The Regulation Of Nano Zinc Oxide For Its Photocatalytic Performance

ZnO,as a semiconductor material,has direct bandgap and possesses excellent physical and chemical properties.It has been applied in many field,such as printing and dyeing,catalyst,antibacterial material,photovoltaic materials and so on.We focus on the photocatalytic degradation of dyes.In this paper,conducted by the theory of semiconductor heterojunction and crystal defects,preformed through compositing and doping respectively,regulation of nano zinc oxide for its photocatalytic performance has carried out from positive and negative two aspects.The main work and achievement are as follows:Firstly,in the semiconductor heterojunction,hydrangea-like silver bromide/zinc oxide(Ag Br/ZnO)nanocomposites were synthesized using a one-pot method.The analytical instruments were used to characterize the structure,morphology and properties of the samples.Besides,the forming process was also studied.The results are as follows:(1)In the synthesis process,PVP plays the role of dispersing agent and the metastable state of the Ag Br colloid was first formed.The formation of ZnO could break the state and induce Ag Br NPs to precipitate on the surface of ZnO NPs.The colloidal Ag Br NPs do not serve as cores although they are formed first.This could be attributed to the steric hindrance effect of PVP.Under the influence of TEOA,the clusters assemble together into a hydrangea like aggregation.(2)The formation of the porous structure of the samples can be attributed to the hydrangea-like structure.The specific surface area of the samples were more than three times than those of traditional ZnO materials.Besides,the nanocomposites exhibit a broader absorption than pure ZnO.With the Ag Br attached on the surface of ZnO,the emission intensity significantly decreases.The sample with 30% Ag Br amount behaves the best photocatalytic activity.Secondly,in the doping control,Mg、F co-doped ZnO nanoparticles were synthesized by precipitation method.And the photocatalytic activity was also studied.In order to understand the effect of magnesium and fluorine element,respectively,the Mg doped ZnO and the F doped ZnO samples were synthesized.The structure,defect and properties of the samples were discussed.The results are as follows:(1)The particle size of Mg、F co-doped ZnO samples is about 100 nm.And the morphology is hexagon.The main forms of Mg and F are F-Mg,F-Zn,Mg-O etc..This is due to the instead of lattice Zn by Mg,while the F replace the O lattice sites.The sample with 4% Mg、F co-doping amount behaves the strongest inhibition effect.(2)All Zn1-x Mgx O samples exhibit high photoactivities comparable to pure ZnO.The sample with 3% Mg doping amount behaves the best photocatalytic activity.On the one hand,the substitution of Mg ions at Zn sites shifted the conduction band toward higher energies and enhanced the photocatalytic activities.On the other hand,the concentration of oxygen vacancies increased.And they could capture the photogenerated electrons to promote the separation of carriers.(3)Photocatalytic results showed that the F-doped ZnO had lower photocatalytic property than that of pure ZnO,the sample with 4% F doping amount behaved the strongest inhibition effect.On one hand,the replacement of lattice O by F led to the formation of the Fo·defect which caused the reduction of oxygen vacancies.On the other hand,passivation effect of F reduced the formation of Os2-/Os-surface state,and thus hindered the movement of photogenerated hole to the surface of ZnO.Therefore,fluorine element plays a dominant role in the Mg、F co-doped ZnO nanoparticles.It is believed that the study could provide ideas for controlling the photocatalytic property of ZnO in practice.