Preparation Of La-N Co-doped TiO₂ Photocatalyst And Research On Degradation Of Printing And Dyeing Wastewater

With the development of industry,people are facing more and more serious environmental problems and pollution problems.Among many pollutant degradation technologies,photocatalysis has attracted wide attention due to its stable,efficient,and environmentally friendly characteristics.As a nano-photocatalyst,titanium dioxide has been widely used.It is widely used in photocatalytic degradation of organic matter in wastewater,especially for difficult-to-degrade printing and dyeing wastewater.Compared with traditional biochemical technology,TiO₂photocatalytic technology has the advantages of lower cost and more thorough organic matter degradation.However,titanium dioxide has the disadvantages of large forbidden band width,poor visible light activity,and easy recombination of photogenerated electron holes.Therefore,the current research focus is to improve the photocatalytic activity of titanium dioxide through modification,especially to improve its utilization efficiency of visible light.In this study,lanthanum and nitrogen co-doped titanium dioxide was modified,the doped samples were analyzed and characterized,and the photocatalytic performance of lanthanum and nitrogen co-doped titanium dioxide was studied.Firstly,nano-TiO₂photocatalyst was prepared by hydrothermal synthesis method with tetrabutyl titanate and absolute ethanol as raw materials.The hydrothermal reaction conditions were optimized by orthogonal experiment.The optimal conditions were as follows:Hydrothermal p H=6,hydrothermal temperature120℃,hydrothermal time 12h.The decrease of hydrothermal p H would transform TiO₂from anatase to rutile,and the increase of hydrothermal time would promote the growth of TiO₂grains,The crystallinity of anatase is affected by hydrothermal temperature.Using tetrabutyl titanate,anhydrous ethanol,lanthanum nitrate and urea as raw materials,La and N Co doped TiO₂was prepared under the optimal hydrothermal reaction conditions.XRD,XPS,TEM,BET,UV-vis,FTIR technology were used to analyze and characterize the La-N co-doped TiO₂photocatalyst prepared under the optimal hydrothermal reaction conditions.XRD analysis showed that the co-doped TiO₂photocatalyst was analyzed and characterized.TiO₂is anatase structure.The grain size of the sample after La and N co-doping is10.69nm,which is significantly smaller than the 14.90nm of pure TiO₂.XPS analysis showed that La and N were successfully doped into TiO₂,forming Ti-O-La bonds and O-Ti-N bonds.TEM analysis shows that the grain size is small and uniformly distributed.The doped TiO₂still has a polycrystalline structure.BET analysis shows that the specific surface area and pore size of TiO₂increase after co-doping.UV-vis analysis shows that co-doping The band gap of the back TiO₂is 2.77 e V,and the light absorption wavelength of the catalyst produces a red shift.FTIR analysis shows that TiO₂has surface hydroxyl groups.Subsequently,the photocatalytic performance of the catalyst was studied.The UV photocatalytic degradation of methylene blue by La-N co-doped TiO₂experiment showed that:（1）The catalyst has the best degradation effect on methylene blue at p H=2,and the degradation rate can reach 98.1%;（2）When the initial concentration of the methylene blue solution is increased,the degradation rate of methylene blue will decrease accordingly;（3）When the catalyst dosage is 150 mg,the degradation rate of methylene blue is the highest;（4）The degradation rate of methylene blue is different for catalysts with different doping methods,In descending order of 1.5%La/3%N-TiO₂>1.0%La/3%N-TiO₂>2.0%La/3%N-TiO₂>3%N-TiO₂>1.5%La-TiO₂>Pure TiO₂.1.5%La/3%N-TiO₂has the largest reaction rate constant K=0.04107min^-1.La-N co-doped TiO₂visible light photocatalytic degradation of Rhodamine B experiments showed that:（1）The catalyst has the best degradation effect on Rhodamine B at p H=8;（2）The light intensity has an effect on the degradation rate of dyes.The degradation rate of rhodamine B is the highest when the surface is 15cm,reaching 95.6%;（3）The degradation rate of rhodamine B to the catalysts with different doping methods is different.La and N co-doped TiO₂have better performance than undoped and single doped TiO₂Higher dye degradation rate and reaction rate.La-N co-doped TiO₂solar photocatalytic degradation of dye wastewater COD experiments show that:（1）the catalyst has the highest degradation rate of wastewater COD at p H=8;（2）the COD degradation rate increases with the increase of catalyst dosage,but excessive The addition of catalyst has no obvious effect on improving the degradation rate of COD;（3）The cycle stability experiment shows that the degradation rate of COD for five cycles of 1.5%La-3%N-TiO₂is79.6%,77.5%,75.6%,respectively.72.9%,70.9%.After five cycles of use,the degradation rate of COD dropped by about 8.7%.The mechanism of La and N co-doped TiO₂photocatalyst was discussed.Since hydroxyl radicals play a major role in dye degradation,the addition of hydrogen peroxide can effectively increase the photocatalytic reaction rate.