회 갈바노스타틱 사이클 후에도 98.7%의 높은 용량을 유지하여 뛰어난 전기 화학
성능을 보였다. 이 연구에서 고전력 밀도 슈퍼커패시터 응용 분야에 나노 구조화된 βMnO2/CNTs 전극의 활용 가능성을 볼 수 있다.
세 번째 연구에서는 산화니켈/기능화탄소나노튜브(NiO/f-CNTs) 나노복합재를 직접
공침법으로 합성하여 전기화학적 성능을 조사하였다. 이 복합재는 390.74 F g
-1 의 특정 용량과 5,000 사이클 후 93.5%의 용량을 유지하며 탁월한 순환 안정성을 확인했다.
이러한 결과는 우수한 전기화학적 특성을 가진 나노 복합재를 슈퍼커패시터 전극
재료로 자리매김하게 한다.
네 번째 작업에서는 초음파 처리 관련 초음파 촉매 및 슈퍼커패시터에 적용을 위해
Fe3O4 와 GO/Fe3O4 로 구성된 다용도 나노복합소재를 소개한다. GO/ Fe3O4
나노복합소재는 직사광선 노출 하에서 메틸렌 블루 염료에 대해 48.41%의 빠른
분해율을 달성하는 등 뛰어난 촉매활성을 나타내며, 또한 Fe3O4 나노입자와 GO 간의
상승효과에 기인하여 690.03 Fg-1의 높은 피크비용량을 보여준다.

다국어 초록 (Multilingual Abstract)

In the pursuit of sustainable energy and environmental remediation solutions, the
development of advanced materials has emerged as pivotal avenue of research. This
dissertation is dedicated to the investigation of a class of materials that holds immense promise
in addressing two pressing global challenges: the development of high-performance energy
storage systems and the enhancement of efficient environmental purification techniques.
Specifically, we delve into the synergistic potential inherent in metal oxides and carbon-based
composites, exploring their synthesis, characterization and application in the fields of
supercapacitors and photocatalysis. In recent years, the escalating demand for rapid energy
storage solutions has necessitated a departure from traditional battery technologies.
Supercapacitors, due to their ability to facilitate rapid charge and discharge cycles, have risen
to prominence as a credible alternative. Furthermore, there is a pressing demand to address
environmental issues, such as water pollution. To do this, we require more advanced materials
that can use light to clean up our surroundings effectively. These special materials play a vital
role in improving our ability to purify the water. It is within this context that the integration of
metal oxides and carbon-based materials has assumed a pivotal role. in this dissertation, we thoroughly investigate metal oxide and carbon-based composites, encompassing their synthesis
methodologies, understand their structures and test their performance in electrochemical
energy storage and photocatalytic degradation. Our objective has two main parts: first, we want
to show the benefits of combining metal oxides with carbon based materials, like improved
electrical conductivity, capacitive performance and photocatalytic efficiency. second, we aim
to explain in detail above a nuanced understanding of the underlying mechanisms governing
these materials' behaviors in practical applications.
In the first work, introduces the hydrothermal synthesis of SnO2-rGO nanocomposites
utilizing tea extract as a reducing agent. These nanocomposites exhibit exceptional
photocatalytic efficiency, achieving a 98% degradation of methylene blue dye within 60
minutes. Moreover, they demonstrate remarkable structural stability, making them promising
candidates for environmental water purification. In addition, the study explores their potential
for supercapacitor applications with the SnO2-rGO nanocomposites displaying a high specific
capacitance of 296 F g-1
, leveraging the conducting nature of rGO.
In the second work, presents a novel β-MnO2 and CNTs composite, synthesized using
a microwave-assisted method, tailored for supercapacitor electrodes. This composite exhibits
outstanding electrochemical performance, boasting a specific capacitance of 263.8 F g-1
and
exceptional capacitance retention, retaining 98.7% after 5000 galvanostatic cycles. The study
underscores the potential of nanostructured β-MnO2/CNTs electrodes in high-power-density
supercapacitor applications.
In the third work, explores the electrochemical performance of a nickel
oxide/functionalized-carbon nanotube (NiO/f-CNTs) nanocomposite, synthesized via direct
co-precipitation. This composite demonstrates a specific capacitance of 390.74 F g
-1
and
exceptional cyclic stability, retaining 93.5% of its capacitance after 5,000 cycles. These results establish the nanocomposite as a promising supercapacitor electrode material with superior
electrochemical properties.
In the fourth work, introduces a versatile nanocomposite material composed of Fe3O4
and GO/Fe3O4 for sonication-involved sonophotocatalytic and supercapacitor applications.
The GO/Fe3O4 nanocomposites exhibit remarkable catalytic activity, achieving a rapid
degradation rate of 48.41% for methylene blue dye under direct sunlight exposure. Additionally,
they demonstrate a peak specific capacitance of 690.03 Fg-1
, attributed to the synergistic effect
between Fe3O4 nanoparticles and GO.

목차 (Table of Contents)

• Chapter 1 4
• 1.1 Background and Motivation 5
• 1.2 Introduction to Supercapacitors 7
• 1.2.1 Storage mechanism of Supercapacitor 8
• 1.2.2 Electrical Double-Layer Capacitors (EDLCs) 11
• 1.2.3 Faradaic (Pseudo) Capacitors 12
• 1.2.4 Hybrid supercapacitors 15
• 1.3 Introduction to catalysis 17
• 1.3.1 Photocatalysis 17
• 1.4 Sonocatalysis 19
• 1.5 Materials for Energy and Environmental systems 20
• 1.5.1 Supercapacitor 20
• 1.5.2 Photocatalysis 23
• 1.5.3 Overview of dyes 25
• 1.6 Synthesis method 32
• 1.6.1 Green synthesis method 32
• 1.6.2 Hydrothermal synthesis method 34
• 1.6.3 Microwave synthesis method 36
• 1.7 Characterization Technique 38
• 1.7.1 X-ray diffraction (XRD) 38
• 1.7.2 Fourier Transform Infrared Spectroscopy (FTIR) 42
• 1.7.3 X-ray photoelectron spectroscopy 46
• 1.7.4 Photoluminescence (PL) spectroscopy 47
• 1.7.5 Field-emission Scanning electron microscopy (FESEM) and Energy-dispersive X-ray spectroscopy (EDS) 48
• 1.7.6 Field-emission transmission electron microscopy 50
• 1.7.7 Cyclic Voltammetry 52
• 1.7.8 Galvanostatic Charge-Discharge (GCD) 52
• 1.7.9 Electrochemical Impedance Spectroscopy 53
• 1.7.10 Cyclic stability 54
• 1.8 References 56
• Chapter 2 66
• 2.1 Introduction 67
• 2.2 Experimental section 70
• 2.2.1 Materials 70
• 2.2.2 Preparation of GO (Graphene Oxide) 71
• 2.2.3 Preparation of SnO2-rGO NCs 71
• 2.2.4 Electrochemical measurements 73
• 2.2.5 Photocatalytic assessment and Kinetics study 74
• 2.3 Result and discussions 75
• 2.3.1 Electrochemical performance of SnO2 and SnO2-rGO NCs electrode: 87
• 2.3.2 Analysis of photocatalytic activity of SnO2-rGO NCs: 96
• 2.3.3 Discussion on the photocatalytic mechanism: 101
• 2.3.4 Characterization of SnO2-rGO NCs after photocatalytic degradation: 102
• 2.4 Conclusions: 104
• 2.5 References 105
• Chapter 3 115
• 3.1 Introduction 116
• 3.2 Experimental section 119
• 3.2.1 Preparation of β-MnO2 119
• 3.2.2 Preparation of β-MnO2/CNTs composite 119
• 3.2.3 Active electrode preparation and electrochemical property. 120
• 3.3 Results and discussion 122
• 3.3.1 Characterization of β-MnO2 and the β-MnO2/CNTs composite. 122
• 3.3.2 Electrochemical performance of β-MnO2/CNTs electrode. 128
• 3.4 Conclusion 134
• 3.5 References 135
• Chapter 4 143
• 4.1 Introduction 144
• 4.2 Experimental section 146
• 4.2.1 Material synthesis. 146
• 4.2.2 Active electrode preparation. 147
• 4.3 Results and discussion 148
• 4.3.1 Electrochemical studies 158
• 4.4 Conclusion 165
• 4.5 References 166
• Chapter 5 174
• 5.1 Introduction 175
• 5.2 Experimental section 178
• 5.2.1 Synthesis of GO/Fe3O4 nanocomposite 178
• 5.2.2 Electrochemical studies 180
• 5.2.3 Photo, Sono and combined Sono-photocatalytic degradation of MB dye: 180
• 5.3 Results and discussion: 182
• 5.3.1 Optical properties 191
• 5.3.2 Electrochemical properties 193
• 5.3.3 Analysis of photocatalytic activity 199
• 5.4 Conclusion 208
• 5.5 References 209
• Chapter 6 218
• 6.1 Summary of thesis 219
• Fig 1.1 Ragone chart illustrating the relationship between energy density and power density across different energy storage systems [12]. 9
• Fig 1.2 Schematic construction of the charged and discharged EDLC. 10
• Fig 1.3 Schematic of pseudo-capacitor. When anions within the electrolyte engage in the reversible redox process, their movement occurs in the opposite direction to that of the cations. 13
• Fig 1.4 Various reversible redox mechanisms leading to pseudocapacitance including (a) under potential deposition, (b) redox pseudocapacitance and (c) intercalation pseudocapacitance 14
• Fig 1.5 Degradation mechanism of Photocatalysis. 18
• Fig 1.6 Types of synthetic dyes. 29
• Fig 1.7 Chemical structure and absorption wavelength of MB dye. 31
• Fig 1.8 Schematic diagram of green synthesis of metal oxide NPs. 33
• Fig 1.9 Schematic diagram of metal oxide NPs synthesis by hydrothermal method. 35
• Fig 1.10 Schematic representation of MW method for synthesis of metal oxide NPs. 37
• Fig 1.11 Schematic diagram of X-ray diffractometer. 40
• Fig 1.12 Working principle of XRD. 41
• Fig 1.13 Schematic diagram of FTIR spectroscopy. 42
• Fig 1.14 Schematic representation of UV-Vis spectroscopy. 45
• Fig 1.15 Schematic diagram of SEM. 49
• Fig 1.16 schematic diagram of TEM. 51
• Fig 2.1 Schematic illustration of the synthesis of SnO2-rGO NCs. 72
• Fig 2.2 XRD pattern of (a) GO, (b) SnO2 and SnO2-rGO NCs 76
• Fig 2.3 SEM images of (a) SnO2 and (b) SnO2-rGO NCs 76
• Fig 2.4 (a, b) The elemental composition by EDX, (c) TEM image and (d) HRTEM images of the SnO2-rGO NCs. 78
• Fig 2.5 XPS spectra of (a) survey scan of SnO2 and SnO2-rGO NCs, (b) Sn 3d (c) O 1s and (d) C 1s of SnO2-rGO NCs. 80
• Fig 2.6 N2 adsorption-desorption isotherms of (a) SnO2 (b) SnO2-rGO NCs and (c) The pore size distribution of SnO2 and SnO2-rGO NCs. 82
• Fig 2.7 UV-visible absorption (inset) and Optical band of SnO2 and SnO2-rGO NCs. 85
• Fig 2.8 Photoluminescence spectra of SnO2 and SnO2-rGO NCs. 86
• Fig 2. 9 CV curves of (a) SnO2 and (b) SnO2-rGO NCs at different scan rates. 88
• Fig 2.10 GCD studies of (a) SnO2 and (b) SnO2-rGO NCs at different current densities. 90
• Fig 2.11 (a) Specific capacitance for different scan rate and (b) different current densities. 91
• Fig 2.12 Cyclic stability of SnO2-rGO NCs electrode. 92
• Fig 2.13 Nyquist plots for SnO2 and SnO2-rGO NCs. 94
• Fig 2.14 Photocatalytic degradation of (a) SnO2 and (b) SnO2-rGO NCs. 97
• Fig 2.15 Photocatalytic degradation efficiency graph. 98
• Fig 2.16 (a) First order and (b) second order kinetics graph. 99
• Fig 2.17 A schematic illustration of the principle of photo-degradation. 101
• Fig 2.18 FTIR characterization for after performing photocatalytic degradation of MB 103
• Fig 3.1 Schematic illustration of the synthesis of β-MnO2/CNTs composites. 121
• Fig 3.2 Powder X-ray diffraction of (a) pure β-MnO2 and (b) β-MnO2/CNTs composites. 123
• Fig 3.3 a) XPS survey spectrum, High-resolution spectrum from β-MnO2/CNTs (b) Mn2p, (c) C 1s and (d) O 1s. 124
• Fig 3.4 SEM images of (a) pure β- MnO2 and (b) β-MnO2/CNTs composites. 127
• Fig 3.5 CV curves of a) pure β-MnO2 and b) β-MnO2/CNTs with different scan rates. 129
• Fig 3.6 Nyquist plots for a) pure β-MnO2 and b) β-MnO2/CNTs. 131
• Fig 3.7 GCD curves of a) β-MnO2 and b) β-MnO2/CNTs with different current densities 131
• Fig 3.8 cyclic stability of β-MnO2/CNTs. 133
• Fig 3.9 Specific capacitance of β-MnO2 and β-MnO2/CNTs samples at different scan rates. 133
• Fig 4.1 XRD patterns of Pure NiO and NiO/3%f-CNTs composite. 149
• Fig 4.2 SEM micrograph of (a) NiO and (b) NiO/3%f-CNTs composite, (c) TEM micrograph of NiO/f-CNTs composite (d)SAED pattern of NiO/3%f-CNTs composite. 151
• Fig 4. 3 (a-c) EDS mappings and (d)EDX graphs of NiO/3%f-CNTs composite. 153
• Fig 4.4 FT-IR spectra of (a) NiO and (b) NiO/3%f-CNTs composite. 154
• Fig 4.5 XPS spectra of NiO/3%f-CNTs composite (a) survey spectrum (b) O1s, (c) C1s, (d) Ni 2p. 156
• Fig 4.6 CV curves of (a) NiO and (b) NiO/3%f-CNTs composite. 159
• Fig 4.7 GCD curves of (a) NiO and (b) NiO/3%f-CNTs composite 160
• Fig 4.8 (a) Nyquist plots of NiO and NiO/3%f-CNTs composite (inset: the equivalent circuit); (b) Cyclic stability of NiO/3%f-CNTs composite; (c) Specific capacitance of NiO and NiO/3%f-CNTs composite at different scan rates. 163
• Fig 5.1 Schematic representation of preparation GO/Fe3O4 NCs. 179
• Fig 5.2 (a & b) FESEM images, (c-e) TEM and HR-TEM images, (f) SAED pattern and (g-i) Elemental distribution analysis of Fe3O4 microspheres recorded by aberration-corrected HAADF-STEM with composite elemental mapping of Fe, and O. 183
• Fig 5.3 (a & b) FESEM images, (c-e) TEM and HR-TEM images, (f) SAED pattern and Elemental distribution analysis of GO/Fe3O4 NCs recorded by aberration-corrected HAADF-STEM with composite elemental mapping of (g) Fe, (h) O and (i) C. 185
• Fig 5.4 (a) Powder XRD patterns, (b) FTIR spectra, Raman spectra of (c) GO and (d) Fe3O4 and GO/Fe3O4 NCs. 186
• Fig 5.5 XPS spectra (a) Full survey of Fe3O4 and GO/Fe3O4 NCs (b) Fe 2p (c) C 1s and (d) O1s 189
• Fig 5.6 (a) UV absorption (b) Tauc’s plot and (c) Photoluminescence spectrum of Fe3O4 and GO/Fe3O4 NCs 192
• Fig 5.7 (a) Comparative CV curves of Fe3O4 and GO/Fe3O4 NCs, (b) CV curve of GO/Fe3O4 at different scan rates (c) Anodic/cathodic peak current vs square root of the various scan rates of GO/Fe3O4 NCs. 193
• Fig 5.8 (a) The comparative GCD curves of Fe3O4 and GO/Fe3O4 NCs (b) GCD curves of GO/Fe3O4 electrode at different current densities and (c) relationship between specific capacitance and current densities. 196
• Fig 5.9 Nyquist plots of Fe3O4 and GO/Fe3O4 NCs. (inset: the equivalent circuit) 198
• Fig 5.10 Sonophotocatalytic degradation of MB dye: (a) Fe3O4 (b) binary GO/Fe3O4 NCs 202
• Fig 5. 11 (a) First order and (b) second order kinetic graph. 203
• Fig 5.12 Graph for degradation efficiency of (a) Fe3O4 and (b) GO/Fe3O4 (c) Sonophotocatalytic stability of GO/Fe3O4 NCs for the removal of MB dye solution. 204
• Fig 5.13 Proposed sonophotocatalytic mechanism for GO/Fe3O4 NCs. 206
• Table 1 Crystallite size, specific surface area, pore volume and pore size of the SnO2 and SnO2-rGO NCs 83
• Table 2 EIS parameters obtained by fitting Nyquist plots. 95
• Table 3 Bandgap, efficiency, Pseudo first and second order kinetics of the SnO2 and SnO2-rGO NCs 100
• Table 4 Crystallite size, Particle size, bandgap and efficiency of the Fe3O4 and GO/Fe3O4 NCs 207

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