Extremely Downsized Materials: Ball-Milling-Enabled Universal Production and Size-Reduction-Induced Performance Enhancement

Abstract

Extremely downsized (including quantum-sized and subnanometer-sized) materials with sizes between atoms and nanoparticles have attracted tremendous attention thanks to their unique structures and exotic physical and chemical properties. Such unusual materials will induce a range of enhanced performances compared with their nanoscale and bulk counterparts, which can be beneficial to driving advancements of materials science as well as nanoscience and nanotechnology. However, it is quite challenging to prepare extremely downsized materials due to their ultrasmall sizes and ultralarge surfaces. Up to now, a variety of strategies have been explored for the preparation of extremely downsized materials, among which the basic categories are top-down and bottom-up methods. The former generally tailors bulk materials into downsized nanomaterials by physical routes, while the latter usually involves chemical (solution) processes to synthesize nanomaterials. During past decades, most efforts have been devoted to bottom-up methods for the synthesis of extremely downsized materials (e.g., colloidal quantum dots, sub-nanometer-sized materials, clusters, and supermolecules). Meanwhile, the production of extremely downsized materials through top-down methods is far from satisfactory, limited by their low manufacturing capacities and relatively expensive facilities. Note that nanomaterials produced by top-down physical methods exhibit entirely exposed surface/edge lattices, while the surface/edge lattices synthesized by bottom-up chemical methods are protected by ligands, making the surface/edge effects greatly obscured. Undoubtedly, exploiting a robust strategy to produce extremely downsized materials with maximized exposed lattices by all-physical top-down methods is required and desired. Our group has been focusing on all-physical production and extreme performances of extremely downsized materials since 2015. We have developed a universal and scalable strategy (i.e., the combination of silica-assisted ball-milling and sonication-assisted solvent exfoliation and treatment) for the all-physical production of quantum-sized materials. A series of quantum-sized materials with intrinsic characteristics have been produced, pushing forward the establishment of a complete database/library. Recently, two-stage silica-assisted ball-milling has been employed to realize the universal production of sub-nanometer-sized materials with entirely exposed and broken intrinsic lattices, suggesting that the top-down fabrication limit has reached the subnanometer (single-lattice) scale. Enhanced performances are demonstrated in both quantum-sized and sub-nanometer-sized materials because of their numerous broken lattices on surfaces/edges.

In this Account, we emphasize the preparation strategies and enhanced performances for extremely downsized materials, particularly highlighting the contributions of our research group in the past few years. The representative key advancements in extremely downsized materials from other groups are briefly introduced, followed by a detailed description of the research progress in our group. The historical development and breakthrough of the all-physical top-down method based on the ball-milling technique is presented. The production and characterization of quantum-sized and sub-nanometer-sized materials are then described in detail. Next, several exciting performances (e.g., nonlinear optics, electrocatalysis, photoluminescence, etc.) of extremely downsized materials are demonstrated. The size-reduction-induced performance enhancement during the progressive downsizing from bulk to sub-nanometer materials is revealed as well. The challenges and prospects in the future development of extremely downsized materials are discussed at the end.