Study On Regulating Photocatalytic And Wetting Properties Of Nano-ZnO By Structure-Directing Agents

Zinc oxide(ZnO)is a direct band gap semiconductor(E_g=3.37 eV),which exhibits excellent optical properties and gas sensing characteristic,and has been widely used in the fields of nano-electronic devices,piezoelectric sensors,solar cells,photocatalysis and so on.Nowadays,ZnO possesses the most abundant nanostructures comparing to other materials.By controlling the composition and proportion of raw materials needed for reaction,various morphologies of zinc oxide nanomaterials can be synthesized.The morphology,size and shape,defect distribution,and/or specific surface area of ZnO influence their physical properties,which can directly determine materials'applications.Therefore,it is of great significance to design and synthesize the novel ZnO structures with unique properties.In this paper,a variety of novel zinc oxide microstructures and nanostructures were synthesized by hydrothermal process using different novel structure directing agents.The specific work is as follows:1)ZnO with flower-like,rod-like and spherical structures were synthesized by hydrothermal method with 2,5-dihydroxyterephthalic acid as structure directing agent.These irregular flower-like structures were staggered by a large number of nanosheets with different aspect ratios.2,5-dihydroxyterephthalic acid contributed to the formation of disordered nanosheets.XRD results show that the solution pH has a great influence on the crystallinity of zinc oxide.With the addition of NaOH,the crystallinity of samples from S1 to S5 increases first,and then decreases.With the change of zinc source and concentration of 2,5-dihydroxyterephthalic acid,the crystallinity of S7 samples is the best.The results of PL spectra show that S3,S5 and S8 have high internal defects.TEM results show that the growth rate in(002)direction can be well regulated by adjusting the amount of NaOH.The S7 samples with abundant mesoporous structure have good photocatalytic activity,which may be related to the more reactive sites on the surface.2)Zinc oxide was synthesized by hydrothermal synthesis using phenyl dicarboxylic acid as a structure-directing agent.The effects of the content of phenyl dicarboxylic acid and three related isomers on the morphology and properties of zinc oxide were studied.With the increase of phthalic acid content,the structure of zinc oxide gradually changes from spherical and rod-like to flower-like,while the ZnO morphologies from different isomers did not influenced significantly,but only difference in the crystallinity and internal defects of samples.Room temperature photoluminescence shows that there are many defects in/on the sample.According to the analysis of photocatalytic experimental data,the main factors,which affect the photocatalytic performance of samples prepared by various isomers and dyes are different,but they have potential commercial value.The trapping experiments of the scavengers show that hydroxyl radical is the main species in the photocatalytic process.3)In the experiment,zinc nitrate and hexamethylenetetramine were used as the precursors,and salicylic acid and cobalt nitrate hexahydrate were added as the structure directing agent and dopant respectively.The intermediate was first synthesized by hydrothermal method,and then Co-doped zinc oxide with a mass ratio of 1%or 3%was obtained after the calcination.XRD results show that the crystallinity of S2 is the best,and the crystallinity decreases after cobalt doping.Infrared spectra show that a small amount of organic compound may be adsorbed on the surface of the sample.PL spectra show that excessive salicylic acid can cause the quenching effect of ultraviolet emission,and cobalt doping may introduce more defects under certain conditions.In the photocatalytic experiments,1%Co-doped ZnO have good self-degradation and photocatalytic activity for MB.4)Zinc oxide nanoarrays were successfully prepared on ITO conductive glass by two-step hydrothermal method using diethanolamine,ethylene glycol and hydrazine hydrate as structure-directing agents.XRD results show that all samples grow preferentially along(002)direction,and the higher the annealing temperature,the better the preferential orientation.The effect of annealing temperature on the morphology of zinc oxide nanoarrays prepared by different seed layer solutions was studied by SEM.It was found that annealing temperature had a great influence on the preferred orientation when seed layer solutions were zinc acetate/ethanol/diethanolamine and zinc chloride/hydrazine hydrate/ethylene glycol,while the annealing temperature mainly affected the diameter and shape of the nanoarrays when seed layer solution was zinc acetate/ethanol.The analysis of wetting property shows that Y1 and Y2 have strong hydrophilicity,while Y5 and Y6 have strong hydrophobicity,which is closely related to their surface morphology.It is also found that ultraviolet light can improve the hydrophilicity of the samples.