Preparation And Characterization Of Magnetic Dy（OH）₃ Modified ZnO Composite Photocatalyst

With the development of society,people’s demand for a better ecological environment is growing.However,the discharge of industrial production wastewater and domestic wastewater poses a serious threat to the safety of water environment.As an advanced oxidation process,photocatalytic technology has attracted great attention due to its low energy consumption,green environmental protection,high efficiency,etc.Traditional photocatalyst zinc oxide has many advantages,such as non-toxic,low preparation cost,good biocompatibility,etc.However,the wide band gap and high recombination rate of photogenerated electrons limit the photocatalytic activity of ZnO,and it is difficult to recover in water.It needs to be modified if it is to be used in practical production.Thus,this paper takes ZnO as photocatalysts,Sr Fe₁₂O₁₉ as magnetic matrix,and as Dy（OH）₃ electron trapping agent,to prepare ZnO/Sr Fe₁₂O₁₉,Dy（OH）₃/ZnO,Dy（OH）₃/ZnO/Sr Fe₁₂O₁₉ photocatalysts by hydrothermal method.XRD,TEM,SEM and UV Vis DRS were used to characterize the structure,micro morphology and photoelectrochemical properties of the samples.The degradation of Rhodamine B（Rh B）under simulated sunlight was used to evaluate the photocatalytic activity of the materials.The main results are as follows:ZnO/Sr Fe₁₂O₁₉（ZS）composite magnetic photocatalysts with different mass ratios were prepared by a two-step hydrothermal method.The photocatalytic activity of ZS-5(mass ratio of Sr Fe₁₂O₁₉ was 5%)was the best.After 70 min,it can degrade 99.5%Rh B.The results of micro morphology show that the ZS composite is composed of irregular sheet ZnO and hexagonal Sr Fe₁₂O₁₉ nanosheets.Compared with pure ZnO,the specific surface area of ZS-5 is slightly reduced,the optical absorption range is increased,the band gap is shortened,the recombination rate of photogenerated charges is significantly reduced,and the conductivity is enhanced.The saturation magnetization of ZS-5 is 4.0emu/g,indicating ZS-5 has the ability of magnetic separation.The results of recovery experiment showed that the degradation rate of Rh B by ZS-5 was still above 90%after five cycles,proving the great stability.Combined with the results of free radical capture experiment,the possible mechanism of photocatalytic reaction of ZS-5 complex was proposed.Under the photosensitization of Sr Fe₁₂O₁₉,ZnO is more easily excited to produce electron-holes,which react with water and dissolved oxygen in solution to form?OH和?O₂^-.Rh B was completely degraded by?OH、?O₂^-and h⁺,in which?OH played a major role.Dy（OH）₃/ZnO（DZ）composite photocatalysts with different composite ratios were synthesized by a simple one-step hydrothermal method.Among all the samples,15-DZ（Dy（OH）₃ accounted for 15%）showed the best photocatalytic efficiency,and the degradation rate of Rh B reached 99.8%in 70 min.The microstructure of the samples tells that the DZ composite is composed of rod-shaped Dy（OH）₃ crystal and irregular ZnO nanosheets.Compared with pure ZnO,the specific surface area of 15-DZ slightly decreased,the recombination rate of photogenerated carriers dramatically decreased and the conductivity was significantly enhanced.The band gap of Dy（OH）₃ is 5.0 e V,which is difficult to be excited by visible light,but the optical response range of DZ complex is not affected.The photodegradation mechanism of 15-dz sample is proposed.The electrons generated by the excited ZnO are trapped by the f-shell conduction band of Dy（OH）₃,while the holes remain in the valence band of ZnO,thus realizing the electron hole separation.The hole in ZnO valence band reacts with water to form?OH,which further degrades Rh B.After five cycles,the degradation rate of Rh B by 15-DZ remained above 97%,proving the high photocatalytic stability.The Dy（OH）₃/ZnO/Sr Fe₁₂O₁₉（DZS）ternary composite magnetic photocatalyst was prepared by adding Sr Fe12o19 into the preparation of Dy（OH）₃/ZnO binary composite.Among all the complexes,15-DZS-5(Dy（OH）₃ 15%,Sr Fe₁₂O₁₉ 5%)had the highest photocatalytic activity,and could completely degrade Rh B after 70 min.The results of kinetic analysis showed that the first-order kinetic constant（k）of 15-DZS-5was significantly higher than that of DZ and ZS,and the k value of the complexes were all higher than that of single-phase ZnO,which revealed the synergistic effect of Dy（OH）₃ and Sr Fe₁₂O₁₉ on the photocatalytic activity of ZnO.Compared with the optimal samples of ZnO and two-phase composite,15-DZS-5 has the smallest specific surface area,the widest photoresponse range,the narrowest band gap,the lowest electron hole recombination rate and the best conductivity.On the one hand,the optimization of DZS performance is due to the photosensitization effect of Sr Fe₁₂O₁₉,which promotes the response of ZnO to visible light;on the other hand,Dy（OH）₃successfully separates the electrons and holes of ZnO by photoelectron capture.Both of them promote the photocatalytic reaction of ZnO based semiconductor.In addition,the saturation magnetization of 15-DZS-5 is 3.9 emu/g,and the degradation of Rh B is over88%after five cycles,showing good magnetic recovery and stable photocatalytic activity.