Research On Synthesis And Photocatalytic Activity Of Graphene Oxide-cerium Co-doped Titanium Dioxide

In recent years,the air pollution incidents occur frequently,has become the global concern of environmental problems.Formaldehyde is one of the main air pollutants,its release period can reach 3-15 years.World Health Organization has defined it as a carcinogen.How to effectively deal with it to improve the air condition is the focus of domestic and foreign experts and scholars.Semiconductor photocatalytic oxidation technology is considered to be the most promising method of air purification.Its main feature is the use of photo-excited catalyst to generate electron-hole pairs and other strong oxidizing substances to degrade organic pollutants into non-toxic carbon dioxide and water.In this paper,a photocatalyst of graphene oxide-cerium-titania?GO-Ce-TiO₂?powder with visible light response was prepared.The photocatalytic activity and degradation mechanism of the catalyst were studied by selecting methylene blue as the target degradation product.Then,on the basis of this,a thin film type GO-Ce-TiO₂ was prepared,which is more suitable for practical use.The photocatalytic degradation of low concentration formaldehyde and the possible application of the catalyst were studied by using formaldehyde as the experimental object.The preparation process of GO-Ce-TiO₂ thin film was optimized by using response surface method?RSM?.The optimal preparation conditions were determinated and the quadratic polynomial mathematical model of Ce-GO-TiO₂ photocatalytic formaldehyde was established for multiple regression analysis.The model can be used to guide and simplify the experiments.Finally,CFD simulation technique was used to study the effect of vehicle air purifier loaded with GO-Ce-TiO₂ film on the velocity field and formaldehyde concentration field in different positions of vehicle.The effect of different airflow patterns on the air quality was also discussed.The main contents of this paper are as follows:Pure TiO₂,GO and Ce single and co-doped TiO₂ photocatalyst powders?GO-TiO₂,Ce-TiO₂ and GO-Ce-TiO₂?were prepared by sol-gel method using tetrabutyl titanate as precursors.The crystal structure,surface microcosm and so on of the photocatalysts were characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The results show that the oxides of cerium and titanium dioxide are distributed on the surface of the graphene sheet to form mesoporous catalysts with a diameter of about 5 nm.The effects of different doping amount and calcination temperature on the photocatalytic degradation ability of methylene blue solution were studied.The optimum calcination temperature of GO-Ce-TiO₂ powder is 300 ? and the best calcination time is 2 h.When the doping amount?mass ratio?of graphene oxide and cerium is 2%and 6%,GO-Ce-TiO₂ has the best catalytic activity.In order to improve the application ability of the powder type catalyst,the experimental study on the catalyst film formation was carried out.It was found that the sol was applied on the glass substrate by impregnation pulling method when GO,Ce and TiO₂ were formed into the sol.And then through the high temperature reaction,a composite visible photocatalytic thin film with GO and Ce co-doped TiO₂ can be prepared.The experimental results show that the spectroscopy of GO-Ce-TiO₂ composite film is obviously redshifted to the visible region compared with absorption wavelength of TiO₂,and the degradation rate of formaldehyde is up to 83.8%in 450 min.The calcination temperature,time and composition ratio of Ce-GO-TiO₂ photocatalyst were optimized by the response surface method.The photocatalytic degradation of formaldehyde was carried out by BBD experimental design.The regression model obtained from the experimental results shows that the calcination temperature and the calcination time have the greatest influence on the degradation rate of formaldehyde,and there is a significant interaction between the two factors.The importance of the four influencing factors is:calcination temperature>calcination time>GO doping amount>Ce doping amount.And under the optimum preparation conditions of calcination temperature of 300 ?,calcination time of 2 h,the GO doping amount of 0.2%and the Ce doping amount of 0.4%,the experimental results of the formaldehyde removal rate are very close to the predicted values given by the response surface model,which shows that the response surface method has reliability in the study of the optimum preparation conditions of Ce-GO-TiO₂.Combining with the physical model of vehicle and CFD simulation technology,the velocity field and formaldehyde concentration field in the vehicle were numerically simulated.The influence of the diffusion characteristics of formaldehyde and the installation position of vehicle air purifier on the removal efficiency of formaldehyde was studied.Research conclusions show:The distribution of formaldehyde concentration is affected by the turbulence intensity of the airflow in the vehicle.In the air inlet,return air outlet and other strong turbulence intensity area,the concentration of formaldehyde will therefore be reduced.In the area where the turbulence intensity is small,the formaldehyde concentration is increased.By comparison,the car air purifier placed in the middle of the roof is better than being placed on the storage box and trunk partition,can better promote the effective reduction of formaldehyde in the breathing area of driver or passengers,so as to achieve the purpose of purification.This study provides some theoretical reference for the practical application of air purifier in the vehicle.