The Synthesis Of Bismuth Tungstate Photocatalysts And Their Photocatalytic Performances Towards Organic Pollutants Under Visible Light

With the rapid development of global economy and industry,environment pollution is becoming more and more serious.The organic pollution in water has attracted widespread attention.Particullarly,antibiotics and endocrine disruptors which causes"three"effects caused the great attention.Effective control of these organic pollutants has become a worldwide research focus.In terms of the low efficiency,secondary pollution,difficult post processing and complex reaction device and the high cost of the traditional control technologies.In recent years,the photocatalysis which can utilize the solar energy in the control of antibiotics and endocrine disruptors is considered to be one of the most promising treatment technologies.However,the low carrier separation efficiency and utilization of light lead to the low photocatalytic activity.In view of the scientific problems mentioned above,we contructed four kinds of new structure of Bi₂WO₆ photocatalytic materials,through morphology control,coupling semiconductor compounds and quantum dot sensitizing in this thesis.Considering the external influence factors of the photocatalytic reactions,we constructed a reaction system which has a high adsorption capacity for the insoluble antibiotics by adding the surfactant.Norfloxacin?NOF?and ibuprofen?IBF?,two common used antibiotics,and bisphenol A?BPA?,are selected as the target pollutants,and their degradation reaction pathway and reaction mechanism were studied.The physical and chemical properties of the photocatalysts including structure,morphologies and the photoelectrical properties were characterized through series of characterization methods.The LC-MS was employed to analyze the reaction product and possible degradation pathways of pollutants were proposed.Density functional theory?DFT?was also used to give a further insight into the catalytic reaction mechanism,thus providing experimental and theoretical basis for construting more efficient photocatalytic materials.The specific research results are as follows:?1?By adjusting the material preparation reaction solution pH value hydrothermal method in the process of the preparation of Bi₂WO₆ with different hierarchical architectures.The experimental results show that Bi₂WO₆ prepared at pH 4 had a larger specific area and higher carrier separation efficiency,and it has good adsorption and catalytic performances towards NOF,which could reach 90%.The catalytic degradation rate reached maximum in the weak alkaline solution,this is due to the weak base solution provides plenty of OH^-,and the photons could react with OH^–adsorbed on the surface of the photocatalysts,thus leading to the generation of more?OH in the reaction,the resulted?OH can decompose organic pollutants by oxidation.?2?We investigated the effect of the nonionic surfactants TX100 on the photodegration of NOF by Bi₂WO₆.This study found that TX100 can effectively improve the degradation efficiency of NOF.Further results showed that when the concentration of TX100 was at its CMC?critical micelle concentration??0.25 mM?in aqueous solution,the adsorption capacitiy Bi₂WO₆ for TX100 reached the maximum?99%in 1 h?,and could accelerate the NOF degradation rate.When the concentration of TX100 was higher than 0.25 mM,the degradation rate of NOF decreased.The solution pH also affects the reaction rate.When the solution pH was 8.06,the degradation rate of NOF reached maximum.Fourier infrared?FTIR?analysis results showed that when the reaction increased to 2 hours,the adsorbed NOF on the catalyst could be degraded completely.LC-MS was employed to analyze the reaction intermediates and final products,and three possible reaction paths were proposed:quinolone ring to add hydroxyl,removal of piperazine ring and F atoms of the benzene ring are replaced by hydroxyl on.Escherichia coli toxicological experiments showed that the toxicity of reaction intermediates and final products to E.coli was lower than that of NOF.?3?Plasmonic Bi metal deposition on g-C₃N₄@Bi₂WO₆ microspheres were successflly fabricated by hydrothermal method.The Bi metal with surface plasmon resonance effect embedded in g-C₃N₄ and Bi₂WO₆ microspheres improved the light absorption of the composite,and also acted as the role of electron transferring bridge,thus promoting the separation rate of the charge carieers.The results showed that the g-C₃N₄?20%?@Bi@Bi₂WO₆ samples had a higher photocatalytic activity than pure g-C₃N₄,Bi₂WO₆ and g-C₃N₄?20%?@Bi₂WO₆.The degradation efficiency of g-C₃N₄?20%?@Bi@Bi₂WO₆ towards MO is 16.7 times as that of Bi₂WO₆.We further illustrate that the synergetic effect of g-C₃N₄,Bi₂WO₆,and metal Bi facilitaes efficient electron transfer,thus achieving higher photocatalytic activity.The photocurrent density of g-C₃N₄?20%?@Bi@Bi₂WO₆ is 2 times as that of Bi₂WO₆.?4?Combining the ultrathin g-C₃N₄ nanosheet?ug-CN?and Bi₂WO₆?m-BWO?monolayer,we successfully prepared the ug-CN/m-BWO?UTCB?2D/2D heterojunction with atomic thickness by hydrothermal reaction.The characteration results showed that the m-BWO was self-assembly evenly dispersed on the surface of ug-CN to form UTCB.UTCB had an efficient light carrier separation rate.When the mass ratio of ug-CN and m-BWO was 1:4,UTCB-25 had the highest of IBF catalytic efficiency towards IBF and which could reach 96.1%in 1 h,which is about 2.7 times as that of pure m-BWO.Analysis shows that the results calculated by DFT the distribution of electrons and holes on the m-BWO.The closely intimate interface between m-BWO and ug-CN promoted the separation rate of the electrons and holes.According to the analysis of LC-MS on degradation products,we put forward five possible IBF degradation path ways.?5?CQDs were evenly dispersed on the surface of m-BWO forming CBW heterojunction.The heterojunction had good full spectrum absorption efficient capacity and efficient carrier separation efficiency.Photocatalytic mechanism analysis reveals the CBW composites of have excellent photocatalytic activity towards BPA because of the up-conversion performance of CQDs and its electronic storage capacity.Under visible and IR light irradiation,the degradation efficiency of CBW-3 towards BPA is 5 and 1.8 times as that of m-BWO,respectively,and the photocurrent density is3 and 2 times as that of m-BWO,respectively.DFT calculation results show that there is a complementary hybridization between the valence band and conduction band of CQDs and m-BWO,which greatly improved the separation efficiency of photoinduced carrier of the CBW composites.According to the results of the ESR and quenching experiment,it shows that three main reactive spicies,O₂?^-,?OH,and h⁺,played a major role during the photocatalytic process.