Silver-montmorillonite

Silver-montmorillonite can be produced from sodium- or calcium-montmoril-lonite. To avoid the hydrolysis of silver ion in the solution, the pH has to be adjusted at 4 so that silver-hydrogen-sodium/calcium ions are present in the interlayer. The SEM picture (Figure 2.23) and thermal analytical studies (Figure 2.24) of this sample show the following features. 

FIGURE 2.23 Scanning electron microscopic (SEM) picture of silver-montmorillonite. Left side morphology of the sample made by backscattered electrons. Right side silver map made by characteristic x-ray photons. Silver concentration is proportional to the density of the light spots. The arrows show spots with 100% silver concentration. (Reprinted from Konya et al. 2005, with permission from Springer.)... 

FIGURE 2.24 Thermoanalytical curves of silver-montmorillonite. (Reprinted from Konya et al. 2005, with permission from Springer.)... 

The thermal analytical curves of silver-montmorillonite in the figure show the usual reactions of monovalent montmorillonites (Section 2.1.2). An additional exothermal reaction appears at 361°C. It corresponds to the oxidation of metallic silver, and this correspondence is further confirmed by the change of the color of silver-montmorillonite, which is originally dark gray and becomes light after heat treatment. 

Alkyl aryl ketones can be converted to arylacetic acid derivatives in an entirely different manner. The reaction consists of treatment of the substrate with silver nitrate and I2 or Br2, ° or with thallium nitrate, MeOH, and trimethyl orthoformate adsorbed on Montmorillonite K-10 clay, an acidic clay. ... 

Glycals can be transformed into 1,6-anhydro sugar derivatives by intramolecular cyclization in the presence of Lewis and Brpnsted acids, a reaction that has been termed the intramolecular Ferrier glycosylation.168 Sharma el al.169 showed that a montmorillonite clay-supported silver reagent can be an efficient catalyst for this transformation. The 1,6-anhydro-2,3-dehydro sugars obtained were then selectively dihydroxylated to furnish 1,6-anhydro saccharides. 

Zeolite channels have provided sites for silver [555, 556], silicon [557], and selenium [558, 559] clusters copper clusters have been generated between the layers of montmorillonite [560] and copper, platinum, and palladium clusters were formed in silicon dioxide matrices [561]. 

In this chapter, the redox and hydrolytic processes that result in the formation of nano- and microparticles will be discussed in metal ions (manganese, iron, lead, zinc, and silver ions)/montmorillonite (bentonite) systems. In addition, the catalytic diacetylation reaction of aromatic aldehydes will be shown. 

The horizontal resolution of SEM is about 0.5-1 pm, and the density of light spots in an SEM picture is proportional to the concentration. Figure 2.23 shows that the distribution of silver ions on montmorillonite is usually uniform, but there are places where the concentration of silver is much higher, which... 

Palladium ions sorbed on the edge sites of montmorillonite (Section 2.5.1.3) can also be reduced to metallic palladium with ethanol. As a result of the reduction, palladium enrichments, similar to silver enrichments in the previous example, can be detected by SEM. 

Thus, the reduction of both silver and palladium ions results in the formation of metallic microparticles on montmorillonite. 

Typical fillers firmed silica, calcium carbonate, carbon black, silver, glass beads, metal powders, precipitated silica, aluminum oxide, montmorillonite. mica, zinc oxide... 

The radioactive chromium (51Cr) found in Columbia River sediments contaminated with effluent from a nuclear reactor facility was not released by the major cations of sea water or by 0.05 M CuS0424 . The results of previous work in this laboratory (New England Aquarium) showed that of the silver(I) and cadmium(II) adsorbed on the clay minerals kaolin and montmorillonite, in essentially deionized water, less than half was desorbed on mixing with sea water25 . One may postulate from results such as these that most of the heavy metals occluded within a complex organic... 

Figure 8.3 NSP as a dispersing agent and carrier for silver NP. MMT montmorillonite. Reproduced with permission from J.J. Lin, W.C. Lin,...

The formation of the M-PILCs involved the use of a suspension of <2pm STx-1 montmorillonite (Source Clay Minerals Repository, University of Missouri), which had been acid washed (2M HCl), neutralized and exchanged three times with 4M NaCl. This clay mineral has a cation exchange capacity of approximately 84 meq/l(X)g, and a surface area of about 83.3 m2/g (Van Olphen and Fripiat 1979). The hydrolyzed metal solutions were added dropwise to vigorously stirred suspensions (ca. 1% w/w) of the Na-STx-1 (or vice versa), to solution loadings of ca. 10 meq metal/g STx-1. The suspensions were then washed with distilled water by centrifugation until testing with silver nitrate revealed the supernatant fluid to be negative for chloride ions. 

The montmorillonite used in this study was the less than 2pm particle-size fraction of bentonite from Milowice, Poland The cation exchange capacity (CEC) of the clay is 76 meq per 100 g. The clay was subjected to exchange with Na+ ions by stirring in 1 TV NaCI solution for 24 h followed by repeated washing with 1 N NaCl. The resulting suspension was washed several times with distilled water until free of Cl ions as indicated by lack of reaction of the supernatant with silver nitrate solution. The solid separated by centrifugation was dried in air at 353 K. This material is henceforth referred to as Na-mt. 

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