Electrochemistry metallic nanoparticles

Metal Nanoparticles on Semiconductor Surfaces Electrochemistry and Photocatalysis... 

Most of the electrochemical phenomena occur in size regimes that are very small. The effects of size on diffusion kinetics, electrical double layer at the interface, elementary act of charge transfer and phase formation have recently been reviewed by Petrri and Tsirlina [12]. Mulvaney has given an excellent account of the double layers, optical and electrochemical properties associated with metal colloids [11]. Special emphasis has been given to the stability and charge transfer phenomenon in metal colloid systems. Willner has reviewed the area of nanoparticle-based functionalization of surfaces and their applications [6-8]. This chapter is devoted to electrochemistry with nanoparticles. One of the essential requirements for electrochemical studies is that the material should exhibit good conductivity. 

This includes two classes of materials namely, semiconductors and metals. There have been excellent reviews on electrochemistry with semiconductor nanoparticles [18-20]. Here, we confine ourselves to electrochemical studies with metallic nanoparticles. 

Metal nanoparticles housed in zeolites and aluminosilicates can be regarded as arrays of microelectrodes placed in a solid electrolyte having shape and size selectivity. Remarkably, the chemical and electrochemical reactivity of metal nanoparticles differ from those displayed by bulk metals and are modulated by the high ionic strength environment and shape and size restrictions imposed by the host framework. In the other extreme end of the existing possibilities, polymeric structures can be part of the porous materials from electropolymerization procedures as is the case of polyanilines incorporated to microporous materials. The electrochemistry of these types of materials, which will be termed, sensu lato, hybrid materials, will be discussed in Chapter 8. 

S. Cho and S.-M. Park, Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy, J. Phys. Chem. B, 110, 25656 (2006). 

Enzyme sensors are another important application of metal nanoparticles in CMEs besides nonenzyme sensors. Many enzymes can keep their activity when anchored onto gold nanoparticles. A novel method for fabrication of a biosensor based on the combination of sol-gel and self-assembled techniques has been introduced very recently. For example, the gold nanoparticles and enzyme horseradish peroxidase (HRP) can be successfully immobilized on gold electrode by the help of sol-gel with thiol groups, and the direct electrochemistry of HRP has been achieved and the biosensor thus prepared exhibits fast response, good reproducibility, and long-term stability. 

Ionic liquid (IL) possesses tunable behaviors based on asymmetric ion-pair combinations. Along with its tmique characteristics, such as high conductivity and wide potential window, it will be desirable to applying IL into the fields of bio-electrochemistry [29]. Incorporating IL with nanomaterials (metallic nanoparticles and carbon materials) into the development of modified... 

Impact of Metal-Ligand Bonding Interactions on the Electron-Transfer Chemistry of Transition-Metal Nanoparticles, Shaowei Chen Sol-Gel Electrochemistry Silica and Silicates, Ovadia Lev and Srinivasan Sampath... 

Besides the electrochemistry route, wet chemistry methods of shape-control synthesis have also been developed in some Chinese laboratories, and the synthesized metal nanoparticles with high-energy surface were apphed mainly as electrocatalysts for alcohol oxidations. 

Microelectrodes, due to their unique properties, such as small size, non-planar diffusion, small capacitance, and small current, have provided a major breakthrough in electrochemistry. Taking advantage of the superior properties of diamond, the diamond microelectrode is a promising new device for several applications in electrochemistry. Furthermore, modification of the diamond microelectrode with appropriate metal nanoparticles increases the quality of the measurements, in the terms of sensitivity, stability, and selectivity. 

The lure of new physical phenomena and new patterns of chemical reactivity has driven a tremendous surge in the study of nanoscale materials. This activity spans many areas of chemistry. In the specific field of electrochemistry, much of the activity has focused on several areas (a) electrocatalysis with nanoparticles (NPs) of metals supported on various substrates, for example, fuel-cell catalysts comprising Pt or Ag NPs supported on carbon [1,2], (b) the fundamental electrochemical behavior of NPs of noble metals, for example, quantized double-layer charging of thiol-capped Au NPs [3-5], (c) the electrochemical and photoelectrochemical behavior of semiconductor NPs [4, 6-8], and (d) biosensor applications of nanoparticles [9, 10]. These topics have received much attention, and relatively recent reviews of these areas are cited. Considerably less has been reported on the fundamental electrochemical behavior of electroactive NPs that do not fall within these categories. In particular, work is only beginning in the area of the electrochemistry of discrete, electroactive NPs. That is the topic of this review, which discusses the synthesis, interfacial immobilization and electrochemical behavior of electroactive NPs. The review is not intended to be an exhaustive treatment of the area, but rather to give a flavor of the types of systems that have been examined and the types of phenomena that can influence the electrochemical behavior of electroactive NPs. 

It was quite surprising (but also quite pleasant) to find that by plasma electrochemistry (see Chapter 10) isolated nanoparticles could be made in an ionic liquid. The physical mechanisms are not yet fully understood but it is likely that the particle size can be influenced by the ionic liquid itself, the metal salt concentration and the temperature. As the particles coagulate on a long time scale, at... 

The use of nanoparticles has extended throughout the field of biosensors in the electrochemical detection of DNA and immunoreactions (Murphy 2006). A wide range of nanoparticles including nanotubes and nanowires, prepared from metals, semiconductor, carbon or polymeric species, have been investigated. The enhanced electrochemistry is due to the ability of the small nanoparticles to reduce the distance between the redox site of a protein and the electrode, since the rate of electron transfer is inversely dependent on the exponential distance between them (Balasubramanian and Burghard 2006). CNT-modified electrodes have been most frequently used for the development of biosensors (Gooding 2005). 

Catalysis and Electrocatalysis at Nanoparticle Surfaces reflects many of the new developments of catalysis, surface science, and electrochemistry. The first three chapters indicate the sophistication of the theory in simulating catalytic processes that occur at the solid-liquid and solid-gas interface in the presence of external potential. The first chapter, by Koper and colleagues, discusses the theory of modeling of catalytic and electrocatalytic reactions. This is followed by studies of simulations of reaction kinetics on nanometer-sized supported catalytic particles by Zhdanov and Kasemo. The final theoretical chapter, by Pacchioni and Illas, deals with the electronic structure and chemisorption properties of supported metal clusters. 

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