Homogeneous Microporous Structures Research Articles

Evaluation of asymmetric poly(vinylidene fluoride)-coated polyimide separator with three-dimensionally homogeneous microporous structure for high-safety lithium-ion battery

Safety hazards associated with separators in lithium-ion batteries are more pronounced in light of the significant improvement of energy density of batteries, hindering their wide application. In this research, asymmetric poly (vinylidene fluoride) (PVDF)-coated polyimide separators with three-dimensionally homogeneous microporous (3DHM API/PVDF) structure are prepared, in which a PVDF layer with a thickness of 6 μm on one side of polyimide. Polyimide, as the base film, has a high heat-resistant temperature which ensures that as-prepared separators will not be shrunk and burned. The coated PVDF layer imparts 3DHM API/PVDF with thermal shutdown function at 175 °C due to the melting of PVDF. The temperature difference between the shutdown and meltdown temperature is over 100 °C, ensuring that the LIB assembled with 3DHM API/PVDF is safe for use. Moreover, the interconnected microporous structure of the separator facilitates the formation of 3D Li+ transport pathways and uniformity of lithium deposition, suppressing lithium dendrite growth. The coin cells assembled by 3DHM API/PVDF exhibit similar electrochemical performance to that of a commercial polypropylene separator at room temperature. Therefore, the novel 3DHM API/PVDF separator may be a promising candidate for a significantly safer LIB.

Chondroitin sulfate and caseinophosphopeptides doped polyurethane-based highly porous 3D scaffolds for tendon-to-bone regeneration

Tendon disorders are common injuries, which can be greatly debilitating as they are often accompanied by great pain and inflammation. Moreover, several problems are also related to the laceration of the tendon-to-bone interface (TBI), a specific region subjected to great mechanical stresses. The techniques used nowadays for the treatment of tendon and TBI injuries often involve surgery. However, one critical aspect of this procedure involves the elevated risk of fail due to the tissues weakening and the postoperative alterations of the normal joint mechanics. Synthetic polymers, such as thermoplastic polyurethane, are of special interest in the tissue engineering field as they allow the production of scaffolds with tunable elastic and mechanical properties, that could guarantee an effective support during the new tissue formation. Based on these premises, the aim of this work was the design and the development of highly porous 3D scaffolds based on thermoplastic polyurethane, and doped with chondroitin sulfate and caseinophosphopeptides, able to mimic the structural, biomechanical, and biochemical functions of the TBI. The obtained scaffolds were characterized by a homogeneous microporous structure, and by a porosity optimal for cell nutrition and migration. They were also characterized by remarkable mechanical properties, reaching values comparable to the ones of the native tendons. The scaffolds promoted the tenocyte adhesion and proliferation when caseinophosphopetides and chondroitin sulfate are present in the 3D structure. In particular, caseinophosphopeptides’ optimal concentration for cell proliferation resulted 2.4 mg/mL. Finally, the systems evaluation in vivo demonstrated the scaffolds’ safety, since they did not cause any inflammatory effect nor foreign body response, representing interesting platforms for the regeneration of injured TBI.

A dual purpose aluminum-based metal organic framework for the removal of chloramphenicol from wastewater

The presence of antibiotics in the aquatic environment can cause significant environmental and human health problems even at trace concentrations. Conventional treatment systems alone are ineffective in removing these resistant antibiotics. To address this problem, oxidation and adsorption techniques were used to explore the removal of recalcitrant antibiotic chloramphenicol (CAP). An aluminum-based metal-organic framework (Al-MIL) with high surface area and extended porosity, was prepared and used both as adsorbent and catalyst for the oxidation of CAP. Characterization of the Al-MIL revealed a large surface area of 1137 m2 g−1, a homogeneous microporous structure, good crystallinity, and particle size in the range of 200–400 nm. Adsorption of CAP on Al-MIL achieved equilibrium after 1 h, reaching a maximum adsorption capacity of 96.1 mg g−1 at the optimum pH value of 5.3. The combination of adsorption and oxidation did not improve the % TOC reduction considerably, indicating an antagonistic rather than synergistic effect between the two processes. Oxidation alone in the presence of persulfate, achieved a % TOC reduction of 71% after 2 h, compared to 56% achieved by adsorption alone at the same duration. The optimum persulfate concentration was determined as 2.5 mM. The Al-MIL structure did not demonstrate any substantial deterioriation after six repeated runs, according to the reusability experiments.

Biologically enhanced starch bio-ink for promoting 3D cell growth.

The excellent rheological property has legitimated the suitability of starch hydrogel for extrusion-based 3D printing. However, the inability to promote cell attachment and migration has precluded the non-modified starch hydrogel from direct applications in the biomedical field. Herein, we develop a novel 3D printable nanocomposite starch hydrogel with highly enhanced biocompatibility for promoting 3D cell growth, by formulating with gelatin nanoparticles and collagen. The rheological evaluation reveals the shear-thinning and thixotropic properties of the starch-based hydrogel, as well as the combinatorial effect of collagen and gelatin nanoparticles on maintaining the printability and 3D shape fidelity. The homogeneous microporous structure with abundant collagen fibers and gelatin nanoparticles interlaced and supplies rich attachment sites for cell growth. Corroborated by the cell metabolic activity study, the multiplied proliferation rate of cells on the 3D printed nanocomposite starch hydrogel scaffold confirms the remarkable enhancement of biological function of developed starch hydrogel. Hence, the developed nanocomposite starch hydrogel serves as a highly desirable bio-ink for advancing 3D tissue engineering.

Peculiarities of Thermodynamic Behaviors of Xenon Adsorption on the Activated Carbon Prepared from Silicon Carbide.

An activated carbon prepared from silicon carbide by thermochemical synthesis and designated as SiC-AC was studied as an adsorbent for xenon. The examination of textural properties of the SiC-AC adsorbent by nitrogen vapor adsorption measurements at 77 K, powder X-ray diffraction, and scanning electron microscopy revealed a relatively homogeneous microporous structure, a low content of heteroatoms, and an absence of evident transport macropores. The study of xenon adsorption and adsorption-induced deformation of the Si-AC adsorbent over the temperature range of 178 to 393 K and pressures up to 6 MPa disclosed the contraction of the material up to −0.01%, followed by its expansion up to 0.49%. The data on temperature-induced deformation of Si-AC measured within the 260 to 575 K range was approximated by a linear function with a thermal expansion factor of (3 ± 0.15) × 10−6 K−1. These findings of the SiC-AC non-inertness taken together with the non-ideality of an equilibrium xenon gaseous phase allowed us to make accurate calculations of the differential isosteric heats of adsorption, entropy, enthalpy, and heat capacity of the Xe/SiC-AC adsorption system from the experimental adsorption data over the temperature range from 178 to 393 K and pressures up to 6 MPa. The variations in the thermodynamic state functions of the Xe/SiC-AC adsorption system with temperature and amount of adsorbed Xe were attributed to the transitions in the state of the adsorbate in the micropores of SiC-AC from the bound state near the high-energy adsorption sites to the molecular associates.

Mechanical modification of bacterial cellulose hydrogel under biaxial cyclic tension

This study presents a novel and simple method to modify the microstructure of bacterial cellulose (BC) hydrogel. BC specimens were produced using Gluconacetobacterxylinus ATCC 53582, then cut into cross-shape specimens and subjected to biaxial cyclic tension in a displacement-control mode. Microstructural changes in the tested specimens were recorded during a biaxial deformation process. The effect of biaxial load on microstructure of BC hydrogel was investigated to understand deformation and fracture mechanisms of a BC fibrous network. The obtained knowledge reveals the fundamental principles of microstructural modifications, which could enhance biological performance of such hydrogels. The mechanically re-constructed BC specimens demonstrated a relatively homogeneous micro-porous structure with an average pore size of 100 μm.

Synthesize polymeric manganese porphyrin with CuI/N,N-dimethyl glycine acid catalytic system and high-efficiency aerobic catalytic oxidation of cyclic ketones

A series of conjugated metalloporphyrin polymers (MPP-AMnPs) were synthesized by using inexpensive, environmentally friendly and high-efficiency CuI/N,N-dimethyl glycine as catalytic system, and 5,10,15,20-mesotetra(4-aminophenyl) porphyrin manganese and p-dibromobenzene as building blocks. Scanning electron microscopy, N2 adsorption-desorption isotherms and scanning electron microscopy indicated that the polymers had large surface areas and homogeneous microporous structures. Thermogravimetric analysis showed that the polymers had remarkable thermostability. The catalytic performance of MPP-AMnP was tested by oxidizing cyclic ketones with dioxygen as oxidant. The conversion was high in a mild environment in l,2-dichloroethane solvent at 60 °C. Moreover, MPP-AMnP remained stable in the reaction process and highly catalytically active after ten successive recycles.

Modification on the Morphology of PU Membranes by CNT Fillers

Phase inversion method is an important strategy for the preparation of polyurethane microporous membranes. In this paper, the blends of polyurethane/carbon nanotubes were prepared by solution blending method, and the influence of carbon nanotubes on the phase inversion behaviors of polyurethane microporous membranes was studied. The results show that with the addition of carbon nanotubes, the phase separation process was inhabited, and the formation of large pores was reduced. As a result, the homogeneous microporous structure was achieved.

Selective dissolution of amorphous Zr–Cu–Ni–Al alloys

Amorphous Zr–Ni–Cu–Al ribbons were dealloyed by electrochemical selective dissolution. As a result three-dimensional microporous structures were obtained at different conditions (electrochemical potential, temperature, dissolution time). The smallest porous were obtained at low temperatures and potentials. To study the effect of precursor microstructure on the porous structure the as-cast alloys were annealed at two different temperatures – above Tg to cause structural relaxation of the amorphous material and at temperature above Tx to produce crystalline alloy. It is shown that only the entirely amorphous (as-cast and low-temperature annealed) alloys form homogeneous microporous structures as a result of the selective dissolution.

Dense carbon monoliths for supercapacitors with outstanding volumetric capacitances

A commercially available dense carbon monolith (CM) and four carbon monoliths obtained from it have been studied as electrochemical capacitor electrodes in a two-electrode cell. CM has: (i) very high density (1.17gcm−3), (ii) high electrical conductivity (9.3Scm−1), (iii) well-compacted and interconnected carbon spheres, (iv) homogeneous microporous structure and (v) apparent BET surface area of 957m2g−1. It presents interesting electrochemical behaviors (e.g., excellent gravimetric capacitance and outstanding volumetric capacitance). The textural characteristics of CM (porosity and surface chemistry) have been modified by means of different treatments. The electrochemical performances of the starting and treated monoliths have been analyzed as a function of their porous textures and surface chemistry, both on gravimetric and volumetric basis. The monoliths present high specific and volumetric capacitances (292Fg−1 and 342Fcm−3), high energy densities (38Whkg−1 and 44WhL−1), and high power densities (176Wkg−1 and 183WL−1). The specific and volumetric capacitances, especially the volumetric capacitance, are the highest ever reported for carbon monoliths. The high values are achieved due to a suitable combination of density, electrical conductivity, porosity and oxygen surface content.

Polyacrylonitrile (PAN) membranes for ultra- and microfiltration

Polyacrylonitrile (PAN) membranes for ultra- and microfiltration were developed by GKSS. They are fabricated on a non-woven by a phase inversion process. It is shown that the formation process mainly depends on the polymer concentration of the casting solution as well as on the temperature of the precipitation bath. Therefore, different membrane morphologies can be obtained. They vary from large finger-like pores to homogeneous microporous structures. The flux of the membranes can be adjusted between 100 up to nearly 2000 l/m2h bar with high rejection. PAN membranes have good chemical stabilities and can be welded by heat or ultrasound. This makes the production of membrane envelopes possible, which are used in several filtration module types like Amafilter PM and Rochem FM. Today the membranes are commercially available and used in several applications such as water treatment, concentration of whey or protein, concentration of oil/water mixtures, etc. In these applications the membrane demonstrated high stability against chemical cleaning agents. It resists sodium hypochlorite, citric acid and weak alkaline solutions.

Sol–gel processing of silatranes

Silatrane complexes are organosilicon compounds synthesized by direct reaction of SiO 2 and trialkanolamines. Here, we explore their potential as ceramic precursors via the hydrolytic sol–gel processing method. Viscoelastic analysis is used to characterize the gelation behavior of silatranes based on triisopropanolamine, under different hydrolysis conditions. Pyrolyzed ceramic products are characterized in terms of surface area and morphology and found to have a homogeneous microporous structure with high surface areas (313–417 m 2/g). Faster hydrolysis rates lead to shorter gelation times, and smaller pore sizes in the derived ceramic.

Adsorption of vapors and gases by carbon sorbents with homogeneous microporous structures in the initial region of the adsorption isotherm

Examination of the adsorption isotherm equation derived from the theory of volume filling of micropores (TVFM) showed that the region of low pressures of experimental isotherms is not always described by this equation. A method for describing the initial region of adsorption isotherms using the parameters of TVFM was proposed.

Estimation of the porous structure of active carbons

Active carbons from apricot, plum, peach, and grape stones were prepared. The analysis of adsorption isotherms of benzene vapor showed that the active carbons obtained from fruit stones have highly homogeneous microporous structures withW0 ∼0.30 cm3 g−1,E0 ∼ 24.5 kJ mol−1, andx0 ∼ 0.42 nm, and they contain ultramicropores along with micropores.

Inhomogeneous microporous structures and adsorption properties of carbon adsorbents. 11. Adsorption properties of active carbons with homogeneous and inhomogeneous microporous structures

1. The relation of the adsorption values of standard benzene vapor at 293 K to the parameters of the Dubinin-Stokley adsorption equation was considered for the case of model microporous carbon adsorbents. 2. Active carbons with low characteristic standard-vapor adsorption energies and a wide micropore-volume size distribution are characterized by higher filling of the micropore volume at low equilibrium pressures in comparison with active carbons with homogeneous microporous structure. 3. Fillings were calculated for micropores under various adsorption conditions for estimation of the adsorption properties of active carbons and selection of adsorbents with parameters most suitable for practical use.

Novel ideas in the theory of the physical adsorption of vapors on micropore adsorbents

A general equation has been derived for the physical adsorption of vapors on adsorbents with nonhomogeneous microporous structure, in which the energy of adsorption is increased as a result of the effect of superposition of dispersion force fields of the opposite micropore walls. The equation is based on experimentally determined reciprocal dependence of the generalized dimensions of the micropores expressed as their radii of inertia and the characteristic adsorption energy. The expression of the inertia radii of micropores takes into account their geometrical sizes. The nonhomogeneity of the microporous structure is described in terms of normal distribution of the micropore volumes with respect to reciprocal values of the characteristic adsorption energies. For a homogeneous elementary micropore volume, the adsorption equation derived from the theory of volume filling of the micropores is used. The adsorption equation obtained contains three parameters: the total micropore volume, the characteristic adsorption energy at the maximum of the distribution curve and the dispersion. The equation can be used for micropores with various geometric shapes. It leads to the following consequences: If the dispersion equals zero, then the Dubinin-Radushkewich equation is obtained for homogeneous microporous structures; the Dubinin-Stoeckli equation is obtained for the model of slitlike micropores in carbonaceous adsorbents. The parameters of the equation were found to be effective quantities for increased mesopore surface areas in microporous adsorbents. We considered methods for determining the specific surface areas of mesopores; these methods are necessary for obtaining realistic parameters for the microporous structure of adsorbent.