Investigation of Phosphonic Acids Based on Raman and Surface-Enhanced Raman Spectroscopy

Phosphonic acids, such as amino tris-(methylenephosphonic acid) (ATMP) and diethylenetriamine penta-(methylenephosphonic acid) (DTPMP), are used in various applications, including scale control, water treatment, and corrosion protection. The increasing use of these compounds has raised environmental concerns due to their slow degradation, which can lead to eutrophication and the release of toxic byproducts. The detection of these compounds using surface-enhanced Raman spectroscopy (SERS) can be an interesting tool for monitoring their presence in aquatic environments. However, the vibrational characterization of these compounds has not yet been fully described in the literature. In this study, phosphonic acids ATMP and DTPMP were analyzed using density functional theory (DFT) and Raman/SERS spectroscopy. The theoretical spectra obtained were consistent with the experimental spectra, and the vibrational assignments aligned with those of organic compounds with similar structures reported in the literature. Furthermore, SERS analysis revealed bands for both compounds at concentrations up to 50 ppm (1.67 × 10^-4 mol L^-1 for ATMP and 8.72 × 10^-5 mol L^-1 for DTPMP).