Nanosized Heterostructures of Au@Prussian Blue Analogues: Towards Multifunctionality at the Nanoscale

Access to multifunctionality at the nanoscale requires the development of hybrid nanostructures that combine materials of different natures. In this line of thought, current research on coordination polymers is not only focusing on their synthesis at the nanoscale, but also on combining these polymers with other materials. According to a novel and rational approach, single‐layer Au@Prussian blue analogue (PBA) and double‐layer Au@PBA@PBA′ core–shell nanoparticles (NPs) may be obtained through the growth of a cyano‐bridged coordination network on the gold surface. The nanosized heterostructures combine the plasmonic optical properties of the gold core and the magnetic properties of the PBA shell. Whereas the single‐layer nanoparticles are paramagnetic, the double‐layer nanostructures display ferromagnetism; therefore, the overall structural motif may be considered as multifunctional. The developed synthetic concept also includes an easy access to hollow PBA NPs.     

Recent Advances in the Synthesis,Surface Modifications and Applications of Core‐Shell Magnetic Mesoporous Silica Nanospheres

The hierarchically structured core‐shell magnetic mesoporous silica nanospheres (Mag‐MSNs) have attracted extensive attention, particularly in studies involving reliable preparations and diverse applications of the multifunctional nanomaterials in multi‐disciplinary fields. Intriguingly, Mag‐MSNs have been prepared with well‐designed synthesis strategies and used as adsorbent materials, biomedicines, and in proteomics and catalysis due to their excellent magnetic responsiveness, enormous specific surface area and readiness for surface modifications. Through a carefully designed surface modification of Mag‐MSNs, the performance and application prospects of the material are greatly improved. Typically, the introduction of various molecular matrices into the shell of Mag‐MSNs facilitates the combination of surface modifications and magnetic separation technology. So far, as sustainable chemistry is concerned, it is important to recover the functionalized core‐shell Mag‐MSNs after the reaction and reuse them without losing activity. In this review, the design conceptions and the construction of core‐shell Mag‐MSNs are discussed. Furthermore, various surface modification approaches of core‐shell Mag‐MSNs are summarized, and recent applications of these functionalized nanomaterials in the fields of biomedicine, catalysis, proteomics and wastewater treatment are exemplified.     

Exchange‐Coupled fct‐FePd/α‐Fe Nanocomposite Magnets Converted from Pd/Fe3O4 Core/Shell Nanoparticles

We report the controlled synthesis of exchange‐coupled face‐centered tetragonal (fct) FePd/α‐Fe nanocomposite magnets with variable Fe concentration. The composite was converted from Pd/Fe₃O₄ core/shell nanoparticles through a high‐temperature annealing process in a reducing atmosphere. The shell thickness of core/shell Pd/Fe₃O₄ nanoparticles could be readily tuned, and subsequently the concentration of Fe in nanocomposite magnets was controlled. Upon annealing reduction, the hard magnetic fct‐FePd phase was formed by the interdiffusion between reduced α‐Fe and face‐centered cubic (fcc) Pd, whereas the excessive α‐Fe remained around the fct‐FePd grains, realizing exchange coupling between the soft magnetic α‐Fe and hard magnetic fct‐FePd phases. Magnetic measurements showed variation in the magnetic properties of the nanocomposite magnets with different compositions, indicating distinct exchange coupling at the interfaces. The coercivity of the exchange‐coupled nanocomposites could be tuned from 0.7 to 2.8 kOe and the saturation magnetization could be controlled from 93 to 160 emu g^?1. This work provides a bottom‐up approach using exchange‐coupled nanocomposites for engineering advanced permanent magnets with controllable magnetic properties.     

Building Nanocomposite Magnets by Coating a Hard Magnetic Core with a Soft Magnetic Shell

Controlling exchange coupling between hard magnetic and soft magnetic phases is the key to the fabrication of advanced magnets with tunable magnetism and high energy density. Using FePt as an example, control over the magnetism in exchange‐coupled nanocomposites of hard magnetic face‐centered tetragonal (fct) FePt and soft magnetic Co (or Ni, Fe₂C) is shown. The dispersible hard magnetic fct‐FePt nanoparticles are first prepared with their coercivity (H_c) reaching 33 kOe. Then core/shell fct‐FePt/Co (or Ni, Fe₂C) nanoparticles are synthesized by reductive thermal decomposition of the proper metal precursors in the presence of fct‐FePt nanoparticles. These core/shell nanoparticles are strongly coupled by exchange interactions and their magnetic properties can be rationally tuned by the shell thickness of the soft phase. This work provides an ideal model system for the study of exchange coupling at the nanoscale, which will be essential for building superstrong magnets for various permanent magnet applications in the future.     

Popcorn‐Shaped Magnetic Core–Plasmonic Shell Multifunctional Nanoparticles for the Targeted Magnetic Separation and Enrichment,Label‐Free SERS Imaging,and Photothermal Destruction of Multidrug‐Resistant Bacteria

Over the last few years, one of the most important and complex problems facing our society is treating infectious diseases caused by multidrug‐resistant bacteria (MDRB), by using current market‐existing antibiotics. Driven by this need, we report for the first time the development of the multifunctional popcorn‐shaped iron magnetic core–gold plasmonic shell nanotechnology‐driven approach for targeted magnetic separation and enrichment, label‐free surface‐enhanced Raman spectroscopy (SERS) detection, and the selective photothermal destruction of MDR Salmonella DT104. Due to the presence of the “lightning‐rod effect”, the core–shell popcorn‐shaped gold‐nanoparticle tips provided a huge field of SERS enhancement. The experimental data show that the M3038 antibody‐conjugated nanoparticles can be used for targeted separation and SERS imaging of MDR Salmonella DT104. A targeted photothermal‐lysis experiment, by using 670 nm light at 1.5 W cm^?2 for 10 min, results in selective and irreparable cellular‐damage to MDR Salmonella. We discuss the possible mechanism and operating principle for the targeted separation, label‐free SERS imaging, and photothermal destruction of MDRB by using the popcorn‐shaped magnetic/plasmonic nanotechnology.     

Synthesis of Multifunctional Metal‐ and Metal Oxide Core@Mesoporous Silica Shell Structures by Using a Wet Chemical Approach

We demonstrate a facile wet chemical approach for fabricating spherical metal/metal‐oxide core@mesoporous silica shell hybrid nanoparticles with different core and shell thicknesses. Vertically aligned mesoporous silica (mSiO₂) shells were fabricated over the pre‐synthesized spherical SiO₂ nanoparticles through a three‐step strategy: 1) synthesis of core materials, 2) covering the core with an organic–inorganic composite layer, and 3) removing the organic template through calcinations in air. The mechanisms of hybrid structure formation are proposed. The multifunctional nature of the hybrid structures could be induced by incorporating guest ions/molecules, such as Ag, Mn, and TiO₂, into the pores of an mSiO₂ shell. Mn and TiO₂ cluster‐ incorporated composite structures have been tested to be antioxidizing agents and effective photocatalysts through electron spin resonance, radical scavenging tests, and the photocatalytic degradation of rhodamine B. The possibility of incorporating several hetero‐element guest clusters in these mesoporous composite particles makes them highly attractive for multifunctional applications.     

Core–Shell Hollow Microspheres of Magnetic Iron Oxide@Amorphous Calcium Phosphate: Synthesis Using Adenosine 5′‐Triphosphate and Application in pH‐Responsive Drug Delivery

Drug nanocarriers with magnetic targeting and pH‐responsive drug‐release behavior are promising for applications in controlled drug delivery. Magnetic iron oxides show excellent magnetism, but their application in drug delivery is limited by low drug‐loading capacity and poor control over drug release. Herein, core–shell hollow microspheres of magnetic iron oxide@amorphous calcium phosphate (MIO@ACP) were prepared and investigated as magnetic, pH‐responsive drug nanocarriers. Hollow microspheres of magnetic iron oxide (HMIOs) were prepared by etching solid MIO microspheres in hydrochloric acid/ethanol solution. After loading a drug into the HMIOs, the drug‐loaded HMIOs were coated with a protective layer of ACP by using adenosine 5′‐triphosphate (ATP) disodium salt (Na₂ATP) as stabilizer, and drug‐loaded core–shell hollow microspheres of MIO@ACP (HMIOs/drug/ACP) were obtained. The as‐prepared HMIOs/drug/ACP drug‐delivery system exhibits superparamagnetism and pH‐responsive drug‐release behavior. In a medium with pH 7.4, drug release was slow, but it was significantly accelerated at pH 4.5 due to dissolution of the ACP shell. Docetaxel‐loaded core–shell hollow microspheres of MIO@ACP exhibited high anticancer activity.     

Structure,thermal stability,and photocrosslinking characterization of HDPE/LDH nanocomposites synthesized by melt‐intercalation

Structure, thermal properties, and influence of layered double hydroxide (LDH) fillers on photocrosslinking behavior of high‐density polyethylene (HDPE)/LDH nanocomposites have been studied in the present article. The X‐ray diffraction and transmission electron microscopy analysis demonstrate that the completely exfoliated HDPE/LDH nanocomposites can be obtained by controlling the organomodified LDH loading via melt‐intercalation. The data from the thermogravimetric analysis show that the HDPE/LDH nanocomposites have much higher thermal stability than HDPE sample. When the 50% weight loss was selected as a comparison point, the decomposition temperature of HDPE/LDH sample with 5 wt % LDH loading is ～40 °C higher than that of HDPE sample. The effects of UV‐irradiation on the HDPE/LDH nanocomposites show that the photoinitiated crosslinking can destroy the completely exfoliated structure to form the partially exfoliated structure, which decreased the thermal stability of the nanocomposites. However, the thermal stability of photocrosslinked samples can increase with increasing the UV‐irradiation time. The effect of LDH loading on the gel content of UV‐irradiated nanocomposites shows that the LDH materials can greatly absorb the UV irradiation and thus decrease the crosslinking efficiency. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3165–3172, 2006     

Multifunctional Core–Shell Structured Nanocarriers for Synchronous Tumor Diagnosis and Treatment In Vivo

Multifunctional, mesoporous, silica‐coated upconversion luminescent/magnetic NaGdF₄:Yb/Er@NaGdF₄:Yb@mSiO₂? PEG (referred to as UCNPS; PEG=polyethylene glycol) nanocomposites were fabricated through a phase‐transfer‐assisted surfactant‐templating coating process, followed by hydrophilic polymer (PEG) functionalization to improve the stability and biocompatibility. The UCNP core imparts the nanomaterials with luminescence and magnetic properties for simultaneous upconversion optical and magnetic resonance (MR) imaging, whereas the mesoporous shell affords the nanomaterials the ability to load the anticancer drug doxorubicin. Proof‐of‐principle in vitro and in vivo experiments are presented to demonstrate that the resultant composite nanomaterials can serve as nanotheranostics for synchronous upconversion luminescence/MR dual modal imaging and anticancer drug delivery; this finally realizes the integration of diagnostics and the treatment of cancers.     

Advances in the Interfacial Assembly of Mesoporous Silica on Magnetite Particles

Interfacing magnetic particles with ordered mesoporous materials is an effective direction for the development of functional porous composite materials with rationally designed core–shell structures. Owing to the combined properties of magnetic nanoparticles and mesoporous silica (high surface area, large pore volume, porosity, and biocompatibility), core–shell magnetic mesoporous silica materials have generated tremendous interest in various disciplines, including chemistry, materials, bioengineering, and biomedicine. Interfacial assembly strategies enable the rational construction of magnetic mesoporous silica materials with well‐defined core–shell structure, morphology, pore parameters, and surface wettability, which can decisively influence their physical and chemical properties and thus improve their application performance. This Minireview summarizes recent progress in the synthesis of core–shell magnetic mesoporous silica and the adjustment of key parameters, including pore size, morphology, and pore orientation.     

Reactive Polymer as a Versatile Toolbox for Construction of Multifunctional Superparamagnetic Nanocomposites

The development of magnetic nanoparticles with multiple functions has been an ever‐growing field because of their diverse applications in drug delivery, biosensing, cell labeling, and so on. In this study, a facile method was developed to construct multifunctional magnetic nanocomposites. The approach is based on the use of poly(glycidyl methacrylate), PGMA, with numerous epoxy groups as reactive polymer to combine with fluorescent dye, the surface of magnetic nanoparticles, and targeting ligands directly without expatiatory functionality design. The resultant nanocomposites with good superparamagnetic and fluorescent properties could be exploited for bioimaging. Moreover, after conjugation with a model protein, namely, transferrin, which specifically targets cells overexpressing transferrin receptors, the nanocomposites could be used selectively to recognize Hela cells in comparison with nonconjugated ones. These results indicate that the newly designed magnetic nanocomposites with PGMA as functional polymer could serve as a novel versatile platform to conjugate with various molecules for construction of diverse multifunctional magnetic nanocomposites to meet different requirements and potential uses in nanomedicine and biological chemistry.     

Facile Synthesis of Ge@C Core–Shell Nanocomposites for High‐Performance Lithium Storage in Lithium‐Ion Batteries

Herein, we report a facile and “green” synthetic route for the preparation of Ge@C core–shell nanocomposites by using a low‐cost Ge precursor. Field‐emission scanning electron microscopy and transmission electron microscopy analyses confirmed the core–shell nanoarchitecture of the Ge@C nanocomposites, with particle sizes ranging from 60 to 100 nm. Individual Ge nanocrystals were coated by a continuous carbon layer, which had an average thickness of 2 nm. When applied as an anode materials for lithium‐ion batteries, the Ge@C nanocomposites exhibited a high initial discharge capacity of 1670 mAh g^?1 and superior rate capability. In particular, Ge@C nanocomposite electrodes maintained a reversible capacity of 734 mAh g^?1 after repeated cycling at a current density of 800 mA g^?1 over 100 cycles.     

Precisely Size‐Tunable Magnetic/Plasmonic Core/Shell Nanoparticles with Controlled Optical Properties

Star‐like amphiphilic triblock copolymers were rationally designed and synthesized by combining two sequential atom‐transfer radical polymerization reactions with a click reaction. Subsequently, a family of uniform magnetic/plasmonic core/shell nanoparticles was crafted by capitalizing on these triblock copolymers as nanoreactors. The diameter of the magnetic core and the thickness of the plasmonic shell could be independently and accurately controlled by varying the molecular weights (i.e., the chain lengths) of the inner and intermediate blocks of the star‐like triblock copolymers, respectively. The surface plasmonic absorption of core/shell nanoparticles with different core diameters and shell thicknesses was systematically studied and theoretically modeled. This robust strategy provides easy access to a large variety of multifunctional nanoparticles with large lattice mismatches for use in optics, optoelectronics, catalysis, or bioimaging.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

General Route to Multifunctional Uniform Yolk/Mesoporous Silica Shell Nanocapsules: A Platform for Simultaneous Cancer‐Targeted Imaging and Magnetically Guided Drug Delivery

Hollow mesoporous SiO₂ (mSiO₂) nanostructures with movable nanoparticles (NPs) as cores, so‐called yolk‐shell nanocapsules (NCs), have attracted great research interest. However, a highly efficient, simple and general way to produce yolk‐mSiO₂ shell NCs with tunable functional cores and shell compositions is still a great challenge. A facile, general and reproducible strategy has been developed for fabricating discrete, monodisperse and highly uniform yolk‐shell NCs under mild conditions, composed of mSiO₂ shells and diverse functional NP cores with different compositions and shapes. These NPs can be Fe₃O₄ NPs, gold nanorods (GNRs), and rare‐earth upconversion NRs, endowing the yolk‐mSiO₂ shell NCs with magnetic, plasmonic, and upconversion fluorescent properties. In addition, multifunctional yolk‐shell NCs with tunable interior hollow spaces and mSiO₂ shell thickness can be precisely controlled. More importantly, fluorescent‐magnetic‐biotargeting multifunctional polyethyleneimine (PEI)‐modified fluorescent Fe₃O₄@mSiO₂ yolk‐shell nanobioprobes as an example for simultaneous targeted fluorescence imaging and magnetically guided drug delivery to liver cancer cells is also demonstrated. This synthetic approach can be easily extended to the fabrication of multifunctional yolk@mSiO₂ shell nanostructures that encapsulate various functional movable NP cores, which construct a potential platform for the simultaneous targeted delivery of drug/gene/DNA/siRNA and bio‐imaging.     

Facile Preparation of a Stable Fe3O4@LDH@NiB Magnetic Core‐Shell Nanocomposite for Hydrogenation

A novel NiB deposited layered double hydroxide (LDH ) coated ferroferric oxide (Fe₃O₄ @LDH @NiB ) magnetic core‐shell nanocomposite was successfully fabricated by the combination of coprecipitation and impregnation‐reduction. During the Fe₃O₄ @LDH preparation, a facile template‐free approach was employed to introduce the LDH shell, which was more efficient than the conventional method for the preparation of mesoporous materials that always needs to introduce and remove templates. The resulted Fe₃O₄ @LDH has a relatively high surface area and abundant surface hydroxyl group, which can adsorb metal ions, making it favorable to disperse and stabilize the active Ni species, as demonstraed by TEM , XPS , FT‐IR and BET characterizations. Therefore, it exhibited good activity in the selective hydrogenation of cinnamic acid to hydrocinnamic acid with the conversion and selectivity both approaching to 100%. Notably, the obtained Fe₃O₄ @LDH @NiB can be easily separated by an external magnetic field and recycled eleven times without appreciable loss of its initial catalytic activity.     

Synthesis and characterization of Co/CdSe core/shell nanocomposites: bifunctional magnetic-optical nanocrystals

Nanocomposite materials provide the possibility for multifunctional properties in contrast with their more-limited single-component counterparts. Here, we report the synthesis and characterization of the first all-inorganic core/shell hybrid magnetic-optical nanoparticle, cobalt/cadmium selenide. The core/shell nanocrystals are prepared in a facile one-pot reaction, and their microstructure is analyzed using low- and high-resolution transmission electron microscopy. Using magnetic and optical characterization, we demonstrate bifunctional behavior, whereby the core retains the magnetic properties of the starting Co nanoparticle, and the shell emits similarly to a single-component CdSe nanoparticle. Interestingly, while the coercivity was found to be unchanged by shell formation, the blocking temperature for the composite structure was observed to be substantially lower (Co: >350 K; Co/CdSe: 240 K). In addition, we observed that at low temperatures (20 K) shell CdSe photoluminescence (PL) decay was very rapid (<1 ns). In contrast, nanocrystalline CdSe PL decay is typically much slower at such temperatures (>50 ns). Finally, we propose possible explanations for the unusual magnetic and optical behavior of the core/shell hybrid nanostructures.     

Nacre-inspired polyglutamic acid/layered double hydroxide bionanocomposite film with high mechanical,translucence and UV-blocking properties

Due to the various needs in the current applications,multifunctional composite materials with high strength and high toughness were highly desired now.Many scholars dedicated their time to find a simple,green and fast method for the preparation of multi-functional materials.In this study,inspired by the hierarchical "brick-and-mortar" structure and excellent mechanical performance of nacre,a fast green vacuum-filtration method was used to fabricate strong and multifunctional polyglutamic acid/layered double hydroxide (PGA/LDH) films mimicking nacre.The experimental results confirm that the artificial nacre has hierarchical "brick-and-mortar" structure.It exhibits excellent strength (93.5 MPa) and flexibility (easily bendable fold),combining with outstanding properties of UV-blocking and translucence properties.This work provides a way of fabricating multifunctional organic-inorganic hybrid films,which has potential applications in the areas of optical,transportation and construction fields.     

One‐Step Synthesis of Hybrid Core–Shell Metal–Organic Frameworks

Epitaxial growth of MOF‐on‐MOF composite is an evolving research topic in the quest for multifunctional materials. In previously reported methods, the core–shell MOFs were synthesized via a stepwise strategy that involved growing the shell‐MOFs on top of the preformed core‐MOFs with matched lattice parameters. However, the inconvenient stepwise synthesis and the strict lattice‐matching requirement have limited the preparation of core–shell MOFs. Herein, we demonstrate that hybrid core–shell MOFs with mismatching lattices can be synthesized under the guidance of nucleation kinetic analysis. A series of MOF composites with mesoporous core and microporous shell were constructed and characterized by optical microscopy, powder X‐ray diffraction, gas sorption measurement, and scanning electron microscopy. Isoreticular expansion of microporous shells and orthogonal modification of the core was realized to produce multifunctional MOF composites, which acted as size selective catalysts for olefin epoxidation with high activity and selectivity.     

Core‐Shell Structured Cobalt Sulfide/Cobalt Aluminum Hydroxide Nanosheet Arrays for Pseudocapacitor Application

The direct synthesis of nanostructured electrode materials on three‐dimensional substrates is important for their practical application in electrochemical cells without requiring the use of organic additives or binders. In this study, we present a simple two‐step process to synthesize a stable core–shell structured cobalt sulfide/cobalt aluminum hydroxide nanosheet (LDH‐S) for pseudocapacitor electrode application. The cobalt aluminum layered double hydroxide (CoAl‐LDH) nanoplates were synthesized in basic aqueous solution with a kinetically‐controlled thickness. Owing to the facile diffusion of electrolytes through the nanoplates, thin CoAl‐LDH nanoplates have higher specific capacitance values than thick nanoplates. The as‐grown CoAl‐LDH nanoplates were transformed into core–shell structured LDH‐S nanosheets by a surface modification process in Na₂S aqueous solution. The chemically robust cobalt sulfide (CoS) shell increased the electrochemical stability compared to the sulfide‐free CoAl‐LDH electrodes. The LDH‐S electrodes exhibited high electrochemical performance in terms of specific capacitance and rate capability with a galvanostatic discharge of 1503 F g^?1 at a current density of 2 A g^?1 and a specific capacitance of 91 % at 50 A g^?1.