Metal Nanocrystals Research Articles

High-index facets Pt concave nanocubes with small interface angles induced by N-defective sites in the integrated electrode for methanol oxidation

The construction of an integrated electrode with self-organized growth is of great significance in reducing the Pt loading and improving the performance of the membrane electrode assembly (MEA) in proton exchange membrane fuel cells (PEMFCs). Herein, the square-wave pulse electrodeposition method is used to grow Pt{510}CNC and Pt{720}CNC nanocrystals on carbon fiber paper (CFP)-based reduced graphene oxide (rGO/CFP) and nitrogen-doped reduced graphene oxide (N-rGO/CFP) supports, respectively. Experimental and density functional theory (DFT) calculations show that the introduction of N makes it easier for hydrogen to adsorb on Pt, and the arrangement order of more Pt atoms is disrupted by hydrogen, resulting in the formation of Pt concave nanocubes (Pt CNCs) with small interface angles (α), consisting of {720} facets with more atomic steps. Moreover, the catalytic activities of the prepared two catalysts for methanol oxidation are 3.17 and 2.35 times higher than that of commercial Pt/C, and the maximum power densities of direct methanol fuel cell (DMFC) are also better than that of commercial Pt/C. This work can provide important guidance for the future research of high-index facets noble metal nanocrystals for growth on the surface of defective carbon carriers as integrated electrodes in MEA.

A Joule-heating-derived multiphase porous TiO2 support for reinforcing high-entropy alloy catalysts

Single-crystal nanocrystals of catalytic metals and oxides are essential for understanding chemical interactions on well-defined catalyst surfaces. However, a comprehensive understanding of the crystallographic origins for such enhancement has been lacking. This work provides formal evidence of the structure–property relationship through a model study on single-crystal TiO2. Our approach involves transient pulse heating to manipulate porosity and phase in epitaxially-grown TiO2 nanosheets along the (0 0 1) plane. Furthermore, we could introduce high-entropy alloy nanoparticles into the system, which exhibited excellent catalytic activity toward CO oxidation, achieving T90 at 143 °C. This improved performance is attributed to the interplay between the catalytic nanoparticles and the multiphase support, facilitating CO and O2 adsorption. Our study contributes to a fundamental understanding of structure–property relationships in heterogeneous catalyst systems. Overall, our thermal shock synthesis approach shows much promise for developing single crystal-based advanced nanocatalysts with broad practical implications.

Surface Engineering of Noble Metal Nanocrystals for Selective Hydrogenation

The selective hydrogenation has attracted increasing attention to chemists for the production of value‐added products in chemical industry. Over the past several decades, substantial effort has been devoted to the design of catalyst for the selective hydrogenation of light alkynes and α, β‐unsaturated aldehydes, two classic cases for selective hydrogenation in chemical industry. Despite the great progress, it remains great challenges to achieve the selective hydrogenation because the desired products are generally thermodynamically unfavored. Here, we summarize the recent advances on selective hydrogenation using noble metal nanocrystals, with an emphasis on the surface engineering of noble metal nanocrystals for the selective hydrogenation of light alkynes and α, β‐unsaturated aldehydes. We will highlight the strategies for surface engineering, the advanced techniques for characterizations, as well as mechanism studies. We hope this review will promote chemists to develop efficient and robust catalysts for selective hydrogenation.

Open-Nanogap-Induced Strong Electromagnetic Enhancement in Au/AgAu Monolayer as a Stable and Uniform SERS Substrate for Ultrasensitive Detection.

Nanogap-based plasmonic metal nanocrystals have been applied in surface-enhanced Raman scattering detection, while the closed and insufficient electromagnetic fields as well as the nonreproducible Raman signal of the substrate greatly restrict the actual application. Herein, a highly uniform Au/AgAu monolayer with abundant nanogaps and huge electromagnetic enhancement is prepared, which shows ultrasensitive and reproducible SERS detection. Au/AgAu with an inner nanogap is first prepared based on Au nanotriangles, and the nanogap is opened from the three tips via a subsequent etching process. The open-gap Au/AgAu displays much higher SERS efficiency than Au and Au/AgAu with an inner nanogap on detecting crystal violet due to the open-gap induced electromagnetic enhancement and improved molecular absorption. Furthermore, the open-gap Au/AgAu monolayer is prepared via interfacial self-assembly, which shows further improved SERS due to the dense and strong hotspots in the nanocavities induced by the electromagnetic coupling between adjacent open gaps. The monolayer possesses excellent signal stability, uniformity, and reproducibility. The analytic enhancement factor and relative standard deviation reach to 2.12 × 108 and 4.65% on detecting crystal violet, respectively. Moreover, the monolayer achieves efficient detection of thiram in apple juice, biphenyl-4-thiol, 4-mercaptobenzoic, melamine, and a mixed solution of four different molecules, showing great promise in practical detection.

Size, shape, and dimension effects on the melting temperature of metallic nanocrystals

Melting is the most common phenomenon in nature and one of the most important properties of metallic materials. Exploring the size D, shape α, and dimension d effects on the melting temperature T m of nanocrystals is of great significance for the design, fabrication, and application of quantum devices. In this work, by redefining the critical diameter D 0 and introducing shape factor α, a unified model without any adjustable parameters has been developed to describe the T m(D, α, d) function. The model is compared with the available experimental and simulation data of Cu, Pd, In, Pb, Au, Ag, and Ni nanocrystals and other theoretical works, and a consistent agreement is obtained, which verifies the accuracy of the prediction. This model is also compared with other theoretical works, and we find that it agrees well with Lu’s model, while the BOLS method underestimates the melting point. This work not only gives a new perspective on the relationship between size, shape, dimension, and melting temperature but also provides theoretical guidance for the design and optimization of low-dimensional quantum devices.

Thermal Shape Stability of fcc Metal Nanocrystals Synthesized with Faceted Nonequilibrium Shapes

Thermal Shape Stability of fcc Metal Nanocrystals Synthesized with Faceted Nonequilibrium Shapes

Steering the Selective Production of Glycolic Acid by Electrocatalytic Oxidation of Ethylene Glycol with Nanoengineered PdBi-Based Heterodimers.

Heterodimers of metal nanocrystals (NCs) with tailored elemental distribution have emerged as promising candidates in the field of electrocatalysis, owing to their unique structures featuring heterogeneous interfaces with distinct components. Despite this, the rational synthesis of heterodimer NCs with similar elemental composition remains a formidable challenge, and their impact on electrocatalysis has remained largely elusive. In this study, Pd@Bi-PdBi heterodimer NCs are synthesized through an underpotential deposition (UPD)-directed growth pathway. In this pathway, the UPD of Bi promotes a Volmer-Weber growth mode, allowing for judicious modulation of core-satellite to heterodimer structures through careful control of supersaturation and growth kinetics. Significantly, the heterodimer NCs are employed in the electrocatalytic process of ethylene glycol (EG) with high activity and selectivity. Compared with pristine Pd octahedra and common PdBi alloy NC, the unique heterodimer structure of the Pd@Bi-PdBi heterodimer NCs endows them with the highest electrocatalytic performance of EG and the best selectivity (≈93%) in oxidizing EG to glycolic acid (GA). Taken together, this work not only heralds a new strategy for UPD-directed synthesis of bimetallic NCs, but also provides a new design paradigm for steering the selectivity of electrocatalysts.

Revolutionizing the Treatment of Idiopathic Pulmonary Fibrosis: From Conventional Therapies to Advanced Drug Delivery Systems.

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive interstitial lung disease that has been well-reported in the medical literature. Its incidence has risen, particularly in light of the recent COVID-19 pandemic. Conventionally, IPF is treated with antifibrotic drugs-pirfenidone and nintedanib-along with other drugs for symptomatic treatments, including corticosteroids, immunosuppressants, and bronchodilators based on individual requirements. Several drugs and biologicals such as fluorofenidone, thymoquinone, amikacin, paclitaxel nifuroxazide, STAT3, and siRNA have recently been evaluated for IPF treatment that reduces collagen formation and cell proliferation in the lung. There has been a great deal of research into various treatment options for pulmonary fibrosis using advanced delivery systems such as liposomal-based nanocarriers, chitosan nanoparticles, PLGA nanoparticles, solid lipid nanocarriers, and other nanoformulations such as metal nanoparticles, nanocrystals, cubosomes, magnetic nanospheres, and polymeric micelles. Several clinical trials are also ongoing for advanced IPF treatments. This article elaborates on the pathophysiology of IPF, its risk factors, and different advanced drug delivery systems for treating IPF. Although extensive preclinical data is available for these delivery systems, the clinical performance and scale-up studies would decide their commercial translation.

Feasible preparation of preferentially oriented (111) Pd nanocrystals supported on cyano-COFs for ultrahigh activity in C-C cross-couplings

It is much challenging to synthesize highly dispersed noble metal nanocrystals (MNCs) and prevent their aggregation during the catalytic cycles. Choosing suitable solid supports to mediate the growth of MNCs can provide stable yet ultra-highly active heterogenous catalysts. However, very few studies have provided the controllable preparation of ultrafine MNCs. Herein, cyano-functionalized covalent organic frameworks (cyano-COFs)-mediated ultrafine preferentially oriented (111) PdNCs with particle diameter of 2.88 ± 0.60 nm were easily prepared in MeOH without any other external reducing agent. The obtained Pd/cyano-COFs presented ultrahigh activity in Suzuki-Miyaura couplings, with TOF of 2578 h−1 and chemo-selectivity of > 99 % for the cross-coupling between p-iodotoluene and phenylboronic acid at room temperature in the air. Furthermore, outstanding catalytic performance of Pd/cyano-COFs was found in Heck couplings as well. This study provides a new idea for the controllable preparation of metallic nanomaterials with high performance, which could facilitate the research on the regulation of catalytic performance by the chemical composition of supports.

Metal Organic Frameworks Synthesis: The Versatility of Triethylamine.

Metal Organic Frameworks (MOFs) are organic-inorganic hybrid materials with exceptionally customizable composition and properties. MOFs intrinsically possess open metal sites, tunable pore size/shape and an ultra-large specific surface area, and have obtained significant attention over the past 30 years. Furthermore, through the integration of functional moieties such as, molecules, functional groups, noble metal clusters and nanocrystals or nanoparticles into MOFs, the resulting composites have greatly enriched the physical and chemical properties of pure MOFs, enabling their application in a wider range of fields. Triethylamine (TEA) as an organic base has consistently played a fundamental role in the development of MOFs. In this Concept, the versatility of triethylamine when involved in the synthesis of MOFs is discussed. Four sections are used to elaborate on the role of TEA including: (1) Single crystal synthesis; (2) Size and morphology control; (3) Counterion of MOFs; (4) MOFs composites synthesis. In the last part, we highlight the potential of TEA for further developments.

Construction of Gold/Rhodium Freestanding Superstructures as Antenna-Reactor Photocatalysts for Plasmon-Driven Nitrogen Fixation.

Precisely controlling the architecture and spatial arrangement of plasmonic heterostructures offers unique opportunities to tailor the catalytic property, whereas the lack of a wet-chemistry synthetic approach to fabricating nanostructures with high-index facets limits their practical applications. Herein, we describe a universal synthetic strategy to construct Au/Rh freestanding superstructures (SSs) through the selective growth of ordered Rh nanoarrays on high-index-faceted Au nanobipyramids (NBPs). This synthetic strategy works on various metal nanocrystal substrates and can yield diverse Au/Rh and Pd/Rh SSs. Especially, the obtained Au NBP/Rh SSs exhibit high photocatalytic activity toward N2 fixation as a result of the spatially separated architecture, local electric field enhancement, and the antenna-reactor mechanism. Both theoretical and experimental results reveal that the Au NBPs can function as nanoantennas for light-harvesting to generate hot charge carriers for driving N2 fixation, while the Rh nanoarrays can serve as the active sites for N2 adsorption and activation to synergistically promote the overall catalytic activity in the Au NBP/Rh SSs. This work offers new avenues to rationally designing and constructing spatially separated plasmonic photocatalysts for high-efficiency catalytic applications.

Facile Synthesis of a Broad Range of Colloidal Nanocrystals by Membrane-Mediated pH Gradient under Ambient Conditions

We report a simple synthesis process for a wide variety of ultrasmall nanocrystals. Simply immersing a dialysis bag containing an aqueous solution of a metal salt mixed with citric acid in a NaOH solution reservoir for 10 min, nanocrystals measuring only a few nanometers in size are formed inside the dialysis bag. We demonstrated the synthesis of ultrasmall nanocrystals of Co, Ni, Cu, Ag, Au, Pd, Cu2O, FeO, and CeO2, and found that the gradual change in pH caused by the diffusion of OH− ions through the dialysis membrane played an essential role in the formation of these nanocrystals. This method can be readily adapted for almost all transition metal elements, providing researchers in the fields of catalysis and nanomedicine an easy access to a wide range of ultrasmall metal and oxide nanocrystals.

Controllable Pseudoelasticity in Metallic Nanocrystals by Grain Boundary Engineering.

Materials with pseudoelasticity can recover from large strains exceeding their elastic limits during unloading, making them promising damage-tolerant building blocks for advanced nanodevices. Nevertheless, a practical approach to realize controllable pseudoelastic behavior at nanoscale remains challenging. Here, we proposed a grain boundary (GB) engineering approach to endow metallic nanocrystals with a controllable pseudoelasticity. Both in situ nanomechanical testing and atomistic simulations demonstrate that such controllable pseudoelasticity is governed by the extension and contraction of an inherent stacking fault array at the GB. By precisely tuning GB misorientation and inclination, our simulation results reveal that metallic nanocrystals can exhibit tailored pseudoelastic performance across a broad spectrum of GBs in different face-centered cubic metals. These findings enrich our understanding of the intrinsic pseudoelasticity of GBs and provide a GB engineering approach toward metallic materials with reversible deformability.

Hybrid oxide coatings generate stable Cu catalysts for CO2 electroreduction

Hybrid organic/inorganic materials have contributed to solve important challenges in different areas of science. One of the biggest challenges for a more sustainable society is to have active and stable catalysts that enable the transition from fossil fuel to renewable feedstocks, reduce energy consumption and minimize the environmental footprint. Here we synthesize novel hybrid materials where an amorphous oxide coating with embedded organic ligands surrounds metallic nanocrystals. We demonstrate that the hybrid coating is a powerful means to create electrocatalysts stable against structural reconstruction during the CO2 electroreduction. These electrocatalysts consist of copper nanocrystals encapsulated in a hybrid organic/inorganic alumina shell. This shell locks a fraction of the copper surface into a reduction-resistant Cu2+ state, which inhibits those redox processes responsible for the structural reconstruction of copper. The electrocatalyst activity is preserved, which would not be possible with a conventional dense alumina coating. Varying the shell thickness and the coating morphology yields fundamental insights into the stabilization mechanism and emphasizes the importance of the Lewis acidity of the shell in relation to the retention of catalyst structure. The synthetic tunability of the chemistry developed herein opens new avenues for the design of stable electrocatalysts and beyond.

In Situ X-ray Scattering Reveals Coarsening Rates of Superlattices Self-Assembled from Electrostatically Stabilized Metal Nanocrystals Depend Nonmonotonically on Driving Force.

Self-assembly of colloidal nanocrystals (NCs) into superlattices (SLs) is an appealing strategy to design hierarchically organized materials with promising functionalities. Mechanistic studies are still needed to uncover the design principles for SL self-assembly, but such studies have been difficult to perform due to the fast time and short length scales of NC systems. To address this challenge, we developed an apparatus to directly measure the evolving phases in situ and in real time of an electrostatically stabilized Au NC solution before, during, and after it is quenched to form SLs using small-angle X-ray scattering. By developing a quantitative model, we fit the time-dependent scattering patterns to obtain the phase diagram of the system and the kinetics of the colloidal and SL phases as a function of varying quench conditions. The extracted phase diagram is consistent with particles whose interactions are short in range relative to their diameter. We find the degree of SL order is primarily determined by fast (subsecond) initial nucleation and growth kinetics, while coarsening at later times depends nonmonotonically on the driving force for self-assembly. We validate these results by direct comparison with simulations and use them to suggest dynamic design principles to optimize the crystallinity within a finite time window. The combination of this measurement methodology, quantitative analysis, and simulation should be generalizable to elucidate and better control the microscopic self-assembly pathways of a wide range of bottom-up assembled systems and architectures.

Probing the Interaction between Individual Metal Nanocrystals and Two-Dimensional Metal Oxides via Electron Energy Loss Spectroscopy.

Metal nanoparticles can photosensitize two-dimensional metal oxides, facilitating their electrical connection to devices and enhancing their abilities in catalysis and sensing. In this study, we investigated how individual silver nanoparticles interact with two-dimensional tin oxide and antimony-doped indium oxide using electron energy loss spectroscopy (EELS). The measurement of the spectral line width of the longitudinal plasmon resonance of the nanoparticles in absence and presence of 2D materials allowed us to quantify the contribution of chemical interface damping to the line width. Our analysis reveals that a stronger interaction (damping) occurs with 2D antimony-doped indium oxide due to its highly homogeneous surface. The results of this study offer new insight into the interaction between metal nanoparticles and 2D materials.

Bridging colloidal and electrochemical syntheses of metal nanocrystals with seeded electrodeposition for tracking single nanocrystal growth.

Metal nanocrystals (NCs) produced by colloidal synthesis have a variety of structural features, such as different planes, edges, and defects. Even from the best colloidal syntheses, these characteristics are distributed differently in each NC. This inherent heterogeneity can play a significant role in the properties displayed by NCs. This manuscript reports the use of electrochemistry to synthesize Au NCs in a system evaluated to track individual NC growth trajectories as a first step toward rapid identification of NCs with different structural features. Au nanocubes were prepared colloidally and deposited onto a glassy carbon electrode using either electrospray or an airbrush, resulting in well-spaced Au nanocubes. The Au nanocubes then served as seeds as gold salt was reduced to deposit metal at constant potential. Deposition at constant potential facilitates overgrowth on the Au nanocubes to achieve new NC shapes. The effects of applied potential, deposition time, precursor concentration, and capping agents on NC shape evolution were studied. The outcomes are correlated to results from traditional colloidal syntheses, providing a bridge between the two synthetic strategies. Moreover, scanning electron microscopy was used to image the same NCs before and after deposition, linking individual seed features to differences in deposition. This ability is anticipated to enable tracking of individual growth trajectories of NCs to elucidate sources of heterogeneity in NC syntheses.

Metal dimer nanojunction-magnetic material composites for magnetic field sensing.

Noble metal nanocrystals are used as high sensitivity optoelectronic sensors, such as surface-enhanced Raman scattering, SERS. The sensing performance of metal nanocrystals can be further improved by forming dimer nanojunctions with strong "plasmonic coupling". Since the strength of "plasmonic coupling" is highly sensitive to the sub-nanoscale spacing between plasmonic nanocrystals in nanojunctions, nanojunctions can be used to detect external stimuli that can change the spacing of nanocrystals in the nanojunction and thus change the sensitivity of the Raman scattering spectrum. Here, we utilize this principle to detect the direction and strength of an external magnetic field (MF) using dimer nanojunctions surrounded by magnetic materials as a sensing platform. The results reveal that the changes in nanocrystal spacing in the nanojunction are caused by the rearrangement of the magnetic material under an external MF, which strongly depends on the interaction between the magnetic material and the ligands on the nanocrystal surface and the steric repulsion generated by the ligand configuration on the nanocrystal surface. Compared with the Raman spectrum without an external MF, the enhancement factors of the Raman scattering spectrum under an external MF can reach up to ∼900%, which makes dimer nanojunctions with magnetic materials suitable for "magnetic field" sensing applications.

Advances in the preparation and biological applications of core@shell nanocrystals based on quantum dots and noble metal.

Core/shell structured nanoparticles (NPs) are a novel category of functional materials that have garnered widespread attention due to their advantageous preparation methods, unique characteristics, and multifunctional application prospects, which have shown significant performance in materials chemistry and many other fields, such as electronics, biomedical, pharmaceutical, optics, and catalysis. Although some reviews about core/shell NPs have been published, there is still an intense requirement for an extensive review about the updated literature and new reported core/shell nanomaterials. Colloidal quantum dots (QDs) and noble metal NPs have a very small size, which results in the large surface-to-volume ratio and under-coordinated chemical bonds. As a result, the effort on the design of core-shell structure has been essential for colloidal QDs and noble metal NPs. In this review, the core-shell structures dominated by traditional QDs and CsPbX3 perovskite QDs, as well as noble metal nanocrystals (NCs) were summarized. The applications of the above core-shell structure NCs in medical or biological fields such as sensing, biological imaging, medical diagnostics and therapeutics, immunological diagnosis were discussed. The main objective of this review is to provide a better basis for the synthesis, properties, and biomedical applications of QDs or noble metal core/shell NPs, which is beneficial for the further development of QDs, noble metal NPs, and other NPs.

Seeded growth of gold-based nanostructures regulated by controlled doping

Recent advancements in regulating the seeded growth of gold-based nanocrystals through controlled doping are discussed. By fine-tuning the doping process, a diverse range of innovative nanostructures can be created.