Adsorption of Weak Polyelectrolytes on Metal Oxide Surfaces:  A Hybrid SC/SF Approach

A hybrid SC/SF model to describe the adsorption of weak polyelectrolytes on metal oxide surfaces is presented. This model couples the surface complexation (SC) model for the effects of surface and solute speciation on the adsorption of monomers on oxides with the Scheutjens−Fleer (SF) model for the effects of macromolecular properties on the adsorption of polymers and polyelectrolytes on surfaces. The average magnitude of the specific interactions between polyelectrolyte functional groups and surface sites, expressed by the parameter χs(hyb), varies systematically with surface and polyelectrolyte speciation and hence with solution chemistry. Measurements of the adsorption of polygalacturonic acid (PGUA) on hematite over wide ranges of pH and ionic strength are used to test the hybrid model. Good agreement of model simulations and adsorption measurements is achieved. A reaction represented by >MeOH + L- = >MeOHL- provides the best representation of the experimental data.