Raman and surface-enhanced Raman spectroscopy of adsorbed phthalic acid on oxidized aluminum foil

Adsorption of phthalic acid on anodically oxidized aluminum has been investigated at different pHs and ionic strengths by means of FT-Raman and surface-enhanced FT-Raman spectroscopy (SERS). The surface-enhancement was achieved by deposition of silver sol after adsorption. The spectra of the surface species obtained by the two techniques were significantly different. Raman spectra of the adsorbed phthalic compounds were pH and ionic strength dependent, but the surface-enhanced spectra appeared to be identical at each conditions. Supported by further spectroscopic evidences of the phthalic acid and the silver sol interaction (without aluminum oxide), it is plausible that the deposition of the silver sol results in a new surface complex. The evolution of the SER effect is therefore suggested to be a result of two steps: at first an adsorption occurs on aluminum oxide, and when depositing the aqueous silver sol onto the surface the phthalate ligands form complexes rather with the silver than with the aluminu...