Facile Synthesis of Yolk–Shell‐Structured Triple‐Hybridized Periodic Mesoporous Organosilica Nanoparticles for Biomedicine

The synthesis of mesoporous nanoparticles with controllable structure and organic groups is important for their applications. In this work, yolk–shell‐structured periodic mesoporous organosilica (PMO) nanoparticles simultaneously incorporated with ethane‐, thioether‐, and benzene‐bridged moieties are successfully synthesized. The preparation of the triple‐hybridized PMOs is via a cetyltrimethylammonium bromide‐directed sol–gel process using mixed bridged silsesquioxanes as precursors and a following hydrothermal treatment. The yolk–shell‐structured triple‐hybridized PMO nanoparticles have large surface area (320 m² g^–1), ordered mesochannels (2.5 nm), large pore volume (0.59 cm³ g^–1), uniform and controllable diameter (88–380 nm), core size (22–110 nm), and shell thickness (13–45 nm). In vitro cytotoxicity, hemolysis assay, and histological studies demonstrate that the yolk–shell‐structured triple‐hybridized PMO nanoparticles have excellent biocompatibility. Moreover, the organic groups in the triple‐hybridized PMOs endow them with an ability for covalent connection of near‐infrared fluorescence dyes, a high hydrophobic drug loading capacity, and a glutathione‐responsive drug release property, which make them promising candidates for applications in bioimaging and drug delivery.     

MoS2/NiS Yolk–Shell Microsphere‐Based Electrodes for Overall Water Splitting and Asymmetric Supercapacitor

Rational designing of the composition and structure of electrode material is of great significance for achieving highly efficient energy storage and conversion in electrochemical energy devices. Herein, MoS₂/NiS yolk–shell microspheres are successfully synthesized via a facile ionic liquid‐assisted one‐step hydrothermal method. With the favorable interface effect and hollow structure, the electrodes assembled with MoS₂/NiS hybrid microspheres present remarkably enhanced electrochemical performance for both overall water splitting and asymmetric supercapacitors. In particular, to deliver a current density of 10 mA cm^?2, the MoS₂/NiS‐based electrolysis cell for overall water splitting only needs an output voltage of 1.64 V in the alkaline medium, lower than that of Pt/C–IrO₂‐based electrolysis cells (1.70 V). As an electrode for supercapacitors, the MoS₂/NiS hybrid microspheres exhibit a specific capacitance of 1493 F g^?1 at current density of 0.2 A g^?1, and remain 1165 F g^?1 even at a large current density of 2 A g^?1, implying outstanding charge storage capacity and excellent rate performance. The MoS₂/NiS‐ and active carbon‐based asymmetric supercapacitor manifests a maximum energy density of 31 Wh kg^?1 at a power density of 155.7 W kg^?1, and remarkable cycling stability with a capacitance retention of approximately 100% after 10 000 cycles.     

Yolk–Shell Fe/Fe4N@Pd/C Magnetic Nanocomposite as an Efficient Recyclable ORR Electrocatalyst and SERS Substrate

A yolk–shell Fe/Fe₄N@Pd/C (FFPC) nanocomposite is synthesized successfully by two facile steps: interfacial polymerization and annealing treatment. The concentration of Pd²⁺ is the key factor for the density of Pd nanoparticles (Pd NPs) embedded in the carbon shells, which plays a role in the oxygen reduction reaction (ORR) and surface‐enhanced Raman scattering (SERS) properties. The ORR and SERS performances of FFPC nanocomposites under different concentrations of PdCl₂ are investigated. The optimal ORR performance exhibits that onset potential and tafel slope can reach 0.937 V (vs reversible hydrogen electrode (RHE)) and 74 mV dec^?1, respectively, which is attributed to the synergistic effects of good electrical conductivity, large electrochemically active areas, and strong interfacial charge polarization. Off‐axis electron holography reveals that interfacial charge polarization could facilitate the ORR of Pd NPs and defective carbon simultaneously and the shell with low density of Pd NPs is easier to form strong interfacial charge polarization. Moreover, FFPC‐3 with maximum EF of 2.3 × 10⁵ results from more hot‐spots, local positive charge centers to attract rhodamine 6G molecules, and magnetic cores. This work not only offers a recyclable multifunctional nanocomposite with excellent performance, but also has instructional implications for interfacial engineering for electrocatalysts design.     

Well‐Defined Metal Nanoparticles@Covalent Organic Framework Yolk–Shell Nanocages by ZIF‐8 Template as Catalytic Nanoreactors

Yolk–shell nanoreactors have received considerable interest for use in catalysis. However, the controlled synthesis of continuous crystalline shells without imperfections or cracks remains challenging. Here, a strategy for the synthesis of yolk–shell metal nanoparticles@covalent organic framework (MNPs@COF) nanoreactors by using MNPs@ZIF‐8 core–shell nanostructures as a self‐template is designed and developed. The COF shell is formed through an amorphous‐to‐crystalline transformation process of a polyimine shell in a mildly acidic solution, while the ZIF‐8 is etched in situ, generating a void space between the MNPs core and the COF shell. With the protection of the COF shell, multiple ligand‐free MNPs are confined inside of the hollow nanocages. Importantly, the synthetic strategy can be generalized to engineer the functions and properties of the designed yolk–shell nanocages by varying the structure of the COF shell and/or the composition of the core MNPs. Representative Pd@H‐TpPa yolk–shell nanocages with active Pd NP cores and permeable TpPa shells exhibit high catalytic activity and stability in the reduction of 4‐nitrophenol by NaBH₄ at room temperature.     

Yolk–Shell Nanostructures: Design,Synthesis, and Biomedical Applications

Yolk–shell nanostructures (YSNs) composed of a core within a hollow cavity surrounded by a porous outer shell have received tremendous research interest owing to their unique structural features, fascinating physicochemical properties, and widespread potential applications. Here, a comprehensive overview of the design, synthesis, and biomedical applications of YSNs is presented. The synthetic strategies toward YSNs are divided into four categories, including hard‐templating, soft‐templating, self‐templating, and multimethod combination synthesis. For the hard‐ or soft‐templating strategies, different types of rigid or vesicle templates are used for making YSNs. For the self‐templating strategy, a number of unconventional synthetic methods without additional templates are introduced. For the multimethod combination strategy, various methods are applied together to produce YSNs that cannot be obtained directly by only a single method. The biomedical applications of YSNs including biosensing, bioimaging, drug/gene delivery, and cancer therapy are discussed in detail. Moreover, the potential superiority of YSNs for these applications is also highlighted. Finally, some perspectives on the future research and development of YSNs are provided.     

Design and Synthesis of Spherical Multicomponent Aggregates Composed of Core–Shell,Yolk–Shell,and Hollow Nanospheres and Their Lithium‐Ion Storage Performances

Micrometer‐sized spherical aggregates of Sn and Co components containing core–shell, yolk–shell, hollow nanospheres are synthesized by applying nanoscale Kirkendall diffusion in the large‐scale spray drying process. The Sn₂Co₃–Co₃SnC_0.7–C composite microspheres uniformly dispersed with Sn₂Co₃–Co₃SnC_0.7 mixed nanocrystals are formed by the first‐step reduction of spray‐dried precursor powders at 900 °C. The second‐step oxidation process transforms the Sn₂Co₃–Co₃SnC_0.7–C composite into the porous microsphere composed of Sn–Sn₂Co₃@CoSnO₃–Co₃O₄ core–shell, Sn–Sn₂Co₃@CoSnO₃–Co₃O₄ yolk–shell, and CoSnO₃–Co₃O₄ hollow nanospheres at 300, 400, and 500 °C, respectively. The discharge capacity of the microspheres with Sn–Sn₂Co₃@CoSnO₃–Co₃O₄ core–shell, Sn‐Sn₂Co₃@CoSnO₃–Co₃O₄ yolk–shell, and CoSnO₃–Co₃O₄ hollow nanospheres for the 200^th cycle at a current density of 1 A g^?1 is 1265, 987, and 569 mA h g^?1, respectively. The ultrafine primary nanoparticles with a core–shell structure improve the structural stability of the porous‐structured microspheres during repeated lithium insertion and desertion processes. The porous Sn–Sn₂Co₃@CoSnO₃–Co₃O₄ microspheres with core–shell primary nanoparticles show excellent cycling and rate performances as anode materials for lithium‐ion batteries.     

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.     

Versatile Yolk–Shell Encapsulation: Catalytic,Photothermal, and Sensing Demonstration

Here, a novel, versatile synthetic strategy to fabricate a yolk–shell structured material that can encapsulate virtually any functional noble metal or metal oxide nanocatalysts of any morphology in a free suspension fashion is reported. This strategy also enables encapsulation of more than one type of nanoparticle inside a single shell, including paramagnetic iron oxide used for magnetic separation. The mesoporous organosilica shell provides efficient mass transfer of small target molecules, while serving as a size exclusion barrier for larger interfering molecules. Major structural and functional advantages of this material design are demonstrated by performing three proof‐of‐concept applications. First, effective encapsulation of plasmonic gold nanospheres for localized photothermal heating and heat‐driven reaction inside the shell is shown. Second, hydrogenation catalysis is demonstrated under spatial confinement driven by palladium nanocubes. Finally, the surface‐enhanced Raman spectroscopic detection of model pollutant by gold nanorods is presented for highly sensitive environmental sensing with size exclusion.     

Synergizing Phase and Cavity in CoMoOxSy Yolk–Shell Anodes to Co‐Enhance Capacity and Rate Capability in Sodium Storage

Sodium‐ion batteries (SIBs) have been recognized as the promising alternatives to lithium‐ion batteries for large‐scale applications owing to their abundant sodium resource. Currently, one significant challenge for SIBs is to explore feasible anodes with high specific capacity and reversible pulverization‐free Na⁺ insertion/extraction. Herein, a facile co‐engineering on polymorph phases and cavity structures is developed based on CoMo‐glycerate by scalable solvothermal sulfidation. The optimized strategy enables the construction of CoMoO_xS_y with synergized partially sulfidized amorphous phase and yolk–shell confined cavity. When developed as anodes for SIBs, such CoMoO_xS_y electrodes deliver a high reversible capacity of 479.4 mA h g^?1 at 200 mA g^?1 after 100 cycles and a high rate capacity of 435.2 mA h g^?1 even at 2000 mA g^?1, demonstrating superior capacity and rate capability. These are attributed to the unique dual merits of the anodes, that is, the elastic bountiful reaction pathways favored by the sulfidation‐induced amorphous phase and the sodiation/desodiation accommodatable space benefits from the yolk–shell cavity. Such yolk–shell nano‐battery materials are merited with co‐tunable phases and structures, facile scalable fabrication, and excellent capacity and rate capability in sodium storage. This provides an opportunity to develop advanced practical electrochemical sodium storage in the future.     

Functionalized Graphene Quantum Dot Modification of Yolk–Shell NiO Microspheres for Superior Lithium Storage

Yolk–shell NiO microspheres are modified by two types of functionalized graphene quantum dots (denoted as NiO/GQDs) via a facile solvothermal treatment. The modification of GQDs on the surface of NiO greatly boosts the stability of the NiO/GQD electrode during long‐term cycling. Specifically, the NiO with carboxyl‐functionalized GQDs (NiO/GQDs? COOH) exhibits better performances than NiO with amino‐functionalized GQDs (NiO/GQDs? NH₂). It delivers a capacity of ≈1081 mAh g^?1 (NiO contribution: ≈1182 mAh g^?1) after 250 cycles at 0.1 A g^?1. In comparison, NiO/GQDs? NH₂ electrode holds ≈834 mAh g^?1 of capacity, while the bald NiO exhibits an obvious decline in capacity with ≈396 mAh g^?1 retained after cycling. Except for the yolk–shell and mesoporous merits, the superior performances of the NiO/GQD electrode are mainly ascribed to the assistance of GQDs. The GQD modification can support as a buffer alleviating the volume change, improve the electronic conductivity, and act as a reservoir for electrolytes to facilitate the transportation of Li⁺. Moreover, the enrichment of carboxyl/amino groups on GQDs can further donate more active sites for the diffusion of Li⁺ and facilitate the electrochemical redox kinetics of the electrode, thus together leading to the superior lithium storage performance.     

Necklace‐Like Structures Composed of Fe3N@C Yolk–Shell Particles as an Advanced Anode for Sodium‐Ion Batteries

It is of great importance to develop cost‐effective electrode materials for large‐scale use of Na‐ion batteries. Here, a binder‐free electrode based on necklace‐like structures composed of Fe₃N@C yolk–shell particles as an advanced anode for Na‐ion batteries is reported. In this electrode, every Fe₃N@C unit has a novel yolk–shell structure, which can accommodate the volumetric changes of Fe₃N during the (de)sodiation processes for superior structural integrity. Moreover, all reaction units are threaded along the carbon fibers, guaranteeing excellent kinetics for the electrochemical reactions. As a result, when evaluated as an anode material for Na‐ion batteries, the Fe₃N@C nano‐necklace electrode delivers a prolonged cycle life over 300 cycles, and achieves a high C‐rate capacity of 248 mAh g^?1 at 2 A g^?1.     

Synthesis of Uniquely Structured Yolk–Shell Metal Oxide Microspheres Filled with Nitrogen‐Doped Graphitic Carbon with Excellent Li–Ion Storage Performance

Novel structured composite microspheres of metal oxide and nitrogen‐doped graphitic carbon (NGC) have been developed as efficient anode materials for lithium‐ion batteries. A new strategy is first applied to a one‐pot preparation of composite (FeO_x‐NGC/Y) microspheres via spray pyrolysis. The FeO_x‐NGC/Y composite microspheres have a yolk–shell structure based on the iron oxide material. The void space of the yolk–shell microsphere is filled with NGC. Dicyandiamide additive plays a key role in the formation of the FeO_x‐NGC/Y composite microspheres by inducing Ostwald ripening to form a yolk–shell structure based on the iron oxide material. The FeO_x‐NGC/Y composite microspheres with the mixed crystal structure of rock salt FeO and spinel Fe₃O₄ phases show highly superior lithium‐ion storage performances compared to the dense‐structured FeO_x microspheres with and without carbon material. The discharge capacities of the FeO_x‐NGC/Y microspheres for the 1st and 1000th cycle at 1 A g^?1 are 1423 and 1071 mAh g^?1, respectively. The microspheres have a reversible discharge capacity of 598 mAh g^?1 at an extremely high current density of 10 A g^?1. Furthermore, the strategy described in this study is generally applied to multicomponent metal oxide–carbon composite microspheres with yolk–shell structures based on metal oxide materials.     

A Simple and Scalable Route to Synthesize CoxCu1−xCo2O4@CoyCu1−yCo2O4 Yolk–Shell Microspheres,A High‐Performance Catalyst to Hydrolyze Ammonia Borane for Hydrogen Production

Yolk–shell structured micro/nano‐sized materials have broad and important applications in different areas due to their unique spatial configurations. In this study, yolk–shell structured Co₃O₄@Co₃O₄ is prepared using a simple and scalable hydrothermal reaction, followed by a calcination process. Then, Co_xCu_1?xCo₂O₄@Co_yCu_1?yCo₂O₄ microspheres are synthesized via adsorption and calcination processes using the as‐prepared Co₃O₄@Co₃O₄ as the precursor. A possible formation mechanism of the yolk–shell structures is proposed based on the characterization results, which is different from those of yolk–shell structures in previous study. For the first time, the catalytic activity of yolk–shell structured catalysts in ammonia borane (AB) hydrolysis is studied. It is discovered that the yolk–shell structured Co_xCu_1?xCo₂O₄@Co_yCu_1?yCo₂O₄ microspheres exhibit high performance with a turnover frequency (TOF) of 81.8 mol_hydrogen min^?1 mol_cat^?1. This is one of the highest TOF values reported for a noble‐metal‐free catalyst in the literature. Additionally, the yolk–shell structured Co_xCu_1?xCo₂O₄@Co_yCu_1?yCo₂O₄ microspheres are highly stable and reusable. These yolk–shell structured Co_xCu_1?xCo₂O₄@Co_yCu_1?yCo₂O₄ microsphere is a promising catalyst candidate in AB hydrolysis considering the excellent catalytic behavior and low cost.     

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.