Effect of Morphology-based Defect Structure of ZnO Nanostructures in Photo-Degradation of Organic Dye
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Effect of Morphology-based Defect Structure of ZnO Nanostructures in Photo-Degradation of Organic Dye Reza Shidpour1,2*, Manouchehr Vosoughi2, Abdolreza Simchi2, Faegheh Ghanbari2 1
Department of chemistry, University of California, 900 University of ave., Riverside, CA 16066, U.S.A. 2 Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran, Iran . ABSTRACT The fabrication of strong photocatalysts applied to the degradation of organic pollutants is necessary in environmental applications. In a single-stage method, acetate precursor and poly vinyl pyrolydine are used to produce ZnO nanostructures with various morphologies in annealing temperatures ranging from 300 oC to 900 oC. The physical properties of the prepared nanostructures were characterized by SEM, XRD and PL spectroscopy. The SEM images exhibit a variety of the as-prepared hexagonal zinc oxides including wires, rods, particles and porous network of welded particles of ZnO nanoparticles. The results of the photocatalytic degradation of methylene blue as an organic dye in aqueous suspension showed that the morphology of ZnO nanostructures influences on the photocatalytic efficiency of ZnO nanostructures, greatly. For the best result, the highest MB degradation occurs by ZnO nanowires within 16 minutes and in others samples, degradation of higher than 95 percent occurs within 20 minutes. The XRD and PL spectroscopy revealed neither VZn nor Oi are in all of samples but only VO−, VO2− and Zni exist in ZnO nanostructures. 1. INTRODUCTION Oxide semiconductors such as titanium dioxide (TiO2) [1-3] and zinc oxide (ZnO) [4,5] are very influential photocatalysts in degradation of organic pollutants dissolved in water and other solvents. Although they both have a band gap of about 3.3 eV, their electronic structure is quite different. This difference offers ZnO some advantages over TiO2. For instance, ZnO has higher exciton energy binding about 60 meV and consequently longer lifetime at room temperature , it absorbs a larger fraction of UV spectrum and absorbs more light than TiO2[6, 7]. In the spite of these advantages, the major disadvantage of ZnO is that surface defects in ZnO lead to the rapid electron-hole recombination. The photocatalytic activity of ZnO nanocrystals is not only sensitive to crystal size but also to morphology. Because of the effects of morphology, it can play an important role in photocatalytic process [8-10]. In this article, a simple and single-stage route has been used to prepare ZnO photocatalysts with various morphologies through altering only annealing temperature. The photocatalytic activity of the prepared ZnO nanostructured photocatalyst was evaluated by the degradation of methylene blue (MB) in the presence of UV light. Afterwards, special optical, and structural properties of these ZnO samples were investigated by XRD, PL spectroscopy and SEM. It was shown that only some surface defects play a role in photocatalytic activity.
2. EXPERIMENT 2.1 Preparation of ZnO photocatalyst First, 5 g Zn(CH3COO)2 .
