Calcium phenylphosphonate as a host for 4-aminobenzoic acid—Synthesis, characterization, and cation adsorption from ethanol solution

Crystalline lamellar calcium phenylphosphonate retained 4-aminobenzoic acid inside its cavity without leaching. The intense infrared bands in the 1160–695 cm−1 interval confirmed the presence of the phosphonate groups attached to the inorganic layer, with sharp and intense peaks in X-ray diffraction patterns, which gave basal distances of 1532 and 1751 pm for the original and the intercalated compounds, respectively. The thermogravimetric curves of both layered compounds showed the release of water molecules and the organic moiety in distinct stages, to yield a final Ca(PO3)2 residue. Solid-state 31P nuclear magnetic resonance spectra presented only one peak for the phenylphosphonate groups attached to the main inorganic polymeric structure near 12.4 ppm. The adsorption isotherms from ethanol gave the maximum adsorption capacities of 1.68 and 0.50 mmol g−1 for copper and cobalt, respectively, whose average stability constants followed Co > Cu; the number of ligands was determined as four for both cations.