Isosteric Heat Of CO2 Adsorption Research Articles

Post‐Synthetic Covalent Grafting of Amines to NH2‐MOF for Post‐Combustion Carbon Capture

AbstractHerein, a post‐synthetic modification strategy is used to covalently graft polyamines, including ethylenediamine (ED), diethylenetriamine (DETA), tris(2‐aminoethyl)amine (TAEA), and polyethyleneimine (PEI) to the amino‐ligand inside of a Cr‐MOF, NH2‐Cr‐BDC, for post‐combustion carbon capture applications. X‐ray absorption spectroscopy (XAS), X‐ray photoelectron spectroscopy (XPS), and ion chromatography (IC) reveal that ≈45% of the MOF ligands are grafted with polyamines. Next, assessment of CO2 uptake, CO2/N2 selectivity, isosteric heats of CO2 adsorption, separation performance during humid CO2/N2 (15/85) breakthrough experiments, and cyclability, reveals an enhanced performance for the polyamine‐containing composites and the following performance trend: NH2‐Cr‐BDC<ED<DETA<TAEA<PEI. The best‐performing materials, including the TAEA and PEI‐grafted MOFs, offer CO2 uptakes of 1.0 and 1.55 mmol g−1, respectively, at 0.15 bar and 313 K. Further, these composites also offer a high CO2 capacity after 200 temperature swing adsorption/desorption (TSA) cycles in simulated humid flue gas. Last, after soaking the composites in water, there is no loss of CO2 capacity; on the contrary, when the same MOF is impregnated with polyamines using traditional approaches, there is ≈85% CO2 capacity loss after soaking. Thus, this covalent grafting strategy successfully immobilizes amines in MOF pores preventing leaching and hence can be an effective strategy to extend the adsorbent lifetime.

Structural modified metal-organic frameworks by hierarchical layer-by-layer method for efficient CO2 capture enhancement

The emission of CO2 has attracted a plenty of concerns owing to its hazardous influence on the climate. In this study, the strategy for structural modification of metal-organic frameworks (MOF) by hierarchical layer-by-layer method is proposed to improve the CO2 capture performance using polyethylenimine-grafted SBA-15 (PEI/SBA) as a substrate. The growth procedure of hierarchical layer-by-layer framework based on HKUST-1 (HLF) was investigated based on the substrate role of PEI/SBA, serving as epitaxial growth sites of the original MOF (HKUST-1) due to the strong coordination interactions between PEI groups and Cu2+ ions. As varying the PEI loading (20, 40, and 60 wt% corresponding to HLF-1, 2, and 3, respectively), the HLFs present superior CO2 adsorption capacity at 25 ℃ and 1 bar, showing the maximum enhancement of 29.2% (4.20 mmol/g at the HLF-2) compared with HKUST-1. The result of CO2 adsorption experiment under post-combustion conditions for the optimal adsorbent (HLF-2) suggests its sufficient feasibility for industrial applications. The structural analysis of HLFs suggests an amelioration in the mass diffusion of CO2 molecules toward the active sites. The isosteric heats of CO2 adsorption for HLFs exhibit an increase compared with that of HKUST-1, indicating the strong interactive affinity toward CO2. The optimal adsorbent confirms stable reusability for 10 cycles under relatively low temperature in the CO2 desorption, suggesting the feasibility of exploiting renewable energy for desorption thermal energy. Abovementioned results can carve out a way to efficiently achieve the carbon neutrality by improving the performance of CO2 adsorbents.

Adsorption of CO2, CO, H2, and N2 on Zeolites, Activated Carbons, and Metal-Organic Frameworks with Different Surface Nonuniformities

The single-component adsorption of CO2, CO, N2, and H2 at 25 and 35 °C was studied using microporous faujasite-framework zeolites (NaY and NaX), activated carbons (GCN and MSP), and metal–organic frameworks (A100 and Z1200) as starting points for the separation of CO2 from syngases produced by gasifying biomass-based solid wastes. The indicated adsorption isotherms and uptake of the adsorbates strongly depended on the adsorbates themselves as well as on the adsorbents because of significant differences in the surface features, such as surface nonuniformity, and in the molecular properties. The selectivity of CO2 to the other gases also varied with the adsorbents due to the distinctive energetic characteristics. The surfaces of the zeolites were the most energetically heterogeneous ones, yielding higher CO2 uptake at low pressures, while the two activated carbons and A100 had moderate surface heterogeneities, and MSP showed the highest CO2 uptake at high pressures, such as 6 bar, at which the micropore volume and surface area are important. Z1200, which has highly homogeneous surfaces and no high-affinity-binding sites, exhibited the lowest CO2 adsorption capacity regardless of equilibrated pressure. The surface nonuniformities of the six sorbents were consistent with the calculated isosteric heats of CO2 adsorption. CO2 could be reversibly adsorbed on NaY and MSP but not on GCN, with some metal impurities, although all these adsorbents showed a fully reversible process for CO adsorption. The estimated working capacity for CO2 adsorption at 25 °C was 0.78–6.50 mmol/g, depending on the sorbents used. The highest value was disclosed for MSP, the surface energetic heterogeneity of which was between that of zeolites and Z1200. Such a high working capacity bodes well for use in our later applications.

Investigating the selective adsorption of CO2 by MIL-101(Cr)-NH2 and modeling the equilibrium data using a new three-parameter isotherm

Compared to MIL-101(Fe)-NH2, MIL-101(Cr)-NH2 has considerably higher adsorption of CO2. On the other hand, the adsorption of CH4 and N2 by MIL-101(Cr)-NH2 is lower than the adsorption of these gases by MIL-101(Fe)-NH2 leading to a higher selectivity of CO2 to CH4 and N2 for MIL-101(Cr)-NH2. The chemisorption mechanism is more influential in higher temperatures and pressure, which can be attributed to the performance of amines which can adsorb more CO2 at higher temperatures and pressure. The isosteric heat of CO2 adsorption on MIL-101(Cr)-NH2 was estimated equal to − 31 kJ mol-1.MIL-101(Cr)-NH2 was synthesized and characterized by the BET, XRD, FESEM, TGA, and DTA methods. The BET surface area of the synthesized MOF was achieved equal to 1768 m2 g-1. The adsorption capacity of pure CO2, CH4, and N2 was estimated using the volumetric method. A new three-parameter equation was presented to model the experimental adsorption data including both types I and II isotherm shapes. Using the Ideal Adsorbed Solution Theory (IAST), the selectivity of CO2 to CH4 at high pressure, and CO2 to N2 at lower pressures was estimated equal to 4.1 and 4.7, respectively. In addition to 25 °C, the adsorption tests were performed at 18 and 30 °C to estimate the adsorption heat of CO2 on MIL-101(Cr)-NH2 achieved equal to − 31 kJ mol-1. The adsorption isotherm of CO2 at 25 and 30 °C have been almost identical showing the role of the chemisorption mechanism of CO2 by the amine functional group, especially at higher temperatures and pressures. Furthermore, the resistance of synthesized MOF to water was investigated by putting it in contact with water for 24 h. The result showed that MIL-101(Cr)-NH2 can be classified as thermodynamically stable to water.

In Situ Dilatometry Measurements of Deformation of Microporous Carbon Induced by Temperature and Carbon Dioxide Adsorption under High Pressures

Adsorption-based carbon dioxide capture, utilization, and storage technologies aim to mitigate the accumulation of anthropogenic greenhouse gases that cause climate change. It is assumed that porous carbons as adsorbents are able to demonstrate the effectiveness of these technologies over a wide range of temperatures and pressures. The present study aimed to investigate the temperature-induced changes in the dimensions of the microporous carbon adsorbent Sorbonorit 4, as well as the carbon dioxide adsorption, by using in situ dilatometry. The nonmonotonic changes in the dimensions of Sorbonorit 4 under vacuum were found with increasing temperature from 213 to 573 K. At T > 300 K, the thermal linear expansion coefficient of Sorbonorit 4 exceeded that of a graphite crystal, reaching 5 × 10−5 K at 573 K. The CO2 adsorption onto Sorbonorit 4 gave rise to its contraction at low temperatures and pressures or to its expansion at high temperatures over the entire pressure range. An inversion of the temperature dependence of the adsorption-induced deformation (AID) of Sorbonorit-4 was observed. The AID of Sorbonorit-4 and differential isosteric heat of CO2 adsorption plotted as a function of carbon dioxide uptake varied within the same intervals of adsorption values, reflecting the changes in the state of adsorbed molecules caused by contributions from adsorbate–adsorbent and adsorbate–adsorbate interactions. A simple model of nanoporous carbon adsorbents as randomly oriented nanocrystallites interconnected by a disordered carbon phase is proposed to represent the adsorption- and temperature-induced deformation of nanocrystallites with the macroscopic deformation of the adsorbent granules.

Enhanced Adsorption Selectivity of Carbon Dioxide and Ethane on Porous Metal–Organic Framework Functionalized by a Sulfur-Rich Heterocycle

Porous metal-organic framework [Zn2(ttdc)2(bpy)] (1) based on thieno [3,2-b]thiophenedicarboxylate (ttdc) was synthesized and characterized. The structure contains intersected zig-zag channels with an average aperture of 4 × 6 Å and a 49% (v/v) guest-accessible pore volume. Gas adsorption studies confirmed the microporous nature of 1 with a specific surface area (BET model) of 952 m2·g-1 and a pore volume of 0.37 cm3·g-1. Extensive CO2, N2, O2, CO, CH4, C2H2, C2H4 and C2H6 gas adsorption experiments at 273 K and 298 K were carried out, which revealed the great adsorption selectivity of C2H6 over CH4 (IAST selectivity factor 14.8 at 298 K). The sulfur-rich ligands and double framework interpenetration in 1 result in a dense decoration of the inner surface by thiophene heterocyclic moieties, which are known to be effective secondary adsorption sites for carbon dioxide. As a result, remarkable CO2 adsorption selectivities were obtained for CO2/CH4 (11.7) and CO2/N2 (27.2 for CO2:N2 = 1:1, 56.4 for CO2:N2 = 15:85 gas mixtures). The computational DFT calculations revealed the decisive role of the sulfur-containing heterocycle moieties in the adsorption of CO2 and C2H6. High CO2 adsorption selectivity values and a relatively low isosteric heat of CO2 adsorption (31.4 kJ·mol-1) make the porous material 1 a promising candidate for practical separation of biogas as well as for CO2 sequestration from flue gas or natural gas.

Benign Synthesis of Metal-organic Framework (MIL-101-Cr) and Evaluation of Carbon- dioxide Adsorption Behaviour Employing Adsorption Isotherm Models.

In today's world, rising temperature due to global warming is caused by higher concentration of carbon dioxide (CO2) emissions in the atmosphere. Metal-Organic Framework (MOF) materials have the potential to be used in carbon dioxide capture and utilization technology. The purpose of this work is to prepare metal-organic framework materials by a benign synthesis method using water as the solvent, followed by the characterization and property evaluation for CO2 adsorption study. MIL-101-Cr metal-organic framework and its derivatives with alkali ion dopants were prepared by benign hydrothermal synthesis route, which were characterized by powder X-ray diffraction method. The adsorption isotherms of CO2 for MIL-101-Cr and its derivatives were studied to comprehend the influence of alkali dopants on CO2 sorption behaviour. The equilibrium uptakes of CO2 were further evaluated by fitting the isotherms with Langmuir, Toth and Dubinin - Astakohv adsorption models to determine the adsorption parameters. The crystalline structural integrity of MIL-101-Cr is not affected by doping with alkali ions. The isosteric heat of CO2 adsorption is diminished with an increase in alkali dopant size, while the induced surface structural heterogeneity increases with increasing alkali dopant size. The equilibrium and thermodynamic parameters calculated from this study are useful for applications in carbon dioxide capture and utilization technology.

Experimental Study on Renewable Porous Carbon Dioxide Adsorbent Materials for Space Shuttles

Porous adsorbent material is promising to be used to regeneratively remove CO2 from space shuttles. In this work, the amount and isosteric heat of CO2 adsorption in solid amine are experimentally studied at pressures ranging from 0 to 6 bar and temperatures ranging from 20 °C to 60 °C. The amount and isosteric heat of water adsorption in the solid amine is tested at different humidities (relative humidity 30–80%). The effective thermal conductivity of the solid amine at different atmospheres (air, N2, CO2 and water), pressures and temperatures is also investigated. The results show that the best temperature for CO2 adsorption in the solid amine is 45 °C under dry conditions. The amount of water adsorption increases with enhanced humidity, while the isosteric heat of water adsorption remains a constant value. The effective thermal conductivity of the solid amine increases with an increase in pressure. The adsorbed phase (CO2 and water) in the solid amine makes a contribution to improving the effective thermal conductivity of solid amine particles. The above findings can help design a better adsorption system in space.

A long-lasting TIF-4 MOF glass membrane for selective CO2 separation

Membrane technology with environmentally friendly and cost-efficient features has been well acknowledged as a promising solution for effective CO2 separation. Metal organic framework (MOF) glasses are one of the most attractive membrane materials currently, because of their easy processability, absence of grain-boundary defects, and permanent porosity. In this study, a mixed linker tetrahedral imidazolate framework-4 (TIF-4) MOF with ultrahigh glass forming ability was selected for fabricating highly CO2 selective membranes. Through adjusting the molar ratio of the imidazole (Im) and 5-methylbenzimidazolate (5-mbIm) linkers in the TIF-4 framework, the melting temperatures as well as the CO2 adsorption property could be controlled systematically. After vitrification, TIF-4 glasses (agTIF-4) with varying 5-mbIm content were prepared, and all of them exhibit higher isosteric heat of CO2 adsorption than the corresponding TIF-4 crystals. Both CO2/CH4 and CO2/N2 uptake ratio (298 K, 1 bar) of agTIF-4 samples are more than twice as that of TIF-4 crystals, suggesting the great potential of agTIF-4 for CO2 separation. Further, agTIF-4 membranes were successfully prepared by the melt-quenching process from the polycrystalline membranes. agTIF-4 membranes are highly CO2 selective with CO2/N2 and CO2/CH4 separation factors of 27 and 30. More importantly, agTIF-4 membrane displays long-term stability up to 10 months, which is highly conductive to its industrial application for CO2 separation.

Synthesis of a novel freestanding conjugated triazine-based microporous membrane through superacid-catalyzed polymerization for superior CO2 separation

This study aims at developing a novel freestanding conjugated triazine-based membrane (ETM-1) with permanent porosity via a low-temperature superacid-promoted polymerization reaction. In this venue, we used the bifunctional 4-ethynylbenzonitrile (4-EBN) monomer featuring ethynyl (CCH) and nitrile (CN) functionalities. At the same time, trifluoromethanesulfonic acid (CF3SO3H) served as both the catalyst and solvent. The cross-linked Polymer's physicochemical properties were systematically examined using TGA, BET, solid-state 13C CP-MAS NMR, ATR-FT-IR, and XPS spectroscopy techniques. With conjugated s-triazine (as a result of cyclotrimerization of nitrile) and CCH (as a result of cationic polymerization of ethynyl), the microporous ETM-1 membrane displayed a superior CO2 uptake capacity of up to 3.87 mmol g−1 (170.3 mg g−1) and enhanced ideal CO2/N2 and CO2/CH4 permselectivity values of 47 ± 2 and 21 ± 1 at 298 K and 1 bar, respectively. The notable selectivity of ETM-1 towards CO2 can be stated in terms of the molecular sieving (i.e., kinetic selection) characteristic of the microporous membrane, its electron-rich π-conjugated skeleton, and enhanced basicity, suitable for interacting with CO2via dipole-quadrupole and acid-base interactions. Moreover, ETM-1 exhibited the isosteric heat of CO2 adsorption ranging from 28.1 to 34.3 kJ mol−1, implying strong physisorption of CO2 upon the high-affinity adsorption sites of the membrane.

Enhanced CO2 Adsorption and Selectivity of CO2/N2 on Amine@ZIF-8 Materials

The ZIF-8 crystals were successfully postsynthetically modified using methylamine (MA), ethylenediamine (ED), and N, N [Formula: see text]-dimethylethylenediamine (MMEN) to improve their adsorption performance toward CO2. Results showed that, compared with the original ZIF-8, the BET specific surface area of MA-ZIF-8, MMEN-ZIF-8, and ED-ZIF-8 has increased by 118.2%, 92.0%, and 29.8%, respectively. In addition, their total pore volume increased separately by 130.8%, 100%, and 48.7%. The adsorption capacities of CO2 on the amine-modified ZIF-8 samples followed the order [Formula: see text]. The CO2 adsorption capacities at 298 K on MA-ZIF-8, MMEN-ZIF-8, and ED-ZIF-8 were increased by 118.2%, 90.2%, and 29.8%, respectively. What is more, the CO2/N2 selectivities calculated using an IAST model of the amine@ZIF-8 samples at 0.01 bar and 298 K were also significantly improved and followed the order [Formula: see text], which increased by 173.0%, 121.4%, and 22.6%, respectively. The isosteric heat of CO2 adsorption ([Formula: see text]) on the MA-ZIF-8, MMEN-ZIF-8, and ED-ZIF-8 all becomes higher, while [Formula: see text] of N2 on these samples was slightly lower in comparison with that on the ZIF-8. Furthermore, after six recycle runs of gravimetric CO2 adsorption-desorption on MA-ZIF-8, the adsorption performance of CO2 is still very good, indicating that the MA-ZIF-8 sample has good regeneration performance and can be applied into industrial CO2 adsorption and separation.

Taming structure and modulating carbon dioxide (CO2) adsorption isosteric heat of nickel-based metal organic framework (MOF-74(Ni)) for remarkable CO2 capture

Though the highest CO2 capture capacity belongs to liquid amine-solutions, solid matters capable of CO2 capture are also highly sought, providing that, they offer at least analogous CO2 adsorption capacity and CO2/N2 selectivity. Herein, a surprisingly high-performance Ni-based metal–organic framework for CO2 adsorption, namely MOF-74(Ni), was synthesized by a facile condensation reflux approach. It was found that the structure and CO2 adsorption isosteric heat of MOF-74(Ni) could tune upon varying the synthesis duration under various temperatures. The optimized MOF-74(Ni)-24-140 (synthesized at 140 °C for 24 h) displays outstanding CO2 adsorption capacity of 8.29/6.61 mmol/g at 273/298 K under normal pressure of 1.0 bar, several times higher than previously reported MOF-74-Ni (2.0/2.1 times), UTSA-16 (1.5/1.6 times), and DA-CMP-1 (3.6/4.9 times) under similar conditions. The excellent CO2 capture capacity is associated to the abundant adsorption sites (mainly arising from the cationic Ni2+ ions) and narrow micropore channels (mainly arising from the cage structure of Ni2+ ions coordinated with organic linkers). Offering a high CO2 selectivity (CO2/N2 = 49) and a well-tuned isosteric heat of CO2 adsorption (27–52 kJ/mol) besides its decent CO2 capture capacity, MOF-74(Ni) strongly stands out as an efficient and strong CO2 capturing material with industrial scale applicability.

A Two Step Postsynthetic Modification Strategy: Appending Short Chain Polyamines to Zn-NH2-BDC MOF for Enhanced CO2 Adsorption.

Functionalizing metal-organic frameworks (MOFs) with amines is a commonly used strategy to enhance their performance in CO2 capture applications. As such, in this work, a two-step strategy to covalently functionalize NH2-containing MOFs with short chain polyamines was developed. In the first step, the parent MOF, Zn4O(NH2-BDC)3, was exposed to bromoacetyl bromide (BrAcBr), which readily reacts with pendant -NH2 groups on the 2-amino-1,4-benzenedicarboxylate (NH2-BDC2-) ligand. 1H NMR of the digested MOF sample revealed that as much as 90% of the MOF ligands could be functionalized in the first step. Next, the MOF samples 60% of the ligands functionalized with acetyl bromide, Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8, was exposed to several short chain amines including ethylenediamine (ED), diethylenetriamine (DETA), and tris(2-aminoethyl)amine (TAEA). Subsequent digested 1H NMR analysis indicated that a total of 30%, 28%, and 19% of the MOF ligands were successfully grafted to ED, DETA, and TAEA, respectively. Next, the CO2 adsorption properties of the amine grafted MOFs were studied. The best performing material, TAEA-appended-Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8, exhibits a zero-coverage isosteric heat of CO2 adsorption of -62.5 kJ/mol, a value that is considerably higher than the one observed for the parent framework, -21 kJ/mol. Although the boosted CO2 affinity only leads to a slight increase in the CO2 adsorption capacity in the low-pressure regime (0.15 bar), which is of interest in postcombustion carbon dioxide capture, the CO2/N2 (15/85) selectivity at 313 K is 143, a value that is ∼35 times higher than the one observed for Zn4O(NH2-BDC)3, 4.1. Such enhancements are attributed to accessible primary amines, which were grafted to the MOF ligand. This hypothesis was further supported via in situ DRIFTS measurements of TAEA-Ac-Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8 after exposure to CO2, which revealed the chemisorption of CO2 via the formation of hydrogen bonded carbamates/carbamic acid and CO2δ- species; the latter are adducts formed between CO2 and [amineH]+Br- salts that are produced during the amine grafting step.

Structure and properties of KNi–hexacyanoferrate Prussian Blue Analogues for efficient CO2 capture: Host–guest interaction chemistry and dynamics of CO2 adsorption

Potassium Nickel hexacyanoferrate Prussian Blue Analogues (K-NiFe-PBAs) offer an excellent platform for efficient CO2 capture due to their porous nature and accessible channels. Herein, the effect of Ni:K atomic ratio on the structure and the CO2 storage capacity was studied by employing K-NiFe-PBAs with Ni:K ratio of ca. 2.5 and 12. The porosity and the isosteric heat of CO2 adsorption can be modulated and optimized by varying the Ni:K atomic ratio in the PB framework and thus, covering the thermodynamic criterion for easy CO2capture and release with acceptable energy costs. The synthesized K-NiFe-PBAs containing only trace amounts of K+ ions (with Ni:K = 12) shows an adsorption capacity (∼3.0 mmol g–1 CO2 at 273 K and 100 kPa) comparable to other well established CO2 adsorbents. In situ FTIR spectroscopy was further employed to elucidate the host–guest interaction chemistry and the dynamics of K-NiFe-PBAs within CO2 and H2O. The analysis enabled, to the best of our knowledge, is the first FTIR spectroscopic observation of the high sensitivity of the material to structural distortions induced by small changes under water vapor pressure. It was found that H2O hardly affects CO2 adsorption and the materials are perspective for CO2 capture in the presence of water.

Efficient synthetic approach for nanoporous adsorbents capable of pre- and post-combustion CO2 capture and selective gas separation

The level of CO2 in the atmosphere has increased rapidly due to vast quantities of fossil fuel combustion emissions, and it is accelerating global warming. Hence, pre- and post-combustion CO2 capture and storage (CCS) has become a vital necessity. Cost-effective and efficient nanoporous adsorbents for pre- and post-combustion CO2 capture were developed in this study. The highly porous and oxygen-rich carbon adsorbents were prepared in a facile one-pot process via the direct chemical activation of a molecularly imprinted polymer (MIP) and a MIP composite with activated carbon. The porous carbon adsorbent prepared from the MIP composite had a large specific surface area and specific pore volume of 3010 m2 g−1 and 1.506 cm3 g−1, respectively. Its bimodal pore structure contained micropores and mesopores. This nanoporous carbon adsorbent was rich in electron-dense oxygen presented in a variety of oxygen surface functional groups, which was also advantageous for CCS. These merits afforded selective CO2 adsorption and a high storage capacity under pre- and post-combustion conditions. The efficient carbon adsorbent can be stored 22.1 mmol g−1 and 3 mmol g−1 of CO2 at 25 bar and 1 bar, respectably, which was in the upper range of values reported for porous carbon. Selective CO2 capture by the carbon adsorbents was confirmed by evaluating their selectivity in CO2/CH4, CO2/N2, and CO2/H2 binary gas mixtures at 298 K based on the ideal adsorbed solution theory (IAST). The most effective adsorbent had CO2/H2 (40:60) and CO2/N2 (50:50) selectivity of 534 and 22.6, respectively. The isosteric heat of CO2 adsorption on the porous carbon adsorbents further corroborated the selective CO2 capture.

High surface area porous carbon from cotton stalk agro-residue for CO2 adsorption and study of techno-economic viability of commercial production

Cost concern of solid CO2 adsorbents has encouraged to synthesize porous carbon from surplus biomass. Porous carbon was derived from abundantly available, non-fodder cotton stalk agro-residue via single step KOH + alum chemical activation. Derived carbon exhibited notable BET surface area of 2695 m2/g, and CO2 adsorption capacity of 6.9 mmol/g at 273 K/1 bar and 4.24 mmol/g at 298 K/1 bar respectively. The isosteric heat of CO2 adsorption at zero loading was 23.5 kJ/mol and CO2/N2 selectivity was calculated to be 42 at 273 K. Techno-economic model of a plant producing 2 tons/day of porous carbon suggested levelized cost of 284.38 ₹/kg (3.78 USD/kg), net present value of 54.79 million ₹ (0.7 million USD), internal rate of return of 39.15% and payback time of 3.47 years. Monte Carlo sensitivity analysis of feedstock price, porous carbon selling price and activating agent recovery was studied. This work opens up possibility of CO2 capture by porous carbon obtained from non-fodder agro-residues through cost-effective methodology particularly for post -combustion CO2 capture.

CO2 capture on natural zeolite clinoptilolite: Effect of temperature and role of the adsorption sites

In this study, the adsorption capacity of the low-cost zeolite clinoptilolite was investigated for capturing carbon dioxide (CO2) emitted from industrial processes at moderate temperature. The CO2 adsorption capacity of clinoptilolite (a commercial natural zeolite) and ion-exchanged (with Na+ and Ca2+) clinoptilolite were tested under both dynamic (using a fixed-bed reactor operating with 10% vol. CO2 in N2) and equilibrium conditions (measuring single component adsorption isotherms). The dynamic CO2 adsorption capacity of bare clinoptilolite and ion-exchanged clinoptilolite were evaluated in the temperature range from 293 K to 338 K and the obtained breakthrough curves were compared with those of the commercial zeolite 13X (Z13X). Although the adsorption capacity of Z13X exceeded those of bare clinoptilolite and ion-exchanged clinoptilolite at 293 K, the clinoptilolite exhibited the highest CO2 uptake at a moderate temperature of 338 K (i.e. 25 % higher than Z13X). This feature appears in agreement with the lower isosteric heat of CO2 adsorption on clinoptilolite compared to the other samples. The surface species affecting the qiso and adsorption capacity were investigated through the FTIR spectroscopy using CO2 as probe molecule. As a whole, it has been observed that CO2 forms linear adducts onto K+ and Mg2+ cations of the bare clinoptilolite, and carbonate-like species onto its basic sites. With the Na-exchanged clinoptilolite, Na+ ions led to a decrease in surface basicity and to the formation of both single (Na+···OCO) and dual (Na+···OCO⋯Na+) cationic sites available for the formation of linear adducts.As a result of the remarkable adsorption capacity of clinoptilolite at 338 K, this material appears to be a promising adsorbent for the direct CO2 removal from different flue gases sources operating at such temperatures.

Facile preparation of N-doped activated carbon produced from rice husk for CO2 capture

Activated carbons (AC) were prepared by carbonization and KOH activation using rice husk as feedstock. The effects of impregnation ratios and activation temperatures on the properties of AC were investigated. Under optimum conditions, BET surface area, total pore volume and micropore volume of AC are as high as 1495.52 m2/g, 0.786 cm3/g and 0.447 cm3/g, respectively. Surface modification with chitosan as nitrogen source was performed simultaneously during KOH activation process. XPS and FT-IR analyses show that N-species was successfully incorporate into AC. Compared with AC-5 (general AC), CAC-5 (modified AC) exhibits better CO2 adsorption performance, reaching 5.83 mmol/g at 273 K and 1 bar, which can be attributed to the formation of the CO2-philic active sites on AC surface by N-species. The linear correlations between CO2 uptake, micropore volume within specific size section and N-content was investigated. The isosteric heat of CO2 adsorption for CAC-5 (average 30.21 kJ/mol) is much higher than that of AC-5 (average 14.48 kJ/mol). The adsorption behavior of CAC-5 can be well described by Freundlich model. The high IAST selectivity factor for N-doped ACs indicates their excellent adsorption selectivity for CO2 over N2. Both physisorption and chemisorption are present in CO2 adsorption process of N-doped ACs.

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.

Solvent-Induced Controllable Supramolecular Isomerism: Phase Transformation, CO2 Adsorption, and Fluorescence Sensing toward CrO42-, Cr2O72-, MnO4-, and Fe3.

Complexes {[Zn(bpdc)(Cz-3,6-bpy)]·DMF·H2O}n (1α-DMF, H2bpdc = biphenyl-4,4'-dicarboxylic acid, Cz-3,6-bpy = 3,6-bis(pyridine-4-yl)-9H-carbazole, DMF = N,N'-dimethylformamide) and {[Zn(bpdc)(Cz-3,6-bpy)]·2DMAc·H2O}n (1β-DMAc, DMAc = N,N'-dimethylacetamide) as a couple of solvent-induced supramolecular isomers were hydro(solvo)thermally synthesized using DMF/H2O and DMAc-only as reaction media, respectively. Complexes 1α-DMF and 1β-DMAc adopt very similar wavy sql sheet structures but present great differences in the 3-fold interweaving 2D → 2D nets, which result in free voids of 17.6 and 33.4%, respectively. Desolvated 1β has about 2 times the free voids compared to that of desolvated 1α; however, the former displays a CO2 uptake of 87.9 cm3 g-1 STP at 195 K and P/P0 = 1 which is only slight larger than that (73.7 cm3 g-1 STP) of the latter under the same conditions. This is mainly interpreted by activation- and adsorption-induced framework distortion that caused partial transformation of crystal phase from 1β to 1α and thus reduced free voids. The isosteric heat of CO2 adsorption (Qst) at zero loading is 29.8 kJ mol-1 for desolvated 1α and 30.6 kJ mol-1 for desolvated 1β. On the other hand, results from XRPD, IR, and TGA measurements imply that 1α-DMF and 1β-DMAc are highly stable in several different solvents, with the exception of 1α-DMF in DMAc, which experienced complete transformation to convert to 1β-DMAc and 1β-DMAc in acetone and methanol, which would respectively completely and partially transform to the crystal phase of 1α-DMF. Remarkably, 1α-DMF and 1β-DMAc display intense blue and cyan fluorescence emissions, respectively, promising them to be multifunctional sensing platforms in sensitive detection of CrO42-, Cr2O72-, MnO4-, and Fe3+ with high selectivity and a fairly low limit of detection through perceptible fluorescence quenching effect. The possible sensing mechanisms were also investigated.