摘要
Efficient composite semiconductor photocatalysts are highly desirable for the visible-light-driven degradation of organic pollutants. In this study, Bi24O31Cl10 photocatalyst was prepared via a hydrothermal method and modified with Pt nanoparticles (NPs) through a facile deposition procedure. The composite photocatalyst was characterized by X-ray diffraction, transmission electronic microscopy, X-ray photoelectron spectroscopy, UV-vis diffusion reflectance spectroscopy, photoluminescence spectroscopy, and electron spin resonance. The 1.0 wt% Pt/Bi24O31Cl10 photocatalyst showed the highest activity for the degradation of methyl orange under visible light (source: 300 W Xe lamp coupled with a UV-cutoff filter), and the photocatalytic degradation efficiency improved about 2.2 times compared to that of pure Bi24O31Cl10. The composite photocatalyst could maintain most of its activity after four runs of the photocatalytic experimental cycle. This study could provide a novel insight for the modification of other desirable semiconductor materials to achieve high photocatalytic activities.
卤氧铋是一类具有独特层状堆叠结构的半导体光催化剂,但单一的卤氧铋存在着光生电子与空穴易复合等缺陷.而贵金属颗粒通常可以充当电子"陷阱",促进电荷转移,延长载流子寿命,从而产生更好的光催化性能.本文成功合成了Bi_(24)O_(31)Cl_(10)光催化剂,并对其进行Pt纳米颗粒修饰,从而获得了具有高光催化性能的光催化剂Pt/Bi_(24)O_(31)Cl_(10).其中,Bi_(24)O_(31)Cl_(10)是以Bi(NO_3)_3·5H_2O和NaCl作为前驱体并用氨水调节pH后水热制得,而Pt的负载使用光还原法.对获得的样品进行XRD测试并将结果与Bi_(24)O_(31)Cl_(10)的标准卡片进行对比,发现各峰的位置都有较好的对应,证明Bi_(24)O_(31)Cl_(10)合成成功.采用TEM观测Pt/Bi_(24)O_(31)Cl_(10)的形貌,发现Bi_(24)O_(31)Cl_(10)呈片状,其表面存在Pt颗粒.XPS测试发现,该样品只含有Pt,Bi,O,Cl四种元素,且它们的价态符合预期.这进一步说明成功合成了Pt/Bi_(24)O_(31)Cl_(10).考察了可见光照射下Bi_(24)O_(31)Cl_(10)和Pt负载量分别为0.5%,1%,2%和3%的Pt/Bi_(24)O_(31)Cl_(10)对甲基橙溶液的降解的光催化性能.结果表明,相比于载体,Pt/Bi_(24)O_(31)Cl_(10)的光催化性能有了显著提高,其中1%Pt/Bi_(24)O_(31)Cl_(10)的光催化活性最佳,并且在循环降解实验中表现出稳定的光催化活性.DRS测试结果表明,Bi_(24)O_(31)Cl_(10)的带隙宽度为2.45 eV,而Pt的负载有效减小了禁带宽度,从而提高了催化剂对光的利用率.对Bi_(24)O_(31)Cl_(10)进行了DFT建模,结果显示,Bi,Cl和O原子的排列遵循分层叠加模型,且每层垂直于内部静电场堆叠.而从它的能带结构和状态密度(DOS)可知,其导、价带边沿较为分散,这意味着光生载流子的有效质量较小,从而使载流子的运输更为容易.利用DRS以及对Bi_(24)O_(31)Cl_(10)能带结构的计算结果,根据半经验公式可知,Bi_(24)O_(31)Cl_(10)的导、价带位置分别为0.395和2.845 eV.而Pt的费米能级为0.8 eV.结合ESR测试结果,可对Pt/Bi_(24)O_(31)Cl_(10)催化降解甲基橙的过程提出合理猜想:Bi_(24)O_(31)Cl_(10)被光激发后,其表面的Pt充当电子"陷阱"以促进电子和空穴分离,被Pt捕获的电子与表面吸附的O_2形成O_2~–,并进一步与甲基橙反应,完成光降解过程.
基金
supported by the National Natural Science Foundation of China(51572295,21273285 and 21003157)
Beijing Nova Program(2008B76)
Science Foundation of China University of Petroleum Beijing(KYJJ2012-06-20 and 2462016YXBS05)~~
