Dubinin-Radushkevich Method Research Articles

Investigation of CO2 adsorption on nitrogen-doped activated carbon based on porous structure and surface acid-base sites

The purpose of this paper is to reveal the effects of porous structure and surface acid-base sites on CO2 adsorption for those nitrogen-doped activated carbons, which were prepared in a tube furnace with anaerobic conditions (TF) and muffle furnace with oxygen-poor conditions (MF), respectively. Subsequently, the porous structure and surface group distribution of the prepared activated carbons TF and MF were characterized in detail through those methods such as scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), Barret-Joyner-Halenda method (BJH), Horvath-Kawazoe method (HK), Dubinin-Radushkevich method (DR), mercury intrusion porosimetry (MIP), non-local density functional theory method (NLDFT), (in-situ) Fourier transform infrared spectroscopy (FTIR), Raman spectra (RS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Then the thermodynamic and kinetic characteristics of CO2 adsorption such as adsorption capacity, selectivity, and activation energy were systematically investigated based on the static volumetric method and dynamic adsorption method. The results showed that the anaerobic or oxygen-poor preparation atmosphere affected the micropore volume and surface functional group distribution of activated carbons. Thus the activated carbon TF exhibited a higher adsorption capacity of CO2 (7.9 mmol g−1, 100 kPa and 273 K) and longer dynamic breakthrough time due to the higher microporosity (Vmic/Vt = 90 %), while the activated carbon MF exhibited the higher selectivity (14.7, CO2/N2 molar ratio of 1:1) and adsorption rate due to the higher nitrogen and oxygen contents (11.23 %, 13.53 %) in the main forms such as pyrrole nitrogen (N-5), carbony, and carboxyl. Overall, CO2 adsorption on the activated carbons was verified to be a dominant physical adsorption and exothermic process, which was suitable to be described by a quasi-first-order dynamic model. Meanwhile, compared with TF, the activated carbon MF exhibited the higher activation energy of CO2 adsorption (12.98 kJ mol−1 for TF and 17.23 kJ mol−1 for MF), accompanied by the larger rate constants (k1) and diffusion coefficients (D). The higher activation energy for MF meant that the adsorption temperature had a stronger effect on the rate constant during CO2 adsorption.

Prospective carbon nanofibers based on polymer of intrinsic microporosity (PIM-1): Pore structure regulation for higher carbon sequestration and renewable energy source applications

Polymer of intrinsic microporosity (PIM-1) is characterized by a developed microporous structure. Needle-free Nanospider™ electrospinning of the PIM-1 solution with subsequent pyrolysis either under vacuum or in argon-hydrogen medium (7 vol% H2) at 900–1200 °C results in PIM-1 based carbon nanofibers (CNF) self-supporting mats. The samples were thoroughly characterized by N2 and CO2 adsorption using the BET, BJH, Dubinin-Radushkevich (DR), NLDFT and GCMC methods, CO2 uptake, and by Raman spectroscopy, elemental analysis, electrical conductivity, SEM. Since the N2 adsorption is found to be inapplicable, the presence of microporosity in the CNF is confirmed by CO2 adsorption (273 K) by the DR, NLDFT and GCMC methods. The CNF reach micropore specific surface area of 919 m2 g−1, micropore volume of 0.257 cm3 g−1 and CO2 uptake of 4.01 mmol g−1, which is higher than for initial PIM-1. Pt/PIM-1 CNF self-supporting mat, was successfully tested as anode for HT-PEM fuel cell.

Effects of Different Experimental Conditions on the Micropore Characteristics of Coal

Low-temperature nitrogen adsorption experiment is widely used to analysis the micropore characteristics of coal. Effects of different experimental conditions including degassing time, degassing temperature, sample weight and sample particle size on the micropore characteristics of a middle rank coking coal produced in Shanxi Province, China was investigated to confirm the optimum experimental conditions. The experimental conditions were as follows: degassing time 4, 8, and 16 h; degassing temperature 125, 150, 175, and 200°C; sample weights 2000.0, 3500.0, and 5000.0 mg; particle sizes <0.5 mm, 0.5–1.0 mm, and 1.0–2.0 mm. The optimum experimental conditions were found to be 8 h degassing time, ~150°C degassing temperature, 5000.0 mg sample weight, and <0.5 mm particle size. Micropore characteristics were estimated using the t-plot method based on the de Boer’s equation and Magee’s equation and Dubinin–Radushkevich (DR) method, and the optimal methods were the t-plot method based on Magee’s equation and DR method.

Feasibility Assessment for Production of Sorbents Based on Secondary Carbon Fibers

A preliminary feasibility assessment for recycling composites reinforced with carbon fibers and cloths was performed. The recommended pyrolysis temperature ranges for extracting secondary carbon fiber from the samples were determined using synchronous thermal analysis as 450-500°C for disperse-reinforced composite EPAN-2B and 500-550°C for composite UTZF-2UMN. The sorption properties of the secondary carbon fibers after activation in CO2 were 222.4 m2/g specific sorption area by BET with 80 and 20% micro- and mesopores, respectively. The limiting adsorption volume for UTZF-2UMN composite fiber was 0.1169 cm3/g with a sorption capacity for benzene vapor of 0.134 cm3/g. The sorbents had high characteristic adsorption energies (by the Dubinin—Radushkevich method) that averaged 14.6 kJ/mol, which was only 30% less than primary fiber sorbents. The sample of UTZF-2UMN consisting of carbon cloth and phenol-formaldehyde resin had higher sorption properties with BET specific sorption areas for sorbents made of it that were three times higher than fibers made of EPAN-2B epoxide carbon-fiber plastic. The specific capacity for benzene vapor was 2.2 times higher, which was explained by the EPAN-2B fibers being highly contaminated by mineral impurities.

The nanoscale pore characteristics of coking coals: Part 1 – Optimization of the experimental conditions and calculation methods of specific surface area and micropore volume

The current evaluation system of the properties of coking coals is not sufficient since the so-called “abnormal coal” appears out control in some cases. In this study, in order to obtain reliable nanoscale pore structural parameters (specific surface area and micropore volume) to supplement and perfect the current evaluation system, a middle rank coking coal was investigated using low-temperature nitrogen physisorption technique to optimize the experimental conditions and calculation methods. the experimental conditions were listed as follows: sample evacuation times 4, 8, and 16 h; target temperatures 125, 150, 175 and 200 °C; sample weights 2000, 3500, and 5000 mg; sample particle size ranges -plot, and Dubinin-Radushkevich (DR) methods only within the adsorption isotherm branch were adopted. The optimal experimental conditions were found to be as follows: 8 h sample evacuation time, 150 °C target temperature, 5000 mg sample weight, and -plot, and DR methods, BET method is more accurate to calculate total specific surface area compared with t -plot method; t -plot method can distinguish between micropore and external specific surface areas; besides, t -plot method based on Magee’s equation is more applicable to the coking coal sample than that based on de Boer’s equation. DR method is more sensitive to evaluate micropore volume than t -plot method. In order to obtain reliable and comprehensive pore parameters, these three methods should be combined with each other.

TEXTURAL AND CATALYTIC CHARACTERISTICS OF DECATIONIZED MORDENITE AND ZSM-5 ZEOLITE

The textural characteristics of acid forms of mordenite and ZSM-5 zeolite (HM and HZSM-5) were described based on the experiments of adsorption of nitrogen at 77 K in a specially constructed apparatus. The specific surface (SP) of catalysts was determined by applying BET-equation (SPBET), Langmuir adsorption isotherm (SPLANG) and t-method. The „t-method” was used to determine the outer specific surface (SPextt) and the volume of micropores (Vμpt) of zeolite. The volume of micropores (VμpDR) was additionally determined also based on Dubinin-Radushkevich method. The reactions of diethyl ether dehydration in the temperature interval from 400 to 480 K got sped up in time on both zeolites (HM and HZSM-5) and did not fully follow the kinetics of the first order reaction. The initial period registered by the experiment (increase of reaction rate in time) is interpreted by the slow reaction of water occurrence in the reaction of dehydration, which is necessary for the occurrence of Brönsted acid centers, where diethyl ether dehydration takes place. Now the overall rate of the dehydration reaction is determined by the rate of water occurrence. When there is a sufficient number of acid centers, the rate of diethyl ether dehydration is determined by the surface reaction and the „initial period“ gradually disappears. In the reaction of diethyl ether dehydration on HZSM-5 catalyst, the reaction is slower, even water (which is a product of dehydration) occurs more slowly, and therefore in the observed temperature interval the reaction was not transferred to the first order reaction. By the adsorption of diethyl ether from gas phase on HM and HZSM-5 zeolite at 300 K, the insight was provided into hydrophilic-hydrophobic characteristics of the surface, as well as the insight into the character and strength of active centers of these zeolites. As the test reaction for determining acidity of the catalyst, the one selected was the reaction of isomerization of 3,3-dimethyl butene-1 (3,3-DMB-1), which takes place on Brönsted acid centers by the mechanism of carbonium ion. The results obtained by the experiments of adsorption of nitrogen and diethyl ether from gas phase are in accordance with the kinetic data of the diethyl ether dehydration reaction.

Comparative pore structure analysis of highly porous graphene monoliths treated at different temperatures with adsorption of N2 at 77.4 K and of Ar at 87.3 K and 77.4 K

We prepared nanoporous graphene monolith of different porosity by high temperature treatment up to 2073 K in Ar. The porosity is comparatively evaluated with N2 adsorption isotherms at 77.4 K and Ar adsorption isotherms at 87.3 K and 77.4 K. N2 adsorption at 77.4 K shows an excess adsorption amount below 3 × 10−3 of the relative pressure which is caused by the quadrupole moment of an N2 molecule. This effect doesn't give significant influence on the determination of the total surface area from subtracting pore effect (SPE) method, the micropore volume from Dubinin-Radushkevich (DR) method and the total pore volumes from the Gurvitch rule. However, the peak of the micropore size distribution determined by Horvath–Kawazoe (HK) method from N2 adsorption at 77.4 K shifts to a smaller size than that from Ar adsorption at 87.3 K by 0.05–0.09 nm.

Surface and porous characterization of activated carbon prepared from pyrolysis of biomass by two-stage procedure at low activation temperature and it's the adsorption of iodine

The textural characteristics of activated carbon prepared from biomass (Elaeagnus angustifolia seeds) activated with zinc chloride and two-stage pyrolysis in air was studied in this paper. The effect of activation temperature, duration time, impregnation concentration of agent and impregnation time was examined. Adsorption capacity was demonstrated with BET and iodine number. The highest iodine number was achieved as 1009mg/g. The Dubinin–Astakhov approach was used to study the pore size diameter of activated carbon. The Dubinin–Radushkevich method was used to evaluate the micropore volume of activated carbon. The structural morphology of activated carbons were evaluated by SEM. The surface chemical characteristics of activated carbons were determined by FTIR spectroscopic method.

Microporous Polystyrene Particles for Selective Carbon Dioxide Capture

This study presents the synthesis of microporous polystyrene particles and the potential use of these materials in CO(2) capture for biogas purification. Highly cross-linked polystyrene particles are synthesized by the emulsion copolymerization of styrene (St) and divinylbenzene (DVB) in water. The cross-link density of the polymer is varied by altering the St/DVB molar ratio. The size and the morphology of the particles are characterized by scanning and transmission electron microscopy. Following supercritical point drying with carbon dioxide or lyophilization from benzene, the polystyrene nanoparticles exhibit a significant surface area and permanent microporosity. The dried particles comprising 35 mol % St and 65 mol % DVB possess the largest surface area, ∼205 m(2)/g measured by Brunauer-Emmett-Teller and ∼185 m(2)/g measured by the Dubinin-Radushkevich method, and a total pore volume of 1.10 cm(3)/g. Low pressure measurements suggest that the microporous polystyrene particles exhibit a good separation performance of CO(2) over CH(4), with separation factors in the range of ∼7-13 (268 K, CO(2)/CH(4) = 5/95 gas mixture), which renders them attractive candidates for use in gas separation processes.

Effect of potassium permanganate pretreatment of pitch on the textural properties of pitch-based activated carbons

Petroleum pitch-based activated carbons (ACs) were obtained in this work from a combination of pretreatment with different amounts of potassium permanganate (KMnO4) and chemical activation with potassium hydroxide. The surface characteristics of the pitch after the KMnO4 pretreatment were characterized by means of Fourier transform infrared spectroscopy (FT-IR). The structural characteristics of the pitch after the KMnO4 pretreatment were determined by means of X-ray diffraction. The influence of the KMnO4 treatment on the textural properties of the petroleum pitch-based ACs was investigated by means of N2/77 K adsorption isotherms. The investigation also involved the use of the Brunauer-Emmett- Teller equation and the Dubinin-Radushkevich method. The FT-IR results show that the pretreatment promotes the formation of surface oxygen functionalities and leads to an increase of the interplanar distance (d002) of the functional groups induced between carbon layers. Moreover, the specific surface area of the pitch-based ACs increases in proportion to the amount of KMnO4 pretreatment and reaches its highest value of 2334 m2/g with 2 g of KMnO4 because the surface oxygen groups of the pitch act as an active site during chemical activation.

Effect of ZnCl2 impregnation ratio on pore structure of activated carbons prepared from cattle manure compost: application of N2 adsorption-desorption isotherms

Activated carbons were prepared from cattle manure compost (CMC) by ZnCl2 activation with various ZnCl2/CMC mass ratios. Based on the N2 adsorption-desorption isotherms, mathematical models including the Dubinin-Radushkevich (DR) equation, the αs plot, and the Horvath-Kawazoe method were used to analyze the pore structural characteristics of the prepared activated carbons. It was found that for carbons possessing both micro-and mesopores, the DR method provided a more accurate estimation than the αs method for the extent of microporosity. The effect of the ZnCl2 impregnation ratio on the pore structure was discussed using the DR method. The results revealed that pore evolution involved three distinct regions with increases in the amount of impregnated ZnCl2: raising the ZnCl2/CMC mass ratio from 0.00 to 0.50 resulted in a 19-fold increase in micropore volume (Vme D) but caused no change in the mesopore volume (Vme D); increasing the ZnCl2/CMC mass ratio from 0.50 to 1.00 led to an increment in Vmi D of about 50% and in Vme D of 170%; while raising the ratio from 1.50 to 2.50 caused a slight decrease in Vmi D but a 200% increment in the value of Vme D.

Characterization of Biomass Chars Formed under Different Devolatilization Conditions: Differences between Rice Husk and Eucalyptus

A comparison between the properties of chars produced by pyrolysis of rice husk and eucalyptus at different temperatures and heating rates has been performed. Low heating rate (LHR) devolatilization experiments were conducted in a fixed bed reactor at temperatures ranging from 600 to 900 °C, while a fluidized bed reactor was used for preparing chars at high heating rate (HHR) and temperatures of 800 and 900 °C. The morphological changes in carbonaceous solids produced in the different thermal treatments were observed by scanning electron microscopy (SEM). X-ray diffraction (XRD) and Raman spectra were obtained to evaluate the degree of char structural order. The chars were characterized by their ultimate analysis, oxygen functional group content, and CO2 adsorption at 0 °C using the Dubinin–Radushkevich method. The results obtained from the different techniques were contrasted to give an overview of the chemical and physical properties of the biomass char samples studied. The influence of the parent mater...

Microporosity of heat-treated manganese dioxide

A structural and micro-pore analysis of a series of heat treated electrolytic manganese dioxide (EMD) samples has been conducted. In terms of crystal structure, the original EMD with γ-MnO 2 structure (orthorhombic unit cell) was found to progressively convert to β-MnO 2 (tetragonal unit cell) at elevated temperatures. The structural transition was kinetically limited, with the higher temperatures leading to a greater degree of transformation. The orthorhombic γ-MnO 2 unit cell was found to contract along the a and b axes, while along the c axis an expansion was observed only at the highest heat treatment temperatures. These changes occur as a result of manganese ion diffusion leading to the formation of a denser, more defect free material. The porosity of these heat treated EMD samples was also examined by N 2 gas adsorption combined with various interpretive techniques such as the Kelvin equation, MP method, Dubinin–Radushkevich method, Dubinin–Astakhov method and a more modern density functional theory based approach. Despite shortcomings associated with certain techniques, all clearly indicated that the EMD micro-pore volume decreased and the meso- and macro-pore volume increased as the heat treatment temperature was increased. This was justified as a result of manganese ion movement during the structural rearrangement causing the small pores to be progressively sintered shut, while the larger pores were formed as a result of stress-induced cracking in the denser final product.

Production and characterization of activated carbons from olive-seed waste residue

Olive-seed waste residue char was employed as the precursor for the production of activated carbons with KOH activation. The effects of activation time and activation temperature on porosity of the prepared carbons were studied. The products were characterized by N 2 adsorption at 77 K, using the BET, α s and Dubinin–Radushkevich methods while the adsorption capacity from liquid phase was demonstrated by the isotherms of methylene blue adsorption from aqueous solutions. In comparison with the commercial grade carbons, the activated carbons from olive-seed waste residue showed considerably higher surface areas and can be characterized as “super-activated carbons”. The pores of the produced carbons are composed of micropores at the early stages of activation and of both micropores and mesopores at the late stages. Surface area and the pore volume were found to increase with the degree of burn-off, i.e. the activation time and temperature. Methylene blue removal capacity appeared to be comparable to commercial products and even higher at high degrees of activation.

Pyrolysis of eucalyptus at different heating rates: studies of char characterization and oxidative reactivity

Biomass is increasingly considered as an important resource for alternative fuels with significant environmental advantages. Recent studies in the literature highlight the importance of the structural modifications which occur after biomass devolatilization is performed under different conditions and their effect on char reactivity. In this context, this work deals with the characterization of chars obtained by the pyrolysis of eucalyptus at different temperatures and heating rates and the influence of their morphological changes on overall reactivity towards oxygen. Pyrolysis experiments at low heating rate (LHR) were carried out in a fixed bed reactor, in the range of 600–900 °C, while a fluidized bed reactor was employed for preparing chars at high heating rate (HHR), at 800 and 900 °C. Results relating to the elemental chemical composition of the chars are reported. In addition, pore volume and surface area of char particles were determined by CO 2 adsorption at 0 °C using the Dubinin–Radushkevich method. Chars were also observed by scanning electron microscopy (SEM) in order to visualize the differences in macro-morphology. LHR and HHR chars obtained at 900 °C were selected in order to investigate their oxidation behaviour and these results are discussed in terms of ultimate, surface area and SEM analyses.

Production of activated carbon from a new precursor: Molasses

Activated carbon has been prepared from molasses, a natural precursor of vegetable origin resulting from the sugar industry in Morocco. The preparation of the activated carbon from the molasses has been carried out by impregnation of the precursor with sulfuric acid, followed by carbonization. The adsorption capacity, the BET surface area, and the pore volume of the activated carbon were determined. The micropore volume was assessed by Dubinin- Radushkevich (DR) equation. The activated materials are mainly microporous and show the type I isotherm of the Brunauer classification for nitrogen adsorption. The activation in steam yielded a carbon that contains both micropores and supermicropores. Analysis of the nitrogen isotherm by BET and DR methods established that most of obtained carbons are highly microporous, with high surface areas (≥1200 m 2 /g) and very low mesoporosity.

Characterization of the microporosity of chromia- and titania-pillared montmorillonites differing in pillar density.: I. Adsorption of nitrogen

The microporosity of chromia- and titania-pillared clays differing in pillar density has been explored. Nitrogen adsorption data determined at very low relative pressures were used. These data were analyzed by means of the α s method and the BET, Langmuir, Dubinin–Radushkevich and Dubinin–Stoeckli approaches. The applicability of these methods for determination of the PILCs' microporosity was studied. The surface area calculated by the α s method can be considered as a total surface area of the materials studied. The BET method underestimates, whereas the Langmuir approach overestimates, the total surface area of these solids. The Dubinin–Radushkevich method can be applied only to characterize textural features of PILCs exhibiting homogeneously distributed narrow micropores (<0.7–1.0 nm width). The same holds for the Dubinin–Stoeckli relation. The method developed by Zhu et al. is useful for the determination of the porous structure of PILCs having a significant contribution of supermicropores (0.7–2.0 nm width). A good agreement between the total micropore volume of the materials studied and that obtained from the α s method was found. All the methods applied demonstrated that these solids possess micropores over a broad pore-size range. Chromia-pillared montmorillonites contain a significant amount of ultramicropores (<0.7 nm width), whereas titania-pillared clays show an important contribution of supermicropores. An alteration of the pillar density can provide a family of pillared clays that differ in the surface area, micropore volume, and micropore size distribution.

Characterization of the textural properties of metal loaded ZSM-5 zeolites

The textural properties of metal ion over-exchanged zeolites, Co–, Cu–, Ni–ZSM-5, were compared with those of the parent ZSM-5 by nitrogen adsorption measurements and photoelectron spectroscopy. The treatment of the adsorption isotherms permitted a thorough characterization of the microstructure of the samples. A first estimation of the microporous volume was made by the Dubinin–Radushkevich method. The “ t-plot” method was used to determine the external surface and to obtain another estimation of the microporous volume. Effective micropore size distribution was obtained with the Horvath–Kawazoe approach. The Dubinin–Radushkevich method overestimated the microporous volume of the zeolites, in particular when the solid had an important external surface. It is shown that Cu–ZSM-5 had micropore size and micropore size distribution very close to those of ZSM-5, whereas Co–ZSM-5 and Ni–ZSM-5 had lower microporous volumes and larger external surfaces. The external to internal (microporous) surface ratios, r s, and the mesoporous to microporous volume ratios, r v, are proposed as practical parameters to classify the solids with respect to their microstructure. ZSM-5, a pure microporous solid, has low values of both r s and r v parameters. Ni– and Co–ZSM-5 have high r s ad r v parameters, indicative of some degree of mesoporous character. Cu–ZSM-5 has intermediate characteristics, typical for micro-mesoporous solid. XPS measurements confirmed that copper ions penetrated to a greater extent in the channels of ZSM-5 zeolite than cobalt and nickel ions, which merely deposited on the external surface of ZSM-5 zeolite as oxidic aggregates.

Surface properties and porous texture of montmorillonite-(Ce or Zr) phosphate cross-linked compounds

In this work, pore texture characteristics of a series of Ce(IV) or Zr(IV) montmorillonite phosphate cross-linked compounds obtained by precipitation of cerium or zirconium phosphate with dilute H 3PO 4 on the micelles of an aqueous montmorillonite suspension, previously submitted to ion-exchange processes to replace its exchange ions with Ce(IV) or Zr(IV), are studied. Surface areas and pore volumes of the different materials prepared are determined by N 2 adsorption at 77 K and mercury porosimetry techniques. Analysis of the N 2 adsorption isotherms by the t-De Boer and Dubinin-Radushkevich methods, revealed the presence of a certain degree of microporosity in all the materials studied. Moreover, analysis of the Hg intrusion data permitted to determine the contribution of the macro- and mesopores to the total surface area and pore volume of the prepared compounds. The results reveal a greater specific surface area for these compounds than for montmorillonite and the evolution of this parameter with thermal treatment is related to the nature and content of phosphate in the different samples. However, the changes recorded in the V p and S/ V p parameters during the thermal process suggest that surface diffusion is the dominant transport mechanism in the sintering process.

Carbon Surface: Area, Porosity, Chemistry, and Energy

Data from the adsorption of nitrogen at 77 K are interpreted in terms of surface area and porosity, for a range of carbon blacks and two porous carbons, using the BET, αs, and Dubinin–Radushkevich methods. Heat of immersion (ΔHi) data, for nonpolar (n-heptane) and polar (water) liquids are correlated with surface structure and chemistry, respectively. An average value of ΔHi≈ 107 mJ m−2is obtained for the dispersion interaction of nonporous carbon blacks by immersion inton-heptane. Where nitrogen adsorption data indicate the presence of microporosity, higher values of ΔHiare observed which are thought to contain a contribution due to enhanced adsorption forces within pores. Data from samples of one specific black, which had been oxidized to varying levels using an oxygen/ozone fluidized bed apparatus, are presented showing a linear relationship between the surface oxygen levels and their polar interaction with water.