Surface Coordination Chemistry of Metal Nanomaterials

Hydrophobic Microenvironment Modulation of Ru Nanoparticles in Metal-Organic Frameworks for Enhanced Electrocatalytic N2 Reduction

The modulation of the chemical microenvironment surrounding metal nanoparticles (NPs) is an effective means to enhance the selectivity and activity of catalytic reactions. Herein, a post-synthetic modification strategy is developed to modulate the hydrophobic microenvironment of Ru nanoparticles encapsulated in a metal-organic framework (MOF), MIP-206, namely Ru@MIP-Fx (where x represents perfluoroalkyl chain lengths of 3, 5, 7, 11, and 15), in order to systematically explore the effect of the hydrophobic microenvironment on the electrocatalytic activity. The increase of perfluoroalkyl chain length can gradually enhance the hydrophobicity of the catalyst, which effectively suppresses the competitive hydrogen evolution reaction (HER). Moreover, the electrocatalytic production rate of ammonia and the corresponding Faraday efficiency display a volcano-like pattern with increasing hydrophobicity, with Ru@MIP-F7 showing the highest activity. Theoretical calculations and experiments jointly show that modification of perfluoroalkyl chains of different lengths on MIP-206 modulates the electronic state of Ru nanoparticles and reduces the rate-determining step for the formation of the key intermediate of N2H2 *, leading to superior electrocatalytic performance.

Multidentate polyoxometalate modification of metal nanoparticles with tunable electronic states

To respond to the increasing demands for practical applications, stabilization and property modulation of metal nanoparticles have emerged as a key research subject. Herein, we present a viable protocol for preparing small metal nanoparticles (<5 nm; Ag, Pd, Pt, and Ru) via multidentate polyoxometalate (POM, [SiW9O34]10-) modification. In addition to enhancing stability, the POMs can modulate the electronic states of metal nanoparticles. Moreover, immobilization of the POM-modified metal nanoparticles on solid supports enables further tuning of the electronic states via a cooperative effect between the POMs and the supports without altering the particle size. Notably, POM-modified Pd nanoparticles on carbon support exhibited superior catalytic activity and selectivity in hydrogenation reactions in comparison with the catalyst without the POM modification.

Structure Effects of Ligands in Gold-Ligand Complexes for Controlled Formation of Gold Nanoclusters

Metal nanoclusters (NCs) are a special class of nanoparticles composed of a precise number of metal atoms and ligands. Because the proportion of ligands to metal atoms is high in metal NCs, the ligand type determines the physical properties of metal NCs. Furthermore, ligands presumably govern the entire formation process of the metal NCs. However, their roles in the synthesis, especially as factors in the uniformity of metal NCs, are not understood. It is because the synthetic procedure of metal NCs is highly convoluted. The synthesis is initiated by the formation of various metal-ligand complexes, which have different numbers of atoms and ligands, resulting in different coordinations of metal. Moreover, these complexes, as actual precursors to metal NCs, undergo sequential transformations into a series of intermediate NCs before the formation of the desired NCs. Thus, to resolve the complicated synthesis of metal NCs and achieve their uniformity, it is important to investigate the reactivity of the complexes. Herein, we utilize a combination of mass spectrometry, density functional theory, and electrochemical measurements to understand the ligand effects on the reactivity of AuI-thiolate complexes toward the reductive formation of Au NCs. We discover that the stability of the complexes can be increased by either van der Waals interactions induced by the long carbon chain of ligands or by non-thiol functional groups in the ligands, which additionally coordinate with AuI in the complexes. Such structural effects of thiol ligands determine the reduction reactivity of the complexes and the amount of NaBH4 required for the controlled synthesis of the Au NCs.

Two-Orders-of-Magnitude Enhancement of Photoinitiation Activity via a Simple Surface Engineering of Metal Nanoclusters

Development of high-performance photoinitiator is the key to enhance the printing speed, structure resolution and product quality in 3D laser printing. Here, to improve the printing efficiency of 3D laser nanoprinting, we investigate the underlying photochemistry of gold and silver nanocluster initiators under multiphoton laser excitation. Experimental results and DFT calculations reveal the high cleavage probability of the surface S-C bonds in gold and silver nanoclusters which generate multiple radicals. Based on this understanding, we design several alkyl-thiolated gold nanoclusters and achieve a more than two-orders-of-magnitude enhancement of photoinitiation activity, as well as a significant improvement in printing resolution and fabrication window. Overall, this work for the first time unveils the detailed radical formation pathways of gold and silver nanoclusters under multiphoton activation and substantially improves their photoinitiation sensitivity via surface engineering, which pushes the limit of the printing efficiency of 3D laser lithography.

Selective Cleavage of α-Olefins to Produce Acetylene and Hydrogen

Acetylene production from mixed α-olefins emerges as a potentially green and energy-efficient approach with significant scientific value in the selective cleavage of C-C bonds. On the Pd(100) surface, it is experimentally revealed that C2 to C4 α-olefins undergo selective thermal cleavage to form surface acetylene and hydrogen. The high selectivity toward acetylene is attributed to the 4-fold hollow sites which are adept at severing the terminal double bonds in α-olefins to produce acetylene. A challenge arises, however, because acetylene tends to stay at the Pd(100) surface. By using the surface alloying methodology with alien Au, the surface Pd d-band center has been successfully shifted away from the Fermi level to release surface-generated acetylene from α-olefins as a gaseous product. Our study actually provides a technological strategy to economically produce acetylene and hydrogen from α-olefins.

Advanced Functionalized Nanoclusters (Cu, Ag, and Au) as Effective Catalyst for Organic Transformation Reactions

A considerable amount of research has been carried out in recent years on synthesizing metal nanoclusters (NCs), which have wide applications in the field of optical materials with non-linear properties, bio-sensing, and catalysis. Aside from being structurally accurate, the atomically precise NCs possess well-defined compositions due to significant tailoring, both at the surface and the core, for certain functionalities. To illustrate the importance of atomically precise metal NCs for catalytic processes, this review emphasizes 1) the recent work on Cu, Ag, and Au NCs with their synthesis, 2) the parameters affecting the activity and selectivity of NCs catalysis, and 3) the discussion on the catalytic potential of these metal NCs. Additionally, metal NCs will facilitate the design of extremely active and selective catalysts for significant reactions by elucidating catalytic mechanisms at the atomic and molecular levels. Future advancements in the science of catalysis are expected to come from the potential to design NCs catalysts at the atomic level.

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Pargyline-phosphine copper(I) clusters with tunable emission for light-emitting devices

Three pargyline-phosphine copper(I) clusters, [Cu4(CC-C9H12N)3(PPh3)4](PF6) (1) and [Cu6(CC-C9H12N)4(dppy)4](X)2 (dppy = diphenyl-2-pyridylphosphine; X = PF6 for 2 and X = ClO4 for 3), were synthesized. Their structures were fully characterized using various spectroscopic methods and X-ray crystallography, which showed that the stoichiometry and nature of pargyline and phosphine ligands play an important role in tuning the structure and photophysical features of Cu(I) clusters. Interestingly, clusters 1, 2 and 3 exhibited red, orange and yellow phosphorescence with high quantum yields of 88.5%, 22.0% and 40.2%, respectively, at room temperature. Moreover, clusters 1-3 show distinct temperature-dependent emissions. The excellent luminescence performance of 1 and 3 was designed and employed for the construction of monochrome and white light-emitting devices (LEDs).

Stable Interfacial Ruthenium Species for Highly Efficient Polyolefin Upcycling

The present polyolefin hydrogenolysis recycling cases acknowledge that zerovalent Ru exhibits high catalytic activity. A pivotal rationale behind this assertion lies in the propensity of the majority of Ru species to undergo reduction to zerovalent Ru within the hydrogenolysis milieu. Nonetheless, the suitability of zerovalent Ru as an optimal structural configuration for accommodating multiple elementary reactions remains ambiguous. Here, we have constructed stable Ru0-Ruδ+ complex species, even under reaction conditions, through surface ligand engineering of commercially available Ru/C catalysts. Our findings unequivocally demonstrate that surface-ligated Ru species can be stabilized in the form of a Ruδ+ state, which, in turn, engenders a perturbation of the σ bond electron distribution within the polyolefin carbon chain, ultimately boosting the rate-determining step of C-C scission. The optimized catalysts reach a solid conversion rate of 609 g·gRu-1·h-1 for polyethylene. This achievement represents a 4.18-fold enhancement relative to the pristine Ru/C catalyst while concurrently preserving a remarkable 94% selectivity toward valued liquid alkanes. Of utmost significance, this surface ligand engineering can be extended to the gentle mixing of catalysts in ligand solution at room temperature, thus rendering it amenable for swift integration into industrial processes involving polyolefin degradation.

Emerging two dimensional metastable-phase oxides: insights and prospects in synthesis and catalysis

Since the discovery of graphene, the development of new two-dimensional (2D) materials has received considerable interest. Recently, as a newly emerging member of the 2D family, 2D metastable-phase oxides that combine the unique advantages of metal oxides, 2D structures, and metastable-phase materials have shown enormous potential in various catalytic reactions. In this review, the potential of various 2D materials to form a metastable-phase is predicted. The advantages of 2D metastable-phase oxides for advanced applications, reliable methods of synthesizing 2D metastable-phase oxides, and the application of these oxides in different catalytic reactions are presented. Finally, the challenges associated with 2D metastable-phase oxides and future perspectives are discussed.

Machine learning predicts atomistic structures of multielement solid surfaces for heterogeneous catalysts in variable environments

Solid surfaces usually reach thermodynamic equilibrium through particle exchange with their environment under reactive conditions. A prerequisite for understanding their functionalities is detailed knowledge of the surface composition and atomistic geometry under working conditions. Owing to the large number of possible Miller indices and terminations involved in multielement solids, extensive sampling of the compositional and conformational space needed for reliable surface energy estimation is beyond the scope of ab initio calculations. Here, we demonstrate, using the case of iron carbides in environments with varied carbon chemical potentials, that the stable surface composition and geometry of multielement solids under reactive conditions, which involve large compositional and conformational spaces, can be predicted at ab initio accuracy using an approach that combines the bond valence model, Gaussian process regression, and ab initio thermodynamics. Determining the atomistic structure of surfaces under working conditions paves the way toward identifying the true active sites of multielement catalysts in heterogeneous catalysis.

Synthesis of functionalized mesoporous silica nanoparticles for colorimetric and fluorescence sensing of selective metal (Fe3+) ions in aqueous solution

The fabrication of red fluorescent hybrid mesoporous silica-based nanosensor materials has promised the bioimaging and selective detection of toxic pollutants in aqueous solutions. In this study, we present a hybrid mesoporous silica nanosensor in which the propidium iodide (PI) was used to conveniently integrate into the mesopore walls using bis(trimethoxysilylpropyl silane) precursors. Various characterization techniques including X-ray diffraction (XRD), Fourier-transform infrared (FTIR), N2 adsorption-desorption, zeta potential, particle size analysis, thermogravimetric, and UV-visible analysis were used to analyze the prepared materials. The prepared PI integrated mesoporous silica nanoparticles (PI-MSNs) selective metal ion sensing capabilities were tested with a variety of heavy metal ions (100 mM), including Ni2+, Cd2+, Co2+, Zn2+, Cr3+, Cu2+, Al3+, Mg2+, Hg2+ and Fe3+ ions. Among the investigated metal ions, the prepared PI-MSNs demonstrated selective monitoring of Fe3+ ions with a significant visible colorimetric pink color change into orange and quenching of pink fluorescence in an aqueous suspension. The selective sensing behavior of PI-MSNs might be due to the interaction of Fe3+ ions with the integrated PI functional fluorophore present in the mesopore walls. Therefore, we emphasize that the prepared PI-MSNs could be efficient for selective monitoring of Fe3+ ions in an aqueous solution and in the biological cellular microenvironment.

Frustrated Lewis pairs on pentacoordinated Al3+-enriched Al2O3 promote heterolytic hydrogen activation and hydrogenation

As an emerging class of metal-free catalysts, frustrated Lewis pairs (FLPs) catalysts have been greatly constructed and applied in many fields. Homogeneous FLPs have witnessed significant development, while limited heterogeneous FLPs catalysts are available. Herein, we report that heterogeneous FLPs on pentacoordinated Al3+-enriched Al2O3 readily promote the heterolytic activation of H2 and thus hydrogenation catalysis. The defect-rich Al2O3 was prepared by simple calcination of a carboxylate-containing Al precursor. Combinatorial studies confirmed the presence of rich FLPs on the surface of the defective Al2O3. In contrast to conventional alumina (γ-Al2O3), the FLP-containing Al2O3 can activate H2 in the absence of any transition metal species. More importantly, H2 was activated by surface FLPs in a heterolytic pathway, leading to the hydrogenation of styrene in a stepwise process. This work paves the way for the exploration of more underlying heterogeneous FLPs catalysts and further understanding of accurate active sites and catalytic mechanisms of heterogeneous FLPs at the molecular level.

Cancer Cell Membrane-Based Materials for Biomedical Applications

The nanodelivery system provides a novel direction for disease diagnosis and treatment; however, its delivery effectiveness is restricted by the short biological half-life and inadequate tumor targeting. The immune evasion properties and homologous targeting capabilities of natural cell membranes, particularly those of cancer cell membranes (CCM), have gained significant interest. The integration of CCM and nanoparticles has resulted in the emergence of CCM-based nanoplatforms (CCM-NPs), which have gained significant attention due to their unique properties. CCM-NPs not only prolong the blood circulation time of core nanoparticles, but also direct them for homologous tumor targeting. Herein, the history and development of CCM-NPs as well as how these platforms have been used for biomedical applications are discussed. The application of CCM-NPs for cancer therapy will be described in detail. Translational efforts are currently under way and further research to address key areas of need will ultimately be required to facilitate the successful clinical adoption of CCM-NPs.

A concise guide to chemical reactions of atomically precise noble metal nanoclusters

Nanoparticles (NPs) with atomic precision, known as nanoclusters (NCs), are an emerging field in materials science in view of their fascinating structure-property relationships. Ultrasmall noble metal NPs have molecule-like properties that make them fundamentally unique compared with their plasmonic counterparts and bulk materials. In this review, we present a comprehensive account of the chemistry of monolayer-protected atomically precise noble metal nanoclusters with a focus on the chemical reactions, their diversity, associated kinetics, and implications. To begin with, we briefly review the history of the evolution of such precision materials. Then the review explores the diverse chemistry of noble metal nanoclusters, including ligand exchange reactions, ligand-induced structural transformations, and reactions with metal ions, metal thiolates, and halocarbons. Just as molecules do, these precision materials also undergo intercluster reactions in solution. Supramolecular forces between these systems facilitate the creation of well-defined hierarchical assemblies, composites, and hybrid materials. We conclude the review with a future perspective and scope of such chemistry.

Parasitism in Metal Nanoclusters: A Case Study of (AuAg)25·(AuAg)27

Studying the interactions of atomically precise metal nanoclusters in their assembly systems is of great significance in the nanomaterial research field, which has attracted increasing interest in the last few decades. Herein, we report the cocrystallization of two oppositely charged atomically precise metal nanoclusters in one unit cell: [Au1Ag24(SR)18]- ((AuAg)25 for short) and [AuxAg27-x(Dppf)4(SR)9]2+ (x = 10-12; (AuAg)27 for short) with a 1:1 ratio. (AuAg)27 could maintain its structure in the presence of (AuAg)25, whether in the crystalline and the solution state, while the metastable (AuAg)27 component underwent a spontaneous transformation to (AuAg)16(Dppf)2(SR)8 after dissociating the (AuAg)25 component from this cocrystal, demonstrating the "parasitism" relationship of the (AuAg)27 component over (AuAg)25 in this dual-cluster system. This work enriches the family of cluster-based assemblies and elucidates the delicate relationship between nanoparticles of cocrystals.

Atomic Distance Engineering in Metal Catalysts to Regulate Catalytic Performance

It is very important to understand the structure-performance relationship of metal catalysts by adjusting the microstructure of catalysts at the atomic scale. The atomic distance has an essential influence on the composition of the environment of active metal atom, which is a key factor for the design of targeted catalysts with desired function. In this review, we discuss and summarize strategies for changing the atomic distance from three aspects and relate their effects on the reactivity of catalysts. First, the effects of regulating bond length between metal and coordination atom at one single-atom site on the catalytic performance are introduced. The bond lengths are affected by the strain effect of the support and high-shell doping and can evolve during the reaction. Next, the influence of the distance between single-atom sites on the catalytic performance is discussed. Due to the space matching of adsorption and electron transport, the catalytic performance can be adjusted with the shortening of site distance. In addition, the effect of the arrangement spacing of the surface metal active atoms on the catalytic performance of metal nanocatalysts is studied. Finally, a comprehensive summary and outlook of the relationship between atomic distance and catalytic performance is given.

Enhanced CO2 Reactive Capture and Conversion Using Aminothiolate Ligand-Metal Interface

Metallic catalyst modification by organic ligands is an emerging catalyst design in enhancing the activity and selectivity of electrocatalytic carbon dioxide (CO2) reactive capture and reduction to value-added fuels. However, a lack of fundamental science on how these ligand-metal interfaces interact with CO2 and key intermediates under working conditions has resulted in a trial-and-error approach for experimental designs. With the aid of density functional theory calculations, we provided a comprehensive mechanism study of CO2 reduction to multicarbon products over aminothiolate-coated copper (Cu) catalysts. Our results indicate that the CO2 reduction performance was closely related to the alkyl chain length, ligand coverage, ligand configuration, and Cu facet. The aminothiolate ligand-Cu interface significantly promoted initial CO2 activation and lowered the activation barrier of carbon-carbon coupling through the organic (nitrogen (N)) and inorganic (Cu) interfacial active sites. Experimentally, the selectivity and partial current density of the multicarbon products over aminothiolate-coated Cu increased by 1.5-fold and 2-fold, respectively, as compared to the pristine Cu at -1.16 VRHE, consistent with our theoretical findings. This work highlights the promising strategy of designing the ligand-metal interface for CO2 reactive capture and conversion to multicarbon products.

Progress on quantum dot photocatalysts for biomass valorization

Biomass with abundant reproducible carbon resource holds great promise as an intriguing substitute for fossil fuels in the manufacture of high-value-added chemicals and fuels. Photocatalytic biomass valorization using inexhaustible solar energy enables to accurately break desired chemical bonds or selectively functionalize particular groups, thus emerging as an extremely creative and low carbon cost strategy for relieving the dilemma of the global energy. Quantum dots (QDs) are an outstandingly dynamic class of semiconductor photocatalysts because of their unique properties, which have achieved significant successes in various photocatalytic applications including biomass valorization. In this review, the current development rational design for QDs photocatalytic biomass valorization effectively is highlighted, focusing on the principles of tuning their particle size, structure, and surface properties, with special emphasis on the effect of the ligands for selectively broken chemical bonds (C─O, C─C) of biomass. Finally, the present issues and possibilities within that exciting field are described.

Halogen bonding-driven chiral amplification of a bimetallic gold-copper cluster through hierarchical assembly

Understanding the fundamentals and applications of chirality relies substantially on the amplification of chirality through hierarchical assemblies involving various weak interactions. However, a notable challenge remains for metal clusters chiral assembly driven by halogen bonding, despite their promising applications in lighting, catalysis, and biomedicine. Here, we used halogen bonding-driven assembly to achieve a hierarchical degree of achiral emissive Au2Cu2 clusters. From single crystals to one-dimensional ribbons and then to helixes, the morphologies were primarily modulated by intermolecular halogen bonding that evoked by achiral or/and chiral iodofluorobenzene (IFBs) molecules. Concomitantly, the luminescence and circularly polarized luminescence (CPL) changed a lot, ultimately leading to a substantial increase in the luminescence dissymmetry g-factor (glum) of 0.036 in the supramolecular helix. This work opens an avenue for hierarchical assemblies using predesigned metal clusters as building blocks though directional halogen bonding. This achievement marks a noteworthy advancement in the field of nanosized inorganic functional blocks.

Bilayer-Coating Strategy for Hydrophobic Nanoparticles Providing Colloidal Stability, Functionality, and Surface Protection in Biological Media

The surface chemistry of nanoparticles is a key step on the pathway from particle design towards applications in biologically relevant environments. Here, a bilayer-based strategy for the surface modification of hydrophobic nanoparticles is introduced that leads to excellent colloidal stability in aqueous environments and good protection against disintegration, while permitting surface functionalization via simple carbodiimide chemistry. We have demonstrated the excellent potential of this strategy using upconversion nanoparticles (UCNPs), initially coated with oleate and therefore dispersible only in organic solvents. The hydrophobic oleate capping is maintained and a bilayer is formed upon addition of excess oleate. The bilayer approach renders protection towards luminescence loss by water quenching, while the incorporation of additional molecules containing amino functions yields colloidal stability and facilitates the introduction of functionality. The biological relevance of the approach was confirmed with the use of two model dyes, a photosensitizer and a nitric oxide (NO) probe that, when attached to the surface of the UCNPs, retained their functionality to produce singlet oxygen and detect intracellular NO, respectively. We present a simple and fast strategy to protect and functionalize inorganic nanoparticles in biological media, which is important for controlled surface engineering of nanosized materials for theranostic applications.

Probing the surface-active sites of metal nanoclusters with atomic precision: a case study of Au5Ag11

The determination of surface-active sites in metal nanoclusters is of great significance for the in-depth understanding of structural evolutions and physicochemical property mechanisms. In this work, the surface-active sites of the Au5Ag11(DMBT)8(DPPOE)2 cluster template towards metal-/ligand-exchange reactions were unambiguously identified at the atomic level. The active-site tailoring of this nanocluster gave rise to three derivative nanoclusters, Au5Ag9Cu2(DMBT)8(DPPOE)2, Au5Ag11(DMBT)6(DCBT)2(DPPOE)2, and Au5Ag11(DCBT)8(DPPOE)2. The single-crystal structural analysis revealed that all these M16 (M = Au/Ag/Cu) clusters exhibited almost the same framework. Besides, the surface-active site tailoring contributed to significant changes in optical absorptions and emissions of these metal nanoclusters. The findings in this work not only provide an in-depth understanding of the active-site tailoring of cluster surface structures but also develop an intriguing template that enables us to grasp the structure-property correlations at the atomic level.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Monolithic Nickel Catalyst Featured with High-Density Crystalline Steps for Stable Hydrogen Evolution at Large Current Density

Producing hydrogen via electrochemical water splitting with minimum environmental harm can help resolve the energy crisis in a sustainable way. Here, this work fabricates the pure nickel nanopyramid arrays (NNAs) with dense high-index crystalline steps as the cata electrode via a screw dislocation-dominated growth kinetic for long-term durable and large current density hydrogen evolution reaction. Such a monolithic NNAs electrode offers an ultralow overpotential of 469 mV at a current density of 5000 mA cm-2 in 1.0 m KOH electrolyte and shows a high stability up to 7000 h at a current density of 1000 mA cm-2 , which outperforms the reported catas and even the commercial platinum cata for long-term services under high current densities. Its unique structure can substantially stabilize the high-density surface crystalline steps on the catalytic electrode, which significantly elevates the catalytic activity and durability of nickel in an alkaline medium. In a typical commercial hydrogen gas generator, the total energy conversion rate of NNAs reaches 84.5% of that of a commercial Pt/Ti cata during a 60-day test of hydrogen production. This work approach can provide insights into the development of industry-compatible long-term durable, and high-performance non-noble metal catas for various applications.

Performance Regulation of Single-Atom Catalyst by Modulating the Microenvironment of Metal Sites

Metal-based catalysts, encompassing both homogeneous and heterogeneous types, play a vital role in the modern chemical industry. Heterogeneous metal-based catalysts usually possess more varied catalytically active centers than homogeneous catalysts, making it challenging to regulate their catalytic performance. In contrast, homogeneous catalysts have defined active-site structures, and their performance can be easily adjusted by modifying the ligand. These characteristics lead to remarkable conceptual and technical differences between homogeneous and heterogeneous catalysts. As a recently emerging class of catalytic material, single-atom catalysts (SACs) have become one of the most active new frontiers in the catalysis field and show great potential to bridge homogeneous and heterogeneous catalytic processes. This review documents a brief introduction to SACs and their role in a range of reactions involving single-atom catalysis. To fully understand process-structure-property relationships of single-atom catalysis in chemical reactions, active sites or coordination structure and performance regulation strategies (e.g., tuning chemical and physical environment of single atoms) of SACs are comprehensively summarized. Furthermore, we discuss the application limitations, development trends and future challenges of single-atom catalysis and present a perspective on further constructing a highly efficient (e.g., activity, selectivity and stability), single-atom catalytic system for a broader scope of reactions.

Critical roles of metal-ligand complexes in the controlled synthesis of various metal nanoclusters

Metal nanoclusters (NCs), an important class of nanoparticles (NPs), are extremely small in size and possess quasi-molecular properties. Due to accurate stoichiometry of constituent atoms and ligands, NCs have strong structure-property relationship. The synthesis of NCs is seemingly similar to that of NPs as both are formed by colloidal phase transitions. However, they are considerably different because of metal-ligand complexes in NC synthesis. Reactive ligands can convert metal salts to complexes, actual precursors to metal NCs. During the complex formation, various metal species occur, having different reactivity and fraction depending on synthetic conditions. It can alter their degree of participation in NC synthesis and the homogeneity of final products. Herein, we investigate the effects of complex formation on the entire NC synthesis. By controlling the fraction of various Au species showing different reactivity, we find that the extent of complex formation alters reduction kinetics and the uniformity of Au NCs. We demonstrate that this concept can be universally applied to synthesize Ag, Pt, Pd, and Rh NCs.

Specific and Long-Term Luminescent Monitoring of Hydrogen Peroxide in Tumor Metastasis

Luminescent monitoring of endogenous hydrogen peroxide (H₂ O₂ ) in tumors is conducive to understanding metastasis and developing novel therapeutics. The clinical transformation is obstructed by the limited light penetration depth, toxicity of nano-probes, and lack of long-term monitoring modes of up to days or months. New monitoring modes are introduced via specific probes and implantable devices, which can achieve real-time monitoring with a readout frequency of 0.01 s or long-term monitoring for months to years. Near-infrared dye-sensitized upconversion nanoparticles (UCNPs) are fabricated as the luminescent probes, and the specificity to reactive oxygen species is subtly regulated by the self-assembled monolayers on the surfaces of UCNPs. Combined with the passive implanted system, a 20-day monitoring of H₂ O₂ in the rat model of ovarian cancer with peritoneal metastasis is achieved, in which the limited light penetration depth and toxicity of nano-probes are circumvented. The developed monitoring modes show great potential in accelerating the clinical transformation of nano-probes and biochemical detection methods.

Hydrogen Bond Network Induced by Surface Ligands Shifts the Semi-hydrogenation Selectivity over Palladium Catalysts

Tuning the metal-ligand interfaces of heterogeneous catalysts has emerged as an effective strategy to optimize their catalytic performance. However, improving the selectivity via organic modification remains a challenge so far. In this work, we demonstrate a simple ligand modification by preparing cysteamine-coated ultrathin palladium nanosheets. The as-prepared catalyst exhibits excellent selectivity with durability during catalytic hydrogenation of terminal alkynes, superior to most previously reported ligand-protected palladium catalysts. Further study reveals that a zwitterionic transformation occurs on the palladium interface under the H₂ conditions, generating a rigid hydrogen bond network. Such an unexpected effect beyond the traditional steric effect derived from van der Waals interactions makes the catalytic surface favor the hydrogenation of alkynes over alkenes without significantly sacrificing the catalytic activity. These results not only provide a unique steric effect concept for surface coordination chemistry but also provide a practical application to improve the selectivity and activity comprehensively.

Insights into the Synthesis Mechanisms of Ag-Cu3P-GaP Multicomponent Nanoparticles

Metal-semiconductor nanoparticle heterostructures are exciting materials for photocatalytic applications. Phase and facet engineering are critical for designing highly efficient catalysts. Therefore, understanding processes occurring during the nanostructure synthesis is crucial to gain control over properties such as the surface and interface facets' orientations, morphology, and crystal structure. However, the characterization of nanostructures after the synthesis makes clarifying their formation mechanisms nontrivial and sometimes even impossible. In this study, we used an environmental transmission electron microscope with an integrated metal-organic chemical vapor deposition system to enlighten fundamental dynamic processes during the Ag-Cu₃P-GaP nanoparticle synthesis using Ag-Cu₃P seed particles. Our results reveal that the GaP phase nucleated at the Cu₃P surface, and growth proceeded via a topotactic reaction involving counter-diffusion of Cu⁺ and Ga³⁺ cations. After the initial GaP growth steps, the Ag and Cu₃P phases formed specific interfaces with the GaP growth front. GaP growth proceeded by a similar mechanism observed for the nucleation involving the diffusion of Cu atoms through/along the Ag phase toward other regions, followed by the redeposition of Cu₃P at a specific Cu₃P crystal facet, not in contact with the GaP phase. The Ag phase was essential for this process by acting as a medium enabling the efficient transport of Cu atoms away from and, simultaneously, Ga atoms toward the GaP-Cu₃P interface. This study shows that enlightening fundamental processes is critical for progress in synthesizing phase- and facet-engineered multicomponent nanoparticles with tailored properties for specific applications, including catalysis.

Dopant triggered atomic configuration activates water splitting to hydrogen

Finding highly efficient hydrogen evolution reaction (HER) catalysts is pertinent to the ultimate goal of transformation into a net-zero carbon emission society. The design principles for such HER catalysts lie in the well-known structure-property relationship, which guides the synthesis procedure that creates catalyst with target properties such as catalytic activity. Here we report a general strategy to synthesize 10 kinds of single-atom-doped CoSe₂-DETA (DETA = diethylenetriamine) nanobelts. By systematically analyzing these products, we demonstrate a volcano-shape correlation between HER activity and Co atomic configuration (ratio of Co-N bonds to Co-Se bonds). Specifically, Pb-CoSe₂-DETA catalyst reaches current density of 10 mA cm^-2 at 74 mV in acidic electrolyte (0.5 M H₂SO₄, pH ~0.35). This striking catalytic performance can be attributed to its optimized Co atomic configuration induced by single-atom doping.

Disordered Au Nanoclusters for Efficient Ammonia Electrosynthesis

The electrochemical nitrogen (N₂ ) reduction reaction (N₂ RR) under mild conditions is a promising and environmentally friendly alternative to the traditional Haber-Bosch process with high energy consumption and greenhouse emission for the synthesis of ammonia (NH₃ ), but high-yielding production is rendered challenging by the strong nonpolar N≡N bond in N₂ molecules, which hinders their dissociation or activation. In this study, disordered Au nanoclusters anchored on two-dimensional ultrathin Ti₃ C₂ T_x MXene nanosheets are explored as highly active and selective electrocatalysts for efficient N₂ -to-NH₃ conversion, exhibiting exceptional activity with an NH₃ yield rate of 88.3±1.7 μg h^-1  mg_cat. ^-1 and a faradaic efficiency of 9.3±0.4 %. A combination of in situ near-ambient pressure X-ray photoelectron spectroscopy and operando X-ray absorption fine structure spectroscopy is employed to unveil the uniqueness of this catalyst for N₂ RR. The disordered structure is found to serve as the active site for N₂ chemisorption and activation during the N₂ RR process.

Recent Developments in the Design and Fabrication of Electrochemical Biosensors Using Functional Materials and Molecules

Electrochemical biosensors are superior technologies that are used to detect or sense biologically and environmentally significant analytes in a laboratory environment, or even in the form of portable handheld or wearable electronics. Recently, imprinted and implantable biosensors are emerging as point-of-care devices, which monitor the target analytes in a continuous environment and alert the intended users to anomalies. The stability and performance of the developed biosensor depend on the nature and properties of the electrode material or the platform on which the biosensor is constructed. Therefore, the biosensor platform plays an integral role in the effectiveness of the developed biosensor. Enormous effort has been dedicated to the rational design of the electrode material and to fabrication strategies for improving the performance of developed biosensors. Every year, in the search for multifarious electrode materials, thousands of new biosensor platforms are reported. Moreover, in order to construct an effectual biosensor, the researcher should familiarize themself with the sensible strategies behind electrode fabrication. Thus, we intend to shed light on various strategies and methodologies utilized in the design and fabrication of electrochemical biosensors that facilitate sensitive and selective detection of significant analytes. Furthermore, this review highlights the advantages of various electrode materials and the correlation between immobilized biomolecules and modified surfaces.

Simple Approach toward N-Heterocyclic Carbene-Protected Gold Nanoclusters

Little advance has been made toward developing alternative bottom-up synthetic strategies for N-heterocyclic carbene (NHC)-stabilized gold nanoclusters, although this unique class of nanomaterials has exhibited exciting properties. We report in this work a simple and straightforward approach toward NHC-ligated gold nanoclusters by using imidazolium salts rather than free carbenes or NHC-coordinated gold complexes (NHC-Au-X, X is counterions) as precursors. Illustrated here is a one-pot and one-step preparation of an NHC-stabilized Au₁₃Br₄ cluster that features a distinct molecular formula, surface motifs, and assembling modes via chemical reduction of dpaAu, NaOMe, and ^FNHC^Bn·HBr by NaBH₄ (Hdpa is dipyridylamine; ^FNHC^Bn·HBr is 1,3-dibenzyl-5,6-difluoro-1H-benzo[d]imidazole-3-ium bromide). In situ UV-vis and NMR studies have elucidated the base-assisted formation of NHCs from imidazolium salts for the protection of the metal core. This work not only reports a new NHC-ligated superatom that completes the Au₁₃ library, thus facilitating structure-property studies, but also opens the door to explore underlying analogues in a facile and reasonable way.

Plate-Like Colloidal Metal Nanoparticles

The pseudo-two-dimensional (2D) morphology of plate-like metal nanoparticles makes them one of the most anisotropic, mechanistically understood, and tunable structures available. Although well-known for their superior plasmonic properties, recent progress in the 2D growth of various other materials has led to an increasingly diverse family of plate-like metal nanoparticles, giving rise to numerous appealing properties and applications. In this review, we summarize recent progress on the solution-phase growth of colloidal plate-like metal nanoparticles, including plasmonic and other metals, with an emphasis on mechanistic insights for different synthetic strategies, the crystallographic habits of different metals, and the use of nanoplates as scaffolds for the synthesis of other derivative structures. We additionally highlight representative self-assembly techniques and provide a brief overview on the attractive properties and unique versatility benefiting from the 2D morphology. Finally, we share our opinions on the existing challenges and future perspectives for plate-like metal nanomaterials.

Reactivity of non-organometallic ruthenium(II) polypyridyl complexes and their application as catalysts for hydride transfer reactions

Recently, we investigated the substitution behavior of a series of ruthenium(II) complexes of the general formula [RuII(terpy)(N∧N)Cl]Cl, where terpy = 2,2′:6′,2″-terpyridine, N∧N = bidentate ligand, in aqueous solutions. We have shown that the most and least reactive complexes of the series are [RuII(terpy)(en)Cl]Cl (en = ethylenediamine) and [RuII(terpy)(phen)Cl]Cl (phen = 1, 10-phenantroline), respectively, as a result of different electronic effects provided by the bidentate spectator chelates. Polypyridyl amine Ru(II) complex, viz. [Ru(terpy)(en)Cl]Cl and [Ru(terpy)(ampy)Cl]Cl (where ampy = 2-(aminomethyl)pyridine), in which the terpy chelate labilizes the metal center, are able to catalyze the conversion of NAD+ to 1,4-NADH using sodium formate as a source of hydride. We showed that this complex can control the [NAD+]/[NADH] ratio and potentially induce reductive stress in living cells, which is accepted as an effective method to kill cancer cells. Polypyridyl Ru(II) complexes, characterized in terms of the behavior in aqueous solutions, can be used as model systems to monitor heterogeneous multiphase ligand substitution reactions at the solid-liquid interface. Colloidal coordination compounds in the submicron range were synthesized from Ru(II)-aqua derivatives of starting chlorido complexes via the anti-solvent procedure and stabilized by a surfactant shell layer.

Double solvent synthesis of ultrafine Pt nanoparticles supported on halloysite nanotubes for chemoselective cinnamaldehyde hydrogenation

The development of highly active, low cost and durable catalysts for selective hydrogenation of aldehydes is imperative and challenging. In this contribution, we rationally constructed ultrafine Pt nanoparticles (Pt NPs) supported on the internal and external surfaces of halloysite nanotubes (HNTs) by a facile double solvent strategy. The influence of Pt loading, HNTs surface properties, reaction temperature, reaction time, H₂ pressure and solvents on the performance of cinnamaldehyde (CMA) hydrogenation was analyzed. The optimal catalysts with the Pt loading of 3.8 wt% and the average Pt particle size of 2.98 nm exhibited outstanding catalytic activity for the hydrogenation of CMA to cinnamyl alcohol (CMO) with 94.1% conversion of CMA and 95.1% selectivity to CMO. More impressively, the catalyst showed excellent stability during six cycles of use. The ultra-small size and high dispersion of Pt NPs, the negative charge on the outer surface of HNTs, the -OH on the inner surface of HNTs, and the polarity of anhydrous ethanol solvent account for the outstanding catalytic performance. This work offers a promising way to develop high-efficiency catalysts with high CMO selectivity and stability by combining clay mineral halloysite and ultrafine nanoparticles.

Hyper crosslinked polymer supported NHC stabilized gold nanoparticles with excellent catalytic performance in flow processes

Highly active and selective heterogeneous catalysis driven by metallic nanoparticles relies on a high degree of stabilization of such nanomaterials facilitated by strong surface ligands or deposition on solid supports. In order to tackle these challenges, N-heterocyclic carbene stabilized gold nanoparticles (NHC@AuNPs) emerged as promising heterogeneous catalysts. Despite the high degree of stabilization obtained by NHCs as surface ligands, NHC@AuNPs still need to be loaded on support structures to obtain easily recyclable and reliable heterogeneous catalysts. Therefore, the combination of properties obtained by NHCs and support structures as NHC bearing "functional supports" for the stabilization of AuNPs is desirable. Here, we report the synthesis of hyper-crosslinked polymers containing benzimidazolium as NHC precursors to stabilize AuNPs. Following the successful synthesis of hyper-crosslinked polymers (HCP), a two-step procedure was developed to obtain HCP·NHC@AuNPs. Detailed characterization not only revealed the successful NHC formation but also proved that the NHC functions as a stabilizer to the AuNPs in the porous polymer network. Finally, HCP·NHC@AuNPs were evaluated in the catalytic decomposition of 4-nitrophenol. In batch reactions, a conversion of greater than 99% could be achieved in as little as 90 s. To further evaluate the catalytic capability of HCP·NHC@AuNP, the catalytic decomposition of 4-nitrophenol was also performed in a flow setup. Here the catalyst not only showed excellent catalytic conversion but also exceptional recyclability while maintaining the catalytic performance.

Reactivity and Recyclability of Ligand-Protected Metal Cluster Catalysts for CO2 Transformation

It remains a significant challenge to construct an integrated catalyst that combines advantages of homogeneous and heterogeneous catalysis with clarified mechanism and high performance. Here we show atomically precise CuAg cluster catalysts for CO₂ capture and utilization, where two functional units are combined into the clusters: metal and ligand. Due to atomic resolution on total and local structures of such catalysts to be achieved, which disentangles heterogeneous imprecise systems and permits tracing the reaction processes via experiments coupled with theory, site-specific catalysis induced by metal-ligand synergy can be accurately elucidated. The CuAg cluster catalysts exhibit excellent reactivity and recyclability to forge the C-N bonding from CO₂ formylation with secondary amines that can make the cluster catalysts more unique compared with typically homogeneous complexes.

Metallene-related materials for electrocatalysis and energy conversion

As a member of graphene analogs, metallenes are a class of two-dimensional materials with atomic thickness and well-controlled surface atomic arrangement made of metals or alloys. When utilized as catalysts, metallenes exhibit distinctive physicochemical properties endowed from the under-coordinated metal atoms on the surface, making them highly competitive candidates for energy-related electrocatalysis and energy conversion systems. Significantly, their catalytic activity can be precisely tuned through the chemical modification of their surface and subsurface atoms for efficient catalyst engineering. This minireview summarizes the recent progress in the synthesis and characterization of metallenes, together with their use as electrocatalysts toward reactions for energy conversion. In the Synthesis section, we pay particular attention to the strategies designed to tune their exposed facets, composition, and surface strain, as well as the porosity/cavity, defects, and crystallinity on the surface. We then discuss the electrocatalytic properties of metallenes in terms of oxygen reduction, hydrogen evolution, alcohol and acid oxidation, carbon dioxide reduction, and nitrogen reduction reaction, with a small extension regarding photocatalysis. At the end, we offer perspectives on the challenges and opportunities with respect to the synthesis, characterization, modeling, and application of metallenes.

An atomically precise Ag18Cu8 nanocluster with rich alkynyl-metal coordination structures and unique SbF6- assembling modes

Elucidating the coordination structures and assembling modes of atomically precise metal nanoclusters (NCs) remains a hot topic as it gives answers to the underlying mechanism of nanomaterials and bulk materials in terms of structure-property relationships. Here we report a novel silver-copper alloy NC featuring rich alkynyl-metal coordination modes and unique SbF₆^- assembling structures. The NC, with the composition of [Ag₁₈Cu₈(dppp)₄(^tBu-C₆H₄CC)₂₂](SbF₆)₄ (dppp = 1,3-bis(diphenylphosphino)-propane), was prepared by a stepwise synthetic approach. Single-crystal X-ray diffraction analysis revealed that such a NC featured a staircase-like Ag₁₈Cu₈ kernel, which was protected by hybrid alkynyl and dppp ligands in diverse coordination structures and multiple environments. The structural analysis also revealed the unique function of SbF₆^- in inducing the assembly of cluster moieties, highlighting the importance of counterions in assembling nanomolecules. The diverse coordination structures of the protective ligands with metal ions and the indispensable roles of counterions in assembling the cluster moieties have also been supported by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) studies, making it a model system to showcase the uniqueness of atomically precise metal NCs in illustrating the coordination chemistry of nanomaterials and bulk materials at the molecular level.

Etching suppression as a means to Pt dendritic ultrathin nanosheets by seeded growth

2D ultrathin metal nanostructures are emerging materials displaying distinct physical and chemical properties compared to their analogues of different dimensionalities. Nanosheets of fcc metals are intriguing, as their crystal structure does not favour a 2D configuration. Thanks to their increased surface-to-volume ratios and the optimal exposure of low-coordinated sites, 2D metal nanostructures can be advantageously exploited in catalysis. Synthesis approaches to ultrathin nanosheets of pure platinum are scarce compared to other noble metals and to Pt-based alloys. Here, we present the selective synthesis of Pt ultrathin nansosheets by a simple seeded-growth method. The most crucial point in our approach is the selective synthesis of Pt seeds comprising planar defects, a main driving force for the 2D growth of metals with fcc structure. Defect engineering is employed here, not in order to disintegrate, but for conserving the defect comprising seeds. This is achieved by in situ elimination of the principal etching agent, chloride, which is present in the PtCl₂ precursor. As a result of etching suppression, twinned nuclei, that are selectively formed during the early stage of nucleation, survive and grow to multipods comprising planar defects. Using the twinned multipods as seeds for the subsequent 2D overgrowth of Pt from Pt(acac)₂ yields ultrathin dendritic nanosheets, in which the planar defects are conserved. Using phenylacetylene hydrogenation as a model reaction of selective hydrogenation, we compared the performance of Pt nanosheets to that of a commercial Pt/C catalyst. The Pt nanosheets show better stability and much higher selectivity to styrene than the commercial Pt/C catalyst for comparable activity.

Coordination-Induced Trigger for Activity: N-Heterocyclic Carbene-Decorated Ceria Catalysts Incorporating Cr and Rh with Activity Induction by Surface Adsorption Site Control

A coordination-induced trigger for catalytic activity is proposed on an N-heterocyclic carbene (NHC)-decorated ceria catalyst incorporating Cr and Rh (ICy-r-Cr_0.19Rh_0.06CeO_z). ICy-r-Cr_0.19Rh_0.06CeO_z was prepared by grafting 1,3-dicyclohexylimidazol-2-ylidene (ICy) onto H₂-reduced Cr_0.19Rh_0.06CeO_z (r-Cr_0.19Rh_0.06CeO_z) surfaces, which went on to exhibit substantial catalytic activity for the 1,4-arylation of cyclohexenone with phenylboronic acid, whereas r-Cr_0.19Rh_0.06CeO_z without ICy was inactive. FT-IR, Rh K-edge XAFS, XPS, and photoluminescence spectroscopy showed that the ICy carbene-coordinated Rh nanoclusters were the key active species. The coordination-induced trigger for catalytic activity on the ICy-bearing Rh nanoclusters could not be attributed to electronic donation from ICy to the Rh nanoclusters. DFT calculations suggested that ICy controlled the adsorption sites of the phenyl group on the Rh nanocluster to promote the C-C bond formation of the phenyl group and cyclohexenone.

Iron(II) Mediated Supramolecular Architectures with Schiff Bases and Their Spin-Crossover Properties

Supramolecular architectures, which are formed through the combination of inorganic metal cations and organic ligands by self-assembly, are one of the techniques in modern chemical science. This kind of multi-nuclear system in various dimensionalities can be implemented in various applications such as sensing, storage/cargo, display and molecular switching. Iron(II) mediated spin-crossover (SCO) supramolecular architectures with Schiff bases have attracted the attention of many investigators due to their structural novelty as well as their potential application possibilities. In this paper, we review a number of supramolecular SCO architectures of iron(II) with Schiff base ligands exhibiting varying geometrical possibilities. The structural and SCO behavior of these complexes are also discussed in detail.

Surface and Interface Coordination Chemistry Learned from Model Heterogeneous Metal Nanocatalysts: From Atomically Dispersed Catalysts to Atomically Precise Clusters

The surface and interface coordination structures of heterogeneous metal catalysts are crucial to their catalytic performance. However, the complicated surface and interface structures of heterogeneous catalysts make it challenging to identify the molecular-level structure of their active sites and thus precisely control their performance. To address this challenge, atomically dispersed metal catalysts (ADMCs) and ligand-protected atomically precise metal clusters (APMCs) have been emerging as two important classes of model heterogeneous catalysts in recent years, helping to build bridge between homogeneous and heterogeneous catalysis. This review illustrates how the surface and interface coordination chemistry of these two types of model catalysts determines the catalytic performance from multiple dimensions. The section of ADMCs starts with the local coordination structure of metal sites at the metal-support interface, and then focuses on the effects of coordinating atoms, including their basicity and hardness/softness. Studies are also summarized to discuss the cooperativity achieved by dual metal sites and remote effects. In the section of APMCs, the roles of surface ligands and supports in determining the catalytic activity, selectivity, and stability of APMCs are illustrated. Finally, some personal perspectives on the further development of surface coordination and interface chemistry for model heterogeneous metal catalysts are presented.

Upgrading heterogeneous Ni catalysts with thiol modification

Precious metal catalysts are the cornerstone of many industrial processes. Replacing precious metal catalysts with earth-abundant metals is one of key challenges for the green and sustainable development of chemical industry. We report in this work a surprisingly effective strategy toward the development of cost-effective, air-stable, and efficient Ni catalysts by simple surface modification with thiols. The as-prepared catalysts exhibit unprecedentedly high activity and selectivity in the reductive amination of aldehydes/ketones. The thiol modification can not only prevent the deep oxidation of Ni surface to endow the catalyst with long shelf life in air but can also allow the reductive amination to proceed via a non-contact mechanism to selectively produce primary amines. The catalytic performance is far superior to that of precious and non-precious metal catalysts reported in the literature. The wide application scope and high catalytic performance of the developed Ni catalysts make them highly promising for the low-cost, green production of high-value amines in chemical industry.

Effects of Ionic Liquids on the Stabilization Process of Gold Nanoparticles

Improving the stability of the gold nanoparticles (AuNPs) is an important challenge in nanoscience, given that the activity and ubiquitous application of the AuNPs in different fields depend largely on their stability in the solution phase. Ionic liquids (ILs) can be used as new alternatives in comparison to water and organic solvents due to their considerable properties to elevate the stability and resistance of the AuNPs against aggregation for a long period of storage. In this study, we employ molecular dynamics simulation and quantum chemistry calculations to investigate the effects of amino acid ILs ([BMIM][Gly], [BMIM][Leu], [BMIM][Pro], [BMIM][Val], and [BMIM][Ala]) on the stability and aggregation process of the AuNPs from the molecular viewpoint. Our results suggest that ILs can prevent AuNP aggregation. These ILs penetrate the solvation shell of the nanoparticles and by increasing the electrostatic repulsions on the surface of the AuNPs improve their stability against aggregation. Moreover, the [BMIM]⁺ cation is more effective on the stability of the AuNPs in comparison with the corresponding anions. The ring of the cation, due to the stronger interaction with the AuNPs compared to the side chain, contributes predominantly to the stability of the nanostructures. Our quantum chemistry calculations confirm that dispersion interactions between the cation and anions of the ILs and the surface of gold play a key role in the stability of the IL-AuNP complexes. [Leu]^- anion has the strongest dispersion interactions with the metal surface and forms the most stable complex with the AuNPs. Overall, the results of this study offer new insights into the properties of amino acid ILs as effective agents to improve the stability of AuNPs for long-term storage.

Interactions Balancing Competition and Cooperation between Covalent-Organic Framework Additives and PEG Base Oil toward Advanced Lubrication

Severe competition between nanolubricant additives and polar lubricating oil molecules for the formation of lubricant films has been hindering the progress of green and advanced lubricants. In this work, based on the tautomerism of cyanuric acid molecule (trione and triol configurations), two kinds of triazine-based covalent-organic frameworks (COFs), that is, Ton-COFs and Tol-COFs, were synthesized as additives of the polar PEG 400 oil, realizing compromise between them by providing delicate interactions. The triazine matrix bonding with intense polar groups in the framework of additives offers more powerful interactions to competitively form the adsorbed lubricant film on the surface of the metal substrate over PEG 400 oil and also bolts PEG 400 oil molecules by the hydrogen bonding inside the pore of the framework to cooperatively bear against the load. Molecular quantum chemical calculations further confirm that Ton-COFs can produce a more intense interaction with Fe atoms in the form of coordination and ions···π than Tol-COFs, far beyond PEG 400, and the cross-sectional profile of the worn surface definitely exhibits a protective lubricant film only composed of Ton-COFs. Consequently, at the low concentration of 0.3 wt %, the excellent friction reduction (41.2%) and antiwear property (97.4%) are achieved for the Ton-COFs compared to pure PEG 400 oil; moreover, 28.6% and 79.0% for Tol-COFs at the essential concentration of 0.7 wt % are achieved. This finding provides a novel insight from molecules to materials into guiding the development of additives for advanced lubricants.

Tuning the Micro-coordination Environment of Al in Dealumination Y Zeolite to Enhance Electron Transfer at the Cu-Mn Oxides Interface for Highly Efficient Catalytic Ozonation of Toluene at Low Temperatures

The development of stable, highly active, and inexpensive catalysts for the ozone catalytic oxidation of volatile organic compounds (VOCs) is challenging but of great significance. Herein, the micro-coordination environment of Al in commercial Y zeolite was regulated by a specific dealumination method and then the dealuminated Y zeolite was used as the support of Cu-Mn oxides. The optimized catalyst Cu-Mn/DY exhibited excellent performance with around 95% of toluene removal at 30 °C. Besides, the catalyst delivered satisfactory stability in both high-humidity conditions and long-term reactions, which is attributed to more active oxygen vacancies and acidic sites, especially the strong Lewis acid sites newly formed in the catalyst. The decrease in the electron cloud density around aluminum species enhanced electron transfer at the interface between Cu-Mn oxides. Moreover, extra-framework octahedrally coordinated Al in the support promoted the electronic metal-support interaction (EMSI). Compared with single Mn catalysts, the incorporation of the Cu component changed the degradation pathway of toluene. Benzoic acid, as the intermediate of toluene oxidation, can directly ring-open on Cu-doped catalysts rather than being further oxidized to other byproducts, which increased the rate of the catalytic reaction. This work provides a new insight and theoretical guidance into the rational design of efficient catalysts for the catalytic ozonation of VOCs.