The Study On Preparation And Photocatalysis Of Nanometer Zinc Oxide

In this article,the methods of polyacrylamide-gel,sol-gel and homogeneous precipitation in preparation of nanometer ZnO powder were studied in detail.The influence of ion implantation on particle size,appearance and photocatalysis performance of nanometer zinc oxide was researched,which have been separately characterized by X-ray powder diffractometer,transmission electron microscope and ultraviolet spectrophotometer.The experimental result was listed as follows.Well-crystallized and high-purity nanometer ZnO powders were all obtained by polyacrylamide-gel method,sol-gel method and homogeneous precipitation method, and the patterns of nano-ZnO particles all belonged to hexagonal system in type of zincite structure.But every method has its advantage and disadvantage respectively as the limit of technological conditions.The production cycle of polymer network method is quite short(it is about 15h),but the cost is much higher due to the using of excessive organic reagents,moreover it is extraordinarily strict to the request of equipment.So polymer network method is difficult to realize industrialization on accout of bad repeatability.Although the cost of raw material is lower in sol-gel method,drying gelatin is quitely hard.The producetion cycle is very long(it is about 38h),and the gelatin is much easy to stick on the vessel wall to bring for a lot of inconvenience in the follwing processing.So sol-gel method is also hard to realize industrialization.The craft of homogenous precipitation is relatively simple,the production cycle is short(it is about 11h),but the grain-size distribution of nanpmeter ZnO powders is quite wide,and the reunion is quite serious.Nanometer zinc oxide was synthesized by polyacrylamide-gel method,and the mean particle size of zinc oxide powders was range from 20nm to 60nm.Overall considering the diffraction peak shape,half peak width,mean particle size,average crystallinity and energy conservation,the optimum technological conditions preparing nanometer ZnO by polyacylamide-gel method were that the ratio of monomer and lattice reagent was 5:1,the starting concentration of Zn²⁺ions was 0.35 mol/L,the ratio of reaction initiator content and the monomer double-bond was 1:20(mol ratio),the range of pH value was 5～6,the reaction temperature was at 80℃,reaction time was for 2h,the dry temperature was at 100℃,the drying time was for 4h,the heat treatment temperature was at 650℃.The pure nanometer zinc oxide of smallest grain size was synthesized by sol-gel method,when the heat treatment was for 550℃.The heat treatment temperature had a directly influence on the crystallization and grain size.With the increasing of heat treatment temperature,the mean particle size of nanometer zinc oxide decreased firstly and increased afterwards,while the average crystallininty presented opposite trend.La³⁺ion dopant would immediately influence the grain size of nanometer zinc oxde.When the La³⁺ion dopant was 0.2%,the smallest mean particle size of nano-ZnO was acquired,the size of which is 21.27nm.But when the content of La³⁺ ion dopant surpassed the fixed quantity,the grain size of nanometer zinc oxide would increase again.The pure nanometer ZnO powder and Bi³⁺-doped nanometer ZnO powder were synthesized by homogeneous precipitation method.The pattems of them all belonged to hexagonal system in type of zincite structure.Bi³⁺-doping has not changed the crystal system structure,but had an influence on the grain appearance. Besides spherical appearance,massive clavate strunctrure was arised,the length of which was range from 30nm to 200nm.The result of photocatalysis performance of nanometer zinc oxide indicated that La³⁺ion dopant has a distinct improvement to the photocatalysis performance of nanometer zinc oxide,compared with pure nanometer zinc oxide.With the increasing of La³⁺ion dopant,the photocatalysis performance of nanometer zinc oxide increased firstly and decreased afterwards.When the La³⁺ion dopant was 0.2%, light application time was 15min,the degradation ratio of methylene blue reached the highest 68.31%.while Bi³⁺ion dopant presented opposite trendency,which reduced the photocatalysis performance of nanometer zinc oxide.When the light application time was 80min,the degradation ration of MB decreased from 68.26%to 10.02%.But the photocatalsis activity improved with increasing of Bi³⁺ion dopant. When the Bi³⁺ion dopant reached to 3%,photocatalysis degradation ratio rasied to 46.98%again.