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.

Impact of choice of alkane deposition solvent on 4-fluorobenzoic acid layers adsorbed on silver nanostructures

“…1 SEIRA spectrum (bottom) of the 5 lL exposure of 4FBA adsorbed from n-pentane there is a band at 1397 cm À1 attributed to a COO stretching/ring deformation mode(s) from 4-fluorobenzoate ion (4FBI) formation in the monolayer. It is well known that benzoic acids ionize to benzoate ions at least in the monolayer during deposition on most transition metal surfaces [15][16][17][18][19][20]. The COO stretching band does not grow much in intensity as the amount of 4FBA deposited onto the silver film is increased in Fig.…”

“…It has been previously demonstrated that a seven nanometer silver film as determined by the QCM is optimal for SEIRA [16]. Earlier scanning electron and atomic force microscopy studies have shown these silver films to be rough with an average particle size of 50-100 nm in diameter and an average particle height of about 5 nm [16,19]. Henceforth, the phrase a 'silver film' is with reference to seven nanometers of silver as determined by the QCM evaporated on a CaF 2 substrate.…”

“…These calculations were conducted with a B3LYP functional and a LANL2DZ basis set according to the method of Goulet et al, and all frequencies are reported without correction [20]. This approach has been shown to yield theoretical spectra that compare well qualitatively to experimental SERS and sometimes SEIRA spectra [15,[17][18][19][20].…”

“…On the other hand, the more famous surface-enhanced Raman spectroscopy (SERS), being a more short-range phenomenon, cannot be applied routinely to studies in the multilayer. Along these lines, it has been shown that SEIRA can enhance the infrared signal of an adsorbate on rough silver films from the sub-monolayer all the way through a multilayer coverage [15][16][17][18][19].…”

Surface chemical modification on hyper-cross-linked resin by hydrophilic carbonyl and hydroxyl groups to be employed as a polymeric adsorbent for adsorption of p-aminobenzoic acid from aqueous solution

“…Many literatures reported the synthesis of resins based on hydrogen bonding [23][24][25], and adsorption mechanism on basis of hydrogen bonding is usually clarified by thermodynamic or theoretical calculation [26][27][28]. To the best of our knowledge, direct evidence to testify hydrogen bonding between the resin and the adsorbate is little discussed [29].…”