A real time in situ ATR-FTIR spectroscopic study of linear phosphate adsorption on titania surfaces

Abstract

A real time in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) technique was developed to study the adsorption of linear phosphates with different number of P atoms on titania surface from aqueous solutions. The species adsorbed on titania surface from orthophosphate solution in a wide pH range were identified as two kinds of species. One is a bridging bidentate surface complex (TiO) 2PO 2 with C 2v symmetry, the other is an electrostatically adsorbed ion with T d symmetry. The linear polyphosphate species interact through the P–O groups with the titanium ions exposed on titania surface to form P–O–Ti bond and adsorb in a “flat” conformation on the surface. Significant change of the adsorbed phosphate species on titania surface during the initial few minutes of the adsorption process has been detected by the real time in situ ATR-FTIR spectroscopic technique. The polyphosphate species displace the monomeric species adsorbed earlier and become dominant on titania surface. The chemisorption of the phosphate species attains equilibrium faster than the physical adsorption of the phosphate species. The adsorption of phosphate species attains equilibrium faster in solution of higher concentration. The adsorption of polymeric phosphate species attains equilibrium at a lower speed than the monomers.