Sonophotocatalytic (42kHz) degradation of Simazine in the presence of Au-TiO₂ nanocatalysts

The nano-size gold loaded visible light driven Au-TiO₂ nanophotocatalysts were synthesized using a commercial sonicator bath producing 42kHz ultrasound. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) analyses revealed the gold nanoparticles incorporated in the TiO₂ resides at the surface of the nanocatalysts. An increased BET surface area was observed for the Au-TiO₂ when compared with the bare TiO₂ which gave the first notation that the gold nanoparticles modified the physicochemical characteristics of the TiO₂. The RAMAN spectrum shows the shift by ~5cm^-1 at 639cm^-1 which indicated that the loaded gold nanoparticles were loaded on the surface of TiO₂ nanoparticles and thus confirms that the gold nanoparticles readily accepts the electronic charges created during the photoexcitation of Au-TiO₂ nanocatalysts. The Simazine (triazine based pesticide) was taken as the model pollutant to evaluate its sonocatalytic, photocatalytic and sonophotocatalytic degradation in the presence of TiO₂ and Au-TiO₂ nanocatalysts. The first order kinetics was observed for the Simazine degradation. The observed rate constants indicate that the order of degradation of Simazine was, sonophotocatalysis>sonocatalysis>photocatalysis. The additive effect was observed for the Au-TiO₂ assisted sonophotocatalytic degradation of Simazine. A 1.65 and 1.38 fold enhanced mineralization was achieved for the sonophotocatalytic degradation of Simazine when compared with the photocatalytic and sonocatalytic processes. The intermediates produced during the mineralization of Simazine were analyzed using ESI-MS analysis and based on that a suitable mechanism has been proposed.