الفهرس 
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Abstract
The present work is focused on the synthesis and characterization of Ag@Pd, Pd@Ag, Ag@Pt , and Pt@Ag core/shell nanoparticles in order to investigate their catalytic activity towards the reductive removal of Congo red (CR), Direct blue 14(DB 14)and Sunset yellow (SY) from aqueous solutions. The thesis consists of four chapters. The first chapter embraces an introduction about colloids, problems of water pollution by dyes, nanotechnology, nanoparticles and core/shell nanoparticles, application of nanoparticles and core/shell nanoparticles in wastewater treatment.It also contains a literature survey on the chemistry of core/shell nanoparticles and its application. The second chapter includes the experimental part which describes the materials and instruments that have been used. The method of preparation of nanocatalysts, the kinetics of the removal process, and biological measurements are also included. The third chapter comprises the results and discussion. It shows the characterization of the core/shell nanocatalysts by conventional techniques such as FT-IR, X- ray, UV-Vis, and TEM. The kinetics of in situ reduction of three dyes by sodium borohydride (NaBH4) in the presence of the four core/shell nanoparticles were displayed in details. The catalytic reactions were followed by measuring the decrease with time in the absorbance of Congo red (CR) (λmax= 496 nm), Direct blue 14 (DB 14) (λmax= 590 nm) and Sunset yellow (SY) (λmax= 480 nm). The effect of reaction parameters such as the concentration of the dye, nanocatalyst, and NaBH4. in water and in alkaline medium (pH 12) have been studied. In case of CR the rate of reaction increased gradually to reach a maximum then decreased with increasing the initial dye concentration. With DB 14 and SY the rate of reaction only increased by increasing the initial dye concentration. In general, the reaction rate increased by increasing reducing agent concentration (NaBH4) as well as the concentration of nanocatalyst(core/shell nanoparticles). The obtained results have proved that the catalytic activity of Pd@Ag was greater than Ag@Pd, Ag@Pt, and Pt@Ag and therefore a comparative study was made between the reductive affinities of the three investigated dyes. A mechanism illustrating the removal process was proposed.