Mechanistic insights and selected synthetic routes of atomically precise metal nanoclusters

Abstract

During the last few decades, noble metal nanoclusters (NCs) have become an exciting building block in the field of nanoscience. With their ultrasmall size that ranges between 1 and 2 nm, NCs fill the gap between atoms and nanoparticles (NPs), and they show significantly different physicochemical properties compared to their bulk counterparts, such as molecule‐like HOMO‐LUMO discrete electronic transitions, photoluminescence, etc. These properties made NCs potential candidates in various applications, including catalysis, chemical/bioimaging, biomedicine, sensing, and energy conversion. Controlling the size of NPs, which usually exhibit a degree of polydispersity, has been a significant challenge for nano‐scientists. However, metal NCs with atomic precision pave the way to accurately fabricate NPs based on an atom‐by‐atom assembly. This Perspective is directed to the community of nano‐scientists interested in the field of NCs and summarizes the most commonly used synthetic routes of atomically precise metal NCs. Moreover, this Perspective provides an understanding of the different techniques used to control the size of metal NCs with insights on switching the surface ligands from phosphine to thiol. This Perspective also explains the role of physicochemical parameters in different synthetic routes such as high‐temperature route, CO‐directed route, solid‐state route, ligand‐exchange‐induced size/structure transformation (LEIST), etc. We finally give a brief outlook on future challenges of currently used synthetic routes with some suggestions to improve them.

Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting

“…[31][32][33][34][35] Easy synthetic routes, either by reducing the metal ions with thiol ligands or core etching of MNPs, have gained scientific attention across various research areas. [36][37][38][39] The high photostability of the MNCs is advantageous over the conventional organic fluorophores that are frequently used as biomarkers. 14,40,41 MNCs are thus widely used in sensing, bio-imaging, photodynamic therapy, electrochemiluminescence, biological tracking, and photovoltaic applications.…”

Facile Biological-Based Synthesis of Size-Controlled Palladium Nanoclusters Anchored on the Surface of Geobacter sulfurreducens and Their Application in Electrocatalysis

“…The nanocluster size range varies from 1 to 10 nm and is typically composed of up to 100 atoms. − Their ultra-small size is not the only characteristic that makes them different from nanoparticles; their physicochemical properties, such as the availability of a large number of surface active sites for catalytic reactions, discrete energy levels, and unique electronic properties, could differentiate them from nanoparticles . Similar to metal nanoparticles, metal nanoclusters can be synthesized following the top-down or bottom-up approaches involving chemical and/or physical methods, and the synthesis approach is normally complex involving multiple steps where toxic ligands (used as stabilizers and protecting agents), reducing agents, solvents, and high temperature or pressure are applied. , The presence of ligands on the surface of the metallic nanoclusters can decrease the catalytic activity by blocking the accessibility of the reactant to the nanocluster’s surface. For this reason, post-treatment processes are warranted to remove (partial or complete) the ligand after the nanocluster synthesis to enhance the catalytic activity of the nanocluster .…”

“…5 Similar to metal nanoparticles, metal nanoclusters can be synthesized following the top-down or bottom-up approaches involving chemical and/or physical methods, and the synthesis approach is normally complex involving multiple steps where toxic ligands (used as stabilizers and protecting agents), reducing agents, solvents, and high temperature or pressure are applied. 6,7 The presence of ligands on the surface of the metallic nanoclusters can decrease the catalytic activity by blocking the accessibility of the reactant to the nanocluster's surface. For this reason, posttreatment processes are warranted to remove (partial or complete) the ligand after the nanocluster synthesis to enhance the catalytic activity of the nanocluster.…”

Metal nanocluster‐based devices: Challenges and opportunities

“…[24][25][26] Besides such a plethora of studies focused on NP-based applications, sizecontrolled nanoclusters (NCs), have become another fastgrowing interest in nanomaterial science. [27][28][29] Metal NCs, consisting of a few to hundreds of atoms, have been intensively studied because of their unique physical and chemical properties, resulting from their molecule-like discrete energy levels. [30][31][32][33][34][35] These make NCs suitable candidates in various applications from sensing to photovoltaics.…”