Synthesis Of Bismuth-base Photocatalyst And The Photocatalysis Reaction Mechanism For No_x Purification

High-quality air is a necessary condition for the life survive on the earth.The NO_x as one of the air pollutions will damage the organs such as the throat and lungs.It s also affect the nervous system to cause brain damage,what worse is carcinogenic,which greatly jeopardizes health.In recent years,photocatalytic oxidation has been extensively studied as a technology for removing low-eoneentration NO_x by using sustainable energy solar energy.Thus,in this paper,in order to explore the influence of the plasma effect of metal Bi.and the construction of high-efficiency new bismuth-base semiconductor photocatalysts.Firstly,the Bi/BiPO4 system was synthesized.The Bi plasma effect and surface oxygen vacancy for catalyst light absorption were studied.The electronic structure and the electron-hole pair separation were studied by theoretical calculation.Secondly,the Bi/Bi4MoO9 system was constructed.The core-shell structure of the metallic Bi-shell was studied for photocatalytic activity.Then,systematic research analyzes the mode of role of metallic Bi.Finally,the multi-component heterojunction systems(Bi2O3/Bi2WO6 and Bi/Bi2O3/Bi2WO6) were established by changing of the reducing agent dosage.The coordinated effects of the surface plasma effect and the heterojunction effect of the metallic Bi were controlled by adjusting the structural components of the catalyst material.And explored the both effects on the activation of amorphous Bi2WO6.All three systems have been employed in-situ FT-IR to study the reaction process of pollutants catalytic oxidation,which provides a feasible idea and theoretical basis for broadening the photo-absorption region of the catalyst to improve carrier separation efficiency and composited high-efficiency photocatalyst.The specific conclusions as follows:Bi/BiPO4 photocatalysts:With the rapid development of economy,factories and vehicles make the air pollution became a worldwide focused issue.As one of the major air pollutants,nitric oxide(NO) would lead to serious atmospheric problems such as acid rain,haze,and photochemical smog.However,low concentration nitric oxide is hard to be removed by the way of industrialization.Photocatalysis,as a green and effective technology,has become one of the most promising technologies for solving air pollution problems and that works on low concentration air pollutant.As one of the typical photocatalyst,BiPO4 consists of alternating layers of[Bi2O2]2+ and PO43-groups and has the better UV-light photocatalysis performance when compare with TiO2,emerging as an attractive photocatalyst.At present,the study to enable BiPO4 respond visible light which comes up with many ways,such as element doping,build heterojunction and surface hybridization.The recent investigation shows that metal Bi possess the property of Surface Plasmon Resonance(SPR) as well as noble metal like gold could enhance the photocatalysis activity by increasing light absorption and raising the separation efficiency of photogenerated electron-hole pair.In this study,Bi/BiPO4 composite photocatalyst was synthesized via a two steps method.Firstly,the hexagonal phase BiPO4 was prepared by a precipitation method.And then,the metal Bi was deposited on the surface of BiPO4 in the presence of NaBH4.The as-prepared photocatalyst was applied to the photocatalytic removal of low concentration of NO in air.The microstructures of the catalysts were characterized by XRD,SEM,TEM,UV-vis DRS and ESR.The in situ FT-IR was used to analyze the reaction intermediates of photocatalytic NO oxidation under visible light irradiation.On the basis of free radicals capture from ESR,the reaction mechanism was proposed.The results show that the surface plasmon resonance of Bi metal promoted the visible light absorption and separation of photogenerated charge on BiPO4.The DFT calculation results indicated that the presence of oxygen defects induced the formation of the intermediate energy level between the valence band and the conduction band of the bismuth phosphate,which is beneficial to the electron transition from valence band.The results of electronic structure calculations manifest that the metal Bi also plays a role of storing and transferring electrons from the conduction band of BiPO4.The generation and rapid transfer of photogenerated carriers could decrease the photogenerated electron-hole pair recombination rate.As a result,the BiPO4 can be converted into a highly performance visible light photocatalyst.The present work could provide new insights into the understanding of the Bi-based plasmonic photocatalyst and the mechanism of gas-phase photocatalytic reaction.Bi/Bi4MoO9 photocatalysts:Bi4MoO9 is a promising photocatalyst for air pollutant mineralization due to its very positive valance band edge at 3.48 eV.However,its performance usually suffers from its wide band gap and high charge recombination rate,which limits its scaled application.To address these issues,one novel Bi4MoO9/Bi0 core/shell heterostructured photocatalyst with considerable number of oxygen vacancies was synthesized through a facile surface chemical reduction treatment over the pre-synthesized Bi4MoO9 microrods in NaBH4 aqueous solution.The combined TEM/HRTEM,UV-Vis DRS,PL and ESR study reveals that the construction of Bi4MoO9/Bi0 heterojunction in the core/shell structure,the surface plasmon resonance(SPR) of Bi metal and the oxygen vacancy-induced formation of defect states all contribute to an intensified photoabsorption,charge separation efficiency and generation of oxidative radicals.The photocatalytic NO removal test under visible light irradiation shows that Bi4MoO9/Bi0-40(40 denotes the molar ratio of NaBH4 to Bi4MoO9 is 40/60) presents a maximum NO removal efficiency of 55.4%,much higher than that of the original Bi4MoO9(12.7%).The reaction pathway of the photocatalytic NO oxidation over the Bi4MoO9/Bi0 was examined by in-situ DRFTS and the NO+ species as a kind of intermediate product in NO conversion is detected and critical for the conversion of NO to nitrate.The present work provides a new approach to activate the non-visible-light response semiconductor for efficient visible light photocatalysis.Bi/Bi2O3/Bi2WO6 photocatalysts:Amorphous semiconductors usually suffer from low photocatalysis efficiency due to the fast charge recombination rate.In this work,to activate the amorphous Bi2WO6,BibO3 and Bi particles were in sequence deposited over its surface via a facile in situ chemical reduction of amorphous Bi2WO6 by NaBH4 at room temperature.In the resultant ternary Bi/Bi2O3/Bi2WO6,the well-formed heterojunctions(i.e.Bi-Bi2O3 and Bi2O3-Bi2WO6)and the surface plasmon resonance effect of Bi both contribute to an increase in charge carrier concentration,an efficient e-/h+ separation and then an enhanced visible light photocatalytic performance.The molar ratio of Bi,Bi2O3 and Bi2WO6 in composite can be modulated by the dosage of NaBH4,and consequently the amount of each heterojunction(i.e.Bi/Bi2O3 or Bi2O3/Bi2WO6) as well as the intensity of SPR effect could be tuned.The photocatalytic NO removal test under visible light irradiation shows that BWO-0.8(0.8 denotes the molar ratio of NaBH4 to Bi2WO6) presents a maximum NO removal efficiency of 55.4%,much higher than that of the pristine amorphous Bi2WO6(10%).The enhanced activity can be attributed to the balanced SPR effect of Bi metal and the heterojunction effeet,making their overall contribution maximized.The pathway study of photocatalytic NO oxidation by in situ FT-IR suggests that NO is converted to nitrates adsorbed over the catalyst surface.The present work could provide a new approach to activate the amorphous semiconductors for efficient visible light photocatalysis.This paper provided the experimental and thoeratical evidence on the activation of wide-band gap bismuth-base semiconductor materials or amorphous semiconductor materials by study the combination of Bi SPR effect,surface oxygen defect or heterojunction effect.And the in situ FT-IR study was employed to explore the photocatalysis reaction path way of NO oxidation.This paper also provides a reference for the application of heterogeneous gas-solid phase reaction of photocatalytic technology to the application of atmospheric pollutant control.