| As important functional materials,metal oxides are widely used in the field of photocatalysis.ZnO is an important n-type semiconductor material with a forbidden band width of 3.37 eV.It is rich in natural resources,non-toxic and stable,exhibits good properties of optical,magnetic,electrical and piezoelectric.FTO is F-doped SnO2,a kind of transparent conductive material,diffusely used as liquid crystal display,solar cell substrate,photocatalytic material,and so on.In this paper,the photoelectrochemical properties of Sn-doped ZnO composite films prepared by electrodeposition-thermal oxidation on FTO substrates were investigated.The deposition current density,deposition time,add polyethylene glycol into photoelectric and thermal oxidation conditions were investigated,to study the effect of ZnO thin film photoelectrochemical performance under different preparation conditions.The morphology,structure and composition of the films were characterized by scanning electron microscopy?SEM?,X-ray powder diffractometry?XRD?,X-ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?,and photoluminescence?PL?.The photoelectrochemical properties of the samples were tested in time-current curve in0.2 mol·L-1 Na2SO4 solution at zero bias.The main research contents and results are as follows:1.The influence of electrodeposition current density and deposition time.The zinc plate used as counter electrode,the FTO as the working electrode,set the deposition current density form 1.0 mA/cm2 to 9.0 mA/cm2,deposited 100 s to obtain the metal zinc film,and then oxidized at 600°C for 2 h in air atmosphere transformed to ZnO.The results show that all films exhibit typical n-type semiconductor photocurrent characteristics.As the current density increase,the photocurrent of the obtained ZnO film first increases and then decreases.The surface morphologies of the films are porous with agglomerated nanoparticles with a few one-dimensional nanoneedle.The pores are gradually packed,and the size of nanoparticles increases with the current density increases.The photoelectrochemical property of the film obtained at 7 mA/cm2 is the best.Control the deposition current density at 7 mA/cm2,with the increase of deposition time from 100 s to 400 s,the photoelectrochemical performance of the sample first increases and then decreases,The photocurrent of the oxide film prepared at 7.0 mA/cm2 for 300 s is the largest.Therefore,the parameters of 7.0 mA/cm2 and depositing 300 s are selected to prepare the Zn film.2.The impact of the heat treatment process.The electrodeposited Zn films are heated at 100?to 700?for 2 h,the metal Zn phase in the film gradually transformed to ZnO phase as the temperature increases.At 300?,the film simultaneously present metal Zn and ZnO phases.Above 400?,the film is composed of only zinc oxide phase.The photocurrents of the oxide films are gradually increases then decreases with calcined temperature raised from 300?to700?.The photocurrent of the zinc oxide film obtained at 600?is largest.The substrate FTO will deformed at 700?due to the excessive heat treatment.Controlled heated at 600?for 2 h,the photocurrent of the film increases first and then decreases as heating rate changes form 5?/min to 80?/min.The films prepared at different heating rates are consists of nanoparticles and nano-needle,and the number of nano-needle increases with heating rate increases.At 50?/min the photocurrent of the film is the largest.So we selecte 600?keep 2 h and the heating rate is 50?/min as the optimum heat treatment condition.3.Effect of additive polyethylene glycol?PEG?.The Zn films electrodeposited with different concentrations of PEG in electroplating solution,and the ZnO samples obtained by thermal oxidation.The ZnO films all showed the presence of nanoparticle aggregates accompanied by nano-needle.The morphology and structure of the samples did not change significantly with the change of PEG concentration,but the photocurrents of the ZnO films first increases and then decreases.The photocurrent of the film electrodepsited in an electroplating solution containing 0.05g/L PEG is the largest.XPS and TEM analysis showed that the ZnO films are Sn doped,which should be derived from the FTO substrate.The results of PL and XPS analysis revealed that the concentration of oxygen defects and tin doped are changed in the films prepared with different PEG concentrations. |
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