Surface-Enhanced Raman Spectroscopy of Phosphate Anions:  Adsorption on Silver, Gold, and Copper Electrodes

Abstract

The adsorption of phosphate anions on Ag, Au, and Cu electrodes from H2O and D2O solutions has been studied by means of surface-enhanced Raman spectroscopy (SERS). The interpretation of the spectra based on the solution Raman data and frequency shifts upon solution H2O/D2O exchange are presented. The prominent band at 1070−1100 cm-1, observed from adsorbed PO4 3- and HPO4 2- ions, exhibits downshifts of about 10 cm-1 in D2O solutions and has been assigned to the asymmetric P−O stretching mode. The corresponding asymmetric deformation mode has been assigned to the band located at ∼570 cm-1 which shows an upshift of 9−15 cm-1 in D2O solutions. Monodentate surface coordination of the PO4 3- and HPO4 2- ions is proposed. The dependence of the relative intensity of the internal modes on electrode potential was interpreted in terms of the migration of P−O groups from the surface as potential became more negative. Spectroscopic evidence was found for chemisorption of H2PO4 - ion on the Cu electrodes, but no such evidence was found in the cases of the Au and Ag electrodes. The adsorbed H2PO4 - ion on Cu showed an intense band at ∼907 cm-1 which was assigned to the symmetric stretching mode of the P−OH groups, based primarily on the considerable frequency downshift (∼11 cm-1) and peak broadening (∼15 cm-1) in D2O solutions. The formation of a P−O−P bond in the adsorbed state on Cu electrodes in acidic solutions is suggested. The force constants derived from experimental metal−oxygen frequencies are compared for the three electrodes, and the following strength order has been estimated: k(Cu−O‘) > k(Au−O‘) > k(Ag−O‘).

In-situ STM study of phosphate adsorption on Cu(111), Au(111) and Cu/Au(111) electrodes

“…This structure is well known from other studies of [19]. These studies also revealed a strong dependence of the appar- copper surface under low potential condition [13].…”

“…A previous SERS study [13] it appears reasonable to assign the anodic peak at −250 mV to the adsorption of phosphate anions from the neutral phosphate buffer solution used in the present study. Consequently, the three cathodic peaks appearing close to the onset of the HER correspond to the phosphate desorption.…”

Laser Spectroscopic Studies of Interactions of UVI with Bacterial Phosphate Species

“…Also possible is an enhancement of Raman lines by attachment of phosphate on the surface of cell fragments. [15] Related XAFS studies of U VI [12] and Pu VI [10] precipitated with NaH 2 PO 4 at pH 4.5 confirmed that the precipitate is UO 2 (H 2 PO 4 ) 2 . These data, combined with the fluorescence and Raman spectra, lead to the conclusion that bacterial decomposition released H 2 PO 4 À that complexed the uranyl and formed a precipitate of UO 2 (H 2 PO 4 ) 2 if the solubility product of this species was exceeded.…”

“…Two methods that are suitable www.chemeurj.org for studying interfacial processes of selected metal ions on cell surfaces are time-resolved laser-induced fluorescence spectroscopy (TRLFS) [6,14] and surface-enhanced or resonance Raman spectroscopy. [15,16] TRLFS can detect changes in the chemical environment of fluorescing actinides through changes in their fluorescence spectra. U VI , for example, has excellent fluorescence properties.…”

Surface-modified reusable gold electrode for detection of dissolved oxygen

“…However, even the simplest phosphate-buffered solutions (PBS), commonly used for analysis of biological species, tend to foul Au electrodes as a consequence of phosphate anion adsorption on their surface [7][8][9].…”