Li Yingwei, Jin Rongchao
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Nanoscale Horiz. 2023 Jul 24;8(8):991-1013. doi: 10.1039/d3nh00125c.
When plasmonic metal nanoparticles become smaller and smaller, a new class of nanomaterials-metal nanoclusters of atomic precision-comes to light and has become an attractive research topic in recent years. These ultrasmall nanoparticles (or nanoclusters) are unique in that they are molecularly uniform and pure, often possess a quantized electronic structure, and can grow into single crystals as do protein molecules. Exciting achievements have been made by correlating their properties with the precise structures at the atomic level, which has provided a profound understanding of some mysteries that could not be elucidated in the studies on conventional nanoparticles, such as the critical size at which plasmons are emergent. While most of the reported nanoclusters are spherical or quasi-spherical owing to the reduced surface energies (and hence stability), some anisotropic nanoclusters of high stability have also been obtained. Compared to the anisotropic plasmonic nanoparticles, the nanocluster counterparts such as rod-shaped nanoclusters can provide insights into the growth mechanisms of plasmonic nanoparticles at the early stage (, nucleation), reveal the evolution of properties (, optical), and offer new opportunities in catalysis, assembly, and other themes. In this Review, we highlight the anisotropic nanoclusters of atomic precision obtained so far, primarily gold, silver, and bimetallic ones. We focus on several aspects, including how such nanoclusters can be achieved by kinetic control, and how the anisotropy gives rise to new properties over the isotropic ones. The anisotropic nanoclusters are categorized into three types, (i) dimeric, (ii) rod-shaped, and (iii) oblate-shaped nanoclusters. For future research, we expect that anisotropic nanoclusters will provide exciting opportunities for tailoring the physicochemical properties and thus lead to new developments in applications.
当等离激元金属纳米颗粒变得越来越小时，一类新型的纳米材料——原子精确的金属纳米团簇——开始出现，并在近年来成为一个有吸引力的研究课题。这些超小纳米颗粒（或纳米团簇）具有独特之处，它们在分子层面上是均匀且纯净的，通常具有量子化的电子结构，并且能像蛋白质分子一样生长成单晶。通过将它们的性质与原子水平的精确结构相关联，已经取得了令人兴奋的成果，这为一些在传统纳米颗粒研究中无法阐明的谜团提供了深刻的理解，比如等离激元出现的临界尺寸。虽然由于表面能降低（从而稳定性提高），大多数报道的纳米团簇是球形或准球形的，但也获得了一些具有高稳定性的各向异性纳米团簇。与各向异性的等离激元纳米颗粒相比，纳米团簇类似物，如棒状纳米团簇，可以为等离激元纳米颗粒早期生长机制（即成核）提供见解，揭示性质（如光学性质）的演变，并在催化、组装及其他领域提供新的机遇。在本综述中，我们重点介绍了迄今为止获得的原子精确的各向异性纳米团簇，主要是金、银和双金属纳米团簇。我们关注几个方面，包括如何通过动力学控制实现此类纳米团簇，以及各向异性如何比各向同性纳米团簇产生新的性质。各向异性纳米团簇分为三种类型：（i）二聚体，（ii）棒状，和（iii）扁球形纳米团簇。对于未来的研究，我们期望各向异性纳米团簇将为定制物理化学性质提供令人兴奋的机会，从而在应用方面带来新的发展。
