Sulfur-deficient MoS2 nanoflakes as an electrocatalyst improve the polysulfide conversion kinetics and hence the performance of lithium–sulfur batteries.

Thiolate-protected metal nanoclusters (or thiolated metal NCs) have recently emerged as a promising class of functional materials because of their well-defined molecular structures and intriguing molecular-like properties. Recent developments in the NC field have aimed at exploring metal NCs as novel luminescent materials in the biomedical field because of their inherent biocompatibility and good photoluminescence (PL) properties. From the fundamental perspective, recent advances in the field have also aimed at addressing the fundamental aspects of PL properties of metal NCs, shedding some light on developing efficient strategies to prepare highly luminescent metal NCs. In this Perspective, we discuss the physical chemistry of a recently discovered aggregation-induced emission (AIE) phenomenon and show the significance of AIE in understanding the PL properties of thiolated metal NCs. We then explore the unique physicochemical properties of thiolated metal NCs with AIE characteristics and highlight some recent developments in synthesizing the AIE-type luminescent metal NCs. We finally discuss perspectives and directions for future development of the AIE-type luminescent metal NCs.

CONSPECTUS: Total synthesis, where desired organic-and/or biomolecules could be produced from simple precursors at atomic precision and with known step-by-step reactions, has prompted centuries-lasting bloom of organic chemistry since its conceptualization in 1828 (Woḧler synthesis of urea). Such expressive science is also highly desirable in nanoscience, since it represents a decisive step toward atom-by-atom customization of nanomaterials for basic and applied research. Although total synthesis chemistry is less established in nanoscience, recent years have witnessed seminal advances and increasing research efforts devoted into this field. In this Account, we discuss recent progress on introducing and developing total synthesis routes and mechanisms for atomically precise metal nanoclusters (NCs). Due to their molecular-like formula and properties (e.g., HOMO−LUMO transition, strong luminescence and stereochemical activity), atomically precise metal NCs could be regarded as "molecular metals", holding potential applications in various practical sectors such as biomedicine, energy, catalysis, and many others. More importantly, the molecular-like properties of metal NCs are sensitively dictated by their size and composition, suggesting total synthesis of them as an indispensable basis for reliably realizing their practical applications. Atomically precise thiolate-protected Au, Ag and their alloy NCs are employed as model NCs to exemplify design strategies and governing principles in total synthesis of inorganic nanoparticles. This Account starts with a brief summary of total synthesis methodologies of atomically precise metal NCs. Following the methodological summary is a detailed discussion on the mechanisms governing these synthetic strategies, which is the main focus of this Account. Based on unprecedented precision (at atomic resolution) and ease (ensured by size-dependent properties) of tracking clusters' size/structure changes, mechanisms driving growth (e.g., reduction growth and seeded growth) and functionalization (e.g., alloying reaction and ligand exchange) of metal NCs have been explored at molecular level. With def initive step-by-step reaction routes, two-electron (2 e − ) reduction (driving the growth reactions) and surface motif exchange (SME, prompting alloying and ligand exchange reactions) are discussed in depth and details. In addition to those sub-and/or individual-cluster level understandings, the self-assembly chemistry delivering high orderliness and enhanced materials performance in NC assemblies/supercrystals is also deciphered. This Account is then concluded with our perspectives toward potential development of cluster chemistry. Advances in total synthesis chemistry of metal NCs could not only serve as guidelines for future synthetic practice of NCs, but also provide molecular-level clues for many pending fundamental puzzles in nanochemistry, including nucleation growth, alloying chemistry, surface engineering and evolution of metamaterials.

A new and facile way to synthesize a free-standing and flexible surface-enhanced Raman scattering (SERS) substrate has been successfully developed, where high SERS-active Ag dimers or aligned aggregates are assembled within poly(vinyl alcohol) (PVA) nanofibers with chain-like arrays via electrospinning technique. The aggregation state of the obtained Ag nanoparticle dimers or larger, which are formed in a concentrated PVA solution, makes a significant contribution to the high sensitivity of SERS to 4-mercaptobenzoic acid (4-MBA) molecules with an enhancement factor (EF) of 10(9). The superiority of enhancement ability of this Ag/PVA nanofiber mat is also shown in the comparison to other substrates. Furthermore, the Ag/PVA nanofiber mat would keep a good reproducibility under a low concentration of 4-MBA molecule (10(-6) M) detection with the average RSD values of the major Raman peak less than 0.07. The temporal stability of the substrate has also been demonstrated. This disposable, easy handled, flexible free-standing substrate integrated the advantages including the superiority of high sensitivity, reproducibility, stability, large-scale, and low-cost production compared with other conventional SERS substrates, implying that it is a perfect choice for practical SERS detection application.