Porous Capsules Research Articles

Multi-scale microporous silica microcapsules from gas-in water-in oil emulsions

Controlling the surface area, pore size and pore volume of microcapsules is crucial for modulating their activity in applications including catalytic reactions, delivery strategies or even cell culture assays, yet remains challenging to achieve using conventional bulk techniques. Here we describe a microfluidics-based approach for the formation of monodisperse silica-coated micron-scale porous capsules of controllable sizes. Our method involves the generation of gas-in water-in oil emulsions, and the subsequent rapid precipitation of silica which forms around the encapsulated gas bubbles resulting in hollow silica capsules with tunable pore sizes. We demonstrate that by varying the gas phase pressure, we can control both the diameter of the bubbles formed and the number of internal bubbles enclosed within the silica microcapsule. Moreover, we further demonstrate, using optical and electron microscopy, that these silica capsules remain stable under particle drying. Such a systematic manner of producing silica-coated microbubbles and porous microparticles thus represents an attractive class of biocompatible material for biomedical and pharmaceutical related applications.

Encapsulating soluble active species into hollow crystalline porous capsules beyond integration of homogeneous and heterogeneous catalysis.

Homogeneous molecular catalysts and heterogeneous catalysts possess complementary strengths, and are of great importance in laboratory/commercial procedures. While various porous hosts, such as polymers, carbons, silica, metal oxides and zeolites, have been used in an attempt to heterogenize homogeneous catalysts, realizing the integration of both functions at the expense of discounting their respective advantages, it remains a significant challenge to truly combine their intrinsic strengths in a single catalyst without compromise. Here, we describe a general template-assisted approach to incorporating soluble molecular catalysts into the hollow porous capsule, which prevents their leaching due to the absence of large intergranular space. In the resultant yolk (soluble)–shell (crystalline) capsules, the soluble yolks can perform their intrinsic activity in a mimetic homogeneous environment, and the crystalline porous shells endow the former with selective permeability, substrate enrichment, size-selective and heterogeneous cascade catalysis, beyond the integration of the respective advantages of homogeneous and heterogeneous catalysts.

Interfacial Charge Field in Hierarchical Yolk–Shell Nanocapsule Enables Efficient Immobilization and Catalysis of Polysulfides Conversion

AbstractInhibiting the shuttle effect of lithium polysulfides and accelerating their conversion kinetics are crucial for the development of high‐performance lithium–sulfur (Li–S) batteries. Herein, a modified template method is proposed to synthesize the robust yolk–shell sulfur host that is constructed by enveloping dispersive Fe2O3 nanoparticles within Mn3O4 nanosheet‐grafted hollow N‐doped porous carbon capsules (Fe2O3@N‐PC/Mn3O4‐S). When applied as a cathode for Li–S batteries, the as‐prepared Fe2O3@N‐PC/Mn3O4‐S can deliver capacities as high as 1122 mAh g−1 after 200 cycles at 0.5 C and 639 mAh g−1 after 1500 cycles at 10 C, respectively. Remarkably, even as the areal sulfur loading is increased to 5.1 mg cm−2, the cathode can still maintain a high areal specific capacity of 5.08 mAh cm−2 with a fading rate of only 0.076% per cycle over 100 cycles at 0.1 C. By a further combination analysis of electron holography and electron energy loss spectroscopy, the outstanding performance is revealed to be mainly traced to the oxygen‐vacancy‐induced interfacial charge field, which immobilizes and catalyzes the conversion of lithium polysulfides, assuring low polarization, fleet redox reaction kinetics, and sufficient utilization of sulfur. These new findings may shed light on the dependence of electrochemical performance on the heterostructure of sulfur hosts.

Alcohols as Latent Hydrophobes: Entropically Driven Uptake of 1,2-Diol Functionalized Ligands by a Porous Capsule in Water.

Alcohols, with hydroxyl groups compositionally identical to water itself, are consummate hydrophiles, whose high solubilities preclude spontaneous self-assembly in water. Nevertheless, the solute-solvent interactions associated with their highly favorable solvation enthalpies impose substantial entropic costs, similar in magnitude to those that drive the hydrophobic assembly of alkanes. We now show that under nanoconfined conditions this normally dormant "hydrophobicity" can emerge as the driving force for alcohol encapsulation. Using a porous molecular capsule, the displacement of endohedrally coordinated formate ligands (HCO2-) by 1,2-hydroxyl-functionalized l-glycerate (l-gly, l-HOCH2(HO)CHCO2-) was investigated by van't Hoff analysis of variable-temperature 1H NMR in D2O. At pD 5.8, l-gly uptake is enthalpically inhibited. Upon attenuation of this unfavorable change in enthalpy by cosequestration of protons within the alcoholic environment provided by encapsulated diol-functionalized ligands, - TΔ S° dominates over Δ H°, spontaneously filling the capsule to its host capacity of 24 l-gly ligands via an entropically driven hydrophobic response.

Silica microcapsules as containers for protein drugs: Direct and indirect encapsulation

Hollow silica particles are promising platform for development of novel oral dosage forms of protein drugs with improved pharmacological and consumer properties. Encapsulation of proteins in silica containers can be carried out using two different approaches: direct (one-step) or indirect (multi-step). In this work, the influence of the encapsulation approaches of model protein in porous silica capsules on functional properties of the obtained particles as drug delivery systems (the protein loading, structural state of the encapsulated protein and in vitro kinetics of its release) was studied for the first time. Direct encapsulation of bovine serum albumin (BSA) and preparation of silica capsules for indirect encapsulation was performed using sol-gel/W/O/W emulsion technology. The effects of nature of silica precursor (tetraethoxysilane and sodium silicate) and composition of oil phase on the indicated functional properties were investigated. The comparative analysis of the obtained data allowed ascertaining the optimal conditions of BSA encapsulation in hollow silica particles by sol-gel/emulsion method for the protein delivery application.

Dynamics of sulfate and basic cations in soil solution as affected by gypsum fertilization in an Ultisol of Southern Brazil

ABSTRACTThe objective of this study was to evaluate the short-term dynamics of chemical species of sulfate and the main basic cations in the soil solution affected by the application of different sulfur (S) rates using agricultural gypsum. The experiment was carried out in an Ultisol with 14% clay, managed under no-tillage for 14 yrs in Southern Brazil. Four rates of S (0, 5, 10 and 20 kg of S ha−1) were evaluated using agricultural gypsum (CaSO4) as S-source. The soil solution was collected using porous capsule lysimeters before and at 9, 17, 37, 60, 76 and 109 d after the gypsum application, at depths of 20 and 60 cm. Surface application of gypsum rapidly increases the sulfate concentration in the soil solution at 20 cm depth. However, in less than 30 d, the effect of the S rates on the soil solution at 20 cm was minimal, with an increase in sulfate concentration in the soil solution at 60 cm depth after 17 d. Sulfated fertilization via agricultural gypsum at rates greater than 10 kg ha−1 in sandy soil with low cation exchange capacity increased the mobility of Ca and Mg in the soil profile.

Self-Assembly of TiO2 Nanofiber-Based Microcapsules by Spontaneously Evolved Multiple Emulsions.

We demonstrate hierarchical nest/crust-like colloidosomes composed of interlocked titanium dioxide (TiO2) nanofibers using spontaneously evolved n-butanol/water/ n-butanol (B/W/B) emulsions. We find two mechanisms to produce colloidosomes from B/W/B droplets due to their mutual solubility and dewetting discrepancy. Porous TiO2 colloidal capsules with loosely intertwined nanofibers were obtained after the dewetting of nanofiber-coated B/W/B droplets, while crustlike TiO2 colloidosomes with a thin shell and large hollow interior are developed from amphiphilic polymer-stabilized B/W/B droplets. We further investigate the effect of experimental parameters, including the initial droplet size, the nanofiber concentration, and the water/butanol ratios in butanol phases, on the droplet-to-colloidosome evolution and resultant morphology of colloidosomes. Our simple and versatile approach for fabricating TiO2 colloidosomes can be extended to a range of irregular colloidal particles, and the products have great potential to act as host systems in electrochemical catalysis, photothermal therapy, or filtration materials.

General Synthetic Strategy for Libraries of Supported Multicomponent Metal Nanoparticles.

Nanoparticles comprising three or more different metals are challenging to prepare. General methods that tackle this challenge are highly sought after as multicomponent metal nanoparticles display favorable properties in applications such as catalysis, biomedicine, and imaging. Herein, we report a practical and versatile approach for the synthesis of nanoparticles composed of up to four different metals. This method relies on the thermal decomposition of nanostructured composite materials assembled from platinum nanoparticles, a metal-organic framework (ZIF-8), and a tannic acid coordination polymer. The controlled integration of multiple metal cations (Ni, Co, Cu, Mn, Fe, and/or Tb) into the tannic acid shell of the precursor material dictates the composition of the final multicomponent metal nanoparticles. Upon thermolysis, the platinum nanoparticles seed the growth of the multicomponent metal nanoparticles via coalescence with the metallic constituents of the tannic acid coordination polymer. The nanoparticles are supported in the walls of hollow nitrogen-doped porous carbon capsules created by the decomposition of the organic components of the precursor. The capsules prevent sintering and detachment of the nanoparticles, and their porosity allows for efficient mass transport. To demonstrate the utility of producing a broad library of supported multicomponent metal nanoparticles, we tested their electrocatalytic performance toward the hydrogen evolution reaction and oxygen evolution reaction. We discovered functional relationships between the composition of the nanoparticles and their electrochemical activity and identified the PtNiCu and PtNiCuFe nanoparticles as particularly efficient catalysts. This highlights how to generate diverse libraries of multicomponent metal nanoparticles that can be synthesized and subsequently screened to identify high-performance materials for target applications.

Gene expression in a synthetic eukaryotic cell‐mimic

Eukaryotic cells are highly ordered and complex structures that constitute the smallest functional units of multicellular organisms. We aimed to mimic capabilities and organization of natural eukaryotic cells in a synthetic, non-living artificial cell. Using a microfluidic method we produce porous polymeric capsules with an artificial nucleus where DNA is immobilized. Upon addition of transcription and translation reagents capsules synthesize proteins encoded in their nuclei. Proteins can be targeted to different locations in the artificial cell such as the nucleus or the cell wall by specific binding interactions. Arranged in synthetic tissues artificial cells communicate with each other through diffusible signals that influence gene expression in neighboring cells. Our results suggest that artificial cells may serve as simplified models to study signaling and spatial organization in natural, living cells and tissues. Support or Funding Information This work was supported by the Department of Defense (Army Research Office) through the Multidisciplinary University Research Initiative (MURI) under Award No. W911NF-13-1-0383. H.N. acknowledges support through an Advanced Postdoc. Mobility fellowship from the Swiss National Science Foundation. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Self-Assembled Tea Tannin Graft Copolymer as Nanocarriers for Antimicrobial Drug Delivery and Wound Healing Activity.

Green chemistry polymers from renewable resources have recently received much more attention from pharmaceutical researchers. However, the appropriate application of a polymer depends on its chemical nature, biocompatibility and microstructure. Here, tannin polyphenols from the common beverage, tea, are used to develop a novel self-assembled porous capsule as a microstructure of hydrogel for versatile biological applications, such as drug delivery, antioxidant and wound healing activity. Hydrogel has been successfully used for the delivery of both anticancer and antimicrobial drugs. The developed material shows excellent biocompatibility and antioxidant activity in vitro. The scratch assay for in vitro wound healing activity reveals their higher potential to repair the damaged cells in comparison to control.

Cobalt nanoparticles incorporated into hollow doped porous carbon capsules as a highly efficient oxygen reduction electrocatalyst

MOF nanocrystals are employed for the design and synthesis of cobalt nanoparticles embedded into hollow doped porous carbon electrocatalyst.

Metal-organic frameworks derived platinum-cobalt bimetallic nanoparticles in nitrogen-doped hollow porous carbon capsules as a highly active and durable catalyst for oxygen reduction reaction

Pt-based nanomaterials are regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, widespread adoption of PEMFCs requires solutions to major challenges encountered with ORR catalysts, namely high cost, sluggish kinetics, and low durability. Herein, a new efficient method utilizing Co-based metal-organic frameworks is developed to produce PtCo bimetallic nanoparticles embedded in unique nitrogen-doped hollow porous carbon capsules. The obtained catalyst demonstrates an outstanding ORR performance, with a mass activity that is 5.5 and 13.5 times greater than that of commercial Pt/C and Pt black, respectively. Most importantly, the product exhibits dramatically improved durability in terms of both electrochemically active surface area (ECAS) and mass activity compared to commercial Pt/C and Pt black catalysts. The remarkable ORR performance demonstrated here can be attributed to the structural features of the catalyst (its alloy structure, high dispersion and fine particle size) and the carbon support (its nitrogen dopant, large surface area and hollow porous structure).

DEVELOPMENT AND EVALUATION OF AN IRRIGATION MANAGEMENT TOOL

This study aimed to develop a tool for irrigation management and to evaluate its performance. To this end, 10 lysimeters, developed from plastic buckets, 20 L in volume, were installed. The inner volume of the buckets was divided into two parts. The lower half was filled with water. The upper half was filled with soil, grown with Bermuda grass. In the interior of the soil, a porous capsule was installed, connected to a plastic tube, which the lower border was immersed into the water of the lower part. As the crop extracted water from the soil, the soil sucked water from the lower part through the porous capsule. By lowering the water level in the bucket between two periods, the initial level was restored by addition of water through the feeder tube. The volume of water spent to restore the initial level divided by the bucket superficial area determines the evapotranspiration in that period. The tool was called Simplified Lysimeter - SIL. To evaluate the performance of the SIL, the following were considered: the correlation (r) and determination (r 2 ) coefficients, Willmott agreement (d), and Camargo & Sentelhas performance (c) and standard error estimate (SEE), taking Penman-Monteith-FAO as reference. According to results obtained, the SIL, developed with easily accessible and low cost materials and easy to construct, had a performance classified as very good and overestimated the evapotranspirarion obtained by PM at 0.30 mm d -1 , on average, showing good operating conditions and allowing to estimate evapotranspiration in agreement with Penman-Monteith estimates.

Structural Control of Carbon-Free Catalyst Layer Using Connected Platinum-Iron Nanoparticle Catalyst for Improved Mass-Transport in Polymer Electrolyte Fuel Cells

We have developed the connected platinum-iron (PtFe) nanoparticle catalyst with a porous hollow capsule structure as a carbon-free catalyst-layer material for polymer electrolyte fuel cells (PEFCs). [1,2] As shown in Fig. 1A, this catalyst consists of a nanosized beaded network by the fusion of PtFe nanoparticles with a crystallite size of 6~7 nm and an L10type chemically-ordered (face centered tetragonal) structure. The beaded metal network is electrically conductive, enabling the removal of carbon supports form a catalyst layer. The carbon-free cathode catalyst layer using a connected PtFe catalyst exhibits high durability against start-stop cycles, because of elimination of carbon corrosion problems. In addition, the specific activity of a connected PtFe catalyst for oxygen-reduction-reaction (ORR) is about 9 times enhanced, compared with that of a commercial Pt-nanoparticle catalyst supported on carbon black (Pt/C). On the other hand, inside a cathode catalyst layer, complex phenomena occur during a fuel-cell operation, such as ORR on catalyst surface, diffusion of oxygen molecules, proton conduction via ionomers, etc. Thus, a high performance of PEFC requires not only high ORR activity and stability but also lower resistance of oxygen mass transport. In this study, the following structural effects on fuel-cell performances for the carbon-free catalyst layers using connected PtFe catalysts were investigated; (i) inner-space in hollow capsule, and (ii) inter-space between capsules (Fig. 1B). The effect of inner-space in hollow capsule was discussed by the comparison of the connected PtFe catalysts with hollow structure or on solid (silica) support. The inter-space between capsules was controlled by the use of different capsule sizes (capsule size = 300 nm, or 500 nm in diameter). The electrochemical analyses of the prepared catalyst layers revealed that the hollow structure and the enlargement of inter-space between capsules improved the IV performance, especially at the high current density region, implying an improved oxygen mass-transport due to a sufficient space for oxygen diffusion in the catalyst layer and/or effective removal of liquid water from the catalyst layer. Moreover, in this study, the structural effect of gas-diffusion layer on fuel-cell performances was also investigated. It was found that the gas diffusion layer with higher gas permeability would facilitate the removal of liquid water from the capsule catalyst layer, resulting in a lower oxygen-transport resistance. In this presentation, by means of structural and electrochemical analyses of the capsule catalyst layers, the relationship between the catalyst-layer nanostructures and the fuel-cell performances will be discussed in details. The knowledge obtained in this study will provide new insights into the design of a carbon-free catalyst layer to achieve an enhanced PEFC performance. [1] T. Tamaki, H. Kuroki, S. Ogura, T. Fuchigami, Y. Kitamoto, and T. Yamaguchi, Energy Environ. Sci., 8, 3545-3549 (2015). [2] H. Kuroki, T. Tamaki, and T. Yamaguchi, J. Electrochem. Soc., 163(8), F927-F932 (2016). Figure 1

Porous microcapsules comprised inter-locked nano-particles by evaporation-induced assembly: Evaluation of dye sorption

Evaporation induced assembly of colloidal particles in an aerosol droplet has been utilized to synthesize nano-structured porous silica microcapsules comprising of interlocked correlated nano-particles. Morphology of the microcapsules was tuned by controlling the rate of evaporation. In the present work, we demonstrate that such porous capsules can efficiently take up cationic dye from aqueous solution. In-situ UV–vis spectroscopy has been utilized to monitor the time dependence of sorption by these capsules. Small-angle X-ray scattering and scanning electron microscopy have been used to probe the multi-level structure of the powder granules. Thermal analysis was performed on the dye-sorbed granules to investigate the effect of confinement on the thermal degradation behaviour of the dye molecules within the granules.

Fundamental Rheology of Disperse Systems Based on Single-Particle Mechanics

A comprehensive review of the fundamental rheology of dilute disperse systems is presented. The exact rheological constitutive equations based on rigorous single-particle mechanics are discussed for a variety of disperse systems. The different types of inclusions (disperse phase) considered are: rigid-solid spherical particles with and without electric charge, rigid-porous spherical particles, non-rigid (soft) solid particles, liquid droplets with and without surfactant, bubbles with and without surfactant, capsules, core-shell particles, non-spherical solid particles, and ferromagnetic spherical and non-spherical particles. In general, the state of the art is good in terms of the theoretical development. However, more experimental work is needed to verify the theoretical models and to determine their range of validity. This is especially true for dispersions of porous particles, capsules, core-shell particles, and magnetic particles. The main limitation of the existing theoretical developments on the rheology of disperse systems is that the matrix fluid is generally assumed to be Newtonian in nature. Rigorous theoretical models for the rheology of disperse systems consisting of non-Newtonian fluid as the matrix phase are generally lacking, especially at arbitrary flow strengths.

Surfactant assisted enrichment of nucleosides by using a sorbent consisting of magnetic polysulfone capsules and mesoporous silica nanoparticles modified with phenylboronic acid

Boronate affinity materials have been widely used for selective extraction of cis-diols, but their extraction efficiency is far from adequate. We have synthesized porous magnetic polysulfone capsules containing mesoporous silica nanoparticles of type SBA-15 that were functionalized with boronic acid derivative. The spheres were then coated with the cationic surfactant hexadecyltrimethylammonium bromide which binds to the surface due to hydrophobic and ionic interactions. The surfactant coated sorbents possess an enrichment capability and selectivity that is distinctly better than that of non-coated sorbents. The limits of detection for four nucleosides extracted from aqueous sample solutions are in the range from 1.13 to 1.74 ng mL−1. The selective enrichment of trace quantities of nucleosides is illustrated by quantifying nucleosides after extraction from HepG2 cells.

Tuning the Surface Hydrophobicity of Keplerate {Mo72Fe30} Porous Molecular Capsules by Surface Ligand-Replacement Process

A spontaneous ligand-replacement process at the external surface of Keplerate polyoxometalate molecular nanocapsules {Mo72Fe30} occurs when dissolving {Mo72Fe30} in pure methanol, with the water ligands coordinated to the Fe(III) centers of {Mo72Fe30} gradually being replaced by CH3OH ligands, resulting in the formation of partially hydrophobic nanocapsules. The new nanocapsules have negligible deprotonation capability and different solution behaviors. The methanol ligands can be easily exchanged back to water ligands when a small amount of water is added into the system. The exchange of water ligands dramatically changed the self-assembly behaviors of the {Mo72Fe30} clusters in solution.

Structural Effects on Oxygen Reduction Activity of Carbon-Free Connected Platinum-Iron Nanoparticle Catalysts

We developed connected carbon-free platinum-iron (PtFe) nanoparticle catalysts with porous hollow capsule structure (Fig. 1) as oxygen-reduction-reaction (ORR) electrocatalysts for polymer electrolyte fuel cells (PEFCs).[1] This catalysts consist of a beaded network by connected PtFe nanoparticles with a crystallite size of 6~7 nm and a chemically-ordered (face centered tetragonal) superlattice structure. The beaded network is electrically conductive; thus, carbon-supports can be removed from catalyst layers in PEFCs. We have demonstrated that an MEA prepared using a carbon-free cathode of connected PtFe-nanoparticle catalysts was highly durable against start-up/shut-down operations because of the elimination of carbon-corrosion problems. Moreover, an ORR specific activity of a connected PtFe catalyst is about 9 times higher than that of a commercial Pt-nanoparticle catalyst supported on carbon black (Pt/C). In this study, the structural effects of a connected PtFe catalyst on an ORR activity were investigated in order to elucidate the factors of its high ORR activity. Note that the connected PtFe catalyst exhibited about twice higher ORR specific activity than the PtFe-nanoparticle catalyst (just nanoparticles without any connection between them) on carbon black. In addition, the ORR specific activity of the connected PtFe nanoparticles with hollow structure (with no supports) was 1.5 times higher than that of the connected PtFe nanoparticles on the electroconductive carbon support. These results indicate that the unique structures of connected nanoparticle catalysts, such as connected beaded network and hollow structure, enhance an ORR activity. We also have performed the refined structural analyses of a connected PtFe catalyst by using in-situ X-ray absorption spectroscopy (XAS) combined with Rietveld structure refinement with powder X-ray diffraction data, and spherical aberration corrected scanning transmission electron microscope (Cs-corrected STEM). The in-situ XAS analysis disclosed shorter Pt‒Pt bond distance and more Pt 5d vacancy of the connected PtFe catalyst compared with the commercial Pt/C. In addition, the Cs-corrected STEM observations revealed that the beaded network formed by connected PtFe nanoparticles possessed polycrystalline structure. In this presentation, the effects of the geometric and electronic structures of a connected PtFe catalyst on an ORR activity will be discussed in details. The knowledge obtained in this study provides guidelines for the design of ORR catalysts with enhanced ORR activities to achieve a high performance PEFC. [1] T. Tamaki, H. Kuroki, S. Ogura, T. Fuchigami, Y. Kitamoto, and T. Yamaguchi, “Connected nanoparticle catalysts possessing a porous, hollow capsule structure as carbon-free electrocatalysts for oxygen reduction in polymer electrolyte fuel cells”, Energy Environ. Sci., 2015, 8, 3545-3549. Figure 1

Catalytically Active Bimetallic Nanoparticles Supported on Porous Carbon Capsules Derived From Metal-Organic Framework Composites.

We report a new methodology for producing monometallic or bimetallic nanoparticles confined within hollow nitrogen-doped porous carbon capsules. The capsules are derived from metal-organic framework (MOF) crystals that are coated with a shell of a secondary material comprising either a metal-tannic acid coordination polymer or a resorcinol-formaldehyde polymer. Platinum nanoparticles are optionally sandwiched between the MOF core and the shell. Pyrolysis of the MOF-shell composites produces hollow capsules of porous nitrogen-doped carbon that bear either monometallic (Pt, Co, and Ni) or alloyed (PtCo and PtNi) metal nanoparticles. The Co and Ni components of the bimetallic nanoparticles are derived from the shell surrounding the MOF crystals. The hollow capsules prevent sintering and detachment of the nanoparticles, and their porous walls allow for efficient mass transport. Alloyed PtCo nanoparticles embedded in the capsule walls are highly active, selective, and recyclable catalysts for the hydrogenation of nitroarenes to anilines.