Yolk-shell Nanospheres Research Articles

Fabrication of Efficient Hydrogenation Nanoreactors by Modifying the Freedom of Ultrasmall Platinum Nanoparticles within Yolk-Shell Nanospheres.

The synthesis of silica-based yolk-shell nanospheres confined with ultrasmall platinum nanoparticles (Pt NPs) stabilized with poly(amidoamine), in which the interaction strength between Pt NPs and the support could be facilely tuned, is reported. By ingenious utilization of silica cores with different surface wettability (hydrophilic vs. -phobic) as the adsorbent, Pt NPs could be confined in different locations of the yolk-shell nanoreactor (core vs. hollow shell), and thus, exhibit different interaction strengths with the nanoreactor (strong vs. weak). It is interesting to find that the adsorbed Pt NPs are released from the core to the hollow interiors of the yolk-shell nanospheres when a superhydrophobic inner core material (SiO2 -Ph) is employed, which results in the preparation of an immobilized catalyst (Pt@SiO2-Ph); this possesses the weakest interaction strength with the support and shows the highest catalytic activity (88 500 and 7080 h(-1) for the hydrogenation of cyclohexene and nitrobenzene, respectively), due to its unaffected freedom of Pt NPs for retention of the intrinsic properties.

Nanofibers Comprising Yolk-Shell Sn@void@SnO/SnO2and Hollow SnO/SnO2and SnO2Nanospheres via the Kirkendall Diffusion Effect and Their Electrochemical Properties

Nanofibers with a unique structure comprising Sn@void@SnO/SnO2 yolk-shell nanospheres and hollow SnO/SnO2 and SnO2 nanospheres are prepared by applying the nanoscale Kirkendall diffusion process in conventional electrospinning process. Under a reducing atmosphere, post-treatment of tin 2-ethylhexanoate-polyvinylpyrrolidone electrospun nanofibers produce carbon nanofibers with embedded spherical Sn nanopowders. The Sn nanopowders are linearly aligned along the carbon nanofiber axis without aggregation of the nanopowders. Under an air atmosphere, oxidation of the Sn-C composite nanofibers produce nanofibers comprising Sn@void@SnO/SnO2 yolk-shell nanospheres and hollow SnO/SnO2 and SnO2 nanospheres, depending on the post-treatment temperature. The mean sizes of the hollow nanospheres embedded within tin oxide nanofibers post-treated at 500 °C and 600 °C are 146 and 117 nm, respectively. For the 250th cycle, the discharge capacities of the nanofibers prepared by the nanoscale Kirkendall diffusion process post-treated at 400 °C, 500 °C, and 600 °C at a high current density of 2 A g(-1) are 663, 630, and 567 mA h g(-1), respectively. The corresponding capacity retentions are 77%, 84%, and 78%, as calculated from the second cycle. The nanofibers prepared by applying the nanoscale Kirkendall diffusion process exhibit superior electrochemical properties compared with those of the porous-structured SnO2 nanofibers prepared by the conventional post-treatment process.

Yolk–shell nanospheres with soluble amino-polystyrene as a reservoir for Pd NPs

Pd NPs immobilized in yolk–shell nanospheres confined with soluble amino-polystyrene could efficiently catalyze the selective hydrogenation of acetophenone.

One-pot fabrication of yolk-shell nanospheres with ultra-small Au nanoparticles for catalysis.

We report a "one-pot" method for the direct synthesis of an organosilica shell/silica core nanoreactor confined with ultra-small metal (Au, Pd, and Ru) nanoparticles. The nano-reactor confined with Au nanoparticles showed high activity towards styrene oxidation using O2 as the oxidant under 1 atm pressure and could be stably recycled without deterioration of both conversion and selectivity. The strategy could be adapted onto other nanostructures with little modification to obtain yolk-shell nanoreactors for catalysis application.

Design of Au@ZnO yolk-shell nanospheres with enhanced gas sensing properties.

The Au@ZnO yolk-shell nanospheres with a distinctive core@void@shell configuration have been successfully synthesized by deposition of ZnO on Au@carbon nanospheres. Various techniques were employed for the characterization of the structure and morphology of as-obtained hybrid nanostructures. The results indicated that the Au@ZnO yolk-shell nanospheres have an average diameter of about 280 nm and the average thickness of the ZnO shell is ca. 40 nm. To demonstrate how such a unique structure might bring about more excellent gas sensing property, we carried out a comparison of the sensing performances of ZnO nanospheres with different inner structures. It was found that Au@ZnO yolk-shell nanospheres exhibited an obvious improvement in response to acetone compared with the pure ZnO nanospheres with hollow and solid inner structures. For instance, the response of the Au@ZnO nanospheres to 100 ppm acetone was about 37, which was about 2 (3) times higher than that of ZnO hollow (solid) nanostructures. The enhanced sensing properties were attributed to their unique microstructures (porous shell and internal voids) and the catalytic effect of the encapsulated Au nanoparticles.

Facile synthesis of Mn–Co oxide nanospheres with controllable interior structures and their catalytic properties for methane combustion

Uniform Mn–Co mixed oxide solid, hollow and yolk–shell nanospheres with nanometer-sized building blocks have been successfully fabricated by heat-treatment of their Mn–Co alkoxyacetate precursors at a proper ramping rate. The formation of the hollow and yolk–shell structures during the thermal decomposition is mainly based on the heterogeneous contraction caused by non-equilibrium heat treatment. In virtue of the unique structural features, the resultant Mn–Co oxide nanospheres with different interiors were used as catalysts in CH4 combustion, and showed an excellent catalytic activity. Catalytic results suggest that the (Co,Mn)(Co,Mn)2O4 yolk–shell nanospheres show relatively higher activity.

Controllable synthesis of SnO2@C yolk–shell nanospheres as a high-performance anode material for lithium ion batteries

In this work, we report a facile synthesis of uniform SnO2@C yolk-shell nanospheres as high-performance anode materials for lithium ion batteries (LIBs). The yolk-shell structured SnO2@C nanospheres were fabricated through a two-step sol-gel coating process by using tetraethyl orthosilicate (TEOS) and resorcinol-formaldehyde (RF) as precursors, where the silica interlayer not only acts as a template to produce the void space, but also promotes the coating of the RF layer. The synthesis is easy to operate and allows tailoring the carbon shell thickness and void space size. The resultant SnO2@C yolk-shell nanospheres possess a hollow highly crystalline SnO2 core (280-380 nm), tailored carbon shell thickness (15-25 nm) and a large void space size (100-160 nm), a high surface area (∼205 m(2) g(-1)), a large pore volume (∼0.25 cm(3) g(-1)), as well as a high SnO2 content (77 wt%). When evaluated as an anode of LIBs, the materials manifest superior electrochemical performance with a high lithium storage capability (2190 mA h g(-1) in initial discharge capacity; >950 mA h g(-1) in the first 10 cycles), a good cycling performance and an excellent rate capability.

Formation of Sn@C Yolk–Shell Nanospheres and Core–Sheath Nanowires for Highly Reversible Lithium Storage

As one promising anode material with high theoretical capacity, metallic tin has attracted much research interest in the field of lithium‐ion batteries. Here, two types of tin/carbon (Sn@C) core–shell nanostructures with inner buffering voids are fabricated from SnO2 hollow nanospheres via a facile chemical vapor deposition (CVD) method. The crystallinity and surface topography of SnO2 hollow nanospheres are found to affect the morphology of resultant Sn@C materials. Sn@C yolk–shell nanospheres and core–sheath nanowires are obtained from the as‐prepared SnO2 and high‐temperature annealed SnO2 nanospheres, respectively. The unique Sn@C nanostructures can mitigate the agglomeration/pulverization of Sn nanoparticles and electrical disconnection from the current collector caused by the large volume change during the lithium alloying/dealloying process. Both Sn@C yolk–shell and core–sheath nanostructures show stable cycling performance up to 500 cycles with specific capacities of ca. 430 and 520 mA h g−1, respectively.

Encapsuled nanoreactors (Au@SnO2): a new sensing material for chemical sensors

New Au@SnO2 yolk-shell nanospheres have been successfully synthesized by using Au@SiO2 nanospheres as sacrificial templates. This process is environmentally friendly and is based on hydrothermal shell-by-shell deposition of polycrystalline SnO2 on spheriform Au@SiO2 nanotemplates. Au nanoparticles can be impregnated into the SnO2 nanospheres and the nanospheres show outer diameters of 110 nm and thicknesses of 15 nm. The possible growth model of the nanospheres is proposed. The gas sensing properties of the Au@SnO2 yolk-shell nanospheres were researched and compared with that of the hollow SnO2 nanospheres. The former shows lower operating temperature (210 °C), lower detection limit (5 ppm), faster response (0.3 s) and better selectivity. These improved sensing properties were attributed to the catalytic effect of Au, and enhanced electron depletion at the surface of the Au@SnO2 yolk-shell nanospheres.

Template-free synthesis of zinc citrate yolk–shell microspheres and their transformation to ZnO yolk–shell nanospheres

A novel, facile, green and template-free approach was developed for the fabrication of amorphous zinc citrate yolk–shell microspheres and crystalline ZnO yolk–shell nanospheres. In this approach, the amorphous zinc citrate yolk–shell microspheres were prepared through a single chemical reaction at low temperature (90 °C) and with room temperature ageing. The zinc citrate yolk–shell microspheres have an average size of about 1.25 μm. The average diameter of the inner cores and the average thickness of the outer shells are 500 nm and 150 nm, respectively. The effect of ageing time on the morphology of the zinc citrate microstructures was analysed. As the ageing time increases from 0 to 12 h, the zinc citrate microstructure transforms from a solid microsphere through a yolk–shell microsphere to a hollow microsphere. The ZnO solid nanospheres, yolk–shell nanospheres and hollow nanospheres can be prepared via the perfect morphology inheritance of the zinc citrate solid microspheres, yolk–shell microspheres and hollow microspheres, by calcination at 600 °C for 2 h. The ZnO yolk–shell nanospheres show the largest visible emission and the highest photocatalytic activity.