Preparation and Photocatalytic Activity Study of p-CuO/n-ZnO composites
- PDF / 2,631,853 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 3 Downloads / 201 Views
Preparation and Photocatalytic Activity Study of p-CuO/n-ZnO composites Bedanga B Sapkota and Sanjay R Mishra Department of Physics, The University of Memphis, Memphis, TN 38152 ABSTRACT In this paper, efficacy of p-n junction p-CuO/n-ZnO composite is assessed as a potential photocatalyst by monitoring degradation of methylene blue (MB) in the presence of UV light. The p-n junction photocatalyst, p-CuO/n-ZnO, was prepared by ball milling of ZnO and CuO in water. The structural properties of p-CuO/n-ZnO composite were characterized by x-ray diffractometer and surface charge properties via zeta potential measurement. The degradation of MB in the presence of composite powder was monitored via UV-vis spectrometer. Various studies affecting the degradation rate of MB were conducted as a function of weight fraction of CuO in the composite and ball milling time. The highest degradation rate of MB was achieved in CuO (10 Wt.%)/ZnO for which high negative zeta potential was recorded. The MB degradation efficiency was found to decrease with the samples ball milled for time longer than 12 hours due to increased agglomeration of particles. The mechanisms that influence the photocatalytic activity of p-CuO/n-ZnO are discussed based on the p-n junction principle. INTRODUCTION In recent years, the photocatalytic degradation of various kinds of organic and inorganic pollutants using semiconductor powders as photocatalyst has been extensively studied [1]. ZnO, a traditional n-type semiconductor has been widely used as a photocatalyst owing to its high activity, low cost, and environmentally friendly features [2,3,4]. However, the photocatalytic activity of ZnO is limited to irradiation wavelengths in the UV region because ZnO semiconductor has a wide band-gap of about 3.37 eV and can only absorb UV light with wavelengths below 391 nm. Some problems still remain to be solved in its application, such as the fast recombination of photo-generated electron-hole pairs. Therefore, improving photocatalytic activity (PCA) by surface modification has become an important topic among researchers in recent years [5,6,7,8,9]. One approach is to dope transition metals into ZnO, and the other is to form coupled photocatalyst [10,11,12,13,14]. CuO (Eg: 1.85 eV), a p-type semiconductor, can be used in conjunction with ZnO to further improve its PCA. The enhanced PCA is anticipated from the improved junction potential between ZnO-CuO, which helps in efficient electron/hole (e-/p+) pair charge separation upon excitation. The n-n type composite photocatalyst, such as ZnO/TiO2, SnO2/ZnO, SnO2/ TiO2 and WO3/ TiO2, and so on have been investigated extensively. However, the study of the p-n type composite photocatalyst is limited. Theoretically, when p-type semiconductor CuO and n-type semiconductor ZnO form p–n junction, the inner electric field will be formed at the interface. At the equilibrium, the inner electric field makes p-type semiconductor CuO region have the negative charge, while ZnO region have the positive charge. Under near UV illumination, e
Data Loading...
