Preparation And Optical Properties Of ZnWO₄ Microcrystals

With the progress of human being and the development of industry,Dye wastewater pollution has become increasingly serious.In order to provide a good living environment for human beings,it is urgent to develop clean and pollution-free new materials.As a kind of inorganic material,zinc tungstate has been studied at home and abroad,It has a good effect on the degradation of dye wastewater.In view of this,the purpose of this thesis is to study the preparation and photocatalytic properties of zinc tungstate?ZnWO₄?nano crystalline materials.The optimum formula for the preparation of ZnWO₄ nanocrystals were studied by molten salt method and hydrothermal method,respectively.At the same time,the properties of zinc tungstate were studied by means of doping modification,and the degradation efficiency of methylene blue under different preparation conditions and different morphologies was discussedIn this paper,zinc tungstate?ZnWO₄?nanocrystals were successfully prepared by molten salt method.The phase composition,particle size and microstructure of the products were characterized by XRD,SEM,and TEM respectively.The results showed that:pure ZnWO₄ nanocrystals were synthesized at about 200?⁴00? for 12 h in a NaNO₃-LiNO₃ salt system with Na₂WO₄·2H₂O and Zn?NO₃?2·6H₂O as raw materials.Flaky powder generated flower when the temperature reaches 500?;there is a close relationship between the morphology of ZnWO₄ particles?the calcination temperature and the holding time,with the increasing of temperature,the evolution of morphology:Equiaxed nano particles?200 ??-Short rod like nanocrystals?300 ??—Equiaxed micron crystals?400 ??;With the prolonging of the holding time,the evolution of particle morphology is changed into short rod like nano crystals?12 h?by the Equiaxed nanoparticles?8 h?.Secondly,the optimum growth mechanism of ZnWO₄ powders were studied by the hydrothermal method.The products were tested by XRD,SEM and TEM.The results show that:pure phases of ZnWO₄ were synthesized at pH of 5,7,9 at 180 ? for 8 h with Na₂WO₄·2H₂O and Zn?NO₃?2·6H₂O as raw materials,respectively.At the same time,the morphology of ZnWO₄ particles is closely linked to the pH value.With the increase of pH value,the evolution process of particle morphology is:equiaxed nanoparticles?pH=5?—short rod like nanocrystals?pH=7?—rod like nanocrystals?pH=9?.Followed by hydrothermal method and molten salt method,The ZnWO₄ powders with different morphologies and properties were successfully prepared,and doped with different content of MoO₃ and carbon nanotubes?CNT?.The photocatalytic properties of ZnWO₄ powders synthesized under different conditions were tested by degradation of methylene blue solution?Methylene blue,MB?.Research shows that:the MB solution can be degraded from blue to colorless in a certain period of time by doping MoO₃ and CNT samples with different contents.When the content of doped MoO₃ was 2%,the degradation rate of MB solution reached to 96.73%after 180 min.Similarly,when the doping amount of carbon nanotubes is 2%,the degradation efficiency is the best,the degradation rate is about 97.04%.The doped samples synthesized by the molten salt method have good photocatalytic properties,but the performance is related to the grain size and morphology.