Study On Preparation And Photoelectrochemical Properties Of Cu/Zn Composite Oxide Films On A Brass Substrate

Metal oxides as semiconductor materials are widely used in the field of photoelectrocatalysis.CuO and Cu2O are both p-type semiconductors;the band gap of them were 1.2 eV and 1.9?2.2 eV respectively.They can absorb visible light,and be used as visible light photocatalysts.Zinc oxide(ZnO)is an n-type semiconductor material with a band gap of 3.37 eV.Composite films made up with CuO/ZnO or Cu20/ZnO both show good photocatalytic/photoelectrochemical properties.The main components of brass are Cu and Zn,which can form oxides such as CuO,Cu2O and ZnO on the surface,which has great advantages in preparing composite metal oxide semiconductors.In this paper,we studied the process of preparing copper/zinc composite oxide films on brass substrates by oxalic acid etching and the influence of etching conditions on the photoelectrochemical properties of the films.The morphology,structure and composition of the films were characterized by scanning electron microscopy(SEM),X-ray powder diffraction(XRD),laser Raman spectroscopy(Raman)techniques,transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).And the photoelectrochemical properties of the samples were tested by photocurrent-time curve method in 0.1 mol�L-1.The main research contents and results were following:1.Effects of acid type.To prepare a copper/zinc oxide films,the surfaces of the brass pieces were etched with 10%phosphoric acid(1.6 mol�L-1),acetic acid(1.7 mol�L-1)and oxalic acid(1.1 mol�L-1)at 60 ? for 24 hours,following by calcined in a muffle furnace at 300 ? for 2 hours.Compared with the brass sample calcined directly by heating,the photocurrents of acid-etched samples was enhanced.Among them,the samples treated with 10%oxalic acid showed the largest cathodic photocurrent,which are lamellar and massive structures,and composed of CuO,Cu2O and ZnO.2.Effects of oxalic acid concentration.The morphologies of the oxide film prepared by etching in 0.1?15%oxalic acid solutions at 60 ?are also composed of lamellar and massive structures.With the increase of the concentration of oxalic acid,the photocurrent first increase and then decreased.When the concentration of oxalic acid is 10%,the photocurrent of the oxide film prepared is the largest.However,as the concentration of oxalic acid continues rising,the photoelectrochemical performance of the oxide film decreases.3.Effects of preparation temperature.The morphology and structure of oxide film prepared in 10%oxalic acid solution,at the temperature range of 20?80 ? is basically the same.With the increase of the temperature,the photocurrent of the sample first increase and then decrease,too.The photocurrent of the oxide film prepared at 60 ? is the largest,which is-19.10 ?pA�cm-2 at zero bias.4.Effects of acetic acid.In order to further improve the photoelectrochemical properties of the samples,a small amount of acetic acid were add to the oxalic acid solution.It was found that the addition of acetic acid did not significantly change the morphology and structure of the sample,but it caused obvious dissociation of the massive particles on the surface and led to a significant increase of the photocurrent of the sample.However,acetic acid concentration is too large,the photocurrent of the sample will be reduced.When 1%acetic acid solution was added to 10%oxalic acid solution,the photocurrent density of the oxide film measured is-42.19 ?A cm-2 at zero bias.