High Micropore Volume Research Articles

Preparation of nanoporous activated carbon and its application as nano adsorbent for CO2 storage

Nanoporous activated carbons, as adsorbent for CO2 storage, were prepared from walnut shells via two chemical processes including phosphoric acid treatment and KOH activation at high temperature. Specific surface area and porosities were controlled by KOH concentration and activation temperature. The obtained adsorbents were characterized by N2 adsorption at 77.3 K. Their carbon dioxide adsorption capacities were measured at different pressures at 290 K by using volumetric adsorption equipment. The KOH-treated nanoporous carbons typically led to the production of high specific surface areas and high micropore volumes and showed better performance for CO2 adsorptions. The maximum experimental value for adsorption capacity happened when pressure increased from 5 to 10 bar (1.861-2.873mmol·g−1). It was found that in order to improve the highest capacity of CO2 adsorption for KOH-modified carbon (9.830-18.208mmol·g−1), a KOH: C weight ratio of 3.5 and activation temperature of 973 K were more suitable for pore development and micro-mesopore volume enhancement.

Activated carbons derived from tamarind seeds for hydrogen storage

To make hydrogen economy a reality, the key technical challenges that need to be addressed are Hydrogen generation, transmission and storage for application in fuel cells. Among them, H2 storage presents a major challenge to material scientists to meet the USDOE target of 5.5wt%. The present paper investigates the hydrogen storage capacity of activated carbons derived from tamarind seeds by thermal, microwave and by chemical KOH activation treatment. The various parameters optimised to obtain high hydrogen storage capacity are KOH concentration, duty cycle of microwave pulsing, carbonization, hydrogen adsorption conditions etc., The surface area, micropore volume, pore size and nitrogen adsorption measurements were determined for all the samples and found that the carbonization temperature and concentration of KOH play a major role in increasing the surface area, micropore volume and pore size. We have obtained a high surface area activated carbon of 1785m2g−1, micropore volume of 0.94cm3g−1 and pore size of around 0.8–1.1nm. The maximum hydrogen storage capacity of these activated carbons from tamarind seeds at RT and 4.0MPa was found to be 4.73wt%, which is about 80% of the USDOE target. The samples also show good cyclic stability for hydrogen adsorption and desorption studies. These results suggest that activated carbons fabricated from tamarind seeds with high surface area and micropore volume will be an ideal candidate for hydrogen storage.

Amphiphilic organosilane and seed assisted hierarchical ZSM-5 synthesis: Crystallization process and structure

The synthesis, characterization, and catalytic applications of hierarchical zeolite has drawn a lot of research interest. During hierarchical zeolite synthesis, different products can be formed due to the difference in crystallization mechanism. Here we detail the crystallization process and structure of the hierarchical ZSM-5 synthesized with amphiphilic organosilane and seed. First, the effects of synthesis parameters on zeolite products were studied in detail to optimize the hierarchical zeolite synthesis process. Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC), seed and rotation are the required conditions for the synthesis of high quality hierarchical ZSM-5 with both high micropore and mesopore volume. The obtained hierarchical zeolite samples were then subjected to detailed structural analysis including XRD, SEM, TEM, nitrogen sorption and a sonication fragmentation method. Hierarchical ZSM-5 synthesized herein was a mesoporous aggregate of ZSM-5 nanoparticles with a core/shell structure based on the characterization results. The core part is hierarchical ZSM-5 with a higher degree of connectivity between zeolite nanoparticles or even the so-called mesoporous zeolite single crystal. The shell component is the hierarchical ZSM-5 aggregate with loosely packed ZSM-5 nanoparticles. The formation process and structure change was finally investigated by monitoring the morphology, crystallinity, and porosity of samples obtained with different crystallization times. The results indicated that hierarchical ZSM-5 is a kinetically controlled product in ZSM-5 crystallization process through a nanoparticle-oriented aggregation mechanism. The TPOAC, seed, and crystallization time are the conditions kinetically controlling the crystallization process.

Systematic investigation of the pore structure and surface properties of SBA-15 by water vapor physisorption

In order to establish a structure-property correlation in water vapor sorption, various sets of the ordered mesoporous silica SBA-15 with systematically varying properties were synthesized and characterized. General trends concerning the surface polarity, aging temperature during synthesis and micropore volume were observed. Calcining the materials with increasing temperatures of 300–800 °C decreases the performance in water vapor sorption which correlates mainly with the amount and type of silanol groups on the silica surface. Furthermore, the aging temperature during synthesis influences the water vapor sorption capacity of SBA-15 at low relative pressure. The best results in terms of an increased uptake of water over a broad range of relative pressure can be obtained for materials with high micropore volume and high surface polarity. They can be tailor-made by using a routine to remove the template, i.e., a combination of extraction with ethanol and subsequent calcination at 300 °C.

Rapidly reversible adsorption of methane with a high storage capacity on the zeolite templated carbons with glucose as carbon precursors

Abstract Microporous carbon material with a high surface area of 1562 m 2 /g is prepared via an impregnation method with NaY zeolite as hard template. The results indicate that glucose, an environmental friendly material, could be used as the carbon precursor of zeolite templated carbons, in comparison with the toxicity of furfuryl alcohol and lower surface area of carbons generated from sucrose. Effects of reactant molar ratios and carbonization conditions on the textural properties are addressed. Although higher carbonization temperature favors more complete carbonization reactions, it also causes the collapse of small pores and the formation of large pores at the same time. Further characterizations of the obtained carbon materials with XRD, SEM and N 2 adsorption–desorption measurements are presented. Methane adsorption tests on carbon materials are investigated with the static volumetric method at 300 K. The higher adsorption amount of 9.9 wt.% was achieved at 3.5 MPa on sample with a higher micropore volume, indicating that micropores were playing a crucial role for the methane storage process.

Conventional hydrothermal synthesis of nanoporous molecular sieve 13X for selective adsorption of trace amount of hydrogen sulfide from mixture with propane

Nanoporous molecular sieve 13X was successfully synthesized through the conventional hydrothermal method by using sodium aluminates as Al source and water-glass solution as an economic reagent for Si source. The hydrothermal reaction was performed under a static condition in an air oven maintained at 90 ± 5 °C for 24 h. Nano molecular sieve was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and nitrogen adsorption desorption tests. The adsorption capacity of molecular sieve 13X for trace amount of hydrogen sulfide (72 ppm) mixed with propane was investigated using the volumetric method by two different detectors. After adsorption process the amount of H2S in output gas was about 27 ppm and this confirms approximately more than 62% adsorption at 25 bar and 298 K. As compare CO2 adsorption capacity was measured by the same method. The high adsorption capacity of CO2 is attributed to the high micropore volume on 13X sample. Therefore a cost-effective adsorbent was synthesized successfully to separate the small amounts of acidic and corrosive gas (H2S) from propane.

Novel synthesis of a micro-mesoporous nitrogen-doped nanostructured carbon from polyaniline

Nanostructured carbons with relatively high nitrogen content (3–8%) and different micro and mesoporosity ratio were prepared by activation of polyaniline (PANI) with a ZnCl2–NaCl mixture in the proportion of the eutectic (melting point 270 °C). It was found that the activated carbons consisted of agglomerated nanoparticles. ZnCl2 plays a key role in the development of microporosity and promotes the binding between PANI nanoparticles during heat treatment, whereas NaCl acts as a template for the development of mesoporosity of larger size. Carbons with high micropore and mesopore volumes, above 0.6 and 0.8 cm3/g, respectively, have been obtained. Furthermore, these materials have been tested for CO2 capture and storage at pressures up to 4 MPa. The results indicate that the nitrogen groups present in the surface do not seem to affect to the amount of CO2 adsorbed, not detecting strong interactions between CO2 molecules and nitrogen functional groups of the carbon, which are mainly pyridinic and pyrrolic groups.

Large-scale synthesis of high-quality zeolite-templated carbons without depositing external carbon layers

Zeolite-templated carbons (ZTCs) possess extra-large surface areas (⩾2000m2g−1) and micropore volumes (⩾1.0cm3g−1), which allow superior electrochemical performances and gas adsorption properties compared with conventional activated carbons. Unfortunately, ZTCs have been mostly synthesized at a small laboratory-scale due to the limited reproducibility of carbon structures at a large-scale synthesis. The biggest challenge in the carbon replication of zeolites is the deposition of dense carbon layers at the external surface of zeolite crystallites before the complete zeolite micropore filling with carbon. The formation of external carbon layers hinders a faithful carbon replication of zeolite structure, and also significantly limits the adsorption properties of the resultant template-free ZTCs. Here, we demonstrate that acetylene chemical vapor deposition (CVD) at a relatively mild temperature (823K), followed by thermal treatment at 1073K, can selectively deposit carbons in the micropores of zeolites, regardless of the synthesis batch size. By combining the mild CVD condition and the use of a rotary tubular furnace, which allows the continuous agitation of zeolites during the synthesis, 50g NaX and BEA zeolite could be faithfully replicated to ZTCs with a high BET surface area (>2700m2g−1) and micropore volume (>1.10cm3g−1) without depositing nonporous external carbon layers that significantly hinder the bulky molecular diffusion.

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1cm3/g) and high packing density (0.7g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160cm3 (STP)/cm3 at 25°C and 3.5MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700°C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175cm3 (STP)/cm3 at 25°C and 5MPa and 200cm3 (STP)/cm3 at 25°C and 10MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5nm at pressure up to 10MPa was estimated to understand their contribution to the total adsorption capacity.

Effect of the Adsorbent Pore Structure on the Separation of Carbon Dioxide and Methane Gas Mixtures

The role of the pore structure of the adsorbent in separating CO2/CH4 mixtures was investigated in this study. Three carbon materials with different pore structures, activated carbon (AC), superactivated carbon (Super-AC), and ordered mesoporous carbon (OMC), were used to represent the different porosity characteristics of adsorbents. Some valuable conclusions were obtained via the experiments and analysis: (1) The adsorption capacity and affinity of CH4 are more dependent on the specific surface area and the micropores than those of CO2 at low pressure. (2) When the coverage of CO2 reaches a certain level, the interaction between mesoporous materials and CO2 is stronger than that between microporous materials and CO2. The mesoporous materials can absorb more CO2 than the microporous materials in high pressure. (3) At atmospheric pressure, high specific surface area and micropore volume are adverse to adsorption separation of CO2/CH4 gas mixtures. The mesoporous materials in this work showed higher select...

Methane Adsorption Microcalorimetry of Activated Carbon Fibre Synthesized from Empty Fruit Bunch Fibre

In this article, the methane adsorption behaviour of activated carbon fibre (ACF), a nanoporous material, was examined for adsorbed natural gas (ANG) applications. The ACF was produced from palm fibre-based materials through carbonization, followed by CO2 activation. The carbonization of empty fruit bunch (EFB) fibres was conducted at temperatures of 85–250 °C in an oxidative atmosphere. The produced ACF showed well-developed pore structure with high micropore volume and excellent pore-size distribution. The ACF, predominantly with microporous pores, fulfils the requirements as an excellent adsorbent for methane adsorption. The optimal carbonization conditions for improving methane adsorption capacity were achieved using concentrated H2SO4at 250 °C, followed by activation at 900 °C. Only physisorption occurred during the adsorption of methane on ACF. The EFB fibre-derived ACF has high potential for use in NG adsorption and storage applications via ANG technology.

Nitrogen and oxygen co-doped microporous carbons derived from the leaves of Euonymus japonicas as high performance supercapacitor electrode material

Bio-inspired nitrogen and oxygen heteroatom-doped porous carbons are prepared by facile pyrolysis of leaves of Euonymus japonicas (LEJ) with KOH activation. The pore textures of the carbons derived from LEJ (LEJCs) have been well controlled by adjusting the activation temperature. The obtained LEJCs possess large specific surface areas between 613 and 2071 m2 g−1 and moderate pore volumes of 0.281–0.872 cm3 g−1 with high micropore volume ratio of 74–96% and pore size distributions in the range of 0.5–2 nm. The optimized LEJC sample has 4.0 wt% N and 7.3 wt% O heteroatom-doped two-dimensional microporous structure as well as suitable specific surface area of 1268 m2 g−1 and pore volumes of 0.486 cm3 g−1 with the highest micropore volume ratio of 96% and main pore size distribution at 0.55 nm. The optimized LEJC material combining double layer and Faradaic redox electrochemical capacitance contributions, exhibits the max specific capacitance of 303 F g−1 at 0.2 A g−1, and 87% of the capacitance (264 F g−1) may be preserved when the current density increases to 40 A g−1 in 6 M KOH aqueous electrolyte. A high cycle stability with 80% capacitance retention has been observed after 5000 charge–discharge cycles at 5 A g−1. The max energy density of 15.2 Wh kg−1 has been gotten at the power density of 60.3 W kg−1, and a good energy density of 5.0 Wh kg−1 can be found at the high power density of 8.6 kW kg−1 in 6 M KOH.

Preparation and Structure Regulation of Silicon Carbide-Derived Carbon/ Spherical Natural Graphite Composites

To meet the requirements of the energy storage materials for high energy density and high power density, porous silicon carbide/derived carbon-spherical natural graphite (SiC-CDCs@NG) composites were prepared. The composites were composed of tailored porous carbide-derived carbon and graphitized carbon with excellent conductivity and a high energy storage capacity. The composition, structure, morphology, pore structure, and specific surface area of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and N2 adsorption/ desorption analysis. The composites exhibited a high and adjustable specific surface area and micro-pore volume, with a micro-pore size of between 0.5 and 0.7 nm. Varying the molar ratio of NG and Si allowed optimization of the micro-pore volume, pore size distribution, specific surface area, and composition and content of the CDCs shell and NG core.

Hg0 removal from flue gas over different zeolites modified by FeCl3

The elemental mercury removal abilities of three different zeolites (NaA, NaX, HZSM-5) impregnated with iron(III) chloride were studied on a lab-scale fixed-bed reactor. X-ray diffraction, nitrogen adsorption porosimetry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and temperature programmed desorption (TPD) analyses were used to investigate the physicochemical properties. Results indicated that the pore structure and active chloride species on the surface of the samples are the key factors for physisorption and oxidation of Hg0, respectively. Relatively high surface area and micropore volume are beneficial to efficient mercury adsorption. The active Cl species generated on the surface of the samples were effective oxidants able to convert elemental mercury (Hg0) into oxidized mercury (Hg2+). The crystallization of NaCl due to the ion exchange effect during the impregnation of NaA and NaX reduced the number of active Cl species on the surface, and restricted the physisorption of Hg0. Therefore, the Hg0 removal efficiencies of the samples were inhibited. The TPD analysis revealed that the species of mercury on the surface of FeCl3–HZSM-5 was mainly in the form of mercuric chloride (HgCl2), while on FeCl3–NaX and FeCl3–NaA it was mainly mercuric oxide (HgO).

Effect of the morphological and surface properties of CeO2-based catalysts on the soot oxidation activity

In diesel particulate filters, a solid (soot)–solid (catalyst) reaction occurs and, in these cases, the catalyst morphology plays a relevant role, being the number of contact points a critical feature for the resulting reaction rate.For this reason, two different ceria-based catalyst morphologies have been investigated in this work, for the soot oxidation reaction: first, a ceria catalyst was prepared by solution combustion synthesis (SCS), which lead to a specific surface area of 29m2/g. On the other hand, three-dimensional self-assembled (SA) stars ceria, so-called due to their branched morphology starting from a central nucleus, exhibited a higher specific surface area (124m2/g), a high availability of contact points between soot particles and the catalyst itself, due to the concavities of the obtained morphology, and interesting surface features at the nanoscale. The synthesis method was tuned in order to resort to a desired and well-defined morphology in terms of shape and size.Aged stars were also taken into account, in order to fully evaluate the advantages and drawbacks of this new material against classic SCS catalysts.Compared to the SCS ceria catalyst, the SA stars have a much higher microporous volume, being of about 0.04cm3/g, and a finer crystallite size. SA stars showed a better activity towards soot oxidation: the peak oxidation temperature dropped from 614°C (in the non-catalytic case) to 403°C in tight contact conditions, and to 552°C in loose ones. XPS analysis elucidated that this can be due to a higher surface oxygen availability as compared to SCS ceria, while HRTEM revealed that surface crystallites show oxygen defective structures, almost absent at the SCS catalyst surface, which also might involve a higher redox capability.In loose contact conditions, being the most realistic testing condition because soot deposits on the catalytic layer of the diesel particulate filter without any force exertion, the SA stars exhibited the lowest onset temperature, even after aging, thus proving their higher intrinsic activity. Moreover, aged stars, which are less active than fresh SCS powders in tight contact conditions, regain good results in the loose ones, thanks to intrinsic capability to catch soot particles, peculiar of the SA star morphology.In the perspective of applying such engineered morphologies in diesel particulate filters, the three-dimensional shape of SA stars may involve an enhancement of the number of contact points between the cake layer and the catalyst one, thus fostering the final activity.

K2S-activated carbons developed from coal and their methane adsorption behaviors

The main purpose of this work is to prepare various activated carbons by K2S activation of coal with size fractions of 60–80 meshes, and investigate the microporosity development and corresponding methane storage capacities. Raw coal is mixed with K2S powder, and then heated at 750 °C–900 °C for 30 min–150 min in N2 atmosphere to produce the adsorbents. The texture and surface morphology are characterized by a N2 adsorption/desorption isotherm at 77 K and scanning electron microscopy (SEM). The chemical properties of carbons are confirmed by ultimate analysis. The crystal structure and degree of graphitization are tested by X-ray diffraction and Raman spectra. The relationship between sulfur content and the specific surface area of the adsorbents is also determined. K2S activation is helps to bring about better development of pore texture. These adsorbents are microporous materials with textural parameters increasing in a range of specific surface area 72.27 m2/g–657.7 m2/g and micropore volume 0.035 cm3/g–0.334 cm3/g. The ability of activated carbons to adsorb methane is measured at 298 K and at pressures up to 5.0 MPa by a volumetric method. The Langmuir model fits the experimental data well. It is concluded that the high specific surface area and micropore volume of activated carbons do determine methane adsorption capacity. The adsorbents obtained at 800 °C for 90 min with K2S/raw coal mass ratios of 1.0 and 1.2 show the highest methane adsorption capacities amounting to 106.98 mg/g and 106.17 mg/g, respectively.

Adsorbents with sustainable CO2 capture capacity prepared from carboxymethylcellulose

Abstract

Preparing two-dimensional microporous carbon from Pistachio nutshell with high areal capacitance as supercapacitor materials.

Two-dimensional (2D) porous carbon AC-SPN-3 possessing of amazing high micropore volume ratio of 83% and large surface area of about 1069 m2 g−1 is high-yield obtained by pyrolysis of natural waste Pistachio nutshells with KOH activation. The AC-SPN-3 has a curved 2D lamellar morphology with the thickness of each slice about 200 nm. The porous carbon is consists of highly interconnected uniform pores with the median pore diameter of about 0.76 nm, which could potentially improve the performance by maximizing the electrode surface area accessible to the typical electrolyte ions (such as TEA+, diameter = ~0.68 nm). Electrochemical analyses show that AC-SPN-3 has significantly large areal capacitance of 29.3/20.1 μF cm−2 and high energy density of 10/39 Wh kg−1 at power of 52/286 kW kg−1 in 6 M KOH aqueous electrolyte and 1 M TEABF4 in EC-DEC (1:1) organic electrolyte system, respectively.

국내에서 유통되는 활성탄을 이용한 벤젠, 톨루엔, 아세톤 및 노말 헥산의 등온흡착용량 평가 연구

Objectives: To develop domestic charcoal tubes with good adsorption capacity, breakthrough experiments were performed on four types of activated charcoal. Materials: The adsorption capacity and the adsorption rate were determined using a modified Wheeler equation after the breakthrough experiment. For four types of charcoal (J, K, S and SKC Inc. 226-01), 100 mg were used in the breakthrough experiment. The test was done on benzene, toluene, n-hexane, and acetone in a dynamic chamber. Results: K charcoal had the greatest surface area and the highest micropore volume. J charcoal had a similar surface area and micropore volume to SKC charcoal. S charcoal had the lowest surface area and micropore volume. J charcoal had the highest adsorption capacity at 101, 252 and 609 ppm of benzene. The gap in benzene adsorption capacity among the types of charcoal was the least at 609 ppm and the greatest at 101 ppm. J charcoal showed the highest adsorption capacity at 54, 106, 228 and 508 ppm of toluene. J charcoal and SKC charcoal had a similar adsorption capacity for acetone. J charcoal had the highest adsorption capacity for n-hexane. In the experiment featuring 10% breakthrough volume, 10% breakthrough occurred at 18 liters at <TEX>$2065.9mg/m^3$</TEX> for J charcoal and at 20 liters at <TEX>$1771.2mg/m^3$</TEX> for K charcoal. It was difficult to judge adsorption capacity by surface area and micropore volume of charcoal. J charcoal, which was similar to SKC charcoal in surface area and micropore volume, showed good adsorption capacity at common workplace concentrations. Conclusions: The adsorption capacity of J and K charcoal was superior compared with SKC charcoal. J and K charcoal can be considered appropriate for use as sampling media based on this result.

Removal of lead from aqueous solutions by adsorption with surface precipitation

An activated carbon from Coconut (Cocos nucifera) shells was prepared by physical activation with carbon dioxide and water vapor. The activated carbon obtained has a surface area of 1058 m2 g−1 and such a high micropore volume of 0.49 cm3 g−1. This carbon was studied for the removal of lead from water. Sorption studies were performed at 30 °C, at different pH and adsorbent doses, in batch mode. Lead precipitation was observed on the surface of the activated carbon. Maximum adsorption occurred at pH 9 for an adsorbent dose of 2 g L−1. Kinetic studies, at the initial concentration of 150 mg L−1 of lead, pH 5 and an adsorbent dose of 1 g L−1, yielded an equilibrium time of 50 h for this activated carbon. The kinetic data were modeled with the pseudo first order, the pseudo second order and the Bangham models. The pseudo second order model fitted the data well. The sorption rate constant (7 × 10−4 mol−1 Kg s−1) and the maximum amount of lead adsorbed (0.23 mol kg−1) are quite good compared to the data found in literature. Sorption equilibrium studies were conducted in a concentration range of lead from 0 to 150 mg L−1. In an aqueous lead solution with an initial concentration of 30 mg L−1, at pH 5, adsorbent dose 1 g L−1, activated Coconut shell carbon removed at equilibrium 100 % of the heavy metal. The equilibrium data were modeled with the Langmuir and Freundlich equations, of which the former gave the best fit. The Langmuir constants Qmax eq (0.23 mol kg−1) and KL (487667 L mol−1) are in good agreement with literature. XPS studies identified adsorbed species as lead carbonates and/or lead oxalates and precipitates as lead oxide and/or lead hydroxide on the activated carbon surface. The Coconut shell activated carbon is a very efficient carbon due to its high surface area, to the presence of many micropores on its surface and to the presence surface groups like hydroxyls promoting adsorption in the porous system and lead crystal precipitation on the activated carbon surface.