Preparation And Photocatalytic Properties Of ZnO And ZnO/CeO₂ Nanocomposites

In this thesis,ZnO and ZnO/CeO₂ nanocomposites were prepared by high energy ball milling—calcination method.The photocatalytic activity of metal oxide precursors Zn₅（OH）₆（CO₃）₂ and Ce₂（CO₃）₃ was improved by high energy ball milling activation and calcination.Because Ce4+ can accept electrons into Ce3+under certain conditions,this paper attempts to combine ZnO with CeO₂,which will theoretically inhibit the recombination speed of photogenerated charge of ZnO and improve the photocatalytic activity of the composites.The main contents are as follows:1.The morphology,size and decomposition activation energy of Zn₅（OH）₆（CO₃）₂ particles were studied by wet high energy ball milling with planetary ball mill under different ball milling conditions.The results of SEM,XRD,TG and DSC showed that the milling time had a strong effect on the particle morphology,size and activation energy of thermal decomposition of Zn₅（OH）₆（CO₃）₂.Under the radio of ball to material 10:1 and 200 r/min speed,by adding 64%ethanol control agent,the morphology of the particles changed from 50μm flake to 50 nm isometric after high energy ball milling for 6 h,and the ball was milled to 24 h.There was little further change in the morphology of the product.Activation energy of thermal decomposition of Zn₅（OH）₆（CO₃）₂ after milling for 24 hours.The temperature of thermal decomposition decreased from 138.0 kJ·mol^-1 to 112.4 kJ·mol^-1,and the temperature of thermal decomposition was pushed forward by 14.8℃.2.ZnO nanoparticles with small size and high specific surface area were prepared by high energy ball milling activation of precursor Zn₅（OH）₆（CO₃）₂ and calcination at two different temperatures.The photocatalytic activity of ZnO nanoparticles obtained at different milling time（5 min,600 min,1800 min）and two calcination temperatures（300℃,900℃）was studied.The photocatalytic activity of the product was evaluated by the degradation of Rhodamine B（RhB）in simulated sunlight and visible light（λ>400 nm）.The results of photocatalysis test show that 600 min ball milling time combined with ZnO calcined at 300℃ has the highest photocatalytic performance.RhB can be degraded by 96.63%in simulated sunlight at 60 min.The results show that the average particle size of the product is as low as 10 nm,the specific surface area is 86.5 m²·g^-1 and the band gap is 3.123 eV.Through the characterization of each product,it is found that the photocatalytic activity of ZnO calcined at 300℃ is relatively high.In a certain time,the longer the milling time is,the smaller the particle size of ZnO is,the larger the specific surface area is,and the higher the photocatalytic activity is.However,after milling for more than a certain period of time,ZnO reaches crushing.Limit,agglomeration phenomenon aggravates,particle size increases,photocatalytic activity will begin to weaken.3.ZnO/CeO₂ nanocomposites were prepared by simultaneous high energy ball milling of precursors Zn₅（OH）₆（CO₃）₂ and Ce₂（CO₃）₃ and calcination at the same temperature.The photocatalytic activity of the product was evaluated by the same method as pure ZnO.The results show that the photocatalytic activity of all the products is obviously stronger than that of 300℃ at 900℃.At 900℃,the photocatalytic activity of 10 min,product reached the highest,and the photocatalytic activity began to decrease with the prolongation of milling time.This phenomenon is just related to the change law of pure ZnO.Figure[17]table[6]reference[86].