Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Am Chem Soc. 2012 Apr 18;134(15):6751-61. doi: 10.1021/ja300823a. Epub 2012 Apr 5.
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 (TiO(2)) 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 TiO(2) NCs with tailorable morphology in the 10-100 nm size regime, prepared through a seeded growth technique. Introduction of titanium(IV) fluoride (TiF(4)) 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 TiF(4) into the synthesis results in TiO(2) NCs that are blue in color and display a broad visible/NIR absorbance which peaks in the infrared (λ(max) ≈ 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 TiO(2) 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}.
控制纳米晶体（NCs）的晶面是许多应用的关键，特别是在研究发生在纳米结构表面的催化反应时。锐钛矿二氧化钛（TiO2）是研究最多的光催化剂之一，但它的活性与形状的关系尚未得到令人满意的研究，许多问题仍然没有答案。我们报告了在非水相表面活性剂辅助下合成高度均匀的锐钛矿 TiO2 NCs 的方法，该方法可在 10-100nm 尺寸范围内实现形貌可调，通过种子生长技术制备。通过原位释放氢氟酸（HF），引入四氟化钛（TiF4）优先暴露锐钛矿的{001}面，从而形成基于截角四方双锥几何形状的均匀锐钛矿 NCs。描述了一种通过选择助表面活性剂和钛前体制备具有{001}和{101}面比例的方法。通过与模拟相结合的 X 射线衍射研究来确定 NC 的平均尺寸，该尺寸与使用电子显微镜获得的结果相关。除了改变颗粒形状外，将 TiF4 引入合成中还会导致 TiO2 NCs 呈蓝色，并显示出宽的可见/近红外吸收，峰值在红外（λ（max）≈3400nm）。蓝色是由于氟存在时形成的氧空位所致，这一点通过电子顺磁共振（EPR）和 X 射线光电子能谱（XPS）研究表明。通过简单的配体交换程序去除 NC 表面的表面活性剂，允许使用单分散 TiO2 NCs 研究光催化析氢的形状依赖性。在模拟太阳光照射下，初步实验研究了甲醇的光重整，甲醇作为牺牲剂，在镀铂样品上得到了高达 2.1mmol h-1 g-1的高体积产氢量。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。
