Optimal Pore Size Distribution Research Articles

Preparation and electrochemical characteristics of electrospun water-soluble resorcinol/phenol-formaldehyde resin-based carbon nanofibers

Porous carbon nanofibers prepared by combining electrospinning and one-step activation exhibit remarkable capacitance performances due to the synergistic effect of the optimized pore size distribution, specific surface area and surface properties.

Effects of thermal activation conditions on the microstructure regulation of corncob-derived activated carbon for hydrogen storage

Activated carbons derived from corncob (CACs) were prepared by pyrolysis carbonization and KOH activation. Through modifying activation conditions, samples with large pore volume and ultrahigh BET specific surface area could be obtained. The sample achieved the highest hydrogen uptake capacity of 5.80 wt% at 40 bar and −196 °C. The as-obtained samples were characterized by N2-sorption, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, thermogravimetric analysis was also employed to investigate the activation behavior of CACs. Detailed investigation on the activation parameters reveals that moderate activation temperature and heating rate are favorable for preparing CACs with high surface area, large pore volume and optimal pore size distribution. Meanwhile, the micropore volume between 0.65 nm and 0.85 nm along with BET surface area and total pore volume has great effects on hydrogen uptake capacities. The present results indicate that CACs are the most promising materials for hydrogen storage application.

Synthesis on winged graphene nanofibers and their electrochemical capacitive performance.

Assembly techniques of graphene have attracted intense attention since their performance strongly depends on the manners in which graphene nanosheets are arranged. In this work, we demonstrate a viable process to synthesize winged graphene nanofibers (G-NFs) which could generate optimized pore size distribution by the fiber-like feature of graphene. The G-NF frameworks were achieved by processing the precursor graphene oxide nanosheets with the following procedures: microwave (MW) irradiation, salt addition, freeze-drying, and chemical reduction. The resultant framework composed of winged G-NFs with a diameter of 200-500 nm and a length of 5-20 μm. Moreover, the crimp degree of G-NFs can be rationally controlled by MW irradiation time. A formation mechanism of such winged G-NFs based on the synergistic effects from MW irradiation and solution ionic strength change has been proposed. With a practice in flexible electrode, after decorated with amorphous MnO2, the G-NF frameworks shows an enhanced specific capacitance compared to graphene nanosheets (G-NSs). This research has developed a controllable method to synthesis G-NFs, which can offer hierarchical pore structures, this kind of graphene nanostructure might enhance their performance in supercapacitor and related fields.

Electrochemical desalination of nacl solutions by electrosorption on nano-porous carbon aerogel electrodes

<div> <p>The objective of this study is to elucidate the efficiency of electrosorption on desalination of aqueous NaClsolution using nano-structured carbon aerogel electrodes. The experiments were performed in an electrosorption cell consisting of a pair of carbon aerogel sheets separated by a 0.5cm spacer. The electrosorption performance is investigated with different applied voltages and solution concentrations. It increases with increasing applied voltage, higher concentration gradient and less double-layer overlapping effect. Under the experimental conditions at the optimum applied voltage of 1.2 Volt and initial NaCl concentration 100 - 1000 mg l<sup>-1</sup>, the electrosorption capacity was found to be 5.20 - 14.22 mg NaCl/g carbon aerogel.Na<sup>+</sup> and Cl<sup>-</sup> ions are electro-absorbed at the electrical double layer without electron transfer redox reactions at anode and cathode. The good electrosorption performance of carbon aerogel electrodes might be attributed to their high specific area, high electrical conductivity, chemical inertness and optimal pore size distribution for the passage and easy movement of ions during electrosorption and electrodesorption. The process is reversible, as the electrode charge/discharge procedure can be repeated innumerable times without any significant loss of salt sorption capacity in all cycles. </p> </div> <p> </p>

Relationship between Porous and Mechanical Properties of Hydrothermally Synthesized Porous Materials from Diatomaceous Earth

Hydrothermal solidification/synthesis of diatomaceous earth based material has been carried out so as to investigate the relationship between porous and mechanical properties. Compaction pressure could make contact of particles closer, which accelerated the hydrothermal reaction and thus improved the strength of the solidified specimen; however, it could shrink the pore volume yet seemed to exert a small influence on the surface area. Curing time and temperature affected the porous and mechanical properties of synthesized specimens significantly, and the toughest specimen seemed to possess the largest surface area and optimum pore size distribution. As such, a porous and tough humidity regulating material seemed to be manufactured easily by the hydrothermal solidification/synthesis technology.

The first systematic analysis of 3D rapid prototyped poly(ε-caprolactone) scaffolds manufactured through BioCell printing: the effect of pore size and geometry on compressive mechanical behaviour and in vitro hMSC viability

Novel additive manufacturing processes are increasingly recognized as ideal techniques to produce 3D biodegradable structures with optimal pore size and spatial distribution, providing an adequate mechanical support for tissue regeneration while shaping in-growing tissues. With regard to the mechanical and biological performances of 3D scaffolds, pore size and geometry play a crucial role. In this study, a novel integrated automated system for the production and in vitro culture of 3D constructs, known as BioCell Printing, was used only to manufacture poly(ε-caprolactone) scaffolds for tissue engineering; the influence of pore size and shape on their mechanical and biological performances was investigated. Imposing a single lay-down pattern of 0°/90° and varying the filament distance, it was possible to produce scaffolds with square interconnected pores with channel sizes falling in the range of 245–433 µm, porosity 49–57% and a constant road width. Three different lay-down patterns were also adopted (0°/90°, 0°/60/120° and 0°/45°/90°/135°), thus resulting in scaffolds with quadrangular, triangular and complex internal geometries, respectively. Mechanical compression tests revealed a decrease of scaffold stiffness with the increasing porosity and number of deposition angles (from 0°/90° to 0°/45°/90°/135°). Results from biological analysis, carried out using human mesenchymal stem cells, suggest a strong influence of pore size and geometry on cell viability. On the other hand, after 21 days of in vitro static culture, it was not possible to detect any significant variation in terms of cell morphology promoted by scaffold topology. As a first systematic analysis, the obtained results clearly demonstrate the potential of the BioCell Printing process to produce 3D scaffolds with reproducible well organized architectures and tailored mechanical properties.

Performance of Electric Double Layers Capacitor Using Activated Carbon Materials from Rice Husk as Electrodes

Abstract Activated carbon (AC) was synthesized from rice husks using the chemical activation method with KOH, NaOH,a combination of (NaOH + Na 2 CO 3 ), and a combination of (KOH + K 2 CO 3 ) as the chemical activating reagents. The activatedcarbon with the highest surface area (around 2000 m 2 /g) and high porosity, which allows the absorption of a large number ofions, was applied as electrode material in electric double layer capacitors (EDLCs). The AC for EDLC electrodes is requiredto have a high surface area and an optimal pore size distribution; these are important to attain high specific capacitance of theEDLC electrodes. The electrodes were fabricated by compounding the rice husk activated carbons with super-P and mixed withpolyvinylidene difluoride (PVDF) at a weight ratio of 83:10:7. AC electrodes and nickel foams were assembled with potassiumhydroxide (KOH) solution as the electrolyte. Electrochemical measurements were carried out with a three electrode cell using6 M KOH as electrolyte and Hg/HgO as the reference electrode. The specific capacitance strongly depends on the porestructure; the highest specific capacitance was 179 F/g, obtained for the AC with the highest specific surface area. Additionally,different activation times, levels of heating, and chemical reagents were used to compare and determine the optimal parametersfor obtaining high surface area of the activated carbon.Key wordssupercapacitor, EDLC, activated carbons, specific capacitance, rice husk.

Carbon nanotube and carbon nanofiber composite films grown on different graphite substrate for capacitive deionization

The carbon nanotube and carbon nanofibre (CNT–CNF) composite films are synthesized on different graphite substrate by low-pressure and low-temperature chemical vapor deposition. Scanning electron microscopy measurement and N2 adsorption experiment show that CNT–CNF composite films have network structure with optimal pore size distribution, which is beneficial to capacitive deionization. Atomic force microscopy result indicates that there is a strong correlation between the surface roughness of graphite and their thickness. Furthermore, the electrosorptive performance in salt solutions by employing as-grown CNT–CNF composite film is studied and found that the properties of the graphite substrate play a vital role in electrosorptive performance of CNT–CNF composite films by influencing their network structures.

Pore Size Distribution as a Soil Physical Quality Index for Agricultural and Pasture Soils in Northeastern Iran

Assessment of soil quality is important for optimum production and natural resources conservation. Agricultural and pasture soil qualities of Deh-Sorkh region located at south of Mashhad, northeastern Iran were assessed using the integrated quality index (IQI) and Nemero quality index (NQI) models in combination with two datasets, i.e., total data set (TDS) and minimum data set (MDS). In this study 6 soil properties considered as MDS were selected out of 18 properties as TDS using principle component analysis. Soil samples were divided into 3 groups based on optimum ranges of 8 soil physical quality indicators. Soil samples with the most indicators at optimum range were selected as group 1 and the samples having fewer indicators at optimum range were located in groups 2 and 3. Optimum ranges of soil pore size distribution functions were also determined as soil physical quality indices based on 8 soil physical quality indicators. Pore size distribution curves of group 1 were considered as the optimum pore size functions. The results showed that relatively high organic carbon contents could improve pore size distribution. Mean comparisons of soil physical quality indicators demonstrated that mean weight diameter of wet aggregates, structural stability index, the slope of moisture retention curve at inflection point, and plant available water content in agricultural land use decreased significantly in relation to pasture land use. In addition, the results demonstrated that the studied MDS could be a suitable representative of TDS. 78% of pasture soils had the optimum pore size distribution functions, while this parameter for agricultural soils was only 13%. In general, the soils of the studied region showed high limitations for plant growth according to the studied indicators.

Sol–gel based alumina powders with catalytic applications

The sol–gel process provides a new approach to the preparation of oxide materials and offers many advantages for making catalysts. Since homogeneous mixing can be achieved at the molecular scale, the chemical reactivity of the oxide surface can be greatly enhanced; thus powders with high surface area and optimized pore size distribution can be obtained at low temperatures. In the present work NiO/Al 2O 3 sol–gel catalysts were obtained by simultaneous gelation of aluminium isopropoxide and nickel nitrate. A comparative study with pure sol–gel alumina was also realized. By physical–structural studies the changes induced by the introduction of the Ni precursor, before and after aluminium alkoxide hydrolysis were highlighted. The introduction of Ni at the beginning of the reaction favors γ-Al 2O 3 crystallization. When Ni is added at the end of reaction, it delays the alumina crystallization and induces the disorder of the lattice. The obtained Ni doped sol–gel derived alumina has been used as catalyst in the finished form for glycerol reforming to generate H 2 for fuel cell applications. Some evaluation results of Ni-doped alumina combined with TiO 2 in photocatalytic glycerol reforming reaction have been included.

Electrosorption Behavior of Carbon Nanotube and Carbon Nanofiber Film Electrodes

In this review work, the synthesis of cost-effective, large area carbon nanotube and nanofiber (CNT-CNF) film by low pressure and low temperature thermal chemical vapor deposition and its electrosorption properties in salt solutions are studied. Successful purification of water with good reproducibility by electrosorption of CNT-CNF films is achieved because of optimal pore size distribution that results in lower electrical double-layer overlapping effect. It is found that electrosorption of CNT-CNF film electrodes is mainly due to Coulombic interaction on the electrical double-layer and the ion sorption followed a Langmuir isotherm, indicating monolayer adsorption. The kinetics and thermodynamics analyses indicate that the electrosorption of NaCl onto CNT-CNF electrodes follows first order kinetics model and is driven by a physisorption process. Several experiments are conducted to study the ion removal capacity and selectivity of CNT-CNF film electrodes, showing that multivalent cations are preferentially adsorbed from the aqueous solution. For cations with same charge, the one with smaller hydrated radius will be more effectively removed. Keywords: Electrosorption, Carbon nanotubes, Capacitive deionization, Langmuir isotherm, Hydrated radius, Carbon Nanofiber, CNT-CNF, electrical double-layer overlapping effect, monolayer adsorption, physisorption process, deionization technologies, evaporation, reverse osmosis, electrodialysis, water purification technology, distillation columns, thermal heaters, pore microstructure, pore size distribution, arbon aerogel material, carbon aerogels, mass-transfer resistance, activated carbon cloth, chemical vapor deposition (CVD), Conductive plates, surface morphology, JEOL JSM-6700F, scanning electron microscopy (SEM), JEOL JEM-1200EX transmission electron microscopy (TEM), Raman spectroscopy, pore size distribution and Brunauer-Emmet-Teller (BET), counter electrode, reference electrode, polymethyl methacrylate plate, rectangular nylon spacer, rubber spacer, Batch-mode Electrosorption, CNT-CNF electrode, low mass-transfer, adsorption process, adsorption, –, desorption curves, mesoporous material, oxidation/reduction peaks, interaction, electrochemical reaction, double-layer capacitance (DLC), electrode surface inhomogeneity, Electrosorption Capacity, Freundlich isotherms, Electrosorption Kinetics, first-order, second-order, parabolic diffusion, Electrosorption Thermodynamics, Free energy of adsorption (DG0), enthalpy (DH0), van’t Hoff plots

Determination of the pore size distribution of micro porous layer in PEMFC using pore forming agents under various drying conditions

In this paper, the effect of the pore size distribution of a micro-porous layer (MPL) on the performance of polymer electrolyte membrane fuel cells (PEMFC) was investigated using self-made gas diffusion layers (GDLs) with different MPLs for which the pore size distribution was modified using pore forming agents under different drying conditions. When MPL dried at high temperature, more macro pores, approximately 1,000–20,000 nm in diameter, and less micro pores, below 100 nm, were observed relative to when MPL was dried at low temperature. Self-made GDLs were characterized by a field-emission scanning electron microscope (FE-SEM), mercury porosimetry and self-made gas permeability measurement equipment. The performance of the single cells was measured under two different humidification conditions. The results demonstrate that the optimum pore size distribution of MPL depended on the cell operating humidification condition. The MPL dried at high temperature performed better than the MPL dried at low temperature under a low humidification condition; however, MPL dried at low temperature performed better under a high humidification condition.

Poly(vinylidene chloride)-based carbon as an electrode material for high power electric double layer capacitors

A series of poly vinylidene chloride (PVDC) based activated carbons was prepared by carbonization at 600-1 100 ℃. Their formation,crystallinity,surface area and pore structure were characterized by thermogravimetry,X-ray diffraction and nitrogen adsorption. The electrochemical performance was investigated by cycle voltammetry,AC impedance and galvanostatic charge/discharge in a 30 % (mass fraction) KOH electrolyte. Results showed that the structure of PVDC-based carbons was amorphous and their high surface area (874-969 m2/g) and abundant micropores were formed during the solid phase carbonization. PVDC-based carbon had a high gravimetric capacitance and specific capacitance per surface area,owing to its optimum pore size distribution suitable for the formation of electric double layers. The PVDC-based carbon heat-treated at 900 ℃ had a maximum capacitance and an excellent power performance. The specific capacitance can reach as high as 256.9 F/g at low discharge current density (50 mA/g) and the capacitance retention ratio is 76.5% at high current density (5 000 mA/g). The electrical conductivity of PVDC-based carbon increased and the diffusion resis￣tance of electrolyte ions in pores decreased with increasing carbonization temperature,and the rate performance of the electric double layer capacitor is improved as a result.

Study on ultrafiltration for surface water by a polyvinylchloride hollow fiber membrane

Low pressure membrane filtration processes are increasingly competing against conventional surface water treatment plants. In comparison with conventional processes, UF technology has many advantages, but it is also important that a kind of membrane is suitably selected and operated. In this paper, a pilot plant study on a polyvinylchloride ultrafiltration (MWCO of 80 kD) hollow fiber membrane process was performed for the treatment of surface water. The new membrane had an optimized pore size distribution over membrane thickness while membrane material and fiber dimensions remained the same, the modification resulted in a much higher pure water flux (160 l/(m 2 h bar) at 20°C). The membrane system was operated in the dead-end filtration modes with different constant permeate fluxes. The results showed that the permeate quality was stable, regardless of different surface water for a long duration of filtration. The transmembrane pressure should be operated in less than 1 bar to avoid irreversible fouling. Treating cold raw water below 5°C in constant pressure operation mode was better than in constant permeate flux.

Polycaprolactone Scaffolds Fabricated via Bioextrusion for Tissue Engineering Applications

The most promising approach in Tissue Engineering involves the seeding of porous, biocompatible/biodegradable scaffolds, with donor cells to promote tissue regeneration. Additive biomanufacturing processes are increasingly recognized as ideal techniques to produce 3D structures with optimal pore size and spatial distribution, providing an adequate mechanical support for tissue regeneration while shaping in-growing tissues. This paper presents a novel extrusion-based system to produce 3D scaffolds with controlled internal/external geometry for TE applications.The BioExtruder is a low-cost system that uses a proper fabrication code based on the ISO programming language enabling the fabrication of multimaterial scaffolds. Poly(ε-caprolactone) was the material chosen to produce porous scaffolds, made by layers of directionally aligned microfilaments. Chemical, morphological, and in vitro biological evaluation performed on the polymeric constructs revealed a high potential of the BioExtruder to produce 3D scaffolds with regular and reproducible macropore architecture, without inducing relevant chemical and biocompatibility alterations of the material.

Characterization of nanoporous carbons by combining CO 2 and H 2 sorption data with the Monte Carlo simulations

The Monte Carlo method in its grand ensemble variant (GCMC) is used in combination with experimental data in order to characterize microporous carbons and obtain the optimal pore size distribution (PSD). In particular, the method is applied in the case of AX-21 carbon. Adsorption isotherms of CO 2 (253 and 298 K) and H 2 (77 K) up to 20 bar have been measured, while the computed isotherms resulted from the GCMC simulations for several pore widths up to 3.0 nm. For the case of H 2 at 77 K quantum corrections were introduced with the application of the Feynman–Hibbs (FH) effective potential. The adsorption isotherms were used either individually or in a combined manner in order to deduce PSDs and their reliability was examined by the ability to predict the experimental adsorption isotherms. The combined approach was found to be capable of reproducing more accurately all the available experimental isotherms.

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers composite film electrodes

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers (CNTs-CNFs) composite film electrodes has been demonstrated. The large area CNTs-CNFs film was directly grown on Ni plate by low pressure and low temperature thermal chemical vapor deposition. The CNTs-CNFs electrodes have great advantages such as low cost, easy operation, long-term reproducibility, and integrity of monolithic CNTs-CNFs film and current collector. Batch-mode experiments at low voltage (0.4–2V) were conducted in a continuously recycling system to investigate the electrosorption process. Purification of water with good reproducibility was achieved because of optimal pore size distribution of CNTs-CNFs composite films.

Electrosorption of NaCl Solutions with Carbon Nanotubes and Nanofibers Composite Film Electrodes

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers (CNTs-CNFs) composite film electrodes has been demonstrated. The low-cost, large area CNTs-CNFs composite film was directly grown on Ni plate by low-pressure, low-temperature thermal chemical vapor deposition. Successful purification of water with good reproducibility by electrosorption of CNTs-CNFs composite films was achieved because of optimal pore size distribution, which leads to lower electrical double-layer overlapping effect. The electrosorption capacity of CNTs-CNFs composite film electrodes was ∼ 15-65 μmol/g and comparable to carbon aerogels. The ion sorption followed a Langmuir isotherm, indicating monolayer adsorption.

Optimal distribution of viscous dissipation in a multi-scale branched fluid distributor

This paper examines some theoretical aspects of the optimal design of multi-scale fluid distributors or collectors, built on a binary or quaternary branching pattern of pores. The design aims to distribute uniformly a fluid flow over a specified square surface (uniform irrigation) while simultaneously minimizing the residence time, the residence-time distribution, the pressure drop and the viscous dissipation, leading to an optimization problem of the pore-size distribution, for both length and diameter. For the binary branching, the uniform distribution of outlet points requires a particular, non-monotonous scaling law for pore lengths, and this distinguishes the structure from fractal branching patterns that have been studied previously. The quaternary branching allows a fractal-type structure (constant scale ratios for both pore length and radius). An important general result is established: in the optimal pore-size distribution, the density of viscous dissipation power (W⋅m −3) is uniformly distributed over the volume at all scales.

Preparation and characterization of composite electrodes of coconut-shell-based activated carbon and hydrous ruthenium oxide for supercapacitors

The relationship between the structure-specific capacitance (F g −1) of a composite electrode consisting of activated coconut-shell carbon and hydrous ruthenium oxide (RuO x (OH) y ) has been evaluated by impregnating various amounts of RuO x (OH) y into activated carbon that is specially prepared with optimum pore-size distribution. The composite electrode shows an enhanced specific capacitance of 250 F g −1 in 1 M H 2SO 4 with 9 wt.% ruthenium incorporated. Chemical and structural characterization of the composites reveals a homogeneous distribution of amorphous RuO x (OH) y throughout the porous network of the activated carbon. Electrochemical characterization indicates an almost linear dependence of capacitance on the amount of ruthenium owing to its pseudocapacitive nature.