Reaction of aqueous polyoxometalates with silver and gold surfaces

Reaction of acidic aqueous solutions of α-PVV VWVI₁₁O₄₀4− with Ag(111) yields a new surface phase, hex-PVT/Ag. Scanning tunneling microscopy (STM) studies reveal that hex-PVT/Ag consists of large, ordered domains with a hexagonal unit cell of edge length 1.34 ± 0.06 nm. Studies utilizing UV-visible and inductively coupled plasma spectroscopies, coupled with silver-ion selective electrode measurements, confirmed that the reaction proceeds according to Equation (1). a-PVW11O40 ^4-aq+Ag s=a-PVW1 1O40^5- aq+Ag⁺aq 1 This reaction also occurs in solutions containing mixtures of α-PVW₁₁O₄₀4− and α-PVW₁₁O₄₀5−, but a large excess of α-PVW₁₁O₄₀4− is required for the formation of hex-PVT/Ag. The hex -PVT/Ag surface phase remains on the Ag surface even after thorough rinsing, and the constituent polyoxometalate species was confirmed to be α-PVW ₁₁O₄₀5− by X-ray photoelectron spectroscopy.; The reaction of Ag surfaces with acidic aqueous α-PVW₁₁O ₄₀5− solutions yields another new surface phase, a-PVT/Ag. This second surface phase is amorphous, and displays the electrochemical behavior of adsorbed α-PVW₁₁O₄₀ 5−. The α-PVW₁₁O₄₀5− coverage in a-PVT/Ag was modeled using a random sequential adsorption simulation, which indicated that nearest-neighbor separations were determined not only by van der Waals repulsion, but also by other factors.; Acidic aqueous solutions of both α-PVW₁₁O₄₀ 4− and α-PVW₁₁O₄₀5− react with Au(111) surfaces to form surface phases with limited translational order and possessing multiple domains. The α-PVW₁₁O ₄₀4− molecule forms a surface phase with small domains of multiple structures identical to those previously reported for α-SiW ₁₂O₄₀4− on Au(111). In contrast, α-PVW ₁₁O₄₀5− forms smaller domains of only a single structure. Furthermore, domain sizes appear to be limited to a critical length. Molecules adsorbed around the periphery of the small domains are removed during the course of imaging by STM, but the nucleation sites associated with each domain are not as easily removed.; Preliminary experiments to study the reaction of acidic aqueous solutions of the Preyssler anion, NaP₅W₃₀O₁₁₀ 14−, with Ag(111) show that a surface phase is formed. Immersion of Au(111) in the same solutions yielded STM images that did not show evidence of a surface phase. By using a mixture of α-PVW₁₁O₄₀ 4− and NaP₅W₃₀O₁₁₀ 14− in acidic aqueous solution, the terrace size of the surface phase formed on Ag(111) increased and its translational order improved.