Preparation Of ?-Fe₂O₃/ZnO Composites And Their Photocatalytic Property

ZnO is an important wide band-gap semiconductor material,the band-gap?3.37 eV?of which is almost the same as that of TiO₂,and it also has inexpensive,non-toxic properties.In spite of the fact that there has been more and more reports about ZnO photocatalysts.It is still a great challenge to further enchance the photochemical stability and the photocatailtic activity of ZnO.Metal/non-metal ions doping,semiconductor compositing,precious metals depositing are common ways to improve the performance of ZnO photocatalysts.?-Fe₂O₃ is a semiconductor material with the narrow band gap of 2.2 eV.It can absorb visible light,but the photo-absorption efficiency is not high.In addition,it also has stable,inexpensive,environment-friendly features.Basted on the characteristics of ZnO and?-Fe₂O_3,coupling of?-Fe₂O₃ and ZnO is a good way to improve the photocatalytic performance of ZnO for the existence of?-Fe₂O₃ is helpful in extending the optical absorption range of ZnO and promoting the separation of photo-generated electron-hole pairs.Pure ZnO,pure?-Fe₂O₃ and?-Fe₂O₃/ZnO composites with different particle sizes and morphologies were obtained by boiling reflux method in the absence of surfactants and templates.The products were characterized by XRD,FESEM,FTIR and UV-vis DRS.Photocatalytic activity of the as-prepared samples were evaluated by degradation of cadmium black T and methylene blue under energy saving lamp irradiation.The main contents are as follows:Firstly,using Zn?NO₃?₂ and NaOH as reactants,a series of ZnO particles with different morphologies,such as sphere-/rugby-like,spine-like,flower-like and comb-like,were successfully synthesized by varying the solution alkalinity.Experimental results indicated that the sphere-/rugby-like and flower-like ZnO exhibit relatively high photocatalytic activity.Secondly,using Zn?NO₃?₂,Fe?NO₃?₃ and NaOH as reactants,a series of rod-like?-Fe₂O₃/ZnO composites with different?-Fe₂O₃ contents were prepared.The photocatalytic activity of the composites was evaluated by photocatalytic decolorization of cadmium black T.The results showed that the existence of the?-Fe₂O₃ affects the morphology of ZnO particles,which changes from sphere-/rugby-like to rod-like.Meanwhile,some nanoparticles with mean size of 10 nm are firmly deposited onto the nanorods.With the rising mole ratio of?-Fe₂O₃ to ZnO,nanorods progressively grow smaller while more and more nanoparticles distribute on the surface of the nanorods.Compared with pure ZnO,the?-Fe₂O₃/ZnO composites show higher photocatalytic activity in cadmium black T degradation,and the best mole ratio of?-Fe₂O₃ to ZnO is 1:5.Thirdly,using Zn?NO₃?₂,Fe?NO₃?₃ and NaOH as reactants,a series of flower-like?-Fe₂O₃/ZnO composites with different?-Fe₂O₃ contents were prepared.The photocatalytic activity of the composites was evaluated by photocatalytic decolorization of methylene blue.The results showed that the composites maintain the structure of pure ZnO,and some?-Fe₂O₃nanoparticles with mean size of 10 nm are firmly deposited onto the ZnO nanosheets.With the rising mole ratio of?-Fe₂O₃ to ZnO,more and more nanoparticles distribute on the surfaces of the nanosheets.Compared with pure ZnO,the?-Fe₂O₃/ZnO composites show higher photocatalytic activity in methylene blue degradation,and the best mole ratio of?-Fe₂O₃ to ZnO is 1:8.Fourthly,the photocatalysis mechanism of?-Fe₂O₃/ZnO composites was discussed.It is supposed that the existence of?-Fe₂O₃ is helpful in extending the optical absorption range of ZnO,promoting the efficiency of photo-induced carriers separation,increasing the life-span of the electron-hole pairs and inhibiting the recombination of the two.Therefore,the photocatalytic performance of?-Fe₂O₃/ZnO composites is better than that of pure ZnO.