Alloy Nanoclusters Research Articles

Concentration asymmetry and carbon enrichment in titanium carbide and silicon carbide clusters

The mass spectra of metal clusters obtained by gas aggregation and laser vaporization techniques show variations of the abundance with cluster size, and the best-known manifestation is the magic numbers. The case of nanoalloys adds structural and chemical richness, and asymmetry in the atomic concentrations is sometimes observed. This is the case with ${\mathrm{Ti}}_{x}{\mathrm{C}}_{y}$ and ${\mathrm{Si}}_{x}{\mathrm{C}}_{y}$ clusters, for which the experiments performed until now reveal an enrichment of the clusters in carbon. The structure of the mass spectrum arises when hot clusters evaporate atoms to cool down. By performing density functional calculations, complemented by a thermochemical formalism to obtain Gibbs free energies, we have found that for each cluster in the families ${\mathrm{Ti}}_{x}{\mathrm{C}}_{y}$ and ${\mathrm{Si}}_{x}{\mathrm{C}}_{y}$ with $x$ = 1--4 and $y$ = 1--4, it is easier to remove titanium or silicon atoms as compared to removing carbon atoms, and this explains the carbon enrichment systematically observed in the experiments. The conclusion is that the broad compositional trends expected in the formation of alloy nanoclusters can be anticipated from calculations of the evaporation energies of the alloy components, and this may be particularly interesting in the field of catalysis.

Nitrogen doped carbon-distributed and nitrogen-stabilized ultrafine FeM (M = Pd, Pt, Au) nanoclusters for doxorubicin detoxification

Downsizing supported metal of Fe0-based materials in dealing with ever-growing pharmaceutical contamination issues are highly desired but still challenging. Herein, we develop a modular design protocol to synthesize a family of ultrafine alloy nanoclusters embedded in a nitrogen-enriched carbon framework (NEC@FeM (M=Pd, Pt, Au)). Engineering the fine structure of nitrogen-enriched carbon and interfacial interaction with bimetallic nanoclusters largely suppresses bimetallic overgrowth, eventually producing supported ultrafine (< 4 nm), highly dispersed, well-alloyed nanoclusters. The alloying Fe0 with M for ultrafine nanoclusters optimize the electron flow, chemical stability, and catalytic property, resulting in the obtained NEC@FeM exhibiting excellent doxorubicin (DOX) degradation performance. Density functional theory calculation combined with experimental results attribute the outstanding DOX degradation ability of NEC@FePd originally to the synergistic effect of enhanced DOX affinity and efficient electrons transfer from Fe to DOX. This work provides a paradigm for the design of ultrafine Fe0-based nanocluster with application in pollution control.

Fluorescence or Phosphorescence? The Metallic Composition of the Nanocluster Kernel Does Matter

AbstractIt remains challenging to manipulate the nature of photoluminescence as either fluorescence or phosphorescence for a correlated cluster series. In this work, two correlated nanoclusters, Au5Ag11(SR)8(DPPOE)2 and Pt1Ag16(SR)8(DPPOE)2 with comparable structure features, were synthesized and structurally determined. These two alloy nanoclusters displayed distinct photoluminescent nature—the Au5Ag11 nanocluster is fluorescent, whereas the Pt1Ag16 nanocluster is phosphorescent. The decay processes of the excited electrons in these two nanoclusters have been explicitly mapped out by both experimental and theoretical approaches, disclosing the mechanisms of their fluorescence and phosphorescence. Specifically, the metallic compositions of the nanocluster kernels mattered in determining their photoluminescent nature. The results herein provide an intriguing nanomodel that enables us to grasp the origin of photoluminescence at the atomic level, which further paves the way for fabricating novel nanoclusters or cluster‐based nanomaterials with customized photophysical properties.

Fluorescence or Phosphorescence? The Metallic Composition of the Nanocluster Kernel Does Matter.

It remains challenging to manipulate the nature of photoluminescence as either fluorescence or phosphorescence for a correlated cluster series. In this work, two correlated nanoclusters, Au5 Ag11 (SR)8 (DPPOE)2 and Pt1 Ag16 (SR)8 (DPPOE)2 with comparable structure features, were synthesized and structurally determined. These two alloy nanoclusters displayed distinct photoluminescent nature-the Au5 Ag11 nanocluster is fluorescent, whereas the Pt1 Ag16 nanocluster is phosphorescent. The decay processes of the excited electrons in these two nanoclusters have been explicitly mapped out by both experimental and theoretical approaches, disclosing the mechanisms of their fluorescence and phosphorescence. Specifically, the metallic compositions of the nanocluster kernels mattered in determining their photoluminescent nature. The results herein provide an intriguing nanomodel that enables us to grasp the origin of photoluminescence at the atomic level, which further paves the way for fabricating novel nanoclusters or cluster-based nanomaterials with customized photophysical properties.

Hydride-Containing Eight-Electron Pt/Ag Superatoms: Structure, Bonding, and Multi-NMR Studies.

Recent reports on hydride-doped noble metal nanoclusters strongly suggest that the encapsulated hydride is a part of the superatom core, but no accurate location of the hydride could be experimentally proved, so far. We report herein a hydride-doped eight-electron platinum/silver alloy nanocluster in which the position of four-coordinated hydride was determined by neutron diffraction for the first time. X-ray structures of [PtHAg19(dtp/desp)12] (dtp = S2P(OnPr)2, 1; dsep = Se2P(OiPr)2, 2) describe a central platinum hydride (PtH) unit encapsulated within a distorted Ag12 icosahedron, the resulting (PtH)@Ag12 core being stabilized by an outer sphere made up of 7 capping silver atoms and 12 dichalcogenolates. Solid-state structures of 1 and 2 differ somewhat in the spatial configuration of their outer spheres, resulting in overall different symmetries, C1 and C3, respectively. Whereas the multi-NMR spectra of 2 in solution at 173 K reveal that the structure of C3 symmetry is the predominant one, 1H and 195Pt NMR spectra of 1 at the same temperature disclose the presence of isomers of both C1 and C3 symmetry. DFT calculations found both isomers to be very close in energy, supporting the fact that they co-exist in solution. They also show that the [PtH@Ag12]5+ kernel can be viewed as a closed-shell superatomic core, the μ4-hydride electron contributing to its eight-electron count. On the other hand, the 1s(H) orbital contributes only moderately to the superatomic orbitals, being mainly involved in the building of a Pt-H bonding electron pair with the 5dz2(Pt) orbital.

Insight into the Mechanism of Single-Metal-Atom Tailoring on the Surface of Au-Cu Alloy Nanoclusters.

Tailoring the surface structure of nanomaterials is desirable for investigating their mechanisms and properties from a nanochemistry perspective. The modification of the surface of metal nanoparticles with a single metal atom has proven difficult, which has hindered the understanding of the contribution of different motifs in nanoclusters to their properties. Herein, we report single-metal-atom surface tailoring by thermally etching the nanocluster AuxCu15-x(DPPMH)3(SPhCl2)9 (x = 8 or 9) to obtain AuxCu16-x(DPPMH)2(DPPM)(SPhCl2)9 (x = 9 or 10) nanoclusters. An Au7Cu4 core was observed in both nanoclusters, which can be regarded as part of an icosahedron. Experiments and theoretical simulations revealed the tailoring processes of the icosahedron. Both nanoclusters displayed an NIR-II emission, and the introduction of the surface metal atom led to a red-shift in the emission band from 983 to 1025 nm. This work contributes to the development of precisely tailored nanocluster structures and provides an understanding of structure-property correlations.

Controlled preparation and application of glutathione capped gold and platinum alloy nanoclusters with high peroxidase-like activity

• The Au-PtNCs have been controlled prepared through a hydrothermal method. • The Au-PtNCs show optimal catalytic activity for TMB oxidation. • Doping with platinum is the most efficient way to improve the catalytic properties. • The Au-PtNCs are applied to colorimetric determine H 2 O 2 with high sensitivity. In the present study, we have prepared glutathione capped gold and platinum alloy nanoclusters (Au-PtNCs) in a controlled way by employing the hydrothermal method and optimized through adjusting the ratio of raw materials, reaction temperature, and time. Compared with the corresponding monometallic gold and platinum nanoclusters, the alloy nanoclusters' catalytic activity is improved dramatically in the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 . And the maximum velocity is calculated to be 106 × 10 −8 M · s −1 for TMB as substrate, being much better than that of other reported metallic nanoclusters and nanoparticles. Further study shows that the high catalytic activity mainly attributes to the synergistic effect of gold and platinum. Besides, they have been applied to determine H 2 O 2 in the presence of TMB, which shows high sensitivity with a limit of detection (LOD) at 100 nM. The proposed method has been used to determine H 2 O 2 in milk and contact lens solutions, which shows very good recovery and exhibits high practical application potential. Therefore, the present study provides a new type of alloy nanoclusters with high peroxidase-like activity, which will inspire more research interests on doping and alloying with Pt to improve the catalytic activity of metal nanoclusters.

Catalytic activity of Co–Ag nanoalloys to dissociate molecular hydrogen. New insights on the chemical environment

Adsorption of molecular hydrogen on the surface of catalytic metal nanoparticles and its dissociation in atomic hydrogen are processes of interest in many chemical technologies. As in other chemical reactions, alloying can improve the efficiency of the catalysts. By focusing on Co6, Co5Ag, Co3Ag3 and CoAg5, we explore the effect of changing the relative concentration of the two components in small ComAgn clusters, a peculiar nanoalloy because Co and Ag do not form bulk solid alloys. Molecular hydrogen adsorbs preferentially on the Co atoms, and the binding is mainly due to the electrical polarization of the charges of adsorbate and host. The preference for Co sites and the trend in the strength of the H2-cluster binding are explained by the combination of two effects characterizing the host environment. One of these is geometric, arising from the degree of exposure of the host atom: the lower the atomic coordination of the host atom, the stronger its bonding with H2. The second effect, newly identified, reveals the importance of the chemical nature of the host atom environment: host Co atoms having both Co and Ag neighbors maintain their capacity to bind hydrogen more intact than those with only Co neighbors. The alloy nanoclusters catalyze the dissociation of adsorbed H2 by building up quite small activation barriers. After dissociation, the H atoms occupy bridge positions between Co atoms (between Co and Ag in CoAg5). H2 adsorption and dissociation may trigger structural transformations of the cluster. The work shows that the adsorption and dissociation properties of H2 can be tuned by varying the relative composition of the two atomic species in the nanoalloy.

Homoleptic Silver-Rich Trimetallic M20 Nanocluster.

Two silver-rich M20 alloy nanoclusters (NCs), [Cu3.5Ag16.5{S2P(OnPr)2}12] (1) and [Cu2.5AuAg16.5{S2P(OnPr)2}12] (2), were synthesized and fully characterized by electrospray ionization mass spectrometry, NMR spectroscopy, and X-ray crystallography. Cluster 2, the first structurally characterized trimetallic M20 NC, was produced by doping one Au atom into a bimetallic M20 NC. Structural analyses showed the preferred positions of Group 11 metals in the yielded M20 NCs. Their antioxidation ability has been investigated, and the time-dependent UV-vis spectrum shows that the presence of CuI atoms in structures 1 and 2 can improve the antioxidant ability.

Directional Doping and Cocrystallizing an Open-Shell Ag39 Superatom via Precursor Engineering.

Metal precursors employed in the bottom-up synthesis of metal nanoclusters (NCs) are of great importance in directing their composition and geometrical structure. In this work, a silver nanocluster co-protected by phosphine and thiolate, namely, [Ag39(PFBT)24(TPP)8]2- (Ag39, PFBT = pentafluorobenzenethiol, TPP = triphenylphosphine), was isolated and structurally characterized. It adopts a three-layered Ag13@Ag18@Ag8S24P8 core-shell structure. The Ag13@Ag18 kernel is unusual in multilayer noble metal NCs. By introducing a copper precursor in the synthesis, a bimetallic nanocluster [Ag37Cu2(PFBT)24(TPP)8]2- (Ag37Cu2) with an identical structure to Ag39 apart from two outer Ag atoms being substituted by Cu atoms was obtained. Astoundingly, the Cu precursor used in the synthesis was found to be critical in determining the final structure. The alteration of the Cu precursor led to the cocrystallization of the above alloy nanocluster with a Ag14 nanocluster, namely, [Ag37Cu2(PFBT)24(TPP)8]2-·[Ag14(PFBT)6(TPP)8] (Ag37Cu2·Ag14). The electronic structure analyzed by theoretical calculation reveals that Ag39 is a 17-electron open-shell superatom. The optical absorption of Ag39, Ag37Cu2, and Ag37Cu2·Ag14 was compared and studied in detail. This work not only enriches the family of alloy metallic nanoclusters but also provides a metal NC-based cocrystal platform for in-depth study of its crystal growth and photophysical property.

In Situ Monitoring of Scale Effects on Phase Selection and Plasmonic Shifts during the Growth of AgCu Alloy Nanostructures for Anticounterfeiting Applications

Tailoring of plasmon resonances is essential for applications in anticounterfeiting. This is readily achieved by tuning the composition of alloyed metal clusters; in the simplest case, binary alloys are used. Yet, one challenge is the correlation of cluster morphology and composition with the changing optoelectronic properties. Hitherto, the early stages of metal alloy nanocluster formation in immiscible binary systems such as silver and copper have been accessible by molecular dynamics (MD) simulations and transmission electron microscopy (TEM). Here, we investigate in real time the formation of supported silver, copper, and silver–copper-alloy nanoclusters during sputter deposition on poly(methyl methacrylate) by combining in situ surface-sensitive X-ray scattering with optical spectroscopy. While following the transient growth morphologies, we quantify the early stages of phase separation at the nanoscale, follow the shifts of surface plasmon resonances, and quantify the growth kinetics of the nanogranular layers at different thresholds. We are able to extract the influence of scaling effects on the nucleation and phase selection. The internal structure of the alloy cluster shows a copper-rich core/silver-rich shell structure because the copper core yields a lower mobility and higher crystallization tendency than the silver fraction. We compare our results to MD simulation and TEM data. This demonstrates a route to tailor accurately the plasmon resonances of nanosized, polymer-supported clusters which is a crucial prerequisite for anticounterfeiting.

Regulation of Surface Structure of [Au9Ag12(SAdm)4(Dppm)6Cl6](SbF6)3 Nanocluster via Alloying.

Tailoring of specific sites on the nanocluster surface can tailor the properties of nanoclusters at the atomic level, for the in-depth understanding of structure and property relationship. In this work, we explore the regulation of surface structure of [Au9Ag12(SAdm)4(Dppm)6Cl6](SbF6)3 nanocluster via alloying. We successfully obtained the well-determined tri-metal [Au9Ag8@Cu4(SAdm)4(Dppm)6Cl6](SbF6)3 by the reaction of [Au9Ag12(SAdm)4(Dppm)6Cl6](SbF6)3 with the CuI(SAdm) complex precursor. X-ray crystallography identifies that the Cu dopants prioritily replace the position of the silver capped by Dppm ligand in the motif. The Cu doping has affected the optical properties of Au9Ag12 alloy nanocluster. DPV spectra, CD spectra and stability tests suggest that the regulation of surface structure via Cu alloying changes the electronic structure, thereby affecting the electrochemical properties, which provides insight into the regulation of surface structure of [Au9Ag12(SAdm)4(Dppm)6Cl6](SbF6)3 via alloying.

Ligand removal energetics control CO2 electroreduction selectivity on atomically precise, ligated alloy nanoclusters

Atomically precise, thiolate-protected gold nanoclusters (TPNCs) exhibit remarkable catalytic performance for the electrochemical reduction of carbon dioxide (CO2R) to CO.

Alkynyl and halogen co-protected (AuAg)44 nanoclusters: a comparative study on their optical absorbance, structure, and hydrogen evolution performance.

We report the synthesis, structure, and electrochemical hydrogen evolution reaction (HER) performance of two alkynyl and halogen coprotected AuAg alloy nanoclusters, namely Au24Ag20(tBuPh-CC)24Cl2 (NC 1 for short) and Au22Ag22(tBuCC)16Br3.28Cl2.72 (NC 2 for short). Single crystal X-ray structural analysis revealed that the two nanoclusters possess a rather similar core@shell@shell keplerate metal core configuration to M12@M20@M12 with the main difference in the outermost shell (Au12vs. Au10Ag2). Interestingly, such a subtle difference in the two-metal-atoms results in different optical absorbance features and drastically different HER performances. Both NCs have excellent long-term stability for the HER, but NC 1 possesses superior activity to NC 2, and density functional theory calculations disclosed that the binding energy of hydrogen to form the key *H intermediate for NC 1 is much lower and hence it adopts a more energetically feasible HER pathway.

Ultrasmall Bimetallic Ru-Co Alloy Nanoclusters Immobilized in Amino-Functionalized Uio-66 and N-Doped Carbonaceous Zirconium Oxide Nanocomposite for Hydrogen Generation

Ultrasmall Bimetallic Ru-Co Alloy Nanoclusters Immobilized in Amino-Functionalized Uio-66 and N-Doped Carbonaceous Zirconium Oxide Nanocomposite for Hydrogen Generation

Atomically Precise Ni-Pd Alloy Carbonyl Nanoclusters: Synthesis, Total Structure, Electrochemistry, Spectroelectrochemistry, and Electrochemical Impedance Spectroscopy.

The molecular nanocluster [Ni36–xPd5+x(CO)46]6– (x = 0.41) (16–) was obtained from the reaction of [NMe3(CH2Ph)]2[Ni6(CO)12] with 0.8 molar equivalent of [Pd(CH3CN)4][BF4]2 in tetrahydrofuran (thf). In contrast, [Ni37–xPd7+x(CO)48]6– (x = 0.69) (26–) and [HNi37–xPd7+x(CO)48]5– (x = 0.53) (35–) were obtained from the reactions of [NBu4]2[Ni6(CO)12] with 0.9–1.0 molar equivalent of [Pd(CH3CN)4][BF4]2 in thf. After workup, 35– was extracted in acetone, whereas 26– was soluble in CH3CN. The total structures of 16–, 26–, and 35– were determined with atomic precision by single-crystal X-ray diffraction. Their metal cores adopted cubic close packed structures and displayed both substitutional and compositional disorder, in light of the fact that some positions could be occupied by either Ni or Pd. The redox behavior of these new Ni–Pd molecular alloy nanoclusters was investigated by cyclic voltammetry and in situ infrared spectroelectrochemistry. All three compounds 16–, 26–, and 35– displayed several reversible redox processes and behaved as electron sinks and molecular nanocapacitors. Moreover, to gain insight into the factors that affect the current–potential profiles, cyclic voltammograms were recorded at both Pt and glassy carbon working electrodes and electrochemical impedance spectroscopy experiments performed for the first time on molecular carbonyl nanoclusters.

Inside Cover Picture

This cover picture depicts one of the most promising applications of artificial intelligence (AI) in catalytic chemistry. Herein, neural network potential was trained to fit the complicated configurational space of Au‐Pt alloy nanoclusters, which successfully predicts that it is thermodynamically favorable when all gold atoms are segregated to the outer surface and the shape of the cluster tends to evolve to a distorted reduced core (DRC) structure with a unique gold distribution. Further oxygen adsorption energy calculations show that, in comparison with the Au13@Pt42 icosahedron cluster, the above‐mentioned structural evolution could not only increase the number of adsorption sites but also dramatically improve the ORR catalytic activity of each site, thus enhancing the overall ORR reactivity. More details are given in the article by Wang et al. on page 3029–3036.image

A Ratiometric Fluorescent Probe Based on Carbon Dots and Bimetallic Nanoclusters for the Assay of Copper Gluconate and Copper Sulfate

Doping Ag-enhanced and glutathione-stabilized Au nanoclusters (GSH–Ag/AuNCs) were prepared by the one-step ultraviolet radiation combined with microwave heating method. The effects of the molar ratio of Au–Ag and different types of energy suppliers on the fluorescent performance of GSH–Ag/AuNCs were studied in detail. After that, a new ratio fluorescent probe (RF-probe) based on the mixing of GSH–Ag/AuNCs with carbon dots (CDs) was designed for sensitive and selective determination of copper gluconate (CG) and cupric sulfate (CS). For the CDs–GSH–Ag/AuNCs RF-probe, the fluorescence (FL) of CDs (at 440[Formula: see text]nm) and that of alloy nanoclusters (NCs) (at 605[Formula: see text]nm) were, respectively, unaffected and strongly quenched in the presence of CG/CS at [Formula: see text][Formula: see text]nm coming from the dynamic quenching process. Corresponding linear ranges and limit of detection (LOD) of the RF-probe for the CG/CS assay were estimated to be 0.17–6.20/0.17–5.62[Formula: see text][Formula: see text]mol/L and 16.80/15.95[Formula: see text]nmol/L, respectively. Furthermore, the proposed RF-probe was successfully used for the assays of CG in CG tablets and CG additive, and CS in infant formula and CS additive, respectively.

The doping engineering and crystal structure of rod-like Au8Ag17 nanoclusters.

Alloy nanoclusters protected by ligands were widely studied due to the synergistic effect of metal atoms, and they exhibit enhanced properties in different fields, such as bio-imaging and catalysis. Herein, we obtained Au8Ag17(PPh3)10Cl10 nanoclusters via one-step simple synthesis. The atomically precise crystal structure was determined by x-ray crystallography. It is found that the rod-like Au8Ag17 nanoclusters were composed of two Au4Ag9 icosahedrons via sharing the same Ag atom. Two Au atoms occupy the center of icosahedrons, and the other six Au atoms are all at the neck sites. Four kinds of Cl-Ag connecting modes were observed in Au8Ag17 nanoclusters. Moreover, the ultraviolet-visible absorption spectrum shows that the prominent absorption peaks of Au8Ag17 nanoclusters are at ∼395 and 483nm. This work provides a feasible strategy to synthesize alloy nanoclusters with precise composition via doping engineering.

Fe-Ni Alloy Nanoclusters Anchored on Carbon Aerogels as High-Efficiency Oxygen Electrocatalysts in Rechargeable Zn-Air Batteries.

In this work, Fe-Ni alloy nanoclusters (Fe-Ni ANCs) anchored on N, S co-doped carbon aerogel (Fe-Ni ANC@NSCA catalysts) are successfully prepared by the optimal pyrolysis of polyaniline (PANI) aerogels derived from the freeze-drying of PANI hydrogel obtained by the polymerization of aniline monomers in the co-presence of tannic acid (TA), Fe3+ , and Ni2+ ions. In addition, the optimal molar ratio of the TA, Fe3+ , and Ni2+ ions for synthesis of Fe-Ni ANC@NSCA catalysts are 1:2:5, which can guarantee the formation of carbon aerogel composed of quasi-2D porous carbon sheets and the formation of high-density Fe-Ni ANCs with an ultrasmall size between 2 to 2.8nm. These Fe-Ni ANCs consisting of N4 -Fe-O-Ni-N4 moiety are proposed as a new type of active species for the first time, to the best of the authors' knowledge. Thanks to their unique features, the Fe-Ni ANC@NSCA catalysts show excellent performance in oxygen reduction reaction with a half-wave potential (E1/2 ) of 0.891 V and oxygen evolution reaction (260mV @ 10mA cm-2 ) in alkaline media as bifunctional catalysts, which are better than the state-of-the-art commercial Pt/C catalysts and RuO2 catalysts. Moreover, Zn-air battery assembled with the Fe-Ni ANC@NSCA catalysts also shows a remarkable performance and exceptionally high stability over 500 h at 5mA cm-2 .