Plasmon-assisted photocatalysis of organic pollutants by Au/Ag–TiO2 nanocomposites: a comparative study

The treatment of organic pollutants contaminated by wastewater from textile industries is a serious concern around the globe, and several techniques are being employed for its treatment. Among these, the semiconductor nanocomposite (NC)-assisted photodegradation of organic dyes has recently attracted attention. Herein, we report surface plasmon resonance (SPR) enhanced photocatalytic activities of heterogeneous photocatalysts (Au/Ag–TiO2) for wastewater treatment. To synthesize the Au/Ag–TiO2 NCs, TiO2 nanoflakes (NFs) are decorated with spherical-shaped plasmonic Au and Ag nanoparticles (NPs) of average sizes ∼13 and ∼30 nm, respectively, using a simple and cost-effective sol-gel method. In comparison to the pristine TiO2 nanoflakes and Ag–TiO2 NCs, highly stable Au–TiO2 NCs exhibit enhanced photocatalytic activity for the degradation of dye mixture (organic pollutants) under the sunlight. The optical and structural properties have been studied to find the reason behind the enhanced photocatalytic activities in Au–TiO2 NCs. The more degradation efficiency and rate constant in Au–TiO2 NCs are mainly attributed to the broad range absorption of visible light and the effective charge transfer, monitored using photoluminescence and ultrafast transient absorption spectroscopy. The total removal efficiency of organic dyes is 90.62% and the rate constant is 0.043 min−1 in 60 min degradation for Au–TiO2, higher than that of Ag–TiO2 and TiO2. Furthermore, the Stern-Volmer constant (Ksv) estimated from the photoluminescence quenching measurements is found to be significantly higher in the case of Au–TiO2 (2420 L−1) than Ag–TiO2 (1750 L−1), which corroborates the fact that there is more charge transfer in Au–TiO2. We believe that this research may shed light on the physics underlying the enhanced photocatalytic performance and capabilities of Au–TiO2 NCs for the removal of organic pollutants in wastewater.