Improvement of catalytic activity and mechanistic analysis of transition metal ion doped nanoCeO 2 by aqueous Rhodamine
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We compared the enhancement of photoactivity of transition metal ion (1 mol% Fe, Cu, Mn, and Zn) doped CeO2 nanocatalysts, and examined the effects of oxygen vacancies and the valence of the doped ions. The nanocatalysts were synthesized using a coprecipitation method and were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller isotherm methods and Raman spectroscopy. The photocatalytic activities of these catalysts were tested using aqueous Rhodamine B (RhB) degradation under UV irradiation. The spherical CeO2 nanocatalysts had a mesoporous structure and ;15 nm average particle size. The catalytic activity was closely related to the oxygen vacancies and the valence of the doped ions. An increase in oxygen vacancies of doped CeO2 decreased the photocatalytic activity. The photocatalytic activities of the catalysts decreased in the order: 1 mol% Fe . Cu . Mn . Zn . undoped CeO2. The 1 mol% Fe doped CeO2 degraded ;92.6% of the RhB after 3 h of irradiation, and the degradation obeyed pseudo-first-order kinetics. Liquid chromatography–mass spectrometry indicated that the photodegradation of RhB was a stepwise oxidation process. Under continuous oxidation, over a long reaction time, the RhB was completely oxidized to its final products, such as water and carbon dioxide.
I. INTRODUCTION
The removal of dyes from wastewater has attracted attention because dye effluents from the coloring, food, and textile industries can cause severe damage to the aquatic ecosystem and human health.1,2 Various dye removal techniques include adsorption, flocculation, advanced oxidation processes, photodegradation, and biodegradation.3–7 An alternative technique is photocatalytic degradation, which is an efficient, inexpensive, and clean method.8,9 Researches showed that the nanostructure materials of TiO2, ZnO, CdS–TiO2, etc., are very good photocatalysts, which have been widely applied in environmental pollution removal and photocatalytic hydrogen generation.10–13 Up to now, TiO2 is the most widely used photocatalyst, but its band gap often limits its use of solar irradiation.14,15 The Ag/Au doped composite nanocatalysts enhance the photocatalytic activity due to a better separation of photogenerated charge carriers and improves the oxygen reduction,16,17 while the cost is too high. Recently, several semiconductor materials have been studied for photoactivity enhancement, such as spinel-type ferrite (AB2O4),18 perovskite-type
Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.263
oxide (ABO3),19 and other transition metal oxides.20,21 However, most of these are limited by narrow band gaps, biological toxicity, or low separation rates between photogenerated electrons and holes. Cerium dioxide (CeO2) is a widely used photocatalyst because of its high chemical stability, low biological toxicity, and large oxygen storage capacity.22 However, the application of CeO2 photocatalysts is limited by its rel
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