Preparation And Photocatalytic Activity Of Bismuth Tungstate And Its Composite Photocatalysts

In recent years,the rapid development of modern industry has promoted the progress of humanity.However,the ensuing problems of environmental pollution,especially water pollution,have also become even more prominent.In order to solve this problem,people have developed a variety of methods.Among them,semiconductor materials attracted more and more attention due to their excellent photocatalytic performance on the degradation of organic pollutants.Nevertheless,conventional semiconductor materials such as TiO2,ZnO can only respond in the ultraviolet region due to their large band gaps.Therefore,their application prospects have been greatly limited.Recently,novel photocatalysts with narrow band gaps including bismuth tungstate(Bi2WO6)have become a research hotspot because they can respond both in the ultraviolet and visible light region.Bi2WO6 is one of the simplest Aurivillius type oxides with a band gap of about 2.7 eV,which can absorb visible light at wavelengths up to 450 nm.Therefore,it can photocatalyze the degradation of organic pollutants under visible light irradiation and effectively improve the utilization efficiency of sunlight.In this dissertation,Bi2WO6 was firstly used as the research object to study the preparation and influential factors of Bi2WO6 with different morphologies,the effect of morphology on the photocatalytic performance of Bi2WO6 was also explored.Secondly,the influence of external conditions(such as gamma ray radiation)on the crystal structure and photocatalytic performance of Bi2WO6 was studied.Finally,the composites combined Bi2WO6 with other functional materials were prepared to improve their photocatalytic performance.In this dissertation,Bi2WO6 is the main line of research,and its main research contents and achievements are as follows:1.Bi2WO6 crystal materials were prepared by simple hydrothermal method using Bi(NO3)·5H2O and Na2WO4·2HO as precursors and PVP as stabilizer.It was found that Bi2WO6 with different morphologies can be prepared by simply adjusting the concentration and molecular weight of PVP.XRD and HRTEM results show that the addition of PVP does not change the crystal structure of Bi2WO6.However,the distribution of PVP on the initially formed Bi2WO6 nanosheets induces crystal growth.With the increase of PVP concentration,the morphology of Bi2WO6 changes significantly.Meanwhile,the morphology of Bi2WO6 varied from simple sheet-like(S-BWO)to some complicated morphologies,including flower-like(F-BWO),red blood cell-like(B-BWO),and square-pillar-like(SP-BWO)with the increase of the molecular weight of PVP.The photocatalytic performances of Bi2WO6 with various morphologies on the decomposition of RhB under visible light irradiation reveal that S-BWO has the best photocatalytic performance,while SP-BWO has the worst.This depends mainly on their band gaps and specific surface areas.2.Fe3O4 nanoparticles were first modified by a fibrous hierarchically mesoporous silica layer(F-SiO2).After that,a mesoporous Bi2WO6 shell was grown in situ through hydrothermal reaction.Along with the formation of mesoporous Bi2WO6 shell,the intermediate F-SiO2 layer faded away by the acid etching effect.As a result,novel spherical core-shell mesoporous Fe3O4@Bi2WO6 nanoparticles with a high BET surface area of 127.3 m2/g were fabricated.The photocatalytic performance of the Fe3O4@Bi2WO6 nanoparticles on the decomposition of methylene blue(MB)under visible light had been investigated.The results show that the mesoporous Fe3O4@Bi2WO6 nanoparticles combine the excellent physisorption and visible-light photocatalytic performance on the decomposition of MB so that the total removal ratio of MB from the solution can be achieved as high as 98%.Furthermore,the mesoporous Fe3O4@Bi2WO6 nanoparticles can be easily recycled through magnetic separation,and maintain high photocatalytic activity after five cycles.3.Bi2WO6 powders were first used as target substance to investigate the influence of gamma ray on its crystal structure and photocatalytic performance.It is found that the color of Bi2WO6 powders changed from light yellow to light blue when the absorbed dose reaches 507 kGy(5.28 kGy·h-1,96 h),indicating the change of physical property of Bi2WO6.The XRD spectra of the irradiated Bi2WO6 nanocrystals show the characteristic 20 of(113)plane shifts slightly from 28.37° to 28.45° with the increase of the absorbed dose,confirming the change in the crystal structure of Bi2WO6.And the change is originated from the generation of oxygen vacancies which can be confirmed by XPS spectra.The photocatalytic performances of Bi2WO6 with different absorbed doses on the decomposition of MB under visible light irradiation reveal that the photocatalytic activity of Bi2WO6 increased correspondingly with the increase of absorbed doses.After three cycles of photocatalysis,the photocatalytic performance of Bi2WO6 remains at a high level,indicating that Bi2WO6 with oxygen vacancies has good stability and cyclic photocatalytic performance.4.The Bi2WO6/PEDOT composites were prepared by y-ray radiation method using EDOT as the monomer and Bi2WO6 as the matrix material.The formation of PEDOT nanoparticles is related with the strong oxidative atmosphere in the nitrogen saturated aqueous solution under the irradiation of y-ray.UV-vis diffuse reflectance spectra results showed that after the doping of PEDOT,the absorption of light by the Bi2WO6/PEDOT composites increased from 450 nm to 700 nm,which greatly improves the utilization efficiency of sunlight.The photocatalytic performances of Bi2WO6/PEDOT composites on the decomposition of MB under visible light irradiation showed that the doping of PEDOT can effectively improve the photocatalytic performance of BiWO6,and the photocatalytic performance increased accordingly with the increase of the content of PEDOT.