Enhancement of 2-chlorophenol photocatalytic degradation in the presence Co2+-doped ZnO nanoparticles under direct solar radiation
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The performance of Co2+-doped ZnO nanoparticles, prepared using the sol–gel method, for 2-chlorophenol degradation under direct solar radiation was investigated. Various parameters were investigated during the degradation process, namely solar intensity, Co2+ ion concentration, loading concentrations of Co2+-doped ZnO, and pH. The photocatalytic degradation efficiency increased when the initial concentration of 2-chlorophenol decreased; the optimum concentration was 50 mg/L under similar experimental conditions. Moreover, optimum values, established on a sunny day, were 0.75 wt% of Co2+, a 1 g/L loading concentration, and a pH of 6.0, respectively. The highest degradation efficiency observed was 95 %, after only 90 min of solar light irradiation. The mechanism of visible photocatalytic degradation using Co2+-doped ZnO was explained as a strong electronic interaction between Co2+, Co3+ and ZnO, and a promotion in the charge separation, which enhanced the degradation performance. The fragmentation of 2-chlorophenol under the optimal conditions was investigated using HPLC, comparing standards of all intermediate compounds. The pathway of the fragmentation was proposed as involving hydroxyhydroquinone, catechol, and phenol formation, which were then converted to non-toxic compounds such as oxalic acid and acetic acid with further decomposition to CO2 and H2O.
KeywordsZnO Nanoparticles Solar 2-Chlorophenol
The authors wish to thank the Research Centre for Sustainable Process Technology (CESPRO), Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia for support this study under project iconic-2014-004. Also, one of the authors (M. M. Ba-Abbad) is grateful to the Hadhramout University of Science and Technology, Yemen, for their financial support for his PhD study.
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