Metallic nanocages: synthesis of bimetallic Pt-Pd hollow nanoparticles with dendritic shells by selective chemical etching

A novel one-step immunoassay using mesoporous core-shell Pd@Pt nanoparticles as an alternative to horseradish peroxidase for amantadine detection

The inherent limitations of natural enzymes hinder their stable application under harsh conditions, highlighting the urgent need for a stable alternative signal tracer. Herein, core-shell palladium@platinum (Pd@Pt) nanoparticles (NPs) with mesoporous and dendritic nanostructures were synthesized using a modified ultrasound-assisted chemical reduction method, resulting in a 25 % improvement in relative activity compared to previously reported methods. The yielding nanoparticles exhibited enhanced peroxidase-like activity with specific activity of 54.4 U/mg, and their Michaelis constant and maximum reaction velocity were 6.2 and 48 timers higher, respectively, than those of horseradish peroxidase (HRP). The Pd@Pt NPs were conjugated with antibodies via electrostatic adsorption, demonstrating their potential as a viable alternative to HRP. The rough surface structure of the Pd@Pt NPs not only enhanced the efficiency of antibody immobilization to approximately 90 %, but also, through a pH-regulated antibody immobilization strategy, facilitated the orientation of antibody recognition regions, thereby improving inhibition efficiency. A one-step immunoassay based on the Pd@Pt NPs immunoprobe was then developed, with amantadine (AMD) serving as a proof of concept. The proposed method showed a 2.8-fold increase in sensitivity, a 400-fold expansion in the linear range, and a 1-h reduction in detection time compared to the traditional "gold standard" ELISA. The practical applicability of the proposed method was validated in real chicken and pork samples, with coefficients of variation all less than 17.49 %, and a strong correlation with commercial kits was observed. These results suggest that Pd@Pt NPs are a promising signal-generating probe with significant potential as an alternative to HRP, offering improvements in sensitivity, linear range, stability, and other key performance characteristics.

Accelerated Selective Electrooxidation of Ethylene Glycol and Inhibition of C-C Dissociation Facilitated by Surficial Oxidation on Hollowed PtAg Nanostructures via In Situ Dynamic Evolution

Electro-upgrading of low-cost alcohols such as ethylene glycol is a promising and sustainable approach for the production of value-added chemicals while substituting energy-consuming OER in water splitting. However, the sluggish kinetics and possibility of C-C dissociation make the design of selective and efficient electrocatalysts challenging. Herein, we demonstrate the synthesis of a hollowed bimetallic PtAg nanostructure through an in situ dynamic evolution method that could efficiently drive the selective electrochemical ethylene glycol oxidation reaction (EGOR). The resulting mild surficial oxidation has intrinsically improved EGOR activity, exhibiting a remarkable performance toward glycolate (selectivity up to 99.2% and faradic efficiency ∼97%) at high current density with low overpotential (355 mA·cm-2 at 1.0 V, 16.3 A·mgPt -1), exceeding prior outcomes. Through comprehensive operando characterization and theoretical calculations, this study systematically reveals that the in situ formation of Pt-O(H)ad is pivotal for modulating the electronic structure of surface and facilitating the selective electrooxidation and adsorption of -CH2OH. The competitive C-C dissociation pathway toward HCOO- is concurrently inhibited in comparison to Pt. An industrial-level current coupled with hydrogen production at low cell voltages was also achieved. These findings offer more in-depth mechanistic understanding of the EGOR's reaction pathway mediated by surface environment in Pt-based electrocatalysts.

Recent Advances in Selective Chemical Etching of Nanomaterials for High-Performance Electrodes in Electrocatalysis and Energy Storage

To move beyond an energy economy dominated by fossil fuel utilization, high-performance electrochemical cells must be designed for energy storage and conversion. Selective etching is a promising, cost-effective solution-processing method for the large-scale top-down production of nanomaterials for high-performance electrodes. This review outlines general methodologies and mechanisms by which selective etching can be applied to create nanomaterials, including various template-assisted, facet-selective, and electrochemical methods, as well as in-depth case studies of state-of-the-art research involving selectively etched nanomaterials for electrocatalytic and energy storage applications. In addition, the standard design strategies by which the electrochemical performance of selectively etched nanomaterials is enhanced, including increased surface area, morphology, diffusion channels, heterojunction interfaces, and facet reactivity, are discussed. This review provides a foundation of knowledge for researchers seeking the rational design of nanomaterials for electrode application through selective etching.

2D Carbon-Anchored Platinum-Based Nanodot Arrays as Efficient Catalysts for Methanol Oxidation Reaction

Ultrafine Pt-based alloy nanoparticles supported on carbon substrates have attracted significant attention due to their catalytic potential. Nevertheless, ensuring the stability of these nanoparticles remains a critical challenge, impeding their broad application. In this work, novel nanodot arrays (NAs) are introduced where superfine alloy nanoparticles are uniformly implanted in a 2D carbon substrate and securely anchored. Electrochemical testing of the PtCo NAs demonstrates exceptional methanol oxidation reaction (MOR) activity, achieving 1.25 A mg-1. Moreover, the PtCo NAs exhibit outstanding stability throughout the testing period, underscoring the effectiveness of the anchoring mechanism. Comprehensive characterization and theoretical calculations reveal that the 2D carbon-anchored structure optimizes the electronic structure and coordination environment of Pt, restricts nanoparticle migration, and suppresses transition metal dissolution. This strategy represents a major advancement in addressing the stability limitations of ultrafine nanoparticles in catalytic applications and offers broader insights into the design of next-generation catalysts with enhanced durability and performance.

A dual-signal mode electrochemical aptasensor based on tetrahedral DNA nanostructures for sensitive detection of citrinin in food using PtPdCo mesoporous nanozymes

Citrinin (CIT) is a mycotoxin with nephrotoxicity and hepatotoxicity, presenting a significant threat to human health that is often overlooked. Therefore, a dual-signal mode (DPV and SWV) aptasensor for citrinin (CIT) detection was constructed based on tetrahedral DNA nanostructures (TDN) in this study. Furthermore, PtPdCo mesoporous nanozymes exhibit catalase-like catalytic functions, generating significant electrochemical signals through a Fenton-like reaction. Meanwhile their excellent Methylene Blue (MB) loading capability ensures independent dual signal outputs. The RecJf exonuclease-assisted (RecJf Exo-assisted) process can expand the linear detection range, enabling further amplification of the signal. Under optimized conditions, the constructed aptaensor exhibited excellent detection performance with limits of detection (LODs) of 7.67 × 10-3 ng·mL-1 (DPV mode) and 1.57 × 10-3 ng·mL-1 (SWV mode). Due to its multiple signal amplification and highly accurate dual-signal mode detection capability, this aptasensor shows promising potential for the in situ detection.

Tailored Design of Mesoporous Nanospheres with High Entropic Alloy Sites for Efficient Redox Electrocatalysis

High Entropy Alloys (HEAs) are a versatile material with unique properties, tailored for various applications. They enable pH-sensitive electrocatalytic transformations like hydrogen evolution reaction (HER) and hydrogen oxidation reactions (HOR) in alkaline media. Mesoporous nanostructures with high surface area are preferred for these electrochemical reactions, but designing mesoporous HEA sis challenging. To overcome this challenge, a low-temperature triblock copolymer-assisted wet-chemical approach is developed to produce mesoporous HEA nanospheres composed of PtPdRuMoNi systems with sufficient entropic mixing. Owing to active sites with inherent entropic effect, mesoporous features, and increased accessibility, optimized HEA nanospheres promote strong HER/HOR performance in alkaline medium. At 30 mV nominal overpotential, it exhibits a mass activity of ≈167 (HER) and 151 A gPt -1 (HOR), far exceeding commercial Pt-C electrocatalysts (34 and 48 A gPt -1) and many recently reported various alloys. The Mott-Schottky analysis reveals HEA nanospheres inherit high charge carrier density, positive flat band potential, and smaller charge transfer barrier, resulting in better activity and faster kinetics. This micelle-assisted synthetic enable the exploration of the compositional and configurational spaces of HEAs at relatively low temperature, while simultaneously facilitating the introduction of mesoporous nanostructures for a wide range of catalytic applications.

The Effect of the Pd Precursors on the Shape of Hollow Ag-Pd Alloy Nanoparticles Using Ag Nanocubes as Seeds

Hollow Ag-Pd nanoparticles have potentially high catalytic performance owing to their larger surface area compared to their corresponding solid nanoparticles. We successfully fabricated hollow Ag-Pd alloy nanodendrites and nanoboxes by using different Pd precursors (H2PdCl4 and Pd(acac)2) to achieve large surface area nanoboxes. Interestingly, the use of a H2PdCl4 precursor led to the formation of hollow nanodendrite structures, whereas the slower reduction of Pd(acac)2 led to the formation of hollow nanoboxes. The microstructure and chemical composition of Ag-Pd nanoparticles and properties of their growth solutions were investigated by transmission electron microscopy, energy-dispersive X-ray spectroscopy, and ultraviolet-visible spectroscopy.

Mesoporous multimetallic nanospheres with exposed highly entropic alloy sites

Multimetallic alloys (MMAs) with various compositions enrich the materials library with increasing diversity and have received much attention in catalysis applications. However, precisely shaping MMAs in mesoporous nanostructures and mapping the distributions of multiple elements remain big challenge due to the different reduction kinetics of various metal precursors and the complexity of crystal growth. Here we design a one-pot wet-chemical reduction approach to synthesize core-shell motif PtPdRhRuCu mesoporous nanospheres (PtPdRhRuCu MMNs) using a diblock copolymer as the soft template. The PtPdRhRuCu MMNs feature adjustable compositions and exposed porous structures rich in highly entropic alloy sites. The formation processes of the mesoporous structures and the reduction and growth kinetics of different metal precursors of PtPdRhRuCu MMNs are revealed. The PtPdRhRuCu MMNs exhibit robust electrocatalytic hydrogen evolution reaction (HER) activities and low overpotentials of 10, 13, and 28 mV at a current density of 10 mA cm-2 in alkaline (1.0 M KOH), acidic (0.5 M H2SO4), and neutral (1.0 M phosphate buffer solution (PBS)) electrolytes, respectively. The accelerated kinetics of the HER in PtPdRhRuCu MMNs are derived from multiple compositions with synergistic interactions among various metal sites and mesoporous structures with excellent mass/electron transportation characteristics.

Te-induced fabrication of Pt3PdTe0.2 alloy nanocages by the self-diffusion of Pd atoms with unique MOR electrocatalytic performance

The key to the application of direct methanol fuel cells is to improve the activity and durability of Pt-based catalysts. Based on the upshift of the d-band centre and exposure to more Pt active sites, Pt3PdTe0.2 catalysts with significantly enhanced electrocatalytic performance for the methanol oxidation reaction (MOR) were designed in this study. A series of different Pt3PdTex (x = 0.2, 0.35, and 0.4) alloy nanocages with hollow and hierarchical structures were synthesized using cubic Pd nanoparticles as sacrificial templates and PtCl62- and TeO32- metal precursors as oxidative etching agents. The Pd nanocubes were oxidized into an ionic complex, which was further co-reduced with Pt and Te precursors by reducing agents to form the hollow Pt3PdTex alloy nanocages with a face-centred cubic lattice. The sizes of the nanocages were around 30-40 nm, which were larger than the Pd templates (18 nm) and the thicknesses of the walls were 7-9 nm. The Pt3PdTe0.2 alloy nanocages exhibited the highest catalytic activities and stabilities toward the MOR after electrochemical activation in sulfuric acid solution. CO-stripping tests suggested the enhanced CO-tolerant ability due to the doping of Te. The specific activity of Pt3PdTe0.2 for the MOR reached 2.71 mA cm-2 in acidic conditions, which was higher than those of Pd@Pt core-shell and PtPd1.5 alloy nanoparticles and commercial Pt/C. A DMFC with Pt3PdTe0.2 as the anodic catalyst output a higher power density by 2.6 times than that of commercial Pt/C, demonstrating its practicable application in clean energy conversions. Density functional theory (DFT) confirmed that the alloyed Te atoms altered the electron distributions of Pt3PdTe0.2, which could lower the Gibbs free energy of the rate-determining methanol dehydrogenation step and greatly improve the MOR catalytic activity and durability.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Black Silver Nanocubes@Amino Acid-Encoded Highly Branched Gold Shells with Efficient Photothermal Conversion for Tumor Therapy

Cancers are among the leading causes of death currently. Conventional radiotherapy and chemotherapy are of limited use in the treatment of some tumors due to their high toxicity and drug resistance. Plasma photothermal therapy has attracted extensive attention for the treatment of tumors due to photothermal properties of plasmonic nanoparticles, such as gold (Au) nanoparticles, to achieve local hyperthermia with low toxicity and high efficiency. Herein, we report a kind of special black noble-metal core-shell nanostructure, with silver (Ag) nanocubes as the core and amino acid-encoded highly branched Au nanorods as the shells (l-CAg@Au and d-CAg@Au). The proposed growth of l-CAg@Au and d-CAg@Au nanocomposites was an amino acid-encoded Stranski-Krastanov mode. Both l-CAg@Au and d-CAg@Au exhibited outstanding photothermal conversion compared to the core-shell structure without amino acids (Ag@Au). d-CAg@Au possessed the best photothermal conversion efficiency (87.28%) among the composite nanoparticles. The antitumor therapeutic efficacy of as-prepared samples was evaluated in vitro and in vivo, and apoptosis analysis was done via flow cytometry. This work reports novel insights for the preparation of special bimetallic branched structures and broadens the application of metal nanomaterials in photothermal tumor therapy.

Pt-Based Oxygen Reduction Reaction Catalysts in Proton Exchange Membrane Fuel Cells: Controllable Preparation and Structural Design of Catalytic Layer

Proton exchange membrane fuel cells (PEMFCs) have attracted extensive attention because of their high efficiency, environmental friendliness, and lack of noise pollution. However, PEMFCs still face many difficulties in practical application, such as insufficient power density, high cost, and poor durability. The main reason for these difficulties is the slow oxygen reduction reaction (ORR) on the cathode due to the insufficient stability and catalytic activity of the catalyst. Therefore, it is very important to develop advanced platinum (Pt)-based catalysts to realize low Pt loads and long-term operation of membrane electrode assembly (MEA) modules to improve the performance of PEMFC. At present, the research on PEMFC has mainly been focused on two areas: Pt-based catalysts and the structural design of catalytic layers. This review focused on the latest research progress of the controllable preparation of Pt-based ORR catalysts and structural design of catalytic layers in PEMFC. Firstly, the design principle of advanced Pt-based catalysts was introduced. Secondly, the controllable preparation of catalyst structure, morphology, composition and support, and their influence on catalytic activity of ORR and overall performance of PEMFC, were discussed. Thirdly, the effects of optimizing the structure of the catalytic layer (CL) on the performance of MEA were analyzed. Finally, the challenges and prospects of Pt-based catalysts and catalytic layer design were discussed.

Advances in plasmonic-based MOF composites, their bio-applications and perspectives in this field

INTRODUCTION

Nanomaterials have been used for bio-applications since the late 20st century. In an attempt to tailor and optimize their properties, and by extension their efficiency, composites have attracted considerable attention. In this regard, recent studies on plasmonic nanoparticles and metal-organic framework (NP@MOF) composites suggested these materials show great promise in this field.

AREAS COVERED

This review focused on the more recent scientific advances in the synthetic strategies to optimize plasmonic MOF nanocomposites currently available, as well as their bio-application, particularly as biosensors and therapy.

EXPERT OPINION

Plasmonic MOF nanocomposites have shown great potential as they combine the properties of both materials with proven efficiency in bio-application. On the one hand, nanoMOFs have proven their potential particularly as drug nanocarriers, owing to their exceptional porosity and tunability. On the other hand, plasmonic nanoparticles have been an asset for imaging and phototherapy. Different strategies have been reported to develop these nanocomposites, mainly including core-shell, encapsulation, and in situ reduction. In addition, advanced composite structures should be considered, such as mixed metal nanoparticles, hollow structures or the combination of several approaches. Specifically, plasmonic MOF nanocomposites prove to be attractive stimuli responsive drug delivery systems, phototherapeutic agents as well as highly sensitive biosensors.

Hierarchical Design in Nanoporous Metals

Hierarchically porous metals possess intriguing high accessibility of matter molecules and unique continuous metallic frameworks, as well as a high level of exposed active atoms. High rates of diffusion and fast energy transfer have been important and challenging goals of hierarchical design and porosity control with nanostructured metals. This review aims to summarize recent important progress toward the development of hierarchically porous metals, with special emphasis on synthetic strategies, hierarchical design in structure-function and corresponding applications. The current challenges and future prospects in this field are also discussed.

Engineering ultrathin PdAu nanoring via a facile process for electrocatalytic ethanol oxidation

Ultrathin nanoframes with more available electrocatalytic active sites on both internal and external surfaces have attracted great attention especially in the field of electrocatalysis. Herein, we report a facile process to prepare PdAu nanorings (NRs) in aqueous solution without adding any organic ligands. The growth mechanism of PdAu NRs was explored in detail. The Au precursors were reduced into Au clusters around the edges of Pd nanosheets (NSs) via galvanic replacement, then the center of Pd NSs was oxidatively etched by Cl^-/O₂, and finally the Pd and Au atoms on the edge sites were rearranged to form uniform PdAu alloy. PdAu NRs with different ratios and ternary PdAuPt NRs could be easily prepared using this strategy. Owing to the synergistically structural and compositional advantages, Pd₇₉Au₂₁ NRs exhibited higher electrocatalytic activity and stability, as well as low activation energy (E_a) for the ethanol electrooxidation reaction.

Noble-Metal-Based Hollow Mesoporous Nanoparticles: Synthesis Strategies and Applications

As second-generation mesoporous materials, mesoporous noble metals (NMs) are of significant interest for their wide applications in catalysis, sensing, bioimaging, and biotherapy owing to their structural and metallic features. The introduction of interior hollow cavity into NM-based mesoporous nanoparticles (MNs), which subtly integrate hierarchical hollow and mesoporous structure into one nanoparticle, produces a new type of hollow MNs (HMNs). Benefiting from their higher active surface, better electron/mass transfer, optimum electronic structure, and nanoconfinement space, NM-based HMNs exhibit their high efficiency in enhancing catalytic activity and stability and tuning catalytic selectivity. In this review, recent progress in the design, synthesis, and catalytic applications of NM-based HMNs is summarized, including the findings of the groups. Five main strategies for synthesizing NM-based HMNs, namely silica-assisted surfactant-templated nucleation, surfactant-templated sequential nucleation, soft "dual"-template, Kirkendall effect in synergistic template, and galvanic-replacement-assisted surfactant template, are described in detail. In addition, the applications in ethanol oxidation electrocatalysis and hydrogenation reactions are discussed to highlight the high activity, enhanced stability, and optimal selectivity of NM-based HMNs in (electro)catalysis. Finally, the further outlook that may lead the directions of synthesis and applications of NM-based HMNs is prospected.

Hollow Multicomponent Capsules for Biomedical Applications: A Comprehensive Review

Hollow capsules with multi-shelled or multicomponent structures are essential materials for various applications. Biomedical applications like disease diagnosis, therapy, and monitoring have special significance as they aim to improve health conditions. This review demonstrated a comprehensive overview of hollow, multifunctional structures incorporating meaningful use of nanotechnology and its’ unique prospects in medicine such as patient-specific treatment, multimodal imaging, multimodal therapy, simultaneous delivery of drugs and imaging probes, and actively targeted delivery. The internal hollow cavity provides safe and controlled drug release while also enabling transport of functional moieties to target sites. This review explored the performance of different organic, inorganic, and metallic multicomponent capsules that have been reported for biomedical applications, mainly diagnostic imaging and drug delivery. Material compositions, morphologies, and synthesis strategies involved in fabricating such multifunctional systems have been discussed in detail. It is expected that with time, more sophisticated and precise systems will come to light as the outcome of ongoing concentrated research efforts.

One-Pot Aqueous Synthesis of Porous Hollow PdCu Alloy Nanoparticles for Enhanced Ethanol Electrooxidation

Bimetallic PdCu porous hollow nanoparticles (PHNs) with hierarchical nanostructures and well-alloyed compositions were precisely synthesized through a one-pot aqueous synthetic route. Bimetallic PdCu PHNs exhibited multiple enhancement synergies and thus performed well in ethanol oxidation electrocatalysis with remarkable activity and stability. This work expedites rational design and synthesis of the high-hierarchy alloy electrocatalysts for fuel cell electrocatalysis.

Mesoporous PdBi nanocages for enhanced electrocatalytic performances by all-direction accessibility and steric site activation

An effective yet simple approach was developed to synthesize mesoporous PdBi nanocages for electrochemical applications. This technique relies on the subtle utilization of the hydrolysis of a metal salt to generate precipitate cores in situ as templates for navigating the growth of mesoporous shells with the assistance of polymeric micelles. The mesoporous PdBi nanocages are then obtained by excavating vulnerable cores and regulating the crystals of mesoporous metallic skeletons. The resultant mesoporous PdBi nanocages exhibited excellent electrocatalytic performance toward the ethanol oxidation reaction with a mass activity of 3.56 A mg-1_Pd, specific activity of 17.82 mA cm-2 and faradaic efficiency of up to 55.69% for C1 products.

Mesoporous Core-Shell Pd@Pt Nanospheres as Oxidase Mimics with Superhigh Catalytic Efficiency at Room Temperature

Mesoporous Pt-Pd bimetallic core-shell nanospheres (mPd@Pt NSs) with palladium-rich cores and platinum-rich shells were synthesized via a simple, two-step, wet chemical strategy mediated by nitrogen-doped carbon dots. The BET surface area of mPd@Pt NSs was found to be 210.4 m²·g^-1, which is significantly higher than the currently reported unsupported Pt-based nanomaterials. Because of the large active surface area, the as-prepared mPd@Pt NSs show superhigh oxidase activity and exhibit excellent oxidase-like catalytic efficiency with a catalytic constant (K_cat) as high as 2.1 × 10³ s^-1 at room temperature, which is of the same order of magnitude as the natural horseradish peroxidase (HRP) (K_cat = 4.3 × 10³ s^-1) at 37 °C and five-fold greater than the reported K_cat values of oxidase-like nanozyme obtained at 30 °C.

Mesoporous Noble Metal-Metalloid/Nonmetal Alloy Nanomaterials: Designing Highly Efficient Catalysts

Mesoporous metals have received increasing attention in catalysis and related applications because of their novel physicochemical properties and functional geometric features. Control of multicomponent compositions and crystalline structures of mesoporous metals is critical for their applications. Recently, mesoporous metals have gradually expanded from traditional metal-metal alloys to metal-metalloid/nonmetal alloys with random solids and/or ordered intermetallics. As new, highly efficient nanocatalysts, mesoporous metal-metalloid/nonmetal alloys not only increase the utilization efficiency of precious noble metals and accelerate electron/mass transfer but also introduce new functions and optimize the surface electronic structure of metal sites, all of which enhance their catalytic activity and stability and tune their catalytic selectivity. In this Perspective, we focus on the latest developments in this area, including the findings from our group regarding the rational design and targeted synthesis of mesoporous noble metal-metalloid/nonmetal alloy nanocatalysts. We summarize the current synthetic strategies for mesoporous noble metal-metalloid/nonmetal alloys and discuss key effects of crystalline mesoporosity and metalloid/nonmetal alloys in enhancing catalytic performances of noble metal catalysts. We also describe the current bottlenecks and major challenges to explore further directions in synthesis and applications of mesoporous noble metal-metalloid/nonmetal alloys.

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.

Au/Pt-Egg-in-Nest Nanomotor for Glucose-Powered Catalytic Motion and Enhanced Molecular Transport to Living Cells

Nanostructures converting chemical energy to mechanical work by using benign metabolic fuels, have huge implications in biomedical science. Here, we introduce Au/Pt-based Janus nanostructures, resembling to "egg-in-nest" morphology (Au/Pt-ENs), showing enhanced motion as a result of dual enzyme-relay-like catalytic cascade in physiological biomedia, and in turn showing molecular-laden transport to living cells. We developed dynamic-casting approach using silica yolk-shell nanoreactors: first, to install a large Au-seed fixing the silica-yolk aside while providing the anisotropically confined concave hollow nanospace to grow curved Pt-dendritic networks. Owing to the intimately interfaced Au and Pt catalytic sites integrated in a unique anisotropic nest-like morphology, Au/Pt-ENs exhibited high diffusion rates and displacements as the result of glucose-converted oxygen concentration gradient. High diffusiophoresis in cell culture media increased the nanomotor-membrane interaction events, in turn facilitated the cell internalization. In addition, the porous network of Au/Pt-ENs facilitated the drug-molecule cargo loading and delivery to the living cells.

Graphene-coated nanoporous nickel towards a metal-catalyzed oxygen evolution reaction

Developing highly active electrocatalysts with low costs and long durability for oxygen evolution reactions (OERs) is crucial towards the practical implementations of electrocatalytic water-splitting and rechargeable metal-air batteries. Anodized nanostructured 3d transition metals and alloys with the formation of OER-active oxides/hydroxides are known to have high catalytic activity towards OERs but suffer from poor electrical conductivity and electrochemical stability in harsh oxidation environments. Here we report that high OER activity can be achieved from the metallic state of Ni which is passivated by atomically thick graphene in a three-dimensional nanoporous architecture. As a free-standing catalytic anode, the non-oxide transition metal catalyst shows a low OER overpotential, high OER current density and long cycling lifetime in alkaline solutions, benefiting from the high electrical conductivity and low impedance resistance for charge transfer and transport. This study may pave a new way to develop high efficiency transition metal OER catalysts for a wide range of applications in renewable energy.

Interfacial Electron Engineering of Palladium and Molybdenum Carbide for Highly Efficient Oxygen Reduction

Interfacial electron engineering between noble metal and transition metal carbide is identified as a powerful strategy to improve the intrinsic activity of electrocatalytic oxygen reduction reaction (ORR). However, this short-range effect and the huge structural differences make it a significant challenge to obtain the desired electrocatalyst with atomically thin noble metal layers. Here, we demonstrated the combinatorial strategies to fabricate the heterostructure electrocatalyst of Mo₂C-coupled Pd atomic layers (AL-Pd/Mo₂C) by precise control of metal-organic framework confinement and covalent interaction. Both atomic characterizations and density functional theory calculations uncovered that the strong electron effect imposed on Pd atomic layers has intensively regulated the electronic structures and d-band center and then optimized the reaction kinetics. Remarkably, AL-Pd/Mo₂C showed the highest ORR electrochemical activity and stability, which delivered a mass activity of 2.055 A mg_Pd^-1 at 0.9 V, which is 22.1, 36.1, and 80.3 times higher than Pt/C, Pd/C, and Pd nanoparticles, respectively. The present work has developed a novel approach for atomically noble metal catalysts and provides new insights into interfacial electron regulation.

Recent advances in Pt-based electrocatalysts for PEMFCs

In order to reduce the cost and improve the performance of proton exchange membrane fuel cells (PEMFCs), it is imperative to further enhance the activity and durability of Pt based electrocatalysts for the oxygen reduction reaction (ORR). This article analyzes the latest advances in Pt-based ORR electrocatalysts, including the Pt alloys, Pt–M core–shell structures, particle size effects, support effects, doping in Pt/PtM and post treatment. In addition, the performance of some of the developed novel electrocatalysts in membrane electrode assemblies (MEA) is also included for comparison, as they are rarely available and the superior activity and durability exhibited in RDE frequently doesn't translate into MEA.

In this paper, the latest progress in the design of Pt-based ORR electrocatalysts is reviewed, including the understanding of research progress in the synthesis of high activity and high stability catalysts.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

PtPd hollow nanocubes with enhanced alloy effect and active facets for efficient methanol oxidation reaction

An alternating-reduction approach is developed to fabricate PtPd hollow nanocubes with highly catalytically-favoured {100} facets and enhanced alloy effect for efficient methanol oxidation reaction.

Ruthenium nanodendrites on reduced graphene oxide: an efficient water and 4-nitrophenol reduction catalyst

A green and efficient protocol is reported for the elegant design of reduced graphene oxide (rGO)-supported Ru nanodendrites for promotion of electrochemical water reduction in a wide pH range as well as for environmental remediation.

A universal approach for the synthesis of mesoporous gold, palladium and platinum films for applications in electrocatalysis

High-surface-area mesoporous materials expose abundant functional sites for improved performance in applications such as gas storage/separation, catalysis, and sensing. Recently, soft templates composed of amphiphilic surfactants and block copolymers have been used to introduce mesoporosity in various materials, including metals, metal oxides and carbonaceous compounds. In particular, mesoporous metals are attractive in electrocatalysis because their porous networks expose numerous unsaturated atoms on high-index facets that are highly active in catalysis. In this protocol, we describe how to create mesoporous metal films composed of gold, palladium, or platinum using block copolymer micelle templates. The amphiphilic block copolymer micelles are the sacrificial templates and generate uniform structures with tunable pore sizes in electrodeposited metal films. The procedure describes the electrodeposition in detail, including parameters such as micelle diameters, deposition potentials, and deposition times to ensure reproducibility. The micelle diameters can be controlled by swelling the micelles with different solvent mixtures or by using block copolymer micelles with different molecular weights. The deposition potentials and deposition times allow further control of the mesoporous structure and its thickness, respectively. Procedures for example applications are included: glucose oxidation, ethanol oxidation and methanol oxidation reactions. The synthetic methods for preparation of mesoporous metal films will take ~4 h; the subsequent electrochemical tests will take ~5 h for glucose sensing and ~3 h for alcohol oxidation reaction.

Electrochemical Synthesis of Mesoporous Architectured Ru Films Using Supramolecular Templates

The electrochemical synthesis of mesoporous ruthenium (Ru) films using sacrificial self-assembled block polymer micelles templates, and its electrochemical surface oxidation to RuO_x is described. Unlike standard methods such as thermal oxidation, the electrochemical oxidation method described here retains the mesoporous structure. Ru oxide materials serve as high-performance supercapacitor electrodes due to their excellent pseudocapacitive behavior. The mesoporous architectured film shows superior specific capacitance (467 F g^-1_Ru ) versus a nonporous Ru/RuO_x electrode (28 F g^-1_Ru ) that is prepared via the same method but omitting the pore-directing polymer. Ultrahigh surface area materials will play an essential role in increasing the capacitance of this class of energy storage devices because the pseudocapacitive redox reaction occurs on the surface of electrodes.

NIR Stimulus-Responsive PdPt Bimetallic Nanoparticles for Drug Delivery and Chemo-Photothermal Therapy

The combination of chemotherapy and phototherapy has attracted increasing attention for cancer treatment in recent years. In the current study, porous PdPt bimetallic nanoparticles (NPs) were synthesized and used as delivery carriers for the anti-cancer drug doxorubicin (DOX). DOX@PdPt NPs were modified with thiol functionalized hyaluronic acid (HA-SH) to generate DOX@PdPt@HA NPs with an average size of 105.2 ± 6.7 nm. Characterization and in vivo and in vitro assessment of anti-tumor effects of DOX@PdPt@HA NPs were further performed. The prepared DOX@PdPt@HA NPs presented a high photothermal conversion efficiency of 49.1% under the irradiation of a single 808 nm near-infrared (NIR) laser. Moreover, NIR laser irradiation-induced photothermal effect triggered the release of DOX from DOX@PdPt@HA NPs. The combined chemo-photothermal treatment of NIR-irradiated DOX@PdPt@HA NPs exerted a stronger inhibitory effect on cell viability than that of DOX or NIR-irradiated PdPt@HA NPs in mouse mammary carcinoma 4T1 cells in vitro. Further, the in vivo combination therapy, which used NIR-irradiated DOX@PdPt@HA NPs in a mouse tumor model established by subcutaneous inoculation of 4T1 cells, was demonstrated to achieve a remarkable tumor-growth inhibition in comparison with chemotherapy or photothermal therapy alone. Results of immunohistochemical staining for caspase-3 and Ki-67 indicated the increased apoptosis and decreased proliferation of tumor cells contributed to the anti-tumor effect of chemo-photothermal treatment. In addition, DOX@PdPt@HA NPs induced negligible toxicity in vivo. Hence, the developed nanoplatform demonstrates great potential for applications in photothermal therapy, drug delivery and controlled release.

Controllable Conversion of CdNCN Nanoparticles into Various Chalcogenide Nanostructures for Photo-driven Applications

Semiconductor nanocrystals of tunable shell/core configurations have great potential in photo-driven applications such as photoluminescence and photocatalysis, but few strategies realize a controllable synthesis with respect to both the size of the core and the shell with high crystallinity. Here, a new synthetic method based on cadmium cyanamide (CdNCN) nanoparticle anion exchange reactions was developed to access solid or hollow CdSe nanocrystals with tunable size and CdNCN@CdS heterostructures with modulated shell/core thickness. The gradual shift and narrow width of photoluminescence features demonstrate the high crystallinity and monodispersity of the resulting CdSe nanocrystals. In the CdNCN@CdS heterostructures, synergistic effects of the photocarrier separation is observed between the CdS shell and CdNCN core, which leads to great improvement in photocatalysis with optimized shell/core ratio.

Nanoengineering 2D Dendritic PdAgPt Nanoalloys with Edge-Enriched Active Sites for Enhanced Alcohol Electroxidation and Electrocatalytic Hydrogen Evolution

Lots of research studies reveal that the surface atoms on the top/bottom facets of the nanosheets are the key features in enhancing electrocatalytic activity while the edge and corner sites of electrocatalysts often possess superior activity. Herein, we report 2D dendritic PdAgPt ternary nanoalloys with abundant crystal defects such as steps, twin boundary, and atomic holes, which can effectively work as catalytic active-sites. The morphology of PdAgPt nanoalloys can be regulated readily from dendritic nanosheets to nanowheels. Compared with binary Pd₆₈Ag₃₂ nanodendrites, Pd₆₂Pt₃₈ nanospheres, and Pt/C catalyst, the composition- and morphology-optimized Pd₄₃Ag₂₁Pt₃₆ nanowheels exhibit the best mass/specific activity and stability for methanol/ethanol oxidation reaction (MOR/EOR). The mass peak current density for EOR/MOR of Pd₄₃Ag₂₁Pt₃₆ is 7.08/3.50 times of the Pt/C catalyst. Simultaneously, the hydrogen evolution reaction performance of the Pd₄₃Ag₂₁Pt₃₆ nanowheels in terms of the lowest overpotential of 9 mv at a current density of 10 mA/cm² and high electrochemical stability is much better than that of binary Pd₆₈Ag₃₂ nanodendrites, Pd₆₂Pt₃₈ nanospheres, and Pt/C.

Nanocatalosomes as Plasmonic Bilayer Shells with Interlayer Catalytic Nanospaces for Solar-Light-Induced Reactions

Interest and challenges remain in designing and synthesizing catalysts with nature-like complexity at few-nm scale to harness unprecedented functionalities by using sustainable solar light. We introduce "nanocatalosomes"-a bio-inspired bilayer-vesicular design of nanoreactor with metallic bilayer shell-in-shell structure, having numerous controllable confined cavities within few-nm interlayer space, customizable with different noble metals. The intershell-confined plasmonically coupled hot-nanospaces within the few-nm cavities play a pivotal role in harnessing catalytic effects for various organic transformations, as demonstrated by "acceptorless dehydrogenation", "Suzuki-Miyaura cross-coupling" and "alkynyl annulation" affording clean conversions and turnover frequencies (TOFs) at least one order of magnitude higher than state-of-the-art Au-nanorod-based plasmonic catalysts. This work paves the way towards next-generation nanoreactors for chemical transformations with solar energy.

Engineering bunched Pt-Ni alloy nanocages for efficient oxygen reduction in practical fuel cells

Development of efficient and robust electrocatalysts is critical for practical fuel cells. We report one-dimensional bunched platinum-nickel (Pt-Ni) alloy nanocages with a Pt-skin structure for the oxygen reduction reaction that display high mass activity (3.52 amperes per milligram platinum) and specific activity (5.16 milliamperes per square centimeter platinum), or nearly 17 and 14 times higher as compared with a commercial platinum on carbon (Pt/C) catalyst. The catalyst exhibits high stability with negligible activity decay after 50,000 cycles. Both the experimental results and theoretical calculations reveal the existence of fewer strongly bonded platinum-oxygen (Pt-O) sites induced by the strain and ligand effects. Moreover, the fuel cell assembled by this catalyst delivers a current density of 1.5 amperes per square centimeter at 0.6 volts and can operate steadily for at least 180 hours.

A convenient detection system consisting of efficient Au@PtRu nanozymes and alcohol oxidase for highly sensitive alcohol biosensing

Effective alcohol detection represents a substantial concern not only in the context of personal and automobile safety but also in clinical settings as alcohol is a contributing factor in a wide range of health complications including various types of liver cirrhoses, strokes, and cardiovascular diseases. Recently, many kinds of nanomaterials with enzyme-like properties have been widely used as biosensors. Herein, we have developed a convenient detection method that combines Au@PtRu nanozymes and alcohol oxidase (AOx). We found that the Au@PtRu nanorods exhibited peroxidase-like catalytic activity that was much higher than the catalytic activities of the Au and Au@Pt nanorods. The Au@PtRu nanorod-catalyzed generation of hydroxyl radicals in the presence of H₂O₂ was used to develop an alcohol sensor by monitoring the H₂O₂ formed by the oxidation of alcohol to acetaldehyde in the presence of AOx. When coupled with AOx, alcohol was detected down to 23.8 μM in a buffer solution for biological assays. Notably, alcohol was successfully detected in mouse blood samples with results comparable to that from commercial alcohol meters. These results highlight the potential of the Au@PtRu nanorods with peroxidase-like activity for alcohol detection, which opens up a new avenue for nanozyme development for biomedical applications.

Formation Mechanism and Gram-Scale Production of PtNi Hollow Nanoparticles for Oxygen Electrocatalysis through In Situ Galvanic Displacement Reaction

Galvanic displacement reaction has been considered a simple method for fabricating hollow nanoparticles. However, the formation of hollow interiors in nanoparticles is not easily achieved owing to the easy oxidization of transition metals, which results in mixed morphologies, and the presence of surfactants on the nanoparticle surface, which severely deteriorates the catalytic activity. In this study, we developed a facile gram-scale methodology for the one-pot preparation of carbon-supported PtNi hollow nanoparticles as an efficient and durable oxygen reduction electrocatalyst without using stabilizing agents or additional processes. The hollow structures were evolved from sacrificial Ni nanoparticles via an in situ galvanic displacement reaction with a Pt precursor, directly following a preannealing process. By sampling the PtNi/C hollow nanoparticles at various reaction times, the structural formation mechanism was investigated using transmission electron microscopy with energy-dispersive X-ray spectroscopy mapping/line-scan profiling. We found out that the structure and morphology of the PtNi hollow nanoparticles were controlled by the acidity of the metal precursor solution and the nanoparticle core size. The synthesized PtNi hollow nanoparticles acted as an oxygen reduction electrocatalyst, with a catalytic activity superior to that of a commercial Pt catalyst. Even after 10 000 cycles of harsh accelerated durability testing, the PtNi/C hollow electrocatalyst showed high performance and durability. We concluded that the Pt-rich layers on the PtNi hollow nanoparticles improved the catalytic activity and durability considerably.

Point-of-care assay for drunken driving with Pd@Pt core-shell nanoparticles-decorated ploy(vinyl alcohol) aerogel assisted by portable pressure meter

Alcohol abuse causes health problems and security accidents. A reliable and sensitive detection system for alcohol has been an instinctive demand in law enforcement and forensic. More efforts are demanded in developing new sensing strategy preferably with portable and non-invasive traits for the pushforward of point-of-care (POC) device popularization.

Methods: We developed a POC diagnosis system for alcohol assay with the aid of alcohol oxidase (AOX) pre-joining in the system as well as Pd@Pt core-shell nanoparticles (abbreviated to Pd@Pt) that were decorated on ploy(vinyl alcohol) aerogel with amphiphilicity. Biological samples like saliva and whole blood can be absorbed by the aerogel in a quick process, in which the analyte would go through a transformation from alcohol, H₂O₂, to a final production of O₂, causing an analyte dose-dependent signal change in the commercial portable pressure meter. The cascade reactions are readily catalyzed by AOX and Pd@Pt, of which the latter one possesses excellent peroxidase-like activity.

Results: Our design has smartness embodied in the aerogel circumvents the interference from methanol which is more ready to be catalyzed by AOX. Under the optimal conditions, the limit of detection for alcohol was 0.50 mM in saliva, and is able to distinguish the driving under the influence (DUI) (1.74 mM in saliva) and driving while impaired (DWI) (6.95 mM in saliva) in the national standard of China.

Conclusion: Our proof-of-concept study provides the possibility for the establishment of POC device for alcohol and other target detection, not only owing to the sensing qualification but also thanks to the architecture of such sensor that has great flexibility by replacing the AOX with glucose oxidase (GOX), thenceforth realizing the accurate detection of glucose in 0.5% whole blood sample. With the advantages of easy accessibility and anti-interference ability, our sensor exhibits great potential for quantitative diagnostics in biological system.