Fourier transform infrared spectroscopic studies on the interaction between copper(II), amino acids and marine solid particles

Abstract

Fourier transform infrared (FTIR) spectroscopy was employed to characterize the interaction between Cu^II, amino acids (AAs) and solid particles. The ion exchange between Cu^II, and marine solid particles causes a stepwise change in ν(OH) of surface H-bonding hydroxyl groups with an increase of the [ion-exchange amount] of Cu^II, at room temperature. The bands of the —COO^– and —NH₃⁺ vibrational modes of adsorbed AA and Cu^II–AA surface complexes in a solid matrix are first isolated from the overlapping solid particle matrix by use of the spectral substraction approach. With respect to the corresponding free AA, ν(NH₃⁺) and δ(NH₃⁺) of the adsorbed AA shift 10–39 and 13–49 cm^–1, respectively, toward higher and lower frequencies, whereas the variation of ν(COO^–, as) and ν(COO^–, s) is less than 4 cm^–1, nearly equal to the resolution of the IR spectrometer. This indicates that the surface hydroxyl group associates with the amino group of the amino acid in a solid matrix rather than with the carboxyl group. Similarly, not only do the ν(NH₃⁺) and δ(NH₃⁺) of the Cu^II–AA surface complex in the solid matrix shift 16–27 and 34–42 cm^–1, respectively, toward higher and lower frequencies, but also ν(COO^–, as) and ν(COO^–, s) shift 15–32 and 10–25 cm^–1, respectively, toward higher and lower frequencies, indicating that as a [bridging] reagent the AA joins Cu^II and the surface hydroxyl group, respectively, through the amino group and the carboxyl group to form a Model II ternary surface complex (TSC). The IR bands at 287–360 cm^–1, due to the Cu–O stretching mode, were detected and thus further confirmed the formation of the TSC model between Cu^II, AAs and marine solid particles.