Yolk-shell Microspheres Research Articles

MoS2 yolk–shell microspheres with a hierarchical porous structure for efficient hydrogen evolution

Yolk–shell architectures have attracted extensive attention owing to their unique structure and infusive applications. MoS2 is regarded as one of the most promising catalytic materials for hydrogen evolution by the splitting of water. In this work, a simple self-template solvothermal approach is developed for the synthesis of novel MoS2 yolk–shell microspheres with a hierarchical porous structure by reacting MoO2 microspheres with L-cysteine. A dissolutionrecrystallization formation mechanism is proposed for the MoS2 yolk–shell microspheres. Owing to structural superiority, the new material architecture exhibits improved photoelectrochemical properties, including efficient hydrogen evolution reaction catalytic activities, a high photocurrent density, a small overpotential, and a low charge-transfer resistance.

Highly Active and Stable Pt-Loaded Ce0.75Zr0.25O2 Yolk-Shell Catalyst for Water-Gas Shift Reaction.

Multishelled, Pt-loaded Ce0.75Zr0.25O2 yolk-shell microspheres were prepared by a simple spray pyrolysis process for use in the water-gas shift (WGS) reaction. The Pt-loading was optimized, obtaining highly active Pt/Ce0.75Zr0.25O2 yolk-shell nanostructures for the WGS. Of the prepared catalysts, a 2% Pt loading of the Ce0.75Zr0.25O2 yolk-shell microspheres showed the highest CO conversion. The high catalytic activity of the 2% Pt/Ce0.75Zr0.2O2 catalyst was mainly due to its easier reducibility and the maintenance of active catalytic Pt species. The Pt-loaded Ce0.75Zr0.25O2 catalyst microspheres were highly resistant to Pt sintering because of their unique yolk-shell structure. Spray pyrolysis was found to be highly efficient for the production of precious-metal-loaded, multicomponent metal oxide yolk-shell microspheres for catalytic applications.

Magnetic Core–Shell Nanostructured Palladium Catalysts for Green Oxidation of Benzyl Alcohol

Multifunctional catalysts are highly attractive for green oxidation process integrating excellent conversion and selectivity with high separability and recyclability. In this regards, a facile method is developed to fabricate yolk–shell microspheres consisting of Fe3O4 cores, mesoporous CeO2 shells and loaded Pd nanoparticles. Microspheres with 2.6 % Pd loading exemplify excellent catalytic activity for solvent-free, selective oxidation of benzyl alcohol to benzaldehyde by molecular oxygen at 373 K and atmospheric pressure, resulting in 80.5 % conversion of benzyl alcohol with 94.8 % selectivity for benzaldehyde. The catalyst can be magnetically separated and recycled without significant loss of catalytic efficiency even after seven catalytic runs.

Magnetic metal-organic nanotubes: An adsorbent for magnetic solid-phase extraction of polychlorinated biphenyls from environmental and biological samples

A new type of three-dimensional, echinus-like magnetic Fe3O4 @ cobalt(Ⅱ)-based metal-organic nanotube (Fe3O4 @ Co-MONT) yolk-shell microspheres, have been designed and synthesized for the first time. Fe3O4 @ Co-MONTs yolk-shell microspheres were characterized by scanning electron micrographs, transmission electron microscopy, Fourier transform infrared spectra, X-ray diffraction, and vibrating sample magnetometry. The feasibility of the new material for use as an absorbent was investigated for magnetic solid phase-extraction (MSPE) of polychlorinated biphenyls (PCBs) from environmental water samples and biological samples. The Plackett-Burman design and Box-Behnken design were used to determine and optimize the extraction parameters influencing the extraction efficiency through response surface methodology. Under the optimized conditions, the developed method showed good linearity within the range of 5–1000ngL−1, low limits of detection (0.31–0.49ngL−1), and good reproducibility (RSD<10%). The proposed method was successfully applied for the analysis of PCBs in real environmental water samples. These results demonstrated that Fe3O4 @ Co-MONTs is a promising adsorbent material for the MSPE of PCBs at trace levels from environmental water samples and biological samples.

Preparation of yolk–shell microspheres as temperature switch on/off catalysts

A novel kind of yolk–shell microspheres was presented in this Letter. First, 250 nm of magnetic Fe3O4 nanoparticles was prepared by solvothermal reaction. Then, the Fe3O4 particles were coated with Au nanoparticles (AuNPs), SiO2, and poly(N-isopropylacrylamide) (PNIPAM). After the removal of the SiO2 layer by etching with HF solution, the yolk–shell microspheres were prepared. Each yolk–shell microsphere had a movable core (Fe3O4 self-assembled AuNPs) and temperature-responsive shell (PNIPAM). The yolk–shell structure of these microspheres was confirmed by transmission electron microscopy and Fourier-transform infrared spectroscopy. The catalytic performances of these yolk–shell microspheres were investigated under different environmental temperatures. The results indicated that the reduction from 4-nitrophenol to 4-aminophenol by NaBH4 was slowed when the temperature was increased because of the hydrophobic and the shrinking sate of PNIPAM shell and the yolk–shell microspheres had a characteristic of temperature switch on/off when the cross-linking degree was about 20%.

Hierarchical nanosheet-assembled yolk–shell TiO2microspheres with improved photocatalytic activity

Nanosheet-assembled yolk–shell anatase TiO2 microspheres were synthesized utilizing the slow hydrolysis of K2TiO(C2O4)2 in a mixed solution of H2O2 and HNO3. Under a temperature near to the ambient one, microspheres assembled with nanoparticles were firstly obtained at the early reaction stage. Prolonging the reaction duration led to the formation of urchin-like microspheres, which further developed into nanosheet-assembled yolk–shell microspheres through a dissolution–precipitation procedure. The intermediate acid washing and final calcination transformed the microspheres to phase-pure anatase TiO2. The yolk–shell anatase microspheres exhibited a photocatalytic activity twice that of the urchin-like microspheres when utilized to assist the photodegradation of both rhodamine B and phenol in water under the illumination of UV light.

Template-free synthesis of hierarchical ZnFe2O4 yolk-shell microspheres for high-sensitivity acetone sensors.

Metal oxides with hierarchical microstructures have attracted tremendous attention with respect to their enhanced gas sensing properties. Herein, we reported the facile synthesis of hierarchical ZnFe2O4 yolk-shell microspheres via a template-free solvothermal strategy and the subsequent annealing and chemical etching process. Electron microscopy images undoubtedly demonstrated that the novel ZnFe2O4 architecture was constructed of a large number of nanosheet subunits with a thickness around 20 nm. As a proof-of-concept demonstration of the function, when evaluated as gas sensing materials, the as-prepared ZnFe2O4 yolk-shell microspheres manifested an extremely high response and a low detection limit to acetone at the operating temperature of 200 °C. Significantly, the response to 20 ppm acetone was retained well even after 200 cycles and continuous measurement for 30 days, indicating superior cyclability and long-term stability.

CoNi@SiO2 @TiO2 and CoNi@Air@TiO2 Microspheres with Strong Wideband Microwave Absorption.

The synthesis of CoNi@SiO2 @TiO2 core-shell and CoNi@Air@TiO2 yolk-shell microspheres is reported for the first time. Owing to the magnetic-dielectric synergistic effect, the obtained CoNi@SiO2 @TiO2 microspheres exhibit outstanding microwave absorption performance with a maximum reflection loss of -58.2 dB and wide bandwidth of 8.1 GHz (8.0-16.1 GHz, < -10 dB).

Synergetic Effect of Yolk-Shell Structure and Uniform Mixing of SnS-MoS₂ Nanocrystals for Improved Na-Ion Storage Capabilities.

Mixed metal sulfide composite microspheres with a yolk-shell structure for sodium-ion batteries are studied. Tin-molybdenum oxide yolk-shell microspheres prepared by a one-pot spray pyrolysis process transform into yolk-shell SnS-MoS2 composite microspheres. The discharge capacities of the yolk-shell and dense-structured SnS-MoS2 composite microspheres for the 100th cycle are 396 and 207 mA h g(-1), and their capacity retentions measured from the second cycle are 89 and 47%, respectively. The yolk-shell SnS-MoS2 composite microspheres with high structural stability during repeated sodium insertion and desertion processes have low charge-transfer resistance even after long-term cycling. The synergetic effect of the yolk-shell structure and uniform mixing of the SnS and MoS2 nanocrystals result in the excellent sodium-ion storage properties of the yolk-shell SnS-MoS2 composite microspheres by improving their structural stability during cycling.

Mesoporous TiO2 Yolk-Shell Microspheres for Dye-sensitized Solar Cells with a High Efficiency Exceeding 11%.

Yolk-shell TiO2 microspheres were synthesized via a one-pot template-free solvothermal method building on the aldol condensation reaction of acetylacetone. This unique structure shows superior light scattering ability resulting in power conversion efficiency as high as 11%. This work provided a new synthesis system for TiO2 microspheres from solid to hollow and a novel material platform for high performance solar cells.

Activation of the Solid Silica Layer of Aerosol-Based C/SiO₂ Particles for Preparation of Various Functional Multishelled Hollow Microspheres.

Double-shelled C/SiO2 hollow microspheres with an outer nanosheet-like silica shell and an inner carbon shell were reported. C/SiO2 aerosol particles were synthesized first by a one-step rapid aerosol process. Then the solid silica layer of the aerosol particles was dissolved and regrown on the carbon surface to obtain novel C/SiO2 double-shelled hollow microspheres. The new microspheres prepared by the facile approach possess high surface area and pore volume (226.3 m(2) g(-1), 0.51 cm(3) g(-1)) compared with the original aerosol particles (64.3 m(2) g(-1), 0.176 cm(3) g(-1)), providing its enhanced enzyme loading capacity. The nanosheet-like silica shell of the hollow microspheres favors the fixation of Au NPs (C/SiO2/Au) and prevents them from growing and migrating at 500 °C. Novel C/C and C/Au/C (C/Pt/C) hollow microspheres were also prepared based on the hollow nanostructure. C/C microspheres (482.0 m(2) g(-1), 0.92 cm(3) g(-1)) were ideal electrode materials. In particular, the Au NPs embedded into the two carbon layers (C/Au/C, 431.2 m(2) g(-1), 0.774 cm(3) g(-1)) show a high catalytic activity and extremely chemical stability even at 850 °C. Moreover, C/SiO2/Au, C/Au/C microspheres can be easily recycled and reused by an external magnetic field because of the presence of Fe3O4 species in the inner carbon shell. The synthetic route reported here is expected to simplify the fabrication process of double-shelled or yolk-shell microspheres, which usually entails multiple steps and a previously synthesized hard template. Such a capability can facilitate the preparation of various functional hollow microspheres by interfacial design.

Mixed surfactant controlled syntheses of solid Ni2P and yolk–shell Ni12P5 via a hydrothermal route and their photocatalytic properties

In this paper, Ni2P solid spheres and Ni12P5 yolk–shell microspheres have been fabricated successfully via two different hydrothermal systems, using sodium dodecyl benzene sulfonate/sodium dodecyl sulfate (SDBS/SDS) and sodium dodecyl benzene sulfonate/cetyltrimethyl ammonium bromide (SDBS/CTAB) as stabilized system, respectively. The yolk–shell Ni12P5 spheres exhibited the size of around 900nm, which made up mainly the shells with a thickness of 110nm and the cores with a diameter of 350nm on average. With the heating time increasing from 0 to 36h, Ni12P5 structures transformed from yolk–shell microspheres to hollow spheres. Based on a series of surfactant-dependent and time-dependent experiments, the optimum proportion of mixed surfactant and the formation mechanism of Ni12P5 yolk–shell microstructures were discussed. Importantly, the as-prepared Ni2P and Ni12P5 possess excellent photocatalytic activities for both degradation Congo red (CR) and Safranine T (ST) dyes.

Facile fabrication of various zinc-nickel citrate microspheres and their transformation to ZnO-NiO hybrid microspheres with excellent lithium storage properties.

Zinc-nickel citrate microspheres are prepared by a simple aging process of zinc citrate solid microspheres in nickel nitrate solution. As the concentration of nickel nitrate solution increases, the morphology of the produced zinc-nickel citrate evolves from solid, yolk-shell to hollow microspheres. The formation mechanism of different zinc-nickel citrate microspheres is discussed. After annealing treatment of the corresponding zinc-nickel citrate microspheres in air, three different ZnO-NiO hybrid architectures including solid, yolk-shell and hollow microspheres can be successfully fabricated. When applied as the anode materials for lithium ion batteries, ZnO-NiO hybrid yolk-shell microspheres demonstrate the best electrochemical properties than solid and hollow counterparts. After 200th cycles, ZnO-NiO hybrid yolk-shell microspheres deliver a high reversible capacity of 1176 mA h g−1. The unique yolk-shell configuration, the synergetic effect between ZnO and NiO and the catalytic effect of metal Ni generated by the reduction of NiO during discharging process are responsible for the excellent lithium storage properties of ZnO-NiO hybrid yolk-shell microspheres.

In situ carbon-coated yolk-shell V2O3 microspheres for lithium-ion batteries.

Metal oxide-based materials with yolk-shell morphology have been intensively investigated as important anodes for Li-ion batteries due to their large ion storage ability, high safety, and excellent cycling stability. In this work, in situ carbon-coated yolk-shell V2O3 microspheres were synthesized via a template-free polyol solvothermal method. The growth of yolk-shell microspheres underwent coordination and polymerization, followed by an inside-out Ostwald-ripening process and further calcination in N2 atmosphere. The thin amorphous carbon layers coating on the microspheres' surface came from polyol frameworks which could protect V2O3 during the charge-discharge process and led to a better stability in Li-ion batteries. The in situ carbon-coated yolk-shell V2O3 microspheres showed a capacity of 437.5 mAh·g(-1) after 100 cycles at a current density of 0.1 A·g(-1), which was 92.6% of its initial capability (472.5 mAh·g(-1)). They were regarded as excellent electrode materials for lithium-ion batteries and exhibit good electrochemistry performance and stability.

General formation of tin nanoparticles encapsulated in hollow carbon spheres for enhanced lithium storage capability.

A new simple process for synthesis of heterogeneous yolk-shell microspheres is introduced. The core/shell-structured microspheres are prepared by a one-pot spray pyrolysis process. The removal of one kind of metal oxide by a dry process produces heterogeneous yolk-shell microspheres. The yolk-shell Sn@C microspheres show superior electrochemical properties as anode materials for lithium-ion batteries.

Magnetic yolk–shell mesoporous silica microspheres with supported Au nanoparticles as recyclable high-performance nanocatalysts

Multifunctional yolk–shell microspheres are synthesized through a combined interfacial sol–gel coating and surfactant-templating co-assembly method and are demonstrated as efficient and easily recyclable nanocatalysts for catalytic epoxidation of styrene.

Subunits controlled synthesis of α-Fe2O3 multi-shelled core–shell microspheres and their effects on lithium/sodium ion battery performances

Two kinds of Fe2O3 yolk–shell microspheres with different subunits were synthesized by a solvothermal method. The electrochemical performances of lithium and sodium ion batteries using Fe2O3 anodes were greatly affected by the distinctive subunits.

Magnetic MSP@ZrO₂ microspheres with yolk-shell structure: designed synthesis and application in highly selective enrichment of phosphopeptides.

Magnetic yolk-shell MSP@ZrO2 microspheres consisting of a movable magnetic supraparticle (MSP) core and a crystalline ZrO2 shell were synthesized via a two-step controlled "sol-gel" approach for the first time. First, a large amount of the generated hydrolyzate Zr(OH)4 was firmly fixed onto the surface of the cross-linked polymethylacrylic acid matrix via a strong hydrogen-bonding interaction between Zr(OH)4 and the carboxyl groups. Then a calcination process was adopted to convert the Zr(OH)4 into a continuous ZrO2 shell and simultaneously make the ZrO2 shell crystallized. At the same time, the polymer matrix could be selectively removed to form a yolk-shell structure, which has better dispersibility and higher adsorbing efficiency of phosphopeptides than its solid counterpart. The formation mechanism of such yolk-shell microspheres could be reasonably proved by the results of TEM, TGA, VSM, XRD, and FT-IR characterization. By taking advantage of the unique properties, the yolk-shell MSP@ZrO2 exhibited high specificity and great capability in selective enrichment of phosphopeptides, and a total of 33 unique phosphopeptides mapped to 33 different phosphoproteins had been identified from 1 mL of human saliva. This result clearly demonstrated that the yolk-shell MSP@ZrO2 has great performance in purifying and identifying the low-abundant phosphopeptides from real complex biological samples. Moreover, the synthetic method can be used to produce hybrid yolk-shell MSP@ZrO2-TiO2.

Yolk-shell ZnO-C microspheres with enhanced electrochemical performance as anode material for lithium ion batteries

Three ZnO-C samples with distinct structures including yolk-shell microspheres, hollow microspheres and solid microspheres are fabricated through a facile chemical solution reaction followed by calcination in argon. When employed as the anode materials for lithium ion batteries, yolk-shell ZnO-C microspheres exhibit the best electrochemical properties than the hollow and solid microspheres. After 150 cycles, yolk-shell ZnO-C microspheres demonstrate a relative high capacity of 520mA h g−1 at a current density of 100mAg−1 with a Coulombic efficiency of about 99.3%. The excellent cycling stability and good rate capability of yolk-shell ZnO-C microspheres stem from the synergistic effect of the unique yolk-shell structures and extra carbon support.

Excellent Electrochemical Properties of Yolk–Shell MoO3 Microspheres Formed by Combustion of Molybdenum Oxide–Carbon Composite Microspheres

Yolk-shell MoO3 microspheres are prepared by a two-step process in which molybdenum oxide-carbon (MoO(x)-C) composite microspheres are first obtained by spray pyrolysis, followed by combustion at 400 °C in air. The yolk-shell microspheres exhibit excellent electrochemical properties and structural stability.