Effect of Precursor Type on Zinc Oxide Formation and Morphology Development during Hydrothermal Synthesis

Abstract

Semiconducting metal oxide sensors have been widely studied due to their small dimensions, low cost and low power consumption. ZnO is a potential material for gas sensor applications because of its high piezoelectric coefficient, great stability of its hexagonal phase and its pyroelectric property. Hydrothermal synthesis is one of the most useful methods to produce homogeneous, nanosized ZnO powders with high purity, controlled particle size and morphology. The research objectives of this study were to understand formation and growth process of ZnO particles with various morphologies and to investigate role of starting materials, i.e., zinc chloride ZnCl2 and zinc nitrate hexahydrate Zn NO3 2 .6H2 O on the particle morphology. ZnO particles with various morphologies were synthesized via an unstirred hydrothermal method. When using ZnCl2 as a precursor, the final morphology was rod like with a taped tip length of the rod 0.5-1 μm after 12 h at 100 °C. On the other hand, final morphology of the produced ZnO particles was branch rod like 5-10 μm when using Zn NO3 2 .6H2 O as precursor under the same synthesis conditions. Accordingly, a proposed growth mechanism has been suggested.

Keywords

• ZO0 ydrothermal syntheTJs 1hase developmenU .PrpholoHZ SPwth mechanism

References

1. 1. Polsongkram D, Chamninok P, Pukird S, Chow L, Lupan O, Chai G, Khallaf H, Park S, Schulte A. Effect of synthesis conditions on the growth of ZnO nanorods via hydrothermal method. Physica B 403 (2008) 3713-3717.
2. 2. Zhang J, Sun L, Yin J, Su H, Liao C, Yan C. Control of ZnO morphology via a simple solution route. Chem. Mater. 14 (2002) 4172-4177.
3. 3. Rai P, Kwack W, Yu Y. Solvothermal synthesis of ZnO nanostructures and their morphology-dependent gassensing properties. Applied Materials Interfaces 5 (2013) 3026-3032.
4. 4. Singh O, Kohli N, Singh RC. Precursor controlled morphology of zinc oxide and its sensing behaviour. Sensors and Actuators B, 178 (2013) 149-154.
5. 5. Korotcenkov G, The role of morphology and crystallographic structure of metal oxides in response of conductometrictype gas sensing. Materials Science and Engineering Reports 61(2008) 1-39.
6. 7. Zhang H, Yang D, Yi YJ, Ma XY, Xu J, Que DL. Low temperature synthesis of flowerlike ZnO nanostructures by cetyltrimethylammonium bromide-assisted hydrothermal process. Journal of Physical Chemistry B, 108, 13 (2004) 3955–3958.
7. 8. Li WJ, Shi EW, Zhong WZ, Yin ZW. Growth mechanism and growth habit of oxide crystals. J. Cryst. Growth, 203 (1999) 186-196.
8. 9. Ozer IO, Texture development in ZnO-based varistors, effects of inversion boundaries on texture development and relationships between texture and electrical characteristics, Anadolu University, Doctorate thesis, May 2010.

9. 10. Mullin JW. Crystallisation, third ed. Butterworth/Heinemann, Oxford, 1997.