Study On Photocatalytic Performance Of Bismuth Tungsten Acid Mixed With Different Rare Earth Lon

In order to solve the problem of water pollution,visible light catalyst which can absorb the inexhaustible and safe solar energy has successfully attracted the attention of many scholars.The catalyst is not only highly reusable in the degradation of pollutants,but also environmentally friendly.Of course in sterilization and other aspects also have a certain application.In the early stage of photocatalysis,people mainly studied the non-toxic,highly active and stable TiO₂ which plays a great role in sterilization,antisepsis and organic pollution control,but its forbidden band is relatively wide.It can’t make full use of solar energy.It can only be activated in ultraviolet（UV）light.Therefore,it is limited in practical application.As we all know,solar energy is in the ultraviolet range（290-400nm）of 6.8%,visible light range（400-760nm）of 38.9%,and infrared spectrum range（760-3000nm）of about 54.3%.Therefore,scholars began to search for a new visible light catalyst:Bi₂WO₆,which can not only absorb visible light,but also non-toxic,good stability,high photocatalytic efficiency and low cost.But it has the disadvantages of small specific surface area and easy recombination of free carriers,resulting in low catalytic efficiency.Therefore,in order to improve the shortcomings of bismuth tungstate,the photocatalytic efficiency was improved by means of rare earth co-doping.（1）Firstly,Bi₂WO₆:Yb³⁺,Pr³⁺powders with different concentration ratios were prepared by hydrothermal method.Bi₂WO₆:Yb³⁺,Pr³⁺powders were excited with980nm near-infrared light respectively to emit light with wavelengths of 410nm,488nm,528nm,550nm,661nm and 777nm.It was found that when the doping concentration ratio was Yb³⁺:Pr³⁺=10mol%:2mol%,the up-conversion luminescence was the strongest.Because the energy difference between the only two ²F_7/2 and ²F_5/2levels of Yb³⁺is exactly the same as the light energy at 980nm.By analyzing the up-conversion luminescence mechanism,luminescence corresponds to Pr³⁺¹S₀→³P₂（410nm）,³P₀→³H₄（490nm）,³P₁→³H₅（528nm）,³P₀→³H₅（550nm）,³P₀→³F₂（660nm）,³P₀→¹G₄（840nm）.XRD,SEM,EDS,UV-vis,PL,up-conversion luminescence and specific surface area were used to test the crystal phase,morphology,composition,optical response range,carrier separation capability and up-conversion luminescence of the samples.The results showed that the sample preparation was very successful,and the doped rare earth ions did not change the crystal phase and microstructure of bismuth tungstate,which promoted the separation of free carriers and effectively improved the photocatalytic activity.（2）Secondly,photocatalytic experiments were carried out to degrade methylene blue under visible light and 980nm near-infrared light respectively.It was found that the doping of Yb³⁺ion and Pr³⁺ion indeed enhanced the photocatalytic effect,and when the doping concentrations of Yb³⁺ion and Pr³⁺ion were 10mol%and 2mol%,almost all methylene blue was degraded,and the photocatalytic effect was the best among the samples.Moreover,the photocatalyst with Yb³⁺:Pr³⁺=10mol%:2mol%also had certain photocatalytic activity under near-infrared light.Because the doping of rare earth ions Yb³⁺and Pr³⁺can make Bi₂WO₆ have near-infrared induced photocatalytic properties.（3）Finally,four kinds of Bi₂WO₆ powders doped with 15mol%Yb³⁺,5mol%Er³⁺,5mol%Ho³⁺,5mol%Pr³⁺and 5mol%Tm³⁺were prepared.Finally,four kinds of Bi₂WO₆ powders doped with 15mol%Yb³⁺,5mol%Er³⁺,5mol%Ho³⁺,5mol%Pr³⁺and 5mol%Tm³⁺were prepared.XRD,SEM,EDS,PL,up-conversion luminescence and specific surface area were used to test the crystal phase,morphology,composition,optical response range,promoting carrier separation ability,up-conversion luminescence intensity.The results show that the sample preparation is very successful.The doped bismuth tungstate with the same concentration of rare earth ions and different kinds of bismuth tungstate did not change the crystal phase and microscopic morphology,but it broadened the optical response range,promoted the separation of free carriers,which provided a good prerequisite for improving the photocatalytic activity.Finally,methylene blue was photocatalyzed in liquid phase under visible light and 980nm near infrared light.The comparison shows that Bi₂WO₆:Yb³⁺,Tm³⁺powder have the highest photocatalytic degradation efficiency.