Tunable Shell Thickness Research Articles

Plasmonic Electrons‐Driven Solar‐to‐Hydrocarbon Conversion over Au NR@ZnO Core‐Shell Nanostructures

AbstractThis work demonstrates the long‐range redox reactivity of gold plasmon‐generated hot electrons for solar‐driven CO2 conversion. A series of Au NR@ZnO core‐shell photocatalysts with a tunable shell thickness are rationally designed to achieve the solar‐to‐CH4 conversion, where the hot plasmonic electrons‐induced photoreduction takes place on the polar oxide moiety. The shell thickness‐independent activity implies that the core, gold nanorods, plays a dominant role in the CH4 generation. The ZnO metal oxide semiconductor shell is beneficial to prolong the lifetime of hot electrons, thereby enhancing the photocatalytic efficiency. However, the thickness of ZnO shell is not relevant to the production rate. Both of these two parts are co‐excited by solar light and synergetic enhance the photocatalytic activity.

Synthesis of Au@Cu2O Core-Shell Nanoparticles with Tunable Shell Thickness and Their Degradation Mechanism in Aqueous Solutions.

Metal@semiconductor core-shell nanoparticles (NPs) are widely used in photocatalysts, sensors, and optical applications owing to their unique metal-semiconductor interface and the integration of the properties from both core and shell materials. Although many efforts have been made toward the precise synthesis of Au@Cu2O core-shell structures, the chemical stability of Au@Cu2O aqueous suspensions, which is of great significance in many related applications, is not mentioned in any published research. Herein we report the synthesis of Au@Cu2O core-shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV-vis absorption properties are found to be tunable with Cu2O thickness in the range of 2-40 nm. Furthermore, the chemical stability of Au@Cu2O core-shell nanoparticle suspensions in water/ethanol mixed solvents is investigated. It is found that water/ethanol mixed solvents with a larger amount of water are more likely to deteriorate the stability of Au@Cu2O NPs by oxidizing Cu2O to CuO. The results from this work may provide useful information for the preparation of metal@Cu2O water-based suspensions that are expected to be used for SERS, photocatalyst, or photothermal applications.

Polymer Capsules with Tunable Shell Thickness Synthesized via Janus-to-core shell Transition of Biphasic Droplets Produced in a Microfluidic Flow-Focusing Device

Droplet microfluidics has enabled the synthesis of polymeric particles with controlled sizes, shell thickness, and morphologies. Here, we report the Janus to core-shell structural evolution of biphasic droplets formed in a microfluidic flow-focusing device (MFFD) for the synthesis of polymer microcapsules with oil core/thickness-tunable shell via off-chip photo- and thermally induced polymerization. First, nanoliter-sized biphasic Janus droplets comprising an acrylate monomer and silicone oil were generated in a co-flowing aqueous polyvinyl alcohol (PVA) solution in an MFFD on a glass chip. Immediately following their break-off, the produced Janus droplets started to change their geometry from Janus to core-shell structure comprising a single silicone-oil core and an acrylate-monomer shell by the minimization of interfacial energy. Thus, we could produce monodisperse core-shell drops with average diameters of 105–325 μm, coefficient of variation (CV) values of 1.0–4.5%, and shell thickness of 1–67 μm. Subsequently, these drops were synthesized to fabricate polymeric microcapsules with tunable shell thickness via photo- and thermally induced polymerization. By increasing the concentration of the photo- and thermal initiator, we successfully produced thinner and ultra-thin shell (800 nm thickness) microcapsules. The surface structure of resulting particles was smooth in photopolymerization and porous in thermal polymerization.

Sulfonic acid modified hollow polymer nanospheres with tunable wall-thickness for improving biodiesel synthesis efficiency

A green and efficient method has been developed to fabricate sulfonic acid-functionalized hollow acidic spherical catalysts with tunable shell thicknesses.

One-pot synthesis of highly active and hydrothermally stable Pd@mHSiO2 yolk-shell-structured nanoparticles for high-temperature reactions in hydrothermal environments.

The facile synthesis of yolk-shell-structured nanoparticles (YSNPs) with mobile active metal cores and mesoporous inorganic-organic hybrid silica shells (mHSiO2) is important for their applications. In this work, Pd@mHSiO2 YSNPs have been synthesized in aqueous solution at 95 °C by a one-pot method without the need for extensive purification and separation steps. The method is simple and facile, and ingeniously combines the controlled synthesis of Pd nanocubes, coating of mesoporous silica, and transition from core-shell-structured nanoparticles (CSNPs) to YSNPs. 29Si NMR spectroscopy, FTIR spectroscopy, and detailed control experiments have demonstrated that the incorporation of 1,2-bis(trimethoxysilyl)ethane (BTME) modifies the degree of condensation between the outer hybrid silica layer and the inner pure silica section, and that high temperature water is really responsible for dissolving the inner pure silica layer leading to a transition from the CSNPs to the YSNPs. The obtained Pd@mHSiO2 YSNPs have a controllable diameter, tunable shell thickness, a high specific surface area, and uniform mesoporosity. Thermal stability tests have indicated that the Pd@mHSiO2 YSNPs are remarkably stable at high temperatures up to 650 °C. Importantly, the Pd@mHSiO2 YSNPs exhibit a much higher catalytic activity and hydrothermal stability than Pd@mSiO2 CSNPs or Pd/mHSiO2 NSs in the conversion of levulinic acid (LA) into γ-valerolactone (GVL), because the hollow voids provide low mass-transfer resistance and improve the accessibility of the catalytic sites, and the incorporation of organic groups enhances the hydrothermal stability of the outer shell.

Nitrogen-doped hollow carbon spheres with tunable shell thickness for high-performance supercapacitors.

Nitrogen-doped hollow carbon spheres (NHCSs) are well prepared by using Cu2O microspheres as a hard template and 3-aminophenol formaldehyde resin polymer as carbon and nitrogen precursors. The thickness of the carbon shell can be easily controlled in the range of 15–84 nm by simply adjusting the weight ratios of the precursors to Cu2O microspheres, and the Cu2O templates can also be further reused. Physicochemical characterization demonstrates that the obtained NHCSs possess a well-developed hollow spherical structure, thin carbon shell and high nitrogen doping content. Due to these characteristics, when further utilized as electrodes for supercapacitors, the NHCSs with the carbon shell thickness of 15 nm show a high capacitance of 263.6 F g−1 at 0.5 A g−1, an outstanding rate performance of 122 F g−1 at 20 A g−1 and an excellent long-term cycling stability with only 9.8% loss after 1000 cycles at 5 A g−1 in 6 M KOH aqueous electrolyte. This finding may push forward the development of carbon materials, exhibiting huge potential for electrochemical energy storage applications.

Highly Active and Selective Electrocatalytic CO2 Conversion Enabled by Core/Shell Ag/(Amorphous-Sn(IV)) Nanostructures with Tunable Shell Thickness.

Electrochemical CO2 reduction (ECR) to highly value-added products is regarded as a promising way to capture and utilize atmospheric CO2. While the large overpotential and low selectivity largely hinder its practical application, it is highly desirable to design promising catalysts for efficient ECR catalysis. Herein, we have designed a series of core/shell Ag/(Amorphous-Sn(IV)) (Ag/(A-Sn(IV))) nanoparticles (NPs) as highly active and selective catalysts for ECR. Precise amorphous shell tuning of Ag/(A-Sn(IV)) NPs reveals that Ag/(A-Sn(IV)) NPs exhibit volcano-like activity and selectivity toward ECR as a function of the thickness of amorphous shells. The ultrathin amorphous shell not only effectively suppressed the hydrogen evolution reaction (HER) to increase the ECR activity but also converted the ECR product from CO to HCOOH as the applied voltage increased. As a consequence, the optimized core/shell Ag75/(A-Sn(IV))25 NPs show outstanding performance with a CO faradaic efficiency (FE) of 88.0% and a partial current density of 7.9 mA/cm2 at -0.7 V and a HCOOH FE of 75.1% and a partial current density of 13.4 mA/cm2 at -0.9 V. It also exhibited negligible change in current density and FE of the main products after a 12 h reaction. Theoretical calculation further confirmed that the regulation of the shell thickness effectively inhibited the HER and enhanced ECR with a 0.6 nm shell thickness of Ag/(A-Sn(IV)) NPs exhibiting the best activity.

An in Situ Template for the Synthesis of Tunable Hollow Carbon Particles for High-Performance Lithium-Sulfur Batteries.

Nanostructured materials with hollow interior voids are gaining great attention due to their fantastic geometries and unique physicochemical properties competent for many applications. However, the development of a fast approach to prepare the hollow structured particles remains challenging. Herein, a new and efficient in situ hard-template method was developed to synthesize hollow carbon nano- and microparticles using the as-prepared SiO2 particles as a hard template directly, without any separation, drying, or redispersion. In this way, the hollow carbon particles with tunable diameters and shell thickness can be synthesized readily, which is simpler and more efficient than the traditional ones. In addition, the universality of this strategy allows us to study the different behaviors of hollow carbon particles in lithium–sulfur batteries when the architectures of hollow particles (i.e., diameter, shell thickness, etc.) were changed. We believe that this in situ method is applicable for synthesizing other core–shell or hollow structured materials (e.g., metal oxide), and also, the high performance of hollow carbon particles in lithium–sulfur batteries and beyond can be further explored.

CTAB-assisted fabrication of well-shaped PDA-based colloidosomes

Colloidosomes have gained intensive attention in the past years due to their substantial applications in wide scopes involving encapsulation, catalysis, and drug delivery, etc. In this study, we depicted the templated fabrication of well-shaped colloidosomes with tunable shell thickness by Pickering emulsion at a mild condition. To this end, toluene-in-water Pickering emulsion stabilized by cetyltrimethylammonium bromide (CTAB)–modified polydopamine (PDA) nanoparticles (PDA@CTAB) was prepared. After the covalent cross-linking of PDA nanoparticles assembled on the surface of an oil droplet through chemical reactions occurring in toluene phase, exclusive intra-colloidosomes were afforded. The shell thickness of colloidsomes could be roughly tuned by the adjustment of the amount of the reactive monomers in the oil phase. Our investigations revealed that CTAB was critical for the successful fabrication of well-shaped colloidosomes. Otherwise, only irregular structures were obtained if pristine PDA–stabilized Pickering emulsion was applied. The current strategy could enable hydrophobic cargo, such as 10-hydroxycamptothecin to be encapsulated while colloidosomes were created. The release behavior of the encapsulated cargoes was also investigated.

Preparation of Au@TiO2 yolk-shell nanocomposites for solar-light degradation of methylene blue

A novel synthetic approach has been developed to prepare Au@TiO2 yolk-shell (Au@TiO2-YS) structures using silica as a template with controllable size, shape, crystal phase. This approach shows a few unique features, including tunable TiO2 shell thickness, high repeatability, low cost, and easy operation. The morphology, composition and the corresponding properties were characterized by several advanced techniques, such as TEM, XRD, and UV-vis spectroscopy. The Au@TiO2-YS structures consist of Au NPs as cores and TiO2 hollow spheres as shells. The Au NPs can be controlled in various diameters (e.g., 100 nm, 50nm, and 30 nm), wh ile the TiO2 shell can form cavities with diameters of 255 nm and the thickness of ∼45 nm. The absorption peak of the product can be changed by adjusting the size of Au cores. In addition, the photocatalytic activities of the synthesized composites were systematically measured by degrading methylene blue (MB) under simulated solar light irradiation. The photocatalytic performance test reveals that the reaction kinetic constants of the Au@TiO2-YS structures with different Au core sizes are superior to that of the TiO2 hollow spheres (0.00521 min−1). A mong the yolk-shell structures, the YS-50 show highest kinetic constant (0.00704 min−1), wh ich is 1.35 times higher than that of pure TiO2 hollow spheres. These findings provide an effective way for design and construction of TiO2-based photocatalysts for solar-light degradation of organic pollutant.

Mesoporous carbon hollow microspheres with tunable pore size and shell thickness as efficient electromagnetic wave absorbers

Carbon hollow microspheres with a uniform mesoporous shell (PCHMs) were designed and fabricated using a template-assistant method followed by a pyrolysis-etching process. Through tuning the pyrolysis temperature, PCHMs with various pore size and shell thickness can be obtained. In particular, the PCHMs carbonized at 650 °C (PCHMs-650) are composed of a mesoporous shell (thickness: 52 nm) and an interior void of 153 nm, endowing the materials with large surface area of 925.9 m2/g. The unique core-shell structure generated by carbon shell and void core is critical for the attenuation capability of EM energy. The composites containing 20 wt% PCHMs-650 exhibit favorable microwave absorbing performance with the minimum reflection loss (RLmin) of −39.4 dB at 3.6 mm. The broadest effective absorption bandwidth (EAB) can extend to 5.28 GHz (9.68–14.96 GHz) at only 2.6 mm. It is believed that PCHMs can be used as a promising absorber with lightweight, impressive bandwidth and strong absorption efficiency.

Ultrafast microfluidic synthesis of hierarchical triangular silver core-silica shell nanoplatelet toward enhanced cellular internalization

Microfluidic reactors represent a new frontier in the rational design and controllable synthesis of functional micro-/nanomaterials. Herein, we develop a continuous and ultrafast flow synthesis method to obtain triangular silver (tAg) nanoplatelet using a short range two-loop spiral-shaped laminar flow microfluidic reactor, with one inlet flow containing AgNO3, trisodium citrate, and H2O2 and the other NaBH4. The effect of the reactant concentration and flow rate on the structural changes of tAg is examined. Through the same miniaturized microreactor, hierarchical core-shell Ag@SiO2 can be produced with tunable silica shell thickness using one inlet flow containing the as-synthesized Ag nanoparticles together with tetraethyl orthosilicate and the other ammonia. The enhanced cellular internalization efficiency of triangular nanoplatelets by PANC-1 and MCF-7 cells is further confirmed in comparison with the spherical ones. These results not only bring new insights for engineering nanomaterials from microreactors but also facilitate the rational design of functional nanostructures for enhancing their biological performance.

Controlled synthesis of core-shell composites with uniform shells of a covalent organic framework

We report on the controlled synthesis of core-shell structured composites consisting of TAPB-DMTP-COF shells and SiO2, ZnS, or UiO-66 MOF cores. The core seeds were pre-modified with polyvinylpyrrolidone (PVP) to facilitate their dispersion in the reaction solution and with branched polyethyleneimine (BPEI) to trigger an effective heterogeneous nucleation of the imine COF. Under optimized synthetic conditions, uniform COF layer was grown on the modified seeds to yield well-defined core-shell structures with tunable shell thickness.

Tuning the microstructure of BaTiO3@SiO2 core-shell nanoparticles for high energy storage composite ceramics

Core-shell nanoparticles used as blocks to construct composite ceramics can exhibit high energy storage density, but the effects of original tunable shell thickness on the microstructures and energy storage property of finally sintered bulk ceramics has not been clarified, thus how to achieve the full potential of this technology to improve the energy storage density of ferroelectric-based ceramics remains to be solved. In this study, as precursors to fabricate bulk ceramics, BaTiO3@SiO2 core-shell nanoparticles were successfully synthesized by a wet-chemical method and they were used as models to investigate the effect of the core-shell nanostructured precursors on the energy storage property of the bulk composite ceramics. The original BaTiO3 nanoparticles coated with various homogenous SiO2 shells were acquired by controlling the concentration of tetraethyl orthosilicate (TEOS). The surface microstructure of the bulk composite ceramics observed by scanning electron microscope (SEM) revealed that the SiO2 outer shell of BaTiO3@SiO2 nanoparticles plays an important role in constructing the microstructure of the ceramics. The remodeled microstructure has a great impact on leakage current density and dielectric property, and it makes a leading contribution to the energy storage performance of ceramics. As a result, the optimum SiO2 loading range was confirmed and the maximum energy storage density obtained from BaTiO3@20 wt%SiO2 was ∼4.799 J/cm3 at 370 kV/cm, demonstrating that nanoscale core-shell architecture is an effective strategy to improve the energy storage performance of ferroelectric-based composite ceramics.

Zein-based core–shell microcapsules for the potential delivery of algae oil and lipophilic compounds

Due to the benefits involving brain development and cardiovascular health, algae oil which is rich in omega-3 fatty acids has become a popular dietary supplement in recent years. However, the incompatibility with water and poor oxidative stability limits its addition in foods and beverages. In this work, the formation and characterization of zein-based core-shell microcapsules with tunable shell thicknesses for the potential delivery of algae oil were reported. They were prepared based on the in situ precipitation of zein from the continuous phase onto the surface of oil droplets by self-assembly at a refrigerated temperature without any need for surfactants and cross-linkers. The shell thickness could be controlled by the ratio of algae oil to zein (O/Z), which was indicated by their characterization including static light scattering, confocal laser scanning microscopy and scanning electron microscopy. Evidence from the peroxide value and the hexanal level of the emulsions in a thermally accelerated storage test suggested that the oxidation degree of the loading algae oil was negatively correlated with the shell thickness of the capsules. Furthermore, the release profiles of vanillin, which was used as a model volatile lipophilic compound and masking agent for the off-flavor from algae oil, could be tuned by manipulating their shell thickness. This suggested that the all-natural edible core-shell microcapsule might further be used as a model system for the delivery of lipophilic compounds. They may further promote the sustainable use of underutilized water-insoluble proteins as functional biomaterials in functional foods and pharmaceutical applications.

Synthesis of Au@TiO2 core-shell nanoparticles with tunable structures for plasmon-enhanced photocatalysis.

Plasmonic metal–semiconductor nanocomposites, especially those with core–shell nanostructures, have received extensive attention as they can efficiently expand light absorption and accelerate electron–hole separation thus improving the photocatalytic efficiency. However, controlled synthesis and structure manipulation of plasmonic metal–semiconductor nanocomposites still remain a significant challenge. Herein, a simple and universal method has been developed for the preparation of plasmonic Au@TiO2 core–shell nanoparticles. Using such a method, uniform TiO2 shells are successfully coated on Au nanoparticles with various morphologies including nanorods, nanocubes, and nanospheres, and the thickness and crystallinity of the TiO2 shell can be simply tuned by adjusting the pH value and thermal treatment, respectively. Furthermore, the influence of the morphology of the Au core and the thickness and crystallinity of the TiO2 shell on the photocatalytic performance of Au@TiO2 towards the photodegradation of methylene blue is systematically explored. It is found that Au@TiO2 NPs with nanorod morphology and crystalline TiO2 shells display the best performance, which is 5 times higher than that of bare Au nanoparticles. This work provides a facile strategy for the fabrication of plasmonic core–shell nanostructures that show excellent performance in plasmon-enhanced photocatalysis.

From Hollow to Solid Carbon Spheres: Time-Dependent Facile Synthesis.

Here, we report a facile route for obtaining carbon spheres with fully tunable shell thickness. Using a hard template in chemical vapor deposition (CVD), hollow carbon spheres, solid carbon spheres, and intermediate structures can be obtained with optimized process time. The resulting carbon spheres with particle diameters of ~400 nm, as well as a controllable shell thickness from 0 to 70 nm, had high Brunauer–Emmett–Teller (BET) specific surface area (up to 344.8 m2·g−1) and pore volume (up to 0.248 cm3·g−1). The sphere formation mechanism is also proposed. This simple and reproducible technique can deliver carbon materials for various applications, e.g., energy storage and conversion, adsorption, catalytic, biomedical, and environmental applications.

Facile construction of Mn2O3@CeO2 core@shell cubes with enhanced catalytic activity toward CO oxidation

Heterogeneous core@shell nanostructures bring unique synergetic catalytic properties in comparison with their single-component materials, because the two-phase interface could render hybrid junctions with rich redox reactions. Herein, a series of Mn2O3@CeO2 core@shell cubes with tunable CeO2 shell thickness have been controllably synthesized by a facile multi-step process, which involved the annealing treatment of MnCO3 precursor to produce Mn2O3 microcubes, followed by a refuxing process to deposit a uniform CeO2 layer on the Mn2O3 surface. The CeO2 shell was assembled by nanoparticles with sizes in the range of 2–10 nm, and the thickness could be facilely manipulated by changing the Mn/Ce molar ratios of reactants used in the synthetic process. The Mn2O3@CeO2 core@shell cubes exhibited enhanced catalytic activity toward CO oxidation compared with both pure CeO2 and Mn2O3, which was attributed to the synergistic interaction between CeO2 and Mn2O3. Impressively, Mn2O3@CeO2-0.1 sample with a proper CeO2 thickness exhibited the highest catalytic performance, attaining 100% CO conversion at 220 °C.

Carbon Nanotube@Microporous Carbon Core–Shell Nanowires for NO Oxidation: The Multiple Roles of Micropore Structure

Carbon nanotube@microporous carbon core–shell nanowires with tunable shell thicknesses and controllable pore size distributions were prepared by a one-pot resorcinol-formaldehyde resin coating of t...

Fabrication and study of superficially porous core-shell SiO2@SiO2 microspheres

ABSTRCTCore-shell structure particles are attracting considerable attention because of their applications in drug delivery and catalysis carrier. In this study, SiO2@SiO2 core-shell structure with tunable shell thickness was successfully prepared by using tetraethoxysilane (TEOS) as the silica source. Monodisperse nonporous silica spheres with a diameter of 1.7 μm were synthesized by a modified Stöber method. An template CTAB was first grafted onto the SiO2 microsphere surface. Then TEOS was hydrolyzed with the addition of ammonia. Finally, superficially porous core-shell SiO2@SiO2 microspheres were obtained through calcination to remove the template.