da Silva Anderson G M, Rodrigues Thenner S, Haigh Sarah J, Camargo Pedro H C
Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-000, São Paulo, SP, Brazil.
Chem Commun (Camb). 2017 Jun 29;53(53):7135-7148. doi: 10.1039/c7cc02352a.
Metallic nanoparticles have been extensively studied towards applications in catalysis. Among the several methods for their controlled synthesis, galvanic replacement is particularly attractive as it enables the production of bimetallic and hollow nanomaterials displaying ultrathin walls in a single reaction step. This procedure is versatile, but final morphologies are often limited to shapes that represent the hollow analogues of the starting template nanocrystals. For catalytic applications, it is highly desirable to broaden the scope of physicochemical control that can be achieved by this method. This feature article discusses recent strategies developed in our group for the synthesis of hollow bimetallic nanomaterials by galvanic replacement that enable a further level of control over surface morphologies and composition. We begin by briefly explaining the fundamentals of the conventional galvanic replacement reaction between Ag and AuCl. This is one of the most characteristic galvanic replacement reactions, and it can be tuned to create a huge variety of nanoparticle morphologies. We will discuss how advanced electron microscopy characterization enables us to uncover surface-segregation behavior as a function of compositions, and relate this to the detected catalytic performance. We will also discuss how galvanic replacement can be extended to trimetallic compositions, leading to improvements in catalytic activities compared to mono or bimetallic counterparts. Furthermore, we will show how surface morphology, size, and anisotropic growth can be controlled by tuning the temperature during the synthesis and by combining galvanic replacement reaction with co-reduction. Finally, we will demonstrate how these approaches are promising for large-scale synthesis of controlled hollow nanostructures and their incorporation into supports to produce catalysts at the gram-scale. We believe the developments described herein shed important insights and may inspire the development of sophisticated and controlled nanomaterials at relatively larger scales for catalytic applications.
金属纳米颗粒在催化应用方面已得到广泛研究。在其多种可控合成方法中，电化置换特别具有吸引力，因为它能在单一反应步骤中制备出具有超薄壁的双金属和中空纳米材料。该方法用途广泛，但最终形态往往局限于起始模板纳米晶体的中空类似形状。对于催化应用而言，非常希望拓宽通过该方法可实现的物理化学控制范围。这篇专题文章讨论了我们小组最近开发的通过电化置换合成中空双金属纳米材料的策略，这些策略能进一步控制表面形态和组成。我们首先简要解释Ag与AuCl之间传统电化置换反应的基本原理。这是最具代表性的电化置换反应之一，可对其进行调整以创造出多种多样的纳米颗粒形态。我们将讨论先进的电子显微镜表征如何使我们能够揭示作为组成函数的表面偏析行为，并将其与检测到的催化性能联系起来。我们还将讨论电化置换如何扩展到三金属组成，与单金属或双金属对应物相比，这会导致催化活性的提高。此外，我们将展示如何通过在合成过程中调节温度以及将电化置换反应与共还原相结合来控制表面形态、尺寸和各向异性生长。最后，我们将展示这些方法对于大规模合成可控中空纳米结构以及将其结合到载体中以制备克级催化剂具有怎样的前景。我们相信本文所述的进展提供了重要的见解，并可能激发在相对更大规模上开发用于催化应用的复杂且可控的纳米材料。
