La掺杂BiFeO_3对苯酚光催化降解性能的影响(英文)

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苯酚是一种稳定、毒性大且难降解的有机物,对人类和生态环境产生很大威胁,因此急需研发出能有效移除工业废水中苯酚污染物的方法.其中,绿色、高效的光催化氧化技术得到研究人员青睐.在半导体光催化剂中,BiFeO_3具有带隙窄(2.2–2.5eV)、化学稳定性好及成本低等优点,被看作是最有潜力的光催化剂.但是,BiFeO_3存在光生电子空穴对复合率高,制备过程中易形成杂质相的缺点,使得其光催化活性很差,限制了BiFeO_3在光催化领域的应用.异种离子的引入能产生杂质能级或裁剪半导体带隙,同时促进光生载流子分离,故可考虑采用离子掺杂改性BiFeO_3的手段来抑制杂质相生成,提高载流子分离,从而提高BiFeO_3的光催化性能.本文以柠檬酸为络合剂,通过一步溶胶凝胶法合成了系列样品Bi_(1-x)La_xFeO_3(摩尔分数x=0,0.10,0.15,0.20).通过X射线衍射(XRD)、扫描电镜(SEM)、能谱(EDS)、透射电镜(TEM)、X射线光电子能谱(XPS)、紫外可见漫反射(UV-VisDRS)及荧光光谱(PL)等手段对不同样品的物相、形貌、表面价态和光学性能进行了表征.并通过活性物种捕获实验和羟基自由基(·OH)产生实验分析了Bi0.85La0.15FeO_3样品在苯酚降解过程中的主要活性物种和降解机理.相对于单相BiFeO_3,La改性BiFeO_3催化剂的光降解苯酚性能均有提高,其中La最佳掺杂量为0.15.在模拟太阳光下照射180min后,Bi0.85La0.15FeO_3的光催化活性达到96%,同时COD去除率达到81.53%,并表现出好的循环使用活性和稳定性.研究发现,该光催化过程中主要的活性物种为·OH.XRD,SEM,TEM和EDS结果表明,La元素掺杂进BiFeO_3结构中,且各元素分布均匀,同时,适量La元素掺杂能有效抑制杂质相Bi25FeO_40的形成,而且La掺杂BiFeO_3样品的颗粒尺寸略有减小,有利于电子空穴转移.XPS显示,La改性BiFeO_3样品的表面有氧空位形成,将有利于有机物的吸附和降解;另外,羟基氧和吸附氧含量增大,有利于活性氧物种形成.UV-VisDRS和PL测试证明,La改性后的样品对可见光的响应增强,样品带隙变窄,产生杂质能级,抑制了光生载流子复合,有利于产生更多载流子来促进活性物种形成,从而提高光催化活性.氧物种捕获实验说明,在Bi_(0.85)La_(0.15)FeO_3参与的苯酚降解过程中的主要活性物种是·OH,同时·OH的产生实验也证明了在光照下·OH在Bi_(0.85)La_(0.15)FeO_3光催化剂表面持续产生,并提出了光催化降解机理. Phenol is a stable, toxic and refractory organic matter, which poses a great threat to human beings and the ecological environment. Therefore, it is urgently necessary to develop a method that can effectively remove phenol pollutants from industrial wastewater. Among them, green and efficient photocatalytic oxidation Technology has been favored by researchers in the semiconductor photocatalyst, BiFeO_3 has narrow band gap (2.2-2.5eV), good chemical stability and low cost, is considered as the most promising photocatalyst.BeFeO_3 existence of photogenerated High electron-hole recombination rate and easy formation of impurity phase in the preparation process, making the photocatalytic activity of BiFeO3 poor, limiting the application of BiFeO3 in photocatalysis. The introduction of different ions can generate impurity levels or cut the semiconductor band gap , And to promote the separation of photo-generated carriers, we can consider the use of ion-doped modified BiFeO_3 means to suppress the impurity phase, increase carrier separation, thereby enhancing the BiFeO_3 photocatalytic performance.In this paper, citric acid as a complexing agent, A series of samples Bi_ (1-x) La_xFeO_3 (molar fraction x = 0,0.10,0.15,0.20) were synthesized by a one-step sol-gel method.According to XRD, SEM, EDS, ,transmission The phase, morphology, surface valence and optical properties of different samples were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-VisDRS and fluorescence spectroscopy (PL) The main active species and degradation mechanism of Bi0.85La0.15FeO_3 during the degradation of phenol were investigated by means of active species capture experiment and hydroxyl radical (· OH) production.Compared with single phase BiFeO_3, La modified BiFeO_3 catalyst The photodegradation of phenol was improved, and the optimal doping amount of La was 0.15.The photocatalytic activity of Bi0.85La0.15FeO_3 was 96% and the COD removal rate was 81.53% after 180min irradiation in simulated sunlight The results showed that the main active species in the photocatalytic process was · OH · XRD, SEM, TEM and EDS results show that the La element is doped into the BiFeO_3 structure, and the elements are evenly distributed , While proper La doping can effectively inhibit the formation of the impurity phase Bi25FeO_40, and the particle size of the La-doped BiFeO_3 sample slightly decreases, which is conducive to electron hole transfer.XPS shows that the surface of the La-modified BiFeO_3 sample has oxygen Vacancy formation will benefit In addition, the content of hydroxyl oxygen and adsorbed oxygen increased, which is conducive to the formation of reactive oxygen species.UV-VisDRS and PL tests showed that the response of La-modified sample to visible light is enhanced and the band gap of the sample is narrowed (0.85) La_ (0.15) FeO_3 (0.85) La_ (0.15) Fe_3 is obtained by the experiments of oxygen species capture, which results in the formation of impurity levels and the suppression of photocarrier recombination, which is conducive to the generation of more carriers to promote the formation of active species and improve the photocatalytic activity. The main active species involved in phenol degradation was · OH, and · OH production experiment also demonstrated that · OH was continuously produced on the surface of Bi_ (0.85) La_ (0.15) FeO_3 photocatalyst under light irradiation, and proposed photocatalytic degradation mechanism.
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