Band Gap Tuning In ZnO And Research On ZnO/Graphene Composite

Zinc oxide（ZnO）as the basic material for doping and compounding is a typical representative of photocatalysts.Its advantages are wide source of raw materials,low cost and large-scale production.It has important applications in the field of environmental protection and new energy development.In this thesis,the preparation and properties of Mn-doped ZnO and its composites with graphene are studied,including the following three parts:（1）nano-Zn_1-x-x Mn_xO with Mn-doping gradients of 0 at%,0.5 at%,1 at%,2 at%,4at%and 8 at%were prepared by co-precipitation and argon annealing using Zn（NO₃）₂·6H₂O as raw material,Mn（NO₃）₂·6H₂O as doping source and NaOH as precipitator.X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and scanning electron microscopy（SEM）were used.The structure and properties were characterized by scanning electron microscopy（SEM）,photoluminescence spectrometer（PL）and ultraviolet-visible spectroscopy（Uv-vis）.The results showed that the defects induced by Mn doping at 0.5 at%was the most,and the visible luminescence in PL was the strongest.When the concentration was from 4 at%to 8at%,the ultraviolet luminescence was the strongest,the visible luminescence band was the weakest,and the number of effective photogenerated free electron-hole pairs was the most,which is beneficial to the photocatalytic reaction.In addition,Uv-vis absorption spectra and PL spectra show that all Mn-doped nano-ZnO enhances the band gap of ZnO,which means that the electrons and holes are more energetic.（2）Graphene oxide（GO）was prepared from high purity graphite powder with KMnO4 as intercalating agent and 98%concentrated sulfuric acid as solvent by modified Hummers method.The structure and morphology of GO were characterized by Raman spectrum,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and transmission microscope（TEM）.The results showed that the graphite powder was successfully peeled off into few layers of GO.（3）ZnO and GO composite powders with Mn doping concentration of 0 at%,4at%and 8 at%were synthesized by precipitation and argon annealing using Zn（NO₃）₂·6H₂O and GO as raw materials,Mn（NO₃）₂·6H₂O as doping source and NaOH as precipitator.Then,Mn doped zinc oxide/graphene(nano-Zn_1-xMn_xO/G)composite photocatalyst was successfully prepared after reduced under the irradiation of ultraviolet light.The structure and properties of the samples were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）and ultraviolet-visible spectroscopy（Uv-vis）,and the photocatalytic activity was compared.The results show that nano-Zn_1-xMn_xO/G has been successfully prepared.Compared with nano-ZnO,nano-ZnO/G and nano-Zn_0.92Mn_0.08O/G,nano-Zn_0.96Mn_0.04O/G has better photocatalytic performance,and its photocatalytic efficiency reaches 100%.