Synthesis of Novel Photocatalysts Based on Polyoxovanadates Supported onto Zeolites Employed for Azo Dye Degradation

Abstract

Heterogeneous photocatalysts based on polyoxovanadates with Keggin structure (POV) supported onto zeolite (NH₄ZSM-5) were developed. The amount of POV incorporated was varied from 5% to 30% wt. Catalysts were characterized by N₂ adsorption–desorption isotherms, FT-IR, XRD, DRS UV–vis, TGA, and ³¹P MAS-NMR techniques; and the catalytic activity was evaluated in azo dye degradation. The specific surface area decreased as the POV content increased because of zeolite pore blocking. The XRD patters presented the characteristic peaks of NH₄ZSM-5 and POV, with no additional diffraction peaks, assigned to a well dispersed POV. FT-IR and ³¹P MAS-NMR results confirm that the Keggin structure of [PVW₁₁O₄₀]⁴⁻ anions remain unaltered after their inclusion in the zeolite. The incorporation of POV generated a redshift at the absorption border, determined by DRS UV–vis, which promotes its activity in the visible range. Moreover, while POV content increase the bandgap energy diminishes and the photocatalytic activity increased. The higher photoactivity was 80% of discoloration when 30% wt of POV was incorporated. The characterization and catalytic evaluation indicated that these materials present suitable properties to be used as catalysts in the photocatalytic treatment of wastewater, being the main advantage their easy separation and reuse without significant decrease of the photoactivity.