Nanoparticles spectroscopic techniques

Thus, characterization of surfaces is important to the field of catalysis and electrocatalysis of nanoparticles. In the past 30 years, numerous electron and ion spectroscopic techniques, in addition to microscopic or imaging techniques, have been established to provide this information. Figure 1 provides high-resolution transmission electron microscopy (TEM) images of a practical (real), high-surface-area, Au/anatase-Ti02 heterogeneous catalyst that show the small Au nanoparticles... 

This chapter is organized into sections corresponding to various electrochemical characteristics of nanometallic particles. The introduction gives a brief idea of the basics of colloids together vith related literature. Subsequently, the electrochemistry with nanoparticles and ensembles of nanoelectrodes is explained followed by the electrochemical coulomb staircase behaviour of monolayer-protected nanometallic clusters. The investigation of nanoparticles using techniques based on combinations of different spectroscopic and electrochemical techniques is then reviewed. Sensors and electrocatalysis form the next sections and finally a summary and perspectives are given. 

Other spectroscopic techniques that have been used with electrochemistry to probe nanoparticles include electronic and vibrational spectroscopies. The spec-troelectrochemistry of nanosized silver particles based on their interaction with planar electrodes has been studied recently [146] using optically transparent thin layer electrodes (OTTLE). Colloidal silver shows a surface plasmon resonance absorption at 400 nm corresponding to 0.15 V vs. Ag/AgCl. This value blue shifts to 392 nm when an Au mesh electrode in the presence of Ag colloid is polarized to —0.6 V (figure 20.12). The absorption spectrum is reported to be quite reproducible and reversible. This indicates that the electron transfer occurs between the colloidal particles and a macroelectrode and vice versa. The kinetics of electron transfer is followed by monitoring the absorbance as a function of time. The use of an OTTLE cell ensures that the absorbance is due to all the particles in the cell between the cell walls and the electrode. The distance over which the silver particles will diffuse has been calculated to be 80 pm in 150 s, using a diffusion coef-... 

The ramifications of nanotechnology in the food arena have yet to be fully realized. This requires further research into biopolymer assembly behavior and applications of nanomaterials in the food industry. Researchers should keep abreast of the development of research tools and what is being done to push resolution limits for techniques such as atomic force spectroscopy or the synchrotron coupled to various spectroscopic techniques and higher resolution microscopy. New techniques should be exploited and the knowledge gained used to understand the dynamics and interactions of food materials at the single-molecule level and to describe assembly behavior in quantitative thermodynamic terms. There are questions about the interactions of nanoparticles with the food matrix and within the human body. These questions need to be addressed by future research (Simon and Joner, 2008 Sletmoen et ah, 2008). 

Structure of Alloy Type Sn-Pt/Si02 Catalysts used in Low Temperature CO Oxidation. Both Mossbauer and FTIR spectroscopy provided sufficient proof of surface reconstruction during the low temperature CO oxidation. However, the above reconstruction appeared to be reversible as the reversible interconversion of PtSn Sn -I- Pt was demonstrated by both spectroscopic techniques. This reversibility can only be achieved if the segregation described above is within the supported nanoparticle, i.e., when surface reactions involved in CO oxidation do not result in formation of separate Pt and tin-oxide phases on the silica support. 

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. 

In this system, the adsorption of the stabilizer was characterized throroughly employing various spectroscopic techniques. Especially, H and C liquid state NMR spectroscopy proved as a useful probe for the surface chemistry of nanoparticles in concentrated dispersions, as species adsorbed to the surface can be identified, however the functional groups directly adjacent to the surface are motionally hindered, which results in spectral broadening [85], It is hence possible to assess the amount of surface-bound species, determine the functional groups binding to the particle surface, and qualitatively investigate the chemistry of both particle surface and bulk solution. In the zirconia case, it was detected that indeed only partially the initially bound benzyl alcohol solvent is replaced by the stabilizer... 

The interest in formic acid oxidation (FAO) rose up in the 1970s with the aim of shedding light on the mechanism of methanol oxidation beyond the commercial interest in direct formic acid oxidation in fuel cells [90]. The FAO in acid solution was extensively investigated on surfaces of platinum [91-100] The FAO on other pure metallic surfaces seems to have been restricted to the palladium surface [98, 101-104]. In the 1980s, the remarkable contribution was done by the studies on the influence of the ad-atom in the activity of the platinum electrode [91—94]. In the 1990s, superficial spectroscopic techniques were employed to describe the electrochemical mechanism on palladium surface [98, 101—103] as well as platinum surface [97, 98, 105]. In the last 10 years, there was a triplication of publications about the FAO, specially driven by the use of nanoparticles. 

Several future developments of the experimental techniques and materials are anticipated. For example, the study of bimetallic crystals relevant to applications in electrocatalysis, nanoparticle systems, and further applications of spectroscopic techniques in combination with X-ray scattering studies. The work highlighted in this chapter lays the foundation for these developments. 

In 2000, Terrill et al presented a method that relied on the electrochemical desorption of alkanethiols from a fully covered SAM by apphcation of a potential. The width of the potential window and the position of the electrodes thereby determine the width and slope of the gradients (see Fig. 2). Alkanethiol gradients prepared by this method were used in a variety of other experiments, for example to test new mass-spectroscopic techniques, to study cell adhesion, or to investigate nanoparticle attachment. In addition to electrochemical desorption,... 

The study of the functionalization of nanoparticles by molecules requires a good knowledge of both the structure and the chemical nature of the surface state but the chemical procedure may influence on the density of grafting, the chemical and structural evolution of the surface and the chemical bonding at the interface defined by the molecule and the nanoparticulate substrate. It is important to emphasize that the characterization of the chemical bonding is crucial in order to make the functionalized nanoparticles useful and suitable for some biomedical applications as drug delivery. Some relevant information can be obtained by comparing Mossbauer spectra recorded in the same conditions on nanoparticles before and after functionalization, combined to further spectroscopic techniques. 

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