Magnetic nanoparticles with core/shell structures

Magnetic nanoparticles with core/shell structures are an important class of functional materials, possessing unique magnetic properties due to their tailored dimensions and compositions. This paper reviews mainly our recent advances in the preparation and characterizations of core/shell structured magnetic materials, focusing in nonmagnetic, antiferromagnetic, or ferro/ferri-magnetic shell coated magnetic core particles. And some of the unique properties of core-shell materials and their self-assembly are presented. Shell layers are shown to serve various functions. A broad demonstration of the successful blend of these types of materials synthesis, microstructural evolution and control, new physics and novel applications that is central to research in this field is presented.     

Hollow‐Structured Mesoporous Materials: Chemical Synthesis,Functionalization and Applications

Hollow‐structured mesoporous materials (HMMs), as a kind of mesoporous material with unique morphology, have been of great interest in the past decade because of the subtle combination of the hollow architecture with the mesoporous nanostructure. Benefitting from the merits of low density, large void space, large specific surface area, and, especially, the good biocompatibility, HMMs present promising application prospects in various fields, such as adsorption and storage, confined catalysis when catalytically active species are incorporated in the core and/or shell, controlled drug release, targeted drug delivery, and simultaneous diagnosis and therapy of cancers when the surface and/or core of the HMMs are functionalized with functional ligands and/or nanoparticles, and so on. In this review, recent progress in the design, synthesis, functionalization, and applications of hollow mesoporous materials are discussed. Two main synthetic strategies, soft‐templating and hard‐templating routes, are broadly sorted and described in detail. Progress in the main application aspects of HMMs, such as adsorption and storage, catalysis, and biomedicine, are also discussed in detail in this article, in terms of the unique features of the combined large void space in the core and the mesoporous network in the shell. Functionalization of the core and pore/outer surfaces with functional organic groups and/or nanoparticles, and their performance, are summarized in this article. Finally, an outlook of their prospects and challenges in terms of their controlled synthesis and scaled application is presented.     

Core–Shell Structured Nanoenergetic Materials: Preparation and Fundamental Properties

Energetic materials, including explosives, pyrotechnics, and propellants, are widely used in mining, demolition, automobile airbags, fireworks, ordnance, and space technology. Nanoenergetic materials (nEMs) have a high reaction rate and high energy density, which are both adjustable to a large extent. Structural control over nEMs to achieve improved performance and multifunctionality leads to a fascinating research area, namely, nanostructured energetic materials. Among them, core–shell structured nEMs have gained considerable attention due to their improved material properties and combined multiple functionalities. Various nEMs with core–shell structures have been developed through diverse synthesis routes, among which core–shell structured nEMs associated with explosives and metastable intermolecular composites (MICs) are extensively studied due to their good tunability and wide applications, as well as excellent energetic (e.g., enhanced heat release and combustion) and/or mechanical properties. Herein, the preparation methods and fundamental properties of the abovementioned kinds of core–shell structured nEMs are summarized and the reasons behind the satisfactory performance clarified, based on which suggestions regarding possible future research directions are proposed.     

Yolk–Shell Nanostructure: An Ideal Architecture to Achieve Harmonious Integration of Magnetic–Plasmonic Hybrid Theranostic Platform

Magnetic–plasmonic hybrid nanoparticles (MPHNs) have attracted great interest in cancer theranostics. However, the relaxivity of the magnetic component is typically reduced by the plasmonic component in conventional core–shell structured MPHNs, due to the presence of a water‐impenetrable coating which severely restricts the proximity of protons to the magnetic portion. To circumvent this issue, yolk–shell structured MPHNs comprising a Fe₃O₄ core within a hollow cavity encircled by a porous Au outer shell are designed. As expected, the introduction of hollow cavity between the magnetic and plasmonic portions significantly prevents the decline in relaxivity of the Fe₃O₄ core caused by the Au layer. Moreover, in addition to conferring high near‐infrared absorption to plasmonic component, the hollow cavity and the pores in the outer shell can also provide a large storage space and release channels for anticancer drugs. Furthermore, the multicomponent nanoparticles (NPs) still have a compact size of less than 100 nm to ensure efficient tumor accumulation. Taken together, the yolk–shell Fe₃O₄@Au NPs can be regarded as an ideal magnetic–plasmonic theranostic platform for magnetic resonance/photoacoustic/positron emission tomography multimodal imaging and light‐activated chemothermal synergistic therapy.     

Nature‐Inspired Lightweight Cellular Co‐Continuous Composites with Architected Periodic Gyroidal Structures

Shell‐core cellular composites are a unique class of cellular materials, where the base constituent is made of a composite material such that the best distinctive physical and/or mechanical properties of each phase of the composite are employed. In this work, the authors demonstrate the additive manufacturing of a nature inspired cellular three‐dimensional (3D), periodic, co‐continuous, and complex composite materials made of a hard‐shell and soft‐core system. The architecture of these composites is based on the Schoen's single Gyroidal triply periodic minimal surface. Results of mechanical testing show the possibility of having a wide range of mechanical properties by tuning the composition, volume fraction of core, shell thickness, and internal architecture of the cellular composites. Moreover, a change in deformation and failure mechanism is observed when employing a shell‐core composite system, as compared to the pure stiff polymeric standalone cellular material. This shell‐core configuration and Gyroidal topology allowed for accessing toughness values that are not realized by the constituent materials independently, showing the suitability of this cellular composite for mechanical energy absorption applications.

     

Synthesis and characterization of core∕shell Fe(3)O(4)∕ZnSe fluorescent magnetic nanoparticles

We report on the successful preparation and characterization of fluorescent magnetic core∕shell Fe(3)O(4)∕ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core∕3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission∕excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core∕shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe(3)O(4)) and nonmagnetic (ZnSe) phases. Compared to a reference Fe(3)O(4) NP sample, the room-temperature Néel relaxation time in core∕shell NPs is three times longer.     

Synthesis of Engineered Zeolitic Materials: From Classical Zeolites to Hierarchical Core–Shell Materials

The term “engineered zeolitic materials” refers to a class of materials with a rationally designed pore system and active‐sites distribution. They are primarily made of crystalline microporous zeolites as the main building blocks, which can be accompanied by other secondary components to form composite materials. These materials are of potential importance in many industrial fields like catalysis or selective adsorption. Herein, critical aspects related to the synthesis and modification of such materials are discussed. The first section provides a short introduction on classical zeolite structures and properties, and their conventional synthesis methods. Then, the motivating rationale behind the growing demand for structural alteration of these zeolitic materials is discussed, with an emphasis on the ongoing struggles regarding mass‐transfer issues. The state‐of‐the‐art techniques that are currently available for overcoming these hurdles are reviewed. Following this, the focus is set on core–shell composites as one of the promising pathways toward the creation of a new generation of highly versatile and efficient engineered zeolitic substances. The synthesis approaches developed thus far to make zeolitic core–shell materials and their analogues, yolk–shell, and hollow materials, are also examined and summarized. Finally, the last section concisely reviews the performance of novel core–shell, yolk–shell, and hollow zeolitic materials for some important industrial applications.     

Hollow Micro/Nanomaterials with Multilevel Interior Structures

In this Review, recent achievements in the multilevel interior‐structured hollow 0D and 1D micro/nanomaterials are presented and categorized. The 0D multilevel interior‐structured micro/nanomaterials are classified into four main interior structural categories that include a macroporous structure, a core‐in‐hollow‐shell structure, a multishell structure, and a multichamber structure. Correspondingly, 1D tubular micro/nanomaterials are of four analogous structures, which are a segmented structure, a wire‐in‐tube structure, a multiwalled structure, and a multichannel structure. Because of the small sizes and complex interior structures, some special synthetic strategies that are different from routine hollowing methods, are proposed to produce these interior structures. Compared with the same‐sized solid or common hollow counterparts, these fantastic multilevel hollow‐structured micro/nanomaterials show a good wealth of outstanding properties that enable them broad applications in catalysis, sensors, Li‐ion batteries, microreactors, biomedicines, and many others.     

Observation of Self‐Assembled Core–Shell Structures in Epitaxially Embedded TbErAs Nanoparticles

Self‐assembled core–shell structured rare‐earth nanoparticles (TbErAs) are observed in a III–V semiconductor host matrix (In_0.53Ga_0.47As) nominally lattice‐matched to InP, grown via molecular beam epitaxy. Atom probe tomography demonstrates that the TbErAs nanoparticles have a core–shell structure, as seen both in the tomographic atom‐by‐atom reconstruction and concentration profiles. A simple thermodynamic model is created to determine when it is energetically favorable to have core–shell structures; the results strongly agree with the observations.     

Synthesis,Functionalization, and Biomedical Applications of Multifunctional Magnetic Nanoparticles

Synthesis of multifunctional magnetic nanoparticles (MFMNPs) is one of the most active research areas in advanced materials. MFMNPs that have magnetic properties and other functionalities have been demonstrated to show great promise as multimodality imaging probes. Their multifunctional surfaces also allow rational conjugations of biological and drug molecules, making it possible to achieve target‐specific diagnostics and therapeutics. This review first outlines the synthesis of MNPs of metal oxides and alloys and then focuses on recent developments in the fabrication of MFMNPs of core/shell, dumbbell, and composite hybrid type. It also summarizes the general strategies applied for NP surface functionalization. The review further highlights some exciting examples of these MFMNPs for multimodality imaging and for target‐specific drug/gene delivery applications.     

Nonsacrificial Self‐Template Synthesis of Colloidal Magnetic Yolk–Shell Mesoporous Organosilicas for Efficient Oil/Water Interface Catalysis

Using interfacial reaction systems for biphasic catalytic reactions is attracting more and more attention due to their simple reaction process and low environmental pollution. Yolk–shell structured materials have broad applications in biomedicine, catalysis, and environmental remediation owing to their open channels and large space for guest molecules. Conventional methods to obtain yolk–shell mesoporous materials rely on costly and complex hard‐template strategies. In this study, a mild and convenient nonsacrificial self‐template strategy is developed to construct yolk–shell magnetic periodic mesoporous organosilica (YS‐mPMO) particles by using the unique swelling–deswelling property of low‐crosslinking density resorcinol formaldehyde (RF). The obtained YS‐mPMO microspheres possess an amphiphilic outer shell, high surface area (393 m² g^?1), uniform mesopores (2.58 nm), a tunable middle hollow space (50–156 nm), and high superparamagnetism (34.4–37.1 emu g^?1). By tuning the synthesis conditions, heterojunction structured yolk–shell Fe₃O₄@RF@void@PMO particles with different morphologies can be produced. Owing to the amphipathy of PMO framworks, the YS‐mPMO particles show great emulsion stabilization ability and recyclability under a magnetic field. YS‐mPMO microspheres with immobilized Au nanoparticles (≈3 nm) act as both solid emulsifier for dispersing styrene (St) in water and interface catalysts for selective conversion of St into styrene oxide with a high selectivity of 86%, and yields of over 97%.     

Amphiphilic Block Copolymers Directed Interface Coassembly to Construct Multifunctional Microspheres with Magnetic Core and Monolayer Mesoporous Aluminosilicate Shell

Core–shell magnetic porous microspheres have wide applications in drug delivery, catalysis and bioseparation, and so on. However, it is great challenge to controllably synthesize magnetic porous microspheres with uniform well‐aligned accessible large mesopores (>10 nm) which are highly desired for applications involving immobilization or adsorption of large guest molecules or nanoobjects. In this study, a facile and general amphiphilic block copolymer directed interfacial coassembly strategy is developed to synthesize core–shell magnetic mesoporous microspheres with a monolayer of mesoporous shell of different composition (FDUcs‐17D), such as core–shell magnetic mesoporous aluminosilicate (CS‐MMAS), silica (CS‐MMS), and zirconia‐silica (CS‐MMZS), open and large pores by employing polystyrene‐block‐poly (4‐vinylpyridine) (PS‐b‐P4VP) as an interface structure directing agent and aluminum acetylacetonate (Al(acac)₃), zirconium acetylacetonate, and tetraethyl orthosilicate as shell precursors. The obtained CS‐MMAS microspheres possess magnetic core, perpendicular mesopores (20–32 nm) in the shell, high surface area (244.7 m² g^?1), and abundant acid sites (0.44 mmol g^?1), and as a result, they exhibit superior performance in removal of organophosphorus pesticides (fenthion) with a fast adsorption dynamics and high adsorption capacity. CS‐MMAS microspheres loaded with Au nanoparticles (≈3.5 nm) behavior as a highly active heterogeneous nanocatalyst for N‐alkylation reaction for producing N‐phenylbenzylamine with a selectivity and yields of over 90% and good magnetic recyclability.     

Dynamically Reconfigurable,Multifunctional Emulsions with Controllable Structure and Movement

Dynamically reconfigurable oil‐in‐water (o/w) Pickering emulsions are developed, wherein the assembly of particles (i.e., platinum‐on‐carbon and iron‐on‐carbon particles) can be actively controlled by adjusting interfacial tensions. A balanced adsorption of particles and surfactants at the o/w interface allows for the creation of inhomogeneity of the particle distribution on the emulsion surface. Complex Pickering emulsions with highly controllable and reconfigurable morphologies are produced in a single step by exploiting the temperature‐sensitive miscibility of hydrocarbon and fluorocarbon liquids. Dynamic adsorption/desorption of (polymer) surfactants afford both shape and configuration transitions of multiple Pickering emulsions and encapsulated core/shell structured can be transformed into a Janus configuration. Finally, to demonstrate the intrinsic catalytic or magnetic properties of the particles provided by carbon bound Pt and Fe nanoparticles, two different systems are investigated. Specifically, the creation of a bimetallic microcapsule with controlled payload release and precise modulation of translational and rotational motions of magnetic emulsions are demonstrated, suggesting potential applications for sensing and smart payload delivery.     

Fabrication of Carbon Nanoscrolls from Monolayer Graphene

A simple way of synthesizing carbon nanotube (CNT)/graphene (GN) nanoscroll core/shell nanostructures is demonstrated using molecular dynamics (MD) simulations. The simulations show that GN sheets can fully self‐scroll onto CNTs when the CNT radius is larger than a threshold of about 10 Å, forming a stable core/shell structure. Increasing the length of the GN sheet results in multilayered carbon nanoscroll (CNS) shells that exhibit a tubular structure similar to that of multiwall CNTs. The distances between the CNT and the GN wall or adjacent GN walls are about 3.4 Å. It is found that the van der Waals force plays an important role in the formation of the CNT/GN nanoscroll core/shell‐composite nanostructures. However, the chirality of the CNT and the GN sheet does not affect the self‐scrolling process, which thus provides a simple way of controlling the chirality and physical properties of the resulting core/shell structure. It is expected that this preparation method of CNT/GN nanoscroll core/shell composites will lead to further development of a broad new class of carbon/carbon core/shell composites with enhanced properties and even introduce new functionalities to composite materials.     

Synthesis and Characterization of Mn:ZnSe/ZnS/ZnMnS Sandwiched QDs for Multimodal Imaging and Theranostic Applications

In this work, a facile aqueous synthesis method is optimized to produce Mn:ZnSe/ZnS/ZnMnS sandwiched quantum dots (SQDs). In this core–shell co‐doped system, paramagnetic Mn²⁺ ions are introduced as core and shell dopants to generate Mn phosphorescence and enhance the magnetic resonance imaging signal, respectively. T1 relaxivity of the nanoparticles can be improved and manipulated by raising the shell doping level. Steady state and time‐resolved optical measurements suggest that, after high level shell doping, Mn phosphorescence of the core can be sustained by the sandwiched ZnS shell. Because the SQDs are free of toxic heavy metal compositions, excellent biocompatibility of the prepared nanocrystals is verified by in vitro MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay. To explore the theranostic applications of SQDs, liposome‐SQD assemblies are prepared and used for ex vivo optical and magnetic resonance imaging. In addition, these engineered SQDs as nanocarrier for gene delivery in therapy of Panc‐1 cancer cells are employed. The therapeutic effects of the nanocrystals formulation are confirmed by gene expression analysis and cell viability assay.     

Architected Lattices with High Stiffness and Toughness via Multicore–Shell 3D Printing

The ability to create architected materials that possess both high stiffness and toughness remains an elusive goal, since these properties are often mutually exclusive. Natural materials, such as bone, overcome such limitations by combining different toughening mechanisms across multiple length scales. Here, a new method for creating architected lattices composed of core–shell struts that are both stiff and tough is reported. Specifically, these lattices contain orthotropic struts with flexible epoxy core–brittle epoxy shell motifs in the absence and presence of an elastomeric silicone interfacial layer, which are fabricated by a multicore–shell, 3D printing technique. It is found that architected lattices produced with a flexible core‐elastomeric interface‐brittle shell motif exhibit both high stiffness and toughness.     

Nanostructures for Thermoelectric Applications: Synthesis,Growth Mechanism,and Property Studies

Both heterostructures and hollow nanostructures have been predicted as candidates with excellent thermoelectric performance. In this Research News areticle, recent advances with regard to synthetic strategies, growth mechanisms, and thermoelectric properties of one‐dimensional heterostructures (segmented and core/shell) and tubular nanostructures are reported. The thermoelectric property studies of Te/Bi core/shell heterostructured nanowires and Bi₂Te₃ nanotubes indicate that the Seebeck coefficient and thermal conductivity of these materials can be optimized to improve their thermoelectric performance. In addition, the current issues and future research directions for promising thermoelectric nanostructures will be discussed on the basis of these experimental results.     

多孔壳微胶囊对硬化砂浆抗渗性的影响

采用原位聚合与水解缩聚法,以四乙氧基硅烷（TEOS）、环氧树脂（E51）、苯乙烯（St）等为主要原料,合成了一种二氧化硅多孔壳微胶囊（Porous silica shell microcapsules,PSSM）。分别采用SEM、FTIR、TGA对PSSM外观形貌、化学组分、核壳比进行表征。通过对掺加PSSM的砂浆试块进行80%抗压强度荷载预压、养护（浸水或干湿循环养护）处理后,运用交流阻抗法与压汞法研究了PSSM对硬化砂浆抗渗性与孔结构的影响规律。结果表明:制备的PSSM粒径约为10~100 μm,其含有聚苯乙烯网络支架、环氧树脂和聚硅氧烷囊芯,支架聚合物和多孔壳,核壳质量比为1.54。与未预压-养护处理的试块相比,经预压-养护处理后的空白试块的连通孔溶液电阻R_CH和扩散阻抗系数σ均降低,孔隙率升高,表明预压使试块内形成微裂纹缺陷,经养护仍未愈合,因此试块抗渗性降低;而对于掺加8% PSSM的试块,经预压-养护处理后其R_CH和σ均增加,孔隙率降低,表明试块抗渗性提高。这是由于PSSM的破壳-固化作用以及长期浸水或干湿循环养护,导致试块中PSSM发生了渗出-固化作用,封堵愈合了试块内的微裂隙,抗渗性得到提高。      

芯壳结构竹塑复合材料密度及微观结构的CT分析

以竹屑、高密度聚乙烯(HDPE)、竹浆纤维、纳米碳酸钙及白泥为主要材料,采用聚合物共挤出技术制备芯壳结构竹塑复合材料。利用Micro-CT扫描技术对复合材料内部结构进行了观测,同时还对断面密度进行了分析。结果表明,通过对不同壳层材料的复合材料断面CT图像进行二值化处理后,可清晰地反映复合材料内部缺陷。Micro-CT三维空间分析技术能够实现对4种不同壳层材料的芯壳结构竹塑复合材料的内部微观结构可视化的精细表征,且重建密度表现出与实测密度趋势一致。壳层加入白泥或纳米碳酸钙的复合材料的剖面密度在厚度方向上呈现出壳层密度高而芯层密度低。不同壳层材料的复合材料CT图像阈值分布在26.1到95.6之间,在此基础上建立了CT图像阈值与密度的关系。     

A Magnetic‐Field Guided Interface Coassembly Approach to Magnetic Mesoporous Silica Nanochains for Osteoclast‐Targeted Inhibition and Heterogeneous Nanocatalysis

1D core–shell magnetic materials with mesopores in shell are highly desired for biocatalysis, magnetic bioseparation, and bioenrichment and biosensing because of their unique microstructure and morphology. In this study, 1D magnetic mesoporous silica nanochains (Fe₃O₄@nSiO₂@mSiO₂ nanochain, Magn‐MSNCs named as FDUcs‐17C) are facilely synthesized via a novel magnetic‐field‐guided interface coassembly approach in two steps. Fe₃O₄ particles are coated with nonporous silica in a magnetic field to form 1D Fe₃O₄@nSiO₂ nanochains. A further interface coassembly of cetyltrimethylammonium bromide and silica source in water/n‐hexane biliquid system leads to 1D Magn‐MSNCs with core–shell–shell structure, uniform diameter (≈310 nm), large and perpendicular mesopores (7.3 nm), high surface area (317 m² g^?1), and high magnetization (34.9 emu g^?1). Under a rotating magnetic field, the nanochains with loaded zoledronate (a medication for treating bone diseases) in the mesopores, show an interesting suppression effect of osteoclasts differentiation, due to their 1D nanostructure that provides a shearing force in dynamic magnetic field to induce sufficient and effective reactions in cells. Moreover, by loading Au nanoparticles in the mesopores, the 1D Fe₃O₄@nSiO₂@mSiO₂‐Au nanochains can service as a catalytically active magnetic nanostirrer for hydrogenation of 4‐nitrophenol with high catalytic performance and good magnetic recyclability.