Photocatalytic activity of nanoparticle gold/iron oxide aerogels for azo dye degradation

Nanoparticle gold/iron oxide (maghemite) aerogels were used as photocatalysts to degrade Disperse Blue 79 azo dye in water under ultraviolet light illumination. They were characterized by diffuse reflection spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. Addition of gold species caused the light absorption to shift towards the red visible region, and thus the band gap energy reduced. Photocatalytic activity enhanced with increasing Au loading up to 8 wt%, and the activity increase was dependent upon catalyst pretreatment. The dye degradation was accelerated remarkably when carried out in alkaline media or in the presence of hydrogen peroxide. In the photocatalysis system, metallic gold particles serve to facilitate the transfer of surface electrons, and hydroxyl radicals near the catalyst surface act as the main oxidative species to attack dye molecules. At high catalyst concentrations, the use of ultrasound and light irradiation improved the activity declined by catalyst particle aggregation. Results demonstrate the feasibility of aerogel powders as a model photocatalyst for dye decontamination in textile wastewater.