Mesoporous titania directly modified with tungstophosphoric acid: synthesis, characterization and catalytic evaluation

VANESA FUCHS, LETICIA MENDEZ, MIRTA BLANCO, LUIS PIZZIO

APPLIED CATALYSIS A-GENERAL

Elseiver B.V.

Lugar: Amsterdam; Año: 2009 vol. 358 p. 73 - 78

0926-860X

The materials were synthesized by the sol–gel method, using titanium isopropoxide as precursor andurea as pore-forming agent. During the gelation, an alcoholic solution of tungstophosphoric acid (TPA)was added. Its concentration was varied in order to obtain TPA contents of 0, 10, 20 and 30% (w/w) in thesolid. The urea was extracted with water and the solids were thermally treated between 100 and 600 8C.Mesoporous solids were obtained, with a mean pore diameter (Dp) larger than 3.1 nm. The specificsurface area (SBET) decreased and Dp slightly increased when the TPA content was raised. SBET alsodiminished when the calcination temperature was increased, the decrease being lower for higher TPAcontents. The X-ray diffraction patterns of the solidsmodifiedwith TPA only presented the characteristicpeaks of the anatase phase. The crystalline degree and the crystal size increased for higher calcinationtemperatures. According to the Fourier transform infrared and 31P magic angle spinning-nuclearmagnetic resonance spectra, the [PW12O40]3 species is the one mainly present in the solids. The bandgap values obtained fromthe UV–vis diffuse reflectance spectra are slightly lower than those reported forthe anatase phase. The catalytic activity of the materials in the photodegradation of methyl orange washigher when the TPA content and the calcination temperature of the samples were raised. The lowerrecombination degree of the photogenerated electrons and holes caused by the increase in the crystallinedegree, implying a lower number of defects which act as recombination centers, and in the modified