Standard Contact Porosimetry Research Articles

Effect of porous structure of LiCoPO4 on its performance in hybrid supercapacitor

Hybrid supercapacitors (HSCs) based on the mechanochemically prepared LiCoPO4 samples with different specific surface area and porosity as cathodes and the activated carbon (AC) Kuraray K-50 as anode were fabricated and studied. The effect of porosity and specific surface area of LiCoPO4 on its performance in HSC was investigated. The porosity was measured within the widest possible range (compared to other methods) of pore size (1–105 nm) using standard contact porosimetry (MSCP). The LiCoPO4 samples, prepared from different precursors, varied in a number of meso- and macropores and the specific surface area (13.9 m2 g−1 and 9.3 m2 g−1), while the specific surface area of AC anode was equal to 1340 m2 g−1. The capacity of the LiCoPO4 cathode with a larger specific surface area and amount of mezopores was superior. To achieve the highest specific power of the LiCoPO4/AC HSC, the active mass ratio of anode and cathode, the electrolyte composition, and the operating voltage range were optimized. As a result, the specific power of 2300 W kg−1 was achieved, which exceeds that observed earlier in the literature.

A Porous Structure of Nanofiber Electrospun Polyacrylonitrile-Based Materials: a Standard Contact Porosimetry Study

The formation regularities and quantitative porosity characteristics of nanofibrous electrospun composite materials based on polyacrylonitrile and its mixtures with polyvinylpyrrolidone and commercially available Vulcan® XC72 or Ketjenblack® EC-600 carbon blacks were studied by standard contact porosimetry. It was shown that a significant increase in the total specific surface area could be achieved due to an increase in the temperature of oxidative warming up of mats from 250 to 330°C followed by vacuum pyrolysis at 900–1000°C. Such carbon materials, after deposition of nanocrystalline platinum onto them, can be used as gas-diffusion electrodes in an intermediate temperature hydrogen–air fuel cell on a polybenzimidazole membrane.

Synthesized nanostructured FeS2 for Li-batteries application. Influence of Microstructure

The powders of natural FeS2 (pyrite) and synthesized nanostructured iron disulfide have been studied using the methods of Standard Contact Porosimetry (MSCP), XRD spectroscopy, and SEM. The results obtained by applying the MSCP for investigating the process distinction in porous multicomponent electrodes based on natural and nano-FeS2 are discussed. It has been shown that a porous structure of the initial powder of FeS2 and a porous structure of the electrode that is based on these powder influence electrode performances during the galvanostatic cycling in Li-FeS2 batteries with the polymer electrolyte.

In English

The aim of the investigation is to develop multifunctional adsorbent, which is able to remove both inorganic ions and molecular organic substances from aqueous solutions. Oxidized graphene has been obtained by Hammer’s method. The composite, which includes hydrated zirconium dioxide and graphene oxide (» 2 mass. %), has been synthesized by deposition from sol containing dispersed particles of the carbon material. The adsorbent as well as its constituents were investigated with methods of XRD analysis, FTIR spectroscopy, TEM and standard contact porosimetry involving octane (ideally wetting liquids) and water as working liquids. Strong hydration of graphene oxide in water has been found: the volume of micro- and mesopores in water medium is higher than that in octane. It means that the oxidized graphene behaves similarly to ion exchange polymers. This is evidently due to its hydrophilic functional groups (hydroxyle carboxyl and epoxy groups). High specific surface area of graphene oxide reaches 1200 (in the organic solvent) or 2250 m 2 g –1 (in aqueous medium). It has been shown that graphene covers the particles of the inorganic matrix loosening its structure within the wide interval of pore size (from 10 nm to 1.5 µm). As found, adsorption isotherms of Pb(II) and HCrO 4 - ions obeys with Langmuir model. The filler improves adsorption of Pb(II) ions increasing the capacity in 1.7 times due to its expressed cation exchange properties. Contrary, anion exchange function of the composite is depressed, since the sheets of graphene oxide screen adsorption centers of the inorganic matrix. Other reason can be electrostatic repulsion of anions due to the shift of the point of zero charge of the composite to acidic field. By reason of the carbon filler, the oxide material acquires the capability to adsorb both slightly dissociated (phenol) and molecular (lactose) organic substances. When the initial content of phenol is 5 mg dm –3 , it is possible to reduce its content in water down to maximal permeable concentration. After adsorption, the content of lactose is much lower than this parameter. It means, that the composite provides practically complete removal of organics from water.

Hydrophilic and hydrophobic pores in reduced graphene oxide aerogel

Aerogel is obtained from graphene oxide reduced by a mixture of H3PO2 and I2. The porous structure of an aerogel has been studied at room temperature using the method of standard contact porosimetry. Both water and octane were used as working fluids, which allowed us to study the pore size distributions of hydrophilic and hydrophobic pores separately. It was found that very small pores, with the radius < 2.5 nm, and very large pores, with the radius more than 100 nm, were mostly hydrophobic, while the intermediate pores were hydrophilic.

In English

Weakly acidic cation exchange resin was modified with nanoparticles of zirconium hydrophosphate. The materials were investigated with methods of standard contact porosimetry and transmission electron microscopy. Both non-aggregated nanoparticles (4–15 nm) and larger formations (from 250 nm to several microns) have been found. Single particles in clusters and channels of the polymer depress dissociation of carboxylic groups due to counter-ions (H + ) in electric double layer around the particles. This causes transformation of porous structure of the polymer: the contribution of micropores to total porosity increases. These additional selective sites provide stronger interaction of Brilliant Green molecules with the surface in comparison with the pristine polymer. Removal of the dye from deionized water and Ni(II) ions from water containing also hardness ions was studied under dynamic conditions. The composite shows higher break-through capacity than that of the pristine resin. The modifier also facilitates regeneration of the weakly acidic ion-exchanger.

The Effect of Electrochemical Modification of Activated Carbons by Polypyrrole on Their Structure Characteristics, Composition of Surface Compounds, and Adsorption Properties

The electrochemical modification of activated carbons (AC) by a conducting polymer polypyrrole (PPy) has a substantial effect on the AC structure characteristics, electrochemical properties, and adsorption activity with respect to natural substances (by the example of free hemoglobin). Using the method of standard contact porosimetry (SCP), the porous structure and hydrophilic–hydrophobic properties are studied for the activated carbon SKT-6A, the [SKT-6A/PPy/Cl–] composite, and individual polypyrrole. The chemistry of the activated carbon surface is studied by the standardized Boehm method. It is shown that the nature of activated carbon and its initial surface substantially affect the character of its interaction with the conducting polymer polypyrrole. The effect of such modification on the AC surface chemistry should be considered in aggregate by taking into account each component of such modification. The increase in the sorption ability of [AC/PPy/Cl–] composites with respect to hemoglobin is largely associated with the stronger hydrophilicity of polypyrrole as compared with activated carbons.

Preparation of graphene oxide-humic acid composite-based ink for printing thin film electrodes for micro-supercapacitors

An aqueous suspension of a reduced composite of graphene oxide and humic acid has been prepared and used as ink to print conductive films and electrodes for supercapacitors. The dry powders of the composite ink before and after hydrazine reduction were characterized by IR and Raman spectroscopies and XPS. The surface areas of the reduced composite measured using the Brunauer-Emmett-Teller (BET) and standard contact porosimetry (SCP) methods were 6.5 and 200 m2/g, respectively. Moreover, the composite thin films obtained by printing exhibited island-like character. Further, the specific capacitance and other electrochemical properties of the supercapacitor using the composite electrode were studied.

Hybrid porous carbon materials derived from composite of humic acid and graphene oxide

Two materials have been derived from a composite of humic acid and graphene oxide (HA-GO). First material was obtained by high-temperature carbonization of the HA-GO composite in an inert atmosphere, and second material was produced by reduction of the HA-GO composite with hydrazine hydrate. The results of comparative studies of the materials using IR, Raman and XPS spectroscopies are presented. In IR spectra, no absorption due to stretching of vibrations OH is observed for both the materials. The XPS spectra of humic acids and its composite show sufficiently high content of carbon atoms, which are bonded with oxygen atoms, the C1s peak in the XPS spectra of both the materials under study show asymmetry inherent of graphite material, which confirms the outcomes of IR and Raman studies. This could be attributed to high conductivity of the materials. It has also been established that specific surface area SBET is equal to 36.2 and 6.5 m2/g for thermally treated composite and chemically treated composites materials, respectively. However, the values of specific surface area SSCP, measured by the method of standard contact porosimetry with octane as a working liquid, is equal to 470 m2/g and 200 m2/g in the case of thermally treated composite and chemically treated composites materials, respectively.

Structure, morphology, and transport characteristics of profiled bilayer membranes

A procedure for the fabrication of profiled cation-exchange bilayer membranes with the homogenized surface based on the commercial membrane MK-40 has been developed. The surface morphology and membrane microstructure have been studied by atomic-force microscopy, electron microscopy, and standard contact porosimetry. The concentration dependences of the electrical conductivity and diffusion permeability of the profiled and bilayer profiled membranes have been studied. It has been shown that the application of an MF-4SK film on the surface of the profiled membrane results in a decrease in its diffusion permeability and some increase in specific conductivity. Based on the data obtained, the transport and structure parameters have been calculated in terms of the microheterogeneous model to assess the influence of the modification on the properties of the support membrane. The current–voltage characteristics of the membranes have been measured in sodium chloride solutions, and it has been shown that profiling leads to an increase in the limiting current by 40%. The investigation of mass transfer of ions in the channels formed by the support and modified membranes has shown that under intense current regimes, the mass transfer coefficient through the profiled bilayer membrane is one and a half times that through the initial profiled membrane.

In Russian

In order to obtain organic-inorganic ion-exchanger, a method has been proposed involving reorganization of n gel-like cation exchange matrix in non-aqueous media followed by zirconium hydrophosphate precipitation. Reorganization, which is confirmed with methods of standard contact porosimetry and NMR 23 Na spectroscopy, means a narrowing of transport pores of the polymer. As a result of precipitation in the reorganized matrix, aggregates of zirconium hydrophosphate nanoparticles are formed. Scanning electron microscopy has shown the size of these formations to be of 200 nm in diameter. It has been found with a method of X-ray fluorescence analysis, a molar ratio of Zr:P in the inorganic constituent is 1:0.31. The regularities of precipitation are considered from the point of view of Ostwald-Freundlich and Volfkovich equations. inorganic method with a low content of phosphorus. Small size of the incorporated particles provides high rate of removal of U(VI) cationic compounds from individual aqueous solution containing also HCl (pH 2.5). The regime of sorption is mixed-diffusion, the coefficients of U(VI) → H + exchange for particle diffusion are 5.45∙10 –12 (composite), 3.86∙10 –12 (unmodified resin), 4.75∙10 –14 (individual zirconium hydrophosphate) m 2 s –1 . In the case of sorption from the solution containing also Fe(III), U(VI) sorption is complicated with a chemical reaction of the pseudo-second order. In opposite to unmodified resin, the composite removes U(VI) compounds in a wide range of the solution pH (2–10).

COMPOSITE OF GRAPHENE OXIDE AND HUMIC ACIDS: RESULTS OF HIGH-TEMPERATURE TREATMENT

Humic acids (HA) and HA derived carbon (HADC), obtained by heating HA at 900 oC in inert atmosphere, has been studied by solid-state nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Raman spectroscopy and the method of standard contact porosimetry (SCP). Mass spectrometry was also used for analysis of gases released upon heating of the samples. The composite of HA with graphene oxide (HA+GO) derived carbon has been prepared using carbonization of HA+GO in an inert atmosphere at 900 °C. Small agglomerates of carbon with sharply defined edges have been obtained because of carbonization of HA, and the composite of HA+GO forms only large aggregates at the same condition. The values of specific surface area of HADC and (HA+GO)DC are 173 and 474 m2 /g, respectively. The value of specific surface correspond to the area of all pores (Spore) is equal to only 3 m2 /g in the case of HADC. In the case of the (HA+GO)DC, Spore is equal to 237 m2 /g.

New hydrophobic materials based on poly(tetrafluoroethylene-co-vinylidene fluoride) fiber

The structural features of poly(tetrafluoroethylene-co-vinylidene fluoride) (F42) nonwovens with electrospun fibers were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and standard contact porosimetry (SCP). Thermal pressing modification of polymeric nonwovens was considered. Such modification allows variation in their surface morphology and water wettability of these surfaces, which demonstrates the possibility for preparation of materials with a wetting gradient. For the starting and modified samples, we studied in detail how the contact angle evolves with an increase in the aqueous phase contact time, as well as how the wettability of materials immersed in water changes after repeated crystallization and melting of water. The morphological structural features of nonwovens formed by poly(tetrafluoroethylene-co-vinylidene fluoride) microfibers were revealed. The method for the thermal pressing modification of materials was proposed and the effects of modification on the structures, wettability, and water sorption of materials were studied. The materials were found to be highly hydrophobic and promising for the design of samples with gradient wettability.

Pressure influence on the structural characteristics of modified absorptive glass mat separators: A standard contact porosimetry study

The article presents a comparative analysis of the structural characteristics of absorptive glass mats manufactured by “Hollingsworth & Vose” (a 2.8 mm thickness) and “Bernard Dumas” (a 3.0 mm thickness) modified by impregnation with polymeric emulsions based on polyvinylidene fluoride, a polyvinylpyrrolidone styrene copolymer, and polytetrafluoroethylene, by means of standard contact porosimetry. The key study is influence of features of the porous structure on the compression properties, the rate of wicking, and the oxygen cycle efficiency in lead-acid battery mock-ups under several plate-group compression pressures. It is found that the treatment of the absorptive glass mat separators with polymeric emulsions leads to redistribution of their pores by size. An increased pressure in the electrode unit insignificantly changes the pore structure of the modified absorptive glass mat separators, and the oxygen cycle efficiency rises in comparison with unmodified separators.

Supercapacitors with graphene oxide separators and reduced graphite oxide electrodes

A supercapacitor (SC) with electrodes fabricated from graphite oxide reduced by a microwave exfoliation (MEGO) method and the separator made from the graphite oxide paper (GOP) formed after precipitation of water suspension of graphene oxide was designed for the first time. The specific capacitance of this SC exceeded 200 F/g. The specific area of our MEGO is 2400 m2/g when measured using the standard contact porosimetry method, whereas it is several times smaller (∼600 m2/g) when measured by using the Brunauer–Emmett–Teller method based on the low-temperature nitrogen adsorption. By using the angle resolved X-ray photoelectron spectroscopy we found that surface layers of the GOP separator contain smaller oxygen concentration than the bulk layers.

Ion-exchange resin modified with aggregated nanoparticles of zirconium hydrophosphate. Morphology and functional properties

Organic–inorganic ion-exchangers based on gel-like strongly acidic resin, which contain different amount of zirconium hydrophosphate, have been obtained. The samples were investigated using methods of transmission and scanning electron microscopy, standard contact porosimetry, NMR 35P spectroscopy. Nanoparticles of the inorganic constituent (10nm) are deposited in voids between geld field and in structure defects of the polymer forming aggregates of micron size. These large particles squeeze and stretch pores of the polymer, where –SO3 groups are located, a radius of these pores decreases from 10nm down to 2nm. A part of functional groups of the polymer component are excluded from ion exchange due to squeezing of pores, ion exchange properties are determined mainly by the inorganic constituent. Ion exchange capacity of the composites reaches 0.6–1.3mmolcm−3. These materials sorb preferably Cd2+ and Ni2+ from solutions, which contain also hardness ions. The highest break-through capacity has been found for the composite with the smallest microporosity of the polymer constituent, this value reaches 80% of total ion-exchange capacity.

Composite inorganic membranes containing nanoparticles of hydrated zirconium dioxide for electrodialytic separation.

The aim of the work was to elucidate the nature of charge-selective properties of macroporous composite inorganic membranes modified with nanoparticles of hydrated zirconium dioxide. The membranes have been investigated using methods of standard contact porosimetry, potentiometry, electron microscopy and small-angle X-ray scattering. The ion exchanger has been found to deposit inside pores of ceramics. Differential curves of pore volume distribution have been resolved using Lorentz functions; each maximum has been related to structure elements of the matrix and ion exchanger by means of calculations according to homogeneous and heterogeneous geometrical models. It was found that the voids, the radius of which is 4 to 8 nm, are responsible for charge selectivity of the composite membranes. These pores are formed due to blocking of macropores of ceramics with aggregates of nanoparticles of the ion exchanger; the radius of these aggregates is 20 to 24 nm. The membranes were applied to desalination of the solution containing NaCl. The removal degree of the salt from the solution reached 95% and 9% for the composite and unmodified membranes, respectively.

Specific features of the structural organization of composite fibrous membranes polycon and their electrotransport properties

Peculiarities of the porous structure and hydrophilic-hydrophobic properties of composite ion-exchange membranes Polycon K based on novolac phenolformaldehyde fibers are studied by the method of standard contact porosimetry. Differences are revealed in the values of maximum porosity, internal specific surface, volume of macropores, and other structural characteristics associated with different conditions of sulfonation of fibers. The formation of pores in the fibrous phase at the diffusion of monomers during the preparation of membranes is confirmed by the data of scanning electron microscopy and differential scanning calorimetry. Correlation is found between the structural characteristics and electrotransport properties of composite membranes. It is shown that the increase in the macropore volume in the modified fibers enhances the sensitivity of specific conductivity of membranes with respect to the concentration of equilibrium solution and leads to the lower selectivity.

Effect of process parameters of manufacturing of composite fibrous membranes on their structure and ion selectivity

The porous structure of Polikon K composite ion-exchange membranes based on polyacrylonitrile fibers has been studied by standard contact porosimetry. Differences in maximum porosity, internal specific surface area, macropore volume, and other structural characteristics attributed to the use of different molding pressures during the preparation of the membranes have been revealed. According to the analysis of the porometric curves measured in octane and water, it has been found that the volume of hydrophobic pores in the Polikon membranes is an order of magnitude lower than the total volume of hydrophilic pores. The ion selectivity of the membrane materials has been estimated from the porometric curves. A comparison of the ion transport numbers measured by the potentiometric method to the calculated values has shown that they are in good agreement.

Polymer Ion-Exchangers Modified with Zirconium Hydrophosphate for Removal of Cd2+ Ions from Diluted Solutions

Hybrid ion-exchangers have been synthesized by modification of strongly acidic cation-exchange resin with zirconium hydrophosphate. The samples were investigated with scanning and transmission electron microscopy and standard contact porosimetry. Single nanoparticles and their aggregates have been found in the polymer. The nanoparticles in transport pores increase the electrical conductivity of ion-exchanger from 0.21 to 0.65 Ohm−1 m−1. The diffusion coefficient of Cd2+ ions reaches 2.43 × 10−11 m2 s−1 for initial resin and (2.50–4.34) × 10−11 m2 s−1 for nanocomposites. The inorganic constituent improves Cd2+ recovery from a solution, which contains also Ca2+ and Mg2+. The degree of Cd2+ removal is 18% for non-modified resin and 99% for the sample containing 38 mass% zirconium phosphate.