TUNGSTOPHOSPHORIC ACID HETEROGENIZED ONTO NH4ZSM5 AS AN EFFICIENT AND RECYCLABLE CATALYST FOR THE PHOTOCATALYTIC DEGRADATION OF DYES

CANDELARIA LEAL MARCHENA; SILVINA GOMEZ; CLARA SAUX; LUIS R. PIZZIO; LILIANA B. PIERELLA

QUíMICA NOVA

SOC BRASILEIRA QUIMICA

Lugar: San Pablo; Año: 2015 vol. 38 p. 518 - 525

0100-4042

Materials based on tungstophosphoric acid (TPA) immobilized on NH4ZSM5 zeolite were prepared by wet impregnation of thezeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, 31P MAS-NMR, TGADSC,DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (SBET)decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modifiedwith TPA only presented the characteristic peaks of NH4ZSM5 zeolites, and an additional set of peaks assigned to the presence of(NH4)3PW12O40. According to the Fourier transform infrared and 31P magic angle spinning-nuclear magnetic resonance spectra, themain species present in the samples is the [PW12O40]3- anion, which was partially transformed into [P2W21O71]6- anion during thesynthesis and drying steps. The thermal stability of the NH4ZSM5TPA materials is similar to that of their parent zeolites. Moreover,the samples with the higher TPA content present band gap energy values similar to those reported for TiO2. The immobilization ofTPA on NH4ZSM5 zeolite allowed us to obtain catalysts with high photocatalytic activity in the degradation of methyl orange dye(MO) in water, at 25 °C. They can be reused at least three times without an important decrease in the degradation degrees.