PHYSICOCHEMICAL PROPERTIES OF WO3 TIO2 SYSTEMS EMPLOYED FOR 4-NITROPHENOL PHOTODEGRADATION IN AQUEOUS-MEDIUM/

A series of polycrystalline WOx/TiO2 samples were prepared by means of a conventional impregnation method. The samples were characterized by means of X-ray diffraction, Vis-UV diffuse reflectance and Raman spec troscopies, nitrogen adsorption at 77 K for determining specific surfa ce areas and surface texture, scanning electron microscopy, and FT-IR monitoring of pyridine adsorption for measuring the surface acidity. C atalytic activity of the samples has been assessed by carrying out as a ''probe'' reaction the photodegradation of 4-nitrophenol in aqueous medium. The results obtained indicate that incorporation of tungsten o n titania leads to formation of different surface species, depending o n the tungsten loading. Tungsta microcrystals were detected by X-ray d iffraction when the nominal molar W/Ti ratio reached a value of 8.0%. FT-IR investigation indicated that the presence of tungsten induces fo rmation of Bronsted and Lewis surface acid sites. The photoactivity re sults confirm the beneficial effect of tungsten in TiO2 for 4-nitrophe nol photodegradation in aqueous medium. The reaction rates are higher than those reported in literature for another set of samples and maxim um photoactivity was achieved for a sample containing 1.96 moles of W per 100 moles of Ti.