Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
J Am Chem Soc. 2013 Feb 6;135(5):1845-52. doi: 10.1021/ja309948y. Epub 2013 Jan 28.
Shape-controlled metal nanocrystals are a new generation of nanoscale catalysts. Depending on their shapes, these nanocrystals exhibit various surface facets, and the assignments of their surface facets have routinely been used to rationalize or predict their catalytic activity in a variety of chemical transformations. Recently we discovered that for 1-dimensional (1D) nanocrystals (Au nanorods), the catalytic activity is not constant along the same side facets of single nanorods but rather differs significantly and further shows a gradient along its length, which we attributed to an underlying gradient of surface defect density resulting from their linear decay in growth rate during synthesis (Nat. Nanotechnol.2012, 7, 237-241). Here we report that this behavior also extends to 2D nanocrystals, even for a different catalytic reaction. By using super-resolution fluorescence microscopy to map out the locations of catalytic events within individual triangular and hexagonal Au nanoplates in correlation with scanning electron microscopy, we find that the catalytic activity within the flat {111} surface facet of a Au nanoplate exhibits a 2D radial gradient from the center toward the edges. We propose that this activity gradient results from a growth-dependent surface defect distribution. We also quantify the site-specific activity at different regions within a nanoplate: The corner regions have the highest activity, followed by the edge regions and then the flat surface facets. These discoveries highlight the spatial complexity of catalytic activity at the nanoscale as well as the interplay amid nanocrystal growth, morphology, and surface defects in determining nanocatalyst properties.
形状可控的金属纳米晶体是新一代纳米级催化剂。根据其形状，这些纳米晶体表现出不同的表面晶面，并且其表面晶面的分配通常用于在各种化学转化中合理化或预测其催化活性。最近，我们发现对于一维（1D）纳米晶体（金纳米棒），其催化活性不是沿着单根纳米棒的相同侧晶面保持不变，而是存在显著差异，并沿着其长度进一步显示出梯度，我们将其归因于由于其在合成过程中生长速率的线性衰减而导致的表面缺陷密度的潜在梯度（Nat. Nanotechnol.2012, 7, 237-241）。在这里，我们报告称，这种行为也扩展到二维纳米晶体，即使对于不同的催化反应也是如此。通过使用超分辨率荧光显微镜在单个三角和六角形金纳米板内映射出催化事件的位置，并与扫描电子显微镜相关联，我们发现金纳米板的平 {111} 表面晶面内的催化活性表现出从中心到边缘的二维径向梯度。我们提出，这种活性梯度是由生长相关的表面缺陷分布引起的。我们还量化了纳米板内不同区域的特定位置活性：角区域具有最高的活性，其次是边缘区域，然后是平面表面晶面。这些发现突出了纳米尺度上催化活性的空间复杂性，以及纳米晶体生长、形态和表面缺陷在确定纳米催化剂性质中的相互作用。
