Aggregation of metallic particles

The same protocol based on aggregation of metallic particles may be used for detection and determination of various biomolecules and even simple inorganic ions. Antibodies, enzymes, biotin, streptavidin, or lectins can be used for nanoparticle modification [138] (Figure 16.24). 

The effects of support on the breakup of metal films and aggregation of metal particles are also measures of thermal stability for supported metal systems. Two previous studies of model catalysts provide data in this regard. 

Boyle was not alone in attempting to apply the atomic hypothesis to chemistry. Nicolas Lemery (1645-1715) suggested that the properties of substances could be explained in terms of the shapes of their atoms. The sharp taste of acids was due to their atoms being pointed and able to prick the tongue. Metals dissolved in acids because the points of the acid particles were able to break up the aggregation of metal particles. Lemery described his theories in his book Cours de Chymie published in 1675 (Figure 3.3). Lemery s book was also a comprehensive treatise on the practical chemical knowledge of the time. It ran to many editions and was very influential. 

As was found in Ref. [13], the method of catalytic decomposition of acetylene on graphite-supported catalysts provides the formation of very long (50 fim) tubes. We also observed the formation of filaments up to 60 fim length on Fe- and Co-graphite. In all cases these long tubules were rather thick. The thickness varied from 40 to 100 nm. Note that the dispersion of metal particles varied in the same range. Some metal aggregates of around 500 nm in diameter were also found after the procedure of catalyst pretreatment (Fig. 2). Only a very small amount of thin (20-40 nm diameter) tubules was observed. 

The first one is the direct synthesis of metallic nanoclusters, not via formation of (hydro)oxides and their reduction in gas-phase, because the successive reduction for formed (hydro)oxides sometimes results in the size growth of metal particles due to the aggregation and/or sintering. The second one is the use of precisely designed metal complexes, which are well adsorbed on the support surfaces, as shown in Figure 1. 

Atoms of metals are more interesting tiian hydrogen atoms, because they can form not only dimers Ag2, but also particles with larger number of atoms. What are the electric properties of these particles on surfaces of solids The answer to this question can be most easily obtained by using a semiconductor sensor which plays simultaneously the role of a sorbent target and is used as a detector of silver adatoms. The initial concentration of silver adatoms must be sufficiently small, so that growth of multiatomic aggregates of silver particles (clusters) could be traced by variation of an electric conductivity in time (after atomic beam was terminated), provided the assumption of small electric activity of clusters on a semiconductor surface [42] compared to that of atomic particles is true. 

Plasmon absorption of dispersions of coin metal fine particles like gold was often used to estimate the size of particles. The absorption peak can be calculated on the basis of Mie theory. However, this is not always true. The peak position can move, depending on not only the size of the particles but also the environment of the particles and the extent of aggregation of the particles. Thus, UV-Vis absorption is only used just for understanding the rough image of particle dispersions. 

In the case of powders, if the particles are of fairly simple form, the surface area (excluding submicroscopic cracks) can be estimated from microscopic measurement of the size of the particles.5 Powders, or porous solids composed of aggregations of small particles, can have the particle size approximately estimated by the width, and imperfection of definition, of the lines in an X-ray diffraction photograph.6 This method has been used by Levi and others7 for finely divided metal such as platinum black the particles were usually extremely small, of the same order of size as the particles in a colloidal sol of the metal. For the platinum group, the size of crystalline particles was estimated as from 20 to 120 A. across only. 

Freeze drying is used to dry either salt solutions or ceramic suspensions in a gentle way, avoiding thermal decomposition of the metal salts and aggregation of the particles. There are fovir steps in fieeze drying ... 

In the model catalysts described so far, the interparticle distances were more or less random, governed by the separation of substrate defects which control the nucleation and growth process of the metal particles (74,101). The position and separation of metal particles can be controlled accurately by electron beam lithography (EBL) (which has also been used to fabricate model catalysts), but the minimum size of the metal aggregates is currently still approximately lOnm. Figure 3g shows an example of a platinum nanoparticle array on Si02 (mean size 28 nm interparticle separation 200 nm) (53,106,107). 

Another recent article by Kneipp et al. demonstrates the use of multiplexing within live cells [69]. Two different SERS particles, aggregates of metal nanoparticles functionalized with two different reporter molecules could be imaged within cells using SERS. The data obtained was analyzed using cluster methods and principal components analysis to detect the two SERS reporters within the live cells. 

At first we observed XRD to confirm whether any aggregation was caused by Li addition or not. No detectable growth of metal particles was observed upon Lidoping. We also carried out XPS measurements to observe modification of charge of surface Rh species by Li addition, which might verify reactivity. However, Rh... 

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