A nuclear magnetic resonance (NMR) and fourier-transform infrared (FTIR) study of glycine speciation on a Cd-rich montmorillonite

As a consequence of treatments with glycine solutions, glycine molecules enter the interlayer of both Ca- and Cd-rich montmorillonite. Measurements of d value suggest that at low glycine concentration (0.01 and 0.1 M glycine solutions) a "flat" arrangement of the glycine molecules occurs in the interlayer. In contrast, intercalation of more than one monolayer of glycine molecules occurs for the montmorillonite treated with a higher concentration of glycine (1 M glycine solution). Interlayer complexation of glycine occurs only for the Cd-rich form of montmorillonite, whereas no complexation is observed for Ca-rich montmorillonite. Both nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) results suggest that the adsorbed glycine, which fully protonates in the interlayer of montmorillonite to give the GlyH(2)(+) species, interacts with the interlayer Cd-2(+) to form the CdGly(x) complex mainly through the carboxylate group. The interlayer cadmium, present as both Cd2+ and CdCl+, is complexed by the ligand glycine. In contrast, the cadmium adsorbed on the external surfaces of montmorillonite does not interact with the ligand. Complexation of CdCl+ only occurs for large amounts of adsorption of glycine (e.g., for samples treated with 1 M glycine solution).