Tungstophosphoric acid heterogenized onto NH₄ZSM5 as an efficient and recyclable catalyst for the photocatalytic degradation of dyes

• Autores: Leal Marchena, Candelaria; Gomez, Silvina; Saux, Clara; Pierella, Liliana B.; Pizzio, Luis René
• Año de publicación: 2015
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas; Methyl orange; NH4ZSM5 zeolite; Photocatalytic degradation; Tungstophosphoric acid
• Institución: Universidad Nacional de La Plata

Materials based on tungstophosphoric acid (TPA) immobilized on NH₄ZSM5 zeolite were prepared by wet impregnation of the zeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and 30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, ³¹P MAS-NMR, TGA.-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (S_BET) decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modified with 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, the main species present in the samples was the [PW₁₂O₄₀]^3- anion, which was partially transformed into the [P₂W₂₁O₇₁]^6- anion during the synthesis and drying steps. The thermal stability of the NH₄ZSM5TPA materials was similar to that of their parent zeolites. Moreover, the samples with the highest TPA content exhibited band gap energy values similar to those reported for TiO₂. The immobilization of TPA on NH₄ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 °C. These can be reused at least three times without any significant decrease in degree of degradation.
Facultad de Ciencias Exactas
Centro de Investigación y Desarrollo en Ciencias Aplicadas