Nonaqueous Synthesis of TiO2 Nanocrystals Using TiF4 to Engineer Morphology, Oxygen Vacancy Concentration, and Photocatalytic Activity
Nonaqueous Synthesis of TiO2 Nanocrystals Using TiF4 to Engineer Morphology, Oxygen Vacancy Concentration, and Photocatalytic Activity
复制标题
DOI：
10.1021/ja300823a
复制
发表时间：
2012-04-18
影响因子：
15
通讯作者：
Murray, Christopher B.
中科院分区：
文献类型：
--
作者：
Gordon, Thomas R.;Cargnello, Matteo;Murray, Christopher B.
对纳米晶体 (NC) 中刻面的控制对于许多应用都至关重要，但最值得注意的是在研究纳米结构表面发生的催化反应时。锐钛矿型二氧化钛（TiO2）是研究最多的光催化剂之一，但其活性的形状依赖性尚未得到令人满意的研究，许多问题仍未得到解答。我们报告了非水表面活性剂辅助合成高度均匀的锐钛矿型 TiO2 NC，其形态可调节，尺寸范围为 10-100 nm，通过晶种生长技术制备。引入氟化钛（IV）（TiF4）通过原位释放氢氟酸（HF）优先暴露锐钛矿的{001}面，从而形成基于截断四方双锥几何形状的均匀锐钛矿NC。描述了一种通过选择助表面活性剂和钛前体来设计{001}和{101}面的百分比的方法。 X 射线衍射研究与模拟相结合，以确定平均 NC 尺寸，该尺寸与使用电子显微镜获得的结果相关。除了改变颗粒形状之外，在合成中引入 TiF4 还可以生成蓝色的 TiO2 NC，并显示出广泛的可见光/近红外吸收率，其峰值位于红外区（λ（最大值）大约为 3400 nm）。电子顺磁共振 (EPR) 和 X 射线光电子能谱 (XPS) 研究表明，蓝色是氟存在时形成的氧空位的结果。通过简单的配体交换程序去除NC表面的表面活性剂，从而可以使用单分散TiO2 NC来研究光催化析氢的形状依赖性。甲醇作为模型牺牲剂的光重整初步实验在模拟太阳光照下产生了大量的氢气（高达 2.1 mmol h(-1) g(-1)）。值得注意的是，数据表明，在我们的实验条件下，锐钛矿的 {101} 面比 {001} 面更活跃。
Control over faceting in nanocrystals (NCs) is pivotal for many applications, but most notably when investigating catalytic reactions which occur on the surfaces of nanostructures. Anatase titanium dioxide (TiO2) is one of the most studied photocatalysts, but the shape dependence of its activity has not yet been satisfactorily investigated and many questions still remain unanswered. We report the nonaqueous surfactant-assisted synthesis of highly uniform anatase TiO2 NCs with tailorable morphology in the 10-100 nm size regime, prepared through a seeded growth technique. Introduction of titanium(IV) fluoride (TiF4) preferentially exposes the {001} facet of anatase through in situ release of hydrofluoric acid (HF), allowing for the formation of uniform anatase NCs based on the truncated tetragonal bipyramidal geometry. A method is described to engineer the percentage of {001} and {101} facets through the choice of cosurfactant and titanium precursor. X-ray diffraction studies are performed in conjunction with simulation to determine an average NC dimension which correlates with results obtained using electron microscopy. In addition to altering the particle shape, the introduction of TiF4 into the synthesis results in TiO2 NCs that are blue in color and display a broad visible/NIR absorbance which peaks in the infrared (lambda(max) approximate to 3400 nm). The blue color results from oxygen vacancies formed in the presence of fluorine, as indicated by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) studies. The surfactants on the surface of the NCs are removed through a simple ligand exchange procedure, allowing the shape dependence of photocatalytic hydrogen evolution to be studied using monodisperse TiO2 NCs. Preliminary experiments on the photoreforming of methanol, employed as a model sacrificial agent, on platinized samples resulted in high volumes of evolved hydrogen (up to 2.1 mmol h(-1) g(-1)) under simulated solar illumination. Remarkably, the data suggest that, under our experimental conditions, the {101} facets of anatase are more active than the {001}.