Controllable Preparation Of Cu₂O Thin Films For Photocatalytic Degradation Of Methylene Blue

Cu₂O is a kind of semiconductor material which bandgap is of 1.9 to 2.38 eV. It possess numerous advantages properties such as innocuous and low costs.Therefore it is considered to be one of the promising in the wastewater treatment. Since its photocatalytic efficiency is largely restricted.The coupling of semiconductor Cu₂O and wide band semiconductor TiO₂ could form Cu₂O/TiO₂ heterostructure with high catalytic efficiency.Cu₂O can not only expands the light response range of TiO₂ be from the ultraviolet region to the visible region, and the of sunlight utilization efficiency,but can also transfer photoelectrons generated of Cu₂O onto TiO₂ conduction band to Reduce the probability of holes-electron pairs which could improve their catalytic efficiency.So it has immeasurable prospect for photocatalysis application in the field of wastewater degradation.The paper proposes an electrodeposition method to prepare Cu₂O/ITO thin films and Cu₂O/TiO₂ films on ITO conductive glass.XRD, XPS, SEM, Raman, PL and UV-Vis,are used to characterized and analyzed thin films microstructure,surface morphology and banding state and optical properties respectively.The results are as follows:（1）Cu₂O/ITO Micron-thin films is prepared onto ITO conductive glass.And its structure is characterized. The results indicated that the Cu₂O of high purity, had excellent（111） surface orientation and had high photoelectric response.The absorption boundary of Cu₂O thin films are about 600-640 nm.（2）Cu₂O/TiO₂ / ITO Nano-thin films is prepared onto ITO,the preparation conditions of Cu₂O thin films are investigated as follows: pH 10.50, stirring rate is 100 rmp,deposition potential is -0.60 V（vs SCE）, and deposition time is 1.5h. The result indicate that the prepared Cu₂O/TiO₂ thin film with the preferential orientation of（111）showing high photocatalytic activity is of high-purity.The crystal structure of the sample exhibit high quality and characterized by novel Raman of nano spheres morphology.Moreover,compared to Cu₂O,the absorbance intensity of Cu₂O/TiO₂ thin film doubled when the wavelengh within 200 nm to 600 nm,which bandgap is estimated to be 2.20 eV.（3）Influence factors such as types of substrate,temperature of system,addictive agent KCl and annealing treatment for morphology and properties of Cu₂O nano film are discussed.It is found that these factors all have obvious influences on the structure and properties of Cu₂O nano film.The morphology of Cu₂O with substrate of Cu₂O/TiO₂ are changes significantly relative to the substrate of TiO₂/ITO,which proved to be dense rod-like structure with the diameter and length of crystallite about 50nm and 150～200nm,respectively.Whereas,the morphology of former is shaped as 150～200nm spheres;In addition,the morphology of Cu₂O would evolve into 1μm tetrahedral structure with higher temperature of system while the preferential orientation of which transformed from（111）into（200）;And there is a huge change by adding KCl into electrolyte,it could found that the morphology of Cu₂O composed of top and bottom layer.The top layer is spherical particles and the bottom layer exhibits dispersive 10μm flower-like morphology,and it shows novel Raman properties as well;Furthermore,the morphology of film can also change with the rising of annealing temperature,it would become 6μm flower-like structure on the top layer and spheres particles on the bottom layer first,then it would turn into 100nm undefined structure,finally the morphology would prove to be 50～100nm denser and regular spheres structure.The annealing treatment of Cu₂O/TiO₂ thin film can further enhance 60%of（111）crystal plane intensity and 50%of UV-Vis absorption intensity respectively.Moreover,the open circuit potential up from around 17.4mV to 38.7mV and the surface resistivity could decrease four magnitude order.（4）The photocatalytic performance of Cu₂O are studied as well.Based on single factor experiment,response surface methodology is employed to optimize the main influences of photocatalytic degradation by Cu₂O/ITO micron-thin film,and the quadratic multinomial mathematical model is also established.Moreover,the degradation process and photocatalytic effect of methylene blue by Cu₂O are also studied.The results indicate that R2 in the established quadratic model is 0.9888,with better fitness and higher significance.The calculated value of degradation rate is very satisfied with data of experimentation,the relative error is found only to be 0.31%.Recycling use of the catalyst revealed that the prepared Cu₂O/TiO₂ thin film can be reused for 18 times,which shows high photocatalytic activity and separation efficiency of electron-hole,and the methylene blue can be decomposed completely.After 300℃ annealing to Cu₂O/TiO₂ thin film,the reaction rate constant and the fluorescent spectrum is 2.8 and 3.4 times larger than before it is tempered.As eff-icient catalysts,more than 99.9%of methylene blue can be degraded in 3 h by Cu₂O/TiO₂ thin film.For Cu₂O/ITO thin film obtained in acid system,the film can be reused for 11 times.Only 74.5%of methylene blue can be degraded while the catalytic activity improved greatly after electronic aids H2O₂ is employed to cooperate with Cu₂O.The results indicate that more than 92.1%of methylene blue can be degraded in 3 h by Cu₂O.Compared with Cu₂O/ITO thin film,Cu₂O/TiO₂ thin film has better catalytic activity and recycle performance due to its own heterostructure.