金/板钛矿二氧化钛复合材料的制备及其可见光催化活性研究

Plasmonic metal can photosensitize TiO2 to achieve visible-light-driven photocatalytic properties, which exhibits promising application for high-utilization of solar energy. To date, the investigations of the visible-light-driven metal/TiO2 composites are mainly focused on the morphology/size/surrounding control of Au particles to enlarge the visible light absorption; however, very little attention is paid to the effect of conduction band potential of TiO2 on the visible-light-driven photocatalytic performance. Considering the more negative conduction band potential is beneficial for the more reductive hot-electrons, brookite TiO2, which own more negative conduction band potential in comparison with that of anatase and rutile TiO2, will be chosen to synthesize the Au/brookite TiO2 composite photocatalysts. Firstly, brookite TiO2 with high percentage of active facets exposed will be synthesized via controlling the experimental parameters, aiming to optimize both the electronic band structure and the surface reactivity of brookite TiO2. Then, Au nanoparticles will be selectively loaded on various facets of brookite TiO2, and the photocatalytic performance of the above-synthesized Au/brookite TiO2 composites will be carried out. Finally, the in-situ characterization will be adopted to reveal the micromechanism of the hot-electron transfer, which will help to clarify both the effect of conduction band potential on the charge transfer process and the structure-activity relationship between the exposed facet of brookite TiO2 and the visible-light-driven photocatalytic performance of the Au/brookite TiO2 composites. This project will provide fundamental understanding for developing plasmonic metal/facet-optimized brookite TiO2 composite materials.

金属粒子光敏化TiO2可见光催化技术在太阳光利用领域表现出引人注目的应用前景。目前，金属/TiO2可见光催化研究主要集中在调控Au纳米粒子的形貌、尺寸、接触介质等拓宽其可见光吸收范围，忽略了TiO2基体导带电势对其可见光催化性能的影响。鉴于TiO2导带电势的提升有利于提高热电子还原能力，本项目提出选用比锐钛矿、金红石型TiO2导带电势更负的板钛矿TiO2作为基体材料。通过优化反应条件参数，制备晶面暴露比例高的板钛矿TiO2，调控其能带结构及表面反应活性；并实现Au纳米粒子在板钛矿TiO2不同晶面的选择性沉积，评价其可见光催化分解水产氢活性；结合原位表征技术揭示热电子转移微观机制，阐明导带电势与热电子转移之间规律以及板钛矿TiO2暴露晶面与Au/板钛矿TiO2可见光催化活性之间构效关系。项目的实施将为基于表面等离子共振效应的金属/晶面可控板钛矿TiO2复合光催化材料的研制提供理论及实践基础。

金属粒子光敏化TiO2可有效拓宽其可见光响应，在光催化研究方面意义重大。为了研究基体TiO2导带电势对Au@TiO2间肖特基势垒及TiO2表面光催化还原反应效率的影响，我们开展了一系列研究。首先，系统研究了板钛矿TiO2表面原子结构和表面电子结构对其光催化性能的影响。通过调节前驱体溶液pH值，制备出暴露{121}和{211}晶面的板钛矿TiO2。理论计算与实验结果综合表明：{121}晶面的价带电势较正，有助于氧化半反应；而{211}晶面的导带电势较负，有利于还原半反应。其次，为了充分利用可见光，制备Au光敏化TiO2反应体系，阐明了晶面暴露不同的基体TiO2导带电势对热电子从Au到TiO2转移效率及可见光催化性能影响规律。强光条件下（可见光光强为338 mW cm−2），大量被激发的热电子聚集使Au费米能级负移，降低了Au/TiO2界面处肖特基势垒，有利于热电子从Au颗粒向TiO2导带连续注入，此时T211较负的导带电势和较快的电子迁移率成为产氢活性较高的原因；而在弱光条件下（单色光，光强为2~20 mW cm-2），热电子的聚积程度较低，导致肖特基势垒成为控制热电子转移效率及光催化活性的控制因素。最后，改变反应溶液碱度连续调控了TiO2表面能带结构，解析了TiO2导带电势、Au/TiO2间肖特基势垒与可见光催化活性之间的构效关系。通过改变反应环境碱度从PH=6.0到pH=13.7，TiO2表面还原反应电势电位不断负移，Au@TiO2的光化学阻抗先减小后增大；碱度的增加有利于牺牲剂甲醇氧化以促进电子传输，但当碱度超过一定范围后（pH=13.5），会极大的增加肖特基势垒阻碍电子传递，从而降低光催化性能。