Photocatalytic degradation of azodyes using Ag@TiO2 core-shell structured nanoparticles

Abstract

Wastewater released from textile industries consists of large volume of colored dye effluents and it needs to be treated before discharge to the environment by cost effective technologies. Heterogeneous photocatalysis is a promising technology for the treatment of dye wastewater. Ag@TiO2 nanoparticle comprising of Ag core and TiO2 shell is a promising photocatalyst. In the present study, Ag@TiO2 nanoparticles were engineered to impart and enhance their UV and solar photocatalytic activity for efficient photocatalytic degradation of two azo dyes, namely: Acid Yellow-17(AY- 17) and Reactive Blue-220 (RB-220). Ag@TiO2 was found to be suitable as photocatalyst for UV and solar photocatalysis of these dyes. The engineered Ag@TiO2 nanoparticles were characterized by different techniques. Ag@TiO2 with an average crystallite size of around 39.33 nm, showed its ability to absorb both UV light and visible light. The band gap energy for these nanoparticles was estimated to be 1.85eV, which supported its high solar photocatalytic activity. Ag@TiO2 exhibited better photocatalytic activity as compared to other conventional catalysts. Operational factors such as pH, catalyst loading and oxidant concentration were optimized for photocatalysis of these dyes. Kinetics of photocatalysis of the dyes obeyed modified Langmuir-Hinshelwood model. The rate of photocatalysis of the dyes was inhibited by the presence of salts like sodium chloride and sodium carbonate and was enhanced by increase in light intensity. Efficient decolorization and mineralization of AY-17 and RB-220 were achieved by photocatalysis using Ag@TiO2. Optimum conditions obtained for AY-17 degradation were more favorable for the photocatalysis of water contaminated with mixture of these dyes. Degradation pathways for these dyes were proposed. Immobilized Ag@TiO2 nanoparticles showed similar efficacy as free nanoparticles. Ag@TiO2 was also found suitable for photocatalysis of other classes of dyes. Hence Ag@TiO2 nanoparticles may be considered as effective catalysts for the photocatalytic degradation of dyes/textile wastewater. Solar energy utilization and fast kinetics feature of this process makes it an economical and favorable option for large scale treatment of dye/textile wastewater.