基于异质结作用和上转换效应的CQDs/Bi2O4/TiO2复合物光催化性能研究

Monoclinic Bi2O4 (Bi3+Bi5+O4) exhibits favorable visible light photocatalytic performance, but the loss of photocatalytic activity occurs during photocatalysis process due to the gradual reduction of Bi5+ to Bi3+. In this project, the composites of CQDs/Bi2O4/TiO2(CBT) are designed elaborately, aiming to the improvement of photocatalytic activity and photostability of Bi2O4 under simulated solar. In the CBT, the reduction of Bi5+ is expected to be supressed and the visible light photocatalytic activity of Bi2O4 will be enhanced based on the type II heterojunction interaction between Bi2O4 and TiO2. In addition, photocatalytic activity of CBT under near-infrared light (NIR) will be excited through the upconversion effect of NIR from carbon quantum dots (CQDs). The improvement mechanism of photocatalytic activity and photostability of Bi2O4 will be revealed via the investigation of Bi2O4/TiO2 heterojunction in the role of separation of photoinduced carriers. The essential role of CBT in the transfer and separation of photogenerated carriers will be deduced by the study of charges transfer and separation mechanism between interfaces of CQDs、Bi2O4 and TiO2. The photocatalytic mechanism of CBT under NIR will be elaborated through the research of relations of CQDs’s upconversion effect for NIR to photocatalytic activity of Bi2O4 and TiO2. Based on the above researches, the simulated solar light photocatalytic activity and photostability improvement mechanism of CBT composites will be inferred.

单斜相Bi2O4 (Bi3+Bi5+O4)具有较好的可见光催化活性，但其在光催化反应过程中Bi5+会逐渐被还原为Bi3+导致活性降低。本项目拟设计CQDs/Bi2O4/TiO2复合物(CBT)，通过Bi2O4与TiO2的II型异质结作用抑制Bi5+还原并提高Bi2O4可见光活性，以及CQDs(碳量子点)对 (近)红外光)(NIR)的上转换效应，产生NIR催化活性，从而提高Bi2O4的模拟太阳光催化活性和稳定性。通过研究Bi2O4/TiO2异质结对光生电荷的分离作用，揭示其对Bi2O4光催化活性和稳定性的提高机理；探讨CQDs、Bi2O4、TiO2界面电荷迁移机制，揭示CBT复合物对光生电荷分离与迁移的作用本质；通过CQDs对NIR的上转换效应与Bi2O4、TiO2光催化活性的关系研究，揭示CBT复合物的NIR活性产生机理；通过上述研究来阐述CBT复合物的模拟太阳光催化活性和稳定性增强机理。

Bi2O4具有较好的可见光催化活性，但其单独使用存在光生载流子容易复合、比表面积很低、表面活性位数量少等缺点。针对上述问题，本项目开展了以下几方面工作。一、基于碳量子点(CQDs)优异的导电子作用和上转换效应，用N-CQDs对Bi2O4进行表面修饰，促进光生电荷分离，扩展太阳光谱响应范围，提高光催化性能。在模拟太阳光、可见光和近红外光条件下，0.3% N-CQDs/Bi2O4对甲基橙(MO)的光催化降解速率分别是纯Bi2O4的3.1、2.3和2.9倍。二、构建Bi2O4@TiO2核-壳结构、TiO2纳米带-Bi2O4 II型异质结，不改变Bi2O4形貌，但可明显提高Bi2O4可见光催化降解活性。用烟花状和花球状二种多级结构TiO2微球限域Bi2O4生长，实现Bi2O4纳米化并原位构筑Bi2O4-TiO2 II型异质结，促进光生电荷分离，提高比表面积和表面活性位浓度。 Bi2O4-TiO2(烟花状)异质结最优样品对MO和四环素(TC)的可见光催化降解活性分别是Bi2O4的2.5倍和1.53倍，Bi2O4-TiO2(花球状) 异质结最优样品对MO的可见光催化降解活性是Bi2O4的3.1倍。三、构筑花球状TiO2-Bi2O4-N-CQDs多级结构复合物，复合物显著提高了对MO的近红外光、可见光和模拟太阳光催化降解性能。四、采用一锅水热法制备Bi2O3/Bi2O4 p-n结，既可部分调变Bi2O4形貌，棒状和纳米颗粒Bi2O4共存，又提高了Bi2O4对MO和苯酚的可见光催化降解活性，最优p-n结样品对MO和苯酚的可见光催化降解活性分别是Bi2O4的2.4倍和1.49倍。采用原位酸刻蚀与水热相结合法制备Bi2O3/Bi2O4 p-n结，形成Bi2O4纳米颗粒负着于片状Bi2O3表面的异质结构，增大比表面积，最优p-n结样品对MO和苯酚的可见光催化降解活性分别是Bi2O4的5.06倍和2.16倍。