Surface speciation of phosphate on goethite as seen by InfraRed Surface Titrations (IRST)

ARROYAVE, JEISON MANUEL; PUCCIA, VIRGINIA; ZANINI, GRACIELA P.; AVENA, MARCELO J.

SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY.

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2018 vol. 199 p. 57 - 64

1386-1425

Phosphate adsorption at the metal oxide-water interface hasbeen intensely studied, and the system phosphate-goethite in aqueousmedia is normally used as a model system with abundant informationregarding adsorption-desorption under very different conditions. In spiteof this, there is still discussion on whether the main inner-spheresurface complexes that phosphate forms on goethite are monodentate orbidentate. A new spectroscopic technique, InfraRed Surface Titration(IRST), is presented here and used to systematically explore the surfacespeciation of phosphate on goethite in the pH range 4.5-9.5 at differentsurface coverages. IRST enabled to construct distribution curves ofsurface species and distribution curves of dissolved phosphate species.In combination with the CD-MUSIC surface complexation model it waspossible to conclude that surface complexes are monodentate. Veryaccurate distribution curves were obtained, showing a crossing point atmol m-2, with a mononuclearmonoprotonated species predominating at pH > 5.5 and a mononucleardiprotonated species prevailing at pH < 5.5. On the contrary, at the low-2 there is no crossing point, with themononuclear monoprotonated species prevailing at all pH. IRST can becomea powerful technique to investigate structure, properties and reactionsof any IR-active surface complex at the solid-water interface.