Ni Nanoclusters Research Articles

Growth of Ni nanoclusters on irradiated graphene: a molecular dynamics study.

We studied the soft landing of Ni atoms on a previously damaged graphene sheet by means of molecular dynamics simulations. We found a monotonic decrease of the cluster frequency as a function of its size, but few big clusters comprise an appreciable fraction of the total number of Ni atoms. The aggregation of Ni atoms is also modeled by means of a simple phenomenological model. The results are in clear contrast with the case of hard or energetic landing of metal atoms, where there is a tendency to form mono-disperse metal clusters. This behavior is attributed to the high diffusion of unattached Ni atoms, together with vacancies acting as capture centers. The findings of this work show that a simple study of the energetics of the system is not enough in the soft landing regime, where it is unavoidable to also consider the growth process of metal clusters.

Hydrodeoxygenation of Methyl Laurate over Ni Catalysts Supported on Hierarchical HZSM-5 Zeolite

The hierarchical HZSM-5 zeolite was prepared successfully by a simple NaOH treatment method. The concentration of NaOH solution was carefully tuned to optimal the zeolite acidity and pore structure. Under NaOH treatment conditions, a large number of mesopores, which interconnected with the retained micropores, were created to facilitate mass transfer performance. There are very good correlations between the decline of the relative zeolite crystallinity and the loss of micropores volume. The Ni nanoclusters were uniformly confined in the mesopores of hierarchical HZSM-5 by the excessive impregnation method. The direct deoxygenation in N2 and hydrodeoxygenation in H2 of the methyl laurate were compared respectively over the Ni/HZSM-5 catalysts. In the N2 atmosphere, the deoxygenation rate of the methyl laurate on the Ni/HZSM-5 catalyst is relatively slow. In the presence of H2, the synergistic effect between the hydrogenation function of the metal and the acid function of the zeolite supports can make the deoxygenation level more obvious. The yield of hydrocarbon products gradually reached the maximum with the appropriate treatment concentration of 1M NaOH, which could be attributed to the improved mass transfer in the hierarchical HZSM-5 supports.

Electronic properties of nanostructured metal films: the evolution of Anderson singularity index with size

The results of X-ray photoelectron spectroscopy studies of thin monodispersed Mo and Ni metal nanocluster films deposited with magnetron sputtering method onto silicon dioxide surfaces are presented. The dependence of X-ray photoelectron spectra asymmetry of the core lines of the films on typical sizes of nanoclusters in films are studied. It is found experimentally that the Anderson singularity index α changes differently for different materials with decreasing of nanocluster’s size. It is shown that Seebeck coefficient of Ni nanocluster films consisted of 1.5 nm sized nanoclusters can reach 100 μV/K.

Gold-Doping of Double-Crown Pd Nanoclusters.

Double-crown Ni, Pd, or Pt nanoclusters have attracted extensive interests due to their aesthetic structure and intriguing properties. However, their doping by other metals remains unknown until now. Herein, Pd4 (PET)8 and Pd5 (PET)10 (PET: SCH2 CH2 Ph) were successfully doped with gold and the doped nanoclusters were characterized by using multiple techniques such as mass spectrometry and X-ray crystallography. It is revealed that in the doping not one but two gold atoms replace one Pd with the other double-crown structure essentially unchanged, and the gold-doping results in the blue-shift of the maximum visible absorption, the increase of optical energy gap and the reduction of anti-aromaticity of monometal Pd nanoclusters. Importantly, it is found that Au4 Pd2 (PET)8 nanocluster bears chirality originating from not only the helixed Au4 Pd2 S8 framework, but also unanimous R or S configuration of sulfur atoms in the enantiomer. For the latter chirality origin, it was not previously reported or proposed. Au4 Pd2 (PET)8 reported here also represents the smallest chiral bimetal nanocluster so far to the best of our knowledge. This work advances one step toward both the tailoring of group 10 metal nanoclusters by doping and the understanding of chirality origin for metal nanoclusters.

Ni‐Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction

One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO2 molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni-nanocluster loaded black TiO2 (Ni/TiO2[Vo] ) with built-in dual active sites for selective photocatalytic CO2 conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO2 binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.

H2 adsorption on free and graphene-supported Ni nanoclusters: A theoretical study

Density functional theory (DFT) was used to investigate the applicability of the graphene-supported Nin nanoclusters as catalysts for the hydrogenation reaction. The adsorption and complete dissociation of the H2 on the Nin nanoclusters were investigated at the PBE-G/DNP level of theory. Accordingly, molecularly and dissociatively adsorbed hydrogens were seen on the Nin (n = 2–3) and Nin (n = 4–10) nanoclusters, respectively. The hydrogen adsorption on the Ni6 and Ni4 nanoclusters were more effective than other nanoclusters. Therefore, we investigated the hydrogen adsorption on the graphene-supported Ni2, Ni4 and Ni6 nanoclusters. The nanocluster adsorption energy on the graphene increased with the number of atoms in the nanocluster, whereas the adsorption energy per atom decreased. Hence, due to the stronger interactions of Ni-Ni than those of Ni-C, it seemed that the formation of nanoclusters on the graphene surface was favorable over the dispersion of the separate atoms. The results confirmed that the H2 was dissociatively adsorbed on the graphene-supported Ni4 and Ni6 nanoclusters, which can make them good candidates as catalysts.

Nickel Nanocluster Loaded Black Titania for Photocatalytic Reduction of CO2 into Solar Fuels: Computational and Experimental Studies

The conversion of atmospheric carbon dioxide (CO2) into solar fuels by imitation of a natural photosynthesis using only water vapor and sunlight for energy has attracted widespread attention recently. One of the key challenges is to design a photocatalyst that can bind and activate the CO2 molecule with smallest possible activation energy and produce selective solar fuel production. In this contribution, we report a combined experimental and computational studies on Ni nanocluster loaded black TiO2 (Ni@TiO2[Vo]) with built-in dual active sites for selective photocatalytic CO2 conversion. Our findings reveal that, the synergistic effect of deliberately induced unsaturated Ni nanocluster and oxygen vacancies provide (1) energetically stable CO2 binding sites with lowest activation energy (0.08eV), (2) highly reactive sites, (3) fast electron transfer pathway, (4) enhanced light harvesting by lowering the band gap. The Ni@TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight to the mechanism of interfacial charge transfer and product formation mechanism are explored. The proposed approach to adsorb and activate CO2 molecule on dual active sites can be applied to design other catalysts for photocatalytic CO2 reduction.

Well-dispersed Ni nanoclusters on the surfaces of MFI nanosheets as highly efficient and selective catalyst for the hydrogenation of naphthalene to tetralin

One of the challenges in material science has been to design and prepare highly efficient and selective catalysts for target reactions. Here we demonstrate a one-pot hydrothermal synthesis of hierarchical MFI nanosheets with nickel species chemically bonded on the outer surfaces. It turns out that the growth and morphologies of self-pillared MFI nanosheets are affected by Ni content, and the thickness of MFI nanosheets are determined to be 2.3nm or 3.0nm. Specially, the bonded Ni on the outer surfaces can effectively prevent adjacent nanosheets from forming new SiOSi bonds, and in conjunction with the self-pillared structure, can hamper complete collapse of Ni-MFI-NSs during calcination. In naphthalene hydrogenation, the separated Ni species are previously reduced to highly-dispersed metallic Ni nanoclusters with size below 1.6nm, which are highly active for hydrogenation. And the hierarchical porosity of Ni-MFI-NSs significantly enhances the diffusion of substrates and the accessibility of active sites. As a result, Ni-MFI-NSs achieve 100% selectivity for tetralin and 84.9% conversion of naphthalene with Ni content of only 4.2wt%. Furthermore, the gradually enlarged Ni nanoparticles cause the decline of catalytic activities of catalysts.

Kinetics formation of bimetallic nanoalloys at different simulation times

MD simulations were used for investigation on the kinetic formation of Ni-Pd nanoalloys at different simulation times. We have examined excess energies and bond order parameters for initial gas phase compositions including pure Ni, and Pd, and also Ni0.2Pd0.8, Ni0.4Pd0.6, Ni0.6Pd0.4, Ni0.8Pd0.2 concentrations. Excess energies for created Ni-Pd nanoalloys exhibit more instabilities for larger nanoparticles. Also, bond order results demonstrate amorphous structures for all of created nanoclusters. Moreover, number of formed clusters for pure Ni at 5ns is more than pure Pd nanoclusters and number of formed clusters decreases when Pd is doped in pure Ni nanocluster.

Stable reduced Ni catalysts for xylose hydrogenation in aqueous medium

Precursor materials with 20wt.% nickel content and formula mater Nd1-xCexAl0.162Ni0.838O3 (x=0.0, 0.1, 0.5, 0.7) were successfully used to prepare reduced Ni nanoclusters to be used as catalysts in the catalytic hydrogenation of xylose to xylitol. Reduction at 500°C led to large reduced nickel content with almost no changes in the structure of the started mixed oxide precursors. The catalytic performance of the Ni-reduced catalysts did not show a clear relation with Ce content while a close dependence of the hydrogenated products with Ni° crystal size and the isomerization product with acidity was obtained. The well-known Ni leaching in aqueous medium was absent in the prepared Ni-reduced catalysts corroborating the promising use of crystalline mixed oxides as precursors to prepare stabilized Ni-reduced catalysts for aqueous-phase processing of biomass-derived compounds.

Nanoscale mechanisms of CNT growth and etching in plasma environment

Plasma-enhanced chemical deposition (PECVD) of carbon nanotubes has already been shown to allow chirality control to some extent. In PECVD, however, etching may occur simultaneously with the growth, and the occurrence of intermediate processes further significantly complicates the growth process.We here employ a computational approach with experimental support to study the plasma-based formation of Ni nanoclusters, Ni-catalyzed CNT growth and subsequent etching processes, in order to understand the underpinning nanoscale mechanisms. We find that hydrogen is the dominant factor in both the re-structuring of a Ni film and the subsequent appearance of Ni nanoclusters, as well as in the CNT nucleation and etching processes. The obtained results are compared with available theoretical and experimental studies and provide a deeper understanding of the occurring nanoscale mechanisms in plasma-assisted CNT nucleation and growth.

Analysis of the applicability of Ni, Cu, Au, Pt, and Pd nanoclusters for data recording

The applicability of individual Ni, Cu, Au, Pt, and Pd nanoclusters as data bits in next generation memory devices constructed on the phase-change carrier principle is studied. To this end, based on the modified tight-binding potential (TB-SMA), structure formation from the melt of nanoparticles of these metals to 10 nm in diameter was simulated by the molecular dynamics method. The effect of various crystallization conditions on the formation of the internal structures of Ni, Cu, Au, Pt, and Pd nanoclusters is studied. The stability boundaries of various crystalline isomers are analyzed. The obtained systematic features are compared for nanoparticles of copper, nickel, gold, platinum, and palladium of identical sizes. It is concluded that platinum nanoclusters of diameter D > 8 nm are the best materials among studied metals for producing memory elements based on phase transitions.

Size-controlled reverse microemulsion synthesis of Ni and Co metal nanoparticles

Microemulsion synthesis of Ni and Co metal nanoparticles with controllable size has been studied in detail to allow replacing expensive metals (Pt and Re) in promising aqueous phase reforming of bio-derivatives. Reduction of nickel or cobalt chloride and nitrate aqueous solutions with N2H4 alkaline solution in the presence of cationic cetyltrimethyl bromide or anionic sodium dodecylsulphosuccinate surfactants provided formation of series of Ni and Co nanoparticles with mean sizes from 2.6 to 3.3 nm and from 1.0 to 5.4 nm, respectively. TEM, XRD, UV-Vis spectroscopy and XPS were applied to determine Ni and Co nanocluster sizes, composition and electronic state.

Cr doping and heat treatment effect on core–shell Ni nanocluster film

Core–shell nickel (CS-Ni) and 5 at.% chromium-doped nickel (CS-Ni5Cr) nanocluster (NC) films, prepared by a nanocluster deposition system, were studied for heat treatment (HT)-induced structural, physical, and magnetic property alterations. Understanding the HT influence and oxidation mechanism at nanoscale can make these nanomaterials potential candidates for applications that involve stainless steel alloys. The contribution of Cr doping in altering the microstructural and relative oxidation kinetics was investigated in detail before and after the HT. The oxidation mechanism describes that the cation diffusivity increases following the doping of 5 at.% of Cr in Ni, which makes the oxidation rate of Ni5Cr HT higher than that of Ni-HT. At a temperature of 600 °C, a dramatic change was observed in surface morphology with many island-like nanostructures on the surface of Ni5Cr. The interface structure of the Cr-rich oxide layer plays a key role in the islands formation via agglomeration of NCs. The as-prepared and HT samples were analyzed by transmission electron microscopy, atomic force microscopy, magnetic force microscopy, energy-dispersive spectroscopy, and vibrating sample magnetometer to provide an insight on the effectiveness of chromium-doped nickel film.

Electrodeposited ultraviolet-durable biomimetic super-hydrophobic surface

An ultraviolet (UV)-durable super-hydrophobic ZnO/Ni lotus-like nanostructure was fabricated via a simple two-step electrodeposition method at low temperature. The as-prepared ZnO/Ni nanostructure showed excellent UV-durable super-hydrophobicity and water ultra repellency. The Ni nanoclusters with different density could be successfully fabricated on the surface of ZnO NR by modulating the electrodeposition time of Ni nanoclusters, which affected surface roughness and wettability. The triple-level roughness resulted from high density Ni nanoclusters played a important role in the super-hydrophobicity of ZnO/Ni nanostructure. This super-hydrophobic surface showed high stability in water for long term. Furthermore, the layer of Ni nanoclusters avoided the photoinduced wettability conversion of ZnO and hence greatly improved the UV-durability of this super-hydrophobic surface, which were essential elements for practical applications. This simple method could be applied to various substrates, such as metal surfaces and other electric conductive substrates.

On the effect of heating and cooling rates on the melting and crystallization of metal nanoclusters

The effect of heating and cooling rates on melting (Tm) and crystallization (Tc) temperatures of metal nanoclusters is investigated in terms of the isothermal molecular dynamics. We report on the results obtained for nickel nanoclusters, although analogous results were also obtained for gold and aluminum nanoclusters. It is found that Tm increases, while Tc decreases with increasing heating and cooling rates, both Tm and Tc tending to the same value for heating and cooling rates tending to zero. The results indicate that the hysteresis of melting and crystallization of nanoparticles must be completely due to nonequilibrium conditions of heating and cooling. The transition of Ni nanoclusters to the amorphous state begins at very high cooling rates exceeding 10 TK/s.

Employment of SnO2:F@Ni3Sn2/Ni nanoclusters composites as an anode material for lithium-ion batteries

Surface modification of SnO2:F particles which obtained from a large-scale electron cyclotron resonance-metal organic chemical vapor deposition system was carried out by two consecutive processes: electroless plating processing and annealing. First, Ni film on the SnO2:F and Ni nanoclusters were observed after Ni electroless plating; the film on the SnO2:F was then converted to Ni3Sn2 after annealing at 800 °C under an argon atmosphere. A Ni3Sn2 bimetallic structure formed instead of NiO during the annealing process because of the presence of carbon impurities in SnO2:F. The surface-modified Ni3Sn2-covered SnO2:F with Ni nanoclusters (SnO2:F@Ni3Sn2/Ni-nc) was employed as an anode material for lithium-ion batteries. The inactive Ni in Ni3Sn2 acts as a buffer matrix against the Sn active material during the charge-discharge reactions, enhancing the electrochemical performance. The Ni nanoclusters in SnO2:F@Ni3Sn2/Ni-nc perform dual functions: they not only improve the conductivity as the contacting media, but also increase the initial columbic efficiency by the decomposition of Li2O—an electrochemically irreversible material. An outstanding reversible capacity of 600.69 mA h g−1 and a coulombic efficiency of 99.23% for SnO2:F@Ni3Sn2/Ni-nc were observed at the 350th cycle under 200 mA g−1 in the our experimental range.

Enhanced light extraction in tunnel junction-enabled top emitting UV LEDs

The efficiency of ultraviolet (UV) light-emitting diodes (LEDs) is critically limited by absorption losses in p-type and metal layers. In this work, surface-roughening-based light extraction structures were combined with tunneling-based top-layer contacts to achieve highly efficient top-side light extraction in UV LEDs. By using self-assembled Ni nanoclusters as an etch mask, the top surface-roughened LEDs were found to enhance the external quantum efficiency by over 40% for UV LEDs with a peak emission wavelength of 326 nm. The method described here can be used for fabricating highly efficient UV LEDs without the need for complex manufacturing techniques such as flip chip bonding.

Formation of structure in Au, Cu and Ni nanoclusters: MD simulations

The molecular dynamics method with the modified tight-binding (TB-SMA) potential has been used to study structure formation in gold nanoparticles 1.6-5.0 nm in diameter. The formation of the internal structure of gold nanoclusters is studied in terms of canonical ensembles. The stability boundaries of various crystalline isomers are analyzed. The obtained dependences are compared with the corresponding data obtained for copper and nickel nanoparticles. The structure formation during solidification is found to be characterized by a clear effect of the particle size on the stability of a crystalline modification.

Perovskite as nickel catalyst precursor – impact on catalyst stability on xylose aqueous-phase hydrogenation

Precursors materials with formula, La1−xCexAl0.18Ni0.82O3(x= 0.0, 0.1, 0.5, 0.7), were successfully used as precursors to prepare Ni nanoclusters to be used as catalysts in the hydrogenation of xylose to xylitol.