Spectroscopic study of the simultaneous adsorption of PVP and azelaic acid on γ-alumina

The adsorption mechanism of 1-vinyl-2-pyrrolidone (VP), poly(1-vinyl-2-pyrrolidone) (PVP), and azelaic acid was investigated on synthetic gamma -aluminum oxide surfaces using FT-IR, FT-Raman, UV, and C-13 NMR spectroscopy (solid state). It was found that VP adsorption from ethylene glycol (EG) solution, as well as PVP adsorption from both aqueous and EG solutions, was negligible. m the case of EC solutions, the solvent adsorbed at the gamma -alumina surface. The presence of dicarboxylic acid enhances the adsorption of the PVP, due to a hydrophobic interaction between the carbon chains of the polymer and the dicarboxylic acid. The simultaneous adsorption of PVP and azelaic acid was studied as a function of time, pH, and solvent in order to establish a more detailed surface complexation model. Surface complexation of azelaic acid in aqueous solution starts with mainly outer sphere coordination, driven by electrostatic forces, which is transformed to an inner sphere complex in time, forming a covalent bond between the carboxylate entity and the alumina surface, especially at low pH. At high pH the outer sphere complex is dominating.