摘要
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.
Efficient composite semiconductor photocatalysts are highly desirable for the visible-light-driven degradation of organic pollutants.In this study,Bi_(24)O_(31)Cl_(10) 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/Bi_(24)O_(31)Cl_(10) 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 Bi_(24)O_(31)Cl_(10).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.
引文
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