Facile Synthesis of Ag-Coated Cu 2 O Nanospheres for Improved Photocatalytic Activity
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Facile Synthesis of Ag-Coated Cu2O Nanospheres for Improved Photocatalytic Activity Drew Hall1, Sanjay Mishra1, Anagh Bhaumik2 and Dr. Kartik Ghosh2 1 Department of Physics, The University of Memphis, Memphis, TN 38152, U.S.A. 2 Department of Physics, Astronomy and Materials Science, Missouri State University, Springfield, MO 65897 ABSTRACT The present study details facile synthesis of hollow Cu2O nanospheres decorated with Ag nanoparticles using a simple surfactant technique for enhanced photocatalytic activity. The morphology and structure is studied via XRD and SEM. Cu2O hollow nanospheres with a diameter of 500-800 nm were synthesized via Ostwald ripening using CuSO4 aqueous solution. The catalytic activity of Cu2O is studied in the presence of UV and visible light using Methyl Orange (MO) as a model pollutant. Ag decorated Cu2O particles showed a 49% increase in photocatalytic activity over the undecorated Cu2O. The improved photocatalytic activity is achieved by surface plasmon resonance effects in the silver nanoparticles, allowing utilization of the lower energy portion of the solar spectrum. INTRODUCTION Azo dyes are widely used in the textile, food, drug, and other industries to dye products. Some of these toxic, carcinogenic, and mutagenic dyes have been found in food and water supplies, and they are mostly nonbiodegradable [1]. Thus, much attention has been given to eliminating the dyes through photocatalysis. Many metal oxide semiconductors have been found to be effective photocatalysts, such as the most widely studied, TiO2. However, TiO2 has a large bandgap (3.2 eV) that limits light absorption to the small UV portion of the solar light spectrum. Cu2O has a smaller bandgap than TiO2, thus allowing utilization of more of the visible light and offering a more effective and cheaper alternative photocatalyst. The photocatalytic activity of Cu2O can be further enhanced by decoration with Ag nanoparticles. Incoming photons induce localized surface plasmon resonance (LSPR) oscillations in the silver nanoparticles. The energy of these oscillations is then transferred to the Cu2O by means of resonant energy transfer [2]. LSPR in the Ag particles can make use of photons much higher wavelengths than would be used by Cu2O alone. The effects of various geometries of Cu2O nanoparticles on the efficiency of light energy conversion have been studied, and hollow spheres have proven to be an ideal geometry for Cu2O photocatalysts [3]. The hollow sphere geometry yields high light harvesting efficiency as well as fast charge carrier motion by forming closely packed clusters of interpenetrating hollow spheres. This structure combines efficient charge transport and high specific surface area [4, 5]. In the present study, the Cu2O spheres were synthesized by introducing hydrazine into a copper (II) sulfate solution. This reduces the Cu2+ ions to form Cu nanoparticles, which are immediately oxidized, producing Cu2O crystals. In the process of reducing the Cu2+ ions, the hydrazine itself produces nitrogen gas bubbles. The liq
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