Nanoparticles at ITIES

The formation of NPs has been intensely studied because of their broad applications in many areas such as catalysis and electronics. ITIES is 

Metal NPs combined with conducting polymers were also produced. Johans et al. synthesized polyphenylpyrrole coated silver particles based on the E C mechanism, in which the reversible facilitated IT of Ag+ to the organic phase was followed by its slow irreversible reduction by phenylpyrrole. ° The process was studied by cyclic voltammetry and UV-VIS. 

To better control the nucleation process, Unwin and co-workers deposited Ag particles on the micropipet- and nanopipet-supported DCE/water interfaces. The number of nuclei was evaluated by analyzing current-time transients, which were shown to be significantly affected by the size of the pipet. Single particles were generated with 0.5 pm-radius or smaller pipets while multi-particle nucleation was observed with larger pipets.  

The kinetics of NP deposition at the ITIES has been studied by the Samec group. They investigated the reproducibility of the potential-step current transients measured under the same experimental conditions for the deposition of the Pt particles at the ITIES and found that the initial rate of the Pt deposition can vary within a broad (over two orders of magnitude) range of values and even approach zero. These findings reflected the random rate of the formation of nuclei with a critical size that is required for a stable growth to occur. Later on, Dryfe et al. noticed that the random nature of the deposition process may be related to the presence of contaminants and found that no solid phase formation could be observed in a perfectly clean environment without defects.In these experiments, the deposition only occurred after adding artificial nucleation sites. 

Most recently, a new analytical technique—spatial scanning spectro-electrochemistry—has been used to study the electrodeposition of Pd nanoparticles at the water/DCE interface. The movable slit for the light beam enabled sampling at well-defined positions on both sides of the interface. It was observed that nanoparticles are not only deposited on the interface, but also diffuse into the bulk aqueous solution. 

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Metal nanoparticles can also be synthesized at a polarized liquid liquid interface. As a matter of fact, the first experimental evidence for heterogeneous electron transfer at an externally biased ITIES featured the electrodeposition of copper and silver [162]. More recently, Cheng and Schiffrin [163] demonstrated the formation of gold nanoparticles at the ITIES by reducing tetraoctylammonium tetrachloroaurate dissolved in DCE by aqu-... 

Of course, it is possible to reduce oxygen at ITIES functionalized with platinum nanoparticles floating at the interface. 

More specifically at ITIES, a lot of effort has been dedicated to nucleation and growth of nanoparticles for electrocatalytic studies. In 1998, Schiffrin deposited gold particles at an ITIES by electrochemical reduction of tetraoctylammonium tetrachloroaurate in 1,2-DCE using ferrocyanide in water as the electron donor. Their growth was monitored in situ by transmission UV-VIS spectroscopy, and the spectra have been qualitatively analyzed using Mie s theory [331]. The nucleation mechanism was later addressed by Johans et al. [334,335] using dibutyl-... 

The theoretical aspects of nanoparticle adsorption at ITIES was recently reviewed by Flatte et al. [355]. In particular, they discuss the effects that drive or hamper the localization at the interface, namely, competitive wetting, solvation of the charged nanoparticles, shift in the external electric field, polarizability drive, and line tension. A simple model is presented to account for these different contributions, and the results are shown in Figure 1.38. 

FIGURE 1.38 Different contributions to the nanoparticle energy profile at ITIES, compared to the total profile. Parameters—potential drop across the interface is -250 mV. (Flatte, M. E., A. A. Kornyshev, and M. Urbakh, 2008, J Phys-Condens Mat, Vol. 20, p. 073102. Used with permission.)... 

Considering the importance of nanoparticles in catalysis, we expect this aspect of electrochemistry at ITIES to develop further in the future. 

The main objective of this chapter is to illustrate how fundamental aspects behind catalytic two-phase processes can be studied at polarizable interfaces between two immiscible electrolyte solutions (ITIES). The impact of electrochemistry at the ITIES is twofold first, electrochemical control over the Galvani potential difference allows fine-tuning of the organization and reactivity of catalysts and substrates at the liquid liquid junction. Second, electrochemical, spectroscopic, and photoelectrochemical techniques provide fundamental insights into the mechanistic aspects of catalytic and photocatalytic processes in liquid liquid systems. We shall describe some fundamental concepts in connection with charge transfer at polarizable ITIES and their relevance to two-phase catalysis. In subsequent sections, we shall review catalytic processes involving phase transfer catalysts, redox mediators, redox-active dyes, and nanoparticles from the optic provided by electrochemical and spectroscopic techniques. This chapter also features a brief overview of the properties of nanoparticles and microheterogeneous systems and their impact in the fields of catalysis and photocatalysis. 

One property of liquid-liquid interfaces in general, and of ITIES in particular, is their ability to adsorb nanoparticles and, in certain cases, to form metal-like films. Pioneering measurements were carried out by Guainazzi et al. [330] who demonstrated that a direct current applied across the interface between Cu ion in water and a vanadium complex in 1,2- DCE causes deposition of a copper layer at the liquid-liquid boundary. Another seminal work is that of Efrima et al. who showed in 1988 the formation of silver metal-like films at the HjO-DCE interface [331], Since then, many publications have addressed this fascinating topic, and the field was excellently reviewed recently by Boerker et al. [332]. 

Nanoscale ITIES and their arrays can be formed by using nanopipets, nanopores, and porous membranes, some of which are created using modern nanofabrication techniques. Both nanoscopic and macroscopic ITIES can serve as a platform for studying the electrochemical behaviours of a variety of nanoscale entities, e.g., nanoparticles and biological macromolecules employed in electrocatalysis and electrochemical sensing. In this chapter, we survey recent progress in electrochemistry at the nanoscale liquid/liquid interfaces in the general context of nanoelectrochemistry. 

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