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Preparation of ZnO Hollow Structures and Their Photocatalytic Activity

Author: ZhangChao
Tutor: YinLongWei
School: Shandong University
Course: Materials Science
Keywords: ZnO hollow spheres nanotubes hydrothermal reaction photocatalytic activity composite surface modification
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 217
Quote: 0
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Abstract


ZnO is an importantⅡ-Ⅵgroup metal oxide semiconductor with a direct and wide band gap at room temperature. ZnO nanomaterials have attracted considerable attention for their unique photoelectric properties. Because of their excellent properties, ZnO has played an important role in many application fields such as solar cell, gas sensors, solid illuminations, protecting coatings, photocatalysis and UV optical devices. Research for ZnO nanomatericals has been a long time, and in the last two decades, various methods has been employed for synthesizing different kinds of morphologies.With the fast development of modern society, environmental problems are becoming more and more serious. For the water purification, ZnO is more efficient than TiO2, the most intensively studied photocatalyst, in the photodegradation of some organic compounds. This paper focuses more on fabricating ZnO hollow structures (including hollow spheres and nanotubes) and characterizing their photocatalytic activities. The main contents are summarized as follows:(1) We used colloidal carbon spheres as templates, which was formed by putting glucose aqueous solution at 180℃for a certain time. ZnO hollow spheres and ZnO-CuO composite hollow spheres were synthesized though a hydrothermal reaction, using Zn(Ac)2·2H2O and CuCl2·2H2O as raw materials. Compared two-step method and one pot fabrication method, we can control the size and morphology of the products using the two step method, size of colloidal carbon spheres can be controlled by changing the polymerization and carbonization time, thus, we can decide the size of the final ZnO hollow spheres, and XRD patterns indicate that the samples is hexagonal wurtzite structure of ZnO; when we used one pot fabrication method, we obtained ZnO and ZnO-CuO composite hollow spheres with a size of 800 nm, these products are all nanoporous and have a thick shell. The photocatalytic activity of ZnO-CuO composite hollow spheres is better than other products.(2) ZnO nanotubes and ZnO-CuO composite nanotubes with size of 400 nm are fabricated on silicon substrate via a simple hydrothermal reaction, using ZnCl2, CuCl2·2H2O and NH3·H2O as raw materials. The formation of ZnO nanotubes can be divided into two stages, deposition at high temperature and dissolution at low temperature. We can not wash the substrate so violently, due to the slight combination of the products and the substrate. XRD and EDS spectra indicated the product contains impurities. When we added CuCl2·2H2O into the reactant, the products of ZnO nanotubes assembled into flowers, and the photocatalytic activity has a significant improvement.(3) Pt nanoparticles have been decorated at the surface of the ZnO nanotubes prepared by a facile chemical reduction method. After Pt nanoparticles were decorated at ZnO nanotubes, the side face of ZnO nanotubes became rough due to the reactant HPtCl5, and parts of ZnO nanotubes turned into nanorods again because of the high reaction temperature. The photocatalytic activity has been slightly enhanced.

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