Diffuse Reflectance Infrared Spectra of 4-Nitrobenzoic Acid and 4-Cyanobenzoic Acid Self-Assembled on Fine Silver Particles

Abstract

Adsorption of 4-nitrobenzoic acid and 4-cyanobenzoic acid on fine silver powders was investigated by diffuse reflectance infrared Fourier transform spectroscopy. It was concluded that both molecules were adsorbed on the surfaces of silver powders as carboxylate, after deprotonation, assuming a perpendicular orientation with respect to the silver surface. In a comparison with the reflection-absorption infrared spectra taken for the same molecules on vacuum-evaporated thick silver films, the usual surface selection rule that applied to flat metal surfaces also seemed applicable to the surface of fine metal particles, as long as the diameter of the particles was near 2 μm. Metal powders with diameters greater than 5μm appeared inappropriate as an adsorbent, however, probably because of particle sizes quite close to the wavelength of the infrared light used.