Atomically precise metal nanoclusters for(photo)electroreduction of CO_(2): Recent advances, challenges and opportunities

To alleviate the global warming by removing excess CO_(2) and converting them into value-added chemicals,(photo)electrochemical reduction has been recognized as a promising strategy.As the CO_(2) reduction reaction(CO_(2) RR) is involved with multiple electrons and multiple products,plus the complexity of the surface chemical environment of the catalyst,it is extremely challenging to establish the structure/function relationship.Atomically precise metal nanoclusters(NCs),with crystallographically resolved structure,molecule-like characters and strong quantum confinement effects,have been emerging as a new type of catalyst for CO_(2) RR,and more importantly,they can provide an ideal platform to unravel the comprehensive mechanistic insights and establish the structure/function relationship eventually.In this review,the recent advances regarding employing molecular metal NCs with well-defined structure including Au NCs,Au-based alloy NCs,Ag NCs,Cu NCs for CO_(2) RR and relevant mechanistic studies are discussed,and the opportunities and challenges are proposed at the end for paving the development of CO_(2) RR by using atomically precise metal NCs.

Single thiolate replacement of metal nanoclusters

Surface thiolates play important roles in evincing the structures and properties of thiolated metal nanoclusters—one type of recently emerging inorganic-organic hybrids,and thus the thiolate substitution,especially single thiolate substitution,is highly desirable for subtly tailoring the structures and properties of metal nanoclusters.However,such a single-thiolate substituting is challenging,and its influence on the metal-metal and metal-sulfur bonds remains mysterious due to the absence of the singlethiolate-substituted structure.Here,we developed a combined method,concurrently synthesized the single-thiolate-substituted nanocluster and its parent nanocluster,and successfully resolved their structures by single crystal X-ray crystallography,which reveals that the single thiolate substitute has an obvious influence on the metal-metal and metal-sulfur bond lengths although it has no effect on the absorption profile.Interestingly,the metal-metal and metal-sulfur bonds show various thermal extensibility and even the negative thermal expansion phenomena of the Au–S bond were observed in the single-thiolate-substituted nanocluster.The bond length-related stability was also observed.Overall,this study highlights a novel synthesis method and offers novel structural insights and an in-depth structure-property correlation of thiolated metal nanoclusters.

Marrying luminescent metal nanoclusters to C_(3)N_(4) for efficient photocatalytic hydrogen peroxide production

Photocatalytic oxygen(O_(2))reduction has been considered a promising method for hydrogen peroxide(H_(2)O_(2))production.However,the poor visible light harvesting and low-efficient separation and generation of charge carriers of conventional photocatalysts strongly limited their photocatalytic H_(2)O_(2) generation performance.Herein,we design a highly efficient photocatalyst in this work by marrying luminescent gold-silver nanoclusters(AuAg NCs)to polyethyleneimine(PEI)modified C_(3)N_(4)(C3N4-PEI).The key design in this work is the utilization of highly luminescent AuAg NCs as photosensitizers to promote the generation and separation of charge carriers of C_(3)N_(4)-PEI,thereby ultimately producing abundant e−for O_(2) reduction under visible light illumination(λ≥400 nm).As a result,the as-designed photocatalyst(C3N4-PEI-AuAg NCs)exhibits excellent photocatalytic activity with an H_(2)O_(2) production capability of 82μM in pure water,which is 3.5 times higher than pristine C_(3)N_(4)(23μM).This interesting design provides a paradigm in developing other high-efficient photocatalysts for visible-light-driven H_(2)O_(2) production.

Cationic antibacterial metal nanoclusters with traceable capability for fluorescent imaging the nano–bio interactions

A thorough understanding of antimicrobial mechanism is of great importance for developing novel,efficient antibacterial agents.While cationic nanoparticles,such as metal nanoclusters(NCs),represent an attractive type of antibacterial nanoagents,their interactions with bacteria remains largely un-elucidated.Herein,we report the synthesis of cationic bovine serum albuminprotected AuAgNCs(cBSA-AuAgNCs),which exhibit both near-infrared(NIR)fluorescence properties and significant antimicrobial effects.With E.coli and S.aureus as the representative bacteria,we investigated the antimicrobial process of cBSAAuAgNCs in real-time based on their intrinsic fluorescence properties via fluorescence imaging.Our results showed that these cBSA-AuAgNCs exert their antimicrobial effects primarily by attaching on the outer membrane of bacteria without obvious internalization,which is significantly different from the antibacterial process of negatively-charged metal NCs.Further mechanistic investigation showed that these cationic NCs will cause serious disruption to the bacterial membrane due to strong electrostatic interactions,which then leads to over accumulation of reactive oxygen species(ROS)that finally causes the bactericidal action.This study demonstrates the great potential of cationic luminescent metal NCs as novel,traceable antimicrobial agents,which also provides new tools for further understanding microbial interactions of nanomedicines.

Atomically Precise Metal Nanoclusters as Single Electron Transferers for Hydroborylation

The emergence of metal nanoclusters with atomically precise compositions and structures provides an opportunity for in-depth investigation of catalysis mechanisms and structure−property correlations at the nanoscale.However,a serious problem for metal nanocluster catalysts is that the ligands inhibit the catalytic activity through deactivating the surface of the nanoclusters.Here,we introduce a novel catalytic mode for metal nanoclusters,in which the nanoclusters initiate the catalysis via single electron transfer(SET)without destroying the integrity of nanoclusters,providing a solution for the contradiction between activity and stability of metal nanoclusters.We illustrated that the novel activation mode featured low catalyst loading(0.01 mol%),high TOF,mild reaction conditions,and easy recycling of catalyst in alkyne hydroborylation,which often suffered from poor selectivity,low functional group tolerance,etc.Furthermore,the catalyst[Au_(1)Cu_(14)(TBBT)_(12)(PPh_(3))_(6)]^(+)(TBBTH:p-tert-butylthiophenol)can be applied in highly efficient tandem processes such as hydroborylation−deuteration and hydroborylation−isomerization,demonstrating the utility of the introduced activation mode for metal nanoclusters.

Activation of Transition Metal(Fe,Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO_(2) Reduction Reaction

The electrochemical carbon dioxide reduction reaction(CO_(2)RR),which can produce value-added chemical feedstocks,is a proton-coupled-electron process with sluggish kinetics.Thus,highly efficient,cheap catalysts are urgently required.Transition metal oxides such as CoO_(x),FeO_(x),and NiO_(x)are low-cost,low toxicity,and abundant materials for a wide range of electrochemical reactions,but are almost inert for CO_(2)RR.Here,we report for the first time that nitrogen doped carbon nanotubes(N-CNT)have a surprising activation effect on the activity and selectivity of transition metal-oxide(MO_(x)where M=Fe,Ni,and Co)nanoclusters for CO_(2)RR.MO_(x)supported on N-CNT,MO_(x)/N-CNT,achieves a CO yield of 2.6–2.8 mmol cm−2 min−1 at an overpotential of−0.55 V,which is two orders of magnitude higher than MO_(x)supported on acid treated CNTs(MO_(x)/O-CNT)and four times higher than pristine N-CNT.The faraday efficiency for electrochemical CO_(2)-to-CO conversion is as high as 90.3%at overpotential of 0.44 V.Both in-situ XAS measurements and DFT calculations disclose that MO_(x)nanoclusters can be hydrated in CO_(2)saturated KHCO_(3),and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions,which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

Noble metal nanoclusters and their in situ calcination to nanocrystals： Precise control of their size and interface with Ti02 nanosheets and their versatile catalysis applications

In this work, we present a new versatile strategy to prepare noble metal （Au, Ag and Cu） nanoclusters on TiO2 nanosheets in large scales with exposed （001） facets with controlled size, crystalline interface, and loading amount. By precise in situ calcination, the metal （M = Au, Ag, and Cu） nanocrystals with controllable size and better crystalline interface with the TiO2 support have been prepared. The potential application of the as-prepared Au, Ag, and Cu nanoclusters on TiO2 nanosheets as potential heterogeneous catalysts for organic synthesis, such as catalytic reduction of 4-nitrophenol to 4-aminophenol, has been demonstrated. After calcination, Au, Ag, and Cu nanocrystals were found to be proficient cocatalysts for photocatalytic H2 evolution, particularly the Au cocatalyst. Based on precise high-resolution transmission electron microscopy （HRTEM） and inductively coupled plasma optical emission spectrometry （ICP-OES） analyses, the flexible control of their size and loading amount as well as their intimate contact with the TiO2 nanosheet enhanced the photocatalytic H2 evolution activity and the sensitivity of the photocurrent response of the film. Furthermore, this aqueous-directed synthesis of metal nanoclusters on a support will generate further interest in the field of nanocatalysis.

Emerging applications of near-infrared fluorescent metal nanoclusters for biological imaging

Fluorescent metal nanoclusters（MNCs） have recently emerged as a novel kind of promising fluorescent probes for biological imaging because of their ultrasmall core size（〈2 nm）, strong photoluminescence,facile availability and good biocompatibility. In this review, we provide an update on recent advances in the development of near infrared（NIR）-emitting MNCs in terms of synthesis strategies and bioimaging applications. We mainly focus on the utilization of NIR-emitting MNCs（including Au, Ag, Cu and alloy NCs） either as single modal imaging（fluorescence intensity-based imaging, fluorescence lifetime imaging, two-photon imaging） probes or as multimodal imaging（such as NIR fluorescence/X-ray computed tomography/magnetic resonance imaging, NIR fluorescence/photoacoustic imaging/magnetic resonance imaging, NIR fluorescence/single photon emission computed tomography） probes in biological cells and tissues. Finally, we give a brief outlook on the future challenges and prospects of developing NIR-emitting MNCs for bioimaging.

In-situ generation and global property profiling of metal nanoclusters by ultraviolet laser dissociation-mass spectrometry

Metal nanoclusters are promising nanomaterials with unique properties, but only a few ones with specific numbers of metal atoms can be obtained and studied up to now. In this study, we establish a new paradigm of in-situ generation and global study of metal nanoclusters with different sizes, constitutions, and charge states, including both accurate constitution characterization and global activity profiling. The complex mixtures of metal nanoclusters are produced by employing single-pulsed 193-nm laser dissociation of monolayer-protected cluster(MPC) precursors within a high-resolution mass spectrometry(HRMS). More than400 types of bare gold nanoclusters including novel multiply charged(2+ and 3+), S-/P-doped, and silver alloy ones can be efficiently generated and accurately characterized. A distinct size(1 to 142 atoms)-and charge(1+ to 3+)-hierarchy reactivity is clearly observed for the first time. This global cluster study might greatly promote the developments and applications of novel metal nanoclusters.

Luminescent metal nanoclusters:Biosensing strategies and bioimaging applications

Metal nanoclusters(MNCs)are ultrasmall metal-organic aggregates,composed of a metal core less than 2 nm and a protecting shell of metal-organic ligand motifs.The controlled aggregation of metal atoms(in the cluster core)and metal-organic ligand motifs(around the cluster core)renders MNCs with numerous molecule-like properties,among which strong and bright luminescence has attracted extensive basic and applied interests.It has now known that aggregation-induced emission is a feasible mechanism for controlling luminescence of MNCs,which makes it particularly useful in biosensing and bioimaging applications.Although the luminescence fundamentals and design principles largely determine the practicality and effectiveness of MNCs in biosensing and bioimaging applications,a systematic summary of this topic is lacking in the current literature.In this review,we aim to provide a concise discussion of the latest developments in biosensing and bioimaging applications of luminescent MNCs,highlighting their luminescence mechanisms,biosensing principles,and bioimaging strategies.Specifically,we first introduce the recent advances in the synthetic chemistry of MNCs,and then briefly discuss the luminescence fundamentals ofMNCs.Then the design strategy and practicality of luminescent MNCs in biosensing and bioimaging applications are exemplified.We conclude the review with our perspectives on the further development of MNC-based optical probes in biosensing and bioimaging applications.Our review is expected to provide guidance for the future practice of designing and synthesizing luminescent MNCs for biomedical and other applications.

Peptide or Protein-Protected Metal Nanoclusters for Therapeutic Application

What is the most favorite and original chemistry developed in your research group?The most favorite and original work we have done is the development of gold nano clusters for diagnostic and therapeutic application.How do you get into this specific field?Could you please share some experiences with our readers?I have a great passion for research on bioanalytical imaging and the biomedical effects of nanomaterials,which may contribute to early diagnosis and treatment of diseases.My research is focused on exploring the mechanism of protein or peptide-protected metal nanoclusters in disease diagnosis and treatment with the expectation of leading to superior therapeutic outcomes.

Ligand Engineering in Metal Nanoclusters: from Structural Control to Functional Modulation

Ligand-protected metal nanoclusters have drawn increasing research interest because of their unique physicochemical properties and practical applications.Great efforts have been made in pursuing rational synthesis of metal nanoclusters and establishing the structure-property relationships.As an indispensable part of ligand-protected metal nanoclusters,ligands play multiple roles in determining their structures and properties.In this perspective,we demonstrate the importance of ligand engineering in terms of the control of structures,optical and catalytic properties of metal nanoclusters.Furthermore,we will show that ligand engineering is prospective in structural design and preorganization of surface metal sites.

Synergistic integration of metal nanoclusters and biomolecules as hybrid systems for therapeutic applications

Therapeutic nanoparticles are designed to enhance efficacy,real-time monitoring,targeting accuracy,biocompatibility,biodegradability,safety,and the synergy of diagnosis and treatment of diseases by leveraging the unique physicochemical and biological properties of well-developed bio-nanomaterials.Recently,bio-inspired metal nanoclusters(NCs)consisting of several to roughly dozens of atoms(<2 nm)have attracted increasing research interest,owing to their ultrafine size,tunable fluorescent capability,good biocompatibility,variable metallic composition,and extensive surface bio-functionalization.Hybrid coreeshell nanostructures that effectively incorporate unique fluorescent inorganic moieties with various biomolecules,such as proteins(enzymes,antigens,and antibodies),DNA,and specific cells,create fluorescently visualized molecular nanoparticle.The resultant nanoparticles possess combinatorial properties and synergistic efficacy,such as simplicity,active bio-responsiveness,improved applicability,and low cost,for combination therapy,such as accurate targeting,bioimaging,and enhanced therapeutic and biocatalytic effects.In contrast to larger nanoparticles,bio-inspired metal NCs allow rapid renal clearance and better pharmacokinetics in biological systems.Notably,advances in nanoscience,interfacial chemistry,and biotechnologies have further spurred researchers to explore bio-inspired metal NCs for therapeutic purposes.The current review presents a comprehensive and timely overview of various metal NCs for various therapeutic applications,with a special emphasis on the design rationale behind the use of biomolecules/cells as the main scaffolds.In the different hybrid platform,we summarize the current challenges and emerging perspectives,which are expected to offer in-depth insight into the rational design of bio-inspired metal NCs for personalized treatment and clinical translation.

Catalytically Active Metal Nanoclusters Inside Cross-linked Functional Polymers:An Overview

1 Results Metal (0) nanoclusters (MNs), "strange morsels of matter"[1], are nanosized systems that are crucial components of industrially relevant catalysts (e. g. NH3 synthesis, catalytic reforming of alkanes, etc.). In recent years MNs have attracted an unprecedented attention among researchers acting in University, Scheme 1 Graphical model for the generation of size-controlled Pd0 nanoclusters inside metallated resins.a) PdⅡ is homogeneously dispersed inside the polymerGovernmental Institutions and ...

Catalytic Conversion of C_(1) Molecules on Atomically Precise Metal Nanoclusters

Metal nanoclusters with accurate compositions and precise crystalline structures hold remarkable attention in serving as a unique model catalyst for well-defined correlations between structure and catalytic activity.More importantly,these metal nanoclusters exhibit strong quantum confinement effects,which differ from their larger nanoparticles in a number of catalytic reactions.This review focuses on recent advances of atomically precise metal nanoclusters for C_(1) compound conversion(C_(O),CO_(2),CH_(4),and HCOOH),including thermally-driven catalysis,photocatalysis,and electrocatalysis.The reaction mechanisms are discussed at an atomic-or even electron-level.It is anticipated that the progress in this research area could be extended to catalytic applications of metal nanoclusters in C_(1) chemistry.

Metal nanocluster-based devices:Challenges and opportunities

Atomically precise nanoclusters(NCs)with fascinating physicochemical characteristics different from their nanoparticles(NPs)counterparts have gained increasing attention in diverse fields of applications.The foremost outcome of such NC-based applications is leading to transform them into devices.In fact,there are already some reports on the development of NC-based devices.For instance,NCs exhibit their potential in solar cells,showing high light-harvesting efficiency comparable to traditional semiconductor solar cells.Further,recent progress in characterizing Au NCs films and micro-crystals shows semiconductor-like properties such as field effect and photoresponse.These successes indicate that metal NCs possess a high potential for application in multidisciplinary areas for advancing the development in fundamental and practical purposes.However,no such comprehensive review is available to highlight recent advances and new applicable devices based on noble metal NCs.Herein,we reviewed the recent development in this area,including synthesis challenges of metal NCs and related applications of NC-sensitized solar cells,strain sensors,chemo-/biosensors,transistors,floating memory,and other devices.Furthermore,the future opportunities such as modifying synthetic methods to make other metal NCs,enhancing the efficiency of solar cells,and exploring more NCbased devices alternative to semiconductors are pointed out.We hope that rapidly increasing interest in NC-based devices will stimulate the research in this area and inspire the advances in combined devices accordingly.

Rationally construction of atomic-precise interfacial charge transfer channel and strong build-in electric field in nanocluster-based Zscheme heterojunctions with enhanced photocatalytic hydrogen production

The lack of effective charge transfer driving force and channel limits the electron directional migration in nanoclusters(NC)-based heterostructures,resulting in poor photocatalytic performance.Herein,a Z-scheme NC-based heterojunction(Pt1Ag28-BTT/CoP,BTT=1,3,5-benzenetrithiol)with strong internal electric field is constructed via interfacial Co-S bond,which exhibits an absolutely superiority in photocatalytic performance with 24.89 mmol·h^(−1)·g−1 H_(2)production rate,25.77%apparent quantum yield at 420 nm,and~100%activity retention in stability,compared with Pt1Ag28-BDT/CoP(BDT=1,3-benzenedithiol),Ag29-BDT/CoP,and CoP.The enhanced catalytic performance is contributed by the dual modulation strategy of inner core and outer shell of NC,wherein,the center Pt single atom doping regulates the band structure of NC to match well with CoP,builds internal electric field,and then drives photogenerated electrons steering;the accurate surface S modification promotes the formation of Co-S atomic-precise interface channel for further high-efficient Z-scheme charge directional migration.This work opens a new avenue for designing NC-based heterojunction with matchable band structure and valid interfacial charge transfer.

The synthesis of fluorescent nanoclusters based on the etching reaction

Thiolate-protected atomically precise nanoclusters(NCs)demonstrate a series of unique luminescent characteristics attributed to their various peculiar electronic structures.Therefore,fluorescent NCs present extraordinary practical values in biosensing and bioimaging research fields.Nevertheless,restricted by the types of fluorescent NCs,there are great difficulties in promoting the development of NCs in fluorescent research areas.As a result,it is of significant necessity for researchers to develop new synthetic pathways to produce high-quality fluorescent NCs.According to the analysis about the structural characteristics of fluorescent NCs,some general features like longer motif and higher ligand-to-metal ratio can be found,consistent to some presented regularities in etching reaction.Consequently,in this work,we used Au_(25)(MHA)_(18)(MHA=6-mercaptohexanoic acid)as a model nanocluster and utilized the etching reaction to systematically explore etching products and their corresponding luminescent properties.Moreover,we also identified three main reaction processes in the entire etching reaction process,which can generate new metal nanocluster species with various fluorescent properties.Hence,the etching reaction will provide a good platform to produce new luminescent metal NC species.

Emerging Strategies in Enhancing Singlet Oxygen Generation of Nano-Photosensitizers Toward Advanced Phototherapy

The great promise of photodynamic therapy(PDT) has thrusted the rapid progress of developing highly effective photosensitizers(PS) in killing cancerous cells and bacteria. To mitigate the intrinsic limitations of the classical molecular photosensitizers, researchers have been looking into designing new generation of nanomaterial-based photosensitizers(nano-photosensitizers) with better photostability and higher singlet oxygen generation(SOG) efficiency, and ways of enhancing the performance of existing photosensitizers. In this paper, we review the recent development of nano-photosensitizers and nanoplasmonic strategies to enhance the SOG efficiency for better PDT performance. Firstly, we explain the mechanism of reactive oxygen species generation by classical photosensitizers, followed by a brief discussion on the commercially available photosensitizers and their limitations in PDT. We then introduce three types of new generation nanophotosensitizers that can effectively produce singlet oxygen molecules under visible light illumination, i.e., aggregation-induced emission nanodots, metal nanoclusters (< 2 nm), and carbon dots. Different design approaches to synthesize these nano-photosensitizers were also discussed. To further enhance the SOG rate of nano-photosensitizers, plasmonic strategies on using different types of metal nanoparticles in both colloidal and planar metal-PS systems are reviewed. The key parameters that determine the metal-enhanced SOG(ME-SOG) efficiency and their underlined enhancement mechanism are discussed. Lastly, we highlight the future prospects of these nanoengineering strategies, and discuss how the future development in nanobiotechnology and theoretical simulation could accelerate the design of new photosensitizers and ME-SOG systems for highly effective image-guided photodynamic therapy.

Orange-emitting bimetallic nanoclusters combined with cyan-emitting Fe@TAOH as white light-emitting materials

White-light-emitting diodes(WLEDs)possess many merits,such as high efficiency and stability.Developing cost-effective,environmentally friendly,high-performance luminophores to achieve high-quality,full-spectrum,white lighting is of great importance to the construction and progress of WLEDs.In this work,solid-state,highly luminescent orange-emitting nanoclusters(MgCl_(2)-Lys-Ag/Au NCs)were prepared via the salt-induced precipitation of Lys-Ag/Au NCs from solution,which showed a high absolute quantum yield of 44.5%.A cyan-emitting metal-organic framework(MOF)-like nanomaterial(named Fe@TAOH)was also prepared by the self-assembly of the coordination compound of Fe^(3+)and TAOH acted upon by H_(3)PO_(4) via H-bonding andπ-πstacking interactions,which showed an emission peak at 485 nm and an absolute quantum yield of 21.7%.The potential application of the two facile-synthesis,low toxicity,and highly luminescent materials in WLEDs was investigated.The WLEDs was constructed by coating powdered Fe@TAOH and MgCl_(2)-Lys-Ag/Au NCs samples on commercial GaN LED chip with 365 nm emissions,and it exhibited acceptable white light characteristics with a CIE color coordinates and a color rendering index(CRI)of(0.28,0.34)and 79.6,respectively,implying good prospects in the field of WLEDs.