Shell Porosity Research Articles

Immersion cooling effect of dielectric liquid and self-rewetting fluid on smooth and porous surface

Dielectric liquid Novec 7300 and 5% 1-butanol aqueous solution are applied for immersion cooling of heater in order to investigate effect of nucleate boiling and self-rewetting on heat transfer. Experimental results are compared with water as common liquid for immersion cooling. In first part of study, bare heater is heated until temperature arrives at certain levels (from 100 °C to 500 °C), and then immersed in liquid for observing rapid cooling performance of these three solutions. In 5% 1-butanol binary solution, heater temperature decreases the fastest and stabilizes at the lowest level. Inversed thermal Marangoni flow induced by vertical temperature difference along heat surface is supposed to assist vapor bubbles separation and improve convective heat dissipation. From 200 °C, vapor film appears on the surface of heater immersed in Novec 7300 and water, whose thickness is dependent of surface temperature but independent of heat flux. In second part of study, immersion cooling performances of three testing liquids on heater with or without porous shells of different porosity are explored with increasing heating power. At different heat flux input, shell porosity, capillary effect, inverse thermal Marangoni effect and pool boiling stages influence heat transfer efficiency of each fluid-heater combination. A curve of optimal heat transfer coefficient is established, which is beneficial for selection of suitable fluid-heater combination.

Comparison on Laser Ignition and Combustion Characteristics of Nano- and Micron-Sized Aluminum

ABSTRACT This paper presents a comparative study on the laser-induced ignition and combustion characteristics between nanometer-sized aluminum (nano-Al) and micron-sized aluminum (micro-Al) powder stacks. Six different sizes of Al powders (56.0 nm, 74.4 nm, 93.4 nm for nano-Al and 2.9 μm, 6.1 μm, 10.8 μm for micro-Al) were selected to conduct ignition and combustion experiments, at the same operation conditions in the static air flow with atmospheric temperature and pressure and 55% relative humidity. The results demonstrated that ignition delay time of nano-Al is much lower than that of micro-Al. The size of nano-Al has a weak effect on ignition delay time. Whereas, the size of micro-Al has an exponential effect on ignition delay time. The combustion of nano-Al is more intense and the self-maintenance performance is better than micro-Al. Finally, a comparative model on the ignition and combustion difference between nano-Al and micro-Al was built, which comprehensively considers the influences of particle core size, oxide shell thickness and porosity. This study will be helpful to recognize the difference of ignition and combustion characteristics between nano-Al and micro-Al and promote the application in solid rockets.

Mesoporous Silica Encapsulated Metal-Organic Frameworks for Heterogeneous Catalysis

Encapsulation of metal-organic frameworks (MOFs) with a shell of mesoporous silica can boost overall performance of MOFs, offering versatility for synthetic architecture of integrated nanocatalysts with reactor-like features. Recently, Yu et al. report a green approach to make yolk-shell nanoreactors.

Effect of Saw Dust Content on Slurry Rheology and Mechanical Properties of the Investment Casting Ceramic Shell

The present investigation aims at determining the optimum quantity of saw dust that can be substituted to the secondary ceramic slurry for increasing the porosity of the destroyable investment casting ceramic shells without affecting its adequate strength. Further, both the slurry responses, namely viscosity, density, plate weight and pH, and shell responses, namely thickness, porosity, green strength and fired strength, determined from the saw dust based secondary ceramic slurry were optimized using Taguchi’s methodology. The input process parameters opted for the conduct of experiments were three different weight per cent of saw dust (3%, 5% and 7%), filler-to-binder ratio (1.5:1, 1.75:1 and 2:1) and slurry stirring time (18, 24 and 48 h). The optimum amount of saw dust that can be substituted in the secondary ceramic slurry for constructing the qualitative ceramic shells was found to be 5 wt%. The best combination of filler-to-binder ratio was established to be 2:1 for most of the responses except shell porosity. The range selected for slurry stirring time was found to be the insignificant process parameter influencing both slurry and shell responses.

Constraining the Role of Shell Porosity in the Regulation of Shell Calcification Intensity in the Modern Planktonic Foraminifer Orbulina Universa d'Orbigny

ABSTRACT Porosity in planktonic foraminifers (the proportion of the shell surface covered by pores) is a conspicuous quantitative trait, well preserved in fossil shells and implicated as a source of environmental information. Despite its potential, the functional importance of porosity remains poorly understood. It is likely that pores are important in gas exchange, and differences in shell porosity among species or within species may reflect differences in metabolic rates or ambient oxygen concentration. Theoretically, porosity also affects the weight of the shell; and differences in porosity may reflect an adaptation to the specific density of the seawater or differences in allocation of resources to calcification (shell calcification intensity). Finally, there is evidence that porosity may differ between closely related cryptic species. Here we analyzed the potential role of porosity as a regulator of calcification intensity in Orbulina universa by combining biometric measurements based on sediment surface samples from the western Atlantic with a modelling approach. Specimens of O. universa were analyzed concerning their shell size, shell thickness, and shell porosity under light and scanning electron microscopy, and weighed using a microbalance. The resulting empirically derived model shows an effect size of shell thickness that is 7.5 times larger than the effect of shell porosity on the overall shell calcification intensity. This indicates that porosity is unlikely to be used by this species to regulate calcification intensity. By implementing the model on literature data which analyzed calcification intensity in O. universa, we also show that porosity differences among cryptic species in O. universa are unlikely to explain the observed differences in calcification intensity within the species. These findings indicate that functional explanations for differences in porosity in planktonic foraminifers have to be sought outside of calcification or density regulation and, conversely, that the observed differences in calcification intensity are likely driven by shell thickness and their relationship with environmental forcing can be applied without correction for porosity.

Synthesis of novel core@shell of MgAl layered double hydroxide @ porous magnetic shell (MgAl-LDH@PMN) as carrier for ciprofloxacin drug

MgAl-layered double hydroxide (MgAl-LDH) derived from a metal-organic framework (MOF), was synthesized by hydrothermal method. A biocompatible MgAl-LDH core-porous magnetic nanoparticles (PMN) shell (MgAl-LDH@PMN) was synthesized using solvothermal method and modified with amino groups as a potential pH-controlled drug delivery carrier. MgAl-LDH with a sheet-like morphology was coated with porous Fe3O4 or porous magnetite via the functionalization of (3-aminopropyl) triethoxysilane using a post-synthesis route (MgAl-LDH@PMN-NH2). The core@shell was characterized using a range of techniques such as x-ray diffraction patterns (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic light scattering (DLS) and transmission electron microscopy (TEM). The MgAl-LDH@PMN-NH2 core@shell indicated a spherical morphology and good porosity. Ciprofloxacin (CIPRO) drug was incorporated in the pore channels and surface of the MgAl-LDH@PMN-NH2 and the drug release properties were examined at pH 4.0 and 7.4. The TG results demonstrated that drug loading contents on the modified carrier was 40%. The delayed release property exhibited by MgAl-LDH@PMN-NH2 was attributed to the strong interactions of the drug molecules with the surface amino-functionality and the charged LDH surface. The characterization and drug release was also investigated for the un-modified carrier (MgAl-LDH@PMN) with drug loading 15% under identical conditions. The porosity and functionalization of the PMN shell and the surface charge density of the layered structure of MgAl-LDH are the major reasons for the controlled release of the CIPRO drug. Moreover, the favorable delay in drug release from both core@shells at pH 4 was attributed to the high level of ionization and dissolution. Biocompatibility was evaluated by examination of the cell line MCF-7 response to the un-modified and modified carriers.

Cenosphere-sourced hydrothermal synthesis of pollucite-analcime solid solutions as a low-temperature method to immobilize 137Cs in a mineral-like form

Two narrow fractions of coal fly ash cenospheres with ∼90 wt % glass phase and different Si/Al ratio (2.1 and 2.9 in the glass phase), shell porosity and thickness, globule size, and content of a mullite phase were used as a glassy source of Si and Al in the hydrothermal synthesis of pollucite-analcime solid solutions at 150 °C and autogenous pressure, 1.0 M NaOH, Cs/Na ratios of 0–0.25. Hollow microsphere globules of about 60–70 and 140–170 μm in sizes are produced as Cs immobilized forms in this process. The microspheres have a composite mullite/ANA wall, where ANA is analcime-pollucite solid solutions. Composition and morphology of solid products as well as composition of ANA phases were characterized by PXRD, SEM-EDS and STA methods. The influence of the mullite content and shell thickness on the preservation of the product spherical shape has been established. The degree of Cs+ recovery from alkaline solutions due to preferential involvement of cesium in the synthesis of ANA phases was up to 96%.

Improved volatile cargo retention and mechanical properties of capsules via sediment-free in situ polymerization with cross-linked poly(vinyl alcohol) as an emulsifier

HypothesisIt is hypothesized that poly(vinyl alcohol) (PVOH) as an emulsifier destabilizes the insoluble molecular aggregates by increasing interparticle interactions and their tendency toward agglomeration into large particle aggregates during the encapsulation process of one-step in situ polymerization. Porosity of capsule shells is expected to decrease with reducing agglomeration tendency to allow dense packing of smaller insoluble aggregates. Cross-linking the polymer network further reduces shell permeability to improve the retention of volatile cargos. PVOH also modifies the short-range order of polymer network to bestow improved mechanical properties in addition to the shell thickening effect at appropriate synthesis conditions. ExperimentsPVOH was used to stabilize a heptane-in-water emulsion as a template for producing capsules via one-step in situ polymerization. Shell morphologies at different PVOH concentrations were compared. Physical freeze-thawing and chemical cross-linking were adopted separately to synthesize capsules with a volatile cargo, and its retention was characterized qualitatively by a solvatochromism-based fluorescent method and quantitative payload calculation. Mechanical properties of capsules were tested with micromanipulation. The effect of graphene oxide (GO) impregnation into capsules was studied with various co-emulsifiers. FindingsWhen PVOH alone was used as the emulsifier for capsule synthesis, the higher its concentration, the more porous the shell structure was. At very low concentrations, visible pores were eliminated. Freeze-thaw cycles reduced the permeability of capsule shells when visible pores were absent. Chemical cross-linking with poly(acrylic acid) (PAA) significantly improved the retention of volatile cargo heptane. PVOH substantially reduced polymer sediment during capsule synthesis, which eliminated the tedious centrifugation procedure that normally would have followed. Superior mechanical strength of capsules was achieved with PAA cross-linked PVOH at appropriate conditions. The impregnation of aqueously dispersed GO into capsules was also promoted by using PVOH but not hydrocolloid emulsifiers.

Aerosol-Assisted Synthesis of Tailor-Made Hollow Mesoporous Silica Microspheres for Controlled Release of Antibacterial and Anticancer Agents.

Hollow mesoporous silica microsphere (HMSM) particles are one of the most promising vehicles for efficient drug delivery owing to their large hollow interior cavity for drug loading and the permeable mesoporous shell for controlled drug release. Here, we report an easily controllable aerosol-based approach to produce HMSM particles by continuous spray-drying of colloidal silica nanoparticles and Eudragit/Triton X100 composite (EUT) nanospheres as templates, followed by template removal. Importantly, the internal structure of the hollow cavity and the external morphology and the porosity of the mesoporous shell can be tuned to a certain extent by adjusting the experimental conditions (i.e., silica to EUT mass ratio and particle size of silica nanoparticles) to optimize the drug loading capacity and the controlled-release properties. Then, the application of aerosol-synthesized HMSM particles in controlled drug delivery was investigated by loading amoxicillin as an antibiotic compound with high entrapment efficiency (up to 46%). Furthermore, to improve the biocompatibility of the amoxicillin-loaded HMSM particles, their surfaces were functionalized with poly(allylamine hydrochloride) and alginate as biocompatible polymers via the layer-by-layer assembly. The resulting particles were evaluated toward Escherichia coli (Gram-negative) bacteria and indicated the bacterial inhibition up to 90% in less than 2 h. Finally, we explored the versatility of HMSMs as drug carriers for pancreatic cancer treatment. Because the pH value of the extracellular medium in pancreatic tumors is lower than that of the healthy tissue, chitosan as a pH-sensitive gatekeeper was grafted to the HMSM surface and then loaded with a pro-apoptotic NCL antagonist agent (N6L) as an anticancer drug. The obtained particles exhibited pH-responsive drug releases and excellent anticancer activities with inhibition of cancer cell growth up to 60%.

Porosity-controllable magnetoplasmonic nanoparticles and their assembled arrays.

Control of the chemical and physical properties of nanoscale colloids and their nanoassemblies remains a challenging issue for enhancing the performance and functionalities of nanodevices. In this study, we report a post-synthesis etching method to tailor the porosity of the Fe3O4 shells coating on Ag NPs, establishing a facile but effective approach to regulate the chemical and optical properties of the colloids and their assembled structures. As the shell porosity increases, the NPs are transformed, producing enhanced catalytic activity and the surface-enhanced Raman spectroscopy (SERS) effect, which results from enhanced chemical diffusion into the Ag core. Magnetoplasmonic (MagPlas) one- (1D) and two- (2D) dimensional arrays fabricated using these porosity-controllable NPs exhibit intriguing plasmon properties that are strongly affected by the porosity of the particle shell. Furthermore, the bright coloration of the 2D arrays is tuned by changing the shell porosity or introducing an additional metallic layer. Such 1D and 2D porous MagPlas metastructures possessing Fe3O4 shells with tunable porosities are a fulcrum for developing recyclable catalysts and tunable optical filters with optimized activity, selectivity, and sensitivity, as well as color displays and sensing platforms.

Architecting hierarchical shell porosity of hollow prussian blue-derived iron oxide for enhanced Li storage.

Delicate architecture of active material enables improving the performacne of lithium ion batteries. Environmental-friendly Fe2 O3 anode has high theoretical specific capacity (1007 mAh g-1 ) in lithium ion batteries, but suffers from structural collapsing and poor electronic conductivity. Herein, we design an unique hierarchical iron oxide by regulating the initial precursor prussian blue and targeting hollow-shell structures with full consideration of temperature controls. Among them, Fe2 O3 with a sheet-crossing structure at 650°C, affords obvious advantages of improved electronic conductivity, short ionic diffusion length, prevented particle agglomeration, and buffer volume change. Thus, we achieve a superior discharge specific capacity of 611 mAh g-1 at 500 mA g-1 . Regulating hierarchical structure of prussian blue-assisted oxides enables effectively enchancing Li storge performance. LAY DESCRIPTION: Nanoparticle self-assembly, one of bottom-up methods is often used to prepare hollow hierarchical structures, whereas it suffers from low productivity and insufficient stability. Hence, we designed a unique hierarchical iron oxide by top-down method with regulating the initial precursor PB and targeting hollow-shell structures through full consideration of temperature controls. Delicate architecture of active material enables improving the performacne of lithium ion batteries. Environmental-friendly Fe2 O3 anode has high theoretical specific capacity (1007 mAh g-1 ) in lithium ion batteries, but suffers from structural collapsing and poor electronic conductivity. Hence, we prepared Prussian Blue (PB) materials with different sizes and calcined them at different temperatures. We found that no matter what the size of PB, the sheet-crossing morphology appeared at 650°C, and the interlaced morphology was the key to improve the performance of lithium batteries. If the size of PB precursor is too large or too small, it has adverse effects on lithium batteries. Only when the size and calcination temperature of PB precursor reach the optimum state, the best performance can be obtained. The calcination PB-K-3 at 650°C has a unique hierarchical structure of sheet-crossing. An obvious advantages include the prevention of particle agglomeration, short ionic diffusion lengths, and buffering volume changes. As a consequence, 611 mAh g-1 was obtained at the current density of 500 mA g-1 . In addition, we observed the structural changes of electrode plates at different reaction potentials, according to the reaction equation of Fe2 O3 +xLi+ +xe→Lix Fe2 O3 . With the proceeding charge process, the voltage increases from 0.01 to 3 V, the lithium ions gradually comes out of the iron oxide electrode surface. Whereas the discharging process reverses the aforementioned phenomena. Even if the changing volumes, however, the shape of cubic blocks for the PB-K-3 is preserved at different potentials. Taking these advantages into account, our designed MOFs-derived struture was an effective way to prepare hollow hierarchical structure with enhanced Li storage performacne. Such work is expected to facilitate the design of new electrode structure of lithium batteries.

Influence of iodine based exogenous antioxidants on the productive indicators of laying hens

The effect of the liposomal form of the antioxidant Polysol Omega-3 on laying hens and on the egg productivity was stated in article. Hens feeding by liposomal form of the antioxidant on protein content in the egg (p≤0.01), the height of dense protein (p≤0.001), the average diameter of dense protein (p≤0.01), the height of the yolk ( p≤0.01), the average diameter of the yolk (p≤0.001) and the quality of the protein in units of How (p≤0.001), by 5.02 g (13.4%), 1.00 mm (20.6%), 1.00 cm (6.99%), 2.2 mm (15.94%), 6.4 mm (13.68%) and 7.4 units. (11.35%) had an impact respectively. An increase in the porosity of the eggs shell in the laying hens of the experimental group was proved by a significant decrease in the Ca content by 0.49 g (p≤0.01). A positive trend in the content of iodine in the eggs of hens of the experimental group at the end of the third month of the experiment was noted at 35.8 μg (828.2 %).

Biodegradable biopolymer network structures to create delayed burst digestive release of encapsulated lipids

This study sought to investigate whether encapsulation of lipids in core-shell hydrogel structures of tailored shell porosity could create a delayed burst release of encapsulated lipids, and examined the underpinning mechanisms. We demonstrated that gastrointestinal digestion of core-shell structures resulted in a delay in the onset of lipid digestion, without affecting lipid digestion kinetics. Systematic increase in hydrogel protein content above 65 g/L lead to an exponential increase in digestive delay (250 min). Whilst an increase in xanthan content between 5 and 9 g/L lead to a modest decrease in digestive delay (40 min). Rheological investigations revealed a linear relationship between hydrogel storage modulus G′ and digestive breakdown delay (T1/2). Given that G’ is directly related to hydrogel mesh size, this result suggests that the main factor controlling the timing of digestive release is the average mesh size of the outer protein hydrogel. A kinetic model was created to describe the delayed burst release behaviour of encapsulated lipids and successfully predicted the influence of shell thickness, shell protein density on the timing of gastro-intestinal release (in vitro). By combining microstructural/rheological experiments with in vitro digestive studies we have understood the main factors controlling the digestive breakdown of hierarchical biopolymer hydrogels. We could successfully miniaturise these core-shell structures so they would easily empty from the stomach whilst maintaining programmable delayed burst release. We have created a novel family of core-shell hydrogel oral dosage forms for the delivery of poorly soluble drugs and the programmed delivery of lipids within the gut.

Progressive ossification of the bone marrow vasculature with advancing age corresponds with reduced red blood cell count and percentage of circulating lymphocytes in male Fischer-344 rats.

Assess the link between bone marrow blood vessel ossification, Tb. and cortical bone, and hematological parameters across the lifespan in rats. Right femora and whole blood samples were taken from male Fischer-344 rats at 1, 6, 12, 18 and 24months. Femora were scanned by micro-computed tomography (MicroCT) to determine bone marrow blood vessel ossification (ie, ossified vessel volume [OsVV], ossified vessel thickness (OsV.Th), ossified vessel density (OsV density), and structural model index [SMI]). Bone microarchitecture (ie, bone volume [BV/TV], trabecular thickness, trabecular number, and trabecular separation), density and SMI, and cortical bone parameters (ie, cortical shell thickness, porosity, and density) were also determined by MicroCT. Complete blood counts with differentials were conducted. Ossified vessel volume increased throughout the lifespan, coinciding with reduced trabecular BV/TV and cortical shell thickness at 24months. Many of the hematological parameters were unchanged (ie, white blood cells, lymphocyte number) or increased (monocyte number, percent monocyte, granulocyte number, percent granulocyte, hemoglobin, hematocrit, mean corpuscular hemoglobin concentration, red blood cell distribution width, platelet, mean platelet volume) with advancing age; however, red blood cells (RBC) and percent lymphocytes (LY%) were reduced at 24months. In addition, OsV density was similar to trabecular bone density. Declines in trabecular BV/TV, cortical shell thickness, RBC, and LY% with advanced age coincided with augmented ossification of bone marrow blood vessels.

Cross-Linked Polystyrene Shells Grown on Iron Oxide Nanoparticles via Surface-Grafted AGET-ATRP in Microemulsion.

Most applications of nanoparticles require robust stabilization, for example, by surface-bound ligands or the encapsulation within polymer shells. Furthermore, for biomedical applications, the particles must be dispersible in a complex biological environment. Thus, high-quality nanoparticles synthesized in organic solvents must be transferred into aqueous media. Here, we present a novel scalable method enabling the robust hydrophilic encapsulation of non-agglomerated nanoparticles by growing polystyrene shells via AGET-ATRP in microemulsion. To demonstrate this approach, we encapsulate iron oxide nanoparticles (diameter: 13.7 ± 0.6 nm). Because the ATRP initiator is grafted onto the nanoparticles' surface, the shells are covalently attached to the iron oxide cores. By varying the amount of monomers, the shell thickness can be adjusted precisely, as indicated by the increasing hydrodynamic size from ∼22 to 26 nm (DLS, number mean) with an increasing amount of added monomers. Moreover, the degree of cross-linking can be controlled by the amount of added divinylbenzene (DVB). To evaluate the robustness of the polymer shells against ion infusion, we introduce a novel colorimetric method, which is based on the formation of the red iron thiocyanate complex. After addition of HCl, the increase in absorbance at 468 nm indicates leaching of iron ions from the polymer-encapsulated core particles. These measurements confirm that with increasing shell thickness, significantly improved shielding is achieved. Furthermore, high concentrations of added DVB [33-50% (v/v) in a monomer mixture] improve the shielding effect. However, when smaller amounts of DVB were added [10-25% (v/v)], the shielding effect was diminished, even in comparison to non-cross-linked polymer shells. This finding suggests a higher porosity of shells with a low degree of cross-linking.

Degradation of Internal Organic Matter is the Main Control on Pteropod Shell Dissolution After Death

AbstractThe potential for preservation of thecosome pteropods is thought to be largely governed by the chemical stability of their delicate aragonitic shells in seawater. However, sediment trap studies have found that significant carbonate dissolution can occur above the carbonate saturation horizon. Here we present the results from experiments conducted on two cruises to the Scotia Sea to directly test whether the breakdown of the organic pteropod body influences shell dissolution. We find that on the timescales of 3 to 13 days, the oxidation of organic matter within the shells of dead pteropods is a stronger driver of shell dissolution than the aragonite saturation state of seawater. Three to four days after death, shells became milky white and nano scanning electron microscope images reveal smoothing of internal surface features and increased shell porosity, both indicative of aragonite dissolution. These findings have implications for the interpretation of the condition of pteropod shells from sediment traps and the fossil record, as well as for understanding the processes controlling particulate carbonate export from the surface ocean.

Hollow Multishelled Structures for Promising Applications: Understanding the Structure-Performance Correlation.

The unique structural features of hollow multishelled structures (HoMSs) endow them with abundant beneficial physicochemical properties including high surface-to-volume ratio, low density, short mass transport length, and high loading capacity. As a result, HoMSs have been considered as promising candidates for various application areas including energy storage, electromagnetic wave (EW) absorption, catalysis, sensors, drug delivery, etc. However, for a long time, the general and controllable synthesis of HoMSs has remained a great challenge using conventional soft-templating or hierarchical self-assembly methods, which severely limits the development of HoMSs. Fortunately, the sequential templating approach (STA), which was first reported by our group and further developed by others, has been proven to be a versatile method for HoMS fabrication. By using the STA and through accurate physical and chemical manipulation of the synthesis conditions, the diversity of the HoMS family has been enriched in both compositional and geometrical aspects. Benefiting from the flourishing of synthetic methodology, various HoMSs have been fabricated and showed application prospect in diverse areas. However, the structure-performance correlation remained obscure, which hinders the design of optimal HoMSs to achieve the best application performance. This Account aims to explore the correlation between HoMS structural characteristics and their application performance. We first briefly summarize the achievements in the compositional and geometrical manipulation of HoMSs by physically and chemically tuning the synthesis process. Then, we systematically discuss the effect of structural engineering on optimizing performance in various application areas, especially for energy storage, EW absorption, catalysis, sensors, and drug delivery. Specifically, HoMSs with multiple thin shells can provide numerous active sites for energy storage, leading to a higher volumetric energy density than their single-shelled counterparts. The high shell porosity permits electrolyte access to the interior of HoMSs, along with shortened mass transport path through the thin shells, resulting in a high power density. The adequate inner cavity effectively buffers the ion-insertion strain, leading to prolonged cycling stability. For EW absorption, HoMSs with high surface-to-volume ratio can provide many sites for EW-sensitive material loading. The multiple separated shells with small intershell space enable multiple EW reflection and scattering, thus improving EW absorption efficiency. For catalysis and sensors, the increased reaction sites along with the facilitated transport of reactants and products can enhance the activity and sensitivity. The selectivity can be improved by optimizing the pore structure and hydrophobic or hydrophilic properties of the shells. Also the stability is improved with inner shells being protected by exterior ones. For drug delivery, the increased exposed sites and the inner cavity improve the drug loading capacity. The adjustable pore structure along with accurately designed shell composition leads to well-targeted drug release responding to different stimuli at different targeting sites. The multiple separated shells endow HoMSs with sustained drug release step-by-step from inside to outside. These in-depth understandings on the structure-performance correlation can guide the design of ideal HoMSs to satisfy the specific requirements for different application areas, thus further improving the application performance and expanding the HoMSs family.

Synthesis of structured hollow microspheres with sandwich-like hybrid shell of RGO/Pd/m-SiO2 for highly efficient catalysis

The development of easy-to-operate strategies for fabricating stable and efficient nanostructured catalysts based on noble metal nanoparticles is of great significance. Here we report a facile method to prepare the hollow microsphere with sandwich-like hybrid shell composed of an interlayer of palladium nanoparticles (Pd NPs) in between the inner shell of reduced graphene oxide (RGO) and outer shell of mesoporous silica (m-SiO2), denoted as RGO/Pd/m-SiO2 hollow microsphere. Our approach involves the use of polystyrene microsphere as template to firstly deposit the RGO and then Pd NPs and finally to coat the hybrid SiO2 containing porogens, followed by the calcination to simultaneously obtain interior cavity and mesoporous outer shell. Our method is facile because it avoids pretreatment of template surface and functionalization/modification of any of shell components. More importantly, the as-prepared RGO/Pd/m-SiO2 hollow microspheres exhibit several distinguished advantages for catalytic applications, including the sandwich-like hybrid shell effectively preventing Pd NPs from aggregation and leaching, and the stabilizer-free surface of Pd NPs as well as the synergistic interaction of the Pd NPs and RGO. Consequently, these hollow microspheres show superior catalytic activity and stability in the reduction of p-nitrophenol by sodium borohydride. Moreover, it is also found that, the thickness and porosity of m-SiO2 outer shell can influence the catalytic activity of the RGO/Pd/m-SiO2 hollow microspheres. Overall, our results have provided important implications for rational design of hybrid shell of hollow microspheres with appropriate composition and configuration to boost the catalytic performance of noble metal NPs.

Gold@silica catalyst: Porosity of silica shells switches catalytic reactions

Gold nanoparticles in the cores coated by non-porous silica shells (Au@nSiO2) and by porous silica shells (Au@pSiO2) were synthesized and used to catalyze the reduction and oxidation reactions to understand the influence of the structure of silica shells on their catalytic activity. Au@pSiO2 nanoparticles well catalyze the reduction and oxidation reactions while Au@pSiO2 nanoparticles are inactive for those reactions. The characterizations combining with catalytic reactions reveal that the porosity of silica shells is responsible for catalytic activity.

Fe2O3 nanoparticles encapsulated with N-doped porous graphitic shells approached by oxidizing Fe3C@C precursor for high-performance sodium-ion batteries

Fe2O3 nanoparticles encapsulated with N-doped porous graphitic shells (Fe2O3@PWSs) were successfully prepared through a facile approach as anodes for SIBs. In such approach, owing to the short synthetic time, ∼7 nm precursor (Fe3C@N-doped graphitic shells core-shell nanoparticles) were prepared by floating catalytic pyrolysis, leading to in situ doped N atoms were well distributed. By partially removing homogeneous N-doped structure, lots of nanopores were created on the shell of the precursor, which made Fe3C cores efficiently oxidized without violently destroying graphitic shells. The excellent structural characteristics of Fe2O3@PWSs could effectively prevent pulverization/agglomeration of Fe2O3 and accommodate its volume changes during long-term cycling processes, exhibiting distinct cycling stability (at current density of 5000 mA g−1, 3000 cycles: a fading rate of only 0.007% per cycle for SIBs). Additionally, small size of Fe2O3 nanoparticles (average size of 5 nm) and higher porosity of carbon shells could offer more diffusion pathway which facilitate the transportation of Na+/Li+ and electrolyte leading to significantly improved electrochemical activity toward Na+/Li+ storage (the specific capacity: 637 and 525 mAh g−1 at current density of 100 and 3000 mA g−1, respectively, for SIBs; the specific capacity: 1506 and 1310 mAh g−1 at current density of 200 and 3000 mA g−1, respectively, for LIBs).