Enhanced reactivity and related optical changes of Ag nanoparticles on amorphous Al₂O₃supports

Abstract

Pairs of samples containing Ag nanoparticles (NPs) of different dimensions have been produced under the same conditions but on different substrates, namely standard glass slides and a thin layer of amorphous aluminum oxide (a-Al₂O₃) on-glass. Upon storage in ambient conditions (air and room temperature) the color of samples changed and a blue-shift and damping of the surface plasmon resonance was observed. The changes are weaker for the samples on-glass and tend to saturate after 12 months. In contrast, the changes for the samples on a-Al₂O₃ appear to be still progressing after 25 months. While x-ray photoelectron spectroscopy shows a slight sulfurization and negligible oxidation of the Ag for the on-glass samples upon 25 months aging, it shows that Ag is strongly oxidized for the on a-Al₂O₃ samples and sulfurization is negligible. Both optical and chemical results are consistent with the production of a shell at the expense of a reduction of the metal core dimensions, the latter being responsible for the blue-shift and related to the small (<10 nm initial diameter) of the NPs. The enhanced reactivity of the Ag NPs on the a-Al₂O₃ supports goes along with specific morphological changes of the Ag NPs and the observation of nitrogen.

Retraction: Gold nanoparticles immobilized on electrospun titanium dioxide nanofibers for catalytic reduction of 4‐nitrophenol

“…[4] However, the stability of metallic NPs is limited and such unstable NPs tend to aggregate due to their high surface energy, which result in a notable reduction of their catalytic activity. [5] In order to solve this problem, NMNPs are usually immobilized onto various supporting materials such as mesoporous silicas, [6] metal oxides, [7,8] and electrospun fibers. [9,10] Despite all the development in heterogeneous catalyst preparation, there is still great attention in developing catalytic supports from stable and inert membranes composed of ceramic fibers.…”

On the origin of the changes in color of Ag/Al2O3 catalysts during storage

“…Since the ageing process was all the more efficient that the Ag loading was high, it is possible that the reduction of Finally, a third ageing step must be considered because once the Ag 0 particles were formed, their surface could be altered as reported in Section 2.2 for bulk silver artifacts and Ag 0 particles in contact with ambient air. According to Pelaez et al [33], Ag 0 particles on alumina preferentially react with O2 in the presence of humidity rather than with S-compounds in air; this could explain why sulfur was not detected in our samples by XPS and X-EDS, however AgOx was not detected either. In contrast, formation of silver carbonates was attested by XRD and only on samples with rather high Ag loadings (3.5 and 4.1 %) (Figure 3).…”

“…The stability of the Ag 0 nanoparticles also depends on the nature of the substrate, and surface alteration can result from oxidation and not only from sulfidation. Pelaez et al [33] compared the behavior in air of Ag 0 particles of small sizes (1.6, 2.1 and 4.3 nm) deposited on glass and on Al2O3 film by pulsed laser deposition. In ambient air, the SPR band blue-shifted from 520 to 470 nm with Al2O3 film and from 500 to 440 nm with glass.…”

Retraction: Gold Nanoparticles Immobilized on Electrospun Titanium Dioxide Nanofibers for Catalytic Reduction of 4‐Nitrophenol

“…[4] However, the stability of metallic NPs is limited and such unstable NPs tend to aggregate due to their high surface energy, which result in a notable reduction of their catalytic activity. [5] In order to solve this problem, NMNPs are usually immobilized onto various supporting materials such as mesoporous silicas, [6] metal oxides, [7,8] and electrospun fibers. [9,10] Despite all the development in heterogeneous catalyst preparation, there is still great attention in developing catalytic supports from stable and inert membranes composed of ceramic fibers.…”