Construction Of Lanthanide Element Modified Bi₂WO₆ Photocatalyst And Catalytic Mechanism

In recent years,the effluent containing dye and antibiotic was produced with the rapid development of industry and textiles.The contaminants seriously threaten survival environmental and ecological,which goes against to the concept of sustainable development.In recent years,photocatalysis technology have the advantages of high-efficiency and no secondary pollution,which become one of the effective ways of solving environmental problems and energy crisis.As the simplest semiconductor materials of Aurivillius family,bismuth tungstate(Bi2WO6)possess layered structure leading to its unique physical and chemical property.Hence,researchers think that Bi2WO6 exist potential application value in photocatalysis field.However,the defects of poor light absorption,rapid the photo-generated electron-holes pairs recombination and poor suface catalytic kinetics caused lower light utilization quantum,which make the photocatalytic degradation performance of Bi2WO6 fail to achieve its theoretical potential.As major photocatalyst,the introduction of one or multiple lanthanide ions(Ln3+)in Bi2WO6 crystal lattice construct defect and redox center or adjust band position,which can improve the utilization of charge carriers and regulate of active groups to obtain the novel system of high-efficiency visible-light-driven photocatalyst.Moreover,this work still research the influence of loaded different lanthanide oxide(Ln2O3)or lanthanide tungstate(Ln2WO6)on Bi2WO6.This study not only find some rules,but also provide new thought for searching novel photocatalysts.The main contributions are as follows:(1)The single ion Ln3+-doped Bi2WO6 composite photocatalyst was synthesized by simple hydrothermal method.The mechanism of enhanced photocatalytic performance was tentative proposed.It can infer that the catalytic mechanism of different lanthanide element modified Bi2WO6 from three aspects:Firstly,part of Ln3+ ions can expand the light absorption region to improve light utilization.Secondly,multivalence ions can form redox center to suppress photo-generated electron-holes recombination.Thirdly,the introduction of smaller radius lanthanide ions can construct oxygen vacancies(OVs)leading to raising the yield of superoxide anions(·O2-).It provides theoretical basis for appropriate Ln3+ion selection.(Ⅱ)On the basis of Ln3+-doped Bi2WO6 result,the mechanism of enhanced performance for co-doped Yb3+/Nd3+-Bi2WO6 was studied.The results was illustrated that Yb3+multivalence ion can not only introduce OVs,but also become in-built Yb3+/Yb2+ redox center,which can respectively improve the production of ·O2-and the separation efficiency of electron-holes pairs.Simultaneously,the addition of Nd3+in Bi2WO6 expand light absorption region and produce a new absorption peak at 584 nm,thereby extremely increase visible light utilization.The synergistic effect of above factors can enhance pure Bi2WO6 photocatalytic performance for degradation rhodamine B(RhB)and methylene blue(MB).According series of characterizations analysis,it determined the catalytic degradation mechanism of Yb3+/Nd3+-Bi2WO6 composite material.It not only provides new thought for synthesis novel high-efficient visible-light-driven catalysts,but also provide basis for improving the photocatalysis mechanism theory of co-doped lanthanide ion.(Ⅲ)Combined different property of Ln3+,triple-doped Bi2WO6 was designed and synthesized.In this study,the regulation of ·O2-and hydroxyl radicals(·OH)as the starting point,the improvement of electron-holes utilization as the auxiliary,both play an unique role in enhancing degradation performance of Bi2WO6.The catalytic performance of this system was evaluated by degrading congo red(CR)and tetracycline(TCs)under visible light illumination.The photocatalytic activity of Yb3+/Er3+/Pr3+-Bi2WO6 composite is superior to pure Bi2WO6,single-doped and co-doped samples.It illustrate that the caused effect by Yb3+,Er3+and Pr3+was beneficial to the improvement of degradation efficiency.The introduction of Yb3+can construct OVs and Yb3+/Yb2+redox center.Er3+can adjust the valence band position of Bi2WO6,which was advantage to producing more OH.The existence of Pr3+ ion can form Pr4+/Pr3+ redox center,which can inhibit the recombination of electron-holes and produce little OH.The above are advantage to improving catalytic degradation activity.Therefore,it provides theoretical support for polylanthanide ion doped Bi2WO6.(Ⅳ)The mechanism of Ln2O3 or Ln2WO6 loaded on Bi2WO6 was studied.The characterization results illustrate as follows:The selected Ln2O3 or Ln2WO6 with different 4f valence electron configurations showed excellent photocatalytic degradation activity.According to series of characterizations for composite materials,the generation of active species and the separation of charge carriers were deduced in the photo-reaction process.Multivalence lanthanide compounds can not only rasie yield of active species,but also promote charge carriers separation.However,single valence state of lanthanide compounds can conduct electrons to suppress electron-hole recombination.This research lucubrated the mechanism of lanthanide compounds modification Bi2WO6 from valence electron configurations aspect.