ClAg14 (C≡Ct Bu)12 Nanoclusters as Efficient and Selective Electrocatalysts Toward Industrially Relevant CO2 Conversion

Atomically precise metal nanoclusters (NCs) have emerged as a promising frontier in the field of electrochemical CO2 reduction reactions (CO2 RR) because of their distinctive catalytic properties. Although numerous metal NCs are developed for CO2 RR, their use in practical applications has suffered from their low-yield synthesis and insufficient catalytic activity. In this study, the large-scale synthesis and electrocatalytic performance of ClAg14 (C≡Ct Bu)12 + NCs, which exhibit remarkable efficiency in catalyzing CO2 -to-CO electroreduction with a CO selectivity of over 99% are reported. The underlying mechanisms behind this extraordinary CO2 RR activity of ClAg14 (C≡Ct Bu)12 + NCs are investigated by a combination of electrokinetic and theoretical studies. These analyses reveal that different active sites, generated through electrochemical activation, have unique adsorption properties for the reaction intermediates, leading to enhanced CO2 RR and suppressed hydrogen production. Furthermore, industrially relevant CO2 -to-CO electroreduction using ClAg14 (C≡Ct Bu)12 + NCs in a zero-gap CO2 electrolyzer, achieving high energy efficiency of 51% and catalyst activity of over 1400 A g-1 at a current density of 400 mA cm-2 is demonstrated.

Anion-templated silver nanoclusters: precise synthesis and geometric structure

Metal nanoclusters (NCs) are gaining much attention in nanoscale materials research because they exhibit size-specific physicochemical properties that are not observed in the corresponding bulk metals. Among them, silver (Ag) NCs can be precisely synthesized not only as pure Ag NCs but also as anion-templated Ag NCs. For anion-templated Ag NCs, we can expect the following capabilities: 1) size and shape control by regulating the central anion (anion template); 2) stabilization by adjusting the charge interaction between the central anion and surrounding Ag atoms; and 3) functionalization by selecting the type of central anion. In this review, we summarize the synthesis methods and influences of the central anion on the geometric structure of anion-templated Ag NCs, which include halide ions, chalcogenide ions, oxoanions, polyoxometalate, or hydride/deuteride as the central anion. This summary provides a reference for the current state of anion-templated Ag NCs, which may promote the development of anion-templated Ag NCs with novel geometric structures and physicochemical properties.

Chiral Nanocluster Complexes Formed by Host-Guest Interaction between Enantiomeric 2,6-Helic[6]arenes and Silver Cluster Ag20: Emission Enhancement and Chirality Transfer

A pair of chiral nanocluster complexes were formed by the host−guest interaction between the enantiomeric 2,6-helic[6]arenes and nanocluster Ag₂₀. The formation and stability of the nanocluster complexes were experimentally and theoretically confirmed. Meanwhile, the chiral nanocluster complexes exhibited enhanced luminescence and induced CD signals at room temperature in the solid state, revealing the stable complexation and chirality transfer from the chiral macrocycles to the nanocluster Ag₂₀.

Stepwise Assembly of Ag42 Nanocalices Based on a MoVI-Anchored Thiacalix[4]arene Metalloligand

Metalloligand strategy has been well recognized in the syntheses of heterometallic coordination polymers; however, such a strategy used in the assembly of silver nanoclusters is not broadly available. Herein, we report the stepwise syntheses of a family of halogen-templated Ag₄₂ nanoclusters (Ag42c-Ag42f) based on Mo^VI-anchored p-tert-butylthiacalix[4]arene (H₄TC4A) as a metalloligand (hereafter named MoO₃-TC4A). X-ray crystallography demonstrates that they are similar C₃-symmetric silver-organic nanocalices capped by six MoO₃-TC4A metalloligands, which are evenly distributed up and down the base of 42 silver atoms. These nanoclusters can be disassembled to six bowl-shaped [Ag₁₁(MoO₃-TC4A)(RS)₃] secondary building units (SBUs, R = Et or ⁿPr), which are fused together in a face-sharing fashion surrounding Cl^- or Br^- as a central anion template. The electrospray mass spectrometry (ESI-MS) indicates their high stabilities in solution and verifies the formation of the MoO₃-TC4A metalloligand, thereby rationalizing the overall stepwise assembly process for them. Moreover, Ag42c shows lower cytotoxicity and better activity against the HepG-2 cell line than MCF-7 and BGC-823. These results not only exemplify the effectiveness of a thiacalix[4]arene-based metalloligand in the assembly of silver nanoclusters but also give us profound insight about the step-by-step assembly process in silver nanoclusters.

Assembling Silver Cluster-Based Organic Frameworks for Higher-Performance Hypergolic Properties

Increasing research efforts have been focused on developing next-generation propellants. In this work, we demonstrated that assembling zero-dimensional (0D) silver clusters with energetic ligands into 3D metal organic frameworks (MOFs) not only inherited the short ignition delay (ID) time of the alkynyl-silver cluster but also significantly increased the output energy. Among them, the open cationic framework of ZZU-363 incorporating counter NO₃ ^- ions achieved a considerably reduced energy barrier and eventually the shortest ID time (26 ms), together with the highest volumetric energy density (40.4 kJ cm^-3) and specific impulse (263.1 s), which is far superior to traditional hydrazine-based propellants. The underlying mechanisms are clearly revealed by theoretical calculations. This work opens a venue to significantly enhancing the hypergolic activity of metal clusters and MOFs.

Silver Zeolite Composite-Based LEDs: Origin of Electroluminescence and Charge Transport

In this contribution, we report on the first time use of silver-exchanged zeolites embedded in the nonconductive polystyrene (PS) and their use as hybrid emitters in light-emitting diodes (ZEOLEDs). The turn on voltage and EL intensity are strongly dependent on the concentration of metal clusters. It is shown that the key to optimize this technology is improving the zeolite anode contact. Such an optimized device based on cheap abundant materials could provide an alternative for the commercial phosphor converted LEDs. A ZEOLED with a voltage polarity dependent color is demonstrated.

Hydrogen Storage, Magnetism and Electrochromism of Silver Doped FAU Zeolite: First-Principles Calculations and Molecular Simulations

The complex configuration, H₂ adsorption binding energy, magnetic, and optical properties of FAU zeolites with Ag cations loaded by ion exchange in the vacant dielectric cavities were investigated by employing the first-principles calculations with all-electron-relativistic numerical atom-orbitals scheme and the Metropolis Monte Carlo molecular simulations. The visible absorption spectrum peaked at distinct wavelengths arranging from red or green to blue colors when changing the net charge load, due to the produced various redox states of Ag cations exchanging at multiple Li⁺-substituted sites. The spin population analyses indicate the ferrimagnetic coupling between Al⁻O⁻Si framework and Ag cations originates from the major ferromagnetic spin polarization in Ag cation cluster coordinating with sodalite cages, with the net spins appreciably depending on the Ag content and exchange site. The H₂ adsorption capacities and binding energies represent significant dependence on the content, location, and electronic property of Ag cations introduced into the FAU zeolites. The evident decrease of H₂ adsorption binding energy with increased loading concentration demonstrates repulsive interaction between H₂ molecules and heterogeneous adsorption configuration on Ag cations. The adsorption sites of H₂ sorted by the binding energy with different adsorption configurations were correlated with exchange sites of Ag cations under different Ag loading to comprehend the H₂ adsorption mechanism.

Atom-precise polyoxometalate-ag2 s core-shell nanoparticles

Atomically precise polyoxometalate-Ag2 S core-shell nanoparticles were generated in a top-down approach under solvothermal conditions and structurally confirmed by X-ray single-crystal diffraction as an interesting core-shell structure comprising an in situ generated Mo6 O22 (8-) polyoxometalate core and a mango-like Ag58 S38 shell. This result demonstrates the possibility to integrate polyoxometalate and Ag2 S nanoparticles into a core-shell heteronanostructure with precisely controlled atomical compositions of both core and shell.

Atomically precise arrays of fluorescent silver clusters: a modular approach for metal cluster photonics on DNA nanostructures

The remarkable precision that DNA scaffolds provide for arraying nanoscale optical elements enables optical phenomena that arise from interactions of metal nanoparticles, dye molecules, and quantum dots placed at nanoscale separations. However, control of ensemble optical properties has been limited by the difficulty of achieving uniform particle sizes and shapes. Ligand-stabilized metal clusters offer a route to atomically precise arrays that combine desirable attributes of both metals and molecules. Exploiting the unique advantages of the cluster regime requires techniques to realize controlled nanoscale placement of select cluster structures. Here we show that atomically monodisperse arrays of fluorescent, DNA-stabilized silver clusters can be realized on a prototypical scaffold, a DNA nanotube, with attachment sites separated by <10 nm. Cluster attachment is mediated by designed DNA linkers that enable isolation of specific clusters prior to assembly on nanotubes and preserve cluster structure and spectral purity after assembly. The modularity of this approach generalizes to silver clusters of diverse sizes and DNA scaffolds of many types. Thus, these silver cluster nano-optical elements, which themselves have colors selected by their particular DNA templating oligomer, bring unique dimensions of control and flexibility to the rapidly expanding field of nano-optics.

DNA-Protected Silver Clusters for Nanophotonics

DNA-protected silver clusters (Ag_N-DNA) possess unique fluorescence properties that depend on the specific DNA template that stabilizes the cluster. They exhibit peak emission wavelengths that range across the visible and near-IR spectrum. This wide color palette, combined with low toxicity, high fluorescence quantum yields of some clusters, low synthesis costs, small cluster sizes and compatibility with DNA are enabling many applications that employ Ag_N-DNA. Here we review what is known about the underlying composition and structure of Ag_N-DNA, and how these relate to the optical properties of these fascinating, hybrid biomolecule-metal cluster nanomaterials. We place Ag_N-DNA in the general context of ligand-stabilized metal clusters and compare their properties to those of other noble metal clusters stabilized by small molecule ligands. The methods used to isolate pure Ag_N-DNA for analysis of composition and for studies of solution and single-emitter optical properties are discussed. We give a brief overview of structurally sensitive chiroptical studies, both theoretical and experimental, and review experiments on bringing silver clusters of distinct size and color into nanoscale DNA assemblies. Progress towards using DNA scaffolds to assemble multi-cluster arrays is also reviewed.

Green preparation and spectroscopic characterization of plasmonic silver nanoparticles using fruits as reducing agents

Chemicals typically available in plants have the capability to reduce silver and gold salts and to create silver and gold nanoparticles. We report the preparation of silver nanoparticles with sizes between 10 and 300 nm from silver nitrate using fruit extract collected from pineapples and oranges as reducing agents. The evolvement of a characteristic surface plasmon extinction spectrum in the range of 420 nm to 480 nm indicates the formation of silver nanoparticles after mixing silver nitrate solution and fruit extract. Shifts in plasmon peaks over time indicate the growth of nanoparticles. Electron microscopy shows that the shapes of the nanoparticles are different depending on the fruit used for preparation. The green preparation process can result in individual nanoparticles with a very poor tendency to form aggregates with narrow gaps even when aggregation is forced by the addition of NaCl. This explains only modest enhancement factors for near-infrared-excited surface enhanced Raman scattering. In addition to the surface plasmon band, UV-visible absorption spectra show features in the UV range which indicates also the presence of small silver clusters, such as Ag4 (2+). The increase of the plasmon absorption correlates with the decrease of absorption band in the UV. This confirms the evolution of silver nanoparticles from silver clusters. The presence of various silver clusters on the surface of the "green" plasmonic silver nanoparticles is also supported by a strong multicolor luminesce signal emitted by the plasmonic particles during 473 nm excitation.

Periodic fluorescent silver clusters assembled by rolling circle amplification and their sensor application

A simple method for preparing DNA-stabilized Ag nanoclusters (NCs) nanowires is presented. To fabricate the Ag NCs nanowires, we use just two unmodified component strands and a long enzymatically produced scaffold. These nanowires form at room temperature and have periodic sequence units that are available for fluorescence Ag NCs assembled which formed three-way junction (TWJ) structure. These Ag NCs nanowires can be clearly visualized by confocal microscopy. Furthermore, due to the high efficiency of rolling circle amplification reaction in signal amplification, the nanowires exhibit high sensitivity for the specific DNA detection with a wide linear range from 6 to 300 pM and a low detection limit of 0.84 pM, which shows good performance in the complex serum samples. Therefore, these Ag NCs nanowires might have great potential in clinical and imaging applications in the future.

Importance of Correctly Describing Charge-Transfer Excitations for Understanding the Chemical Effect in SERS

The enhancement mechanism due to the molecule-surface chemical coupling in surface-enhanced Raman scattering (SERS) is governed to a large extent by the energy difference between the highest occupied molecular orbital (HOMO) of the metal and the lowest unoccupied molecular orbital (LUMO) of the molecule. Here, we investigate the importance of correctly describing charge-transfer excitations, using time-dependent density functional theory (TDDFT), when calculating the chemical coupling in SERS. It is well-known that TDDFT, using traditional functionals, underestimates the position of charge-transfer excitations. Here, we show that this leads to a significant overestimation of the chemical coupling mechanism in SERS. Significantly smaller enhancements are found using long-range corrected (LC) functionals as compared with a traditional generalized gradient approximation (GGA) and hybrid functionals. Enhancement factors are found to be smaller than 530 and typically less than 50. Our results show that it is essential to correctly describe charge-transfer excitations for predicting the chemical enhancement in SERS.

DNA sensing by amplifying the number of near-infrared emitting, oligonucleotide-encapsulated silver clusters

A bifunctional oligonucleotide integrates in situ synthesis of a fluorogenic silver cluster with recognition of a target DNA sequence. With the template C(3)AC(3)AC(3)GC(3)A, a complex forms with 10 silver atoms that possesses electronic transitions in the near-infrared and that is detected at nanomolar concentrations using diode laser excitation. Pendant to this cluster encoding region, the recognition component binds a target DNA strand through hybridization, and decoupling of these two regions of the composite sensor renders a modular sensor for specific oligonucleotides. A target is detected using a quencher strand that bridges the cluster template and recognition components and disturbs cluster binding, as indicated by static quenching. Competitive displacement of the quencher by the target strand restores the favored cluster environment, and our key finding is that this exchange enhances emission through a proportional increase in the number of emissive clusters. DNA detection is also accomplished in serum-containing buffers by taking advantage of the high brightness of this fluorophore and the inherently low endogenous background in the near-infrared spectral region. Cluster stability in this biological environment is enhanced by supplementing the solutions with Ag(+).