【作者】 王丹；

【导师】 刘美英；

【作者基本信息】 辽宁师范大学 ， 无机化学， 2022， 硕士

【摘要】 光催化技术能够将太阳能转化为化学能,在污水处理、分解水制氢、CO₂还原及有机合成等环境和能源领域显示广阔的应用前景。光催化反应是在催化剂表面进行的反应,其活性与催化剂的能带、晶相、晶形、晶粒大小、表面积尤其暴露晶面等密切相关。作为光催化家族的重要成员,BiOBr拥有特殊的层状结构和合适的带隙。本文以BiOBr为研究对象,首次引入生物分子γ-聚谷氨酸（γ-PGA）作为表面活性剂,对其晶相、形貌以及暴露晶面进行灵活地调控,以期获得性能优异的光催化材料。具体研究内容如下:1)以Bi（NO₃）₃·5H₂O为Bi源、CTAB为Br源、γ-PGA为表面活性剂,采用简单的水热法制备了一系列BiOBr光催化材料,利用XRD、SEM、HR（TEM）、XPS、N₂吸附-脱附、UV-vis、Mott-Schottky、PL、TPC与EIS等技术探究Bi³⁺/CTAB（摩尔比）及γ-PGA的加入量与产物的晶相结构、微观形貌、暴露晶面、光生电荷分离与复合以及光催化性能之间的内在关联。结果表明:所得产物均为四方相BiOBr;Bi³⁺/CTAB=1:1时,BiOBr呈方形纳米片,Bi³⁺/CTAB=1:2,BiOBr呈圆形纳米片;随γ-PGA的加入,BiOBr从团聚、不规则微米片逐渐转变为均匀的纳米片,且衍射峰强度I（102）/I（001）比逐渐增大,表明γ-PGA的加入使得（102）晶面择优生长,活性晶面也由{001}转变为{010}晶面。在可见光照射下,暴露{010}晶面的方形BiOBr呈现最佳光催化活性,80 min内RhB分子的降解率约为77.4%,此值为暴露{001}晶面的BiOBr（未加入γ-PGA）活性速率的2.1倍;且四次循环反应后,BiOBr的光催化性能、晶相结构和形貌结构均保持恒定;此优异的光催化性能归因于{010}暴露晶面的BiOBr促进了光生电子-空穴的分离和转移。2)为进一步改善BiOBr的光催化性能,这部分工作以γ-PGA为表面活性剂、同时用Na OH调控溶液的pH,采用水热法制备得到具有多晶结构的3D纳米花状BiOBr,其最佳合成条件为pH=3、γ-PGA=100 mg、Bi³⁺/CTAB=1:2、T=160℃、t=24 h。在可见光照射下,RhB降解和Cr（Ⅵ）还原为Cr（III）的光催化效率可达92.2%和96.8%,分别是未添加γ-PGA的BiOBr光催化速率的3.1倍和16.4倍。优异的光催化性能归因于BiOBr纳米花拥有高的比表面积（29.28 m²/g）和较高的电子-空穴分离和传输速率。3)以NaBiO₃为新型Bi源,探究γ-PGA对产物晶相结构和形貌的调变规律,结果与Bi（NO₃）₃·5H₂O为铋源类似。γ-PGA辅助的水热合成新颖、方便且环保,能够用于其它新型纳米结构的制备和开发,以期获得性能优异的新型光催化剂。更多还原

【Abstract】 Photocatalytic technology,which can convert solar energy into chemical energy,shows promising applications in environment and energy fields such as sewage treatment,water splitting to H₂,CO₂reduction and organic synthesis.It is well known that a photocatalytic reaction is carried out on the surface of a catalyst.Therefore,the photocatalytic performance of a photocatalyst is closely dependent on its band-gap structure,crystalline phase,shape,crystalline size、BET surface area especially the exposed lattice facet.In this thesis,BiOBr,with a lamellar structure and appropriate energy-band for visible light,will be investigated.For the purpose of achieving much superior photocatalytic performance,biomoleculeγ-polyglutamic acid（γ-PGA）is employed firstly as a surfactant to flexibly control the crystal phase,morphology and exposed crystal facets of BiOBr.The specific research contents are as follows:1)A series of BiOBr photocatalyticr materials have been fabricated via a facile hydrothermal synthesis by adopting Bi（NO₃）₃·5H₂O as Bisource、CTAB as Br source andγ-PGA as surfactant.The effects of Bi³⁺/CTAB molar ratios and the amount ofγ-PGA on the crystalline phase,shape,exposed lattice facet,crystalline size,BET surface area and pore-size characteristics of BiOBr have been systematically investigated by XRD,SEM,HR（TEM）,XPS,N₂adsorption-desorption isotherms.More significantly,the intrinsic correlations between the light-absorption as well as the charge-sepation ability and the photocatalytic performance have been revealed based on the results of UV-vis,Mott-Schottky,PL,TPC and EIS.Bi³⁺/CTAB molar ratios exert an obvious effect on the morphology of tetragonal BiOBr.Square and circular nanosheets of tetragonal BiOBr are obtained when the molar ratios of Bi³⁺/CTAB are controlled at 1:1 and 1:2,respectively.Also,the morphologies of BiOBr are depenedent on the presence ofγ-PGA.In presence ofγ-PGA,BiOBr is transformed from many ingregated and irregular sheet-like microparticles into uniform nanosheets.In addition,the XRD diffraction-peak-intensity ratio of I（102）/I（001）gradually increases with increasing the amount ofγ-PGA,indicating the prefered growth of（102）crystal facet.Correspondingly,the exposed crystal-facet of tetragonal BiOBr changes from{001}into{010}crystal facet.Under visible-light illumination,BiOBr square nanosheets with exposed{010}facet shows the optimum photocatalytic activity with the 77.4%degradation effeciency of aqueous RhB within 80 min.The activity is 2.1 times that of BiOBr（in absence ofγ-PGA）with exposed{001}facet.No obvious change in the photocatalytic performance,phase structure and morphology of BiOBr before and after the 4th recycled reaction,indicating the high stability of as-obtained BiOBr nanosheets.Such excellent photocatalytic performance is mainly attributed to the promoted the separation and transfer of photogenerated electrons and holes in tetragonal BiOBr nanosheets with{010}exposed facets.2)In order to improve the photocatalytic performance,BiOBr 3D nanoflowers with polycrystalline structure have been fabricated in appropriate Na OH aqueous solutions via hydrothermal synthesis in presence ofγ-PGA as the structure-directing aget.The optimum synthesis conditions are as follows:pH=3,γ-PGA=100 mg,Bi³⁺/CTAB=1:2,T=160℃and t=24 h.Under visible light illumination,the photocatalytic effeciency of RhB degradation and Cr（Ⅵ）reduced to Cr（III）reaches 92.2%and 96.8%,respectively,which are 3.1 and 16.4times those of BiOBr in absence ofγ-PGA.Such superior photocatalytic performance of BiOBr nanoflowers is ascribed to the high specific surface area（29.28 m²/g）as well as the enhanced electron-hole separation and transport.3)The effects of γ-PGA on the crystal phase structure and morphology of BiOBr have been investigated by adopting NaBiO₃as a novel Bisource.The results are similar to those of using Bi（NO₃）₃·5H₂O as Bisource.Theγ-PGA-assisted hydrothermal synthesis is novel,facile and environment-benign,and can be used for the preparation and development of other nanostructures which is expected to fabricate novel photocatalysts with excellent photocatalytic performance.更多还原