Evidence of specific and nonspecific adsorption of perchlorate (ClO4) on silver(110)

Abstract

The coadsorption of ClO4 with H2O on Ag(110) was studied as a model of anion adsorption at the solid–liquid interface. Thermal desorption spectroscopy, low energy electron diffraction, and high resolution electron energy loss spectroscopy were used to investigate the interactions between perchlorate, water and the metal surface. The vibrational spectrum of adsorbed ClO4 is an indicator of its adsorption geometry. For ClO4 adsorbed on the clean surface, losses at 640, 915, 1020, and 1220 cm−1 indicate that adsorption occurs through three oxygen atoms (tridentate) with a symmetry of C3v or lower. When coadsorbed with H2O, the vibrational spectrum resembles that of fully solvated, tetrahedral ClO4 (Td symmetry) with bands at 610, 880, and 1090 cm−1. The increase in symmetry indicates that direct interaction with the metal is lost and is considered evidence for nonspecifically adsorbed ClO4 in ultrahigh vacuum. The thermodynamic feasibility of this process is also discussed.