Metallic Clusters and Color Changes in Silver-Exchanged Zeolites:  ¹⁰⁹Ag Solid State NMR and Optical Studies

Abstract

We have applied 109Ag solid-state NMR and optical methods to probe dynamics and local environment of silver cations in a series of silver-exchanged zeolites as a function of hydration. In dehydrated samples of Ag−Rho, a Knight shift produced by the conduction electrons of metallic silver particles with cluster size above 400 Å is observed. Temperature dependent color change upon dehydration in zeolites Ag−X and Ag−A is also present. Although the color change in both zeolites is optically similar, NMR spectra demonstrate that fundamentally different effects lead to the color change. The color change in Ag−X zeolite is accompanied by stronger interaction of silver cations with the zeolite substrate that causes a paramagnetic contribution to the Ag shift as dehydration occurs. In Ag−A zeolite the loss of coordinated water dominates the dynamics of silver cations and leads to a more shielded Ag NMR signal upon dehydration.

Identification of the silver state in the framework of Ag-containing zeolite by XRD, FTIR, photoluminescence,109Ag NMR, EPR, DR UV-vis, TEM and XPS investigations

“…The spectral distribution of the SiBEA photoluminescence obtained at 249 nm excitation light shown in Figure 3 is very similar to that recently reported for siliceous MCM-41 and amorphous silica [26]. The emission bands at 400 and 645 nm are likely due to surface defects associated with SiO-and/or SiOH groups, in agreement with earlier reported data [27].…”

“…5) is associated with the presence of metallic nanoparticles, in line with earlier reports [27,52,53]. This is confirmed by DR UV-vis band at 375 nm for Red-C-Ag 3.0 SiBEA and Red-C-Ag 6.0 SiBEA (Fig.…”

A Study of Silver Species on Silver-Exchanged ETS-10 and Mordenite by XRD, SEM and Solid-State 109Ag, 29Si and 27Al NMR Spectroscopy

“…4(b)) is comparable to the reported value of 5220 ppm. 35 This result indicates that, for Ag/ETS-10-H2-400, a substantial portion of the silver nanoparticles should have a diameter that creates some of the properties of a bulk-metal.…”

Magnetic Multi‐Functional Nano Composites for Environmental Applications

“…Similar observations have been reported for other silver zeolite materials. [50] It is well documented that the XPS band of Ag 3d5/2 in metallic form at 368.0-368.3 eV overlaps with that of Ag 2 O, and exhibits only a marginal shift to lower binding energy at 367.3-367.9 eV for the extreme case of AgO. [51] It is therefore reasonable to observe an Ag 3d5/2 XPS band for exchanged monovalent Ag þ at 368.4 eV.…”