Advances in Chemical Engineering and Science, 2011, 1, 9-14 doi:10.4236/aces.2011.11002 Published Online January 2011 (http://www.SciRP.org/journal/aces) Copyright © 2011 SciRes. ACES Investigation of Photocatalytic Degradation of Methyl Orange by Using Nano-Sized ZnO Catalysts Changchun Chen 1* , Jiangfeng Liu 1 , Ping Liu 2 , Benhai Yu 1 1 College of Physics and Electronics Engineering, XinYang Normal University, XinYang, China 2 College of Materials Science and Engineering, Nanjing University of Technology, Nanjing, China E-mail: changchunchen@hotmail.com Received December 30, 2010; revised January 19, 2011; accepted January 22, 2011 Abstract Nano-sized ZnO catalysts were prepared by a direct precipitation method under the optimal conditions (cal- cination of precursors at 550˚C for 120 min). The as-synthesized ZnO catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-Vis spectroscopy. The photocatalytic prop- erties of ZnO nanoparticles were investigated via methyl orange (MO) as a model organic compound under UV light irradiation. The influence of operating parameters on MO degradation including the amount of ZnO catalysts, pH value of solutions, and the photodegradation temperature was thoroughly examined. In addition, the kinetic process of photocatalytic degradation of MO using nano-sized ZnO catalyst was also examined, and the degradation of MO follow the first order kinetics. Keywords: ZnO Nanoparticles, Photocatalytic Degradtion, Methyl Orange 1. Introduction Semiconductor photocatalysts such as TiO 2 and ZnO nano-particles have attracted much attention in recent years due to their various applications to the photocata- lytic degradation of organic pollutants in water and air and dye sensitized photovoltaic solar cell [1-3]. Among these semiconductor photocatalysts, TiO 2 is the most commonly used owing to its stable, harmless and inex- pensive properties. However, two typical defects includ- ing only exciting by high energy UV irradiation and a low quantum yield rate resulted from a low rate of elec- tron transfer to oxygen and a high rate of recombination between excited electron/hole pairs, limit the photo- oxidation rate of TiO 2 nanoparticles. In order to improve the photocatalytic efficiency of TiO 2 nanoparticles, most studies have been focused on the modification of TiO 2 doped by metal ions, especially transition metal ions, which make it possible for TiO 2 to absorb visible light by increasing the charge separation [4,5]. In addition, com- bination of different kinds of semiconductor photocata- lysts also is a promising way to improve the photocata- lytic efficiency [6]. Recently, ZnO nanoparticles appear to be a suitable alternative to TiO 2 nanoparticles used for the photodegradation of pesticide carbetamide [7], herbi- cide triclopyr [8], pulp milling bleaching wasterwater [9], 2-phenylphenol [10], phenol [11], reactive blue 19 [12], and acid red 14 [13]. The substitution of TiO 2 by ZnO used for photo-degradation is ascribed to the photo-degradation mechanism of ZnO being similar to that of TiO2 [3,14]. K. Gouvea et al. has confirmed that ZnO exhibits a better efficiency than TiO 2 in photocata- lytic degradation of some reactive dyes in aqueous solu- tion [15]. As we known, ZnO nanoparticles can be syn- thesized by various approaches including sol-gel proc- essing, homogeneous precipitation, mechanical milling, organometallic synthesis, microwave method, spray py- rolysis, thermal evaporation and mechanochemical syn- thesis. However, ZnO nanoparticles fabricated by the abovementioned methods are prone to aggregate due to the large surface area and high surface energy. In order to improve the dispersion, it is necessary to modify the sur- face of ZnO nanoparticles. Some researches have re- vealed several physical and chemical methods for modi- fying the surface of ZnO nanoparticles. The chemical surface modification, which can be classified as surface grafting and esterification, is the most promising method because of the strong covalent bond between the surface modified particles and polymer chains. In previous re- searches, the ZnO nanoparticles were ever modified by SiO 2 [16], PMMA [17] and PSt [18], and the influence of particles on the mechanical properties of polymer matrix