Pore Structure Morphology Research Articles

The excellent performance of nitrogen-doped porous carbon nanowires modified activated carbon as air cathode catalyst for microbial fuel cells

Nitrogen-doped porous carbon nanowires with polypyrrole as precursor are synthesized by modified oxidation template assembly method. The nitrogen-doped porous carbon nanowires air cathode microbial fuel cells present a maximum power density of 1641.7 ± 0.7 mW m−2, a significant exchange current density of 19.97 × 10−4 A cm−2 and an outstanding open circuit voltage of 0.303 V, which are all higher than the control. Nitrogen-doped porous carbon nanowires modified activated carbon catalyzes oxygen reduction reaction via a four-electron reaction with an electron transfer number of 3.89, which can be comparable with Pt-based catalyst. It is testified that the nitrogen-doped porous carbon nanowires are featured with the structure and morphology of surface porous amorphous nanocarbon structure doped with large content of nitrogen. The incorporation of nitrogen, intertwined hollow nanowires, and the porous three-dimensional network configuration make an outstanding contribution to the oxygen reduction reaction. Nitrogen-doped porous carbon nanowires are expected to be a new catalyst to improve the performance of the microbial fuel cells.

Porous ZnO cubes derived from metal–organic frameworks with excellent sensing performance triethylamine

Recently, the metal organic frameworks (MOFs) structure is concerned by its unique porous structure and regular morphology. In this paper, ZnO has been prepared by calcining MOF-5 precursors which obtained via a solvothermal method. For a better comparison, the reaction time needs to be appropriately changed to control the sizes of samples. The obtained samples were analyzed for composition and morphology by a series of characterization methods, and the results showed that particle size of MOF-5 precursors increased with reaction time. The ZnO particles formed after calcination are composed of crystal grains of 20–30 nm and thus have a porous structure. Gas-sensitive performance tests show that the sensor based on MOF-5-derived ZnO has good gas sensitivity. Among them, the responsiveness of MOF-5-derived ZnO prepared by solvothermal reaction for 4 h was the highest at 300 °C, and the response value to 100 ppm triethylamine (TEA) was 120.6. In addition, MOF-5-derived ZnO has better selectivity and repeatability than ZnO which is prepared using other methods.

Effect of UV irradiation and diffuse plasma on surface properties of micro-arc calcium phosphate coatings

The influence of UV irradiation or plasma of runaway electron preionized diffuse discharge (REP DD) post-modification on the surface properties of the calcium phosphate (CaP) coatings formed by the micro-arc oxidation (MAO) method was investigated. The formed MAO-coatings had porous structure and rough surface morphology with incorporation of spheroidal structural elements with inner pores. It was showed that the UV irradiation or REP DD post-treatment of the MAO-coatings led to the decrease of the coating contact angels with water from 20 to 0 or to 7 degrees, respectively. However, the free surface energy of the coatings did not change after post-treatments and equalled to 74±1 mJ·m−2. The polar component of the free surface energy of the all types of the coatings exceeded almost 5–6 times the dispersion component that indicated the presence of strong polar bonds on the coating surface, e. g. OH- and PO4-groups.

Development and Applications of MOFs Derivative One-Dimensional Nanofibers via Electrospinning: A Mini-Review.

Metal organic frameworks (MOFs) have been exploited for various applications in science and engineering due to the possibility of forming different mesoscopic frameworks and pore structures. To date, further development of MOFs for practical applications in areas such as energy storage and conversion have encountered tremendous challenge owing to the unitary porous structure (almost filled entirely with micropores) and conventional morphology (e.g., sphere, polyhedron, and rod shape). More recently, one-dimensional (1D) MOFs/nanofibers composites emerged as a new molecular system with highly engineered novel structures for tailored applications. In this mini-review, the recent progress in the development of MOFs-based 1D nanofibers via electrospinning will be elaborated. In particular, the promising applications and underlying molecular mechanism of electrospun MOF-derived carbon nanofibers are primarily focused and analyzed here. This review is instrumental in providing certain guiding principles for the preparation and structural analysis of MOFs/electrospun nanofibers (M-NFs) composites and electrospun MOF-derived nanomaterials.

A three-dimensional pore-scale lattice Boltzmann model for investigating the supergravity effects on charging process

Latent heat thermal energy storage with metal foams has been considered as a promising candidate for thermal management in aerospace systems. Thus, there is good cause to deeply explore the heat transfer mechanisms of phase change material (PCM) melting with metal foams. In order to get close to the real situation, a three-dimensional, pore-scale lattice Boltzmann model is explored based on a three-dimensional reconstructed porous structure morphology taken from experimentally observed in this paper, to characterize the distribution of flow and temperature fields during charging of porous PCM. The gravity effects on heat transfer performance are documented by comparison of charging at different accelerates. During the charging process, nonuniform temperature distributions and inclined melting interfaces are presented at the latter stages, caused by the interplay of primary natural convection in the melting direction and secondary convection in the transverse direction. More inclined melting interfaces are observed as gravitational acceleration increases, yielding faster PCM melting in the upper region while melting in the bottom region almost terminated. This implies that natural convection gradually dominates heat transfer and leads to the temperature nonuniformity. Similar shape characteristics of melting interface are observed in two-dimensional model, while there is an apparent difference of the melting fraction, showing it gradually growing from 4.1% to 8.6% with increasing gravitational acceleration. These results indicate that secondary convection effect neglected in the two-dimensional model, leading to a significant error in the prediction of heat transfer performance.

An Experimental Investigation of Humidity Effect on fabrication of Green Ceramic Membrane Prepared Via Dry Phase Inversion

Ceramic membranes are gaining a market demand nowadays due to its characterization and performance. However, in the preparation of ceramic membrane for water and wastewater separation, the processes involved are taking a higher cost. In this work, ceramic membranes were prepared via phase inversion within controlled humidity by using different composition of low cost and green ceramic material, kaolin. The preparation of ceramic membranes was conducted via phase inversion in high humidity; i) 3°C and, ii) room temperature. In this paper, we report on the high humidity affected the viscosity of membrane suspension. Thus, the viscosity of ceramic suspension was giving integration towards membrane characterization and performance. A dense membrane structure was observed when the ceramic membranes were prepared in high humidity and kaolin composition. The morphology of overall, porous and dense structure of ceramic membranes was characterized by field emission scanning electron microscope (FESEM) at x50, x500 and x5000 magnification respectively.

Porous Open-Сell UHMWPE: Experimental Study of Structure and Mechanical Properties

Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that is widely used as bulk material in reconstructive surgery for structural replacements of bone and cartilage. Porous UHMWPE can be used for trabecular bone tissue replacement, and it can be used in living cell studies as bioinert 3D substrate permeable to physiological fluids. It is important to develop techniques to govern the morphology of open-cell porous UHMWPE structures (pore size, shape, and connectivity), since this allows control over proliferation and differentiation in living cell populations. We report experimental results on the mechanical behavior of porous open-cell UHMWPE obtained through sacrificial removal (desalination) of hot-molded UHMWPE-NaCl powder mixtures with pore sizes in the range 75 µm to 500 µm. The structures were characterized using SEM and mechanically tested under static compression and dynamic mechanical analysis (DMA), bending, and tensile tests. Apparent elastic modulus and complex modulus were in the range of 1.2 to 2.5 MPa showing a weak dependence on cell size. Densification under compression caused the apparent elastic modulus to increase to 130 MPa.

A universal strategy towards porous carbons with ultrahigh specific surface area for high-performance symmetric supercapacitor applications

Porous carbons with ultrahigh specific surface area (> 3000 m2/g) prepared at low KOH/char ratio (e.g. less than 0.5) is of great importance for their future applications, yet this remains a significant challenge due to the uneven dispersion of the activating agent within carbon source. Herein, a universal combination strategy (solid-state reaction at room temperature followed by chemical activation) to prepare ultrahigh surface area porous carbons has been developed. The specific surface area can reach to 3775 m2/g even at a very low KOH/char ratio (0.19), and the morphologies, specific surface and pore size distributions of the products can be simply tuned by the KOH/char ratios. We found the solid-state reaction at room temperature prior to chemical activation is an efficient way to achieve the even dispersion of the activating agent and thus improve the utilization of KOH greatly. As a typical example, the as-obtained EDTA-3 K not only have an ultrahigh specific surface area up to 3614 m2/g, but also deliver a large total pore volume of 2.09 m3/g. Benefited from the ultrahigh specific surface area, hierarchically porous structure and unique morphology, the EDTA-3 K based supercapacitor exhibits excellent capacitive performance in both KOH and Li2SO4 electrolyte. Hence, this study not only exploits a new approach for the synthesis of hierarchically porous carbon materials with ultrahigh specific surface area for electrochemical energy storage applications, but also provides a universal combination strategy to improve the utilization ratio of activating reagent for the producing of porous carbons.

Convection-diffusion-reaction of CO2-enriched brine in porous media: A pore-scale study

CO2-enriched brine interaction with reservoir minerals and the subsequent mineral trapping of CO2 alter the morphology of pore structure. Such changes in the pore space modify the storage capacity of reservoirs and increase the long-term security of CO2 storage. The extent of pore space modification depends on the relative weight of advection, diffusion and reaction mechanisms. We present a general framework for a direct simulation of reactive transport in digitized reservoir rock samples based on a pore-scale modeling in two-dimensional (2D) and three-dimensional (3D) pore-throat networks. We examine the impact of transport properties such as Péclet (Pe) and Damköhler (Da) numbers, on the petrophysical properties and dissolution of mineral in pore space. We implement marker-based watershed segmentation to extract pore networks of 3D micro-CT (Computerized Tomography) scan images. The extracted network is used to simulate the reactive solute transport and dissolution on real rock samples. This approach enables us to study reaction of CO2-enriched brine with reservoir rock samples, which is vital in predicting long-term security of CO2 storage. We implement our approach to study CO2 injection in samples from the Cranfield site, Mississippi, U.S.A. We show that for small PeDa numbers, the concentration and dissolution patterns are more uniform.

Supercritical CO2-water-shale interactions and their effects on element mobilization and shale pore structure during stimulation

There are many advantages to using supercritical carbon dioxide (ScCO2) fracturing technology to exploit shale gas reservoirs in China, including minimal damage to the environment or formation, and displacing methane (CH4) in the adsorbed state. When ScCO2 enters fractures in the formation, ScCO2-water-shale interactions may affect the physicochemical properties of shale. In this study, a high-pressure reaction system was adopted to simulate ScCO2-water-shale interactions under ScCO2 stimulation conditions. The element mobilization and pore structure before and after the reaction were measured using ICP-MS, XRF. The results show that the major elements, including Ca, Mg, Na, K, and Al, exhibit varying degrees of mobilization after the interactions because of dissolution of carbonate and silicate minerals in shale samples. Compared with the major elements, trace elements have a lower mobility, quantified as <13.97%. The specific surface areas and pore volumes of two shale samples increase at different degrees after the reaction. The interactions have a more significant influence on the micropores. In addition, fractal features of the shale pore structure were analyzed. The fractal dimensions of the shale samples increase after the reaction, indicating that pore surface roughness increases, and pore structure morphology gradually transforms from regular to complex.

Influence of Hydrogen Peroxide on the Photoanodization of n-Si in the Breakdown Mode

The electrochemical etching of n-Si (100) in an electrolyte composed of 4% HF solution in 30% hydrogen peroxide is experimentally studied at a voltage exceeding the breakdown voltage. The effect of the illuminance of the wafer back side on the porous-structure morphology and such parameters as porosity, effective valence, and pore growth rate are examined. The data obtained are compared with those for structures subjected to photoanodization in an aqueous electrolyte at the same HF concentration. It is found that the presence of hydrogen peroxide strongly changes the morphology of macropores, makes their diameter smaller, and raises by a factor of ~2 the rate of growth deeper into the substrate. In the presence of H2O2, there appear inclined secondary pores oriented at an angle of 15°–35° to the main channel axis and a number of breakthrough mesopores propagating in the 〈100〉 directions in the plane parallel to the sample surface. The effective valence of the electrochemical dissolution of silicon in the HF:H2O2 electrolyte at a low illumination level is close to unity and grows with increasing light intensity, always being smaller than 2.

Feasibility Study on the Design and Synthesis of Functional Porous Organic Polymers with Tunable Pore Structure as Metallocene Catalyst Supports.

Porous organic polymers (POPs) are highly versatile materials that find applications in adsorption, separation, and catalysis. Herein, a feasibility study on the design and synthesis of POP supports with a tunable pore structure and high ethylene-polymerization activity was conducted by the selection of functional comonomers and template agents, and control of cross-linking degree of their frameworks. Functionalized POPs with a tunable pore structure were designed and synthesized by a dispersion polymerization strategy. The functional comonomers incorporated in the poly(divinylbenzene) (PDVB)-based matrix played a significant role in the porous structure and particle morphology of the prepared polymers, and a specific surface area (SSA) of 10–450 m2/g, pore volume (PV) of 0.05–0.5 cm3/g, bulk density with a range of 0.02–0.40 g/cm3 were obtained by the varied functional comonomers. Besides the important factors of thermodynamic compatibility of the selected solvent system, other factors that could be used to tune the pore structure and morphology of the POP particles have been also investigated. The Fe3O4 nanoaggregates as a template agent could help improve the porous structure and bulk density of the prepared POPs, and the highly cross-linking networks can dramatically increase the porous fabric of the prepared POPs. As for the immobilized metallocene catalysts, the pore structure of the prepared POPs had a significant influence on the loading amount of the Zr and Al of the active sites, and the typically highly porous structure of the POPs would contribute the immobilization of the active species. High ethylene-polymerization activity of 8033 kg PE/mol Zr h bar was achieved on the POPs-supported catalysts, especially when high Al/Zr ratios on the catalysts were obtained. The performance of the immobilized metallocene catalysts was highly related to the pore structure and functional group on the POP frameworks.

High Capacity Electrospun MgFe2O4–C Composite Nanofibers as an Anode Material for Lithium Ion Batteries

AbstractMgFe2O4‐C composite nanofibers were prepared via electrospinning technique followed by carbonization at 600 °C. Thermogravimetric‐differential thermal analysis (TG‐DTA) results showed ignition, decomposition and carbonization temperatures of the as‐grown fibers. Formation of the nanocrystalline phase of the MgFe2O4 over the amorphous phase of the carbon fibers sample was confirmed from the analysis of the measured XRD results. FE‐SEM images of the as‐spun and calcined fibers sample showed that the formation of one dimensional (1‐D) MgFe2O4‐C composite nanofibers and the formed 1‐D nanofibers were well interconnected with high porous structured morphology. The electrochemical properties of the MgFe2O4‐C composite nanofibers sample were tested as an anode material for lithium‐ion battery. Lithium‐ion battery made up of the newly developed MgFe2O4‐C composite nanofibers sample, used as an anode material, showed discharge capacity of 575 mAh g−1 at a current density of 100 mA g−1 after 20th cycles. Further, the discharge capacity of the lithium‐ion battery also measured at a high current density of 1 A g−1 and it was found to be 433 mAh g−1 even after 85 cycles. Also, the lithium‐ion battery showed exceptional reversible capacity with the coulombic efficiency of 99.6% even after 85 cycles at a high current density of 1 A g−1. Hence the electrochemical properties suggest that the newly developed MgFe2O4‐C composite nanofibers can be used as high capacity anode materials for lithium‐ion batteries.

Porous surface structures in biomedical Co-Cr-Mo alloy prepared by local dealloying in a metallic melt

A novel method for preparing nano/submicron porous surfaces in biomedical Co-Cr-Mo alloy is presented, which involves local dealloying in a pure Zn melt at 500–800 °C and selective removal of Zn-rich phase formed in the dealloying products. First, reaction layers composed of Zn-rich and Zn-lean phases were formed by partially dealloying of Co from the alloy, which thickness ranges from 6 μm to 90 μm. Then, various nano/submicron porous surface layers containing a small amount of Zn were introduced by selective removing the Zn-rich phase in 1 M HCl aqueous solution. The morphologies of either reaction layers or porous structures were significantly affected by dealloying temperature. The elements of Co, Cr, Mo and Zn in porous surface layers exist predominantly in their metallic states.

Cirsium Japonicum DC ingredients-loaded silk fibroin nanofibrous matrices with excellent hemostatic activity

Regenerated Silk fibroin (SF) from Bombyxmori has emerged in recent years as candidates for wound dressing due to its excellent biocompatibility and low inflammatory response. Cirsium Japonicum DC (CJDC) is a kind of Chinese herb medicine with evident hemostatic and anti-inflammatory analgesic effect. In this study, we aimed to manufacture a novel green electrospun SF nanofibrous matrice loading ingredients extracted from CJDC which should be useful in hemostasis as well as wound healing. FTIR spectra showed that the CJDC extracts were successfully loaded into the SF nanofibrous matrices, which appeared morphology of porous mesh structure. The as-prepared matrices inherited the good skin affinity and hemocompatibility of SF, as indicated by the skin cell viability assay and hemolysis test in vitro. Furthermore, according to the results of plasma recalcification profiles test, the incorporation of CJDC extracts significantly improved the hemostatic performance of SF nanofibrous matrices. Interestingly, the SF nanofibrous matrices loading CJDC components extracted by petroleum ether (peE-CJDC@SF) showed the best antihemorrhagic activity among the tested samples (with astringent time of 9.5 min), even better than some clinically used products such as absorbable gelatin sponge (AGS) and aseptic hemostyptic gauze (AHG). Our findings suggested the peE-CJDC@SF nanofibrous matrices could be a promising candidate using as hemostatic material and wound dressing.

Polypropylene-Based Porous Membranes: Influence of Polymer Composition, Extrusion Draw Ratio and Uniaxial Strain.

Several commercial grades of homo-polymer and its blends were selected to prepare microporous membranes through melt extrusion-annealing-uniaxial stretching technique (MEAUS). Branched or very fluid polypropylene was employed to modify the polymeric composition. In some blends, micro-sized calcium carbonate was added. We analysed the influence of sample composition, extrusion draw ratio, and we performed a deep study concerning the uniaxial strain rate, using in some cases extreme strain rates and strain extents. The crystalline features were studied by Differential Scanning Calorimetry (DSC), and the morphology of porous structure was analyzed through Scanning Electron Microscopy (SEM). Thermal stability and thermomechanical performance was measured by thermogravimetric analysis (TGA) and dynamic-mechanical-thermal (DTMA) study. A close relationship was found between crystalline characteristics, porous morphology and the trends registered for permeability.

CeO2-CuO/Cu2O/Cu monolithic catalysts with three-kind morphologies Cu2O layers for preferential CO oxidation

The supports of copper slices with three-kind morphologies Cu2O layers were prepared by the hydrothermal method. The Cu2O layers are rod-like structure, three-dimensional reticular and porous morphology as well as flower-like morphology, respectively. The CeO2-CuO/Cu2O/Cu monolithic catalysts present porous and network structure or foam morphology after loading CeO2 and CuO. Cu and Ce elements are uniformly dispersed onto the support surface. It is found that the monolithic catalyst with flower-like Cu2O layer displays better low-temperature activity because of highly-dispersed CuO and high Olatt concentration. The monolithic catalysts with rod-like or reticular-morphology Cu2O layers present high-temperature activity due to larger CuO crystallite sizes and good synergistic effect at copper-ceria interfacial sites. The as-prepared CeO2-CuO/Cu2O/Cu monolithic catalysts show good performance in the CO-PROX reaction. The generation of Cu2O layers with three-kind morphologies is beneficial to the loading and dispersion of copper oxides and ceria.

Three-dimensional macro/mesoporosity developments in polydimethylsiloxane

ABSTRACTMacro/mesoporous polydimethylsiloxanes (PDMS) were prepared with the purpose of vascular grafts. Oligoester-containing semi-interpenetrating polymer networks (semi-IPNs) can be used as precursors for generation of networks with tunable pore sizes. Novel poly(methyl methacrylate)/PDMS semi-IPNs were prepared by varying structural parameters. Extraction of uncrosslinked oligoester subchains from semi-IPNs was investigated. To tailor the morphology of porous structure, influence of some factors including porogen type, different polymerization conditions, monomer type, and concentration, crosslinking agent concentration were studied. PDMS networks were examined by field emission scanning electron microscopy. A uniform porous structure with interconnected pores was detected in horizontal and vertical cross sections of PDMS.

Ultra-high mechanical properties of porous composites based on regenerated cellulose and cross-linked poly(ethylene glycol)

The ultra-high mechanical, biocompatible and biodegradable porous regenerated cellulose/poly(ethylene glycol) (RC/PEG) composites with double network structure were fabricated via an simple method to dissolve cellulose followed by UV irradiation. The porous structure of RC/PEG was sensitively altered by PEG contents, which led to the porous structure morphology transition from 3D fibrillar network to close-grained sheet-like-network with the loading of cross-linked PEG. The porous RC/PEG showed excellent mechanical properties, i.e., the compressive strength can reach 33 times higher than that of neat RC (0.07MPa) at the compressive strain of 30%. Porous RC/PEG also displayed outstanding properties with openly porous structure and structural stabilization. Besides, porous RC/PEG exhibited good water absorbency, which the water absorbency ratio at equilibrium state was 83% higher than that of porous RC. This work provides an environmentally friendly and simple pathway to prepare non-toxic and biocompatible porous regenerated cellulose-based composites with high strength, structural stabilization and good water absorbency, which could be useful for packaging, biomedical applications, sewage purification, etc.

Synthesis of ZnO thin film by sol-gel spin coating technique for H2S gas sensing application

In this present work, zinc oxide (ZnO) thin film synthesized by a simple sol-gel spin coating technique. The structural, morphology, compositional, microstructural, optical, electrical and gas sensing properties of the film were studied by using XRD, FESEM, EDS, XPS, HRTEM, Raman, FTIR and UV–vis techniques. The ZnO thin film shows hexagonal wurtzite structure with a porous structured morphology. Gas sensing performance of synthesized ZnO thin film was tested initially for H2S gas at different operating temperatures as well as concentrations. The maximum gas response is achieved towards H2S gas at 300°C operating temperature, at 100ppm gas concentration as compared to other gases like CH3OH, Cl2, NH3, LPG, CH3COCH3, and C2H5OH with a good stability.