Zinc oxide (ZnO) particles were successfully synthesized via sol-gel approach using zinc acetate dihydrate (Zn(CH3COO)2·2H2O) and ammonia (NH4OH) solution as precursors. By adjusting the reaction parameters such as amount of ammonia and reaction time as well as complexing agent aluminium sulphate Al2(SO4)3, ZnO particles with different morphologies, that is, rodlike, ricelike and disklike could be synthesized. The effectiveness of ZnO particles with different morphologies (rodlike, ricelike and disklike) on the photocatalytic activity has been studied. The results showed that rodlike ZnO particles were the most effective in degrading the Rhodamine B (RhB) solution under the illumination of ultraviolet (UV) light. The rate constant was found to be first order, with rodlike particles the highest (0.06329？min？1), followed by rice-like ZnO particles (0.0431？min？1) and disk-like ZnO particles (0.02448？min？1). 1. Introduction Photocatalysis of organic compounds such as methyl green and Rhodamine B (RhB) in water is receiving attention due to the severe ecological impact of various industrial and agricultural pollutants [1, 2]. Photocatalytic activities can be classified into homogeneous or heterogeneous reactions depending on the nature of their reactants and materials (semiconductors). Particularly, heterogeneous photocatalytic study using semiconductor materials such as TiO2 and ZnO, through particulate systems, has become an exciting and rapidly growing area of research in the last few years mainly due to the relatively simple photodecomposition of organic pollutant molecules into less harmful compounds [3–7]. ZnO has been chosen as photocatalyst because of its high catalytic efficiency, low cost, large bandgap (3.37？eV), and nontoxic nature. In fact, it has been shown to be more effective than TiO2 as photocatalysts in recent studies [8, 9]. The effect of various parameters such as UV light intensity [3], initial dye concentration [3, 10, 11], pH of the medium [10], amount of photocatalyst [3, 11], doping [4, 12], and temperature [13] were reported. However, the effect of morphology of ZnO particles remains as a field to be explored. The morphology of ZnO particles can be easily manipulated by tailoring the reaction parameters. By adjusting the temperature, concentration of solution, pH, heating duration, and complexing agent, different morphology of ZnO particles such as nanoprisms [14], nanorods [15], nanoflowers [16], nanosheets [17], and nanodisks [18] could be synthesized, respectively. Different morphology of ZnO particles have different exposed
References
[1]
A. Sugunan and J. Dutta, “Pollution treatment, remediation and sensing,” Nanotechnology, vol. 2, pp. 125–147, 2008.
[2]
F. D. Mai, C. C. Chen, J. L. Chen, and S. C. Liu, “Photodegradation of methyl green using visible irradiation in ZnO suspensions. Determination of the reaction pathway and identification of intermediates by a high-performance liquid chromatography-photodiode array-electrospray ionization-mass spectrometry method,” Journal of Chromatography A, vol. 1189, no. 1-2, pp. 355–365, 2008.
[3]
J. J. Vora, S. K. Chauhan, K. C. Parmar, S. B. Vasava, S. Sharma, and L. S. Bhutadiya, “Kinetic study of application of ZnO as a photocatalyst in heterogeneous medium,” E-Journal of Chemistry, vol. 6, no. 2, pp. 531–536, 2009.
[4]
S. Liu, C. Li, J. Yu, and Q. Xiang, “Improved visible-light photocatalytic activity of porous carbon self-doped ZnO nanosheet-assembled flowers,” CrystEngComm, vol. 13, no. 7, pp. 2533–2541, 2011.
[5]
F. Barka-Bouaifel, B. Sieber, N. Bezzi et al., “Synthesis and photocatalytic activity of iodine-doped ZnO nanoflowers,” Journal of Materials Chemistry, vol. 21, no. 29, pp. 10982–10989, 2011.
[6]
M. A. Kanjwal, N. A. M. Barakat, F. A. Sheikh, S. J. Park, and H. Y. Kim, “Photocatalytic activity of ZnO-TiO2 hierarchical nanostructure prepared by combined electrospinning and hydrothermal techniques,” Macromolecular Research, vol. 18, no. 3, pp. 233–240, 2010.
[7]
K. Byrappa, A. K. Subramani, S. Ananda, K. M. Lokanatha Rai, R. Dinesh, and M. Yoshimura, “Photocatalytic degradation of rhodamine B dye using hydrothermally synthesized ZnO,” Bulletin of Materials Science, vol. 29, no. 5, pp. 433–438, 2006.
[8]
G. Wang, D. Chen, H. Zhang, J. Z. Zhang, and J. Li, “Tunable photocurrent spectrum in well-oriented zinc oxide nanorod arrays with enhanced photocatalytic activity,” Journal of Physical Chemistry C, vol. 112, no. 24, pp. 8850–8855, 2008.
[9]
C. C. Chen, “Degradation pathways of ethyl violet by photocatalytic reaction with ZnO dispersions,” Journal of Molecular Catalysis A, vol. 264, no. 1-2, pp. 82–92, 2007.
[10]
K. Byrappa, A. K. Subramani, S. Ananda, K. M. Lokanatha Rai, R. Dinesh, and M. Yoshimura, “Photocatalytic degradation of rhodamine B dye using hydrothermally synthesized ZnO,” Bulletin of Materials Science, vol. 29, no. 5, pp. 433–438, 2006.
[11]
J. Zhao and L. Wang, “Degradation of rhodamine B in aqueous solution by the UV/ZnO photocatalytic process,” in Proceedings of the International Conference on Materials for Renewable Energy & Environment (ICMREE '11), pp. 1397–14000, Shanghai, China, May 2011.
[12]
F. Barka-Bouaifel, B. Sieber, N. Bezzi et al., “Synthesis and photocatalytic activity of iodine-doped ZnO nanoflowers,” Journal of Materials Chemistry, vol. 21, no. 29, pp. 10982–10989, 2011.
[13]
M. C. M. Alvim Ferraz, S. M？ser, and M. Tonh？euser, “Control of atmospheric emissions of volatile organic compounds using impregnated active carbons,” Fuel, vol. 78, no. 13, pp. 1567–1573, 1999.
[14]
C. Wu, X. Qiao, J. Chen, H. Wang, F. Tan, and S. Li, “A novel chemical route to prepare ZnO nanoparticles,” Materials Letters, vol. 60, no. 15, pp. 1828–1832, 2006.
[15]
Y. Masuda, N. Kinoshita, and K. Koumoto, “Morphology control of ZnO crystalline particles in aqueous solution,” Electrochimica Acta, vol. 53, no. 1, pp. 171–174, 2007.
[16]
D. Vernardou, G. Kenanakis, S. Couris, E. Koudoumas, E. Kymakis, and N. Katsarakis, “pH effect on the morphology of ZnO nanostructures grown with aqueous chemical growth,” Thin Solid Films, vol. 515, no. 24, pp. 8764–8767, 2007.
[17]
J. Zhang, L. Sun, J. Yin, H. Su, C. Liao, and C. Yan, “Control of ZnO morphology via a simple solution route,” Chemistry of Materials, vol. 14, no. 10, pp. 4172–4177, 2002.
[18]
S. Cho, S. H. Jung, and K. H. Lee, “Morphology-controlled growth of ZnO nanostructures using microwave irradiation: from basic to complex structures,” Journal of Physical Chemistry C, vol. 112, no. 33, pp. 12769–12776, 2008.
[19]
H. Xu, H. Wang, Y. Zhang et al., “Hydrothermal synthesis of zinc oxide powders with controllable morphology,” Ceramics International, vol. 30, no. 1, pp. 93–97, 2004.
[20]
Y. Jiang, Y. Sheng, X. Lan et al., “Mechanism and growth of flexible ZnO nanostructure arrays in a facile controlled way,” Journal of Nanomaterials, vol. 2011, Article ID 473629, 12 pages, 2011.
[21]
Y. Jiang, X. Wu, W. Zhang, L. Ni, and Y. Sun, “Evolution of ZnO architecture on a nanoporous TiO2 film by a hydrothermal method and the photoelectrochemical performance,” Journal of Semiconductors, vol. 32, no. 3, 2011.
[22]
C. Ye, Y. Bando, G. Shen, and D. Golberg, “Thickness-dependent photocatalytic performance of ZnO nanoplatelets,” Journal of Physical Chemistry B, vol. 110, no. 31, pp. 15146–15151, 2006.
[23]
K. Vanheusden, W. L. Warren, C. H. Seager, D. R. Tallant, J. A. Voigt, and B. E. Gnade, “Mechanisms behind green photoluminescence in ZnO phosphor powders,” Journal of Applied Physics, vol. 79, no. 10, pp. 7983–7990, 1996.
[24]
K. Vanheusden, C. H. Seager, W. L. Warren, D. R. Tallant, and J. A. Voigt, “Correlation between photoluminescence and oxygen vacancies in ZnO phosphors,” Applied Physics Letters, vol. 68, no. 3, pp. 403–405, 1996.
[25]
L. Wang, L. Chang, B. Zhao, Z. Yuan, G. Shao, and W. Zheng, “Systematic investigation on morphologies, forming mechanism, photocatalytic and photoluminescent properties of ZnO nanostructures constructed in ionic liquids,” Inorganic Chemistry, vol. 47, no. 5, pp. 1443–1452, 2008.
[26]
J. H. Zeng, B. B. Jin, and Y. F. Wang, “Facet enhanced photocatalytic effect with uniform single-crystalline zinc oxide nanodisks,” Chemical Physics Letters, vol. 472, no. 1–3, pp. 90–95, 2009.
