Water on the MgO(001) Surface: Surface Reconstruction and Ion Solvation

The interaction of water with the MgO(001) surface under ambient conditions is investigated by density functional theory combined with statistical thermodynamics. For water loadings of more than one monolayer, we show that the standard structure model, a fully hydroxylated surface, needs to be revised. Reconstructed surfaces, involving hydrated/hydroxylated Mg²⁺ ions above the surface, are more stable. These findings provide a consistent picture for surface hydroxylation between low and high water coverage that is in agreement with available XPS data

Hydration Structures of MgO, CaO, and SrO (001) Surfaces

Using density functional theory (PBE functional), we show that the degree of surface hydroxylation increases in the MgO, CaO, SrO series, accompanied by an increase in water adsorption energy. Already for water coverage of two monolayers, structures with dissolved M²⁺ ions are considerably more stable than the intact, nondissolved surface. The dissolved ions above the surface form different patterns including ordered ones (e.g., an infinite stripe) that are preferred for MgO(001) and CaO(001) and disordered ones that are favored for SrO(001). Contrary to previous assignments, an analysis of calculated X-ray photoelectron spectra shows that O­(1s) signals arising from OH and H₂O groups might coincide in the experimental spectrum

In Situ SERS Study of Azobenzene Derivative Formation from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured Surfaces: What Is the Role of Applied Potential and Used Metal?

The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu

In Situ SERS Study of Azobenzene Derivative Formation from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured Surfaces: What Is the Role of Applied Potential and Used Metal?

The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu

In Situ SERS Study of Azobenzene Derivative Formation from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured Surfaces: What Is the Role of Applied Potential and Used Metal?

The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu

Transforming Anion Instability into Stability: Contrasting Photoionization of Three Protonation Forms of the Phosphate Ion upon Moving into Water

We use photoelectron emission spectroscopy with vacuum microjet technique and quantum chemistry calculations to investigate electronic structure and stability of aqueous phosphate anions. On the basis of the measured photoelectron spectra of sodium phosphates at different pH, we report the lowest vertical ionization energies of monobasic (9.5 eV), dibasic (8.9 eV), and tribasic (8.4 eV) anions. Electron binding energies were in tandem modeled with ab initio methods, using a mixed dielectric solvation model together with up to 64 explicitly solvating water molecules. We demonstrate that two solvation layers of explicit water molecules are needed to obtain converged values of vertical ionization energies (VIEs) within this mixed solvation model, leading to very good agreement with experiment. We also show that the highly charged PO₄^3– anion, which is electronically unstable in the gas phase, gains the electronic stability with about 16 water molecules, while only 2–3 water molecules are sufficient to stabilize the doubly charged phosphate anion. We also investigate the effect of ion pairing on the vertical ionization energy. In contrast to protonation (leading to a formation of covalent O–H bond), sodiation (leading to an anion···Na⁺ ion pair) has only a weak effect on the electron binding energy