Photocatalytic degradation of phenol and 2,4-dichlorophenol using rare earth-doped zno hierarchical micro/nanospheres under fluorescent light and sunlight irradiation
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Date
2014
Authors
Jin Chung, Sin
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Abstract
Widespread concerns continue to be raised about the impacts of exposure to chemical compounds with endocrine disrupting activities. To date, the percolation of endocrine disrupting chemical (EDC) effluent into the aquatic system remains an intricate challenge abroad the nations. Heterogeneous photocatalysis using ZnO hierarchical architectures has recently been emerged as an efficient and feasible technology for the purification of polluted water. In this study, ZnO hierarchical micro/nanospheres doped with rare earth ion (RE/ZnO, RE ion = Ce, Eu and Nd) were synthesized using a chemical precipitation method for the photocatalytic degradation of two EDCs, namely phenol and 2,4-dichlorophenol (2,4-DCP) under fluorescent light and sunlight irradiation. The as-synthesized ZnO photocatalysts were well crystalline and accumulated by large amount of interleaving nanosheets. The RE doping shifted the light absorption of ZnO to longer wavelengths and narrowed the band gap. Under fluorescent light irradiation, the ZnO hierarchical micro/nanospheres exhibited excellent phenol degradation compared to the solvothermally synthesized ZnO nanorods and commercial TiO2. The photocatalytic activity of the synthesized ZnO was further improved by doping with the studied RE ion. The Nd/ZnO exhibited the best performance in the fluorescent light degradation of phenol among the RE/ZnO samples. The optimum doping content of the Ce, Eu and Nd ions was found to be 1.5%, 2.0% and 2.0%, respectively. Moreover, the
adequate calcination temperature for Nd(2.0%)/ZnO was 450oC. The Nd(2.0%)/ZnO also showed favourable recycle use potential because they could settle out of solution within 2 h after irradiation and their photocatalytic activities were still more than 77% after three cycles of reaction. The 2,4-DCP were also successfully photodegraded under identical conditions over the Nd(2.0%)/ZnO. Operating parameters such as initial substrate concentration and solution pH were also investigated. Several degradation intermediates were also detected using high performance liquid chromatography (HPLC) on the photocatalytic degradation of phenol and 2,4-DCP. The kinetic analysis of the EDCs degradation over Nd(2.0%)/ZnO fitted well by first-order kinetics represented by the Langmuir-Hinshelwood model. The electrical energy per order results for EDCs degradation showed that the Nd(2.0%)/ZnO was useful than the pure ZnO and commercial TiO2 in decreasing energetic cost of wastewater treatment. Under sunlight irradiation, considerable photocatalytic activities were also observed on the Nd(2.0%)/ZnO in comparison to pure ZnO and commercial TiO2. Finally, the degradation efficiencies of 2,4-DCP were found to be higher than phenol under fluorescent light and sunlight irradiation.