Core@shell bimetallic nanoparticle synthesis via anion coordination

Structure-driven tuning of catalytic properties of core-shell nanostructures

The annual increase in demand for renewable energy is driving the development of catalysis-based technologies that generate, store and convert clean energy by splitting and forming chemical bonds. Thanks to efforts over the last two decades, great progress has been made in the use of core-shell nanostructures to improve the performance of metallic catalysts. The successful preparation and application of a large number of bimetallic core-shell nanocrystals demonstrates the wide range of possibilities they offer and suggests further advances in this field. Here, we have reviewed recent advances in the synthesis and study of core-shell nanostructures that are promising for catalysis. Particular attention has been paid to the structural tuning of the catalytic properties of core-shell nanostructures and to theoretical methods capable of describing their catalytic properties in order to efficiently search for new catalysts with desired properties. We have also identified the most promising areas of research in this field, in terms of experimental and theoretical studies, and in terms of promising materials to be studied.

Exploring intermixed magnetic nanoparticles: insights from atomistic spin dynamics simulations

Binary nanoparticles, composed of both rare-earth elements with substantial magnetic properties and transition metals known for their high magnetic ordering temperatures, hold great promise as innovative materials for novel magnetic applications. In this study, we employ an atomistic spin dynamics framework to investigate how the magnetic properties change at finite temperatures in mixed NiGd nanoparticles. We specifically examine parameters such as saturation magnetization and spin-reorientation in relation to the nanoparticle's size, which ranges from 4 nm to 16 nm, and composition. Our findings reveal that Ni75Gd25 nanoparticles demonstrate exceptional magnetic properties at finite temperatures, marked by significantly increased saturation magnetizations and magnetic ordering temperatures. In contrast, nanoparticles containing 50% and 75% Gd contents exhibit notably reduced saturation magnetizations and magnetic ordering temperatures. Theoretical findings of our study shed light on the pivotal role that the Gd content plays in determining the magnetic behaviour at finite temperatures.

Core atoms escape from the shell: reverse segregation of Pb-Al core-shell nanoclusters via nanoscale melting

Melting is a phase transition that profoundly affects the fabrication and diverse applications of metal nanoclusters. Core-shell clusters offer distinctive properties and thus opportunities compared with other classes of nano-alloys. Molecular dynamics simulations have been employed to investigate the melting behaviour of Pb-Al core-shell clusters containing a fixed Pb147 core and varying shell thickness. Our results show that the core and shell melt separately. Surprisingly, core melting always drives the core Pb atoms to break out the shell and coat the nanoclusters in a reversed segregation process at the nanoscale. The melting point of the core increases with the shell thickness to exceed that of the bare core cluster, but the thinnest shell always supresses the core melting point. These results can be a reference for the future fabrication, manipulation, and exploitation of the core-shell nanoalloys chosen. The system chosen is ideally suited for experimental observations.

Nano-engineering nanomedicines with customized functions for tumor treatment applications

Nano-engineering with unique "custom function" capability has shown great potential in solving technical difficulties of nanomaterials in tumor treatment. Through tuning the size and surface properties controllablly, nanoparticles can be endoewd with tailored structure, and then the characteristic functions to improve the therapeutic effect of nanomedicines. Based on nano-engineering, many have been carried out to advance nano-engineering nanomedicine. In this review, the main research related to cancer therapy attached to the development of nanoengineering nanomedicines has been presented as follows. Firstly, therapeutic agents that target to tumor area can exert the therapeutic effect effectively. Secondly, drug resistance of tumor cells can be overcome to enhance the efficacy. Thirdly, remodeling the immunosuppressive microenvironment makes the therapeutic agents work with the autoimmune system to eliminate the primary tumor and then prevent tumor recurrence and metastasis. Finally, the development prospects of nano-engineering nanomedicine are also outlined.

Engineering gold-platinum core-shell nanoparticles by self-limitation in solution

Core-shell particles with thin noble metal shells represent an attractive material class with potential for various applications ranging from catalysis to biomedical and pharmaceutical applications to optical crystals. The synthesis of well-defined core-shell architectures remains, however, highly challenging. Here, we demonstrate that atomically-thin and homogeneous platinum shells can be grown via a colloidal synthesis method on a variety of gold nanostructures ranging from spherical nanoparticles to nanorods and nanocubes. The synthesis is based on the exchange of low binding citrate ligands on gold, the reduction of platinum and the subsequent kinetically hindered growth by carbon monoxide as strong binding ligand. The prerequisites for homogeneous growth are low core-binding ligands with moderate fast ligand exchange in solution, a mild reducing agent to mitigate homonucleation and a strong affinity of a second ligand system that can bind to the shell's surface. The simplicity of the described synthetic route can potentially be adapted to various other material libraries to obtain atomically smooth core-shell systems.

Heterogeneous Trimetallic Nanoparticles as Catalysts

The development and application of trimetallic nanoparticles continues to accelerate rapidly as a result of advances in materials design, synthetic control, and reaction characterization. Following the technological successes of multicomponent materials in automotive exhausts and photovoltaics, synergistic effects are now accessible through the careful preparation of multielement particles, presenting exciting opportunities in the field of catalysis. In this review, we explore the methods currently used in the design, synthesis, analysis, and application of trimetallic nanoparticles across both the experimental and computational realms and provide a critical perspective on the emergent field of trimetallic nanocatalysts. Trimetallic nanoparticles are typically supported on high-surface-area metal oxides for catalytic applications, synthesized via preparative conditions that are comparable to those applied for mono- and bimetallic nanoparticles. However, controlled elemental segregation and subsequent characterization remain challenging because of the heterogeneous nature of the systems. The multielement composition exhibits beneficial synergy for important oxidation, dehydrogenation, and hydrogenation reactions; in some cases, this is realized through higher selectivity, while activity improvements are also observed. However, challenges related to identifying and harnessing influential characteristics for maximum productivity remain. Computation provides support for the experimental endeavors, for example in electrocatalysis, and a clear need is identified for the marriage of simulation, with respect to both combinatorial element screening and optimal reaction design, to experiment in order to maximize productivity from this nascent field. Clear challenges remain with respect to identifying, making, and applying trimetallic catalysts efficiently, but the foundations are now visible, and the outlook is strong for this exciting chemical field.

Bimetallic Nanocrystals: Structure, Controllable Synthesis and Applications in Catalysis, Energy and Sensing

In recent years, bimetallic nanocrystals have attracted great interest from many researchers. Bimetallic nanocrystals are expected to exhibit improved physical and chemical properties due to the synergistic effect between the two metals, not just a combination of two monometallic properties. More importantly, the properties of bimetallic nanocrystals are significantly affected by their morphology, structure, and atomic arrangement. Reasonable regulation of these parameters of nanocrystals can effectively control their properties and enhance their practicality in a given application. This review summarizes some recent research progress in the controlled synthesis of shape, composition and structure, as well as some important applications of bimetallic nanocrystals. We first give a brief introduction to the development of bimetals, followed by the architectural diversity of bimetallic nanocrystals. The most commonly used and typical synthesis methods are also summarized, and the possible morphologies under different conditions are also discussed. Finally, we discuss the composition-dependent and shape-dependent properties of bimetals in terms of highlighting applications such as catalysis, energy conversion, gas sensing and bio-detection applications.

Core-shell nanostructures: a simplest two-component system with enhanced properties and multiple applications

With the pace of time, synthesis of nanomaterials has paved paths to blend two or more materials having different properties into hybrid nanoparticles. Therefore, it has become possible to combine two different functionalities in a single nanoparticle and their properties can be enhanced or modified by coupling of two different components. Core-shell technology has now represented a new trend in analytical sciences. Core-shell nanostructures are in demand due to their specific design and geometry. They have internal core of one component (metal or biomolecules) surrounded by a shell of another component. Core-shell nanoparticles have great importance due to their high thermal stability, high solubility and lower toxicity. In this review, recent progress in development of new and sophisticated core-shell nanostructures has been explored. The first section covers introduction throwing light on basics of core-shell nanoparticles. Following section classifies core-shell nanostructures into single core/shell, multicore/single shell, single core/multishell and multicore/multishell nanostructures. Next main section gives a brief description on types of core-shell nanomaterials followed by processes for the synthesis of core-shell nanostructures. Ultimately, the final section focuses on the application areas such as drug delivery, bioimaging, solar cell applications etc.

Area-selective atomic layer deposition of noble metals: Polymerized fluorocarbon layers as effective growth inhibitors

The increasingly complex nanoscale three-dimensional and multilayered structures utilized in nanoelectronic, catalytic, and energy conversion/storage devices necessitate novel substrate-selective material deposition approaches featuring bottom-up and self-aligned precision processing. Here, we demonstrate the area-selective atomic layer deposition (AS-ALD) of two noble metals, Pt and Pd, by using a plasma-polymerized fluorocarbon layer as growth inhibition surfaces. The contact angle, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy measurements were performed to investigate the blocking ability of polymerized fluorocarbon (CFx) layers against ALD-grown metal films. Both Pt and Pd showed significant nucleation delays on fluorocarbon surfaces. Self-aligned film deposition is confirmed using this strategy by growing Pt and Pd on the microscale lithographically patterned CFx/Si samples. CFx blocking layer degradation during ozone exposure was analyzed using XPS measurements, which confirmed the oxygen physisorption as the main responsible surface reaction with further hydroxyl group formation on the CFx surface. Our work reveals that the CFx layer is compatible with an ozone coreactant until the blocking polymer cannot withstand oxygen physisorption. Our results could potentially be used to investigate and develop radical-assisted AS-ALD processes for a wider selection of materials.

Supramolecular Gold Stripping from Activated Carbon Using α-Cyclodextrin

We report the molecular recognition of the Au(CN)₂^- anion, a crucial intermediate in today's gold mining industry, by α-cyclodextrin. Three X-ray single-crystal superstructures-KAu(CN)₂⊂α-cyclodextrin, KAu(CN)₂⊂(α-cyclodextrin)₂, and KAg(CN)₂⊂(α-cyclodextrin)₂-demonstrate that the binding cavity of α-cyclodextrin is a good fit for metal-coordination complexes, such as Au(CN)₂^- and Ag(CN)₂^- with linear geometries, while the K⁺ ions fulfill the role of linking α-cyclodextrin tori together as a result of [K⁺···O] ion-dipole interactions. A 1:1 binding stoichiometry between Au(CN)₂^- and α-cyclodextrin in aqueous solution, revealed by ¹H NMR titrations, has produced binding constants in the order of 10⁴ M^-1. Isothermal calorimetry titrations indicate that this molecular recognition is driven by a favorable enthalpy change overcoming a small entropic penalty. The adduct formation of KAu(CN)₂⊂α-cyclodextrin in aqueous solution is sustained by multiple [C-H···π] and [C-H···anion] interactions in addition to hydrophobic effects. The molecular recognition has also been investigated by DFT calculations, which suggest that the 2:1 binding stoichiometry between α-cyclodextrin and Au(CN)₂^- is favored in the presence of ethanol. We have demonstrated that this molecular recognition process between α-cyclodextrin and KAu(CN)₂ can be applied to the stripping of gold from the surface of activated carbon at room temperature. Moreover, this stripping process is selective for Au(CN)₂^- in the presence of Ag(CN)₂^-, which has a lower binding affinity toward α-cyclodextrin. This molecular recognition process could, in principle, be integrated into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.

Supramolecular Paradigm for Capture and Co-Precipitation of Gold(III) Coordination Complexes

A new supramolecular paradigm is presented for reliable capture and co-precipitation of haloauric acids (HAuX₄ ) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non-covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX₄ ^- , and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X-ray diffraction analysis of four co-crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one-dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co-crystal structures show that the amidinium-π⋅⋅⋅XAu interaction will reliably engage AuX₄ ^- with high directionality. These acyclic compounds are very attractive as co-precipitation agents within new "green" gold recovery processes. They also have high potential as tectons for controlled self-assembly or co-crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next-generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine.

Core-satellite assemblies of Au@polydopamine@Ag nanoparticles for photothermal-mediated catalytic reaction

Engineering plasmonic nanoparticles (NPs) into superstructures comprising two or more distinctive materials is highly desirable because these assemblies can unfold new properties that differ from those exhibited by their individual counterparts. In addition, metal NPs such as Au NPs and Ag NPs have played a major role in environmental remediation. In this study, we designed a heterogeneous NP assembly composed of an Au core and Ag satellite by utilizing a mussel-inspired polydopamine (PDA) strategy. This approach afforded substantial enhancement in the catalytic activity because of the synergistic effect between the Au core and Ag satellite. Specifically, the heat from the localized surface plasmon resonance excitation of the Au NPs can accelerate the reduction reaction of 4-nitrophenol, while the Ag NPs act as a catalyst for reducing the activation energy. Overall, we prepared a facile route to produce heterogeneous metal NP assemblies, which offers promise in scalable synthesis and application in heterogeneous catalysis.

Electrochemical study of 4-chloroaniline in a water/acetonitrile mixture. A new method for the synthesis of 4-chloro-2-(phenylsulfonyl)aniline and N-(4-chlorophenyl)benzenesulfonamide

The electrochemical oxidation of 4-chloroaniline as a model compound in a water/acetonitrile mixture was investigated by cyclic voltammetry and differential pulse voltammetry. It was established that one-electron oxidation of 4-chloroaniline followed by disproportionation reaction affords unstable (4-iminocyclohexa-2,5-dien-1-ylidene)chloronium. In water/acetonitrile mixtures and in the absence of nucleophiles, the most likely reaction on produced chloronium is hydrolysis and p-quinoneimine formation. The electrochemical oxidation of 4-chloroaniline in the presence of arylsulfinic acids was also investigated in a water/acetonitrile mixture at a glassy carbon electrode. It was established that under these conditions, the anodically generated chloronium reacts with benzenesulfinic acid to produce the corresponding diaryl sulfone and N-phenylbenzenesulfonamide derivatives. In addition, Gaussian 09W was applied for prediction of the possible product by the calculation of natural charge, LUMO orbital energies and thermodynamic stability of intermediates and products.

Electrochemical oxidation pathway of p-chloroaniline (PCA) in the presence of benzenesulfinic acid (BSA).

The role of pre-nucleation clusters in the crystallization of gold nanoparticles

The syntheses of metal nanoparticles by reduction in apolar solvents in the presence of long chain surfactants have proven to be extremely effective in the control of the particle size and shape. Nevertheless, the elucidation of the nucleation/growth mechanism is not straightforward because of the multiple roles played by surfactants. The nucleation stage, in particular, is very difficult to describe precisely and requires in situ and time-resolved techniques. Here, relying on in situ small angle X-ray scattering (SAXS), X-ray absorption spectroscopy (XAS) and high-energy X-ray diffraction (HE-XRD), we propose that ultra-small gold particles prepared by reduction of gold chloride in a solution of oleylamine (OY) in hexane with triisopropylsilane do not follow a classical nucleation process but result from pre-nucleation clusters (PNCs). These PNCs contain Au(iii) and Au(i) precursors; they are almost stable in size during the induction stage, as shown by SAXS, prior to undergoing a very fast shrinkage during the nucleation stage. The gold speciation as a function of time deduced from the XAS spectra has been analyzed through multi-step reaction pathways comprising both highly reactive species, involved in the nucleation and growth stages, and poorly reactive species acting as a reservoir for the reactive species. The duration of the induction period is related to the reactivity of the gold precursors, which is tuned by the coordination of OY to the gold complexes, while the nucleation stage was found to depend on the size and reactivity of the PNCs. The role of the PNCs in determining the final particle size and structure is also discussed in relation to previous studies. The multiple roles of OY, as the solubilizing agent of the gold salt, the ligand of the gold complexes determining both the size of the PNCs and the reactivity of the gold precursors, and finally the capping agent of the final gold particles as oleylammonium chloride, have been clearly established. This work opens new perspectives to synthesize metal NPs via metal-organic PNCs and to define new synthesis routes for nanoparticles that may present structure and morphologies different from those obtained by the classical nucleation routes.

N-Functionalised Imidazoles as Stabilisers for Metal Nanoparticles in Catalysis and Anion Binding

Metal nanoparticles (NPs) have physicochemical properties which are distinct from both the bulk and molecular metal species, and provide opportunities in fields such as catalysis and sensing. NPs typically require protection of their surface to impede aggregation, but these coatings can also block access to the surface which would be required to take advantage of their unusual properties. Here, we show that alkyl imidazoles can stabilise Pd, Pt, Au, and Ag NPs, and delineate the limits of their synthesis. These ligands provide an intermediate level of surface protection, for which we demonstrate proof‐of‐principle in catalysis and anion binding.

Microfluidic Generation of Nanomaterials for Biomedical Applications

As nanomaterials (NMs) possess attractive physicochemical properties that are strongly related to their specific sizes and morphologies, they are becoming one of the most desirable components in the fields of drug delivery, biosensing, bioimaging, and tissue engineering. By choosing an appropriate methodology that allows for accurate control over the reaction conditions, not only can NMs with high quality and rapid production rate be generated, but also designing composite and efficient products for therapy and diagnosis in nanomedicine can be realized. Recent evidence implies that microfluidic technology offers a promising platform for the synthesis of NMs by easy manipulation of fluids in microscale channels. In this Review, a comprehensive set of developments in the field of microfluidics for generating two main classes of NMs, including nanoparticles and nanofibers, and their various potentials in biomedical applications are summarized. Furthermore, the major challenges in this area and opinions on its future developments are proposed.

Oxygen Functionalized Copper Nanoparticles for Solar-Driven Conversion of Carbon Dioxide to Methane

Solar conversion of carbon dioxide (CO₂) into hydrocarbon fuels offers a promising approach to fulfill the world's ever-increasing energy demands in a sustainable way. However, a highly active catalyst that can also tune the selectivity toward desired products must be developed for an effective process. Here, we present oxygen functionalized copper (OFn-Cu) nanoparticles as a highly active and methane (CH₄) selective catalyst for the electrocatalytic CO₂ reduction reaction. Our electrochemical results indicate that OFn-Cu (5 nm) nanoparticles with an oxidized layer at the surface reach a maximum CH₄ formation current density and turnover frequency of 36.24 mA/cm² and of 0.17 s^-1 at the potential of -1.05 V vs RHE, respectively, exceeding the performance of existing Cu and Cu-based catalysts. Characterization results indicate that the surface of the OFn-Cu nanoparticles consists of an oxygen functionalized layer in the form of Cu²⁺ (CuO) separated from the underneath elemental Cu by a Cu⁺ (Cu₂O) sublayer. Density functional theory calculations also confirm that presence of the O site at the CuO (101) surface is the main reason for the enhanced activity and selectivity. Using this catalyst, we have demonstrated a flow cell with an active area of 25 cm² that utilizes solar energy to produce 7.24 L of CH₄ after 10 h of continuous process at a cell power density of 30 mW/cm².

Independent control over size, valence, and elemental composition in the synthesis of DNA-nanoparticle conjugates

DNA–nanoparticle conjugates have found widespread use in sensing, imaging, and as components of devices. However, their synthesis remains relatively complicated and empirically based, often requiring specialized protocols for conjugates of different size, valence, and elemental composition. Here we report a novel, bottom-up approach for the synthesis of DNA–nanoparticle conjugates, based on ring-opening metathesis polymerization (ROMP), intramolecular crosslinking, and template synthesis. Using size, valence, and elemental composition as three independent synthetic parameters, various conjugates can be obtained using a facile and universal procedure. Examples are given to show the usefulness of these conjugates as sensing probes, building blocks for self-assembly, and as model particles for structure–property relationship studies.

DNA–nanoparticle conjugates can be synthesized with independent control over size, valence and elemental composition using a template-based strategy.

Altering the stability of nanoislands through core-shell supports

We follow the decay of two-dimensional Ag nanoclusters, called islands, on Cu-Ag core-shell supports by variable low temperature scanning tunneling microscopy in the temperature range between 160 and 260 K. We reveal two qualitatively different types of decay mechanisms, either linear in time, indicative of an interface-limited decay, or non-linear in time, indicative of diffusion-limited decay. In contrast to conventional decay on monometallic supports, the decay exponent of the diffusion-limited decay depends on temperature; it varies by one order of magnitude. Moreover, the decay rate decreases with increasing temperature. This unusual behaviour is traced back to the temperature-dependent shell of the core-shell support.

Near-Infrared Responsive Bimetallic Nanovesicles for Enhanced Synergistic Chemophotothermal Therapy

Limited therapeutic effects and obvious side effects are two critical problems affecting tumor therapy. Herein, we designed an ingenious nanocarrier, platinum/gold bimetallic-nanoshell-coated triptolide liposomes (Pt@Au-TP-Lips), to achieve enhanced chemophotothermal therapy against cancer. Compared to conventional gold nanoflower structures, the platinum/gold bimetallic (Pt@Au) core-shells exhibited broader near-infrared (NIR) absorption due to the ultrastrong plasmonic coupling effect. With NIR light irradiation, the Pt@Au nanostructure could efficiently and sustainably convert light energy into substantial heat. The ultrahigh photothermal conversion efficiency (56.5%) of Pt@Au-TP-Lips was significantly higher than that of gold nanoflowers (35.7%). Specifically, hyperthermia could induce a phase change in the liposome membrane to accelerate the release of triptolide (TP); meanwhile, it could ablate tumor cells directly and facilitate the cellular uptake of drugs to enhance chemotherapy. More importantly, owing to the cooperation of TP and platinum, Pt@Au-TP-Lips exhibited significant tumor growth suppression with a high inhibitory rate of 90.7%, achieving superior chemophotothermal combination therapy. This work provides new insight into the development of a cooperative theranostic agent for oncotherapy.

Particle Shape Control via Etching of Core@Shell Nanocrystals

The application of nanocrystals as heterogeneous catalysts and plasmonic nanoparticles requires fine control of their shape and chemical composition. A promising idea to achieve synergistic effects is to combine two distinct chemical and/or physical functionalities in bimetallic core@shell nanocrystals. Although techniques for the synthesis of single-component nanocrystals with spherical or anisotropic shape are well-established, new methods are sought to tailor multicomponent nanocrystals. Here, we probe etching in a controlled redox environment as a synthesis technique for multicomponent nanocrystals. Our Monte Carlo computer simulations demonstrate the appearance of characteristic non-equilibrium intermediate microstructures that are further thermodynamically tested and analyzed with molecular dynamics. Convex platelet, concave polyhedron, pod, cage, and strutted-cage shapes are obtained at room temperature with fully coherent structure exposing crystallographic facets and chemical elements along distinct particle crystallographic directions. We observe that structural and dynamic properties are markedly modified compared to the untreated compact nanocrystal.

Supported Bimetallic AuPd Nanoparticles as a Catalyst for the Selective Hydrogenation of Nitroarenes

The solvent-free selective hydrogenation of nitrobenzene was carried out using a supported AuPd nanoparticles catalyst, prepared by the modified impregnation method (M_Im), as efficient catalyst >99% yield of aniline (AN) was obtained after 15 h at 90 °C, 3 bar H₂ that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by M_Im, was found to be active and stable even after four recycle experiments, whereas the same catalyst prepared by S_Im was deactivated during the recycle experiments. The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN). The activation energy of CNB to CAN was found to be 25 kJ mol⁻¹, while that of CNB to AN was found to be 31 kJ mol⁻¹. Based on this, the yield of CAN was maximized (92%) by the lowering the reaction temperature to 25 °C.

Origin of symmetry breaking in the seed-mediated growth of bi-metal nano-heterostructures

Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the seed, namely whether the symmetry of resulted nano-heterostructure follows the original crystal symmetry of seed metal, remains an unpredictable issue to date. In this work, we propose that the thermodynamic factor, i.e., the difference of equilibrium electrochemical potentials (corresponding to their Fermi levels) of two metals in the growth solution, plays a key role for the symmetry breaking of bimetal nano-heterostructures during the seed-mediated growth. As a proof-of-principle experiment, by reversing the relative position of Fermi levels of the Pd nanocube seeds and the second metal Au with changing the concentration of reductant (L-ascorbic acid) in the growth solution, the structure of as-prepared products successfully evolved from centrosymmetric Pd@Au core-shell trisoctahedra to asymmetric Pd-Au hetero-dimers. The idea was further demonstrated by the growth of Ag on the Pd seeds. The present work intends to reveal the origin of symmetry breaking in the seed-mediated growth of nano-heterostructures from the viewpoint of thermodynamics, and these new insights will in turn help to achieve rational construction of bimetal nano-heterostructures with specific functions.

Macrocyclic Receptor for Precious Gold, Platinum, or Palladium Coordination Complexes

Two macrocyclic tetralactam receptors are shown to selectively encapsulate anionic, square-planar chloride and bromide coordination complexes of gold(III), platinum(II), and palladium(II). Both receptors have a preorganized structure that is complementary to its precious metal guest. The receptors do not directly ligate the guest metal center but instead provide an array of arene π-electron donors that interact with the electropositive metal and hydrogen-bond donors that interact with the outer electronegative ligands. This unique mode of supramolecular recognition is illustrated by six X-ray crystal structures showing receptor encapsulation of AuCl₄^-, AuBr₄^-, PtCl₄^-2, or Pd₂Cl₆^-2. In organic solution, the 1:1 association constants correlate with specific supramolecular features identified in the solid state. Technical applications using these receptors are envisioned in a wide range of fields that involve precious metals, including mining, recycling, catalysis, nanoscience, and medicine.

Multimetallic AuPd@Pd@Pt core-interlayer-shell icosahedral electrocatalysts for highly efficient oxygen reduction reaction

Incorporating Pt with core metals into Pt-based core-shell catalysts is regarded as a promising strategy to substantially enhance the catalytic properties towards oxygen reduction reaction (ORR) in fuel cells due to the synergetic effect between distinct metals. In this wok, ultrathin Pt skins with two atomic layers were epitaxially coated on as-prepared icosahedral Au₅₀Pd₅₀, Au₆₀Pd₄₀ and Au₆₆Pd₃₄ nanocrystal seeds, which are constructed with alloyed cores and Pd shells with different thickness. Through electron microscopic characterizations, Pd interlayers with tunable thickness of 3, 6, and 12 atomic layers can be found in the Au₆₆Pd₃₄@Pt, Au₆₀Pd₄₀@Pt and Au₅₀Pd₅₀@Pt icosahedra, respectively. These icosahedral AuPd@Pd@Pt nanocrystals show substantially enhanced activities and durabilities in electrocatalytic measurements towards ORR compared to Au₇₅Pd₂₅@Pt icosahedra without Pd interlayer and commercial Pt/C catalysts. Specifically, Au₆₀Pd₄₀@Pt icosahedra with 6 atomically thick Pd interlayer display the best electrocatalytic performances, whose mass activities before and after durability tests of 50,000 cycles are 11.6 and 30.2 times, respectively, as high as that of the commercial Pt/C.

Tuning the structure and magnetic behavior of Ni–Ir-based nanoparticles in ionic liquids

We report on a simple preparation of extremely small diameter (ca. 2 nm) Ni–Ir-based NPs with either core–shell like or alloy-like microstructures.

Microfluidic Synthesis of Nanohybrids

Nanohybrids composed of two or more components exhibit many distinct physicochemical properties and hold great promise for applications in optics, electronics, magnetics, new energy, environment protection, and biomedical engineering. Microfluidic systems exhibit many advantages due to their unique characteristics of narrow channels, variable length, controllable number of channels and multiple integrations. Particularly their spatial-temporarily splitting of the formation stages during nanomaterials formation along the microfluidic channels favors the online control of the reaction kinetic parameters and in situ tuning of the product properties. This Review is focused on the features of the current types of microfluidic devices in the synthesis of different types of nanohybrids based on the classification of the four main kinds of materials: metal, nonmetal inorganic, polymer and composites. Their morphologies, compositions and properties can be adjusted conveniently in these synthesis systems. Synthesis advantages of varieties of microfluidic devices for specific nanohybrids of defined surfaces and interfaces are presented according to their process and microstructure features of devices as compared with conventional methods. A summary is presented, and challenges are put forward for the future development of the microfluidic synthesis of nanohybrids for advanced applications.

Synthesis of Highly Active Sub-Nanometer Pt@Rh Core-Shell Nanocatalyst via a Photochemical Route: Porous Titania Nanoplates as a Superior Photoactive Support

Sub-nanometer Pt@Rh nanoparticles highly dispersed on MIL-125-derived porous TiO₂ nanoplates are successfully prepared for the first time by a photochemical route, where the porous TiO₂ nanoplates with a relatively high specific surface area play a dual role as both effective photoreductant and catalyst support. The resulting Pt@Rh/p-TiO₂ can be utilized as a highly active catalyst.

Multifaceted Gold-Palladium Bimetallic Nanorods and Their Geometric, Compositional, and Catalytic Tunabilities

Kinetically controlled, seed-mediated co-reduction provides a robust and versatile synthetic approach to multimetallic nanoparticles with precisely controlled geometries and compositions. Here, we demonstrate that single-crystalline cylindrical Au nanorods selectively transform into a series of structurally distinct Au@Au-Pd alloy core-shell bimetallic nanorods with exotic multifaceted geometries enclosed by specific types of facets upon seed-mediated Au-Pd co-reduction under diffusion-controlled conditions. By adjusting several key synthetic parameters, such as the Pd/Au precursor ratio, the reducing agent concentration, the capping surfactant concentration, and foreign metal ion additives, we have been able to simultaneously fine-tailor the atomic-level surface structures and fine-tune the compositional stoichiometries of the multifaceted Au-Pd bimetallic nanorods. Using the catalytic hydrogenation of 4-nitrophenol by ammonia borane as a model reaction obeying the Langmuir-Hinshelwood kinetics, we further show that the relative surface binding affinities of the reactants and the rates of interfacial charge transfers, both of which play key roles in determining the overall reaction kinetics, strongly depend upon the surface atomic coordinations and the compositional stoichiometries of the colloidal Au-Pd alloy nanocatalysts. The insights gained from this work not only shed light on the underlying mechanisms dictating the intriguing geometric evolution of multimetallic nanocrystals during seed-mediated co-reduction but also provide an important knowledge framework that guides the rational design of architecturally sophisticated multimetallic nanostructures toward optimization of catalytic molecular transformations.

Bottom-Up Strategy To Prepare Nanoparticles with a Single DNA Strand

We describe the preparation of cross-linked, polymeric organic nanoparticles (ONPs) with a single, covalently linked DNA strand. The structure and functionalities of the ONPs are controlled by the synthesis of their parent linear block copolymers that provide monovalency, fluorescence and narrow size distribution. The ONP can also guide the deposition of chloroaurate ions allowing gold nanoparticles (AuNPs) to be prepared using the ONPs as templates. The DNA strand on AuNPs is shown to preserve its functions.

The selective hydrogenolysis of C–O bonds in lignin model compounds by Pd–Ni bimetallic nanoparticles in ionic liquids

β-O-4 and α-O-4 linkages can be selectively cleaved by Pd–Ni bimetallic nanoparticles in ionic liquids using hydrogen gas as the hydrogen donor under ambient pressure and neutral conditions.

Unraveling the Organotellurium Chemistry Applied to the Synthesis of Gold Nanomaterials

Long-term preservation of the properties of gold nanoparticles in both solution and the dry powder form can be difficult. We have overcome this challenge by using organotellurium derivatives as both reducing agents and stabilizers in the synthesis of gold nanoparticles. This new synthetic protocol takes advantage of the photochemical and oxidative properties of diphenyl ditelluride (Ph₂Te₂), which, so far, have never been exploited in the synthesis of gold nanoparticles. The Au/Te core/shell (inorganic/organic) hybrid nanomaterial can be obtained in a one-step reaction, using only Ph₂Te₂ and HAuCl₄. By modifying the reaction conditions, different resonance conditions of the gold core are achieved due to the formation of external shells with different thicknesses. The organotellurium shell can be easily removed by resuspension of the nanoparticles in environmentally friendly solvents, such as water or ethanol, making the Au core available for subsequent applications. A mechanism for the formation of core/shell nanoparticles has also been discussed.