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2018 | Book

Assemblies of Gold Nanoparticles at Liquid-Liquid Interfaces

From Liquid Optics to Electrocatalysis

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About this book

This book is devoted to various aspects of self-assembly of gold nanoparticles at liquid-liquid interfaces and investigation of their properties. It covers primarily two large fields: (i) self-assembly of nanoparticles and optical properties of these assemblies; and (ii) the role of nanoparticles in redox electrocatalysis at liquid-liquid interfaces. The first part aroused from a long-lasting idea to manipulate adsorption of nanoparticles at liquid-liquid with an external electric field to form 'smart' mirrors and/or filters. Therefore, Chapters 3 to 5 are dedicated to explore fundamental aspects of charged nanoparticles self-assembly and to investigate optical properties (extinction and reflectance) in a through manner. Novel tetrathiafulvalene (TTF)-assisted method leads to self-assembly of nanoparticles into cm-scale nanofilms or, so-called, metal liquid-like droplets (MeLLDs) with remarkable optical properties. The second part (Chapters 6 to 8) clarifies the role of nanoparticles in interfacial electron transfer reactions. They demonstrate how nanoparticles are charged and discharged upon equilibration of Fermi levels with redox couples in solution and how it can be used to perform HER and ORR. Finally, Chapter 9 gives a perspective outlook, including applications of suggested methods in fast, one-step preparation of colloidosomes, SERS substrates as well as pioneer studies on so-called Marangony-type shutters drive by the electric field.

Table of Contents

Frontmatter
Chapter 1. Introduction
Abstract
This Chapter contains general introduction to electrochemistry at ITIES, including interfacial structure and thermodynamics of electron and ion transfer, as well as description of the concept of the Fermi level equilibration. Next, synthetic procedures, the structure of citrate-stabilized gold nanoparticles and implementation of “free electron gas” model to describe optical properties of metal NPs are considered. The Chapter ends with an extensive review on self-assembly of nano- and microparticles at liquid-liquid interfaces, including theoretical questions and potential applications of nanoparticle interfacial films.
Evgeny Smirnov
Chapter 2. Experimental and Instrumentation
Abstract
This Chapter is fully devoted to experimental procedures, to synthesize and analyze assemblies of nanoparticles and to instrumentation techniques used in this work.
Evgeny Smirnov
Chapter 3. Self-Assembly of Nanoparticles into Gold Metal Liquid-like Droplets (MeLLDs)
Abstract
Simple methods to self-assemble coatings and films from nanoparticles are highly desirable in many practical scenarios, yet scarcely any examples of simple, robust approaches to coat macroscopic droplets with continuous, thick (multilayer), reflective, and stable liquid nanoparticle films exist. Here, we introduce a facile and rapid one-step route to form films of reflective liquid-like gold that encase macroscopic droplets, and denote these as gold metal liquid-like droplets (MeLLDs). The present approach takes advantage of the inherent self-assembly of gold nanoparticles at liquid–liquid interfaces and the increase in rates of nanoparticle aggregate trapping at the interface during emulsification. The ease of displacement of the stabilizing citrate ligands by appropriate redox active molecules that act as a lubricating molecular glue is key. Specifically, the heterogeneous interaction of citrate-stabilized aqueous gold nanoparticles with the lipophilic electron donor tetrathiafulvalene under emulsification produces gold MeLLDs. This methodology is novel, relying exclusively on electrochemical reactions, i.e., the oxidation of tetrathiafulvalene to its radical cation by the gold nanoparticle, and electrostatic interactions between the radical cation and nanoparticles. The gold MeLLDs are reversibly deformable upon compression and decompression and kinetically stable for extended periods of time in excess of a year.
Evgeny Smirnov
Chapter 4. Optical Properties of Self-healing Gold Nanoparticles Mirrors and Filters at Liquid–Liquid Interfaces
Abstract
This chapter illustrates a detailed study of optical and morphological properties of lustrous self-healing metal liquid-like nanofilms for different applications (e.g., optical mirrors or filters). Extinction and reflectance of nanofilms were investigated by an integrating sphere in UV, visible and NIR ranges with step-bystep increasing of nanoparticle surface coverage. The interfacial AuNP surface coverage strongly influenced the morphology of the interfacial nanofilms and in turn their maximum reflectance and absorbance. We observed three distinct morphological regimes: (i) smooth 2D monolayers of “floating islands” of AuNPs at low surface coverages, (ii) a mixed 2D/3D regime with the beginnings of 3D nanostructures consisting of small piles of adsorbed AuNPs even at sub-full-monolayer conditions, and, finally, (iii) a 3D regime characterized by the 2D full-monolayer being covered in significant piles of adsorbed AuNPs. Also, comparison of optical properties of nanofilms at different water-organic solvent interfaces is presented. A maximal value of reflectance reached 58% in comparison to a solid gold mirror, when 38 nm mean diameter AuNPs were used at a water–nitrobenzene interface. Meanwhile, interfacial gold nanofilms prepared with 12 nm mean diameter AuNPs exhibited the highest extinction intensities at ca. 690 nm and absorb around 90% of the incident light, making them an attractive candidate for filtering applications. Furthermore, the interparticle spacing, and resulting interparticle plasmon coupling derived optical properties, varied significantly on replacing tetrathiafulvalene with neocuproine as the AuNP capping ligand in the nanofilm.
Evgeny Smirnov
Chapter 5. Self-Assembly of Gold Nanoparticles: Low Interfacial Tensions
Abstract
In this chapter, we would highlight the critical role of the interfacial tension and three-phase contact angle in self-assembly process of gold nanoparticles at a liquid–liquid interface. We demonstrate that gold nanoparticles can spontaneously self-assemble at bare propylene carbonate–water interface upon vigorous shaking, due to the extremely low interfacial tension. However, particles are transferred through the interface in the presence of tetrathiafulvalene molecules.
Evgeny Smirnov
Chapter 6. Electrochemical Investigation of Nanofilms at Liquid–Liquid Interface
Abstract
Soft or “liquid–liquid” interfaces were functionalized by roughly half a monolayer of mirror-like nanofilms of gold nanoparticles using a precise interfacial microinjection method. The surface coverage of the nanofilm was characterized by ion-transfer voltammetry. These gold nanoparticle films represent an ideal model system for studying both the thermodynamic and kinetic aspects of interfacial redox catalysis. The electric polarization of these soft interfaces is easily controllable, and thus the Fermi level of the electrons in the interfacial gold nanoparticle film can be easily manipulated. Here, we consider in details nanofilm preparation procedure, film morphology, and its electrochemical characterization, in particular, influence on ion transfer across the ITIES, as well as demonstrate charging capability of nanoparticle films by electron-donor molecules.
Evgeny Smirnov
Chapter 7. Electron Transfer Reactions and Redox Catalysis on Gold Nanofilms at Soft Interfaces
Abstract
The dispute about the exact and correct mechanism of the electron transfer (ET) reactions at liquid–liquid interfaces has lasted for decades. The ET reaction at ITIES was studied experimentally and by computer simulations for a model system. This model system contains \( {\text{Fc}}^{ + } / {\text{Fc}}^{0} \) as an organic soluble electron donor and \( {\text{Fe}}({\text{CN}})_{6}^{3 - /4 - } \) as a water-soluble electron acceptor. The current results indicate that the ET reaction takes place by a potential independent homogeneous reaction in the aqueous phase, while the observed potential dependence stems from that of the concomitant ion transfer reaction of ferrocenium. Functionalization of the interface with metallic nanoparticles significantly improves kinetics of the interfacial reaction by changing reaction mechanism to a bipolar pathway, when NP is acting as an electrically conducting bipolar electrode between the two phases. Therefore, we highlight the catalytic property of a metal nanoparticle film toward heterogeneous electron transfer reactions and explain this property from the point of view of the Fermi level equilibration theory.
Evgeny Smirnov
Chapter 8. Gold Nanofilm Redox Electrocatalysis for Oxygen Reduction at Soft Interfaces
Abstract
The interfacial reduction of oxygen by a lipophilic electron donor, decamethylferrocene, dissolved in α,α,α-trifluorotoluene was catalyzed at a gold nanoparticle nanofilm modified water–oil interface. A recently developed microinjection technique was utilized to modify the interface reproducibly with the mirror-like gold nanoparticle nanofilm, while the oxidized electron donor species and the reduction product, hydrogen peroxide, were detected by ion transfer voltammetry and UV/vis spectroscopy, respectively. Metallization of the soft interface allowed the interfacial oxygen reduction reaction to proceed via an alternative mechanism with enhanced kinetics and at a significantly lower overpotential in comparison to a bare soft interface. Weaker lipophilic reductants, such as ferrocene, were capable of charging the interfacial gold nanoparticle nanofilm but did not have sufficient thermodynamic driving force to significantly elicit interfacial oxygen reduction.
Evgeny Smirnov
Chapter 9. Perspectives: From Colloidosomes Through SERS to Electrically Driven Marangoni Shutters
Abstract
This Chapter highlights the perspectives to realize the potential of MeLLD-type gold nanoparticle films at liquid-liquid interface. Among them are: microencapsulation for drug-delivery systems and microreactors; transfer of nanofilms from LLI to a solid interface for reusable SERS-substrates and covering large areas with nanoparticles films for various purposes; conductance and thermal properties of nanofilms to use nanofilms for direct writing of conductive tracks with self-terminating welding process; liquid mirrors at water-air interface and electrically driven Maragoni-type shutters.
Evgeny Smirnov
Backmatter
Metadata
Title
Assemblies of Gold Nanoparticles at Liquid-Liquid Interfaces
Author
Dr. Evgeny Smirnov
Copyright Year
2018
Electronic ISBN
978-3-319-77914-0
Print ISBN
978-3-319-77913-3
DOI
https://doi.org/10.1007/978-3-319-77914-0

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