Bi单质/BiPO_4等离子体可见光催化净化NO的反应机理

The reaction mechanism of plasmonic photocatalytic NO oxidation on Bi-metal/BiPO_4

通过化学沉淀法制备出六方相BiPO_4,再经过Na BH_4还原在BiPO_4表面负载Bi单质,制备出Bi单质/BiPO_4复合光催化剂,并将其应用于空气中低浓度NO的净化.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见漫反射光谱(UV-vis DRS)和电子自旋共振(ESR)等表征手段对催化剂微观结构进行表征分析.利用原位红外光谱技术对催化剂可见光催化氧化NO的反应过程进行实时动态监测分析,结合ESR对自由基的捕获结果,提出了其反应机理.研究结果表明,单质Bi的表面等离子体效应促进了BiPO_4对可见光的吸收和光生电荷的分离.密度泛函理论(DFT)计算表明,氧缺陷的存在使得在磷酸铋的价带和导带之间形成了中间能级,有利于价带电子的跃迁.电子结构计算结果表明,单质Bi还充当储存和转移BiPO_4导带上电子的媒介,光生载流子的产生和迅速转移使得光生电子-空穴对复合率降低.通过Bi单质的等离子体效应使BiPO_4转化为可见光响应的高性能光催化剂.本文对于Bi单质基等离子体光催化的研究和气相光催化反应机理的认识提供了新的方法.

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,Bi O4 consists of alternating layers of[Bi2O2]^2＋and PO4^3-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/Bi PO4 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 X-ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,UV-visible diffuse-reflectance spectrum（UV-vis DRS）and electron spin-resonance spectroscopy（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 Bi PO4.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 Bi PO4.The generation and rapid transfer of photogenerated carriers could decrease the photogenerated electron-hole pair recombination rate.As a result,the Bi PO4 can be converted into a high 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.