Preparation And Modification Of Bi₂O₃ Photocatalyst

Semiconductor photocatalysis has been regarded as an ideal technology forthe problems of environmental purification and solar energy conversion.Bi₂O₃are known to be the visible-light-driven photocatalysts due to their appropriate bandgap and chemical stability,which has attracted widely attentions.Unfortunately,the high recombination rate of photogenerated electrons and holes and poor light absorption range limits their practical applications in the field of Bi₂O₃photocatalysis.Therefore,the purpose of this dissertation is the modification of Bi₂O₃photocatalysts for the enhancement of their photocatalytic degradation and reduction efficiency.This investigation not only provides the feasible modification strategies of Bi₂O₃to meet different photocatalytic degradation and reduction requirements,but also offer theoretical and experimental supports for the application of Bi₂O₃in the photocatalytic field.The main contents of this thesis are as follows:（1）Bi₂O₃particles were fabricated by polyacrylamide gel method,after that the Bi₂O₃sample were decorated owing to the Au Ag alloy nanoparticles（6～18 nm）to obtain Au Ag/Bi₂O₃composite.The catalytic activity of the samples for the degradation of rhodamine B（Rh B）and methyl orange（MO）and reduction of Cr（VI）was evaluated under simulated sunlight or visible-light irradiation.It is found that the Au Ag/Bi₂O₃composites exhibit enhanced photocatalytic degradation and reduction activity when compared with bare Bi₂O₃,Ag/Bi₂O₃and Au/Bi₂O₃sample.The photoelectrochemical and photoluminescence measurements show that the separation efficiency of photogenerated charges in the Au Ag/Bi₂O₃composite is much higher than of Bi₂O₃.The photocatalytic reusability experiments show that Au Ag/Bi₂O₃composite has good photocatalytic cycling performance and chemical stability.（2）Au,Pt and Au Pt alloy nanoparticles were attached onto the surface of Bi₂O₃particles by photoreduction method to obtain Au/Bi₂O₃,Pt/Bi₂O₃and Au Pt/Bi₂O₃composite.The photocatalytic activity of as-prepared Au Pt/Bi₂O₃samples was evaluated by the degradation of acid orange 7（AO7）and reduction of Cr（VI）under simulated sunlight irradiation.indicating that Au Pt/Bi₂O₃composite exhibit higher photocatalytic activity than that of Bi₂O₃.The existence of Au Pt alloy and their homogeneous distribution on Bi₂O₃surface were fully confirmed by XPS characterization and HRTEM observation.Combining with the photocatalytic mechanism of Au Pt/Bi₂O₃composite,it can be seen that the formation of appropriate height schottky barrier between Au Pt alloy and Bi₂O₃effectively inhibits the recombination of photogenerated charge,thus improving the photocatalytic efficiency.（3）Bi₂O₃microrods were prepared by hydrothermal method,and Ag₂S nanoplates were deposited on the surface of Bi₂O₃microrods by co-precipitation method to obtain Z-scheme Ag₂S/Bi₂O₃composites.Au nanoparticles were selectively deposited on the Ag₂S nanoplates surface to obtain.Au-Ag₂S/Bi₂O₃composites using near-infrared light photodeposition method.SEM,TEM and HRTEM observations showed that Au nanoparticles were only modified on the surface of Ag₂S,but no Au nanoparticles were found on the surface of Bi₂O₃microrods.The photocatalytic activity of as-prepared samples was evaluated by the degradtion of acid orange 7（AO7）,rhodamine B（Rh B）and AO7/Rh B mixture and reduction of Cr（VI）under simulated sunlight irradiation.It is found that the photocatalytic efficiency is best when the content of Ag₂S is 12%for Ag₂S/Bi₂O₃sample.In addition,the catalytic efficiency of 2Au-12%Ag₂S/Bi₂O₃composite photocatalyst reaches the best through selective modification of Au nanoparticles.The intrinsical photocataltic property of the as-prepared samples is further confirmed by the degradation of phenol.The separation efficiency of photogenerated charge can be enhance by the formation of the Z-type heterojunction between Ag₂S and Bi₂O₃,and the photocatalytic redox capacity of Bi₂O₃can be strengthened.The selective decorated of Au nanoparticles on the surface of Ag₂S can not only capture photogenerated electrons in the conduction band of Ag₂S,but also compensate for the Z-type heterojunction photogenerated charge of Ag₂S/Bi₂O₃is consumed,which improves the photocatalytic efficiency（4）Oxygen vacancies were introduced onto the surface of Bi₂O₃by the simple NaBH₄reduction method to obtain Bi₂O_3-xsamples.After that,carbon quantum dots（CQDs）were decorated on the surface of Bi₂O_3-xsamples via a hydrothermal route to yield CQDs/Bi₂O_3-xcomposites.Comprehensive analysis on the basis of X-ray photoelectron spectrum（XPS）measurement and high-resolution transmission electron microscopy（HRTEM）observation show that the thickness of the surface oxygen vacancies can be controlled by changing concentration of NaBH₄solution.In addition,CQDs was successfully modified on the surface of Bi₂O_3-xsamples.The photocatalytic activity of samples was evaluated by the degradation of acid orange 7（AO7）under simulated sunlight or NIR light irradiation,indicating that Bi₂O_3-xsamples exhibit higher photocatalytic activity than that of Bi₂O₃,and the 3R-Bi₂O_3-x（NaBH₄:3 mmo/L）sample demonstrate the highest photocatalytic efficiency.The further enhanced photocatalytic efficiency of CQDs/Bi₂O_3-xcomposite by CQDs-modified 3R-Bi₂O_3-x,among which 15C/3R-Bi₂O_3-xcomposite has the highest photocatalytic activity.15C/3R-Bi₂O_3-xsamples can also be photocatalyzed under near-infrared light（NIR）irradiation compared with Bi₂O₃and 3R-Bi₂O_3-x,In addition,the obtained Bi₂O_3-xand CQDs/Bi₂O_3-xsample show good photocatalytic reusability.When oxygen vacancies are introduced onto the surface of Bi₂O₃sample after via a NaBH₄reduction method.It can not only reduce the band gap by introducing oxygen vacancy states in the band gap,but also capture photogenerated electrons to promote the separation of photogenerated charges.In addition,The decoration of CQDs on the surface of Bi₂O_3-xsamples:on the one hand,CQDs can generate photogenerated electrons under visible light excitation and can be transferred to the conduction band of Bi₂O₃,and further promote the separation efficiency of photogenerated charges in Bi₂O_3-xsamples due to it is also a good electron acceptors.On the other hand,CQDs also shows good upconversion performance,and its upconversion fluorescence can effectively excite Bi₂O₃and improve the yield of photogenerated charge.