Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity

Thermally activated microstructural evolution of metallic heterophase nanoparticles: insights from molecular dynamics simulations

A crystal phase is a key factor to determine the physical and chemical properties of crystalline materials. As a new class of nanoscale structures, heterophase nanoparticles, which assemble conventional and unconventional phases, exhibit exceptional properties in comparison with their single-phase counterparts. In this work, we explored the thermodynamic stability of Au, Co, and AuCo heterophase nanoparticles with fcc and hcp phases by using molecular dynamics simulations. These heterostructured nanoparticles were continuously heated to examine their thermally activated structural evolutions. Au and Co single-phase nanoparticles were also considered for comparison. The results show that the phase transition between fcc and hcp is absent in these heterophase nanoparticles despite the existence of an unconventional phase. Although the melting of Au and Co heterophase nanoparticles is homogeneous, AuCo heterophase nanoparticles show heterogeneous melting, i.e., the Au fcc domain firstly melts, followed by the melting of the Co hcp domain, exhibiting a typical two-stage melting characteristic and resulting in the existence of a solid-core/liquid-shell structure within a considerable temperature region. Furthermore, the mutual diffusion of atoms between fcc and hcp domains is observed in the Au and Co heterophase nanoparticles. However, the unidirectional diffusion from the Au domain to the Co domain is found in the AuCo heterophase nanoparticles prior to their overall melting. This study deepens the fundamental understanding of the thermodynamic evolution of metallic heterogeneous nanoparticles and provides mechanistic and quantitative guidance for the rational design and applications of nanoscale multiphase heterostructures.

Efficient ABEI-Dissolved O2-Ce(III, IV)-MOF Ternary Electrochemiluminescent System Combined with Self-Assembled Microfluidic Chips for Bioanalysis

A signal-amplified electrochemiluminescent (ECL) sensor chip was developed for sensitive analysis of procalcitonin (PCT). Herein, we first prepared a self-enhanced luminophore, which enhanced ECL responses through intramolecular reactions. Second, Au-Pd bimetallic nanocrystals and mixed-valence Ce-based metal-organic frameworks (MOFs) were introduced as co-reaction promoters to facilitate the reduction of dissolved O₂. Based on the synergistic catalysis of Au and Pd, the spontaneous cyclic reaction of Ce(III)/Ce(IV), and the high electrochemical active surface area of Ce(III, IV) MOF, a large number of superoxide anion radicals (O₂^•-) and hydroxyl radicals (OH^•) were produced. Therefore, the luminescence efficiency of N-(aminobutyl)-N-(ethylisoluminol)-dissolved O₂ (ABEI-O₂) systems were greatly improved, providing a new prospect for the application of dissolved O₂ in ECL analysis. In addition, the affinity peptide ligands were used for the directional connection of antibodies to provide protection for the bioactivity of the proposed sensor. Finally, the microfluidic technology was applied to ECL analysis to integrate the three-electrode detection system into the self-assembled microfluidic chip, which realized the automation and portability of the detection process. The developed sensor showed high sensitivity for PCT detection with a detection limit of 3.46 fg/mL, which possessed positive significance for the clinical diagnosis of sepsis.

Metal-Based Electrocatalysts for Methanol Electro-Oxidation: Progress, Opportunities, and Challenges

Direct methanol fuel cells (DMFCs) are among the most promising portable power supplies because of their unique advantages, including high energy density/mobility of liquid fuels, low working temperature, and low emission of pollutants. Various metal-based anode catalysts have been extensively studied and utilized for the essential methanol oxidation reaction (MOR) due to their superior electrocatalytic performance. At present, especially with the rapid advance of nanotechnology, enormous efforts have been exerted to further enhance the catalytic performance and minimize the use of precious metals. Constructing multicomponent metal-based nanocatalysts with precisely designed structures can achieve this goal by providing highly tunable compositional and structural characteristics, which is promising for the modification and optimization of their related electrochemical properties. The recent advances of metal-based electrocatalytic materials with rationally designed nanostructures and chemistries for MOR in DMFCs are highlighted and summarized herein. The effects of the well-defined nanoarchitectures on the improved electrochemical properties of the catalysts are illustrated. Finally, conclusive perspectives are provided on the opportunities and challenges for further refining the nanostructure of metal-based catalysts and improving electrocatalytic performance, as well as the commercial viability.

Reversing the Thermodynamics of Galvanic Replacement Reactions by Decreasing the Size of Gold Nanoparticles

Here, we describe the surprising reactivity between surface-attached (a) 0.9, 1.6, and 4.1 nm diameter weakly stabilized Au nanoparticles (NPs) and aqueous 1.0 × 10^-4 M Ag⁺ solution, and (b) 1.6 and 4.1 nm diameter weakly stabilized Au NPs and aqueous 1.0 × 10^-5 M PtCl₄^2-, which are considered to be antigalvanic replacement (AGR) reactions because they are not thermodynamically favorable for bulk-sized Au under these conditions. Anodic Stripping Voltammetry (ASV) and Scanning Transmission Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (STEM-EDS) mapping provide quantitation of the extent of Ag and Pt replacement as a function of Au NP diameter. The extent of the reaction increases as the Au NP size decreases. The percentage of Ag in the AuAg alloy following AGR based on ASV is 17.8 ± 0.6% for 4.1 nm diameter Au NPs, 87.2 ± 2.9% for 1.6 nm Au NPs, and an unprecedented full 100% Ag for 0.9 nm diameter Au NPs. STEM-EDS mapping shows very close agreement with the ASV-determined compositions. In the case of PtCl₄^2-, STEM-EDS mapping shows AuPt alloy NPs with 3.9 ± 1.3% and 41.1 ± 8.7% Pt following replacement with 4.1 and 1.6 nm diameter Au NPs, respectively, consistent with qualitative changes to the ASV. The size-dependent AGR correlates well with the negative shift in the standard potential (E⁰) for Au oxidation with decreasing NP size.

Plasmonic Metallic Heteromeric Nanostructures

Binary, ternary, and other high-order plasmonic heteromers possess remarkable physical and chemical properties, enabling them to be used in numerous applications. The seed-mediated approach is one of the most promising and versatile routes to produce plasmonic heteromers. Selective growth of one or multiple domains on desired sites of noble metal, semiconductor, or magnetic seeds would form desired heteromeric nanostructures with multiple functionalities and synergistic effects. In this work, the challenges for the synthetic approaches are discussed with respect to tuning the thermodynamics, as well as the kinetic properties (e.g., pH, temperature, injection rate, among others). Then, plasmonic heteromers with their structure advantages displaying unique activities compared to other hybrid nanostructures (e.g., core-shell, alloy) are highlighted. Some of the main most recent applications of plasmonic heteromers are also presented. Finally, perspectives for further exploitation of plasmonic heteromers are demonstrated. The goal of this work is to provide the current know-how on the synthesis routes of plasmonic heteromers in a summarized manner, so as to achieve a better understanding of the resulting properties and to gain an improved control of their performances and extend their breadth of applications.

Tuning Ion Complexing To Rapidly Prepare Hollow Ag-Pt Nanowires with High Activity toward the Methanol Oxidization Reaction

Hollow Pt-based nanowires (NWs) have important applications in catalysis. Their preparation often involves a two-step process in which M (M=Ag, Pd, Co, Ni) NWs are prepared and subsequently subjected to galvanic reaction in solution containing a Pt precursor. It is challenging to achieve a simple one-step preparation, because the redox potential of Pt^IV /Pt or Pt^II /Pt to Pt is high, and therefore, Pt atoms always form first. This work demonstrates that an appropriate pH can decrease the redox potential of Pt^IV /Pt and allows the one-step preparation of high-quality hollow Pt-Ag NWs rapidly (10 min). Moreover, it is easy to realize large-scale preparation with this method. The NW composition can be adjusted readily to optimize their performance in the electrocatalytic methanol oxidization reaction (MOR). Compared with commercial Pt/C, NWs with appropriate Ag/Pt ratios exhibit high stability, activity, and CO tolerance ability.

From Galvanic to Anti-Galvanic Synthesis of Bimetallic Nanoparticles and Applications in Catalysis, Sensing, and Materials Science

The properties of two alloyed metals have been known since the Bronze Age to outperform those of a single metal. How alloying and mixing metals applies to the nanoworld is now attracting considerable attention. The galvanic process, which is more than two centuries old and involves the reduction of a noble-metal cation by a less noble metal, has not only been used in technological processes, but also in the design of nanomaterials for the synthesis of bimetallic transition-metal nanoparticles. The background and nanoscience applications of the galvanic reactions (GRs) are reviewed here, in particular with emphasis on recent progress in bimetallic catalysis. Very recently, new reactions have been discovered with nanomaterials that contradict the galvanic principle, and these reactions, called anti-galvanic reactions (AGRs), are now attracting much interest for their mechanistic, synthetic, catalytic, and sensor aspects. The second part of the review deals with these AGRs and compares GRs and AGRs, including the intriguing AGRs mechanism and the first applications.

Pd–Au heterostructured nanonecklaces with adjustable interval and size as a superior catalyst for degradation of 4-nitrophenol

A novel type of Pd–Au heteronanostructure with the microscopic shape of a pearl necklace was prepared, which exhibited outstanding catalytic properties.