Study of Adsorption of Aminobenzoic Acid Isomers on Silver Nanostructures by Surface-Enhanced Infrared Spectroscopy

Abstract

o-, m-, and p-aminobenzoic isomers were studied with surface-enhanced infrared absorption (SEIRA) spectroscopy and temperature-programmed desorption (TPD) on vacuum-evaporated silver films and on a silver powder. Each aminobenzoic acid (ABA) isomer was complexed with a silver ion(s) and modeled with density functional theory to aid in the interpretation of the SEIRA results. Atomic force microscopy and scanning electron microscopy compared and contrasted surface roughness between the evaporated silver film and silver powder that leads to surface-enhanced vibrations of adsorbates on the silver substrates. The ability of SEIRA to enhance the infrared signal of an adsorbate monolayer and the subsequent multilayer was essential in exploring ABA adsorption as a function of the polar properties of the deposition solvent. For m- and p-aminobenzoic acids, it was demonstrated that their deposition in alkane solvents with nonpolar bonds resulted in increased intermolecular attraction between amino groups of adjacent ABA molecules in the monolayer. TPD and SEIRA results proved that p-aminobenzoic acid adsorption to silver was stronger than that of m-aminobenzoic acid, which had stronger adsorption than the o-aminobenzoic acid. Outcomes from this work will be important to many diverse areas such as biochemistry, bioengineering, environmental chemistry, nanotechnology, and catalysis where the adsorption of amino acids is important.