Physico-chemical characterization of the colloidal hematite/water interface: experimentation and modelling

The surface of colloidal hematite (α-Fe2O3) of two different batches (synthesized in the present work or commercialized), is first characterized by electrophoretic measurements. The discrepancies about the IsoElectric Point (IEP) values are discussed. A correlation is pointed out between the aggregation of the particles and their surface charge, which is assigned to the importance of the electrostatic interactions in the stability of the colloidal suspensions. Potentiometric titrations are carried out in order to determine the concentration and acidity constants of the surface sites. The Point of Zero Charge (PZC) is in good agreement with the IEP value. The pKa values depend somewhat on the surface complexation model (diffuse layer model, constant capacitance model, model without electrostatic term) used to modelize the experimental curves. The parameters so obtained are compared to each others and to literature data.