Assemblies of Gold Nanoparticles at Liquid-Liquid Interfaces (eBook)

Supervisor’s Foreword 6
Parts of this thesis have been published in the following journal articles: 8
Acknowledgements 9
Contents 10
Abbreviations 15
Symbols 17
1 Introduction 19
1.1 Liquid–Liquid Interfaces: Structure and Galvani Potential Difference 19
1.1.1 Structure of Liquid–Liquid Interfaces 19
1.1.2 Thermodynamics of Electron and Ion Transfer Reactions Across ITIES. BATB Assumption 20
1.2 Equilibration of the Fermi Levels 24
1.2.1 Equilibration of Fermi Level Between NPs and Species in Solution 25
1.2.2 Electron Transfer at a Liquid–Liquid Interface (LLI) 34
1.3 Gold Nanoparticles: Synthesis and Properties 36
1.3.1 Short Review on AuNPs Synthesis 36
1.3.2 Synthetic Details and Structure of Citrate-Stabilized AuNPs 37
1.3.3 “Free Electrons Gas” Model and Optical Properties of Metal Nanoparticles 39
1.4 Self-assembly of Nano- and Microparticles at Liquid Interfaces 46
1.4.1 Theoretical Clues on Interaction Between a Single Particle and a Liquid–Liquid Interface 46
1.4.2 Wetting Properties: Nano Versus Macro 55
1.4.3 Review on Practical Methods to Settle Particles at Liquid–Liquid or Liquid–Air Interfaces 55
1.4.4 Potential Applications of Nanoparticles Assemblies at LLI 58
Appendixes 62
Appendix I. Mathematica Code to Calculate the Fermi Level of Nanoparticles 62
Appendix II. Mathematica Code to Implement Mie Theory 64
Appendix III. Flatte’s Model Without an External Electric Field 67
Appendix IV. DLVO Theory: Forces Between Nanoparticles in Assemblies at LLI 69
References 70
2 Experimental and Instrumentation 82
2.1 Reagents 82
2.2 Instrumental Methods 83
2.2.1 Electron Microscopy (SEM and TEM) 83
2.2.2 Dynamic Light Scattering (DLS) and Zeta(?)-Potential Measurements 83
2.2.3 UV–Vis Spectroscopy 84
2.2.4 X-Ray Photoluminescence Spectroscopy 87
2.2.5 Interfacial Raman Microscopy 87
2.2.6 Electrochemical Measurements 87
2.2.7 Drop Shape Analysis 89
2.3 Synthesis of Aqueous Colloidal AuNP Solution 90
2.3.1 Turkevich–Frens Method 90
2.3.2 Seed-Mediated Growth 90
2.4 AuNP Size Distributions and Concentrations 91
2.4.1 Theoretical Aspects 91
2.4.2 Practical Aspects 92
2.5 Gold Metal Liquid-Like Droplets (MeLLDs): Preparation and Surface Coverage Evaluation 94
2.5.1 MeLLDs Preparation Procedure 94
2.5.2 The Droplet Surface Area and Estimation of the Surface Coverage 96
2.6 Modifying a Soft Interface with a Flat AuNP Nanofilm Inside a Four-Electrode Electrochemical Cell 98
2.7 “Shake-Flask” Experiments to Quantify Biphasic H2O2 Generation 99
Appendixes 100
Sec22 100
References 101
3 Self-Assembly of Nanoparticles into Gold Metal Liquid-like Droplets (MeLLDs) 103
3.1 Introduction 103
3.2 Results and Discussion 106
3.2.1 Optical Characterization of Gold MeLLDs 106
3.2.2 Investigating the Conductivity of Gold MeLLDs 112
3.2.3 Gold MeLLD Formation Mechanism 114
3.2.4 To the Question of Wetting Properties 123
3.2.5 Self-healing Nature and Mechanical Properties 125
3.3 Conclusions 128
References 129
4 Optical Properties of Self-healing Gold Nanoparticles Mirrors and Filters at Liquid–Liquid Interfaces 134
4.1 Introduction 134
4.2 Results and Discussion 136
4.2.1 Probing the Interfacial Gold Nanofilms by Extinction and Reflection Spectra: Experimental Remarks 136
4.2.2 Influence of AuNP Mean Diameter and Interfacial AuNP Surface Coverage ( /theta_{{/rm int}}^{{/rm AuNP}} ) on the Extinction and Reflectance Spectra Obtained for Interfacial Gold Nanofilms Prepared at Water–DCE Interfaces 136
4.2.3 Monitoring the Morphology of the Interfacial Gold Nanofilms with Increasing /theta_{{/rm int}}^{{/rm AuNP}} by Scanning Electron Microscopy (SEM) 142
4.2.4 Determining the Separation Distances Between AuNPs in the Interfacial Gold Nanofilms by High-Resolution Transmission Electron Microscopy (HR-TEM) 144
4.2.5 Comparing the Optical Responses of Interfacial Gold Nanofilms Formed Biphasically Using Alternative Organic Solvents of Low Miscibility with Water and Replacing the Lipophilic Molecule TTF in the Organic Droplet with Neocuproine (NCP) 146
4.3 Conclusions 153
References 154
5 Self-Assembly of Gold Nanoparticles: Low Interfacial Tensions 159
5.1 Introduction 159
5.2 Results and Discussion 159
5.2.1 Experimental Evidences 160
5.2.2 Thermodynamic Modeling 164
5.3 Conclusions 167
References 168
6 Electrochemical Investigation of Nanofilms at Liquid–Liquid Interface 170
6.1 Introduction 170
6.2 Results and Discussion 171
6.2.1 Insights into Functionalization of Soft Interfaces with Mirror-like AuNP Nanofilms 171
6.2.2 Ion-Transfer Voltammetry Characterization of AuNP Nanofilm Functionalized Soft Interfaces 174
6.2.3 Charging of Gold Nanofilm by an Electron Donor in the Organic Phase 179
6.3 Conclusions 183
References 184
7 Electron Transfer Reactions and Redox Catalysis on Gold Nanofilms at Soft Interfaces 186
7.1 Introduction 186
7.2 Theoretical Aspects and Simulation Models 188
7.2.1 Possible Mechanism of Electron Transfer Reactions at ITIES 188
7.2.2 HET and ET-IT Mechanisms at Soft Interfaces 189
7.2.3 EC Mechanism at Soft Interface 192
7.2.4 Description of Simulation Models 192
7.3 Results and Discussion 196
7.3.1 Cell Compositions and Determination of Redox Couples Potentials 196
7.3.2 The Difference Between ET-IT and HET Mechanisms 197
7.3.3 Interfacial Redox Catalysis at a Polarized AuNP Nanofilm Functionalized Soft Interface 202
7.4 Conclusions 207
References 208
8 Gold Nanofilm Redox Electrocatalysis for Oxygen Reduction at Soft Interfaces 211
8.1 Introduction 211
8.2 Theoretical Aspects 212
8.2.1 Standard Redox Potentials of Oxygen Reduction in Trifluorotoluene (TFT) 212
8.2.2 Interfacial O2 Reduction by the Ion Transfer—Electron Transfer Mechanism 214
8.2.3 Interfacial Redox Electrocatalysis 215
8.2.4 Calculations of the Fermi Level of the Gold Nanofilm 217
8.3 Results and Discussion 219
8.3.1 Cell Compositions 219
8.3.2 Insights into the Mechanism of Interfacial O2 Reduction on AuNP Nanofilm at ITIES in the Presence of DMFc 220
8.3.3 Comparison of Cyclic Voltammograms Obtained at ITIES and Physically Separated Oil–Water Phases Connected by Gold Electrodes 222
8.3.4 Effect of pH on Interfacial O2 Reduction on AuNP Nanofilm at ITIES in the Presence of DMFc 224
8.3.5 Quantification of H2O2 Formation by the Interfacial O2 Reduction Under Neutral Conditions on AuNP Nanofilm at ITIES in the Presence of DMFc 225
8.3.6 Mechanism of Interfacial O2 Reduction by Interfacial Redox Electrocatalysis Under Neutral Conditions on AuNP Nanofilm at ITIES 225
8.4 Conclusions 229
References 230
9 Perspectives: From Colloidosomes Through SERS to Electrically Driven Marangoni Shutters 233
9.1 Microencapsulation: Raspberry-like Colloidosomes 233
9.1.1 Raspberry-like Colloidosomes Formation 234
9.1.2 Arrangement of Gold Nanoparticles on the Surface of Colloidosomes 236
9.1.3 Optical Properties of Raspberry-like Colloidosomes 237
9.2 From Liquid–Liquid Toward Liquid–Air Interfaces 241
9.3 Gold Nanoparticles Structures for SERS and Electrochemical SERS 244
9.3.1 Planar Structure on a Solid Substrate (2D) 244
9.3.2 Wrinkled Surfaces Covered by Gold Nanoparticles (Folded 2D) 244
9.3.3 Gold Nanoparticle Sponge (3D) 247
9.3.4 Reusable Substrates and Electrochemical SERS 248
9.4 How to Measure the Conductivity at the Microscale? 250
9.5 Thermal Properties of Self-assembled Gold Nanoparticles: Self-terminated Welding 255
9.6 Electrovariable Plasmonics 257
9.6.1 Arms Setup to Study Angular Dependence of the Reflectance 257
9.6.2 Simulations for the Current Distribution 258
9.6.3 Rectangular Four-Electrode Electrochemical Cell 259
9.6.4 Marangoni-Type Shutters Instead of Mirrors 259
References 265
General Conclusions 269