Adsorption of molybdate monomers and polymers on titania with a multisite approach

Adsorption of polymers on mineral surfaces is of great interest. A represen tative important system is the molybdenum supported titania, used in cataly sis. The well-known chemistry of molybdate polymers in aqueous solutions al lows a detailed study of the contribution of these polymers to the Mo adsor ption on titanium oxide surface. A large range of Mo concentrations was cov ered: from low levels where only Mo monomers are present to high levels whe re extensive polymerization takes place. Data from different techniques, li ke potentiometric titrations, proton-ion titrations, and adsorption edges, were used for the description of the interface "molybdate solution/titania surface". All the data could be modeled very well using the recently introd uced CD-MUSIC approach. The charge of the surface complexes is spatially di stributed in the interface. MoO42- monomers adsorb over the entire pH range forming inner sphere complexes, which are characterized by two types of st ructure, i.e., bidentate and monodentate. Below pH 5.5 and high total molyb date concentrations the heptamolybdate polyanion Mo7O23(OH)(5-) is also ads orbed, forming an outer sphere complex. Due to its relatively large size, i t covers a significant number of surface groups.