催化学报

催化学报 ›› 2019, Vol. 40 ›› Issue (5): 647-655.DOI: 10.1016/S1872-2067(19)63277-8

• 论文 • 上一篇    下一篇

氧空位对Bi2MoO6的关键作用:促进可见光光催化活性和反应机理

孙艳娟a,b, 王红b, 邢倩b, 崔雯b, 李解元c, 吴素娟a, 孙立东a   

  1. a 重庆大学材料科学与工程学院, 机械传动国家重点实验室, 重庆 400044;
    b 重庆工商大学环境与资源学院, 催化与新环境材料重庆市重点实验室, 重庆 400067;
    c 四川大学建筑与环境学院, 四川成都 610065
  • 收稿日期:2018-11-21 修回日期:2018-12-12 出版日期:2019-05-18 发布日期:2019-03-30
  • 通讯作者: 孙艳娟
  • 基金资助:

    国家自然科学基金（21501016，51501024，51871037，21822601）；中央大学基础研究基金（2018CDQYCL0027）.

The pivotal effects of oxygen vacancy on Bi2MoO6: Promoted visible light photocatalytic activity and reaction mechanism

Yanjuan Suna,b, Hong Wangb, Qian Xingb, Wen Cuib, Jieyuan Lic, Sujuan Wua, Lidong Suna   

  1. a State Key Laboratory of Mechanical Transmission, School of Materials Science and Engineering, Chongqing University, Chongqing 400044, China;
    b Chongqing Key Laboratory of Catalysis and New Environmental Materials, College of Environment and Resources, Chongqing Technology and Business University, Chongqing 400067, China;
    c College of Architecture and Environment, Sichuan University, Chengdu 610065, Sichuan, China
  • Received:2018-11-21 Revised:2018-12-12 Online:2019-05-18 Published:2019-03-30
  • Contact: S1872-2067(19)63277-8
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21501016, 51501024, 51871037 and 21822601), and the Fundamental Research Funds for the Central Universities (2018CDQYCL0027).

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摘要：

Bi2MoO6（BMO）作为一种典型的Bi基光催化剂，近年来受到越来越多的关注并被广泛应用.然而，Bi2MoO6的可见光光催化活性仍然存在一些限制，如有限的光响应范围和低电荷分离效率.为了提高光催化活性，研究者采取了各种策略，包括元素掺杂、形成异质结构和形貌控制等.早期研究表明，氧空位可以拓展光催化剂的光吸收区域，并且氧空位是光催化剂表面反应物活化最活跃的位点，可以促进电荷分离和使电子局域化.因此，制备具有氧空位的Bi基光催化剂可能是提高其光催化性能的有效途径.然而，氧空位对Bi2MoO6电子结构和光催化反应机理的影响尚不清楚.
本文通过在制备过程中加入NaBH4诱导氧空位形成，合成出了具有氧空位的可见光驱动的Bi2MoO6微球（BMO-X）.利用UV-vis DRS光谱研究了合成后的光催化剂的光学吸收性能，发现在产生氧空位后，BMO-4在可见区域的吸收显著增强，带隙从BMO的2.40 eV降低到BMO-4的2.07 eV.通常，较强的光吸收能力对光催化反应更有利，因为可以产生更多的光生载流子参与光催化作用.将所制备的催化剂用于光催化净化NO，结果表明具有氧空位的Bi2MoO6（BMO-4）的可见光催化NO净化效率为43.5%，远高于本体Bi2MoO6（BMO）的可见光光催化活性（25.0%）.结合实验表征和理论计算结果，探讨了氧空位对Bi2MoO6电子结构和光催化净化NO反应机理的影响.采用低温固态电子顺磁共振（EPR）检测了催化剂中的氧空位，在BMO中仅检测到弱的EPR信号，表明BMO中几乎没有氧空位，而BMO-4上的EPR信号非常强，表明NaBH4的引入诱导产生了大量的氧空位.DFT计算确认BMO-4的带隙内有中间能级形成.XPS测试结果表明，与BMO相比，BMO-4的Bi-O峰值强度略有下降，可能是由于部分Bi-O中缺少O原子以形成氧空位所致.PL结果表明，具有氧空位的Bi2MoO6（BMO-4）显示出显著降低的光激发电子-空穴对分离效率，可能是由于氧空位改变了Bi2MoO6的电子结构.此外，理论计算结果发现具有氧空位的Bi2MoO6的表面电子可以位于氧空位周围，这有利于电荷分离和反应物活化.同时，该结果表明BMO-4中增强的电荷分离归因于氧缺陷对改进的电子结构的影响.此外，电子局域化可以为反应物活化提供额外的活性位点（O2，NO等），这可以促进BMO-4中自由基的产生和污染物转化.利用原位红外光谱动态监测光催化NO氧化过程.与本体Bi2MoO6相比，引入氧空位后的Bi2MoO6光催化净化NO的反应机理未改变.但是，BMO-4上终产物的特征峰强度显著增大.此外，BMO-4上明显增加的多种形式的最终产物，桥接硝酸盐消失并转化为更稳定的双齿硝酸盐.这些结果可归因于氧空位可以促进电荷分离和自由基的大量产生，从而增强光催化氧化性能.本工作为理解光催化氧气空位和气相光催化反应机理提供了新的见解.

关键词: 氧空位, 光催化, 反应机理, 原位红外光谱, 一氧化氮净化

Abstract:

Bi2MoO6, a typical Bi-based photocatalyst, has received increasing interests and been widely applied in various fields. However, the visible light photocatalytic activity of Bi2MoO6 is still restricted by some obstacles, such as limited photo-response and low charge separation efficiency. In this work, we developed a facile method to introduce artificial oxygen vacancy into Bi2MoO6 microspheres, which could effectively address these problems and realize highly efficient visible light photocatalysis. The experimental and theoretical methods were combined to explore the effects of oxygen vacancy on the electronic structure, photocatalytic activity and the reaction mechanism toward NO removal. The results showed that the addition of NaBH4 during catalyst preparation induced the formation of oxygen vacancy in Bi2MoO6, which plays a significant role in extending the visible light absorption of Bi2MoO6. The visible light photocatalytic activity of Bi2MoO6 with oxygen vacancy was obviously enhanced with a NO removal ratio of 43.5%, in contrast to that of 25.0% with the pristine Bi2MoO6. This can be attributed to the oxygen vacancy that creates a defect energy level in the band gap of Bi2MoO6, thus facilitating the charge separation and transfer processes. Hence, more reactive radicals were generated and participated in the photocatalytic NO oxidation reaction. The in situ FT-IR was used to dynamically monitor the photocatalytic NO oxidation process. The reaction intermediates were observed and the adsorption-reaction mechanism was proposed. It was found that the reaction mechanism was unchanged by introducing the oxygen vacancy in Bi2MoO6. This work could provide new insights into the understanding of the oxygen vacancy in photocatalysis and gas-phase photocatalytic reaction mechanism.

Key words: Oxygen vacancy, Photocatalysis, Reaction mechanism, In situ FT-IR, NO removal