High Micropore Volume Research Articles

CO2 adsorption on carbon molecular sieves

The effect of the textural properties of a series of commercial carbon molecular sieves (CMS), prepared from different polymeric precursors, on their ability for CO2 adsorption at different temperatures has been studied. The adsorbents have been characterized by N2 and CO2 adsorption at 77 and 273K, respectively, together with measurements of immersion calorimetry into liquids of different molecular dimensions. The studied CMSs cover a wide range of porosity, from purely microporous carbons to samples containing wide micropores as well as a certain proportion of mesoporosity. Studies of CO2 adsorption, at atmospheric pressure (1bar) and three different temperatures (273, 298 and 323K), have shown that a high CO2 adsorption capacity requires the presence of a well-developed microporosity, as well as a high volume of narrow micropores. On the other hand, narrow micropores seem to be the key factor leading to a maximum capacity of CO2 adsorption, even at temperatures close to that of anthropogenic emissions of CO2.

Effect of potassium-doping on the microstructure development in polyfurfuryl alcohol – derived activated carbon

Potassium-doped activated carbon was prepared by mixing potassium salt with polyfurfuryl alcohol precursor followed by carbonization and activation. Several experimental techniques, such as thermogravimetric analysis, gas adsorption, X-ray diffraction and Raman scattering spectroscopy were employed to understand the effects of potassium on the texture and pore structures of the activated carbon, which ultimately affects the hydrogen adsorption properties. After doping with potassium, the activated carbon exhibits higher surface area, higher micropore volume, and enhanced hydrogen adsorption capacity. Understanding of how alkali metals affect surface area and micropore development in activated carbon may help to clarify the hydrogen adsorption mechanism and improve the design of suitable carbon-based hydrogen storage materials.

Microwave-Induced Degradation of Atrazine Sorbed in Mineral Micropores

The herbicide atrazine is a common pollutant in reservoirs and other sources of drinking water worldwide. The adsorption of atrazine from water onto zeolites CBV-720 and 4A, mesoporous silica MCM-41, quartz sand, and diatomite, and its microwave-induced degradation when sorbed on these minerals, were studied. Dealuminated HY zeolite CBV-720 exhibited the highest atrazine sorption capacity among the mineral sorbents because of its high micropore volume, suitable pore sizes, and surface hydrophobicity. Atrazine sorbed on the minerals degraded under microwave irradiation due to interfacial selective heating by the microwave, while atrazine in aqueous solution and associated with PTFE powder was not affected. Atrazine degraded rapidly in the micropores of CBV-720 under microwave irradiation and its degradation intermediates also decomposed with further irradiation, suggesting atrazine could be fully mineralized. Two new degradation intermediates of atrazine, 3,5-diamino-1,2,4-triazole and guanidine, were first identified in this study. The evolution of degradation intermediates and changes in infrared spectra of CBV-720 after microwave irradiation consistently indicate the creation of microscale hot spots in the micropores and the degradation of atrazine following a pyrolysis mechanism. These results indicate that microporous mineral sorption coupled with microwave-induced degradation could serve as an efficient treatment technology for removing atrazine from drinking water.

Preparation and characterisation of activated carbon from waste tea using K2CO3

Abstract Biomasses and their wastes have been used to produce various materials including activated carbons (ACs). The properties of the ACs mostly depend on the production method and the type of the raw material. Waste tea that is a biomass as a precursor was employed to prepare activated carbon (AC) in accordance with the conventional method using potassium carbonate (K2CO3). The effects of various process parameters such as carbonisation temperature and period, impregnation ratio and period on the characteristics of the final product were determined. The ACs were characterised in terms of the BET surface area, the true density, the pore volumes, chemical structure and surface morphology. The maximum surface area of the AC was 1722 m2/g produced at 900 °C and impregnation ratio of 1.0. The pore volumes of the samples were found out according to the Non Local Density Functional Theory (NLDFT) method. To produce the AC with high micropore volume fraction, 800 °C is the best convenient temperature for the experiments performed at impregnation ratios of 1.0, 1.5 and 2.0. The BET surface area and the mesopore volume fractions of the AC were substantially increased at 900 °C. The results showed that both the carbonisation temperature and impregnation ratio noticeably affected the micro and mesopore volumes as well as the BET surface area.

Micro-, Mesoporous Boron Nitride-Based Materials Templated from Zeolites

A second generation of boron nitride-based porous materials has been synthesized by a double nanocasting process via a carbonaceous template as a medium starting from a zeolite. In the multistep process, we coupled several synthetic strategies such as chemical vapor deposition (CVD) and polymer-derived ceramic (PDCs) routes to prepare carbonaceous templates through infiltration of zeolite Y (FAU structure type) by propylene in the gaseous phase then infiltration of the carbonaceous replica having a high micropore volume (0.67 cm3/g) with polyborazylene in the liquid phase followed by pyrolysis and mold destruction. These porous BN-based architectures present a bimodal pore size distribution with a high portion of micropores (∼0.20 cm3/g) that are unambiguously evidenced by nitrogen physisorption based on a nonporous BN reference isotherm. They exhibited a high specific area (570 m2/g), a high pore volume (0.78 cm3/g), and a lack of long-range ordering as evidenced by BET, XRD and TEM experiments. The two first properties allow to open catalyst applications of these materials.

Preparation and characterization of activated carbons for SO2 adsorption from Taixi anthracite by physical activation with steam

Taixi anthracite was used as a precursor to prepare activated carbons (AC) for SO2 adsorption from flue gas. In this work the activated carbons were prepared by physical activation with steam. Specifically, the effects of activation temperature and burn-off degree on the physico-chemical properties of the resulting AC samples were comparatively studied. The different types of pore volumes, pore size distributions and surface chemistries of the activated carbons on the SO2 adsorption were also analyzed. The results show that the increasing burn-off leads to samples with continuous evolution of all types of pores except ultramicropore. The ultramicropore volume increases to a maximum of 0.169 cm3/g at around 50% burn-off and then decreases for 850 °C activation. At higher activation temperature, the micropore volume decreases and the mesopore structure develops to a certain extent. For all the resulting AC samples, the quantities of the basic surface sites always appear much higher than the amount of the acidic sites. The activated carbon prepared with higher micropore volume, smaller median pore diameter and higher quantities of the basic surface sites represents better SO2 sorption property.

Physico-chemical surface modification of activated carbon by oxyfluorination and its electrochemical characterization

The surface of a phenol-based activated carbons (ACs) used as an electrode in an electric double-layer capacitor (EDLC) was oxyfluorinated at room temperature with different F 2:O 2 gas mixtures, and the effects of these surface modifications on EDLC electrical performance were investigated. The specific capacitance of the oxyfluorinated AC-based EDLC was measured in a 1 M H 2SO 4 electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g −1 to 391 and 189 F g −1 with the scan rates of 5 and 50 mV s −1, respectively, over compared to those of an untreated AC-based EDLC when the oxyfluorination ratio was at the optimal F 2:O 2 = 5:5. This was attributed to the synergistic effect of surface chemical compositions and textural properties of the resulting oxyfluorinated AC, which had the highest micropore volume, an optimal mesopore volume, and electrochemically active surface functional groups, such as C–F and quinone C O.

Design of activated carbon–clay composites for effluent decontamination

Adsorption offers an efficient technology for removing volatile organic compounds (VOCs) from air pollution sources. Often activated carbons (ACs) are employed owing to their large specific surface areas, high micropore volumes, rapid adsorption capabilities and selectivity towards organic molecules compared to water vapour or air. However, when large volumes of gas are to be treated pressure drop limitations may arise from the use of conventional powder adsorption beds. For these applications conformation of the activated carbon as open channel honeycomb monoliths can take advantage of the almost null pressure drop caused by these structures. Similarly, conformation as extrudates or tubes although increasing the pressure drop due to the turbulent gas flow can improve any diffusion limitations that the open channel monoliths can suffer. Conformation of the AC as a ceramic composite also improves the handling characteristics. By the use of a silicate clay binder a commercially available AC, was conformed in three different monolithic geometries; changing the channel width and the wall thicknesses and as solid extrudates and tubes. The textural and mechanical properties of these conformed composite structures were determined and the results analysed along with their dynamic adsorption capacities towards toluene at 30°C, used as a probe molecule to establish criteria by which the most suitable structure for industrial use could be selected.

Influence of impregnation ratio on coffee ground activated carbon as landfill leachate adsorbent for removal of total iron and orthophosphate

Coffee grounds waste was used to prepare activated carbon with particle size between 1.18 and 2 mm by chemical activation with sulphuric acid. The influence of impregnation ratio on physical properties of activated carbon and removal efficiency of total iron and orthophosphate (PO 4–P) was studied. Impregnation ratio of 0.5 was found optimum for preparing activated carbon with high pore surface area (224.7 m 2/g) and micropore volume (0.07986 cm 3/g). Batch experiments were conducted to study the effects of contact time, pH, particle size and adsorbent dosage. Impregnation ratios of 2.5 and 0.5 were found to be optimum for the adsorption of total iron and PO 4–P, respectively at doses of 10 g and pH 8.1. pH 13 was optimum for iron removal while pH < 5 and > 11 was optimum for PO 4–P removal. The adsorption capacity increased with increasing adsorbent dosage for total iron. However, this trend was exceptional for PO 4–P with fluctuating adsorption capacity. The smaller particle size yielded larger adsorption capacity.

Phase-Transformation Synthesis of SAPO-34 and a Novel SAPO Molecular Sieve with RHO Framework Type from a SAPO-5 Precursor

SAPO-34 and a novel SAPO molecular sieve with the RHO framework (designated as DNL-6) were synthesized using SAPO-5 (the denser phase) as the precursor and diethylamine (DEA) as the template. The entire transition process had been investigated by XRD, SEM, XRF, and NMR spectroscopy, which clearly revealed a solution-mediated transport mechanism attributed to the transformation from SAPO-5 precursor to SAPO-34 via oscillating phases [SAPO-5 (FD = 16.9 T/nm3) => SAPO-34 (15.1) + DNL-6 (14.5) → DNL-6 → SAPO-34]. The initially formed SAPO-34 was different from the final one in this transformation due to very different percentages of organic inclusions, indicating that the host−guest interactions played important roles for the phase selectivity during the synthesis. DNL-6, obtained as an intermediate of the transformation process, possessed good thermal stability, large microporous surface area (724 m2/g), and high micropore volume (0.36 cm3/g). Rietveld refinement showed that the framework of calcined DNL-6 h...

Carvedilol dissolution improvement by preparation of solid dispersions with porous silica

Impregnation of porous SiO 2 (Sylysia) with carvedilol from acetone solution was used to improve dissolution of this poorly water-soluble drug. Solvent evaporation in a vacuum evaporator and adsorption from acetone solution were the methods used to load various amounts of carvedilol into the Sylysia pores. The impregnated carriers were characterized using nitrogen-adsorption experiments, X-ray diffraction, wettability measurements, attenuated total reflectance FTIR spectroscopy and thermal analysis. The impregnation procedures resulted in a significant improvement of drug release compared to dissolution of pure carvedilol or its physical mixtures with Sylysia. The results showed that when the drug precipitated in a thin layer within the carrier the dispersion retained a high specific surface area, micropore volume, and drug-release rate from the solid dispersion. Increasing the amount of drug in the solid dispersion caused particle precipitation within the pores that decreased the carrier's specific surface area and pore volume and decreased the release rate of the drug. The results also suggest that the amorphous form of carvedilol, the improved wettability and weak interactions between the drug and carrier in the solid dispersion also contribute to improved dissolution of the drug from the dispersion.

Comparative study of the textural characteristics of oil palm shell activated carbon produced by chemical and physical activation for methane adsorption

The objective of this study is to relate textural and surface characteristics of microporous activated carbon to their methane adsorption capacity. Oil palm shell was used as a raw material for the preparation of pore size controlled activated carbon adsorbents. The chemical treatment was followed by further physical activation with CO 2. Samples were treated with CO 2 flow at 850 °C by varying activation time to achieve different burn-off activated carbon. H 3PO 4 chemically activated samples under CO 2 blanket showed higher activation rates, surface area and micropore volume compared to other activation methods, though this sample did not present high methane adsorption. Moreover, it was shown that using small proportion of ZnCl 2 and H 3PO 4 creates an initial narrow microporosity. Further physical activation grantees better development of pore structure. In terms of pore size distribution the combined preparation method resulted in a better and more homogenous pore size distribution than the conventional physical activation method. Controlling the pore size of activated carbon by this combined activation technique can be utilized for tuning the pore size distribution. It was concluded that the high surface area and micropore volume of activated carbons do not unequivocally determine methane capacities.

Effect of a GDL based on carbon paper or carbon cloth on PEM fuel cell performance

A commercially available GDL based on carbon paper or carbon cloth as a macroporous substrate was characterized by various physical and electrochemical measurements: mercury porosimetry, surface morphology analysis, contact angle measurement, water permeation measurement, polarization techniques, and ac-impedance spectroscopy. SGL 10BB based on carbon paper demonstrated dual pore size distribution and high water flow resistance owing to less permeable macroporous substrate, and more hydrophobic and compact microporous layer, as compared to ELAT-LT-1400 W based on carbon cloth. The membrane-electrode-assembly fabricated using SGL 10BB showed an improved fuel cell performance when air was used as an oxidant. The ac-impedance response indicated that a microporous layer which has high volume of micropores and more hydrophobic property allows oxygen to readily diffuse towards the catalyst layer due to effective water removal from the catalyst layer to the gas flow channel.

ChemInform Abstract: A Microporous Carbon Produced by Arc-Evaporation.

A carbon soot formed by arc evaporation and activated by heating under carbon dioxide is found to have a surprisingly high internal micropore volume (> 0.25 ml g–1) and an apparent BET surface area of ca. 700 m2 g–1, a large proportion of the pores are ca.⩽5 A; transmission electron microscopy shows a highly disordered microstructure, which electron irradiation readily transforms into quasi spherical concentric nanoparticles of diameter of ca. 60 A, the carbon material, which is highly absorbent to methane, shows molecular sieving properties and is more inert to oxidation than other forms of high surface area carbon.

Adsorptive Removal of Dibenzothiophene in Diesel Fuel on an Adsorbent from Rice Hull Activated by Phosphoric Acid

Rice hull (designated with RH) was activated by phosphoric acid to prepare an adsorbent for the removal of sulfur-containing compounds from diesel fuel. Adsorption tests for both, a 300 µg.g-1 dibenzothiophene (DBT)-containing n-octane solution using as model oil and a commercial hydro-treated diesel fuel, were performed to elucidate the effect of varying phosphoric acid to RH ratio, treating temperature and the removal of silica from the adsorbent on the combination of the textural structure, surface chemical property and adsorption capacity. It was indicated that high surface area and micro-pore volume of the adsorbent favored the adsorption of DBT and its derivatives. Richening of oxygen-containing compounds on the adsorbent surface was advantageous to the adsorption and removal of DBTs. At a phosphoric acid and RH weight ratio of 3:1 by using a two-step treatment, a satisfactory adsorbent with an adsorption capacity of 28.89 mg S/g was successfully prepared. If the silica in the adsorbent was further removed, the product exhibited the highest performance, reaching 30.43 mg S/g for the model oil and 21.79 mg S/g for the commercial diesel fuel. Both the textural structure and the surface chemical property like acidic groups of a RH-based adsorbent play important roles in its adsorption behaviors, and the formation of donor-acceptor complexes between surface acidic groups and DBT may probably benefit DBT adsorption capacity.

Comparison of the Dubinin–Radushkevich and Quenched Solid Density Functional Theory approaches for the characterisation of narrow microporosity in activated carbons obtained by chemical activation with KOH or NaOH of Kraft and hydrolytic lignins

The classical DR method and the Quenched Solid Density Functional Theory (QSDFT) approach have been used to analyse N 2 at 77 K isotherms determined on activated carbons prepared by alkaline chemical activation of different lignins. The QSDFT pore size distributions are bimodal with a narrow peak below 1 nm and a broad peak from 1 to 2.5–3.5 nm. Deconvolution allows estimation of the volumes and widths of the narrow micropores. These are lower than estimated by the DR analysis as this does not separate micropore and non-micropore adsorption. On the basis of the QSDFT analysis, the optimum conditions for obtaining materials with a high volume of narrow micropores were activation temperatures of 550–650 °C, hydroxide/lignin ratio of 1 and dwell time at the maximum activation temperature of 30 min. KOH was preferable to NaOH as it requires lower temperatures and results in materials with higher narrow micropore volumes. The “best” material obtained, prepared with KOH at 550 °C, had mean micropore width of 0.7 nm and micropore volume of 0.37 cm 3 g −1 which compares very favourably with molecular sieve carbons prepared from synthetic polymers. Furthermore, this material was obtained with an activation yield of 32.9%, which is quite high for alkaline chemical activation.

FAU-Type Zeolite Nanocasted Carbon Replicas for CO2 Adsorption and Hydrogen Purification

Microporous ordered carbon have been synthesized by the nanocasting process from zeolite Y using acetylene and furfuryl alcohol as carbon precursors. If the proper synthesis conditions are chosen, these materials retain the long-range order of the zeolite mold. The resulting carbons possess a large surface area (≥2200 m2/g), a high microporosity (≥1.0 cm3/g), and a controlled pore size distribution, which was tailored by the wall thickness of the zeolite template. Because of their high micropore volume, the carbon replicas of zeolite Y are attractive adsorbent materials and might be used to replace conventional activated carbons as adsorbents in pressure swing adsorption processes (PSAs) for H2 purification. In the present contribution, we evaluate the adsorption capacity of the carbon replicas in a H2-PSA based on their single-component adsorption isotherms of CO2, CH4, and N2 measured at room temperature. The ideal adsorbed solution theory (IAST) was used to predict the co-adsorption of CO2/CH4/N2 gas m...

Preparation and hydrogen storage of activated rayon-based carbon fibers with high specific surface area

Activated carbon fibers were prepared from rayon-based carbon fibers by two step activations with steam and KOH treatments. Hydrogen storage properties of the activated rayon-based carbon fibers with high specific surface area and micropore volume have been investigated. SEM, XRD and Brunauer–Emmett–Teller (BET) were used to characterize the samples. The adsorption performance and porous structure were investigated by nitrogen adsorption isotherm at 77 K on the base of BET and density functional theory (DFT). The BET specific surface area and micropore volume of the activated rayon-based carbon fibers were 3144 m 2/g and 0.744 m 3/g, respectively. Hydrogen storage properties of the samples were measured at 77 and 298 K with pressure-composition isotherm (PCT) measuring system based on the volumetric method. The capacities of hydrogen storage of the activated rayon-based carbon fibers were 7.01 and 1.46 wt% at 77 and 298 K at 4 MPa, respectively. Possible mechanisms for hydrogen storage in the activated rayon-based carbon fibers are discussed.

Influence of chemical vapour infiltration conditions of acetylene on the structural and textural properties of EMT-type zeolite nanocasted carbon replica

Ordered microporous carbons were synthesized by the nanocasting process using EMC-2 zeolite (EMT structure type) and acetylene as a mould and a carbon precursor, respectively. In this study, the conditions of the synthesis methods for preparing the ordered microporous carbons were examined. Temperature and duration parameters for the chemical vapour infiltration were optimized to yield an ordered carbon replica that displays up the three XRD diffraction peaks. This faithful replica exhibits also a high micropore volume (1.3–1.4 cm3/g) with mainly supermicroporosity, a high specific surface area (>2900 m2/g) and nearly no mesoporosity. The pore size distribution calculated with NLDFT method from nitrogen physisorption data shows three maxima at 0.6, 1.0 and 1.8 nm diameters. The second is due to the zeolite wall dissolution. The first and the third are attributed to different types of default. Compared to the classical two-step procedure, the direct infiltration with acetylene appears an interesting route for the preparation of ordered microporous carbon replicas with high micropore volume.

Facile Purification of Porous Metal Terephthalates with Ultrasonic Treatment in the Presence of Amides

A facile purification method for metal-organic frameworks (MOFs), especially the ones containing insoluble 1,4-benzenedicarboxylic acid (terephthalic acid) in the pore, has been suggested. The purification method consists of the treatment of the MOF with amides such as N,N-dimethylformamide, especially under ultrasound treatment. The purification is completed within 1 h at 70 degrees C as has been confirmed by XRD, nitrogen adsorption, FTIR and TGA measurements. The purification method proved to be simple, one-step, fast and energy-efficient. The MOFs purified by the proposed method show high surface area and micropore volume, confirming the efficiency of the method. The proposed method will lead to a new access to activate (for example, to remove carboxylic acids) MOFs that are unstable above around 100 degrees C. Additionally, the method may be used to transform a non-porous MOF-type material into a porous MOF structure. However, adequate solvents will be necessary for the facile purification of MOFs.