Subtle interaction between Ag and $$\hbox {O}_{2}$$ O 2 : a near ambient pressure UV photoelectron spectroscopy (NAP-UPS) investigations

Abstract

The AgO 2 interaction, which is at the center-stage of Ag-catalyzed partial oxidation reactions, is studied with NAP-UPS up to 0.2 mbar O 2 pressure between 295 and 550 K. Three temperature regimes were identified for distinct AgO 2 interaction, which are (a) 295-390 K, where mainly dissociative chemisorption of O 2 happens, (b) 390-450 K, where diffusion of O-atoms into the sub-surfaces of Ag is prominent, and (c) >450 K, where metastable oxide forms on polycrystalline Ag surfaces. The work function (WF) of Ag changed from 4.95 (≤390 K) to 5.30 eV (390-450 K), and then to 5.7 eV (≥450 K) at 0.1 mbar O 2 pressure. Oxygen population in the sub-surfaces imparts crucial modifications to Ag at 390-450 K; it makes the surface to be electron-deficient that relates to the change in the WF of Ag and facilitates the formation of space charge layer on Ag surface. Oxygen adsorbed on such modified Ag-surfaces is electrophilic in nature, and this appears at a higher binding energy in core level XPS than the chemisorbed oxygen on metallic Ag. This is supported by angle-dependent NAP-XPS studies. The subsurface population of oxygen in Ag no longer persists at >410 K when the O 2 supply is removed. A high ratio of antibonding/bonding O 2p bands suggests the unique silver-oxygen interaction under the measurement conditions.

Fermi Level Equilibration at the Metal–Molecule Interface in Plasmonic Systems

“…Figure D,E shows the experimental binding energies of the valence band and of the 3d 5/2 and 3d 3/2 spin–orbit partners (368 and 374 eV), respectively, for the two extreme cases in term of Fermi energy change, AgNPs@Cl and AgNPs@I. The upshift of the 4d valence band by 0.3 eV as well as the increase of the Ag + /Ag 0 ratio on AgNPs@I obtained from the 3d doublet deconvolution indicate a charge transfer form I – to the Ag surface and consequently an increase of the amount of oxidized silver of the AgNPs@I compared to AgNPs@Cl due to the subsequent oxidation of Ag 0 by ambient oxygen. ,,− Similar shifts of Fermi level up to ∼0.3 eV, induced by Br – and I – , were observed for silver-perovskite nanocrystals by Saris et al…”

Oxidative Disproportionation of MoS2/GO to MoS2/MoO3–x/RGO : Integrated and Plasmonic 2D-Multifunctional Nanocomposites for Solar Hydrogen Generation from Near-Infrared and Visible Regions

“…Apart from the SPR property, the heterojunction created at the MoS 2 /MoO 3−x interface alters the work function and electronic band structure of the nanocomposite. 22,23 This heterojunction corresponds to a type-II band alignment, where electrons are confined in one semiconductor and holes are confined in the other semiconductor. 24 ■ EXPERIMENTAL SECTION Synthesis of GO.…”

The nature of electrophilic oxygen: Insights from periodic density functional theory investigations

“…[20,26,27] Oxidation of Ag surface to form bulk oxide like Ag 2 O is a complicated process as observed in the recent studies. [28][29][30][31] It is worth noting here some industrial facts regarding epoxidation. For epoxidation process at an industrial scale, apart from Ag catalysts, high pressure (5-30 bar) and controlled temperature in the range of (423-623 K) are necessary conditions.…”

“…[20,26,27] Oxidation of Ag surface to form bulk oxide like Ag 2 O is a complicated process as observed in the recent studies. [28][29][30][31] Thin bulk oxide like Ag 2 O layer formation shows reversible behavior with increase in temperature. [28] Recent experimental studies on Ag clusters supported on silica reveal that, larger clusters with 55 Ag atoms do not undergo complete oxidation.…”

“…[28][29][30][31] Thin bulk oxide like Ag 2 O layer formation shows reversible behavior with increase in temperature. [28] Recent experimental studies on Ag clusters supported on silica reveal that, larger clusters with 55 Ag atoms do not undergo complete oxidation. [32] Instead of forming stable Ag 2 O phase, Ag prefers to maximize its coordination with O through interaction with molecular oxygen and this results in observed propensity of atomic O to occupy subsurface sites.…”