2016 International Conference on Material Science and Civil Engineering (MSCE 2016) ISBN: 978-1-60595-378-6 Preparation of One-dimensional ZnO/Bi2O3 Heterostructures Nanomaterial for Visible Light Photocatalysis Song WANG a, Ying-ying ZHENG b, Jia-qi PAN c, Ming-zhu YOU d and Chao-rong LI e Department of Physics and Key Laboratory of ATMMT Ministry of Education Zhejiang Sci-Tech University, Hangzhou 310018, China a 1046871146@qq.com, b zhengyy1718@zstu.edu.cn, c 532398593@qq.com, d 545164256@qq.com, e crli@zstu.edu.cn We use a simple route to prepare ZnO@Bi2O3 heterostructures at room temperature by the solid-state reaction method. The paper discussed morphology and photocatalytic properties of different content of ZnO@ Bi2O3 composite nanomaterials. The as-prepared different content of ZnO@ Bi2O3 composite with different content were characterized by SEM, TEM, XRD and Uv-vis spectrometry. We find that the Bi2O3 nanoparticles are well dispersed on the ZnO Nano rods. The result shows that we can the absorption of solar light can be enhanced by coating Bi2O3 and zinc oxide /bismuth oxide sample in sunlight irradiation shows the best photocatalytic activity under sunlight irradiation Keywords: Photocatalysis; ZnO @ Bi2O3 Composite; Visible Light. 1. Introduction Owing to the discharged toxic organic pollutants and colored wastewater, the water bodies in nature are seriously damaged, which is harmful to human health and the environment [1, 2]. Photocatalytic degradation of organic pollutants by photocatalysts has been the beneficial technology for water purification. In the field of photocatalysis, ZnO is believed to be an efficient photocatalytic material alternative to TiO 2 because both have similar band gap and photocatalytic mechanism. ZnO is an important semiconductor material with a band gap of 3.37eV at room temperature and its photocatalytic activity has been widely explored and reported [3]. Due to the wide band of ZnO, it only absorbs the UV light, which accounts for only 5% of the solar energy. Therefore, how to improve the photocatalytic activity is necessary to modify ZnO by enlarging the light absorption. Bismuth oxide (Bi 2O 3) is a kind of semiconductor with a band gap of 2.47eV, which is active under visible light irradiation [4]. It is expected that ZnO/Bi 2O 3 heterojunction could improve the photocatalytic properties of pure ZnO [5]. In this paper we intend to synthesize the ZnO/Bi 2O 3 heterojunction by the solid-state reaction at a room temperature and investigate the photocatalytic performance of ZnO/B 3 heterojunction under visible light irradiation. 193
2. Experimental 2.1. Fabriccation of ZnO/ Bi2O3 heterojunction All chemicals reagents are analytical grade and directly used without further purification. Zn(CH 3COO) 2 2H 2O (0.438g, 2.0mmol) and different amount (0, 3%, 5%, 10%) of Bi 2O 3 were blended together in agate mortar and ground thoroughly for 30min at room temperature. Then, NaOH (0.64g, 16mmol) was added to the mixture and ground for further 2h. Finally, the products were washed several times with distilled water and absolute ethanol. Afterwards, we put the products in oven for drying at 100 for 12h. 2.2. Characterization methods The surface morphology of the samples was investigated using Field-emission scanning electron microscope (FESEM, Hitachi S-4800) equipped with an Energy-dispersive X-ray spectroscopy (EDS), and a transmission electron microscope (TEM, JEM 2100, 200 kv). The phase structures of the ZnO/Bi 2O 3 heterojunction nanocomposites were studied by powder X-ray diffraction (XRD, Bruker AXS D8-discover). The UV-visible spectroscopy measurement and Methylene blue (MB) UV absorbance was investigated by UV-vis absorption (Hitachi U-3900). In this experiment, 40mg ZnO/Bi 2O 3 heterojunction nanocomposites were added into 50 ml 10 mg/l MB solutions under visible light irradiation (PHILIPS, 662 nm) for photocatalytic examination under magnetic stirring. The UV absorbance spectra of MB solution were collected every 20 min. 2.3. Result and discussion The SEM images of ZnO/Bi 2O 3 heterojunction and the TEM image of ZnO/ Bi 2O 3 heterojunction were shown in Figure1. From Figure.1a, the prepared ZnO without adding Bi 2O 3 shows flake or irregular Nano rods. While, the surface morphology was changed by adding Bi 2O 3, as shown in Figure.1, we can see that some nanoparticles have attached on the surface of ZnO. As shown in Figure 1c and Figure 1d shows a typical TEM image of ZnO/Bi 2O 3 heterojunction. It can be seen that Bi 2O 3 particles are anchored on the surface of ZnO. 194
Figure 1. The SEM images of (a)pure ZnO,(b)ZnO/ Bi2O3, (c), (d) TEM images of ZnO/ Bi2O3. Figure 2 shows the XRD patterns of as-prepared samples. All the diffraction peaks of ZnO agree well with the wurtzite standard pattern (JCPDS No.36-1451), while the diffraction peaks of α-bi 2O 3 corresponds well to the standard pattern (JCPDSNo.71-2274). 195
Figure 2. The XRD patterns of ZnO, ZnO/ Bi2O3heterojunction, and Bi2O3. Photocatalytic activities of the samples were evaluated by measuring the degradation of MB in aqueous solution under visible light irradiation. Figure 3 shows the UV-vis absorption spectrum of MB aqueous solution with ZnO/ Bi 2O 3 heterojunction as photocatalyst during different exposure time under the light irradiation. The maximum absorbance of MB diminishes gradually with time elapse. The absorption peak nearly disappeared in 50 min under visible light irradiation in the presence of ZnO/ Bi 2O 3 photocatalyst. 196
1.6 Absorption 1.4 1.2 1.0 0.8 0.6 0.4 0min 10min 20min 30min 40min 50min 0.2 0.0-0.2 500 600 700 800 Wavelenth/nm Figure 3. UV-vis spectra for degradation of MB by using ZnO/ Bi2O3 heterojunction and photocatalytic degradation of phenol under solar light by the samples. 3. Conclusion In summary, we have synthesized the zinc oxide /bismuth oxide heterostructures at room temperature. The result indicates the ZnO/Bi 2O 3 heterojunction has excellent photocatalytic efficient for MB solution under visible light irradiation. 197
Acknowledgments This work was supported by Natural Science Foundation of China (Nos. 51172209 and 91122022), and by the Program for Changjiang Scholars and Innovative Research Team in University. References 1. Hoffmann M.R., Martin S.T., Choi W., et al. Environmental applications of semiconductor photocatalysis [J]. Chemical reviews, 1995, 95(1): 69-96. 2. Pekakis P.A., Xekoukoulotakis N.P., Mantzavinos D. Treatment of textile dyehouse wastewater by TiO2 photocatalysis [J]. Water research, 2006, 40(6): 1276-1286. 3. Yang Y., Xu L., Su C., et al. Electro spun ZnO/Bi2O3 nanofibers with enhanced photocatalytic activity [J]. Journal of Nanomaterials, 2014. 4. Qiu Y., Yang M., Fan H., et al. Nanowires of Bi2O3 phase-selective synthesis and application in photocatalysis [J]. CrystEngComm, 2011, 13(6): 1843-1850. 5. Wang X., Ren P., Fan H. Room-temperature solid state synthesis of ZnO/Bi2O3 heterojunction and their solar light photocatalytic performance [J]. Materials Research Bulletin, 2015, 64: 82-87. 198