The Photocatalytic Properties Of Transition Metal Ion-Doped Tungstate Phosphors

With the development of industry,the accompanying environmental problems also affect people’s lives.Therefore,industrial wastewater treatment technology has taken the trend.Photocatalytic technology is a green and environmentally-friendly degradation technology.Unlike traditional degradation technology,it does not cause secondary pollution and plays an important role in environmental protection.The application of photocatalytic technology includes photocatalytic degradation of organic pollutants,photocatalytic cracking of water to produce hydrogen,and photocatalytic reduction of CO₂.Semiconductor photocatalysts are the core of photocatalytic technology and can directly participate in the reaction with pollutants,causing extensive research.The tungstate material has good luminescence and stability,and is a self-activated luminescent material.The absorption of light in the ultraviolet visible light band is strong,mainly due to the interband transition of the group itself.Therefore,people began to study the photocatalytic application of tungstate,and found that the degradation efficiency of pure tungstate is slow,the utilization rate of sunlight is low,and the band gap is wide,which limits the ability of tungstate to degrade pollutants.Therefore,in this thesis,a photocatalyst is obtained by ion-doping and co-doping,which can achieve the application of degrading rhodamine B.The unique electronic layer structure of transition metals has attracted our attention.Due to the sub-orbitality of the transition,it is easy to get or lose electrons and participate in the redox reaction.In this thesis,a photocatalyst of zinc tungstate doped with three transition metal ions was studied to discuss the effect of degrading Rhodamine B:A white powder sample of ZnWO₄:xTi⁴⁺（x=0.005,0.01,0.02）was synthesized by high temperature solid phase method at room temperature.The phase structure of the prepared sample was determined by X-ray diffractometry,and then subjected to performance characterization analysis（XRD,XPS,UV-vis DRS,PL spectrum,Raman spectroscopy,etc.）;finally,the synthetic photocatalyst was used to degrade Rhodamine B.The results of the test were analyzed.The diffraction peak position of XRD shifted to a low angle to indicate that Ti⁴⁺replaced the W⁶⁺ion.The elemental electron orbit corresponding to the binding energy of the XPS test indicates that the doping ion Ti is+4 valence.The combination of excitation spectrum and diffuse reflection analysis shows that the doping ions can narrow the band gap,and the analysis shows that the optimal doping amount of Ti is 0.01,and the rate of degradation of rhodamine B is 97%.ZnWO₄:xLa³⁺（x=0.01,0.015,0.02）white powder sample was prepared by high temperature solid phase method.The XRD diffraction peak position of the sample corresponds to the standard card one by one,indicating that the doped ytterbium ions do not affect the phase structure of ZnWO₄,and the trivalent cerium ions enter the crystal lattice gap of the zinc tungstate.The elemental representation of the XPS test indicates the presence of a bismuth element.The diffuse reflectance spectroscopy indicates that the doping of La³⁺can increase the ultraviolet absorption of zinc tungstate,and the doping of ytterbium ions narrows the band gap of zinc tungstate.The photocatalytic degradation test showed that the optimum doping concentration of 0.02 was 96.6%.ZnWO₄:0.02La³⁺,xY³⁺（x=0.01,0.015,0.02）series samples were prepared by high temperature solid phase method.Similar to the first two doped ion samples,some performance tests were also performed.A specific surface area test was also carried out to show that the specific surface area has a certain influence on the photocatalytic performance in a powdery photocatalyst.It can be seen from the absorption spectrum that ZnWO₄:0.02La³⁺has an increased absorbance after doping with 0.02Y³⁺,and has a better absorption capacity for ultraviolet rays having a wavelength of 200 nm to 400 nm,which can promote the generation of more photogenerated carriers.ZnWO₄:Ti⁴⁺,ZnWO₄:La³⁺and ZnWO₄:La³⁺,Y³⁺photocatalysts are all synthesized by high temperature solid phase reaction at room temperature.The method is convenient and stable.The diffraction peaks doped by the three transition metal ions correspond one-to-one with the standard card.The doping of Ti⁴⁺and La³⁺,Y³⁺makes the zinc tungstate exhibit excellent degradation in the process of degrading rhodamine B.The best effect is the co-doped system ZnWO₄:La³⁺,Y³⁺,and the degradation rate reaches 97.9%.The degradation rate of ZnWO₄:Ti⁴⁺reached 97%.The emission spectrum shows that the doping ions can weaken the luminescence intensity of the sample because the impurity ions suppress the electron-hole pair recombination.Diffuse reflectance spectroscopy shows that doping ions can narrow the forbidden band width of the sample and enhance electron capture.The doping of ions indicates the introduction of defects in the sample,accelerates the separation of carriers,generates more electrons and holes,and effectively participates in the photocatalytic reaction of the target degradation products,and is an effective photocatalyst.