Preparation And Photocatalytic Property Of Multi-stage Structural ZnO Nanomaterials

By using ginkgo leaves?GL?and pomelo peel?PP?as the template,ZnO nanomaterials with different structures-hollow spheres with porous shell and porous sheet structures with enhanced photocatalytic property were prepared via two different template-assisted two-steps methods^solvothermal-calcining and dipping-calcining.In addition,a series of ZnO/rGO composite materials were successfully prepared by solvothermal method.The phase composition,the surface structure and other properties of the target samples were characterized by some technology,such as XRD,SEM,TEM,PL,TG.Photocatalytic property of these nanomaterials was evaluated by the degradation efficiency and kinetic behavior of MB solution on the sample under 300 W high pressure Hg lamp?HPHL?.The detail contents and results of study are described as follows:?1?The hollow sphere ZnO sample with porous shell was prepared via a template-assisted two-steps?solvothermal-calcining?method.The effect of the solvothermal reaction temperature?160²00??,calcination temperature?500⁷50??,calcination time?1.0³.0 h?,the amount of template?0.0000¹.5000 g?on the photocatalytic activity of the samples was investigated.The results showed that the above conditions have different effects on the photocatalytic performance of the samples,especially the effect of the amount of template is the most significant.The photocatalytic activity of the samples prepared by introducing the template is obviously higher than that of the ZnO prepared without template,and the photocatalytic performance of the sample prepared by the template of best amount is about 6.0 times that of ZnO without template.?2?A porous sheet structure ZnO sample with enhanced photocatalytic property was prepared via a simple template-assisted two-steps?dip-calcining?method.The effect of the calcination temperature?500⁷50??,calcination time?1.0³.0 h?,soaking time?10⁶0 min?,the amount of template?0.0000³.0000 g?on the morphology and photocatalytic activity of the samples were investigated.The results showed that the above conditions have different effects on the photocatalytic performance of the samples,especially the effect of the amount of template is the most significant.The photocatalytic activity of the samples prepared by introducing the template is significantly higher than that of the ZnO prepared without template,and the photocatalytic performance of the sample prepared under the best template dosage is about 4.3 times that of ZnO prepared without template.The excellent photocatalytic property of the multi-stage structural ZnO is mainly ascribed to the follows:?1?Highly efficient adsorption and activation of reactant molecules by multi-times adsorption-desorption-adsorption on the multi-stage structural ZnO.So the multi-stage structural ZnO provides more adsorption and activation sites for the reactant molecules;?2?Efficient absorption for the reached light by repeated absorption-reflection-absorption through the porous shells and inner cavity of the porous sheet structure ZnO sample;?3?In the self-assembled structure of nanoparticles,photogenerated electron-hole pairs can be effectively separated by a variety of ways to improve their photocatalytic performance.Such as photogenerated electrons can migrate from the irradiated ZnO particles to no irradiated ones;The electrons?e^-?on the conduction band?CB?easily migrate into anti-banding?molecule orbit??^*-MO?of MB_ad molecules because CB of ZnO is above?^*-MO of MB.?3?A series of ZnO/rGO composite nanomaterials were successfully prepared by a solvothermal method.The effect of the ultrasonic time the GO before mixing?0⁵h?with zinc source and after mixing?0³ h?,GO content?0.0¹0.0 wt.%?,GO oxidation degree?GO-01^GO-03?on the photocatalytic activity of the samples were investigated.The results showed that the content and oxidation degree of GO have a significant effect on the photocatalytic performance of the composites.Moreover,the higher the content and the oxidation degree of GO,the better the photocatalytic performance of the sample,so the sample ZnO/rGO-03 has the best photocatalytic performance.The excellent photocatalytic property of the sample ZnO/rGO-03 is mainly ascribed to the follows:the quick electron transfer from excited ZnO particles to rGO sheets effectively prevents recombination of photo-generated charge carries;The activation of MB_ad molecules absorbed on rGO via?-?interaction between MB and rGO produces the activated species MB_ad^-*;The suitable GO content and the degree of oxidation not only improve the adsorption performance of the MB molecules,produce more activated molecules MB_ad^-*,but also provide the appropriate migration distance of MB_ad^-*from the rGO to the ZnO particles;Besides,ZnO-h⁺has strong oxidizing capacity.So the sample ZnO/rGO-03 relatively has the best photocatalytic performance.