ZnO/Au nanocatalysts for enhanced decolorization of an azo dye under solar, UV-A and dark conditions

Plasmonic nanoparticles have emerged as a promising material for enhancing catalytical properties of wide-bandgap semiconductors. In this work, we report a well-controllable synthesis of new nanocatalysts based on star-shaped zinc oxide (ZnO) decorated with gold nanoparticles for enhanced decolorization of methylene blue under solar, UV-A and dark conditions. ZnO particles were prepared using precipitation method at room temperature and decorated with Au nanoparticles via a simple photodeposition methodology. Morphology, crystallinity, and optical properties of bare ZnO and hybrid ZnO/Au nanocatalysts were fully characterized by standard analytical techniques. The catalytic properties for decolorizing aqueous methylene blue (MB) solutions of these materials were tested via 3 different methods: photocatalysis using UV-A irradiation, photocatalysis using solar irradiation, and sonocatalysis in dark conditions, under low frequency ultrasound. The results revealed the plasmon-enhanced performance of ZnO/Au nanocatalysts when the system is exposed with solar irradiation, which could be attributed to the efficient charge separation of photogenerated electron/hole pairs, as inferred from PL studies. Finally, it was found that the photocatalysis efficiency is influenced by variations on the [MB]/mcatalyst ratio and the size/concentration of dopping Au nanoparticles.