Homoepitaxial size control and large-scale synthesis of highly monodisperse amine-protected palladium nanoparticles

Sulfur fractionation using high-resolution continuum source molecular absorption spectrometry with calcium and hydrophobic palladium nanoparticles as chemical modifiers

The unprecedented use of high-resolution continuum source molecular absorption spectrometry (HR-CS MAS) for the fractionation of organic and inorganic sulfur (S) species through monitoring the CS molecule is presented here. Two separate methods for determining organic (CSorg) and inorganic (CSino) sulfur were developed to work sequentially. The optimized temperature program for both methodologies has two pyrolysis steps and one vaporization step (1st Tpyr: 1800 and 2ndTpyr: 800 °C, and Tvap: 2500 °C). The fractionation was achieved by implementing hydrophobic Pd NPs and Ca as chemical modifiers for the CSorg and CSino methods. Method development was performed by applying different statistical models, allowing the definition of optimal conditions for the chemical modifier mass, and minimizing the S species interconversion, i.e., Doehlert design, and central composite design. The limits of detection (LoD) for CSorg and CSino were 2.4 and 2.1 mg L-1, respectively. Recovery tests evaluated the method's specificity and accuracy; over 92 % recovery was found for both CSorg and CSino. Thus, the proposed methods offer a reliable alternative for fractionating organic and inorganic S by using HR-CS MAS.

Pursuing unprecedent anisotropic morphologies of halide-free Pd nanoparticles by tuning nucleation and growth

In this paper, a highly effective and scalable polyol-based modified procedure is reported, yielding shape controlled Pd nanoparticles (NPs) formed via two distinct growth mechanisms as a function of the...

Formation of strong L10-FePd/α-Fe nanocomposite magnets by visualizing efficient exchange coupling

Conceptual nanocomposite magnets (NCMs) composed of exchange-coupled hard/soft magnetic phases have been expected to show excellent magnetic performance based on simultaneous high coercivity (H _c) and high saturation magnetization (M _s). In our previous works, however, the H _c was considerably lower than its theoretical value (H _a), which prevented us from improving the performance of NCMs. Here, we show that the H _c of isolated particulate L1₀-FePd/α-Fe NCMs is dominated by their phase segregation into core/shell-like structures versus Janus-like structures. Using first-order reversal curve (FORC) analysis, we clearly distinguished a microscopically undetectable difference in the phase-segregation structure in the NCMs, finding both efficient and inefficient exchange coupling. The nanostructurally controlled NCMs dominated by core/shell-like structure with efficient exchange coupling showed the largest energy product ((BH)_max = 17.5 MGOe) in the Fe-Pd system and the highest H _c/H _a value (26.5%) among all NCM powders.

Size and Shape Controlled Synthesis of Pd Nanocrystals

Palladium (Pd) has attracted substantial academic interest due to its remarkable properties and extensive applications in many industrial processes and commercial devices. The development of Pd nanocrystals (NCs) would contribute to reduce overall precious metal loadings, and allow the efficient utilization of energy at lower economic costs. Furthermore, some of the important properties of Pd NCs can be substantially enhanced by rational designing and tight controlling of both size and shape. In this review, we have summarized the state-of-the-art research progress in the shape and size-controlled synthesis of noble-metal Pd NCs, which is based on the wet-chemical synthesis. Pd NCs have been categorized into five types: (1) single-crystalline Pd nano-polyhedra with well-defined low-index facets (e.g. {100}, {111} and {110}); (2) single-crystalline Pd nano polyhedra with well-defined high-index facets, such as Pd tetrahexahedra with {hk0} facets; (3) Pd NCs with cyclic penta-twinned structure, including icosahedra and decahedra; (4) monodisperse spherical Pd nanoparticles; (5) typical anisotropic Pd NCs, such as nanoframes, nanoplate, nanorods/wires. The synthetic approach and growth mechanisms of these types of Pd NCs are highlighted. The key factors that control the structures, including shapes (surface structures), twin structures, single-crystal nanostructures, and sizes are carefully elucidated. We also introduce the detailed characterization tools for analysis of Pd NCs with a specific type. The challenges faced and perspectives on this promising field are also briefly discussed. We believe that the detailed studies on the growth mechanisms of NCs provide a powerful guideline to the rational design and synthesis of noble-metal NCs with enhanced properties.

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A Rational Solid-State Synthesis of Supported Au-Ni Bimetallic Nanoparticles with Enhanced Activity for Gas-Phase Selective Oxidation of Alcohols

A facile confined solid-state seed-mediated alloying strategy is applied for the rational synthesis of supported Au-Ni bimetallic nanoparticles (BMNPs). The method sequentially deposits nickel salts and AuNP seeds into the ordered array of extra-large mesopores (EP-FDU-12 support) followed by a high-temperature annealing process. The size, structure, and composition of the AuNi BMNPs can be well tuned by varying the AuNP seeds, annealing temperature, and feeding ratio of metal precursors. Kinetic studies and DFT calculations suggest that the introduction of the Ni component can significantly prompt the O₂ activation on AuNPs, which is critical for the selective alcohol oxidation using molecular O₂ as the oxidant. The optimal Au-Ni BMNP catalyst showed the highest turnover frequency (TOF) (59 000 h^-1, 240 °C) and highest space-time yield (STY) of benzyl aldehyde (BAD) productivity (9.23 kg·g_Au^-1·h^-1) in the gas-phase oxidation of benzyl alcohol (BA), which is at least about 5-fold higher than that of other supported Au catalysts.

Graphene Oxide-Assisted Synthesis of Pt-Co Alloy Nanocrystals with High-Index Facets and Enhanced Electrocatalytic Properties

Metal nanocrystals (NCs) are grown directly on the surface of reduced graphene oxide (rGO), which can maximize the rGO-NCs contact/interaction to achieve the enhanced catalytic activity. However, it is difficult to control the size and morphology of metal NCs by in situ method due to the effects of functional groups on the surface of GO, and as a result, the metal NCs/rGO hybrids are conventionally synthesized by two-step method. Herein, one-pot synthesis of Pt-Co alloy NCs is demonstrated with concave-polyhedrons and concave-nanocubes bounded by {hkl} and {hk0} high-index facets (HIFs) distributed on rGO. GO can affect the geometry and electronic structure of Pt-Co NCs. Thanks to the synergy of the HIFs and the electronic effect of the intimate contact/interaction between Pt-Co alloy and rGO, these as-prepared Pt-Co NCs/rGO hybrids presents enhanced catalytic properties for the electrooxidation of formic acid, as well as for the oxygen reduction reaction.

Palladium Nanoparticle-Loaded Cellulose Paper: A Highly Efficient, Robust, and Recyclable Self-Assembled Composite Catalytic System

We present a novel strategy based on the immobilization of palladium nanoparticles (Pd NPs) on filter paper for development of a catalytic system with high efficiency and recyclability. Oleylamine-capped Pd nanoparticles, dispersed in an organic solvent, strongly adsorb on cellulose filter paper, which shows a great ability to wick fluids due to its microfiber structure. Strong van der Waals forces and hydrophobic interactions between the particles and the substrate lead to nanoparticle immobilization, with no desorption upon further immersion in any solvent. The prepared Pd NP-loaded paper substrates were tested for several model reactions such as the oxidative homocoupling of arylboronic acids, the Suzuki cross-coupling reaction, and nitro-to-amine reduction, and they display efficient catalytic activity and excellent recyclability and reusability. This approach of using NP-loaded paper substrates as reusable catalysts is expected to open doors for new types of catalytic support for practical applications.

Determination of a localized surface plasmon resonance mode of Cu7S4 nanodisks by plasmon coupling

Plasmon properties such as peak position, extinction cross-section and local electric field intensity are strongly dependent on excited, localized surface plasmon resonance (LSPR) modes. In non-spherical copper chalcogenide nanoparticles, assignment of the LSPR peaks to the corresponding oscillation modes has been controversial and requires experimental verification. We determined the in-plane LSPR mode of roxbyite Cu₇S₄ nanodisks from the plasmon coupling effect of nanodisks in solution. Compared with individual Cu₇S₄ nanodisks, self-assembled Cu₇S₄ nanodisk arrays in chloroform exhibited a blue-shifted LSPR peak with weaker optical density. This strongly suggests that the singular LSPR peak in the near-infrared region mainly originates from the in-plane oscillation mode. In addition, we demonstrate that the same LSPR peak can be readily tuned by controlling the number of disks in the array.

Core-shell bimetallic nanoparticles robustly fixed on the outermost surface of magnetic silica microspheres

The major challenges in practically utilising the immense potential benefits of nanomaterials are controlling aggregation, recycling the nanomaterials, and fabricating well-defined nanoparticulate materials using innovative methods. We present a novel innovative synthetic strategy for core–shell bimetallic nanoparticles that are well-defined, ligand-free, and robustly fixed on the outermost surface of recyclable magnetic silica microspheres. The strategy includes seeding, coalescing the seeds to cores, and then growing shells from the cores on aminopropyl-functionalised silica microspheres so that the cores and aminopropyl moieties are robustly embedded in the shell materials. The representative Au–Ag bimetallic nanoparticles fixed on the microsphere showed excellent catalytic performance that remained consistent during repeated catalytic cycles.

Synthesis of size-controlled monodisperse Pd nanoparticles via a non-aqueous seed-mediated growth

We demonstrated that stepwise seed-mediated growth could be extended in non-aqueous solution (solvothermal synthesis) and improved as an effective method for controlling the uniform size of palladium nanoparticles (Pd NPs) in a wide range. The monodisperse Pd NPs with the size of about 5 nm were synthesized by simply reducing Pd(acac)2 with formaldehyde in different organic amine solvents. By an improved stepwise seed-mediated synthesis, the size of the monodisperse Pd NPs can be precisely controlled from approximately 5 to 10 nm. The as-prepared Pd NPs could self assemble to well-shaped superlattice crystal without size selection process.

Exchange coupling interaction in L10-FePd/α-Fe nanocomposite magnets with large maximum energy products

Nanocomposite magnets (NCMs) consisting of hard and soft magnetic phases are expected to be instrumental in overcoming the current theoretical limit of magnet performance. In this study, structural analyses were performed on L1(0)-FePd/α-Fe NCMs with various hard/soft volume fractions, which were formed by annealing Pd/γ-Fe(2)O(3) heterostructured nanoparticles and pure Pd nanoparticles. The sample with a hard/soft volume ratio of 82/18 formed by annealing at 773 K had the largest maximum energy product (BH(max) = 10.3 MGOe). In such a sample, the interface between the hard and soft phases was coherent and the phase sizes were optimized, both of which effectively induced exchange coupling. This exchange coupling was directly observed by visualizing the magnetic interaction between the hard and soft phases using a first-order reversal curve diagram, which is a valuable tool to improve the magnetic properties of NCMs.