Molybdophosphoric Acid Adsorption on Titania from Ethanol-Water Solutions

CONCELLÓN, A; VAZQUEZ, PATRICIA; CÁCERES, CARMEN; BLANCO, MIRTA

JOURNAL OF COLLOID AND INTERFACE SCIENCE

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: New York; Año: 1998 vol. 204 p. 256 - 267

0021-9797

The equilibrium adsorption at 20 ºC of molybdophosphoric acid solutions, using ethanol?water as solvent, on titania was studied. The molybdenum adsorption isotherm showed a sigmoidal shape; low values of molybdenum adsorbed were observed for final equilibrium concentrations lower than 50 mg Mo/ml, and for higher concentrations, the adsorbed molybdenum amount almost reached a plateau. From this isotherm it could be concluded that the solute?support interaction was not strong. UV?visible and NMR spectra of the solutions before and after the adsorption on titania showed that the species PMo12O3?40 was present. This species also was observed by DRS in the wet samples and by NMR, FT-IR, and DRS, in the solid samples dried at room temperature and calcined at 255, 310, 365, and 4257C, showing that the thermal stability of molybdophosphoric acid adsorbed on titania is similar to that of the bulk acid. The impregnating solutions and the impregnated solid changed with the time to a bluish color as a consequence of the formation of heteropoly blues which presented Mo6/ partially reduced to Mo5/. The XRD patterns indicated that the species adsorbed onto the support surface are highly dispersed like a noncrystalline form.