Core-shell Strategy Research Articles

Triple S-scheme BiOBr@LaNiO3/CuBi2O4/Bi2WO6 heterojunction with plasmonic Bi-induced stability: deviation from quadruple S-scheme and mechanistic investigation

The investigation and understanding of heterointerfaces formation and charge transfer dynamics in two or more semiconductor heterojunctions increased ensuing establishment of S-scheme and dual S-scheme heterojunctions. However, investigations of possible charge transfer at interfaces and their type in four component systems are limited. Herein, a four-component heterojunction was investigated to postulate and demonstrate deviation between quadruple and triple S-scheme heterojunctions possibilities using LaNiO3, BiOBr, CuBi2O4, and Bi2WO6. DFT and XPS were used to construct the band structure and support the charge transfer at the interfaces to follow S-S strategy during OTC and SMX degradation under visible light. IEF, bend bending systematically modulated charge transfer, and the core-shell strategy restricted possible junctions’ formation to three to accord triple S-scheme heterojunction. This work demonstrated the construction of Triple S-scheme heterostructures as a promising strategy for efficient charge separation making it a suitable candidate for elimination of pollutants.

An order-disorder core-shell strategy for enhanced work-hardening capability and ductility in nanostructured alloys

Nanocrystalline metallic materials have the merit of high strength but usually suffer from poor ductility and rapid grain coarsening, limiting their practical application. Here, we introduce a core-shell nanostructure in a multicomponent alloy to address these challenges simultaneously, achieving a high tensile strength of 2.65 GPa, a large uniform elongation of 17%, and a high thermal stability of 1173 K. Our strategy relies on an ordered superlattice structure that excels in dislocation accumulation, encased by a ≈3 nm disordered face-centered-cubic nanolayer acting as dislocation sources. The ordered superlattice with high anti-phase boundary energy retards dislocation motions, promoting their interaction and storage within the nanograins. The disordered interfacial nanolayer promotes dislocation emission and effectively accommodates the plastic strain at grain boundaries, preventing intergranular cracking. Consequently, the order-disorder core-shell nanostructure exhibits enhanced work-hardening capability and large ductility. Moreover, such core-shell nanostructure exhibits high coarsening resistance at elevated temperatures, enabling it high thermal stability. Such a design strategy holds promise for developing high-performance materials.

Investigating replacement core-shell strategies for optimizing photocatalytic chromium reduction with MOF-on-MOF heterostructure on steel mesh

While cerium-based metal-organic frameworks (Ce-MOFs) exhibit inherent limitations in standalone photocatalytic efficacy, their potential amplifies when integrated into heterostructures with other semiconductors, leveraging the advantageous heterojunction effects. This study systematically explores the establishment of heterojunctions between Ce-MOFs and zirconium-based frameworks, delineating the performance variance based on the positioning of Ce-MOFs within the MOF-on-MOF architecture. When situated as the outer shell in these configurations, Ce-MOFs significantly enhance the photocatalytic capabilities compared to their placement in the core. Further, immobilizing these composite structures onto steel substrates demonstrates remarkable efficiency in the purification of hexavalent chromium from water under visible light exposure. Initially, Ce-MOF-801-on-Zr-MOF-801 and Zr-MOF-801-on-Ce-MOF-801 heterojunctions were synthesized to explore their combined and MOF-on-MOF effects. Subsequently, Ce-MOF-801-on-Zr-MOF-801 was applied onto a steel mesh substrate using the spraying method. The results demonstrated exceptional efficiency in Cr(VI) extraction and remarkable durability. Crucially, leaching tests and ICP-OES analysis confirmed the material's strong adhesion to the substrate, enabling repeated use. Impressively, even after multiple cycles, the material efficiently purified Cr(VI) from water within 120 min under visible light. With all these merits, the Cr(VI) removal efficiency of Ce-MOF-801-on-Zr-MOF-801/mesh with an initial Cr(VI) concentration of 5 ppm is near 100% for 2 h. This work presents a feasible and promising route to filter suitable photocatalyst materials by using mesh substrates for fixing environmental issues.

Capillary Suction Properties of Mortar Made with Recycled Plastic Aggregates Elaborated from Waste Electrical and Electronic Equipment

It is possible to revalue the plastic fraction from WEEE using it as a recycled aggregate (RA) in cement mortars. However, this feasibility depends on elaborating a granular material via a core-shell strategy to stabilize the potential contaminants. The core is a plastic particle, and the shell is a cement, fillers, and activated carbon mixture. Due to the hydrophilic characteristics of the shell and the presence of interstitial sites generated by the use of the RA, it is necessary to study the wetting properties of these mortars. This article presents the results of capillary suction and contact angle studies of mortars made with RA having different shell compositions. The capillary suction of the latter is higher than in traditional mortars, which limits their use for structures exposed to water and environmental agents but opens the possibility of new uses in permeable concrete or for the manufacture of building components.

Hollow SiC@MnO2 nanospheres with tunable core size and shell thickness for excellent electromagnetic wave absorption

The hollow microstructure can permit more incident waves to enter the absorber and increase the attenuation ability by multiple reflections and diffraction. In addition, different substances can introduce the heterogeneous interface and further attenuate electromagnetic waves through interfacial polarisation relaxation. Here, hollow SiC@MnO2 nanospheres are synthesised with tunable hollow SiC core size and flower-like layered MnO2 shell thickness. By adjusting the concentration of KMnO4, different shell thicknesses of hollow SiC@MnO2 nanospheres can be prepared, ranging from 40 nm to 110 nm. Furthermore, hollow SiC@MnO2 composites with different inner diameters between 300 nm and 470 nm can be obtained by tailoring the amount of tetraethyl orthosilicate. The results indicate that the effective absorbing bandwidth of hollow SiC@MnO2 can reach 5.71 GHz with a core size of 360 nm and a shell thickness of 90 nm at only 1.8 mm. This work provides a valuable core–shell strategy of hollow SiC@MnO2 towards excellent electromagnetic wave-absorbing properties.

Review of the Scalable Core-Shell Synthesis Methods: The Improvements of Li-Ion Battery Electrochemistry and Cycling Stability.

The demand for lithium-ion batteries has significantly increased due to the increasing adoption of electric vehicles (EVs). However, these batteries have a limited lifespan, which needs to be improved for the long-term use needs of EVs expected to be in service for 20 years or more. In addition, the capacity of lithium-ion batteries is often insufficient for long-range travel, posing challenges for EV drivers. One approach that has gained attention is using core-shell structured cathode and anode materials. That approach can provide several benefits, such as extending the battery lifespan and improving capacity performance. This paper reviews various challenges and solutions by the core-shell strategy adopted for both cathodes and anodes. The highlight is scalable synthesis techniques, including solid phase reactions like the mechanofusion process, ball-milling, and spray-drying process, which are essential for pilot plant production. Due to continuous operation with a high production rate, compatibility with inexpensive precursors, energy and cost savings, and an environmentally friendly approach that can be carried out at atmospheric pressure and ambient temperatures. Future developments in this field may focus on optimizing core-shell materials and synthesis techniques for improved Li-ion battery performance and stability.

Multilayer design of core–shell nanostructure to protect and accelerate sulfur conversion reaction

Although a core–shell design has been suggested to maximize reversible redox reaction of conversion–type electrode materials inside a shell, it is challenging to fulfill the complicated prerequisites collectively. This paper proposes a rational core–shell design composed of single–atom catalytic and protective multilayers for sulfur conversion reaction. A hydrogen bond–based supramolecular network incorporates Fe ions by metal–phenolic coordination, accelerating sluggish kinetics. The polypyrrole layer protects the entire structure to suppress the migration of polysulfides and withstand large volume changes. Comprehensive investigation demonstrates that core–shell sulfur nanostructures preserve the structural integrity and electrocatalytic effect during discharge/charge. The resulting electrodes enable outstanding rate capability and stable cycling performance. Furthermore, the areal capacity of higher sulfur loading cells surpasses current Li–ion batteries even at 1 C. This work reactivates the core–shell strategy as a design guideline for viable next–generation electrode materials.

Insights into the Structural and Thermodynamic Instability of Ni-Rich NMC Cathode

The Ni-rich LiNi1-x-yMnxCoyO2 (NMC) layered oxides have been promising materials to replace the LiCoO2 commercial cathode due to their high operation voltages, low cost, and enhanced capacity. However, structural instability is the main drawback of the Ni-rich NMC system, leading to capacity fading, which prevents its commerce application. While numerous efforts have been made to comprehend and overcome this issue, there remains a lack of systematic phase stability analysis which is an essential factor to be addressed. Herein, systematic first-principles calculations were performed in this study to reveal the structural, oxidation, and phase stability of Ni-rich NMC during delithiation. This is the first report on competing phases of Ni-rich NMC at various states of charge (SoCs). The compounds with the spinel and rock salt structures formed during delithiation and oxygen evolution takes place at highly delithiation cases, which are likely the origins of capacity fading and crack formation at the surface. This work also outlined the thermodynamic foundation of doping and oxidation state gradient-based core–shell strategies for resolving the instability and enhancing the capacity retention of Ni-rich NMC layered oxides as cathode materials in Li-ion batteries.

Unraveling the Growth Process of Core–Shell Structured Upconversion Nanoparticles: Implications for Color Tuning of Upconversion Luminescence

The core–shell strategy has been routinely employed to improve emissive properties of upconversion nanoparticles (UCNPs). However, the underlying process of forming the core–shell structure still remains largely unexplored. In this work, we have performed a time-course study on the growth process of NaErF4@NaYF4 core–shell UCNPs to track time-dependent variations in size, phase, elemental distribution, and luminescence properties throughout the whole synthesis process. Our results show that the formation of core–shell UCNPs includes three major stages: formation of α-phase shell precursors, transition of the α-phase to β-phase, and seed-mediated growth. Among these stages, the first two mainly occur in the early stage of the growth process, while the last one dominates the subsequent process. During the seed-mediated growth process, the elemental distribution of the core–shell nanostructure is observed to change after a short time of reaching the reaction temperature and it continues throughout the rest of the growth process. Most importantly, the emissive properties also showed time-dependent variations, which were attributed to the activation of different optical pathways due to different shell thicknesses over time. This study is believed to provide fundamental insights into the growth mechanism of core–shell UCNPs, which can also be potentially applied for tuning the luminescence of other core–shell luminescent nanostructures.

Development of Hetero-Cell Type Spheroids Via Core-Shell Strategy for Enhanced Wound Healing Effect of Human Adipose-Derived Stem Cells.

Stem cell-based therapies have been developed to treat various types of wounds. Human adipose-derived stem cells (hADSCs) are used to treat skin wounds owing to their outstanding angiogenic potential. Although recent studies have suggested that stem cell spheroids may help wound healing, their cell viability and retention rate in the wound area require improvement to enhance their therapeutic efficacy. We developed a core-shell structured spheroid with hADSCs in the core and human dermal fibroblasts (hDFs) in the outer part of the spheroid. The core-shell structure was formed by continuous centrifugation and spheroid incubation. After optimizing the method for inducing uniform-sized core-shell spheroids, cell viability, cell proliferation, migration, and therapeutic efficacy were evaluated and compared to those of conventional spheroids. Cell proliferation, migration, and involucrin expression were evaluated in keratinocytes. Tubular assays in human umbilical vein endothelial cells were used to confirm the improved skin regeneration and angiogenic efficacy of core-shell spheroids. Core-shell spheroids exhibited exceptional cell viability under hypoxic cell culture conditions that mimicked the microenvironment of the wound area. The improvement in retention rate, survival rate, and angiogenic growth factors secretion from core-shell spheroids may contribute to the increased therapeutic efficacy of stem cell treatment for skin wounds.

Bioprinting microporous functional living materials from protein-based core-shell microgels

Living materials bring together material science and biology to allow the engineering and augmenting of living systems with novel functionalities. Bioprinting promises accurate control over the formation of such complex materials through programmable deposition of cells in soft materials, but current approaches had limited success in fine-tuning cell microenvironments while generating robust macroscopic morphologies. Here, we address this challenge through the use of core-shell microgel ink to decouple cell microenvironments from the structural shell for further processing. Cells are microfluidically immobilized in the viscous core that can promote the formation of both microbial populations and mammalian cellular spheroids, followed by interparticle annealing to give covalently stabilized functional scaffolds with controlled microporosity. The results show that the core-shell strategy mitigates cell leakage while affording a favorable environment for cell culture. Furthermore, we demonstrate that different microbial consortia can be printed into scaffolds for a range of applications. By compartmentalizing microbial consortia in separate microgels, the collective bioprocessing capability of the scaffold is significantly enhanced, shedding light on strategies to augment living materials with bioprocessing capabilities.

Design and characterization of molecular, crystal and interfacial structures of PVDF-based dielectric nanocomposites for electric energy storage.

PVDF-based polymers with polar covalent bonds are next-generation dielectric materials for electric energy storage applications. Several types of PVDF-based polymers, such as homopolymers, copolymers, terpolymers and tetrapolymers, were synthesized by radical addition reactions, controlled radical polymerizations, chemical modifications or reduction with the monomers of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE). Owing to rich molecular structures and complicated crystal structures, PVDF-based dielectric polymers can show versatile dielectric polarization properties, including normal ferroelectrics, relaxor ferroelectrics, anti-ferroelectrics and linear dielectrics, which are beneficial for designing polymer films with high capacity and high charge-discharge efficiency for capacitor applications. Furthermore, to satisfy the requirements of practical high-capacity capacitors, the polymer nanocomposite method is another promising strategy to achieve high-capacitance dielectric materials by the addition of high-dielectric ceramic nanoparticles, moderate-dielectric nanoparticles (MgO, and Al2O3), high-insulation nanosheets (BN), etc. It is concluded with the current problems and future perspectives of interfacial engineering, such as core-shell strategies and hierarchical interfaces in polymer-based composite dielectrics for high-energy-density capacitor applications. In addition, an in-depth understanding of the roles of interfaces on the dielectric properties of nanocomposites can be achieved by indirect analysis techniques (theoretical simulation) and direct analysis techniques (scanning probe microscopy). Our systematic discussions on molecular, crystal and interfacial structures provide guidance for designing fluoropolymer-based nanocomposites for high-performance capacitor applications.

Solvation and Stabilization of Superior Alanate Nanostructures

NaAlH4 and LiAlH4 are promising materials for hydrogen storage due to their high hydrogen density (7.4 and 10.5 mass%, respectively). However, their practical application is hampered from the slow hydrogen kinetics and poor reversibility. To improve the hydrogen properties of alanates, the alternative core–shell strategy has been proposed. In this respect, a simple solvent evaporation method is presented to synthesize the alanate core. In this approach, NaAlH4 and LiAlH4 are stabilized by solvation and electrostatic forces, respectively, through the addition of ionic salts. Remarkably, it is found that the size of the alanate nanoparticles can be tuned by varying the concentration of the introduced ion. More importantly, the partial substitution of Na+ and Li+ with cations of higher electronegativity enables the release of hydrogen at much lower temperatures.

Preserving DNA in Biodegradable Organosilica Encapsulates.

A core-shell strategy was developed to protect synthetic DNA in organosilica particles encompassing dithiol linkages allowing for a DNA loading of 1.1 wt %. DNA stability tests involving bleach as an oxidant showed that following the procedure DNA was sandwiched between core particles of ca. 450 nm size and a protective outer layer, separating the DNA from the environment. Rapid aging tests at 60 °C and 50% relative humidity revealed that the DNA protected within this material was significantly more stable than nonprotected DNA, with an expected ambient temperature half-life of over 60 years. Still, and due to the presence of the dithiol linkages in the backbone of the organosilica material, the particles degraded in the presence of reducing agents (TCEP and glutathione) and disintegrated within several days in a simulated compost environment, which was employed to test the biodegradability of the material. This is in contrast to DNA encapsulated following state of the art procedures in pure SiO2 particles, which do not biodegrade in the investigated timeframes and conditions. The results show that synthetic DNA protected within dithiol comprising organosilica particles presents a strategy to store digital data at a high storage capacity for long time frames in a fully biodegradable format.

Delicate and Independent Manipulation of Dynamic Fluorescence Behavior of Polymer Nanoparticles Based on a Core-Shell Strategy.

Fluorescent polymer nanomaterials with dynamic fluorescence properties hold great potential in many advanced applications, including but not limited to information encryption, adaptive camouflage, and biosensors. The key to improving the application value of materials is to establish an accurate control strategy for dynamic fluorescence behavior. Herein, we develop a core-shell engineering strategy to precisely and independently manipulate the dynamic fluorescence behavior through the shell polymeric matrix. The core-shell fluorescent polymer nanoparticles (CS-FPNPs) are constructed through a sequential process of miniemulsion polymerization and seeded emulsion polymerization. Taking advantage of the core-shell structure, the rigid core matrix ensures the strong initial emission of AIE units, while the photoisomerization behavior of spiropyrane (SP) units is delicately and independently regulated by the rigidness of the shell matrix. Thereby, CS-FPNPs exhibit bright time-dependent reversible dynamic fluorescence behavior under alternating UV/vis irradiation. Benefited from the excellent processability and film formation ability, we have successfully applied CS-FPNPs to dynamic decorative painting, warning labels, and dynamic QR code security. Impressively, the fluorescence manipulation strategy based on core-shell engineering allows the independent regulation of specific luminescent units in complicated emission systems to accurately embody designed emission behavior.

Impact and bonding behavior of core-shell powder particles

Deposition of hard coatings via cold spray, while desirable, has proven challenging due to the lack of plasticity upon the impact of hard powder particles on substrates. We systematically study a core-shell strategy where a hard particle is coated with a softer shell to address this challenge. We use laser-induced projectile impact tests to study the impact behavior of W-Cu core-shell particles at the single powder particle level. Impact and bonding characteristics of the core-shell particles with two different shell thicknesses are studied in-situ and post-mortem, and compared with that of monolithic W and Cu particles. We complement our experimental observations with finite element simulations of the impact behavior of core-shell particles. We find that the core-shell configuration can be used to tune the impact deformation and that the deformable shell can provide the plasticity needed for successful impact bonding. As the thickness of the Cu shell increases, the bonding mode begins to shift from merely mechanical embedment to metallurgical bonding.

STABILIZATION OF LEACHATE IN AGGREGATES MADE WITH PLASTIC FROM WEEE

A recycled plastic aggregate (RPA) was developed using the core-shell strategy, where the core is the plastic fraction of Waste of Electrical and Electronic Equipment (WEEE) and a cement matrix with stabilizing additives acts as the shell. The amount of brominated flame retardant (mainly tetrabromobisphenol-A) leached in curing water of RPAs was quantified using extraction with an organic solvent and gas chromatography methods (CG-FID). A clear relationship can be established between the characteristics of the stabilizing additive used and the amount of tetrabromobisphenol-A and bisphenol-A leached. The additive used was activated carbon, which in a manufacture scale may be provided by different suppliers with different mesoporous characteristics, which can be easily determined by the iodine number. The analysis proposed can be an effective way to determine if a particular activated carbon can be used as stabilizing additive in the production of RPAs with the developed technology.

Molten-Salt-Assisted Annealing for Making Colloidal ZnGa2 O4 :Cr Nanocrystals with High Persistent Luminescence.

Persistent luminescent nanocrystals (PLNCs) in the sub-10 nm domain are considered to be the most fascinating inventions in lighting technology owing to their excellent performance in anti-counterfeiting, luminous paints, bioimaging, security applications, etc. Further improvement of persistent luminescence (PersL) intensity and lifetime is needed to achieve the desired success of PLNCs while keeping the uniform sub-10 nm size. In this work, the concept of molten salt confinement to thermally anneal as-synthesized ZnGa2 O4 :Cr3+ (ZGOC) colloidal NCs (CNCs) in a molten salt medium at 650 °C is introduced. This method led to significantly monodispersed and few agglomerated NCs with a much improved photoluminescence (PL) and PersL intensity without much growth in the size of the pristine CNCs. Other strategies such as i) thermal annealing, ii) overcoating, and iii) the core-shell strategy have also been tried to improve PL and PersL but did not improve them simultaneously. Moreover, directly annealing the CNCs in air without the assistance of molten salt could significantly improve both PL and PersL but led to particle heterogeneity and aggregation, which are highly unsuitable for in vivo imaging. We believe this work provides a novel strategy to design PLNCs with high PL intensity and long PersL duration without losing their nanostructural characteristics, water dispersibility and biocompatibility.

A core-shell catalyst design boosts the performance of photothermal reverse water gas shift catalysis

Photothermal reverse water gas shift (RWGS) catalysis holds promise for efficient conversions of greenhouse gas CO2 and renewable H2, powered solely by sunlight, into CO, an important feedstock for the chemical industry. However, the performance of photothermal RWGS catalysis over existing supported catalysts is limited by the balance between the catalyst loading and dispersity, as well as stability against sintering. Herein, we report a core-shell strategy for the design of photothermal catalysts, by using Ni12P5 as an example, with simultaneously strong light absorption ability, high dispersity and stability. The core-shell structured Ni12P5@SiO2 catalyst with a relatively small Ni12P5 particle size of 15 nm at a high Ni12P5 loading of 30 wt% exhibits improved activity, nearly 100% CO selectivity, and superior stability in photothermal RWGS catalysis, particularly under intense illuminations. Our study clearly reveals the effectiveness of the core-shell strategy in breaking the limitation of supported catalysts and boosting the performance of photothermal CO2 catalysis.

Improved dielectric properties of PVDF nanocomposites with core–shell structured BaTiO 3 @polyurethane nanoparticles

Polymer nanocomposites with improved dielectric permittivity and high breakdown strength are extremely desirable for the flexible electronic devices and power systems. The compatibility of fillers and polymer matrix is important in determining the dielectric and breakdown strength properties. The core–shell structure concept is useful to improve the compatibility of fillers with polymer matrix. Herein, an organic thermoplastic urethanes (TPU) polymer shell was successfully grafted on the surface of barium titanate (BaTiO3, BT) and such a TPU shell improved the permittivity and breakdown strength of TPU@BT/PVDF polymer nanocomposites greatly. The permittivity of TPU@BT/PVDF nanocomposites with 12 wt% fillers at 102 Hz was up to 13.5, which was 1.5 times higher than that of pure poly(vinylidene fluoride) (PVDF). The improvement of the dielectric properties could be attributed to the enhanced interfacial polarisation between BT nanoparticles and TPU shell. Besides, the compatibility of BT nanoparticles and PVDF matrix was improved after the introduction of TPU shell. Accordingly, a highest breakdown strength value about 373 MV/m was obtained for the TPU@BT/PVDF nanocomposites with 7 wt% fillers. The core–shell strategy could be extended to a variety of inorganic fillers to improve the dielectric and breakdown strength properties of polymer nanocomposites.