Core-shell Nanocubes Research Articles

Defect-Assisted Deposition of Au on Ag for the Fabrication of Core–Shell Nanocubes with Outstanding Chemical and Thermal Stability

We report the defect-assisted deposition of Au on Ag nanocubes for the generation of Ag@Au core–shell nanocubes with three to eight atomic layers. In a standard protocol, we disperse Ag nanocubes in an ethylene glycol (EG) solution containing poly(vinylpyrrolidone) and then titrate aqueous HAuCl4 at 110 °C. Initially, the galvanic replacement reaction between HAuCl4 and Ag allows the deposition of Au on the edges of the nanocubes with highest surface energy as the Ag atoms on the side faces are dissolved into the aqueous suspension in the form of Ag(I) ions to create surface defects. These defects then become preferential sites for the codeposition of Ag and Au atoms derived from the coreduction of both the Ag(I) and Au(III) ions in the reaction solution by EG. Once the defect sites have been filled, the additional Ag and Au atoms will rapidly diffuse across the entire surface of each nanocube for the generation of a nanocube with a relatively thin shell made of a Ag–Au alloy. Afterward, the chemical redu...

Facile synthesis of Pd@Pt core-shell nanocubes with low Pt content via direct seed-mediated growth and their enhanced activity for formic acid oxidation.

Pd@Pt core-shell nanocubes with a partially covered Pt shell on the Pd nanocubes were synthesized by a direct seed-mediated growth method without a washing process. The FAO activity of Pd@Pt 0.4 at% was 4.3 times and 2.2 times higher than that of Pd cubes and commercial Pt/C, respectively.

Understanding metal-enhanced fluorescence and structural properties in Au@Ag core-shell nanocubes.

Au@Ag core–shell structures have received particular interest due to their localized surface plasmon resonance properties and great potential as oxygen reduction reaction catalysts and building blocks for self-assembly. In this study, Au@Ag core–shell nanocubes (Au@AgNCs) were fabricated in a facile manner via stepwise Ag reduction on Au nanoparticles (AuNPs). The size of the Au@AgNCs and their optical properties can be simply modulated by changing the Ag shell thickness. Structural characterization has been carried out by TEM, SAED, and XRD. The metal-induced fluorescence properties of probe molecules near the Au@AgNCs were measured during sedimentation of the Au@AgNCs. The unique ring-like building block of Au@AgNCs has dual optical functions as a fluorescence quencher or fluorescence enhancement medium depending on the assembled regions.

Facilitating the C–C bond cleavage on sub-10 nm concavity-tunable Rh@Pt core–shell nanocubes for efficient ethanol electrooxidation

Concavity-tunable Rh@Pt core–shell nanocubes with an engineered Rh–Pt interface and Pt atomic steps facilitate C–C bond cleavage in the EOR.

Toward transparent projection display: recent progress in frequency-selective scattering of RGB light based on metallic nanoparticle’s localized surface plasmon resonance

A transparent display simultaneously enables visualization of the images displayed on it as well as the view behind it, and therefore can be applied to, for instance, augmented reality (AR), virtual reality (VR), and head up display (HUD). Many solutions have been proposed for this purpose. Recently, the idea of frequency-selective scattering of red, green and blue light while transmitting visible light of other colours to achieve transparent projection display has been pro-posed, by taking advantage of metallic nanoparticle’s localized surface plasmon resonance (LSPR). In this article, a review of the recent progress of frequency-selective scattering of red, green and blue light that are based on metallic nanoparticle’s LSPR is presented. A discussion of method for choosing appropriate metal(s) is first given, followed by the definition of a figure of merit used to quantify the performance of a designed nanoparticle structure. Selective scattering of various nanostructures, including sphere-shaped nanoparticles, ellipsoidal nanoparticles, super-sphere core-shell nanoparticles, metallic nanocubes, and metallic nanoparticles combined with gain materials, are discussed in detail. Each nanostructure has its own advantages and disadvantages, but the combination of the metallic nanoparticle with gain materials is a more promising way since it has the potential to generate ultra-sharp scattering peaks (i.e., high frequency-selectivity).

Strengthening Mechanism of a Single Precipitate in a Metallic Nanocube.

Nanoprecipitates play a significant role in the strength, ductility, and damage tolerance of metallic alloys through their interaction with crystalline defects, especially dislocations. However, the difficulty of observing the action of individual precipitates during plastic deformation has made it challenging to conclusively determine the mechanisms of the precipitate-defect interaction for a given alloy system and presents a major bottleneck in the rational design of nanostructured alloys. Here, we demonstrate the in situ compression of core-shell nanocubes as a promising platform to determine the precise role of individual precipitates. Each nanocube with a dimension of ∼85 nm contains a single spherical precipitate of ∼25 nm diameter. The Au-core/Ag-shell nanocubes show a yield strength of 495 MPa with no strain hardening. The deformation mechanism is determined to be surface nucleation of dislocations which easily traverses through the coherent Au-Ag interface. On the other hand, the Au-core/Cu-shell nanocubes show a yield strength of 829 MPa with a pronounced strain hardening rate. Molecular dynamics and dislocation dynamics simulations, in conjunction with TEM analysis, have demonstrated the yield mechanism to be the motion of threading dislocations extending from the semicoherent Au-Cu interface to the surface, and strain hardening to be caused by a single-armed Orowan looping mechanism. Nanocube compression offers an exciting opportunity to directly compare computational models of defect dynamics with in situ deformation measurements to elucidate the precise mechanisms of precipitate hardening.

Atomic-Scale Structure and Stress Release Mechanism in Core-Shell Nanoparticles.

Core-shell nanoparticles find applications in catalysts, sensors, and theranostics. The full internal 3D atomic structure, however, cannot be resolved by current imaging and diffraction techniques. We analyzed the atomic positions and stress-release mechanism in a cubic Au-Pd core-shell nanoparticle in approximately 1000 times higher resolution than current experimental techniques using large-scale molecular dynamics simulation to overcome these limitations. The core-shell nanocube of 73 nm size was modeled similarly to solution synthesis by random epitaxial deposition of a 4 nm thick shell of Pd atoms onto a Au core of 65 nm side length using reliable interatomic potentials. The internal structure reveals specific deformations and stress relaxation mechanisms that are caused by the +4.8% lattice mismatch of gold relative to palladium and differential confinement of extended particle facets, edges, and corners by one, two, or three Au-Pd interfaces, respectively. The three-dimensional lattice strain causes long-range, arc-like bending of atomic rows along the faces and edges of the particle, especially near the Au-Pd interface, a bulging deformation of the Pd shell, and stacking faults in the Pd shell at the corners of the particle. The strain pattern and mechanism of stress release were further characterized by profiles of the atomic layer spacing in the principal crystallographic directions. Accordingly, strain in the Pd shell is several times larger in the extended facets than near the edges and corners of the nanoparticle, which likely affects adsorption, optical, and electrochemical properties. The findings are consistent with available experimental data, including 3D reconstructions of the same cubic nanoparticle by coherent diffractive imaging (CDI) and may be verified by more powerful experimental techniques in the future. The stress release mechanisms are representative for cubic core-shell nanoparticles with fcc structure and can be explored for different shapes by the same methods.

Catalytic Activities of Mono- and Bimetallic (Gold/Silver) Nanoshell-Coated Gold Nanocubes toward Catalytic Reduction of Nitroaromatics.

A new class of core-shell metallic nanostructures with tunable near-surface composition and surface morphology with excellent catalytic activity is reported. Very thin shells of metal nanoassemblies such as monolayer (Ag and Au), bilayer of Ag or Au, and AgAu alloy layer with controlled size and morphology were deposited onto a gold nanocube (AuNC) core. UV-vis absorption spectroscopy and high-resolution transmission electron microscopy analyses along with selected-area electron diffraction, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometer, and X-ray diffraction techniques were used to characterize the prepared core-shell nanocubes. High-angle annular dark field scanning transmission electron microscopy-energy dispersive X-ray spectroscopy mapping images were recorded for the bilayer shell and alloy layer shell in the core-shell nanostructures. Reduction of 4-nitroaniline in the presence of sodium borohydride was chosen to validate the catalytic activity of the prepared core-shell metal nanocubes. Interestingly, the AgAu alloy shell layer over the AuNC (AuNC1@Ag0.25Au0.25) showed excellent catalytic activity compared with the pristine AuNC and monolayer and bilayer core-shell nanostructures.

Fe2+ Deficiencies, FeO Subdomains, and Structural Defects Favor Magnetic Hyperthermia Performance of Iron Oxide Nanocubes into Intracellular Environment.

Herein, by studying a stepwise phase transformation of 23 nm FeO-Fe3O4 core-shell nanocubes into Fe3O4, we identify a composition at which the magnetic heating performance of the nanocubes is not affected by the medium viscosity and aggregation. Structural and magnetic characterizations reveal the transformation of the FeO-Fe3O4 nanocubes from having stoichiometric phase compositions into Fe2+-deficient Fe3O4 phases. The resultant nanocubes contain tiny compressed and randomly distributed FeO subdomains as well as structural defects. This phase transformation causes a 10-fold increase in the magnetic losses of the nanocubes, which remain exceptionally insensitive to the medium viscosity as well as aggregation unlike similarly sized single-phase magnetite nanocubes. We observe that the dominant relaxation mechanism switches from Néel in fresh core-shell nanocubes to Brownian in partially oxidized nanocubes and once again to Néel in completely treated nanocubes. The Fe2+ deficiencies and structural defects appear to reduce the magnetic energy barrier and anisotropy field, thereby driving the overall relaxation into Néel process. The magnetic losses of these nanoparticles remain unchanged through a progressive internalization/association to ovarian cancer cells. Moreover, the particles induce a significant cell death after being exposed to hyperthermia treatment. Here, we present the largest heating performance that has been reported to date for 23 nm iron oxide nanoparticles under intracellular conditions. Our findings clearly demonstrate the positive impacts of the Fe2+ deficiencies and structural defects in the Fe3O4 structure on the heating performance into intracellular environment.

Synthesis of Hollow Silica Nanocubes with Tuneable Size and Shape, Suitable for Light Scattering Studies

We present a preparation method for hollow silica nanocubes with tuneable size and shape in the range required for light scattering studies. Cuprous oxide nanocubes are prepared by a water-assisted polyol method. By adjusting the water content, the size of the nanocubes can be tuned in the range of 40–120 nm. These cubes function as a shape template in the subsequent coating with Stöber silica, resulting in core-shell nanocubes. Dissolving the core with nitric acid results in hollow silica nanocubes with sizes ranging from 80–120 nm and cubicity shape parameters between 3 and 6.5.

Photocatalytic performance of AgCl@Ag core–shell nanocubes for the hexavalent chromium reduction

Plasmonic nanomaterials have wide applications in many fields, such as photocatalysis, solar cell, and new energy generation system. Among them, AgCl–Ag nanomaterials with excellent plasmonic property are getting more and more attention. In this work, AgCl@Ag core–shell nanocubes (AgCl@Ag CS-NCs) with highly uniform morphology and controlled composition have been successfully prepared by the partial reduction of AgCl nanocubes. The morphology, composition, and structure of AgCl@Ag CS-NCs have been investigated systematically. AgCl@Ag CS-NCs with the ratio of AgCl/Ag = 2.7:1 show the optimizational photocatalytic activity for the reduction of representative carcinogenic contaminant (CrVI), which is much higher than that of commercial P25 photocatalyst. The localized surface plasmon resonance and Schottky junction of AgCl@Ag CS-NCs contribute to the high photocatalytic activity for the CrVI photoreduction. After 5 times recyclable catalysis, the high photocatalytic activity of AgCl@Ag CS-NCs can still be maintained well, which demonstrates that AgCl@Ag CS-NCs possess excellent reusability and stability. The high activity and durability make AgCl@Ag CS-NCs to become a promising candidate for the environmental pollution purification under the sunlight irradiation condition.

FexP/C core-shell nanocubes with large inner void space for advanced lithium-ion battery anode

Iron-based phosphides are one good anode candidate for lithium ion batteries except the problem of low conductivity and large volume expansion. To get over these disadvantages, FexP/C core-shell nanocubes are synthesized by a simple approach without high temperature and direct use of toxic gas, involving Prussian Blue as the precursor and a low-temperature phosphidation process. Herein, the FexP/C nanocubes possess enough inner void space, which can accommodate the large volume expansion for internal FexP nanoparticles during Li+ intercalation and deintercalation process. And the carbon shell can enhance conductivity of electrodes, which is beneficial for transportation of Li+. All these advantages endow FexP/C with outstanding performance as anode materials for lithium-ion batteries. As a result, the obtained FexP/C core-shell nanocubes deliver a high reversible capacity of 665 mAh g−1 after 200 cycles at the current density of 100 mA g−1. This work supply one approach for controllable synthesis of metal phosphides for lithium-ion batteries, hydrogen evolution reaction, catalysis, etc.

Plasmonic Heterodimers with Binding Site-Dependent Hot Spot for Surface-Enhanced Raman Scattering.

A novel plasmonic heterodimer nanostructure with a controllable self-assembled hot spot is fabricated by the conjugation of individual Au@Ag core-shell nanocubes (Au@Ag NCs) and varisized gold nanospheres (GNSs) via the biotin-streptavidin interaction from the ensemble to the single-assembly level. Due to their featured configurations, three types of heterogeneous nanostructures referred to as Vertice, Vicinity, and Middle are proposed and a single hot spot forms between the nanocube and nanosphere, which exhibits distinct diversity in surface plasmon resonance effect. Herein, the calculated surface-enhanced Raman scattering enhancement factors of the three types of heterodimers show a narrow distribution and can be tuned in orders of magnitude by controlling the size of GNSs onto individual Au@Ag NCs. Particularly, the Vertice heterodimer with unique configuration can provide extraordinary enhancement of the electric field for the single hot spot region due to the collaborative interaction of lightning rod effect and interparticle plasmon coupling effect. This established relationship between the architecture and the corresponding optical properties of the heterodimers provides the basis for creating controllable platforms which can be exploited in the applications of plasmonic devices, electronics, and biodetection.

Centrifugal Deposited Au-Pd Core-Shell Nanoparticle Film for Room-Temperature Optical Detection of Hydrogen Gas.

In the present work, centrifugal deposited Au-Pd core-shell nanoparticle (NP) film was proposed for the room-temperature optical detection of hydrogen gas. The size dimension of 44, 48, 54, and 62 nm Au-Pd core-shell nanocubes with 40 nm Au core were synthesized following a solution-based seed-mediated growth method. Compared to a pure Pd NP, this core-shell structure with an inert Au core could decrease the H diffusion length in the Pd shell. Through a modified centrifugal deposition process, continues film samples with different core-shell NPs were deposited on 10 mm diameter quartz substrates. Under various hydrogen concentration conditions, the optical response properties of these samples were characterized by an intensity-based optical fiber bundle sensor. Experimental results show that the continues film that was composed of 62 nm Au-Pd core-shell NPs has achieved a stable and repeatable reflectance response with low zero drift in the range of 4 to 0.1% hydrogen after a stress relaxation mechanism at first few loading/unloading cycles. Because of the short H diffusion length due to the thinner Pd shell, the film sample composed of 44 nm Au-Pd NPs has achieved a dramatically decreased response/recovery time to 4 s/30 s. The experiments present the promising prospect of this simple method to fabricate optical hydrogen sensors with controllable high sensitivity and response rate at low cost.

Cu2O@TiO2 core-shell nanocube composite as improved performance anode materials for lithium-ion batteries

Uniform Cu2O nanocubes were large-scale synthesized through a liquid-phase reduction method. TiO2 was further coated onto Cu2O nanocubes to form Cu2O@TiO2 core-shell composite based on hydrolysis reaction of titanium isopropoxide. As-synthesized Cu2O@TiO2 were characterized by XRD, SEM and TEM. As anode materials for lithium ion batteries, Cu2O@TiO2 core-shell composite showed higher discharge capacity and more stable cycling performance than the uncoated Cu2O nanocubes, exhibiting the strong composition effect.

Nanoscale kinetics of asymmetrical corrosion in core-shell nanoparticles

Designing new materials and structure to sustain the corrosion during operation requires better understanding on the corrosion dynamics. Observation on how the corrosion proceeds in atomic scale is thus critical. Here, using a liquid cell, we studied the real-time corrosion process of palladium@platinum (Pd@Pt) core-shell nanocubes via transmission electron microscopy (TEM). The results revealed that multiple etching pathways operatively contribute to the morphology evolution during corrosion, including galvanic etching on non-defected sites with slow kinetics and halogen-induced etching at defected sites at faster rates. Corners are the preferential corrosion sites; both etching pathways are mutually restricted during corrosion. Those insights on the interaction of nanostructures with reactive liquid environments can help better engineer the surface structure to improve the stability of electrocatalysts as well as design a new porous structure that may provide more active sites for catalysis.

Single-Molecule Analysis of MicroRNA and Logic Operations Using a Smart Plasmonic Nanobiosensor.

Analysis of biomolecules at the single-molecule level is a great challenge in molecular diagnostics, gene profiling, and environmental monitoring. In this work, we design a smart plasmonic nanobiosensor based on individual Au@Ag core-shell nanocube (Au@Ag NC) modified with tetrahedron-structured DNA (tsDNA) for detecting microRNA 21 (miR-21) at the single-molecule level. An average localized surface plasmon resonance (LSPR) scattering spectral wavelength shift of approximately 0.4 nm can be obtained for a single miR-21 hybridization event on the nanobiosensor. In addition, the sensing mechanism of the individual Au@Ag NC is further verified by the three-dimensional finite-difference time-domain (3D-FDTD) simulations. Notably, this system not only allows the real-time detection of miR-21 with an aM level sensitivity over a large dynamic range from 1 aM to 1 nM, but also enables DNA-based logic operations as well as biomemory by exploiting miR-21, KpnI, and StuI-responsive assays. Our study opens a unique method for single-molecule detection of biomolecules and thus holds great promise in a variety of biological and biomedical applications.

AuNS@Ag core-shell nanocubes grafted with rhodamine for concurrent metal-enhanced fluorescence and surfaced enhanced Raman determination of mercury ions

Mercury ion (Hg2+) is a highly hazardous and widespread pollutant with bio-accumulative properties. Although the existing Hg2+ detection methods have high sensitivity and reliability, whereas there have few reports concerning bimodal detection for Hg2+ with one sensor. Toward this goal, a novel sensor based on rhodamine derivatives (RhD) grafted AuNS@Ag core-shell nanocubes (CSN) has been synthesized and shown the bimodal detection capabilities with metal enhanced fluorescence (MEF) and surface enhanced Raman scattering (SERS) for Hg2+. Herein, resultant CSN acts as the signal enhancing material; RhD was modified on the outside of the shell to ensure the signal sensitive of the CSN-RhD hybrids. In this work, we investigate the size- and shape-dependent SERS activity of plasmonic CSN comprised of AuNS as cores and Ag cuboids as shells. The SERS activity of CSN with spherical core was found to increase with the increasing thickness of the Ag cubic shell. Sequel, under an optimized condition, a display of strong MEF and SERS signals of the resulting mixtures with increasing of Hg2+ concentrations was observed. The proposed bimodal sensor showed excellent performances for Hg2+ along with wide linear range of 0.001–1000 ppm and 0.01–1000 ppm as well as the relatively low detection limit of 0.94 and 5.16 ppb for MEF and SERS assays, respectively. Furthermore, the ability of the sensor to detect Hg2+was also confirmed in adulterated milk samples.

Self-assembly of Au@Ag core–shell nanocubes embedded with an internal standard for reliable quantitative SERS measurements

Self-assembled Au@Ag nanocubes embedded with 4-MBA as an internal reference were applied for quantitative SERS measurements of aspartame in drinks.

An efficient synthetic strategy for uniform perovskite core–shell nanocubes NaMgF3:Mn2+,Yb3+@NaMgF3:Yb3+ with enhanced near infrared upconversion luminescence

Uniform perovskite core–shell nanocubes NaMn1−xMgxF3@NaMgF3 and NaMn1−xMgxF3:Yb3+@NaMgF3:Yb3+ have been successfully synthesized via a facile one-pot co-precipitation method at room temperature.