Preparation Of Visible Light Responsive TiO₂ Photocatalyst By Rare Earth Doping And Its Performance Research

TiO₂ has higher photocatalytic activity,strong chemical stability,no toxic effect,low energy consumption and other advantages,which are getting more and more attention.However,due to the wide band gap?3.2 eV?of titanium dioxide,the spectral absorption range is narrow,and the corresponding photocatalytic activity can be exhibited only under ultraviolet light.However,ultraviolet light only accounts for 5%of sunlight,so its The photocatalytic efficiency is low.In addition,the higher recombination probability of photogenerated carriers also limits the practical application of TiO₂ photocatalytic treatment of pollutants.Ion doping can improve the photocatalytic efficiency of titanium dioxide.Rare earth atom doping of titanium dioxide can significantly broaden the spectral response range and make its absorption wavelength move towards visible light.Molecular simulation technology can calculate the electronic structure of a material from an atomic point of view,explain the mechanism of its photocatalytic reaction,lay the foundation for theoretical research,and can predict the catalytic activity of the catalyst.In this paper,the CASTEP module of Materials Studio calculation software is used to calculate the energy band structure of TiO₂ doped with rare earth elements such as La,Ce,Pr,Sm,Gd,and Tm.And predicted its photocatalytic activity.Based on the theoretical simulation results,TiO₂nanomaterials with different dispersions and different morphologies were prepared using various preparation methods,and their photocatalytic activity on the target pollutant methylene blue was investigated.It was found that the TiO₂ materials prepared by hydrothermal method had high Dispersion and regularity,showing the best photocatalytic activity;based on this,we prepared Gd,Ce single doped and Gd/Ce co-doped TiO₂photocatalyst by hydrothermal method,and passed SEM,XRD,BET,UV-Vis and XPS technologies were used to characterize the catalyst,and the effect of Gd and Ce doping on the photocatalytic activity of TiO₂ was explored.The main research contents and results are as follows:?1?According to the first principle,the energy band structure,state density and differential charge density of the rutile phase titanium dioxide doped with rare earth elements La,Ce,Pr,Sm,Gd,and Tm were calculated.The results showed that the rare earth element doped TiO₂ band The gap values are all smaller than that of undoped TiO₂,and the theoretical analysis results show that the pure TiO₂,Ce-TiO₂,Gd-TiO₂,and the width of the forbidden band decrease in sequence,which is consistent with the experimental results of UV-visible absorption spectrum.?2?The O/Ti atomic ratio on the catalyst surface is slightly greater than 2,and the reason for the high oxygen content may be the presence of Gd₂O₃ on the catalyst surface.According to XPS,the actual doping amount of Gd in the three samples of 3%Gd-TiO₂,5%Gd-TiO₂ and 10%Gd-TiO₂ was 1.21%,1.84%and 2.3%,respectively.The degradation rate of methylene blue was the fastest with 5%Gd-TiO₂,that is,when the actual doping amount of Gd was 1.84%,the sample activity was the highest.?3?The photocatalytic activity of Gd-doped Gd-TiO₂ is significantly higher than that of Ce-doped Ce-TiO₂.It may be because the built-in electric field is generated inside Gd-TiO₂after Gd doping.The presence of the built-in electric field makes the recombination of electrons and holes The probability is reduced and the life is increased,which improves the photocatalytic activity of the catalyst;and Ce doped rutile TiO₂ will generate impurity levels,making the band gap much smaller than the rutile TiO₂,and a more obvious"red shift"occurs,but As the forbidden band width becomes smaller,the recombination probability of electrons and holes increases,which reduces the photocatalytic activity.This finding indicates that although rare earth doping can narrow the band gap of TiO₂macroscopically,this is not a decisive factor for improving its visible light catalytic activity,and it is also related to the mechanism of doping to adjust the band gap.For Gd and For rare earth elements such as Ce,the effect of the built-in electric field is greater than the effect of impurity levels.?4?Under the visible light source,Gd-doped TiO₂ has a higher photocatalytic efficiency,and the simulated pollutant methylene blue can be completely degraded within35 minutes.When the doping amount of Gd is 1.84%,Gd-TiO₂ and other doping amounts In contrast,the photocatalytic reaction rate is accelerated,the photocatalytic effect of Ce-doped TiO₂ is poor,and the photocatalytic efficiency of 5%Gd/Ce-TiO₂ Gd and Ce co-doped samples is centered;and the study found that Gd and Ce co-doped In the sample,with the increasing amount of Gd doping,the photocatalytic efficiency of TiO₂ showed an upward trend.This may be due to the co-doping of Gd and Ce inhibiting the effective separation of photogenerated electrons and holes,which reduces the photocatalytic activity.