Abstract:

Alloy metal nanoclusters (NCs), including bimetallic and multimetallic clusters, have recently emerged as a novel class of multifunctional nanomaterials. They are widely used in catalysis, optical sensing, and biological imaging due to their excellent physicochemical properties such as unique electronic structure, ultrasmall size, strong photoluminescence, and rich surface chemistry. Although much progress has been made in the development of NCs, a major challenge in the synthesis of the relevant multifunctional nanomaterial is to achieve the synthetic methodological breakthrough, especially for controlling the synthesis and structure of NCs with atomic precision. It is evident that by realizing controlled synthesis and structural regulation at the atomic scale, we can better understand and tune the fundamental properties of NCs for efficient use in various application areas; this could also shed light on the development of new functionalized nanomaterials. Most of the recent research on the controlled synthesis and structural characterization of metal clusters with atomic precision has focused on monometallic NCs, and significant progress has been realized with respect to alloy metal NCs. A number of synthetic strategies have been developed for synthesizing high-quality alloy NCs with well-defined compositions, sizes, and architectures. In this review, we have highlighted some recent advances in strategies for the precise synthesis of ligands-protected alloy metal NCs, especially thiolate-stabilized gold-based alloy NCs. We classified the synthetic strategies for alloy NCs into several strategies, which include one-pot synthesis, metal exchange, ligand exchange, chemical etching, intercluster reactions, surface motif exchange reaction, and in situ two-phase ligand exchange strategy. One-pot synthesis is facile and widely used as a synthetic strategy for monodisperse alloy NCs with well-defined compositions, sizes, architectures, and surface chemistries. However, the alloy NCs obtained through the one-pot strategy often exhibits a relatively somber fluorescence. Therefore, other synthesis strategies have been exploited that can fabricate alloy NCs exhibiting strong photoluminescence. Among them, the surface motif exchange reaction is expected to be extended to the fabrication of new binary alloy NCs with precise alloy sites to broaden the physicochemical properties of the NCs; intercluster reactions has been explored as an emerging and efficient strategy to fabricate atomically precise alloy NCs. It is noted that the two or multiple metal species incorporated in a single alloy NC usually show unexpected synergistic properties like adjustable electronic structures and strong photoluminescence. Such unique properties have rapidly motivated the research community to use alloy NCs in many applications such as catalysis, biosensors, and biomedicine.

Key words: Alloy nanoclusters, Atomically precise, Synthetic strategy, Crystal structure