title: Direct modification with tungstophosphoric acid of mesoporous titania synthesized by urea-templated sol-gel reactions.
abstract: A series of mesoporous titania materials modified with tungstophosphoric acid (TPA) were successfully synthesized by using urea as low-cost template via sol-gel reactions, followed by removing the urea by extraction with water. They were characterized by FT-IR, 31P MAS-NMR, XRD, DTA-TGA, DRS, TEM and BET. The samples presented mesopores with a diameter higher than 3.0 nm. The S(BET) of the solids decreases with the increase of the TPA content and with the increase of the calcination temperature. According to FT-IR and 31P MAS-NMR studies the main species present in the samples is [PW12O40]3- anions, which was partially transformed into [P2W21O71]6- and [PW11O39]7- anion during the synthesis and drying step. The XRD patterns of the modified samples only exhibited the characteristic peaks of anatase phase. The presence of TPA retarded the crystallization of the anatase phase and its transformation into rutile phase. The point of zero charge decreased in parallel with the increment of tungstophosphoric acid in the samples and with the increase of the calcination temperature. The band gap energy decreased as a result of the introduction of TPA into the TiO2 matrix, but remained practically constant with the increase of the calcination temperature.
authors.affiliation: Centro de Investigación y Desarrollo en Ciencias Aplicadas Dr. J.J. Ronc, Departamento de Química, Facultad de Ciencias Exactas, UNLP, CONICET-CCT La Plata, 1900-La Plata, Argentina.
authors.forename: Vanesa M
authors.initials: VM
authors.lastname: Fuchs
authors.forename: Edgardo L
authors.initials: EL
authors.lastname: Soto
authors.forename: Mirta N
authors.initials: MN
authors.lastname: Blanco
authors.forename: Luis R
authors.initials: LR
authors.lastname: Pizzio