Adsorption of styrene sulfonate vs. polystyrene sulfonate on layered double hydroxides

The adsorption properties of a water-soluble polymer, polystyrene sulfonate (PSS), on the surface of a layered double hydroxide (LDH), Zn2Al(OH)(6)Cl . nH(2)O, an anionic clay of the hydrotalcite type, were investigated and compared to the adsorption of the monomer, styrene sulfonate (vinylbenzene sulfonate (VBS)). PSS adsorption can be described by the Freundlich model and is of the S-type, while the adsorption of VBS is of the Langmuir type. Solid-state H-1 and C-13 CP MAS NMR experiments confirm the strong interaction between the adsorbed monomer and the LDH inorganic framework. The shielding of the resonance peak of the aromatic carbon attached to the sulfonate group is transmitted through the carbonaceous skeleton to the vinylic carbon, which is more deshielded. This phenomenon is induced by the electrostatic binding between the molecule and the,clay surface. This situation is observed to a lesser extent for the polymer. The adsorption of polymer changes the pore size distribution, creating a larger macropore volume compared to the, pristine chloride material and to the adsorbed monomer phase. This is explained by the entanglement of the polymer, pushing apart the stacked units of the LDH. (C) 2002 Elsevier Science Inc. All rights reserved.