Agglomeration of Au particles

If ultrafme particles can be agglomerated, the mass of the new entity is equal to the sum of aU particles in the structure and mass related forces as well as inertia increase proportionately. After agglomeration, ultrafine particles, in their new form, can be removed in standard dust collection devices such as cyclones and packed bed filters. 

The spontaneous formation of Au particles at room temperature in air-saturated aqueous solutions of poly(ethylene glycol)s was investigated using optical, potentiometric and conductivity techniques. The kinetic information is consistent with a mechanism in which Au(III) complexes bind through ion-pairs to pseudocrown ether structures of the polymers. Reduction of the metal centers follows through their reactions with the oxyethylene groups that form these cavities. The particle size of the metal crystallites is controlled by the molar mass of the polymers. Agglomerates of small Au particles are formed as final products when polymers of low molar mass are used in the synthesis. 

Au(OH) c. Additionally, silica does not stabilize goldNPs against agglomeration. It appears that, on silica, one of the primary roles of Pt is to help stabilize small particles. Pt may also add additional functionality to the catalyst by binding O2 and locating bound or activated O2 near active Au sites. Alternately, the presence of Pt may affect the surface structure of Au, helping it to adopt a more active geometry. 

In contrast, TEM and PXRD data of Au MOE-5 show polydispersed Au particles in a size range of 5-20 nm (see Fig. 17), with a metal loading in Au MOF-5 determined to be 48 wt%. The gold particles appear to interact more weakly with the host matrix than the Pd, Ru and Cu particles and thus larger agglomerates are formed possibly by diffusion of the particles to the outer surface. 

Two synthesis methods were applied to prepare the TS-1 supports (TS-1 a and TS-lb). It was found that, after deposition of Au by precipitation method HDP-II, TS-1 a was a good catalyst, whereas catalyst TS-lb was totally inactive. In Figs. 1.15(a) and (b), TEM pictures of the Au-TS-1 samples are shown. The morphology of the two samples is quite different. TS-1 a consisted of very small crystallites (10 nm), agglomerated to form 150 nm particles, whereas TS-lb consisted of 35 pm crystals. The size of the gold particles in the TS-1 a sample with the small crystallites, was estimated to be 3-15 nm, which is not significantly smaller than those observed on the edges... 

Dispersing a soUd into a Uquid may be done by trituration in a mortar (see Sect. 29.3). The first step in the preparation is usually the dispersion of agglomerates and wetting of the particles. Then the active substance should be homogeneously distributed into the entire preparation. Dispersion can also be done by vigorous mixing with a rotor-stator mixer. This method is mainly used if the soUd is added at once or in parts, to all of the liquid (or aU of the semisoUd). 

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