Nitrogen Adsorption Isotherms Research Articles

Development of gas phase controlled-release antimicrobial and antioxidant packaging film containing carvacrol loaded with HNT-4M（halloysite nanotubes etched by 4 mol/L hydrochloric acid）

In order to inhibit the spoilage of the packaged food, a gas phase controlled-release low-density polyethylene (LDPE) film containing carvacrol loaded with halloysite nanotubes (HNTs) was prepared and studied in this work. HNTs were etched by 4 mol/L hydrochloric acid to obtain HNT-4M, which increased the carvacrol loading capacity. Then, it was characterized before and after loading with carvacrol by transmission electron microscopy, nitrogen adsorption isotherms, and thermogravimetric analysis. A new LDPE film containing carvacrol adsorbed on HNT-4M was prepared by extrusion, and the physical properties were studied. In addition, the release rate of carvacrol in the film was measured, and the antibacterial and antioxidant properties of the film were evaluated. The results showed that the carvacrol load of HNT increased from 6.7% to 24.2% after acid etching. The diffusion coefficient of carvacrol from the active film containing HNT-4 M/carvacrol was 9.546 × 10-12 cm2·s-1, which was decreased by 57.3% compared with the films directly adding carvacrol. Moreover, according to the DPPH radical scavenging assay and micro-atmosphere diffusion antibacterial test, it was verified that carvacrol retained its antioxidant activity and antibacterial activity in the new film.

Hydrothermal Synthesis of Silicoaluminophosphate with AEL Structure Using a Residue of Fluorescent Lamps as Starting Material.

Silicoaluminophosphate molecular sieves of SAPO-11 type (AEL structure) were synthesized by the hydrothermal method, from the residue of a fluorescent lamp as a source or Si, Al, and P in the presence of water and di-propyamine (DPA) as an organic template. To adjust the P2O5/SiO2 and Si/Al and ratios, specific amounts of silica, alumina, or alumina hydroxide and orthophosphoric acid were added to obtain a gel with molar chemical composition 1.0 Al2O3:1.0 P2O5:1.2 DPA:0.3 SiO2:120 H2O. The syntheses were carried out at a temperature of 473 K at crystallization times of 24, 48, and 72 h. The fluorescent lamp residue and the obtained samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and BET surface area analysis using nitrogen adsorption isotherms. The presence of fluorapatite was detected as the main crystalline phase in the residue, jointly with considered amounts of silica, alumina, and phosphorus in oxide forms. The SAPO-11 prepared using aluminum hydroxide as Al source, P2O5/SiO2 molar ratio of 3.6 and Si/Al ratio of 0.14, at crystallization time of 72 h, achieves a yield of 75% with a surface area of 113 m2/g, showing that the residue from a fluorescent lamp is an alternative source for development of new materials based on Si, Al, and P.

Facile preparation of lotus seedpod-derived magnetic porous carbon for catalytic oxidation of Ponceau 4R

In this research, magnetic porous carbon was directly synthesized through one-step pyrolysis of FeCl3 – lotus seedpod mixture. Properties of the obtained material were analysed by X-ray powder diffraction, SEM image, nitrogen adsorption isotherm and vibrating sample magnetometer. The results showed that magnetic Fe3O4 particles were successfully formed over material template in 1 hour. The magnetic porous carbon possessed the specific magnetization of 7.13 emu/g, high specific surface area of 288 m2/g and total pore volume of 0.18 cm3/g. The material was subsequently applied as a potential catalyst for Ponceau 4R degradation by H2O2. Parameters including pH, H2O2 concentration, and different types of catalysts were investigated. At pH 3, 200 ppm H2O2, and 0.40 g/L magnetic porous carbon, 83% Ponceau 4R 50 ppm was removed after 120 minutes treatment. Moreover, the catalyst powders were separated from the treated mixture easily by a magnet. Summarily, magnetic porous carbon can promise to be an efficient catalyst in decomposition of Ponceau 4R.

Enhanced Breaking of Lignin and Mesopore Formation in Zinc Chloride Assisted Hydrothermal Carbonization of Waste Biomasses

Hydrochars from hydrothermal carbonization of different biowaste materials (dried dandelion, sawdust, coconut shell powder) formed in the presence of aqueous salt solutions were compared to those obtained by the common method in pure water. Hydrochars with increased carbon contents, pore volume and surface areas were specifically obtained from coconut shell powder in the presence of zinc chloride. Compositional and structural changes within the hydrochar products caused by the process conditions and/or the additive were characterized by solid state 13C NMR spectroscopy, proving that cellulose and, in particular, lignin units in the biomass are more easily attacked in the presence of the salt. Under saline conditions, a distinct particle break-up led to the creation of mesoporosity, as observable from hysteresis loops in nitrogen adsorption isotherms, which were indicative of the presence of pores with diameters of about 3 to 10 nm. The obtained hydrochars were still rich in functional groups which, together with the mesoporosity, indicates the compounds have a high potential for pollutant removal. This was documented by adsorption capacities for the methylene blue and methyl orange dyes, which exceeded the values obtained for other hydrochar-based adsorbers. A subsequent physical activation of the mesoporous hydrochars in steam at different temperatures and times resulted in a further drastic increase in the surface areas, of up to about 750 m2/g; however, this increase is mainly due to micropore formation coupled with a loss of surface functionality. Consequently, the adsorption capacity for the quite large dyes does not provide any further benefit, but the uptake of smaller gas molecules is favored.

Mechanism of solvent extraction-induced changes to nanoscale pores of coal before and after acidification

As the most widely used reservoir stimulation method, hydraulic fracturing requires the injection of large volumes of fluid with certain viscosity, mainly formed by water and various additives in a certain proportion, into coal seam for the purpose of improving the permeability of coal reservoir, and thus the selection of appropriate fracturing fluid is very important to improve the fracturing effect. In the study, using a medium-volatile bituminous coal as the research object, solvent extraction experiments of coal samples before and after acidification under different solvent concentrations were carried out. After the soluble low molecular weight compounds in coal were extracted and dissolved, and the differences in pore structure parameters and their mechanisms in coal were investigated by using low-temperature liquid nitrogen adsorption apparatus and capillary coalescence theory. The research results show that, after tetrahydrofuran (THF) extraction with different concentrations, the pore volume (PV) of each pore size section for raw coal decreases, and with the increase of the pore size, the decreasing PV tends to be stable. The PV of acidified coal increases significantly in all pore size ranges, especially in the range of 5 ∼ 10 nm. Compared with unacidified coals, the low-temperature nitrogen adsorption isotherm of acidified coals after extracted with different concentrations of THF were more prominent in the relative pressure of 0.8 ∼ 1.0. As THF concentration increases, the fractal dimension D of raw coal and nitrogen adsorption capacity decrease, while the fractal dimension D of acidified coal and nitrogen adsorption capacity increase and are significantly bigger than those of raw coal. The nitrogen adsorption capacity of raw coal and acidified coal shows an inverted “N” and “N” trend, respectively, and the nitrogen adsorption capacity of the residue with 50%THF extraction after acidification reaches the maximum value of 1.47 cm3/g. This study suggests that adding a certain proportion of organic solvent (THF) and acid into fracturing fluids can be beneficial to improve reservoir porosity and thus increasing gas production.

PEGylated green halloysite/spinel ferrite nanocomposites for pH sensitive delivery of dexamethasone: A potential pulmonary drug delivery treatment option for COVID-19

Dexamethasone (Dex) is used in drug regimen for treatment of Coronavirus disease (COVID-19). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) fusion and entry into the cell occurs at pH 5.5. In our present study, we have identified a green, cheap clay based halloysite (Hal) nanoformulation with release capability of Dex at such interactive pH condition. 30%ZnFe2O4/Hal and 30%NiFe2O4/Hal were prepared by one-pot synthesis technique. Dex (5% wt/wt) was functionalized over both nanocomposites. Finally, polyethylene glycol (PEG) was coated over ZnFe2O4/Hal/Dex and NiFe2O4/Hal/Dex nanocomposite using lyophilization technique (0.08 μl/mg of nanocarrier). The release ability of Dex was studied under pulmonary infection and normal pH conditions (pH = 5.6 and 7.4). The characterization study using X-ray diffraction (XRD) and UV–visible diffuse reflectance (DRS) spectra confirmed the presence of spinel ferrites over Hal. Nitrogen adsorption isotherm showed the surface area of ZnFe2O4/Hal (75 m2/g), pore volume (0.27 cm3/g) with average pore size (14.5 nm). Scanning electron microscope/Energy dispersive spectroscopy (SEM-EDS) and Transmission electron microscopy analysis revealed a textural change in halloysite tubular type indicating drug adsorption and PEG adhesion. DRS spectra indicated an intergrowth of zinc ferrite nanoparticles on the halloysite nanotubes. Interestingly, ZnFe2O4/Hal/Dex/PEG exhibited a high Dex release ability (17.5%, 168 h) at pH = 5.6 relevant to SARS-CoV-2 fusion entry into the cell pH condition of 5.5. Comparatively, the nanocomposite showed a less Dex release (<5%) release for 168 h at neutral pH = 7.4. The drug release kinetics were studied and the obtained data were fitted for the release constant and release exponent, using the Korsmeyer-Peppas model. To test the compatibility of our nanocomposites, we performed the cell viability assay (MTT) using HEK293 cells. Our results showed that at 0.3 mg/ml, Dex-loaded nanocomposite had a statistically significant improvement in cell viability compared to Dex alone. These results suggest that our nanocomposite has prevented the toxic effect of Dex and has huge potential to act as pulmonary drug delivery system for targeted lung infection therapeutics.

Ga2O3(Sn) Oxides for High-Temperature Gas Sensors.

Gallium(III) oxide is a promising functional wide-gap semiconductor for high temperature gas sensors of the resistive type. Doping of Ga2O3 with tin improves material conductivity and leads to the complicated influence on phase content, microstructure, adsorption sites, donor centers and, as a result, gas sensor properties. In this work, Ga2O3 and Ga2O3(Sn) samples with tin content of 0–13 at.% prepared by aqueous co-precipitation method were investigated by X-ray diffraction, nitrogen adsorption isotherms, X-ray photoelectron spectroscopy, infrared spectroscopy and probe molecule techniques. The introduction of tin leads to a decrease in the average crystallite size, increase in the temperature of β-Ga2O3 formation. The sensor responses of all Ga2O3(Sn) samples to CO and NH3 have non-monotonous character depending on Sn content due to the following factors: the formation of donor centers and the change of free electron concentration, increase in reactive chemisorbed oxygen ions concentration, formation of metastable Ga2O3 phases and segregation of SnO2 on the surface of Ga2O3(Sn) grains.

A preliminary study on assessing the Brunauer-Emmett-Teller analysis for disordered carbonaceous materials

The surface area is an important property of porous materials, commonly evaluated through the Brunauer-Emmett-Teller (BET) analysis applied to nitrogen adsorption isotherms at 77 K. However, the applicability of the BET analysis for disordered carbonaceous materials remains under debate. In this work, the disordered carbonaceous materials (coal, kerogen of shale and artificial samples), were chosen as the objective for their BET evaluation. These samples were considered as collections of independent graphite slit pores; the isotherms of these uniform slit pores (kernels) were calculated with Grand Canonical Monte Carlo (GCMC) simulation. Then, the kernels were integrated by following the pore size distribution (PSD) of these real samples to simulate nitrogen adsorption isotherms at 77 K. The BET analysis was conducted for both these simulated isotherms and the uniform slit pores. The results show that the performance of the BET analysis for the carbon slit pores varies with the pore size. As for the mesoporous materials, we found that the BET area derived from the two consistency criteria is reliable, with a maximum overestimation of 18%. For micropores-containing materials, the two consistency criteria shows no obvious advantage over the standard method when the micropore is smaller than 1.8 nm and the micropore volume is non-negligible; the prediction of the BET area (consistency criteria) can be justified by considering the micropore size and percentage of micropore volume. These findings improve the understanding of the BET area and verify the BET analysis on some relevant disordered carbonaceous materials.

PREPARATION AND CHARACTERIZATION OF PORE STRUCTURE BY PHOSPHORIC ACID ACTIVATED CARBON FROM UNUSED WOOD OF CITRUS SHRUB

Present study aimed to prepared large surface area activated carbon from unused wood of citrus with 45%w/w concentration of phosphoric acid as activating agent after maintaining optimum condition related to activation time of 25- minute, activation temperature at 550˚C and impregnation ratio 4:1 during chemical activation process by means of two stage process. The effect of optimum condition related to activation parameter was studied, the surface and pore structure of activated carbon was characterized by nitrogen adsorption isotherm method. The pore and surface properties of the resultant carbon including Langmuir surface area, BET surface area, pore size distribution, micropore volume and average pore radius were identified by nitrogen adsorption isotherm data using the BET, DFT, DA and BJH method. BET surface area, Langmuir surface area, micropore volume and average pore radius were obtained as high as 649m2/g, 3015m2/g, 0.34cc/g and 1.34 nm respectively which exhibit resultant carbon has high surface area and with welldeveloped micropores.

Synthesis, characterization and phosphate adsorption of (Fe, Al, Cu) oxit/bentonite nanocomposite

(Fe, Al, Cu) oxide/bentonite nanocomposite – FACB, was simply prepared by co-precipitation of salts of Fe, Al and Cu, which were impregnated previously in the exfoliated bentonite suspension. Characterization of the FACB is performed by X-ray diffraction, Fourier transform infrared spectrometry, Field emission scanning electron microscopy, Energy-dispersive X-ray spectroscopy, Nitrogen adsorption isotherm, and Thermal analysis. The adsorption behavious of phosphate ion on the FACB was assessed. The material has a good ability of phosphate adsorption with high adsorption rate and adsorption capacity of 55.87 mg P/g at equilibrium concentration of phosphate solution of 24.13 mg/l.

Upcycling simulated food wastes into superactivated hydrochar for remarkable hydrogen storage

In an effort of developing hydrogen storage material, the goal of this study was to explore the potential of the abounding food waste biomass as a precursor for the development of porous carbon materials for remarkable hydrogen storage. Therefore, in this study, simulated food waste, a mixture of six commonly disposed food items (apple, bread, green bean, cabbage, cheese, and canned chicken), was hydrothermally carbonized at 220 °C followed by chemical activation at 800 °C using various activating agent (KOH) to food waste hydrochar ratio (i.e., 2:1, 3:1 and 4:1). The solid products, hereafter called superactivated hydrochars, were characterized by proximate and ultimate analyses as well as X-ray diffractometer (XRD) and through nitrogen adsorption isotherms at 77 K to analyze the changes in the material including its surface porosity parameters (surface area, pore volume, and pore size distribution) as the food waste underwent chemical and morphological modifications. The gravimetric (wt%) hydrogen storage capacity of the superactivated hydrochars were then conducted under 77 K and various pressure of 0–23 bar. Results showed that the surface area and total pore volume in the superactivated hydrochars were in the range of, as high as, 2070 to 2885 m2/g and 0.98 to 1.93 cm3/g, respectively. The remarkable hydrogen storage capacity was observed of as high as 6.15 wt% at 23 bar and 77 K for the superactivated hydrochar produced with a KOH to food waste hydrochar ratio of 4:1. This distinctly highlights the pertinent upcycling technique of food waste to be effective in developing efficient hydrogen storage material.

Adsorption of light gases in covalent organic frameworks: comparison of classical density functional theory and grand canonical Monte Carlo simulations

A classical density functional theory (cDFT) based on the PC-SAFT equation of state is proposed for the calculation of adsorption equilibria of pure substances and their mixtures in covalent organic frameworks (COFs). Adsorption isotherms of methane, ethane, n-butane and nitrogen in the COFs TpPa-1 and 2,3-DhaTph are calculated and compared to results from grand canonical Monte Carlo (GCMC) simulations. Mixture adsorption is investigated for the methane/ethane and methane/n-butane binary systems. Excellent agreement between PC-SAFT DFT and GCMC is obtained for all adsorption isotherms up to pressures of 50 bar. The cDFT formalism accurately predicts the selective accumulation of longer hydrocarbons for binary mixtures in the considered COFs. This application shows substantial predictive power of PC-SAFT DFT solved in three-dimensional geometries and the results suggest the method can in the future also be applied for efficient optimization of force field parameters or of structural properties of the porous material based on an analytical theory as opposed to a stochastic simulation.

Metal nanoparticle ornated mesoporous silica: A potential nano-interface for uric acid detection

Uric acid is a significant biomarker generated inside the human body as the function of purine metabolism which takes place inside the body. This is majorly reabsorbed by kidney and it also has other vital roles such as pathogenic indicator and possesses the antioxidative and defensive properties. However, when the levels of uric acid exceed inside the body by losing the balance between production and excretion, the uric acid levels in blood and urine will increase significantly which serves as the biomarker for the diseases like gout, hyperuricaemia, diabetes, hypertension and other relative heart and renal disorders. Hence, the meticulous monitoring of uric acid levels become inevitable which leads to the requirement of simple but robust method for its analysis. For the efficient detection of uric acid levels, a post functionalised mesoporous silica material (SBA-S-Au) has been employed as a potential nano-interface in electroanalytical estimation. This material is synthesised by post functionalization of well-known mesoporous silica (SBA-15) with thiol followed by introduction of metal nanoparticles (AuNPs) in their terminal groups. This synthesised interfacing material is subjected to various physio-chemical characterisations to ensure its formulation and electrochemical investigations were performed to guarantee its efficacy towards the detection of uric acid even in lower levels. Fourier transform – infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed its functional groups and elemental presence and the nitrogen adsorption isotherms established its mesoporous nature. This fabricated SBA-S-Au/Nf@GCE sensor exhibited an excellent electrocatalytic activity for uric acid detection with limit of detection value 0.48 μM and very high sensitivity value of 0.0038 μA/μM. • Post functionalised and metal nanoparticle incorporated mesoporous silica (SBA-S-Au) is synthesised effectively. • This aforementioned mesoporous silica has not been used in electrochemical sensing by far and it showed a competent performance in sensing. • SBA-S-Au is employed as nano – interface material for the electrochemical detection of natural biomarker – uric acid. • Real – time analysis was carried out using multi-purpose artificial urine (MP-AU) and surfaced an efficient sensing of uric acid in the specimens.

Functionalized mesoporous silicas SBA-15 for heterogeneous photocatalysis towards CECs removal from secondary urban wastewater

The photocatalytic activity of TiO2 nanoparticles (NPs) supported on mesoporous silica SBA-15 (TiO2/SBA-15) was evaluated for the photodegradation of sulfadiazine (SDZ), as target contaminant of emerging concern (CEC), using either pure water solutions (PW) or a real secondary urban wastewater (UWW) spiked with SDZ. For this purpose, TiO2/SBA-15 samples with 10, 20 and 30% TiO2 (w/w) were prepared by the sol-gel post synthetic method on pre-formed SBA-15, using titanium (IV) isopropoxide as a precursor. The TiO2/SBA-15 materials were characterized by HRTEM, SAXS and XRD, nitrogen adsorption isotherms and UV–vis diffuse reflectance spectroscopy. TiO2 NPs were shown to be attached onto the external surface, decorating the SBA-15 particles. The TiO2/SBA-15 catalysts were active in SDZ photodegradation using the annular FluHelik photoreactor, when irradiated with UVA light. The 30% TiO2/SBA-15 sample presented the best performance in optimization tests performed using PW, and it was further used for the tests with UWW. The photocatalytic activity of 30% TiO2/SBA-15 was higher (56% SDZ degradation) than that of standard TiO2–P25 (32% SDZ degradation) in the removal of SDZ spiked in the UWW ([SDZ] = 2 mg L−1). The photodegradation of SDZ with 30% TiO2/SBA-15 eached 90% for UWW spiked with a lower SDZ concentration ([SDZ] = 40 μg L−1). Aside of SDZ, a suit of 65 other CECs were also identified in the UWW sample using LC-MS spectrometry. A fast-screening test showed the heterogeneous photocatalytic system was able to remove most of the detected CECs from UWW, by either adsorption and/or photocatalysis.

An in-situ Blowing-etching strategy for preparation of Macro-meso-micro hierarchical porous carbon and its supercapacitive property

With the development of society, there exists a great need for symmetric supercapacitors that can be charged and discharged in long cycles, which puts forward higher requirements for symmetric supercapacitor materials. Porous carbon supercapacitors have attracted much attention because of their excellent performance, yet it is still difficult to build a structure with hierarchical pore carbon. Here, we report a new idea of constructing hierarchically porous carbon materials (HPC) by an in-situ blowing-assisted high-temperature etching method, and the pore structure can be tuned to a certain extent. It has a large number of meso-microporous structure with three-dimensional macro- interconnections, which is confirmed by electron microscope and nitrogen isothermal adsorption experiments. As an electrode material for supercapacitors, the optimized HPC exhibits an outstanding rate capability of 255.5F·g−1 at a current density of 3 A·g−1 and 201.6F·g−1 at a current density of 10 A·g−1 as well as an excellent cycle stability (capacity retention of 97.5% after 5000 cycles). The excellent performance originates from the favorable pore configuration that the macro-mesopores effectively accelerate ion transport and the micropores’ interface store a large amount of charge. This work offering a new synthesis strategy and a new pore configuration prototype for the preparation of high-performance symmetric supercapacitor devices.

Anionic Methyl Orange Removal from Aqueous Solutions by Activated Carbon Reinforced Conducting Polyaniline as Adsorbent: Synthesis, Characterization, Adsorption Behavior, Regeneration and Kinetics Study

This work investigated the elimination of Methyl Orange (MO) using a new adsorbent prepared from Activated Carbon (AC) with polyaniline reinforced by a simple oxidation chemical method. The prepared materials were characterized using XRD, TGA, FTIR and nitrogen adsorption isotherms. Furthermore, PANI@CA highest specific surface area values (near 332 m2 g−1) and total mesoporous volume (near 0.038 cm3 g−1) displayed the better MO removal capacity (192.52 mg g−1 at 298 K and pH 6.0), which is outstandingly higher than that of PANI (46.82 mg g−1). Besides, the process’s adsorption, kinetics, and isothermal analysis were examined using various variables such as pH, MO concentration and contact time. To pretend the adsorption kinetics, various kinetics models, the pseudo first- and pseudo second- orders, were exercised to the experimental results. The kinetic analysis revealed that the pseudo second order rate law performed better than the pseudo first order rate law in promoting the formation of the chemisorption phase. In the case of isothermal studies, an analysis of measured correlation coefficient (R2) values showed that the Langmuir model was a better match to experimental results than the Freundlich model. By regeneration experiments after five cycles, acceptable results were observed.

Structured silica materials as innovative delivery systems for the bacteriocin nisin

Nisin was encapsulated in silica through sol–gel process by acid-catalyzed routes. The silica xerogels were characterized through nitrogen adsorption isotherms, small-angle X-ray scattering (SAXS), zeta potential, X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and Fourier transform infrared spectroscopy (FTIR). SAXS results showed that the particle diameters in a second level of aggregation varied from 4.78 to 5.86 nm. Zeta potential of silica particles were from −9.6 to −25.3 mV, while the surface area and pore diameters ranged from 216 to 598 m2 g−1 and 2.53 to 2.90 nm, respectively, indicating the formation of mesoporous nanostructures. Nisin retained the antimicrobial activity against all microorganisms tested after encapsulation in silica materials. These novel silica-based structures can be valuable carriers for nisin delivery in food systems.

Influence of Structure on Catalytic Properties of La0.7Sr0.3BO3 (B = Mn, Fe, Ni) Perovskite Catalysts in Total Oxidation Reaction of M-Xylene

In this study, the influence of structure on catalytic properties of La0.7Sr0.3BO3 (B = Mn, Fe, Ni) perovskite catalysts in total oxidation reaction of m-xylene was studied. Perovskite oxides of La0.7Sr0.3BO3 (B = Mn, Fe, Ni) were prepared by sol-gel citrate method. Structural properties of these materials were determined by various physico-chemical methods such as X-ray diffraction method (XRD) with Rietveld analytical method using Fullprof program, infra - red spectroscopy method (IR), temperature - programmed desorption of oxygen (TPDO) method and nitrogen adsorption and desorption isotherms method (BET). Obtained results show that there is a close relationship between the structural properties and catalytic activity of these materials: the catalyst that has the more of structural distortion, the larger of specific surface area, the greater of the amount of chemically adsorbed oxygen on the catalyst and the less durable of B-O link that has the higher of catalytic activity in total oxidation recation of m-xylene. Perovskite of La0.7Sr0.3MnO3 has structural features the best, so it has the highest of catalytic activity in total oxidation recation of m-xylene.

Assessing the contribution of micropores and mesopores from nitrogen adsorption on nanoporous carbons: Application to pore size analysis

Adsorption isotherms in micropores and mesopores are assessed from nitrogen adsorption isotherm measured on micro-mesoporous carbons and used to determine the micropore and mesopore size distributions. These carbons were obtained by self-assembly of phloroglucinol and formaldehyde in the presence of poly(ethylene oxide)–poly(propylene oxide) – poly(ethylene oxide) triblock copolymer (Pluronic F127) as a soft-template under acidic conditions and subjected to KOH activation. The template used afforded carbons with ordered cylindrical mesopores, while KOH activation enlarged their microporosity. The proposed method allows for the assessment of contributions arising from adsorption in micropores and mesopores, which can be beneficial for further development of pore size analysis of micro-mesoporous carbons.

Deriving coal fractal dimensions from low-pressure nitrogen adsorption isotherms applying an integrated method

The internal surface roughness of coals determines, to an extent, the quantity of natural gas, specifically methane, that they can readily adsorb/store and the ease with which that gas can flow and be produced from coal formations. Coals’ fractal dimensions (D) provide a quantitative measure of the degree of roughness of their internal surfaces (pores and microfractures). Low pressure nitrogen adsorption isotherms are commonly used to derive D values for coal applying the Frenkel–Halsey–Hill (FHH) method. However, the isotherm data points for many coals do not conform to the theoretically expected FHH trends. In this study, two other fractal determination methods, those of Neimark (NMK) and Wang & Li (W&L), are evaluated, together with the FHH method for 26 published coal isotherms. The NMK method is considered unsuitable as it generates unreasonably high D values. For many coals W&L and FHH methods are observed to derive consistently close D values. Detailed graphical analysis of the isotherm data points and their trends can explain the discrepancies that exist in the D values derived from the whole isotherms of some coals. Discrepancies are also observed in the fractal dimensions derived by the different methods for the low (D1) and high (D2) relative pressure portions of the coal isotherms. More realistic D1 values are derived by the W&L method than the FHH method. A novel workflow integrating detailed graphical analysis with optimized curve fitting is proposed to better quantify and verify the derivation of coal fractal dimensions from nitrogen adsorption isotherms.