Porous Frame Research Articles

A Novel Enzyme-Free Biosensor Based on Porous Core-Shell Metal Organic Frame Nanocomposites Modified Electrode for Highly Sensitive Detection of Uric Acid and Dopamine.

A novel enzyme-free biosensor based on porous metal organic frame nanocomposites, i.e., core-shell structured Au@NC@GC nanocomposites, has been constructed for simultaneous determination of uric acid (UA) and dopamine (DA). Au@ZIF-8@ZIF-67 was prepared through a seed-mediated growth method and carbonized in nitrogen atmosphere to synthesize a nanoporous hybrid carbon materials (Au@NC@GC). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies demonstrate that the as-prepared Au@NC@GC modified glassy carbon electrode (Au@NC@GC-GCE) possesses a high selectivity and sensitivity for simultaneous detections of UA and DA. It exhibited wide linear responses for UA and DA in the range from 10 μM to 600 μM and 10 μM to 150 μM, with the detection limits of 0.773 nM and 0.746 nM, respectively (S/N = 3). Moreover, this novel electrochemical biosensor could be further utilized in biological analysis (i.e., human serum), and the satisfactory recovery results of UA and DA could be readily obtained. These afore-mentioned results further manifest that the as-prepared biosensors are capable for quantitatively monitoring UA and DA in serum, verifying the possibility for its future promising applications in real biological or clinic samples analysis.

Propagation of seismic waves in patchy‐saturated porous media: double‐porosity representation

ABSTRACTPropagation of harmonic plane waves is studied in a patchy‐saturated porous medium. Patchy distribution of the two immiscible fluids is considered in a porous frame with uniform skeletal properties. A composition of two types of patches, connected through continuous paths, constitutes a double‐porosity medium. Different compressibilities of pore‐fluids in two porous phases facilitate the wave‐induced fluid‐flow in this composite material. Constitutive relations are considered with frequency‐dependent complex elastic coefficients, which define the dissipative behaviour of porous aggregate due to the flow of viscous fluid in connected patches. Relevant equations of motion are solved to explain the propagation of three compressional waves and one shear wave in patchy‐saturated porous solids. A numerical example is solved to illustrate dispersion in phase velocity and quality factor of attenuated waves in patchy‐saturated porous materials. Role of fluid–solid inertial coupling in Darcy's law is emphasized to keep a check on the dispersion of wave velocities in the porous composite. Effects of patchy saturation on phase velocities and quality factors of attenuation are analysed using the double‐porosity formulation as well as the reduced single‐porosity equivalents.

Quasi-Liquid Layer on Ice and Its Effect on the Confined Freezing of Porous Materials

Freezing of the water confined in thin pores can be destructive to the porous frame, but the effect of the quasi-liquid layer (QLL) between the confined ice and the pore walls remains still far from being fully understood. In the present study, the physical origins of the intermediate phase of QLL were discussed by thermodynamic analyses. Different interactions on QLL bring different models to estimate its thickness, which generally decays with temperature decreasing. Four representative models of QLL thickness were selected to unveil its effect on the growing rates and extents of ice in a concrete. The engineering consequences of the confined freezing were then discussed in the aspects of effective pore pressures built from the confined ice growth and deformations framed by a poro-elastic model. Overall, thickening QLL depresses ice growing rates and contents and, consequentially, decreases pore pressures and material deformations during freezing. The QLL corrections also narrow the gaps between the predicted and measured freezing deformations. The findings of this study contribute to profound understandings of confined freezing that may bridge over physical principles and engineering observations.

Effect of reaction sintering modes on the structure and properties of carbide ceramics

Experimental studies of the structure, phase composition, physical and mechanical properties of the reaction-sintered ceramics based on silicon carbide and boron obtained by reaction sintering have been performed. It has been shown that the properties of the reaction-sintered ceramics based on carbides are largely determined by the quality of impregnation of the porous carbide frame with silicon, which depends on the total and open porosity, shape and size of the pores of the compact, the composition of the charge from the carbide powder. High-temperature sintering, followed by impregnation of the carbide frame with silicon and its interaction with the carbon constituent of the frame, largely determines the properties of the material. The main task in the implementation of this process is to create conditions that ensure the full filling of pores in the initial compact during impregnation with silicon melt and, secondly, maximum activation of chemical interaction between the melt of silicon, carbon and other components that compose the charge. A complex of studies on the effect of compacting pressure and annealing temperature of the charge based on silicon carbide and boron powders with the addition of graphite on the pore structure of the compact and the quality of its impregnation with a silicon melt has been carried out in this work. It has been shown that the density, bending strength, hardness of ceramics based on silicon carbide and boron carbide obtained by reaction sintering are increased with a rise in compacting pressure of carbide frames. The optimum porosity of the carbide frame is 25–30 %; the pore size is 1.0–1.5 μm. It has been also demonstrated that ceramics based on boron carbide and boron carbide with 50 % silicon carbide impregnated with silicon at high-temperature sintering has higher strength and hardness values than those based on silicon carbide due to higher adhesion strength at the interface of boron carbide particles and binder, caused by the dissolution of boron carbide in the silicon melt and the formation of complex carbide particles on the surface.

Facile synthesis of petal-like NiCo/NiO-CoO/nanoporous carbon composite based on mixed-metallic MOFs and their application for electrocatalytic oxidation of methanol

Porous carbon template decorated with mixed transition metals/metal oxides with tunable architecture is becoming increasingly important and attractive as a kind of novel electrode materials. In this way, mixed-metallic metal-organic frameworks (MOFs) provide an opportunity for fabrication of homogeneous mixed metals/metal oxides distribution in the porous carbon frame without any carbon precursor additive. Also, structures, dimensions and electrochemical performance of MOFs can be readily manipulated by simply tuning the metals molar ratio. In this study, we demonstrate the design and fabrication of petal-like NiCo/NiO-CoO metal/metal oxides with a rational composition embedded in 3D ultrathin nanoporous carbon composite)NiCo/NiO-CoO/NPCC(. This nanocomposite is synthesized by a two-steps procedure involving preparation of bimetallic MOFs by partially substituting Ni2+ in the Ni-MOF structure with Co2+ (Ni-Co/BDC [BDC = 1,4-Benzene dicarboxylic acid]) and direct carbonization process in the N2 atmosphere at 900 °C. The prepared nanocomposite was used directly as a non-precious electrocatalyst for methanol oxidation reaction. The results indicated that, in comparison to the monometallic metal/metal oxides distributed in nanoporous carbon composite (Ni/NiO/NPCC and Co/CoO/NPCC), the mixed metals/metal oxides NiCo/NiO-CoO/NPCC exhibits excellent electrochemical performance toward the anodic oxidation of methanol. The unique ultrathin porous petal-like structure with free pores and the enlarged specific surface area provides fast ion/electron transfer, leading to faster kinetics, lower over-potential, and higher electro-catalytic reactivity. Besides their intriguing structural features, the excellent conductivity of carbon frame, as well as a rational composition of two constituents and synergistic effects from cobalt, nickel and their oxides provides favorable catalytic activity for the electro-oxidation of methanol. Therefore, it is believed that this novel multi-component composites demonstrates good electrocatalytic activity and suitable stability towards the methanol oxidation.

Nickel foam–caged Ag-Au bimetallic nanostructure as a highly rugged and durable SERS substrate

A three-dimensional nickel foam (NF) caging Ag-Au bimetallic nanostructure (Ag-Au@NF) has been demonstrated as a highly rugged and sensitive surface-enhanced Raman scattering (SERS) substrate. The main concept employed in designing this substrate was the protection of SERS-active nanostructures by holding them within a sturdy frame. For this purpose, NF was readily chosen as a strong porous frame to secure the internal nanostructures owing to its excellent structural strength and ability to easily incorporate analytes due to its porous structure. The next issue was the construction of stable and SERS-efficient nanostructures within the NF frame. To meet this need, an Ag-Au bimetallic nanostructure was chosen, combining the high SERS efficiency of Ag and the good surface stability of Au. To fabricate the Ag-Au nanostructure, first a Sn-Ag alloy was constructed on the NF frame by means of electrodeposition (producing Sn-Ag@NF) and then Sn was selectively leached from the alloy by means of free corrosion in NaOH solution (producing Ag@NF). This selective leaching was adopted to make the surface rough to enhance the SERS efficiency in the final substrate. Finally, Au was incorporated into the Ag@NF by means of a galvanic replacement reaction (producing Ag-Au@NF). The use of Ag-Au@NF enabled identification of rhodamine 6G at concentrations as low as 0.1 nM. The Ag-Au@NF substrates were rugged, showing small Raman signal drops after 100 cycles of sandpaper abrasion or 30 min of sonication. Also, the signal decrease was only 4.26% upon 3 days of exposure to ambient air without special care. Overall, the Ag-Au@NF developed herein shows practical merits for adoption in routine and field SERS analyses.

Finite element modeling of fluid-saturated metallic foams from micro-computed tomography

Open-cell metallic foams are high stiffness-to-weight cellular materials whose microstructure allows for saturation of viscous liquid. Such a composite has advantages for underwater sound absorption over traditional rubbers due to minimal compression from hydrostatic pressure, composite tunability, and potential for specific gravity less than one. Semi-phenomenological and hybrid numerical models have been shown to predict sound absorption performance of metallic foams, however difficulty arises in determining parameters for the numerical models such as tortuosity, viscous characteristic length, thermal characteristic length, and flow resistivity. Such models also assume that the porous frame is rigid, an assumption valid for only a limited frequency range. In this presentation, finite element models of fluid-saturated metallic foams are created from micro-computed tomography scans and analyzed to determine sound absorption performance. The advantage of this method is that the entire foam microstructure and surrounding fluid can be accurately modeled through a finite element mesh. In addition, experimental measurement of model parameters is not required and the rigid frame assumption can be removed.

Wheat Straw-Derived N-, O-, and S-Tri-doped Porous Carbon with Ultrahigh Specific Surface Area for Lithium-Sulfur Batteries.

Recently, lithium-sulfur (Li-S) batteries have been greeted by a huge ovation owing to their very high theoretical specific capacity (1675 mAh·g−1) and theoretical energy density (2600 Wh·kg−1). However, the full commercialization of Li-S batteries is still hindered by dramatic capacity fading resulting from the notorious “shuttle effect” of polysulfides. Herein, we first describe the development of a facile, inexpensive, and high-producing strategy for the fabrication of N-, O-, and S-tri-doped porous carbon (NOSPC) via pyrolysis of natural wheat straw, followed by KOH activation. The as-obtained NOSPC shows characteristic features of a highly porous carbon frame, ultrahigh specific surface area (3101.8 m2·g−1), large pore volume (1.92 cm3·g−1), good electrical conductivity, and in situ nitrogen (1.36 at %), oxygen (7.43 at %), and sulfur (0.7 at %) tri-doping. The NOSPC is afterwards selected to fabricate the NOSPC-sulfur (NOSPC/S) composite for the Li-S batteries cathode material. The as-prepared NOSPC/S cathode delivers a large initial discharge capacity (1049.2 mAh·g−1 at 0.2 C), good cycling stability (retains a reversible capacity of 454.7 mAh·g−1 over 500 cycles at 1 C with a low capacity decay of 0.088% per cycle), and superior rate performance (619.2 mAh·g−1 at 2 C). The excellent electrochemical performance is mainly attributed to the synergistic effects of structural restriction and multidimensional chemical adsorptions for cooperatively repressing the polysulfides shuttle.

Asymptotic model of size-exclusion grouting

In the construction of foundations of buildings and structures on fragile ground, various technologies of soil grouting are used. When pouring fine-grained concrete into the porous soil, the concrete grains are filtered in the pores of the soil. The filtration process depends on the ratio of the pore sizes of the soil and the solid particles of the injected concrete mortar.Injection of a carrier fluid with small solid particles in a porous medium forms a dynamic concentrations front of suspended and retained particles, separating the suspended particles and the hollow part of the porous frame. The purpose of the study is to construct and calculate an asymptotic model near the concentrations front for the filtration of monodisperse suspension in a porous medium with size-exclusion mechanism of particles retention.The classical mathematical model for one-dimensional filtration of suspensions and colloids in a porous medium is based on the geometric ratio of the particles and pores sizes: the particles freely pass through the large pores and get stuck in the pore throats with sizes smaller than the particles diameter. The model is determined by a system of two quasilinear first-order partial differential equations with the gap between boundary and initial conditions. To construct an asymptotic expansion in the vicinity of the concentrations front, a special small parameter is used that specifies the distance to the front. This parameter provides direct determination of the asymptotic terms from the recurrent system of ordinary linear differential equations of the first order.Near the concentrations front of the suspended and retained particles, a nonlinear high-order asymptotics is constructed for the filtration problem of solid particles transported by a carrier fluid in a porous medium. The obtained solution is zero before the front and nonzero behind the front. Approbation of the asymptotic expansion is carried out. It is shown that, for a linear blocking filtration coefficient, the asymptotics coincides with the exact solution.The asymptotic model of deep bed filtration makes it possible to obtain exact formulas for the high-order asymptotic expansion near the dynamic concentrations front of suspended and retained particles. The asymptotics improves the ability to fine-tune the filtration model depending on the properties of the porous soil and the grout.

Enhancing hydrogen evolution of g-C3N4 with nitrogen vacancies by ethanol thermal treatment

A highly photoactive nitrogen-deficient g-C3N4 photocatalyst with porous frame work has been prepared by a simple, effective, and environmental-friendly method of ethanol thermal treatment. It is found that the as-synthesized catalyst exhibits an enhanced visible light photocatalytic activity for H2 evolution. The H2-evolution rate on the treated g-C3N4 is 4.2 times higher than the untreated-C3N4. The treated g-C3N4 and untreated g-C3N4 are characterized by Fourier transform-infrared spectra (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), UV-Vis absorption (UV-Vis), photocurrent measurement, and electrochemical impedance spectroscopy (EIS). Characterization results show that the ethanol thermal treatment induces nitrogen vacancies and hierarchical porous structure in g-C3N4. Such a structural reconstruction is beneficial for improving optical absorption and hindering photoinduced charger recombination on g-C3N4, resulting in the enhanced photocatalytic activity. This work would offer a reference route to develop high-performance metal-free photocatalysts.

Efficient collective shape shifting and locomotion of massively-modular robotic structures

We propose a methodology of planning effective shape shifting and locomotion of large-ensemble modular robots based on a cubic lattice. The modules are divided into two groups: fixed ones, that build a rigid porous frame, and mobile ones, that flow through the frame. Mobile modules which flow out of the structure attach to the frame, advancing its boundary. Conversely, a deficiency of mobile modules in other parts of the boundary is corrected by decomposition of the frame. Inside the structure, appropriate module flow is arranged to transport the modules in a desired direction, which is planned by a special distributed version of a maximum flow search algorithm. The method engages a volume of modules during reconfiguration, which is more efficient than common surface-flow approaches. Also, the proposed interpretation as a flow in porous media with moving boundaries seems particularly suitable for further development of more advanced global reconfiguration scenarios. The theoretical efficiency of the method is assessed, and then partially verified by a series of simulations. The method can be possibly also applied to a wider class of modular robots, not necessarily cubic-lattice-based.

Pd–P nanoalloys supported on a porous carbon frame as an efficient catalyst for benzyl alcohol oxidation

A 3D carbon frame (PCF) acted as a support for Pd–P nanoalloys and was used as an efficient catalyst for benzyl alcohol oxidation.

Microstructure Defects and Properties Analysis of Maraging Steel Porous Frame by Selective Laser Sintering

Microstructure Defects and Properties Analysis of Maraging Steel Porous Frame by Selective Laser Sintering

Modeling the heat and mass transfer in the pores of the thermal protection carbon-carbon frame during the gas-phase deposition of silicon carbide

This paper is dedicated to the numerical simulation of the gas-phase deposition into the porous carbon-carbon frame for the gradient thermal protection of reentry vehicles. The paper presents the specifics of creating the representative volume elements of the porous carbon-carbon frames based on the microstructure data from the computed tomography scanner, electronic scanning microscope and porosimetry results. The finite-element models of the representative volume elements are created in order to obtain the net independent solution, including the special finite elements at the phase interfaces. The finite-element and finite-volume method was used for calculation, implemented in MSC.Digimat and ANSYS software packages. The effect of the reagent parameters on the gas-phase deposition process, uniformity and rate of silicon carbide deposition was simulated parametrically, and the results are presented.

Porous Pt Aggregates Deposited on a Carbon Nanotube Film with High Catalytic Activity and Durability

AbstractFor decades, the low durability of Pt‐based catalysts has hindered the application of fuel cells. Here, Pt catalysts with different morphologies and porous structures are prepared by electrochemical deposition on a carbon nanotube film without the use of any surfactants or templates. The Pt particles with spherical, flower‐like, and cubic morphologies consist of fine polyhedron‐ and flake‐shaped Pt crystals. Owing to the presence of faceted crystals, the Pt particles are assembled with porous frame structures. As an example of potential applications, such Pt crystals are demonstrated to have high catalytic activity and durability in hydrogen oxidation and oxygen reduction reactions under harsh electrochemical cycling conditions. Even in the case of the largest particles consisting of fine polyhedrons, the catalytic performance is much superior to that of a commercial Pt/C catalyst. Therefore, this study suggests a new strategy for morphology control of Pt catalysts and their performance optimization.

Solid viscosity of fluid-saturated porous rock with squirt flows at seismic frequencies

We have developed a macroscopic model for a two-phase medium (solid porous rock frame plus saturating pore fluid) with squirt flows based on Lagrangian continuum mechanics. The model focuses on improved physics of rock deformation, including explicit differential equations in time domain, causality, linearity, frequency-independent parameters with clear physical meanings, and an absence of mathematical internal or memory variables. The approach shows that all existing squirt-flow models can be viewed as microscopic models of viscosity for solid rock. As in existing models, the pore space is differentiated into compliant and relatively stiff pores. At lower frequencies, the effects of fluid flows within compliant pores are described by bulk and shear solid viscosities of the effective porous frame. Squirt-flow effects are “Biot consistent,” which means that there exists a viscous coupling between the rock frame and the fluid in stiff pores. Biot’s poroelastic effects associated with stiff porosity and global flows are also fully included in the model. Comparisons with several squirt-flow models show good agreement in predicting wave attenuation to approximately 1 kHz frequencies. The squirt-flow viscosity for sandstone is estimated in the range of [Formula: see text], which is close to field observations. Because of its origins in rigorous mechanics, the model can be used to describe any wavelike and transient deformations of heterogeneous porous media or finite bodies encountered in many field and laboratory experiments. The model also leads to new numerical algorithms for wavefield modeling, which are illustrated by 1D finite-difference waveform modeling.

Effect of linear bubble vibration on wave propagation in unsaturated porous medium containing air bubbles

Biot model has widely been used in geophysics, petroleum engineering, civil engineering, and ocean engineering since it was presented, and thus the research on the wave propagation in saturated porous medium has made much progress. However, fully saturated porous medium is rarely found in nature. Almost all the rocks or soils contain two kinds of fluids, such as gas and petroleum. Many researches have been done on the wave propagation in unsaturated porous medium. As is well known, a small volume of gas bubbles existing in a liquid can greatly change the velocity and attenuation of acoustic wave in the liquid. Evidences are beginning to be accumulated that the velocity and attenuation of acoustic wave in a saturated marine sediment can be affected by the gas bubbles existing in the saturated liquid. To investigate the sound propagation in a porous medium when the pore water contains a small number of air bubbles, in this paper we integrate the volume vibrations of bubbles in pore water into the continuity equation of pore-fluid filtration in porous medium based on Biot theory, so as to obtain the continuity equation of pore-fluid filtration with bubble volume vibration. On this basis, according to the relationship between the instantaneous radius of bubble and the background pressure of the medium under the linear vibration of bubble, as well as the equations of motion of the fluid medium and porous medium, a new displacement vector wave equation of porous medium under the influence of bubble is derived, which establishes the model for the sound velocity dispersion and attenuation prediction under the unsaturated porous medium. The presence of air bubbles increases the compressibility of pore fluid, which leads to the decrease in the sound velocity of the bubbly saturated porous medium. When the wave frequency equals the resonance frequency of the bubbles, the bubbles in pore water will produce resonance; the medium will present high dispersion and the velocity can greatly exceed the gas-free velocity. However, these have not been measured in field data. The absorption cross section of the air bubble can reach a maximum value, which leads to the maximum attenuation of the porous medium. It should be noted that the attenuation coefficient calculated with this model is related to the damping of the bubble motion due to radiation, thermal and internal friction, and the dissipation of the relative motion between the pore water and porous solid frame. The obtained numerical analysis is consistent with the above conclusion, which indicates that the volume concentration, the bubble size and the excitation frequency of the sound field are important parameters affecting the sound wave propagation in the saturated porous medium containing few bubbles.

Application of Metal Organic Frameworks in Catalytic Organic Reactions

Metal organic frameworks (MOFs) as a new type of organic/inorganic hybrid materials have attracted great focus of scientists in almost twenty years. It is composed of organic ligands and inorganic metal units and generally has a varied topological structure and unique physical/chemical properties. Due to its porous frame structure, large specific surface area and great variety, MOFs are widely used in functional materials, gas adsorption, drug sustained release, catalysis and organic synthesis. It can choose different ligands and metal ions, or change the strategy of synthesis to adjust the size, shape and structure of porous structure. The different ligands can determine the different structure and then affect the properties of MOFs. In this review, the preparation of particular functional MOFs structure and the application of various MOFs in organic synthesis and catalytic organic reactions are reviewed in detail. The summary and prospects about MOFs catalyzed organic reactions and the applications are proposed.

An Experimental Study of Auricular Reconstruction Using a Thin Porous Silastic Frame Assisted by Tissue Expansion: An Animal Study.

In the 1960s, the silastic ear frame was used for auricular reconstruction. Most surgeons abandoned the use of the silastic ear frame in the 1980s because of the high incidence of exposure. In this study, we introduce the computer-aided design and manufacture of a thin, porous silastic auricle frame and investigate the possibility of auricular reconstruction using this frame assisted by tissue expansion. An adult male with average sized, normal ears was selected. A spiral CT scan was performed to obtain primitive data on his external ear. Mimics-8.1 and Geomagic studio-12 were used for 3D reconstruction and image processing. A thin, porous silastic auricle frame 1.4 mm in thickness was manufactured. A 50 ml kidney-shaped tissue expander was implanted between the panniculus carnosus and the deep fascia through an incision on the back of each of 10 New Zealand white rabbits. Each week the expander was inflated with 10 ml saline to a total of 160 m1. Maintenance of the expansion lasted for a month. The expander was then removed, and the silastic auricle frame was inserted into the pocket. The reconstructed ears were observed for 6 months postoperatively. The reconstructed ears remained soft and flexible, with no deformation, contracture, or extrusion observed 6 months postoperatively. The scaphoid fossa, triangular fossa, cavum, helix, and antihelix remained defined. The silastic frame, 1.4 mm in thickness manufactured by computer-aided design, stood up to the contraction of the overlying expanded flap. It is possible to be used for auricular reconstruction assisted by tissue expansion.

Numerical investigation of thermo-magneto-solutal flow of ferrocolloid through ordered and disordered permeable membranes

We explore the mechanism of ferroparticle transfer in porous structures in the conditions of simultaneous action of the thermal gradient and the magnetic field. We show that when a ferrocolloid saturated porous matrix is placed in a homogeneous magnetic field the grains of the porous frame notably distort the uniformity of the internal field by creating sharp gradients in the vicinity of the interface. On the other hand, the application of the temperature gradient creates an imbalance of the ferroparticle concentration in the bulk of the porous structure due to colloidal thermophoresis. The combination of the imbalance of concentration of the magnetic nanoparticles and the internal gradients of the magnetic field creates a magnetic force and convective flow of solution through the porous structure. We report the results of the pore-scale numerical simulations of the ferrocolloid thermo-magneto-solutal flow in geometrically simple ordered and disordered permeable structures and membranes with different porosity.