Core-shell Architecture Research Articles

An Individualized Core–Shell Architecture Derived from Covalent Triazine Frameworks: Toward Enhancing the Flame Retardancy, Smoke Release Suppression, and Toughness of Bismaleimide Resin

Although the bismaleimide (BMI) resin is a star material in industries, its further applications have been plagued by the serious brittleness and fire hazard for a long time. Hence, a core–shell architecture (MPPM) derived from covalent triazine frameworks was designed to overcome the shortcomings. Excitedly, compared to those of neat BMI, the resultant BMI-2 with only 1 wt % MPPM was capable of achieving 23.4%, 48.6%, and 39.7% decrements on the peak of heat release rate, total heat release, and total smoke release, respectively, exhibiting unprecedented flame-retardant effects under a low addition of flame retardants. Besides, the impact strength of BMI-2 was enhanced by 62.7% with a close tensile strength and storage modulus to those of neat BMI, implying that the toughness of BMI was improved successfully without sacrificing its rigidity. This work provided a unique clue for designing efficient multifunctional modifiers and promoted the development of advanced BMI.

Co3+-rich CoFe-PBA encapsulated in ultrathin MoS2 sheath as integrated core-shell architectures for highly efficient OER

Highly active and stable oxygen evolution reaction (OER) electrocatalyst is the key component of sustainable water splitting reaction. Controllable core-shell engineering is one of the most effective strategies for modulating the local electronic structure of active sites to enhance catalytic activity. Herein, we design a nano-cube of Co3+-rich CoFe Prussian blue analogues coated with controllable MoS2 shell heterostructures as OER electrocatalyst by simple solvothermal method, named as CoIIIFe-PBA/MoS2. Importantly, CoIIIFe-PBA/MoS2 possesses an extremely low overpotential of 306 mV at the current density of 100 mA cm−2, a small Tafel slope of 36.2 mV dec−1 and excellent stability for OER. The results of spectroscopic characterizations reveal that the Co3+ species with more 3d electron orbits origin from the charge transfer between CoFe-PBA and MoS2 core-shell interface, which promotes the electron accepting and results in the higher electrochemical activity. This research offers unique insight to design other advanced electrocatalysts with high-valent transition metal ions and core-shell structure.

On the thermal and hydrothermal stability of spinel iron oxide nanoparticles as single and core-shell hard-soft phases

The thermal and hydrothermal stability of oleate-capped nanosized spinel iron oxides is of primary importance for the plethora of applications and environments for which they are employed. An in-situ XRD and ex-situ autoclave treatments have been set up for monitoring the thermal and hydrothermal stability in different samples. In detail, spinel iron oxide nanoparticles (NPs) were studied as (i) single-phase alone at three different sizes (about 6, 10, and 15 nm); (ii) as core in a core-shell architecture having cobalt ferrite as shell, at different core sizes (about 6 and 10 nm); (iii) as shell in a core-shell architecture with cobalt ferrite as core, at different shell thicknesses (about 3 and 4 nm). The Rietveld refinement of the diffraction patterns and 57Fe Mössbauer spectroscopy have been exploited to monitor the evolution of the structural parameters and the hematite fraction. Moreover, transmission electron microscopy has permitted to deepen the morphological details on the phases. The spinel iron oxide-hematite transition has been found size- and time-dependent for the single-phase iron oxide NPs (360–455 °C). The transition temperature has increased significantly when iron oxide is incorporated in a core-shell architecture, both as core (630 °C) and shell (520 °C), suggesting a stabilizing effect of cobalt ferrite. The hydrothermal stability of iron oxide and core-shell NPs has been found dependent on water content, time, and temperature, with a reducing effect of pentanol toward the formation of magnetite from maghemite, highlighted by 57Fe Mössbauer spectroscopy. The synergic effects of cobalt ferrite and pentanol have limited the formation of hematite, leading to the obtainment of magnetite-covered cobalt ferrite NPs upon the hydrothermal treatment.

Optical Modeling of Plasmonic Nanoparticles with Electronically Depleted Layers.

Doped metal oxide (MO) nanocrystals (NCs) are well-known for the localized surface plasmon resonance in the infrared range generated by free electrons in the conduction band of the material. Owing to the intimate connection between plasmonic features and the NC's carrier density profile, proper modeling can unveil the underlying electronic structure. The carrier density profile in MO NCs is characterized by the presence of an electronically depleted layer as a result of the Fermi level pinning at the surface of the NC. Moreover, the carrier profile can be spatially engineered by tuning the dopant concentrations in core-shell architectures, generating a rich plethora of plasmonic features. In this work, we systematically studied the influence of the simulation parameters used for optical modeling of representative experimental absorption spectra by implementing multilayer models. We highlight in particular the importance of minimizing the fit parameters by support of experimental results and the importance of interparameter relationships. We show that, in all cases investigated, the depletion layer is fundamental to correctly describe the continuous spectra evolution. We foresee that this multilayer model can be used to design the optoelectronic properties of core-shell systems in the framework of energy band and depletion layer engineering.

Synthesis of Synergistic Ni(OH)2@ZnO Core–Shell Nanostructured Electrodes by a Hydrothermal Method and Atomic Layer Deposition for High‐Performance Supercapacitors

A novel nanoporous Ni(OH)2@ZnO core–shell architecture is successfully synthesized via a hydrothermal reaction and atomic layer deposition (ALD). This hybrid material exhibited a well‐defined core–shell nanostructure with high purity and good crystallinity. The conductivity of the electrodes is obviously enhanced by the ALD ZnO thin film. Compared to the conventional Ni(OH)2, the Ni(OH)2 coated with 10 nm of ZnO exhibited significantly enhanced performance, with a maximum specific capacitance value of ≈1,400 F g−1 at a current density of 1 A g−1, which is attributed to the improved charge‐transfer resistance. The asymmetric Ni(OH)2@ZnO//graphene supercapacitor exhibited a good capacitance retention rate and an energy density of 32 Wh kg−1 at a power density of 480 W kg−1, which are higher than those of pure nanostructured Ni(OH)2 and ZnO‐based asymmetric supercapacitors. The remarkable electrochemical performance is contributed to the synergetic presence of the core–shell nanostructure with a high surface area and the highly conductive ZnO films with optimized thickness, which achieve appropriate mass ratio control of the active material. The design of the core–shell architectures demonstrated in this work is expected to be a new and promising approach to ALD for the development of hybrid electrode materials for high‐performance supercapacitor applications.

Room-Temperature Optoelectronic Gas Sensor Based on Core-Shell g-C3N4@WO3 Heterocomposites for Efficient Ammonia Detection.

The ever-growing modern industry promotes the evolution of gas sensors for environmental monitoring and safety inspection. However, traditional chemiresistive gas sensors still suffer from drawbacks of high power consumption and detection limit, mainly due to the insufficient charge-transfer ability of gas-sensing materials. Here, an optoelectronic gas sensor that can detect ppb-level ammonia at room temperature is constructed based on core-shell g-C3N4@WO3 heterocomposites. The growth of WO3 nanosheets on graphitic g-C3N4 nanosheets was precisely controlled, achieving well-defined g-C3N4@WO3 core-shell architectures. Based on the synergism between light activation and the amplification effect of in situ-formed heterojunctions, the g-C3N4@WO3 sensor exhibits improved sensing characteristics for reliable ammonia detection. As compared with the pristine g-C3N4 sensor, the sensor response toward ammonia is enhanced 21 times and the detection limit is reduced from 308 to 108 ppb. This work provides a successful approach for the in situ formation of core-shell g-C3N4@WO3 interfacial composites and offers an easy solution for the rational design of advanced optoelectronic gas sensors.

Inner-stress-dissipative, rapid self-healing core-shell sulfide quantum dots for remarkable potassium-ion storage

Metal chalcogenides are considered as one of the most attractive anode materials for potassium ion batteries (PIBs), owing to their abundant resource, low cost and high energy density. Nevertheless, the issues of poor structure stability and capacity degradation caused by the intrinsic inner stress during (de)potassiation processes, have impeded the practical applicability. Herein, an effective inner-stress-dissipative strategy of constructing a core-shell architecture is designed for PIBs. Specifically, binary metal sulfide CoFeS2 quantum dots are intimately wrapped by in-situ formed carbon layer, which are also homogeneously distributed into the graphene matrix, establishing a robust core-shell structure. This rational constructed CoFeS2/C can effectively relieve the inner mechanical stress, restraining the continuous pulverization of active material. Furthermore, the covalent interaction formed between internal quantum dots and external carbon shell can strengthen the electrode integrity, achieving the effect of self-healing during the long-term potassiation processes. Additionally, the reaction kinetics can also be vastly improved with this unique nanostructure. Consequently, the CFS/C electrode operates an excellent nanostructure stability with enhanced cycling lifespan (1200 cycles at 2 A g−1 with a capacity of 205 mAh g−1) and a desirable rate capability (172.4 mAh g−1 at 10 A g−1) for PIBs. More importantly, combined with multiple in-situ/ex-situ characterizations and COMSOL simulations, the mechanism of effective inner-stress-dissipative are comprehensively revealed, providing an instructive guidance for designing other anode materials of advanced energy storage devices.

Magnetically induced construction of core–shell architecture Fe3O4@TiO2–Co nanocomposites for effective photocatalytic degradation of tetracycline

In this work, the magnetic Fe3O4@TiO2–Co nanocomposites were successfully synthesized as a highly recyclable and effective photocatalyst with various cobalt loading percentages and assessed for photodegradation of model tetracycline (TC) antibiotics.

Metal-organic framework-assisted Co3O4/CuO@CoMnP with core-shell nanostructured architecture on Cu fibers for fabrication of flexible wire-typed enzyme-free micro-sensors

Flexible fiber-based sensors have recently received increasing interest for real-time monitoring personal health, owing to their small size, high flexibility, lightweight, and application potentials in next-generation wearable electronics. Herein, we report a flexible wire-typed micro-sensor based on CoMnP@Co3O4/CuO core–shell nanohybrid array on 1D Cu wire substrate for sensitive detection of glucose. The synthesis process involves in-situ growth of ZIF-67 rhombic dodecahedron on the surface of CuO nanotubes, followed by thermal annealing and electrodeposition of CoMnP nanoparticles to form core–shell nanostructured architectures. Benefiting from desirable hybrid nanostructures, the as-made binder-free fiber microelectrode exposes more electroactive sites for transport of ions and electrons during the catalytic process and provides strong adhesion between electroactive species and metal fiber substrate. As a glucose sensor, the CoMnP@Co3O4/CuO fiber microelectrode displays favorable analytical properties, including two linear dynamic ranges of 0.001 mM – 0.55 mM and 0.55 mM – 3.03 mM with the sensitivities of 2445 μA mM−1cm−2 and 1774 μA mM−1cm−2, respectively, fast response time (1.62 s), excellent selectivity toward glucose at the presence interfering substances, and a low detection limit of 11.42 μM (S/N = 3). Moreover, the proposed wire-typed micro-sensor was successfully applied for measurement of glucose in human blood serum and saliva samples. Taking advantage of the versatility of 1D metal fiber current collector, MOF-assisted strategy and transition metal phosphides, the presented protocol here can be extended to the construction of other wearable and implantable sensing micro-devices.

The core-shell junctionless MOSFET

The core–shell architecture fundamentally improves the performance of regular junctionless (JL) MOSFETs. An undoped shell surrounding a heavily doped core results in normally-off operation, high charge, excellent mobility, and very high current drive. The weaknesses of a classical JL transistor (negative threshold voltage, poor mobility, random dopant fluctuations (RDF)), are suppressed while its unique features (no junctions, simple processing) are maintained.

Sunlight-active hierarchical Ag@insulator@ZnO core-shell array based on natural diatoms for environmental remediation

A nature inspired plasmonic core-shell architecture was proposed by incorporating a natural siliceous insulator shell (Navicula salinicola frustules) in Ag/diatomite/ZnO hierarchical nanostructures to overcome the recombination of energetic charge carriers (e−/h+), corrosion of bare metal, and to facilitate the composite separation after reaction. The photocatalytic performance of the as-prepared composites, monitored by decomposition of methylene blue (MB), was investigated under both UV and simulated sunlight irradiation. Ag/diatomite/ZnO exhibited efficient photocatalytic performance (near 100% degradation and 95% mineralization) under simulated sunlight irradiation with apparent rate constant of 0.0246 min−1, which was found to follow pseudo-first order kinetics. The enhanced photocatalysis action of metal/insulator/semiconductor as compared to metal/semiconductor and the semiconductor alone could be ascribed to the synergistic effects of the photonic structure of regular frustules, improved sunlight harvesting efficiency, suppressed back electron transfer, and prohibited oxidization of Ag. While the as-synthesized composite was easy to separate from the reaction, however, it was in the throes of losing the photocatalytic activity after three rounds of reuse. A possible mechanism of photocatalytic degradation of MB induced by Ag/diatomite/ZnO under sunlight irradiation was proposed based on dye degradation measurements and reactive species trapping experiments. While the reusability of as-prepared composite will doubtless be much scrutinized, our study may provide a new insight into the design and fabrication of plasmonic-based nanomaterials for use in industry applications under solar light illumination.

Reconfiguring the Electronic Structure of Heteroatom Doped Carbon Supported Bimetallic Oxide@Metal Sulfide Core-Shell Heterostructure via In Situ Nb Incorporation toward Extrinsic Pseudocapacitor.

High-energy-density battery-type materials have sparked considerable interest as supercapacitors electrode; however, their sluggish charge kinetics limits utilization of redox-active sites, resulting in poor electrochemical performance. Here, the unique core-shell architecture of metal organic framework derived N-S codoped carbon@Cox Sy micropetals decorated with Nb-incorporated cobalt molybdate nanosheets (Nb-CMO4 @Cx Sy NC) is demonstrated. Coordination bonding across interfaces and π-π stacking interactions between CMO4 @Cx Sy and N and, S-C can prevent volume expansion during cycling. Density functional theory analysis reveals that the excellent interlayer and the interparticle conductivity imparted by Nb doping in heteroatoms synergistically alter the electronic states and offer more accessible species, leading to increased electrical conductivity with lower band gaps. Consequently, the optimized electrode has a high specific capacity of 276.3mAh g-1 at 1Ag-1 and retains 98.7% of its capacity after 10 000 charge-discharge cycles. A flexible quasi-solid-state SC with a layer-by-layer deposited reduced graphene oxide /Ti3 C2 TX anode achieves a specific energy of 75.5Wh kg-1 (volumetric energy of 1.58 mWh cm-3 ) at a specific power of 1.875kWh kg-1 with 96.2% capacity retention over 10 000 charge-discharge cycles.

Jadeite original stone inspired PBA core-shell architecture endowed fire-safe and mechanic-robust EP composites with low toxicity

Epoxy resin (EP) has been favored in extensive fields. Nevertheless, the notorious issue of high fire hazard has been a nonnegligible bottleneck for its extended application. Here, a Jadeite original stone inspired PBA core-shell architecture (Co–Fe–Co PBA) is constructed towards fire retardation and toxicity elimination of EP. This architecture holds high strengths in physically blocking and chemically catalyzing towards released volatiles, leading to markedly impaired fire hazard. By using 2.0 wt% Co–Fe–Co PBA, the peak heat release rate and total heat release values are decreased by 40.2% and 33.8% whilst the peak smoke production rate and total smoke production are reduced by 43.7% and 35.2%. Also, the inhibited emissions of toxic gases including CO, NO and HCN, are discovered. Of note, the promotion in impact strength can be acquired. In brief, this work may be encouraging for the construction of PBA based hierarchical architecture, as cornerstones for fire-safe polymer composites with low toxicity.

Multifunctional Polymeric Micelles for Cancer Therapy.

Polymeric micelles, nanosized assemblies of amphiphilic polymers with a core-shell architecture, have been used as carriers for various therapeutic compounds. They have gained attention due to specific properties such as their capacity to solubilize poorly water-soluble drugs, biocompatibility, and the ability to accumulate in tumor via enhanced permeability and retention (EPR). Moreover, additional functionality can be provided to the micelles by a further modification. For example, micelle surface modification with targeting ligands allows a specific targeting and enhanced tumor accumulation. The introduction of stimuli-sensitive groups leads to the drug's release in response to environment change. This review highlights the progress in the development of multifunctional polymeric micelles in the field of cancer therapy. This review will also cover some examples of multifunctional polymeric micelles that are applied for tumor imaging and theragnosis.

Core-shell 2D/2D FeCo2O4@Ni(OH)2 nano-on-microsheet array architecture for excellent asymmetric supercapacitor performance

Core-shell designed electrode architectures with favorable material components are a promising approach to enhance electrochemical performance. Herein, binder-free 2D/2D FeCo2O4@Ni(OH)2 core–shell architectures were successfully grown on a Ni-foam (NF) substrate, where the FeCo2O4 microsheets were hydrothermally processed following the electro-grafting of Ni(OH)2 nanosheets as a “shell” around a FeCo2O4 “core.” These core–shell array architectures were utilized as a discrete electrode system; they exhibited a high specific capacitance of 1944 F g−1 at a current density of 5 A g−1, which is better than the performance of individual FeCo2O4 and Ni(OH)2. This improved performance was attributed to the synergistic effects of the robust core–shell array architectures developed over the NF substrate as well as the enhanced electrical conductivity through electroactive sites at the interface while maintaining the structural integrity of the Ni(OH)2 shell. In addition, the two-electrode device was assembled constituting a FeCo2O4@Ni(OH)2 ΙΙ activated carbon asymmetric supercapacitor, resulting in a maximum energy density of 136 W h kg−1 and power density of 8500 W kg−1, with 78% capacitance retention and 93% coulombic efficiency over 5000 cycles at a current density of 8 A g−1. These results validate the effectiveness of this approach for improving the performance of energy storage devices.

Constructing bidirectional-matched interface between polymer and 2D nanosheets for enhancing energy storage performance of the composites

Interfacial engineering, specifically core-shell architecture with highly insulating inorganic shell layer is generally adopted to improve the energy storage density (Ue) of polymer composites. However, the amorphous inorganic shell layer seems to be the only choice, as substantial interfacial tension arose from the core-shell lattice mismatch. Especially for the 2D nanosheets with high aspect ratio and highly crystallized surface, free volume between interfacial region is inevitably formed, restricting further Ue improvements of polymers. Here, bidirectional matched (bm) aluminum oxide interface transition regions are constructed between polyimide (PI) and Ca2Nb3O10 (CNO) nanosheets to prepare the composites (PI/CNO@AO). The bm-interface includes the inner core-shell lattice matched region and the outer shell-matrix structure matched region, and the gradual transition between them has been confirmed. Numerous experimental and characterization results manifested the successful construction of the bm-interface, and the interface could intrinsically depress the carrier transportation and electric conduction of the composites. Meanwhile, the simulated electric breakdown paths evolution in the PI/CNO@AO composites further confirms the results. Consequently, excellent energy storage performance of the composites is obtained at both conventional and high-temperature environments. The bm-interface design strategy holds great promises and may blaze new trails in preparing high energy density polymer dielectric capacitors.

Core-shell and hollow meso@microporous carbon derived from ZIF-8 @CMK-3 composites for Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted much attention because of their potential as a new technology for high-energy batteries. However, the “shuttle effect” of polysulfide intermediates and poor conductivity of sulfur active species limit the development of Li-S batteries. Herein, a novel core-shell and hollow meso@microporous carbon matrix (ZIF-8(C)@CMK-3) is designed, which wraps N-doped carbon shell in the outer layer of ordered mesoporous CMK-3 through in-situ carbonization of thin zeolitic-imidazolate framework ZIF-8 layer. The combination of advantages of unique pore size, N-doping and core-shell architecture renders the resultant carbon matrix with enhanced electron/Li+ transport and the synergistic chemical/physical polysulfide anchoring. As a result, ZIF-8(C)@CMK-3 @S exhibits high reversible capacity (1597.2 mAh/g at a current density of 0.1 C) and well stability (596 mAh/g after 300 cycles at 2 C), and the fading rate per cycle capacity is 0.11%. The results indicated ZIF-8(C)@CMK-3 has a great potential to be used as efficient sulfur immobilizer for Li-S batteries.

Direct strain correlations at the single-atom level in three-dimensional core-shell interface structures

Nanomaterials with core-shell architectures are prominent examples of strain-engineered materials. The lattice mismatch between the core and shell materials can cause strong interface strain, which affects the surface structures. Therefore, surface functional properties such as catalytic activities can be designed by fine-tuning the misfit strain at the interface. To precisely control the core-shell effect, it is essential to understand how the surface and interface strains are related at the atomic scale. Here, we elucidate the surface-interface strain relations by determining the full 3D atomic structure of Pd@Pt core-shell nanoparticles at the single-atom level via atomic electron tomography. Full 3D displacement fields and strain profiles of core-shell nanoparticles were obtained, which revealed a direct correlation between the surface and interface strain. The strain distributions show a strong shape-dependent anisotropy, whose nature was further corroborated by molecular statics simulations. From the observed surface strains, the surface oxygen reduction reaction activities were predicted. These findings give a deep understanding of structure-property relationships in strain-engineerable core-shell systems, which can lead to direct control over the resulting catalytic properties.

(Invited) A Novel Pathway for the Construction of Core–Shell Photocathodes for PEC Applications

Semiconductor hetero-nanostructures are of great interest for practical use. In this presentation, a novel approach to production of CuO|CuFe2O4 core-shell structure by thermal conversion of CuFe Prussian Blue Analogues will be demonstrated. It represents a new family of photocatalysts that can be used as photoelectrodes able to produce hydrogen under broad spectrum of the visible light. The outstanding photoelectrochemical properties of the photocathodes of CuO|CuFe2O4 have been studied with use of combinatory photo-electrochemical instrumental techniques which proved the electrodes were stable over the whole water photolysis run under relatively positive potentials. Their outstanding performance have been explained by coupling of two charge transfer mechanisms occurring in core-shell architectures. Then, the CuO:Zn nanostructures, in which the photoelectrochemical properties were governed by Fermi level pinning of Zn ions would be presented as well. The implementation of Zn ions enlarged the space charge region and triggered electron availability for the photolysis of water which is unusual for p-type semiconductors. Furthermore, the excellent crystallinity, high surface area, and adhesion to the FTO remarkably improved the photocatalytic activity of the CuO:Zn thin film with cathodic photocurrent of 4 mAcm-2 and a quantum efficiency of 35%, making it promising for hydrogen production.

Ultrasmall Copper Nanoclusters in Zirconium Metal‐Organic Frameworks for the Photoreduction of CO2

AbstractEncapsulating ultrasmall Cu nanoparticles inside Zr‐MOFs to form core–shell architecture is very challenging but of interest for CO2reduction. We report for the first time the incorporation of ultrasmall Cu NCs into a series of benchmark Zr‐MOFs, without Cu NCs aggregation, via a scalable room temperature fabrication approach. The Cu NCs@MOFs core–shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs, regardless of their very similar intrinsic properties at the atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the CuIsites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze CO2photoreduction. This synergetic effect may pave the way for the design of low‐cost and efficient catalysts for CO2photoreduction into high‐value chemical feedstock.