Fcc Nanoparticles Research Articles

Green synthesis of palladium nanoparticles using Asterarcys sp. and their applications

Asterarcys-mediated algal extract, which is non-toxic and renewable, was used to synthesize palladium nanoparticles (PdNPs) efficiently and ecologically friendly. The palladium nanoparticle's fabrication was seen within two hours. UV spectroscopy, FTIR, XRD, SEM, EDX and TEM with SAED pattern were used to confirm the properties of the synthesized nanoparticles. Palladium nanoparticles have been developed, indicated by their deep brown color and broad UV-visible absorption spectra. The SAED and XRD patterns of the manufactured nanoparticles provided evidence of their face-centred cubic crystal structure. Because of reflections from the (1 1 1), (2 0 0), (2 2 0), (3 1 1), and (2 2 2) planes, the XRD pattern is broad, indicating that the FCC nanoparticles are crystalline in nature. The biomolecule responsible for Pd2+ reduction and PdNPs capping has been found by analyzing the FTIR spectra of dried PdNPs and dry algal powder. The average particle size, according to a TEM image, is 13 nm, whereas it ranges from 4 to 24 nm. In moderate reaction conditions, the catalytic activity of PdNPs was investigated in C-C cross-coupling processes including Mizoroki-Heck and Suzuki-Miyaura reactions. 1H NMR and 13C NMR were used to characterize the isolated product. The PdNPs exhibited strong catalytic activity and produced excellent conversion of the corresponding products.

Tuning the Selectivity of Catalytic Nitrile Hydrogenation with Phase-Controlled Co Nanoparticles Prepared by Hydrosilane-Assisted Method.

Cobalt (Co) is a promising candidate to replace noble metals in the hydrogenation process, which is widely employed in the chemical industry. Although the catalytic performance for this reaction has been considered to be significantly dependent on the Co crystal phase, no satisfactory systematic studies have been conducted, because it is difficult to synthesize metal nanoparticles that have different crystalline structures with similar sizes. Here we report a new method for the synthesis of cobalt nanoparticles using hydrosilane as a reducing agent (hydrosilane-assisted method). This new method uses 1,3-butanediol and propylene glycol to successfully prepare fcc and hcp cobalt nanoparticles, respectively. These two types of Co nanoparticles have similar sizes and surface areas. The hcp Co nanoparticles exhibit higher catalytic performance than fcc nanoparticles for the hydrogenation of benzonitrile under mild conditions. The present hcp Co catalyst is also effective for highly selective benzyl amine production from benzonitrile without ammonia addition, whereas many catalytic systems require ammonia addition for selective benzyl amine production. Mechanistic studies revealed that the fast formation of the primary amine and the prevention of condensation and secondary amine hydrogenation promote selective benzonitrile hydrogenation for benzylamine over hcp Co nanoparticles.

Thermal stabilizing and toughening of a dual-phase Nb alloy by tuning stabilizing element C in Nb-BCC

Niobium alloys have found extensive application in industries, such as aerospace, nuclear reactor, and emerging electronic technologies, owing to their high melting point, low density, and remarkable formability. Nevertheless, they still fall short in terms of comprehensive strength, toughness, and thermal stability when subjected to complex impacts and/or torsional forces during service. Here, a dual-phase (BCC/FCC) Nb alloy with attractive mechanical properties and thermal stability was designed by tuning stable element C in the Nb-BCC matrix assisted by hot deformation and aging processes. Our findings reveal that the formation of discontinuous carbides at the grain boundary promotes the phase transformation of the matrix from BCC to FCC (K-S orientation relationship), resulting in the formation of FCC thin layers and nano particles. This unique configuration hinders the slipping of dislocations during deformation and impedes the degeneration of microstructures during the thermal cycling process from 200 °C to 900 °C. Moreover, the discontinuous carbides at GBs provide channels to transfer dislocations between various phases and/or grains, which results in attractive mechanical properties and thermal stability. The ultimate tensile strength, yield strength, elongation, and elasticity modulus of the designed Nb alloy reach impressive values of 790.5 MPa, 436.5 MPa, 39.1 %, and 63.5 MPa, respectively. These observations provide guidelines for designing dual-phase Nb alloys with remarkable strength, toughness, and thermal stability for aerospace applications by tuning the stabilizing element C in the Nb-BCC matrix.

Size and shape effects on chemical ordering in Ni-Pt nanoalloys.

The atomic structure and chemical ordering of Ni-Pt nanoalloys of different sizes and shapes are studied by numerical simulations using Monte Carlo methods and a realistic interatomic potential. The bulk Ni-Pt ordering tendency remains in fcc nanoparticles but we show some chemical ordering frustrations linked to surface reconstructions depending on the cluster size and shape. A reversed temperature dependence of Pt surface segregation is also established. In the particular case of fivefold symmetry as in icosahedra, ordering is observed in the core and on the facets at low temperatures with segregation of the smaller element (Ni) in the core because of atomic strain. We show that the icosahedral shape favors Pt surface segregation in comparison with octahedral and truncated octahedral structures.

Do dislocations always decrease thermal conductivity?

Dislocations play a significant role in introducing disorder and distortion within an ideal bulk crystal lattice, resulting in the degradation of phonon thermal conductivity. In this study, we employ non-equilibrium Molecular Dynamics (NEMD) simulations to investigate the thermal conductivity of two spherical, single-crystal face-centered cubic (fcc) nanoparticles (NP) with a radius denoted as R. Our analysis encompasses pristine interfaces as well as interfaces containing dislocations, at the NP contact. Surprisingly, our findings reveal that the presence of dislocations leads to an increase in thermal conductivity, contrary to the expectations derived from bulk models and simulations. This counterintuitive behavior can be attributed to the expansion of the contact radius (ac) between the nanoparticles, facilitated by the dislocations. Notably, the thermal conductivity demonstrates a substantial reduction of approximately 90% compared to bulk values, and in all simulated cases, it scales effectively as a function of (ac/R). We explore various models to elucidate the impact of dislocations on thermal conductivity and ascertain that, under our specific conditions, only a marginal decrease would be anticipated. In alignment with these models, our results indicate that the introduction of localized dislocation arrays spanning nearly ten lattice parameters into a bulk sample elicits a thermal conductivity decrease of less than 10%. These findings provide compelling evidence that dislocations per se do not significantly affect thermal conductivity. Instead, the enhanced contact area generated by dislocations governs the heat flux within the simulated nanostructures. Notably, the analysis of thermal boundary conductance, which evaluates the conductivity across the interfaces, does exhibit a decrease in interfaces featuring dislocations. Considering that the dislocation content can be influenced by various synthesis conditions of the nanoparticles, these findings hold promising implications for tailoring the thermal conductivity of nanoparticle beds or coatings.

DeepStruc: towards structure solution from pair distribution function data using deep generative models.

Structure solution of nanostructured materials that have limited long-range order remains a bottleneck in materials development. We present a deep learning algorithm, DeepStruc, that can solve a simple monometallic nanoparticle structure directly from a Pair Distribution Function (PDF) obtained from total scattering data by using a conditional variational autoencoder. We first apply DeepStruc to PDFs from seven different structure types of monometallic nanoparticles, and show that structures can be solved from both simulated and experimental PDFs, including PDFs from nanoparticles that are not present in the training distribution. We also apply DeepStruc to a system of hcp, fcc and stacking faulted nanoparticles, where DeepStruc recognizes stacking faulted nanoparticles as an interpolation between hcp and fcc nanoparticles and is able to solve stacking faulted structures from PDFs. Our findings suggests that DeepStruc is a step towards a general approach for structure solution of nanomaterials.

DFT, molecular docking, photocatalytic and antimicrobial activity of coumarin enriched Cinnamon bark extract mediated silver nanoparticles

• Silver nanocatalysts synthesized by simple precipitation process. • Structural phase formation shows Face centred cubic structure. • The photocatalytic degradation of cationic dye and antimicrobial activity were examined. • Silver nanocatalyst shows maximum degradation efficiency of 96% for MB. Water pollution is a severe and urgent issue on a global scale. Nanoparticles are capable of purifying contaminated water. Using plant extracts for green nanoparticle manufacturing minimises hazardous chemicals or energy requirements. This paper focuses on the eco-friendly synthesis of plasmonic Ag nanoparticles from cinnamon-derived natural materials and its potential in biomedicine, water treatment, and catalysis. An SPR peak confirmed the reduction of Ag + ions to Ag o nanoparticles at 449 nm in UV–Vis spectroscopy. The XRD and TEM analyses indicate FCC and polydisperse nanoparticles with a spherical shape. Under visible light illumination, the photocatalytic activity of plasmonic AgNPs was evaluated against Methylene Blue (MB) dye. After 120 minutes, plasmonic Ag NPs displayed high antibacterial activity and 97% photo degradation efficiency. Metallic Ag NPs exhibited more catalytic activity than commercial TiO 2 NPs. According to DFT experiments, coumarin in cinnamon bark reduces Ag + ions to Ag o . To the best of our knowledge, the current paper is the first to use cinnamon-mediated plasmonic Ag photocatalysis for efficient antibacterial action and degradation of MB dye.

Topology of active site geometries in HCP and FCC nanoparticles and surfaces

• A common convention is found to label local catalytic site arrangements in metals. • We have used molecular models to generate 18 active site arrangements in metals. • In this analytical geometry approach we find that there are five b5-sites. In this study the various local site topologies on metal NP and metal surfaces of HCP and FCC metals have been identified. The analysis with physical ball-and-stick molecular models demonstrates that the local site geometry can be fully described by triangular or square atom motifs that are either bridge or atop bound with additional labels that indicate whether the local site is on top of a tetrahedral or octahedral hole. Additionally, an angle between the structural motif surfaces is needed that shows the relative orientation between them. With this theoretical approach we find that there are 5 different b5-sites [1] , [2] , [3] .

The delicate balance of phase speciation in bimetallic nickel cobalt nanoparticles.

Bimetallic nickel-cobalt nanoparticles are highly sought for their potential as catalytic and magnetic nanoparticles. These are typically prepared in organic solvents in the presence of strong stabilizing ligands such as tri-n-octylphosphine (TOP). Due to the variety of cobalt crystallographic phases and to the strong interaction of the ligands with the metallic surfaces, forming fcc nanoparticles rather than a phase mixture is a challenging endeavor. Here, using a two-step synthesis strategy that aims at a core-shell nickel-cobalt morphology, we demonstrated that many parameters have to be adjusted: concentration of the metal precursors, stoichiometry of TOP, and heating program from room temperature to 180 °C. We found optimized conditions to form size-controlled fcc NiCo nanoparticles from preformed Ni nanoparticles, and the phase attribution was confirmed with a combination of X-Ray diffraction on powder and X-Ray absorption spectroscopy at the Co K edge. We then investigated the early stages of Co nucleation on the nickel using a lower stoichiometry of Co, down to 0.05 equiv. vs. Ni. Using X-ray photoelectron spectroscopy and scanning transmission electron microscopy coupled to energy-dispersive X-Ray spectroscopy and electron energy loss spectroscopy, we showed that cobalt reacts first on the nickel nanoparticles but easily forms cobalt-rich larger aggregates in the further steps of the reaction.

Incompressibility of face-centered cubic structure in Metallic Nanosolids

A simple and general theoretical model has been constructed to study the bulk modulus ‘B’ of FCC nanoparticles and nanostructures. In order to justify the experimental results of the anomalous behavior of B in nanosolids, this method considers the competing effect of both size and shape of a nanoparticle on B. In this work, the relationship between B and the surface energy has been derived based on the dangling bond energy model. The results show that B depends on size, shape and structure of FCC nanocrystalline solids (nanosolids). Our results show that as the shape changes from spherical to deformed, nanosolids become incompressible and B increases as the size decreases. The obtained theoretical results were compared with the experimental predictions for silver, gold and nickel. A very good agreement between theoretical results and experiments was found for silver and nickel. While in gold, we noticed a deviation from the experiment, which is attributed to extreme deformation of the nanogold.

Size and Structure Dependence of the Anomalous Bulk Modulus for FCC Metallic Nanoparticles

The purpose of this work is to develop a theoretical model to calculate the bulk moduli of FCC nanoparticles that account for their size and structure. The bulk modulus for spherical nanoparticles has been derived from the cohesive energy which had been calculated by summing up the potential energy function of every pair of atoms of these metallic nanoparticles. The ab initio pair potential energy function has been formed by inverting the cohesive energy function proposed by (Rose et al., 1981), using the Chen-Mobius method. The results show that, as the size decreases, the bulk modulus decreases for spherical nanoparticles, which agrees with previous experimental and theoretical predictions. The results also predicted an “amorphous” structure for ultra-small nanoparticles and were consistent with previous experimental work.

Surface atomic packing fraction as a figure of merit for the structural transition and the bulk-to-nano transformation of spherical FCC and BCC nanosolids

Abstract We report on the development of a simple and efficient method to predict the structural transition and the bulk-to-nano transformation of spherical FCC and BCC solid nanoparticles using the surface atomic packing fraction ( g s ). For both structures, g s ’s are maxima at radii equal to the nearest neighbor distances. These g s values are smaller than the maximum values of their bulk counterparts. Compared to the bulk phase, the volume packing fraction (f) of a FCC nanoparticle decreases with size and approaches 0.810 at shells greater than 208. Our predictions show that bulk-to-nano transition starts at N ~ 10 4 , in a good agreement with the relevant literature. The disturbing the spherical shape of small FCC nanoparticles is found to be easier than breaking them across {100} and {111} crystal planes. However, for BCC, small NPs are more difficult to break through {100} and {111} planes. The current results highlight possible mechanisms for controlling the physical properties of matter at the nanoscale through their morphological characteristics. This study demonstrates that the interplay between packing, structural transition and shape can be utilized to develop new nanomaterials with controlled properties.

Gas-assisted transformation of gold from fcc to the metastable 4H phase

The metastable hexagonal 4H-phase gold has recently attracted extensive interest due to its exceptional performance in catalysis. However, gold usually crystallizes to its lowest free energy structure called face-centered cubic (fcc). The phase transformation from the stable fcc phase to the metastable 4H phase is thus of great significance in crystal phase engineering. Herein, we report this unusual phenomenon on a 4H gold nanorod template with the aid of CO gas and an electron beam. In situ transmission electron microscopy was used to directly visualize the interface propagation kinetics between the 4H-Au-nanorod and fcc-Au nanoparticle. Epitaxial growth was initiated at the contact interface, and then propagated to convert all parts of these fcc nanoparticles to 4H phase. Density functional theory calculations and ab initio molecular dynamics simulations show that the CO molecules can assist the Au diffusion process and promote the flexibility of Au particles during the epitaxial growth. The phase transformation was driven by the reduction of Gibbs free energy by eliminating the interface between fcc and 4H phases.

Effect of phase and size on surface sites in cobalt nanoparticles

Molecular dynamics was applied to simulate cobalt nanoparticles to understand the effects of particles size and crystal phases on the distribution of surfaces sites relevant for Fischer-Tropsch catalysis. The results indicate a minimal change (<5%) in the coordination number distribution of surface atoms for particles larger than 4 nm even at 500 K, implying that temperature is not sufficient to drive surface reconstruction. We found that the distribution of B5 sites differ significantly between hcp and fcc particles, suggesting different CO adsorption properties for the two phases. HCP particles offer different types of B5 sites which are sterically less hindered for CO adsorption and maybe the reason for differences in catalytic behaviors of hcp vs. fcc nanoparticles. Finally, the smaller nanoparticles have higher radial contraction on the surface, which could impact the deactivation mechanism of these particles by inhibiting the sub-surface diffusion of adsorbate species.

Large Wiedemann effect in (Co70Fe30)99.8(NbC)0.2 wires with strong 〈100〉 circumferential texture

In this work, 0.5mm diameter magnetostrictive (Co70Fe30)99.8(NbC)0.2 wires were prepared using forging and drawing processes. A Wiedemann twist up to 1348″/cm has been achieved in the annealed wires and to our knowledge is the largest value of Wiedemann effect in magnetoelastic materials. Microstructure analyses of the annealed wires indicate that large Wiedemann twist was attributed to the 〈100〉 circumferential texture and the fcc nanoparticles embedded in bcc matrix. The results indicate that the favorable circumferential texture and heterogeneous structure can be used to guide exploration of materials with large Wiedemann effect.

“Save money” during hydrogenation reactions by exploiting the superior performance of Pd-NPs deposited on carbon black by magnetron sputtering

The magnetron-sputtering approach was used for the deposition of small (ca. 3.7 nm) and uniformly distributed Pd(0)-fcc nanoparticles (Pd-NPs) with partially oxidised surfaces on commercially available carbon black. The pores of the support were uniformly filled by Pd-NPs, and the surface area was drastically reduced by blockage of the pores. The metal concentration increases with the augmentation of the sputtering time without changing the metal NP size. These Pd-nanocatalysts are high efficient for the hydrogenation of nitrobenzene to aniline (TOF up to 141.7 min−1), 1,3-cyclohexadiene to cyclohexene (TOF up to 24.0 s−1), and cyclohexene to cyclohexane (TOF up to 35.1 s−1) under 4 bar of dihydrogen (H2) at mild temperatures (75–90 °C). The magnetron sputtering is one of the simplest, reliable, fast, clean and cheap methods for the preparation of Pd/C catalysts.

Size dependence of structural parameters in fcc and hcp Ru nanoparticles, revealed by Rietveld refinement analysis of high-energy X-ray diffraction data.

To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data. For hexagonal close-packed (hcp) Ru NPs, the CO oxidation activity decreased with decreasing domain surface area. However, for face-centered cubic (fcc) Ru NPs, the CO oxidation activity became stronger with decreasing domain surface area. In comparing fcc Ru NPs with hcp Ru NPs, we found that the hcp Ru NPs of approximately 2 nm, which had a smaller domain surface area and smaller atomic displacement, showed a higher catalytic activity than that of fcc Ru NPs of the same size. In contrast, fcc Ru NPs larger than 3.5 nm, which had a larger domain surface area, lattice distortion, and larger atomic displacement, exhibited higher catalytic activity than that of hcp Ru NPs of the same size. In addition, the fcc Ru NPs had larger atomic displacements than hcp Ru NPs for diameters ranging from 2.2 to 5.4 nm. Enhancement of the CO oxidation activity in fcc Ru NPs may be caused by an increase in imperfections due to lattice distortions of close-packed planes and static atomic displacements.

Distribution of Active Site Types on Au Nanoparticles with Different Structures: Study of Thermal Dependence

For gold nanoparticles dependencies of low-coordinated atoms count and areas of different faces from nanoparticle size, shape and structure and temperature have been studied. The following recommendations for catalyst developers are proposed: for catalysis of reactions that occur on (111) face icosahedral nanoparticles smaller than 400 atoms must be preferred; reaction that occur on (100) and (110) faces and near low-coordinated atoms, should be better catalyzed by FCC nanoparticles; it should be taken into account, that temperature growth decreases amount of atoms on (111) and (110) faces, and, increases number of low-coordinated atoms and an area of (100) faces.

Effect of gamma radiation on alkanethiolate-capped gold nanoparticles: Theoretical studies

Abstract Theoretical studies of the effect of gamma irradiation on alkanethiolate-capped gold nanoparticles are presented. Icosahedral, decahedral and fcc nanoparticles protected with 1-dodecanethiolate (SC12) were obtained by molecular mechanics simulations, analyzing the effect of gamma irradiation through MonteCarlo. The studied doses were 1, 10 and 20 kGy. It was observed that slight structural modifications of the metallic core might occur and these are dependent on the shape of the nanoparticle. However, the most significant effect was observed on the organic passivating layer, where torsions, bending and scission of the alkyl chains were detected.

Unravelling the Formation of Pt–Ga Alloyed Nanoparticles on Calcined Ga-Modified Hydrotalcites by in Situ XAS

The chemical transformations taking place during the formation of catalytic Pt–Ga alloyed nanoparticles supported on calcined Ga-modified hydrotalcite Mg(Ga)(Al)Ox are investigated. The starting point is a Pt(acac)2 precursor impregnated onto a Mg(Ga)(Al)Ox support. An oxidative treatment first yields Pt nanoparticles, while subsequent reduction efficiently delivers Ga from the support framework to Pt, forming Pt–Ga alloyed clusters. Different steps are discerned in this process based on in situ XAS analysis. During oxidative heating to 350 °C, the initially adsorbed Pt(acac)2 precursor molecules decompose and form atomically dispersed Pt4+ species with 5-/6-fold oxygen coordination. A fraction of the formed Pt–O bonds consists of strong anchoring points between Pt4+ species and support oxygen, decreasing the Pt mobility induced by the basic support. Further calcination to 650 °C leads to scission of these Pt–O support bonds, allowing more mobile Pt species to form 3–11 atom Pt fcc nanoparticles with an oxidized external surface. These subnanometer clusters are proposed to be bound to the Mg(Ga)(Al)Ox support by extended 2.5 Å Pt0–(OH)− induced dipole-ion interfacial bonds. Cooling down and subsequent heating in H2 up to 450 °C causes sintering and reduction of these nanoparticles. In the course of this reduction, the proposed 2.5 Å Pt0–(OH)− interfacial bonds are replaced by common 2.0 Å Pt–O bonds. Further heating in H2 to 650 °C causes reduction of framework Ga, allowing Ga transport from the support to the Pt clusters to form 1.5 nm Pt–Ga alloyed nanoparticles. This activated Pt–Ga/Mg(Ga)(Al)Ox catalyst is subjected to one O2/H2 redox cycle at 650 °C to mimick the catalyst regeneration procedure. The redox cycle induces an alloy restructuring, leading to a decrease in the degree of Pt–Ga alloying. Wavelet transformed XAS—complemented by XANES and EXAFS—is shown to be a key tool to disclose the mechanistic details occurring during Pt–Ga formation.