| The rapid development of various industries at the beginning of the 21st century has been leading to the fast growing amount of wastewater at the speed which never been observed in the past.Photocatalytic technology has the advantages of low energy consumption,easy operation and reducing secondary pollution,so it is widely applied on the treatment of water pollutants.Semiconductor photocatalyst is widely used as photocatalyst because of its good photocatalytic performance.The common semiconductor photocatalysts are TiO2,MnO2,SnO2,WO3,Fe2O3 and etc.Co3O4 has been widely used as a new efficient semiconductor material in the field of photocatalysis among various metal oxide photocatalysts,studied at present.In order to improve the photocatalytic activity of Co3O4 materials,a great deal of researches have been done on the doping and noble metal loading of Co3O4 materials at home and abroad.In this paper,the preparation of Co3O4/ZnO composites was studied,and their photocatalytic properties were studied by degradation of methyl orange?MO?.The details are as follows:?1?Preparation of Co3O4 particles with high photocatalytic activity.The preparation process of Co3O4 particles was optimized by orthogonal experimental method with Co?NO3?2·6H2O and 28 wt.%NH3·H2O as raw materials and nickel foam as matrix by hydrothermal thermal decomposition method.The precursor Co?OH?2 was prepared by hydrothermal method at different temperatures?80?C,100?C,120?C?and different heating time?8h,10h,12h?.Then the precursor Co?OH?2 was calcined for 1 h at different temperatures?250?C,350?C,450?C?to obtain Co3O4 particles.The results of X-ray diffraction?XRD?and Fourier transform infrared spectroscopy?FTIR?showed that Co3O4 with high purity is successfully prepared by hydrothermal thermal decomposition method.The degradation rate of MO by different Co3O4 particles irradiated by ultraviolet light was taken as the test index.The orthogonal test data were analyzed by variance method and range difference method.The results show that calcination temperature has the greatest effect on the photocatalytic properties of Co3O4 particles.The optimum conditions for the preparation of Co3O4 were hydrothermal temperature of 120?C,hydrothermal time of 10 h,calcination temperature of 250?C.The photocatalytic activity of the prepared Co3O4 sample was the best,and the degradation rate of Co3O4 was 18.13%in 72 h.The optimum reaction conditions were as follows:the hydrothermal temperature was 120?C,the hydrothermal time was 10 h,and the calcination temperature was250?C.?2?Preparation and properties of micro-and nano-sized Co3O4/ZnO composite particles with high photocatalytic activity.On the basis of orthogonal hydrothermal decomposition experiment,combined with impregnation and calcination method and Zn?CH3COO?2·2H2O as ZnO precursor,micro and nano Co3O4/ZnO composite particles with nickel foam as matrix were successfully prepared.The effects of Zn?CH3COO?2·2H2O concentration on the morphology,structure and photocatalytic properties of Co3O4/ZnO composite particles were investigated.The structure and morphology of the samples were characterized by X-ray diffraction?XRD?,Raman spectroscopy?Raman?,scanning electron microscopy?SEM?and X-ray energy dispersive spectroscopy?SEM-EDS?.The results show that the purity of Co3O4/ZnO composite particles prepared by this method is high.The morphology of Co3O4/ZnO varies greatly with the concentration of Zn?CH3COO?2·2H2O.Co3O4/ZnO composite microparticles with high purity were prepared at different Zn?CH3COO?2·2H2O concentrations.When the concentration of Zn?CH3COO?2·2H2O is 35 mM,the prepared Co3O4/ZnO-35 is a heterostructure sphere with a diameter of 20?m and is assembled from many nanosheets with thickness of 100200 nm.The photocatalytic activity of Co3O4/ZnO was higher than that of pure Co3O4.With the increase of the concentration of Zn?CH3COO?2·2H2O,the photocatalytic performance of Co3O4/ZnO increased firstly and then decreased.The photocatalytic performance of Co3O4/ZnO-35 is the best,and the degradation rate of methyl orange is 89.38%after 72 h.This is mainly due to the fact that its special morphology provides a larger specific surface area,thus providing more active sites for photocatalytic reactions,resulting in its high photocatalytic activity.Meanwhile,the p-n junction formed at the interface between Co3O4 and ZnO can reduce the recombination of photogenerated electrons and holes,and improve the photocatalytic activity.?3?Investigation of photocatalytic mechanism of micro-and nano-sized Co3O4/ZnO composite particles.The effects of different light intensities and trapping agents?silver nitrate,triethanolamine and isopropanol?on the photocatalytic properties of Co3O4/ZnO were studied.The results show that Co3O4/ZnO can produce electron hole pairs under ultraviolet irradiation,and can effectively realize the transfer and separation of electron-hole pairs.With the increase of light intensity,the photocatalytic activity of Co3O4/ZnO composite particles is improved.When the light intensity is 90 W,the degradation rate of methyl orange can reach 97.26%after72 h.In the process of photocatalytic degradation of methyl orange?MO?by the micro-and nano-sized Co3O4/ZnO composite particles,the active species h+produced by the separation of electrons and holes plays a major role.After adding h capture agent?triethanolamine?,the degradation rate of methyl orange is 30.55%after 72 h. |
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