Narrow Micropores Research Articles

Underlying mechanism of CO2 uptake onto biomass-based porous carbons: Do adsorbents capture CO2 chiefly through narrow micropores?

Biomass-based porous carbon materials, as promising CO2 adsorbents, have demonstrated their superiority and inherent potential. However, most of the previous reports simply attributed the unprecedented CO2 capture of porous carbon to the presence of abundant narrow micropores of less than 0.7 nm. Here, we have successfully prepared microporous carbons with analogous textural properties and oxygen functional groups by KOH activated from hydrothermally treated biomass. Based on the experimental results and theoretical calculations, we have found that the oxygen-containing functional groups on porous carbons are critically sensitive to CO2 uptake, especially with carboxyl and hydroxyl groups. We can roughly estimate that oxygen groups and pore structure of OC700 contribute 37% and 63% respectively to the CO2 capture, which can be elucidated by grand canonical Monte Carlo (GCMC) simulations. The introduction of oxygen functional groups into porous carbon materials firmly grasps CO2 through electrostatic interactions by density function theory (DFT) calculations. These oxygen groups provide new adsorption sites for the efficient CO2 capture. The OC700 achieves an extremely high CO2 adsorption capacity of 8.0 mmol g−1 and 4.8 mmol g−1 at 0° C and 25 °C (1 bar), respectively.

Scalable synthesis of zeolite-templated ordered microporous carbons without external carbon deposition for capacitive energy storage

Abstract Zeolite-templated carbons (ZTCs) have unique ordered microporous structures composed of 3-dimensionally connected graphene nanoribbons and buckybowl-like frameworks. ZTCs can exhibit extra-large surface areas, narrow micropore size distributions, and electrical conductivity, which make them promising for adsorption, catalysis, and energy storage. However, the synthesis of ZTCs still remains a great challenge when the synthesis scale is larger than just a few grams. Carbon deposition within narrow zeolite micropores is diffusion-limited, and unwanted dense carbon layers are often deposited at the external surface of zeolite, substantially diminishing ZTCs' structural properties and performances in various applications. In this study, we conducted the large-scale synthesis of ZTCs (>80 g) in a bubbling fluidized bed, which enables efficient mass/heat transfer. Compared to conventional synthesis in a fixed bed, ZTCs with superior structural properties could be synthesized in much shorter time. The resultant ZTCs showed ordered microporous structures with large surface areas (~3000 m2 g−1) and microporosity (~1.1 cm3 g−1). Most importantly, these ZTCs were free of undesirable external carbon deposition, which greatly diminishes the mass transfer of guest molecules (e.g., electrolytes) into the micropores. As a result, the ZTCs showed superior electrical double-layer capacitance compared to those synthesized in a typical fixed bed.

Rapid, repetitive and selective NO2 gas sensor based on boron-doped activated carbon fibers

In the current work, a high performance NO2 gas sensors has been fabricated from activated carbon fibers containing enriched boron moieties. The porous carbon fibers decorated with boron moieties exhibited rapid, repetitive and selective NO2 sensing performance at room temperature. The shallow, narrow and uniform micropores on the surface of the carbon fiber allowed target gases to be adsorbed and desorbed very easily whereas boron moieties induced high selectivity toward NO2 over NH3 via the strong binding energy. The excellent NO2 gas sensing performance of boron doped porous carbon fibers is attributed to synergetic effect of intrinsic pore structure of the carbon fibers and the boron moieties decorated on their surface.

Selectable Microporous Carbons Derived from Poplar Wood by Three Preparation Routes for CO2 Capture.

Biomass-derived porous carbons are one kind of sustainable, extensive, and flexible carbon material for CO2 capture. Here, we prepared several microporous carbons from poplar wood by three preparation routes. Especially, the residues of the poplar wood after the bioethanol process were explored as precursors to prepare activated carbon by KOH and ZnCl2 activation. By the adjustment of the preparation routes and the optimization of the activation conditions, these porous carbons exhibited diversified morphology (sponge, nanosheets, and honeycomb structure), tunable porosity (specific surface areas: 511–2153 m2/g), and narrow micropore distribution (0.55–1.2 nm). These carbons had a high CO2 uptake of up to 217 mg/g at 273 K and 1 bar, which was comparable with those of many N-doped porous carbons, and possessed moderate isosteric heat of CO2 adsorption (21.1–43.2 kJ/mol), good cyclic ability, and high CO2/N2 selectivity (Henry’s law: 44.0). The results indicated that CO2 uptake of these carbons was mainly decided by their micropore volume (d < 1.0 nm) at 273 K and 1 bar. This work provides an important reference for preparing promising CO2 adsorbents with tunable structures from similar biomass resources.

Characterization of Carbon Materials for Hydrogen Storage and Compression

Carbon materials have proven to be a suitable choice for hydrogen storage and, recently, for hydrogen compression. Their developed textural properties, such as large surface area and high microporosity, are essential features for hydrogen adsorption. In this work, we first review recent advances in the physisorption characterization of nanoporous carbon materials. Among them, approaches based on the density functional theory are considered now standard methods for obtaining a reliable assessment of the pore size distribution (PSD) over the whole range from narrow micropores to mesopores. Both a high surface area and ultramicropores (pore width &lt; 0.7 nm) are needed to achieve significant hydrogen adsorption at pressures below 1 MPa and 77 K. However, due to the wide PSD typical of activated carbons, it follows from an extensive literature review that pressures above 3 MP are needed to reach maximum excess uptakes in the range of ca. 7 wt.%. Finally, we present the adsorption–desorption compression technology, allowing hydrogen to be compressed at 70 MPa by cooling/heating cycles between 77 and 298 K, and being an alternative to mechanical compressors. The cyclic, thermally driven hydrogen compression might open a new scenario within the vast field of hydrogen applications.

Synthesis and Characterization of Activated Carbon Foam from Polymerization of Furfuryl Alcohol Activated by Zinc and Copper Chlorides

Polymerization of furfuryl alcohol carried out using ZnCl2 or CuCl2 as Lewis acid activators was investigated by exploring various synthesis parameters in order to produce activated carbons with different porosity and metal load. The temperature of polymerization was changed according to Lewis acidity strength of the two metal chlorides: 0 °C for CuCl2 and 80 °C for ZnCl2. The polymer obtained was pyrolyzed under pure He flow or under 1000 ppm O2/He flow at 600 or 850 °C in order to produce activated carbons with specific textural features. The load and nature of the residual metal after pyrolysis were determined by ICP and XRD analyses, respectively. Copper was mostly preserved even at high pyrolysis temperature in contrast to zinc, which was almost totally lost at 850 °C. A foamy structure was detected by SEM analysis for all samples. Textural properties were determined by both N2 and CO2 physisorption; surface areas and pore size distributions were evaluated according to BET, DFT and DR models. The polymerization activated by ZnCl2 produced carbons with larger surface areas were also related to the presence of some mesopores, whereas CuCl2 promoted the prevailing formation of narrow micropores, making these materials particularly suited to H2 storage applications.

Selection of established tumour cells through narrow diameter micropores enriches for elevated Ras/Raf/MEK/ERK MAPK signalling and enhanced tumour growth

ABSTRACT As normal cells become cancer cells, and progress towards malignancy, they become progressively softer. Advantages of this change are that tumour cells become more deformable, and better able to move through narrow constraints. We designed a positive selection strategy that enriched for cells which could move through narrow diameter micropores to identify cell phenotypes that enabled constrained migration. Using human MDA MB 231 breast cancer and MDA MB 435 melanoma cancer cells, we found that micropore selection favoured cells with relatively higher Ras/Raf/MEK/ERK mitogen-activated protein kinase (MAPK) signalling, which affected actin cytoskeleton organization, focal adhesion density and cell elasticity. In this follow-up study, we provide further evidence that selection through micropores enriched for cells with altered cell morphology and adhesion. Additional analysis of RNA sequencing data revealed a set of transcripts associated with small cell size that was independent of constrained migration. Gene set enrichment analysis identified the ‘matrisome’ as the most significantly altered gene set linked with small size. When grown as orthotopic xenograft tumours in immunocompromised mice, micropore selected cells grew significantly faster than Parent or Flow-Sorted cells. Using mathematical modelling, we determined that there is an interaction between 1) the cell to gap size ratio; 2) the bending rigidity of the cell, which enable movement through narrow gaps. These results extend our previous conclusion that Ras/Raf/MEK/ERK MAPK signalling has a significant role in regulating cell biomechanics by showing that the selective pressure of movement through narrow gaps also enriches for increased tumour growth in vivo.

CF4 adsorption on porous carbon derived from silicon carbide

Abstract Considering the increasing industrial demand for CF4 and its high global warming potential, appropriate disposal methods for CF4 are required. Adsorption can not only be used for CF4 capture but is also promising for increasing CF4 concentration, which enhances the efficiency of conventional combustion methods. In this study, porous carbons were synthesized through the chlorination of silicon carbide (SiC) with two different polymorphs at high temperatures (ranging from 800 to 1200 °C) for application to CF4 separation. The effects of the pore structure and surface morphology of the porous carbons on the CF4 adsorption performance were analyzed. The porous carbon treated at a higher temperature had a well-developed pore structure, and the maximum total pore volume and specific surface area were obtained in the sample chlorinated at 1200 °C. However, the CF4 adsorption uptake was well correlated with the narrow micropore volume for which the pore size was

Preparation of new carbon molecular sieves for optimized carbon dioxide adsorption and product yield

Chemical vapor deposition (CVD)from methane on activated carbon prepared by zinc chloride activation of residue extracted from sunflower seeds, has been optimized to produce carbon molecular sieves using the Taguchi method, targeted at achieving maximum CO2 adsorption capacity and an increased product yield. The carbon molecular sieves were characterized by N2 adsorption, CO2 adsorption, elemental analysis, SEM and FTIR. The CO2 adsorption capacities were measured at 1 bar/273 K. The optimized carbon molecular sieve with the highest product yield of 91 wt.% had amaximum CO2 adsorption of 2.6228 mmol g-1. Both nitrogen and oxygen surface functional groups and the narrow micropores are crucial for CO2 adsorption. The Taguchi method is a powerful tool to simultaneously optimize the carbon dioxide adsorption capacity and the yield of carbon molecular sieves.

Upcycling of waste polyethylene terephthalate plastic bottles into porous carbon for CF4 adsorption

Thermo-chemical processes for converting plastic wastes into useful materials are considered promising technologies to mitigate the environmental pollution caused by plastic wastes. In this study, polyethylene terephthalate (PET) plastic wastes were used to develop cost-effective and value-added porous carbons; the developed porous carbons were subsequently tested for capturing CF4, a greenhouse gas with a high global-warming potential. The activation temperature was varied from 600 °C to 1000 °C and the mass ratio of KOH/carbon ranged from 1 to 3 in the preparation process and their effects on the textural properties and CF4-capture performance of the PET plastic waste-derived porous carbons were investigated. The CF4-adsorption uptake was dictated by the specific surface area and pore volume of narrow micropores less than 0.9 nm in diameter. PET-K(2)700, which was developed by KOH activation at 700 °C and KOH/carbon mass ratio of 2, showed the highest CF4-adsorption uptake of 2.43 mmol g−1 at 25 °C and 1 atm. Also, the CF4-adsorption data were fitted well with the Langmuir isotherm model and pseudo second-order kinetic model. The PET plastic waste-derived porous carbons exhibited a high CF4 uptake, good CF4/N2 selectivity at relatively low CF4 pressures, easy regeneration, rapid adsorption/desorption kinetics, and excellent recyclability, which are promising for practical CF4-capture applications.

CO2 derived nanoporous carbons for carbon capture

Nanoporous carbons (NPCs) were synthesized from CO2 with magnesiothermic reduction for CO2 capture applications. The yield of NPCs was enhanced by a modified magnesiothermic reduction process, in which CO2 instead of Ar was applied to the reactor during heating Mg powders from 500 degrees C to a given reaction temperature (800-900 degrees C). The yields, microstructures, pore structures and CO2 adsorption properties were investigated for a variety of NPCs synthesized under various conditions of reaction temperature and duration (15-60 min). The results show that the synthesized NPCs are mainly mesoporous and composed of well crystalline carbon nanosheets interwoven with amorphous carbon. The yield, BET surface area, total pore volume, narrow microporosity (pore size < 1 nm) and CO2 adsorption capacity were decreased with an increase of reaction temperature and duration. The highest CO2 uptake of 39.7 mg g(-1) at 273 K and 1 bar was obtained in the NPC that was synthesized at 800 degrees C for 15 min and with flowing CO2 during heating at above 500 degrees C. The high CO2 adsorption capacity is resulted from its large surface area and volume of narrow micropores smaller than 1 nm, being of 34.9 m(2) g(-1) and 0.011 cm(3) g(-1), respectively.

Simple synthesis of spent coffee ground-based microporous carbons using K2CO3 as an activation agent and their application to CO2 capture

Microporous carbons were prepared from spent coffee grounds via solid-state K2CO3 activation. Activation temperature and time were changed to manipulate the properties and CO2 adsorption performance of porous carbons. As the activation temperature and time increased, textural properties such as specific surface area and total pore volume increased, reaching 2337 m2 g−1 and 1.15 cm3 g−1, respectively. Among the prepared samples, the highest CO2 uptake (4.54 mmol g−1) at 25 °C and 1 atm was obtained in the porous carbon activated at 700 °C for 5 h. Depending on adsorption temperature and pressure, a dominant factor for CO2 uptake was different. Nitrogen content and narrow microporosity were crucial at the low-pressure, 0.15 atm, and the narrow micropore volume was decisive but the significant pore size range was different depending on the adsorption temperature at atmospheric pressure. In addition to high CO2 uptake, the developed porous carbons showed excellent cyclic stability and good selectivity for CO2 over N2. The high value-added porous carbons prepared from spent coffee grounds using the simple and less hazardous method have a potential of industrial application for CO2 capture.

Control of pore structure and surface chemistry of activated carbon derived from waste Zanthoxylum bungeanum branches for toluene removal in air.

Activated carbon adsorption has been considered the most efficient technology toward VOC removal. The waste biomass as alternates solved the problems of high price and nonrenewable of traditional raw materials. The waste Zanthoxylum bungeanum branches were firstly selected as raw materials to prepare activated carbons. Interestingly, the pore structure and surface chemistry can be successfully controlled by adjusting the heating rate. The hierarchical porous carbons exhibited great potential for toluene adsorption. The micro-mesopore structure possessed unique spatial effect; micropores played a dominant role in adsorption process, especially narrow micropores (pore size ≤ 1.0 nm) emerged stronger adsorptive force toward toluene molecules due to overlapping attractive forces from neighboring pore walls. And mesopores not only displayed excellent transport diffusion but also provided adsorption sites. Additionally, the high graphitization degree enhanced the interaction between graphene layer equipped electron-rich regions and π-electrons on the aromatic ring by the π-π conjugated effect. The hydroxyl and carbonyl functional groups served as chemisorption sites and led to higher adsorption amounts. Fortunately, the regeneration can be achieved by thermal treatment at the low temperature (≤ 150 °C) or even gas purging at room temperature (20 °C), which avoided an explosion accident in the process of high-temperature regeneration.

The impact of having an oxygen-rich microporous surface in carbon electrodes for high-power aqueous supercapacitors

Lignin-based free-standing electrodes are tested as symmetric supercapacitor electrodes. The simultaneous polarisation of the electrodes upon charge discharge indicates that just a small increase in oxygen species within the micro pores is enough to enhance the performance of the device. The growth of electrical transportation is crucially important to mitigate rising climate change concerns regarding materials supply. Supercapacitors are high-power devices, particularly suitable for public transportation since they can easily store breaking energy due to their high-rate charging ability. Additionally, they can function with two carbon electrodes, which is an advantage due to the abundance of carbon in biomass and other waste materials (i.e., plastic waste). Newly developed supercapacitive nanocarbons display extremely narrow micropores (<0.8 nm), as it increases drastically the capacitance in aqueous electrolytes. Here, we present a strategy to produce low-cost flexible microporous electrodes with extremely high power density (>100 kW kg −1 ), using fourty times less activating agent than traditionnal chemically activated carbons. We also demonstrate that the affinity between the carbon and the electrolyte is of paramount importance to maintain rapid ionic diffusion in narrow micropores. Finally, this facile synthesis method shows that low-cost and bio-based free-standing electrode materials with reliable supercapacitive performances can be used in electrochemistry.

Comparison of micro- and macropore evolution of coal char during pyrolysis

To characterize the changing morphology of a solid fuel with ongoing pyrolysis and gasification, we investigated the evolution of the micropore structure of a high volatile bituminous Colombian coal. In a previous study, Colombian coal was pyrolyzed in a laminar drop tube reactor, whereby the residence time, the pyrolysis temperature, and the gas atmosphere were varied. Here, we present new experimental data on the micropore structure of those chars and compare them with their meso-/macropore analysis. The micropores were investigated using volumetric adsorption measurements with CO2 at a temperature of T = 273.15 K. Micropore volumes, surface areas and homogeneities were determined on the basis of the adsorption isotherm model of Dubinin-Astakhov and, thus, a comprehensive analysis of the pore structure is presented in this work. Differences in the evolution of micropores and meso-/macropores were observed. The dry coal and the chars pyrolyzed for residence times of around 45 ms are dominated by micropores, but as pyrolysis progresses this dominance decreases, since micropores are expanding to mesopores. Nevertheless, the formation of new narrow micropores during the pyrolysis could be observed as well.

Superior CO2 uptake on nitrogen doped carbonaceous adsorbents from commercial phenolic resin

In this study, N-doped porous carbons were produced with commercial phenolic resin as the raw material, urea as the nitrogen source and KOH as the activation agent. Different from conventional carbonization-nitriding-activation three-step method, a facile two-step process was explored to produce N-incorporated porous carbons. The as-obtained adsorbents hold superior CO2 uptake, i.e. 5.01 and 7.47 mmol/g at 25 °C and 0 °C under 1 bar, respectively. The synergistic effects of N species on the surface and narrow micropores of the adsorbents decide their CO2 uptake under 25 °C and atmospheric pressure. These phenolic resin-derived adsorbents also possess many extremely promising CO2 adsorption features like good recyclability, quick adsorption kinetics, modest heat of adsorption, great selectivity of CO2 over N2 and outstanding dynamic adsorption capacity. Cheap precursor, easy preparation strategy and excellent CO2 adsorption properties make these phenolic resin-derived N-doped carbonaceous adsorbents highly promising in CO2 capture.

Hybrid cathode materials for lithium-sulfur batteries

Abstract This review demonstrates the approaches to fabricate hybrid cathode materials for lithium-sulfur batteries. This short review does not claim to cover all recently published data; instead, an effort is aimed to show how the critical issues on carbon – sulfur hybrid are addressed based on selected articles in last couple of years. The influence of porous structure of carbon, the confinement effect of polysulfides in narrow micropores, and importance of hierarchical porosity are explained. Besides, the heteroatom doping on carbon in carbon–sulfur hybrids plays a vital role on improvement of bulk electronic conductivity of electrode. This review presents the twin polymerization strategy for direct preparation of nanoscale intermixed hybrid materials. Finally, the formation of sulfur containing copolymers by reacting sulfur melt with functional vinyl monomers are shown in this review with selected examples postulating the respective potential for future generation energy storage technology from the viewpoint of industrial applications.

Chemically modified self-doped biocarbon via novel sulfonation assisted sacrificial template method for high performance flexible all solid-state supercapacitor

The development of lignin-based carbon electrodes for high-performance flexible, solid-state supercapacitors in next-generation soft and portable electronics, has received much attention. Herein, a self-doped multi-porous lignin-based biocarbon (SUMBC) has been prepared via a simple sulfonation assisted sacrificial template method for the effective formation of oxygenated C-S-C moieties in the carbon network. In this proposed method, the sulfonate moieties in lignin are responsible for the successful decoration of oxygen enriched C-S-C moieties as well as for creating the optimal multilevel porous architecture (ultra-micropores, micropores and mesopores) in the carbon matrix with a large surface area (3149 m2 g−1). Because the sulfonate functionalities yield more sulfur species and induce further defects into carbon framework, in the activation process, these sulfur functionalities produce additional narrow micropores. Benefiting from the above unique feature, the supercapacitor (SC) with the SUMBC electrode delivers excellent capacitive behavior in both acidic (2 M H2SO4) and alkaline (6 M KOH) liquid electrolytes. More prominently, the all-solid state, symmetric supercapacitors assembled by SUMBC show outstanding capacitance of ~140 F g−1 at 0.5 A g−1 in two different devices and reveals high energy density (~5.41 W h kg−1 at 0.5 k W kg−1 power density) and excellent stability. In addition, the solid-state supercapacitors manifest a remarkable flexibility at different bending angles. Hence, the present work provides a new strategy for the preparation of efficient biocarbons via a facile sulfonation assisted sacrificial template method; moreover, the high-performance all-solid supercapacitors based on sulfonated modified lignin has great potential in the field of portable and wearable energy storage devices.

Effect of activation and exfoliation on the formation of carbon nanosheets derived from natural materials

Carbon is abundantly found in nature with a wide range of applications. It can be synthesized through physical and chemical processes. Chemical activation is considered as a very efficient method to obtain carbon with high surface area and narrow micropore distribution. Among all the chemical activating agents, alkaline hydroxides such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) are reported to be of high interest in the production of carbon with higher performance. In our research, Nettle stem and peanut shell (natural materials) were used as raw materials for the preparation of carbon. Natural structures of nettle and peanut shell consists of cellulose, which is an important precursor in the preparation of highly ordered carbon nanosheets. Aqueous solutions of KOH and NaOH were used for activation and sulphuric acid (H2SO4) was used for exfoliation. The process employed here has yielded a high percentage of carbon nanostructured particles.

Porous Carbons Derived from Sustainable Biomass via a Facile One-Step Synthesis Strategy as Efficient CO2 Adsorbents

In this work, porous carbons were achieved from sustainable biomass lotus stalk. Unlike the common carbonization-activation two-step method, a facile one-step KOH activation procedure was explored to make the carbonaceous sorbents. The as-made adsorbents have advanced porous structures and hold superior CO2 uptake, up to 3.68 and 5.11 mmol/g at 1 bar, 25 and 0 °C, respectively. After carefully checking the relationship of CO2 uptake with each porous characteristic, the volume of narrow micropores is found to be the leading factor that determines the CO2 adsorption abilities of the adsorbents under ambient conditions. Moreover, the narrower pore size distribution is also preferential to the adsorption of CO2. Apart from the high CO2 uptake, these lotus stalk-derived adsorbents also possess extra excellent CO2 capture properties such as good recyclability, fast adsorption kinetics, reasonable CO2/N2 selectivity, suitable heat of adsorption, and high dynamic adsorption capacity. These results demonstrate that these cost-effective carbonaceous adsorbents developed by the facile one-step method have potential in the application of actual CO2 capture.