Preparation Of Bismuth Tungstate Nanocomposites And Themechanism Of Enhanced Photocatalytic Activity

Bismuth tungstate?Bi₂WO₆?is one of the simplest compounds in the Aurivillius family.The internal electric field formed by this unique layered structure is conducive to the effective separation of photogenerated electrons and holes,resulting in higher carrier transfer efficiency,which is more beneficial to the photocatalytic reaction.Although bismuth tungstate is a kind of visible-light-drivensemiconductor material,the narrow range of photoresponse?<450 nm?and fast recombination rate of photogenerated carriers limited its application in environmental catalysis.Therefore,in this thesis,we try to improve bismuth tungstate by constructing a composited system and the surface modification.Through the analysis of the composition,morphology and energy band structure,as well as the investigation of the photoelectric properties and catalytic activity of the material,the mechanism of enhanced photocatalytic activity is discussed.Based on this,the main work are summarized as follows:1.Bi/Bi₂WO_6-x composites were prepared via one-step hydrothermal method by using bismuth nitrate pentahydrate and sodium tungstate dihydrate as raw materials and ethylene glycol as solvent.The metallic bismuth?Bi?and surface oxygen vacancies?Vo?could be mediated by adjusting the Bi/W and reaction time,respectively.The electron paramagnetic resonance?EPR?spectra demonstrates that the ability of generation singlet oxygen?¹O₂?is significantly improved after the introduction of Bi and Vo in the Bi₂WO₆.The photocatalytic activity of Bi/Bi₂WO_6-x was determined by the degradation of bisphenol A and bisphenol analogues,which is much highter than the single-component Bi2WO6.The total organic carbon analysis shows that the material could mineralize the contaminants.The interference experiments were performed in the presence of different interference of anions,cations,and natural organic matter.It illustrates that ¹O₂ is an effective active oxygen species in the degradation process of bisphenol pollutants,whic has stronger anti-interference ability than·OH.This work lays the foundation for the Bi2WO6materialin actual water treatment.2.The carbon-modified bismuth tungstate material?C/Bi2WO6?was prepared via one-step hydrothermal method by using bismuth nitrate pentahydrate,sodium tungstate dihydrate and sodium citrate.The amount of carbon modification could be mediated by adjusting the amount of sodium citrate.The composition and chemical state of the material were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,Fourier transform infrared spectroscopy,Raman spectra,and scanning electron microscopy,demonstrating the existence of amorphous carbon.Photocatalytic degradation offluoroquinolone?FLQ?antibioticsexperiments showed that the degradation ability of C/Bi2WO6 was significantly improved compared to the single-component Bi₂WO₆.Photoelectrochemical experiments illustrates that carbon modification on the surface of the material caould effectively improve the photocarrier mobility and separation ability.It also could generate more reactive sites on the surface of the material,which is favorable for the photocatalytic reaction.The antibacterial experiment illustratesthat the degradation products of quinolone antibioticsoverC/Bi2WO6 lostantibacterial activity,which is not beneficial for the generation of drug-resistance of antibiotics in water.3.p-n junction BiOCl/Bi2WO6 composites were successfully prepared via ion exchange methodby using bismuth nitrate pentahydrate,sodium tungstate dihydrate and sodium chloride.The X-ray diffraction and Fourier transform infrared spectrademonstrate that the composition of the material changes is related to the melar ratio of W/Cl.Scanning electron microscopyimages shows that the prepared BiOCl/Bi₂WO₆present a nanosheet structure.The photocatalytic degradationof Rhodamine B experiments and total organic carbon analysis indicate that BiOCl/Bi₂WO₆ composites could degrade RhB in water more effectively than single-component BiOCl and Bi₂WO₆.The separation efficiency,lifetime,concentration and migration ability of carriers in the material were characterized by steady-state fluorescence,transient fluorescence,photocurrent,and AC impedance.The results show that the p-n heterojunction in BiOCl/Bi2WO6 can effectively reduce the recombination rate of electrons and holes,and increase the lifetime,concentration,and migration ability of carriers,thus resulting in the improvement of photocatalytic ability of C/Bi₂WO₆.