Enhancing electromagnetic wave absorption with core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres

Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2) as the core,MXene as the intermediate layer,and MoS_(2) as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2) nanosheets.Notably,the synergistic combination of SiO_(2) and MoS_(2) with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”

Control and vibration analyses of a sandwich doubly curved micro-composite shell with honeycomb,truss,and corrugated cores based on the fourth-order shear deformation theory

Curved shells are increasingly utilized in applied engineering due to their shared characteristics with other sandwich structures,flexibility,and attractive appearance.However,the inability of controlling and regulating vibrations and destroying them afterward is a challenge to scientists.In this paper,the curve shell equations and a linear quadratic regulator are adopted for the state feedback design to manage the structure vibrations in state space forms.A five-layer sandwich doubly curved micro-composite shell,comprising two piezoelectric layers for the sensor and actuator,is modeled by the fourth-order shear deformation theory.The core(honeycomb,truss,and corrugated)is analyzed for the bearing of transverse shear forces.The results show that the honeycomb core has a greater effect on the vibrations.When the parameters related to the core and the weight percentage of graphene increase,the frequency increases.The uniform distribution of graphene platelets results in the lowest natural frequency while the natural frequency increases.Furthermore,without taking into account the piezoelectric layers,the third-order shear deformation theory(TSDT)and fourth-order shear deformation theory(FOSDT)align closely.However,when the piezoelectric layers are incorporated,these two theories diverge significantly,with the frequencies in the FOSDT being lower than those in the TSDT.

Facile in situ synthesis and characterization of Fe@Si/zeolite Na composites with magnetic core–shell structures from natural materials for enhanced curcumin loading capacity

Curcumin is a natural polyphenol that is used in various traditional medicines.However,its inherent properties,such as its rapid degradation and metabolism,low bioavailability,and short half-life,are serious problems that must be resolved.To this end,a drug carrier incorporating natural magnetic cores in a zeolite framework was developed and applied to the loading of curcumin in ethanol solutions.In this system,curcumin is encapsulated in a zeolite Na(ZNA)magnetic core–shell structure(Fe@Si/ZNA),which can be easily synthesized using an in situ method.Synthesis of Fe_(3)O_(4) nanoparticles was carried out from natural materials using a co-precipitation method.Analysis of the prepared magnetic core–shell structures and composites was carried out using vibrating-sample magnetometery,Fourier transform infrared spectroscopy,transmission electron microscopy,and x-ray diffraction.The cumulative loading of curcumin in the ZNA composite with 9%nanoparticles was found to reach 90.70%with a relatively long half-life of 32.49 min.Stability tests of curcumin loading in the composite showed that adding magnetic particles to the zeolite framework also increased the stability of the composite structure.Adsorption kinetics and isotherm studies also found that the system follows the pseudo-second-order and Langmuir isotherm models.

Heterostructural NiFeW disulfide and hydroxide dual‐trimetallic core‐shell nanosheets for synergistically effective water oxidatio

A stable and highly active core‐shell heterostructure electrocatalyst is essential for catalyzing oxygen evolution reaction(OER).Here,a dual‐trimetallic core‐shell heterostructure OER electrocatalyst that consists of a NiFeWS_(2) inner core and an amorphous NiFeW(OH)_(z)outer shell is designed and synthesized using in situ electrochemical tuning.The electrochemical measurements of different as‐synthesized catalysts with a similar mass loading suggest that the core‐shell Ni_(0.66)Fe_(0.17)W_(0.17)S_(2)@amorphous NiFeW(OH)_(z) nanosheets exhibit the highest overall performance compared with that of other bimetallic reference catalysts for the OER.Additionally,the nanosheet arrays were in situ grown on hydrophilic‐treated carbon paper to fabricate an integrated three‐dimensional electrode that affords a current density of 10 mA cm^(−2) at a small overpotential of 182 mV and a low Tafel slope of 35 mV decade^(−1) in basic media.The Faradaic efficiency of core‐shell Ni_(0.66)Fe_(0.17)W_(0.17)S_(2)@amorphous NiFeW(OH)_(z) is as high as 99.5% for OER.The scanning electron microscope,transmission electron microscope,and X‐ray photoelectron spectroscopy analyses confirm that this electrode has excellent stability in morphology and elementary composition after long‐term electrochemical measurements.Importantly,density functional theory calculations further indicate that the core‐shell heterojunction increased the conductivity of the catalyst,optimized the adsorption energy of the OER intermediates,and improved the OER activity.This study provides a universal strategy for designing more active core‐shell structure electrocatalysts based on the rule of coordinated regulation between electronic transport and active sites.

Interface formation energy,bonding,energy band alignment in α-NaYF4 related core shell models:For future multi-layer core shell luminescence materials

To break through the bottle-neck of quantum yield in upconversion （UC） core-shell system, we elucidated that the energy transfer efficiency in core-shell system had an evident contribution from the charge transfer of interface with related to two factors： （i） band offsets and （2） binding energy area density. These two variables were determined by material intrinsic properties and core-shell thickness ratio. We further unraveled the mechanism of non-radiative energy transfer by charge transfer induced dipole at the inter- face, based on a quasi-classical derivation from F6rster type resonant energy transfer （FRET） model. With stable bonding across the interface, the contributions on energy transfer in both radiative and non-radiative energy transfer should also be accounted together in Auzel＇s energy transfer （ETU） model in core-shell system. Based on the discussion about interface bonding, band offsets, and forma- tion energies, we figured out the significance of interface bonding induced gap states （IBIGS） that played a significant role for influ- encing the charge transfer and radiative type energy transfer. The interface band offsets were a key factor in dominating the non-radiative energy transfer, which was also correlated to core-shell thickness ratio. We found that the energy area density with re- lated to core/shell thickness ratio followed the trend of Boltzman sigmoidal growth function. By the physical trend, this work contrib- uted a reference how the multi-layered core-shell structure was formed starting from the very beginning within minimum size. A route was paved towards a systematic study of the interface to unveil the energy transfer mechanism in core-shell systems.

A core-shell copper oxides-cobalt oxides heterostructure nanowire arrays for nitrate reduction to ammonia with high yield rate

Electrochemical nitrate reduction to ammonia(NRA) can realize the green synthesis of ammonia(NH3) at ambient conditions, and also remove nitrate contamination in water. However, the current catalysts for NRA still face relatively low NH3yield rate and poor stability. We present here a core-shell heterostructure comprising cobalt oxide anchored on copper oxide nanowire arrays(CuO NWAs@Co_(3)O_(4)) for efficient NRA. The CuO NWAs@Co_(3)O_(4)demonstrates significantly enhanced NRA performance in alkaline media in comparison with plain CuO NWAs and Co_(3)O_(4)flocs. Especially, at-0.23 V vs. RHE, NH_(3) yield rate of the CuO NWAs@Co_(3)O_(4)reaches 1.915 mmol h^(-1)cm^(-2),much higher than those of CuO NWAs(1.472 mmol h^(-1)cm^(-2)), Co_(3)O_(4)flocs(1.222 mmol h^(-1)cm^(-2)) and recent reported Cu-based catalysts.It is proposed that the synergetic effects of the heterostructure combing atom hydrogen adsorption and nitrate reduction lead to the enhanced NRA performance.

Wrinkling in graded core/shell systems using symplectic formulation

Wrinkles in flat graded elastic layers have been recently described as a timevarying Hamiltonian system by the energy method.Cylindrical core/shell structures can also undergo surface instabilities under the external pressure.In this study,we show that by treating the radial direction as a pseudo-time variable,the graded core/shell system with radially decaying elastic properties can also be described within the symplectic framework.In combination with the shell buckling equation,the present paper addresses the surface wrinkling of graded core/shell structures subjected to the uniform external pressure by solving a series of ordinary differential equations with varying coefficients.Three representative gradient distributions are showcased,and the predicted critical pressure and critical wave number are verified by finite element simulations.The symplectic framework provides an efficient and accurate approach to understand the surface instability and morphological evolution in curved biological tissues and engineered structures.

Structural Analysis of TiC and TiC-C Core-Shell Nanostructures Produced by Pulsed-Laser Ablation

This paper reports on the ablation process of a pure Ti solid target immersed in a C-enriched acetone solution, leading to the production of titanium carbide (TiC) and Ti-C core-shell nanostructures. The used route of synthesis is generally called pulsed laser ablation in liquid (PLAL). The presence of carbon structures in the solution contributed to the carbon content in the produced Ti-based nanomaterials. The atomic composition of the produced nanostructures was analyzed using SEM-EDS, while TEM micrographs revealed the formation of spherical TiC and core-shell nanostructures ranging from 40 to 100 nm. The identification of atomic planes by HRTEM confirmed a 10 nm diameter C-shell with a graphite structure surrounding the Ti-core. Raman spectroscopy allowed for the identification of D and G peaks for graphite and a Raman signal at 380 and 600 cm−1, assigned to TiC. The results contribute to the state-of-the-art production of TiC and Ti-C core-shell nanostructures using the PLAL route.

Au_(core)Co_(shell)纳米粒子的制备、表征及其表面增强拉曼光谱研究

AucoreCoshell nanoparticles with different shell thicknesses were prepared by using chemical reduction method and characterized by scanning electron microscopy（SEM） and cyclic voltammetry（CV）. The results reveal that the prepared core-shell nanoparticles were covered by Co shell and exhibited the similar electrochemistry property with the Co nanoparticles surface. Surface enhanced Raman spectroscopy（SERS） activities of these nanoparticles were studied by using pyridine as a probe molecule. It was found that the SERS intensity depended on the Co shell thickness of the core-shell nanoparticles and was weakened with the increasing shell thickness. The SERS intensity of these AucoreCoshell nanoparticles is found to be about twenty times higher than that obtained on an electrochemically roughened cobalt electrode.

Fe_(core)-Pt_(shell)/C核壳型纳米催化剂电催化还原氧的性能

应用两步化学还原法合成不同壳层厚度的Fecore-Ptshell纳米粒子,并用SEM、TEM、EDS和XRD手段对其进行物理表征,应用动电位、交流阻抗和循环伏安法进行氧还原电催化活性及抗甲醇性测试。结果表明,样品Fecore-Ptshell纳米颗粒粒径分布集中,其中Fecore,1-Ptshell,0.5平均值为50nm,核芯直径约34nm,壳层厚度约8nm;与Pt/C相比,Fecore-Ptshell/C对氧还原的催化活性和抗甲醇性明显提高,Fe与Pt原子比为1:0.5的Fecore-Ptshell/C在0.5mol·L-1H2SO4中氧还原的最大峰电流密度可达到184.7mA·mg-1,是相同反应条件下Pt/C电流密度的1.45倍,抗甲醇性显著提高。

Fabrication of a highly dispersed Pd_(core)@Pt_(shell) electrocatalyst for the oxygen reduction reaction

Core-shell nanostructures have been widely investigated to improve the electrocatalytic perfor-mance of platinum. However, organic precursors, surfactants or high temperature are usually nec-essary during the preparation procedure. Unfortunately, these requirements limit the application of these methods on a large scale. Herein, a Pdcore@ Pt shell nanostructure was fabricated through the reduction of fcPtCU by dissociated hydrogen at room temperature without the assistance o f either a surfactant or a high-boiling point solvent. The shell thickness of this nanostructure was successfully controlled by varying the amount of fcPtCU; core-shell nanoparticles with a shell thickness of 0.45, 0.75 and 0.90 nm w ere obtained, as determined by TEM. The remarkable crystallinity and epitaxial growth of the Pdcore@ Pt shell nanostructure were revealed by HRTEM and EDS. According to ICP and XPS, surface segregation of Pt was established. The impressive ORR performance was attributed to the weak adsorption strength of the OHads species, which resulted from the electron transfer impact between the Pdcore and Ptshell. The facile and clean preparation method can be used to prepare other core-shell nanostructures under a mild atmosphere.

Synthesis of Various Metal/TiO2 Core/shell Nanorod Arrays

We present a general approach to fabricate metal/TiO2 core/shell nanorod structures by twostep electrodeposition. Firstly, TiO2 nanotubes with uniform wall thickness are prepared in anodic aluminum oxide （AAO） membranes by electrodeposition. The wall thickness of the nanotubes could be easily controlled by modulating the deposition time, and their outer diameter and length are only limited by the channel diameter and the thickness of the AAO membranes, respectively. The nanotubes＇ tops prepared by this method are open, while the bottoms are connected directly with the Au film at the back of the AAO membranes. Secondly, Pd, Cu, and Fe elements are filled into the TiO2 nanotubes to form core/shell structures. The core/shell nanorods prepared by this two-step process are high density and free-standing, and their length is dependent on the deposition time.

Cu_(core)Pt_(shell)/C纳米催化剂电催化氧还原性能

通过控制前驱体材料的比例分别为1∶1、1∶0.5、1∶2,采用两步化学还原法合成了不同壳层厚度的Cu_(core)Pt_(shell)纳米粒子。使用XRD表征纳米粒子的结构和组成,动电位扫描法测试其对氧还原反应的活性和抗甲醇性能。结果显示:所制备的材料为核壳结构,Pt壳层平均厚度约5.5 nm;Cu_(core)Pt_(shell)/C催化剂的氧还原活性随着Pt元素比例的增加而增加,都小于Pt/C催化剂,但其抗甲醇性能优于Pt/C催化剂。

A Hybrid Electrode of Co_3O_4@PPy Core/Shell Nanosheet Arrays for High-Performance Supercapacitors

Herein, combining solverthermal route and electrodeposition, we grew unique hybrid nanosheet arrays consisting of Co_3O_4 nanosheet as a core, PPy as a shell. Benefiting from the PPy as conducting polymer improving an electron transport rate as well as synergistic effects from such a core/shell structure, a hybrid electrode made of the Co_3O_4@PPy core/shell nanosheet arrays exhibits a large areal capacitance of 2.11 F cm-2at the current density of 2 m A cm^(-2), a *4-fold enhancement compared with the pristine Co_3O_4electrode; furthermore, this hybrid electrode also displays good rate capability(*65 % retention of the initial capacitance from 2 to 20 m A cm^(-2)) and superior cycling performance(*85.5 % capacitance retention after 5000 cycles). In addition, the equivalent series resistance value of the Co_3O_4@PPy hybrid electrode(0.238 X) is significantly lower than that of the pristine Co_3O_4electrode(0.319 X). These results imply that the Co_3O_4@PPy hybrid composites have a potential for fabricating next-generation energy storage and conversion devices.

One-dimensional ZnS-based Hetero-,Core/shell and Hierarchical Nanostructures

A focus of the current nanotechnology has shifted from routine fabrication of nanostructures to designing functional electronic devices and realizing their immense potentials for applications. Due to infusion of multi-functionality into a single system, the utilization of hetero-, core/shell and hierarchical nanostructures has become the key issue for building such devices. ZnS, due to its direct wide bandgap, high index of refraction, high transparency in the visible range and intrinsic polarity, is one of the most useful semiconductors for a wide range of electronics applications. This article provides a dense review of the state-of-the-art research activities in one-dimensional （1D） ZnS-based hetero-, core/shell and hierarchical nanostructures. The particular emphasis is put on their syntheses and applications.

Synthesis of novel MnO_x@TiO_2 core-shell nanorod catalyst for low-temperature NH_3-selective catalytic reduction of NOx with enhanced SO_2 tolerance

In this study,a MnOx@TiO2 core‐shell catalyst prepared by a two‐step method was used for the low‐temperature selective catalytic reduction of NOx with NH3.The catalyst exhibits high activity,high stability,and excellent N2 selectivity.Furthermore,it displays better SO2 and H2O tolerance than its MnOx,TiO2,and MnOx/TiO2 counterparts.The prepared catalyst was characterized systematically by transmission electron microscopy,high‐resolution transmission electron microscopy,X‐ray diffraction,Raman,BET,X‐ray photoelectron spectroscopy,NH3 temperature‐programmed desorption and H2 temperature‐programmed reduction analyses.The optimized MnOx@TiO2 catalyst exhibits an obvious core‐shell structure,where the TiO2 shell is evenly distributed over the MnOx nanorod core.The catalyst also presents abundant mesopores,Lewis‐acid sites,and high redox capability,all of which enhance its catalytic performance.According to the XPS results,the decrease in the number of Mn4+active centers after SO2 poisoning is significantly lower in MnOx@TiO2 than in MnOx/TiO2.The core‐shell structure is hence able to protect the catalytic active sites from H2O and SO2 poisoning.

Preparation of a p-n heterojunction BiFeO_3@TiO_2 photocatalyst with a core–shell structure for visible-light photocatalytic degradation

Magnetically separable bismuth ferrite(BiFeO3)nanoparticles were fabricated by a citrate self‐combustion method and coated with titanium dioxide(TiO2)by hydrolysis of titanium butoxide(Ti(OBu)4)to form BiFeO3@TiO2core-shell nanocomposites with different mass ratios of TiO2to BiFeO3.The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet(MV)under both ultraviolet and visible‐light irradiation.The BiFeO3@TiO2samples exhibited better photocatalytic performance than either BiFeO3or TiO2alone,and a BiFeO3@TiO2sample with a mass ratio of1:1and TiO2shell thickness of50-100nm showed the highest photo‐oxidation activity of the catalysts.The enhanced photocatalytic activity was ascribed to the formation of a p‐n junction of BiFeO3and TiO2with high charge separation efficiency as well as strong light absorption ability.Photoelectrochemical Mott-Schottky(MS)measurements revealed that both the charge carrier transportation and donor density of BiFeO3were markedly enhanced after introduction of TiO2.The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field.In addition,the unique core-shell structure of BiFeO3@TiO2also promotes charge transfer at the BiFeO3/TiO2interface by increasing the contact area between BiFeO3and TiO2.Finally,the photocatalytic activity of BiFeO3@TiO2was further confirmed by degradation of other industrial dyes under visible‐light irradiation.

Sonochemical Synthesis of Core/Shell Structured CdS/TiO_2 Nanocrystals Composites

A simple sonochemical route for the surface coating of titanium dioxide on cadmium sulfide nanocrystal was reported. After 2 h ultrasonic irradiation treatment, the mixture of CdS nanocrystals and tetrabutyl titanate in an aqueous medium yielded CdS/TiO2 nanocrystals composites with core/shell structure. The thickness of TiO2 layer with smooth interface could be easily controlled via changing the concentration of the precursors and the time of irradiation. The core/shell nanocrysrals were characterized by X-ray diffraction, transmission electron microscope and UV-vis spectrometry techniques. The prepared semiconductor composites with particular band structure present appealing properties especially in photochemical activity.

Lithium Storage Performance of Hollow and Core/Shell TiO_2 Microspheres Containing Carbon

TiO2 microspheres containing carbon have been synthesized viaa one-pot hydrothermal process using CTAB as the mesoporous template and nanoparticle stabilizer and Ti(SO4)2and sucrose as titanium and carbon precursors,respectively. Through well designed calcinations, Ti O2 microspheres with various amounts of carbon-residue,such as core/shell C@TiO2, hollow neat H–TiO2, and hollow C/TiO2 composites, are obtained. When these microspheres are used as anode materials for lithium ion batteries, the lithium storage performance is significantly influenced by the structure and carbon-residue. With a thin shell of TiO2 nanoparticles and carbon-residue, the capacity of hollow C/TiO2 composites maintains at 143.3 m A·h·g-1at 0.5 C(83.5 m A·g-1) after 100 cycles.Moreover, after high rate charge/discharge cycles from 0.2 C to 20 C and back to 0.2 C again, the reversible capacity recovers atas high as 195.1 m A·h·g-1with respect to its initial value of 205.0 m A·h·g-1. The results of cycle voltammograms and electrochemical impedance spectroscopy further reveal that Li+insertion/extraction processes are reversible, and the diffusion coefficient of Li+in the hollow C/TiO2 composites is much higher than those of others, because the hollow structure can act as the ion-buffering reservoir and facilitate Li+transfer from both sides of the shell, and the carbon-residue in the shell improves the conductivity as well.

Cardiogenic differentiation of mesenchymal stem cells on elastomeric poly (glycerol sebacate)/collagen core/shell fibers

AIM: To facilitate engineering of suitable biomaterials to meet the challenges associated with myocardial infarction. METHODS: Poly (glycerol sebacate)/collagen (PGS/ collagen) core/shell fibers were fabricated by core/ shell electrospinning technique, with core as PGS and shell as collagen polymer; and the scaffolds were characterized by scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), contact angle and tensile testing for cardiac tissue engineering. Collagen nanofibers were also fabricated by electrospinning for comparison with core/shell fibers. Studies on cell-scaffold interaction were carriedout using cardiac cells and mesenchymal stem cells (MSCs) co-culture system with cardiac cells and MSCs separately serving as positive and negative controls respectively. The co-culture system was characterized for cell proliferation and differentiation of MSCs into cardiomyogenic lineage in the co-culture environment using dual immunocytochemistry. The co-culture cells were stained with cardiac specific marker proteins like actinin and troponin and MSC specific marker protein CD 105 for proving the cardiogenic differentiation of MSCs. Further the morphology of cells was analyzed using SEM.RESULTS: PGS/collagen core/shell fibers, core is PGS polymer having an elastic modulus related to that of cardiac fibers and shell as collagen, providing natural environment for cellular activities like cell adhesion, proliferation and differentiation. SEM micrographs of electrospun fibrous scaffolds revealed porous, beadless, uniform fibers with a fiber diameter in the range of 380 ± 77 nm and 1192 ± 277 nm for collagen fibers and PGS/collagen core/shell fibers respectively. The obtained PGS/collagen core/shell fibrous scaffolds were hydrophilic having a water contact angle of 17.9 ± 4.6° compared to collagen nanofibers which had a contact angle value of 30 ± 3.2°. The PGS/collagen core/shell fibers had mechanical properties comparable to that of native heart muscle with a young's modulus of 4.24 ± 0.7 MPa, while that of collagen nanofibers was comparatively higher around 30.11 ± 1.68 MPa. FTIR spectrum was performed to confirm the functional groups present in the electrospun scaffolds. Amide Ⅰ and amide Ⅱ of collagen were detected at 1638.95 cm -1 and 1551.64 cm -1 in the electrospun collagen fibers and at 1646.22 cm -1 and 1540.73 cm -1 for PGS/collagen core/shell fibers respectively. Cell culture studies performed using MSCs and cardiac cells co-culture environment, indicated that the cellproliferation significantly increased on PGS/collagen core/shell scaffolds compared to collagen fibers and the cardiac marker proteins actinin and troponin were expressed more on PGS/collagen core/shell scaffolds compared to collagen fibers alone. Dual immunofluorescent staining was performed to further confirm the cardiogenic differentiation of MSCs by employing MSC specific marker protein, CD 105 and cardiac specific marker protein, actinin. SEM observations of cardiac cells showed normal morphology on PGS/collagen fibers and providing adequate tensile strength for the regeneration of myocardial infarction. CONCLUSION: Combination of PGS/collagen fibers and cardiac cells/MSCs co-culture system providing natural microenvironments to improve cell survival and differentiation, could bring cardiac tissue engineering to clinical application.