CO2 Adsorption Isotherms Research Articles

Dynamic CO2 separation performance of nano-sized CHA zeolites under multi-component gas mixtures

To identify and evaluate promising adsorbents for CO2 separation, we synthesized CHA zeolites with different cations (Na+, K+, Cs+) and crystal sizes (45 nm – CHA45 and 500 nm – CHA500), and evaluated their explored CO2 adsorption performance from CO2/N2/He and CO2/CH4/He mixtures. Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations predicted CO2, N2, and CH4 adsorption isotherms and CO2 mobilities, respectively, which were compared to experimental data. Breakthrough curve analysis was used to assess the CO2 dynamic adsorption performance. The breakthrough curve analysis shows the smaller crystal sizes (45 nm) enhance the CO2 separation due to shorter interacrystalline diffusion pathways. Notably, Cs-CHA45 removed 2.2 times more CO2 from CO2/N2/He than Cs-CHA500. K-CHA45 showed the highest CO2/N2 selectivity (108) and achieved 841mmol g−1 for CO2 capture from N2 and 721mmol g−1 for CO2 from CH4. These findings underscore the potential of CHA nanocrystals for effective CO2 separation in various applications.

A Facile Two-Step Utilization of Sorghum Waste Derived Activated Carbon

Sorghum (Sorghum bicolor (L.) Moench) is an agricultural commodity that produces waste, including stems, during its cultivation. Sorghum stems can be used as an alternative precursor for forming activated carbon (AC) with a high surface area by utilizing ZnCl2 as an activator and followed by a pyrolysis process at 750 °C under N2 gas. In this study, AC from sorghum stems was sequentially used as an adsorbent for heavy metals in wastewater, as well as applied as an anode material for lithium-ion batteries. From the characterization analysis, the synthesized AC has an amorphous structure, a high carbon content of > 90%, and a surface area of 1189 m2/g. AC was applied to adsorb 10, 50, and 100 ppm of metal cobalt (Co) at 30 °C. The adsorption isotherm and kinetics of metal Co showed an adsorption capacity of around 28.2 mg/g. The Langmuir isotherm model also describes Co adsorption and follows the pseudo-first-order equation. As for the Li-ion anode material, the ACs material is fabricated on a cylindrical battery with LiNi0.8Co0.1Mn0.1O2 as the counter cathode material. The specific discharge capacity results are 104 mAh/g at the voltage window of 2.7-4.3 V. The sequential utilization of sorghum stem-derived activated carbon can improve the product’s sustainability, and such an approach is promising to be applied in other biomass-based waste treatments.Keywords: Activated carbon, adsorption, battery, biomass, sorghum

Synthesis, structural characterization, water ad‐/de‐sorption isotherm, and CO2 uptakes of a 2D Cu(I) metal organic framework with 1,3,5‐tris(4‐pyridylethynyl)benzene (L) and Tricyanomethanide (tcm−) ligands

AbstractA d10 Cu(I) two‐dimensional (2D) metal–organic framework (MOF) with chemical formulas, {[Cd(L)(tcm)(H2O)]⋅2H2O}n (1) (L = 1,3,5‐tris(4‐pyridylethynyl)benzene; tcm−1 = tricyanomethanide) was synthesized and structurally characterized by single crystal X‐ray diffraction method. In 1, the coordination geometry of Cu(I) ion is distorted tetrahedral coordinated to four N atoms from three L and one tcm− ligands. A 2D puckered honeycomb‐like layer is formed via the bridges of Cu(I) ions and L ligands with tris‐monodentate coordination mode. Two 2D layers are mutually interpenetrated via the π–π stacking interaction between benzene ring of L ligand and pyridyl ring of neighboring L ligand to form a two‐fold interpenetrated 2D net and then arranged orderly to construct its 3D supramolecular network. Thermal stability and in‐situ temperature‐dependent structural variations of 1 are performed by TG analysis associated with temperature‐dependent PXRD measurement. The water vapor ad‐/de‐sorption isotherm and CO2 adsorption isotherm of 1 are measured and discussed.

Hydrazino-containing Zr-MOF for enhanced Lewis acid-base catalysis of CO2 fixation into cyclocarbonate

Developing an effective catalyst for converting CO2 into high-value chemicals is greatly desirable but remains a big hurdle. Herein, Zr-MOF derivative-bearing hydrazino groups were synthesized by mixing the ligands of terephthalic acid and 4-hydrazinobenzoic acid (HBA), resulting in UiO-66-HBA as heterocatalyst for epoxide cycloaddition with CO2. Compared to UiO-66, the optimal UiO-66-HBA0.2 displayed outstanding activity for epichlorohydrin cycloaddition, with 96.03 % cyclocarbonate yield under 0.1 MPa CO2 at 70 ℃. The great activity of UiO-66-HBA0.2 was attributed to the synergistic cooperation of Lewis base offered by HBA moiety and Lewis acid originated from Zr6 clusters, which was affirmed by NH3/CO2-temperature-programmed desorption experiments and CO2 adsorption isotherms. Moreover, UiO-66-HBA0.2 exhibited excellent stability and great substrate compatibility. In addition, a possible mechanism for catalyzing CO2 conversion into cyclocarbonate was suggested. This study provides an effective way to design functionalized MOFs-based heterocatalysts for CO2 utilization.

Exploitation of Pore Structure for Increased CO2 Selectivity in Type 3 Porous Liquids.

CO2 capture requires materials with high adsorption selectivity and an industrial ease of implementation. To address these needs, a new class of porous materials was recently developed that combines the fluidity of solvents with the porosity of solids. Type 3 porous liquids (PLs) composed of solvents and metal-organic frameworks (MOFs) offer a promising alternative to current liquid carbon capture methods due to the inherent tunability of the nanoporous MOFs. However, the effects of MOF structural features and solvent properties on CO2-MOF interactions within PLs are not well understood. Herein experimental and computational data of CO2 gas adsorption isotherms were used to elucidate both solvent and pore structure influences on ZIF-based PLs. The roles of the pore structure including solvent size exclusion, structural environment, and MOF porosity on PL CO2 uptake were examined. A comparison of the pore structure and pore aperture was performed using ZIF-8, ZIF-L, and amorphous-ZIF-8. Adsorption experiments here have verified our previously proposed solvent size design principle for ZIF-based PLs (1.8× ZIF pore aperture). Furthermore, the CO2 adsorption isotherms of the ZIF-based PLs indicated that judicious selection of the pore environment allows for an increase in CO2 selectivity greater than expected from the individual PL components or their combination. This nonlinear increase in the CO2 selectivity is an emergent behavior resulting from the complex mixture of components specific to the ZIF-L + 2'-hydroxyacetophenone-based PL.

CO2 adsorption in biochars obtained from soursop (Anonna muricata) seeds by chemical activation with metallic salts

Environment remediation is one of the primary goals of sustainable development and anthropogenic activities, and the use of fuels in various industrial processes through combustion has led to an increase in CO2 as well as big damage to the atmosphere by the greenhouse effect. Biochar has been used for the capture of carbon dioxide due to its high surface area. In this study, we obtained biochar from soursop seeds. The materials were synthesized by pyrolysis of precursor materials and chemical activation with chlorides of Ca and Mg at a concentration of 5% w/v. The effect of the defatting process of the soursop seeds on the obtained carbon was also researched. The absorbed solids were characterized through thermogravimetric analysis, X-ray diffraction, and CO2 adsorption, followed by infrared spectroscopy, N2-physisorption, CO2-physisorption, CO2, XPS, DRIFTS and TPD of NH3. The type of activating agent and pretreatment conditions used were more favorable than the defatted process at obtaining carbons with N2 surface areas between 26 and 220 m2g−1. The biochars were analyzed by CO2 surface area to describe the microporous framework, and the solid with the best CO2 surface area was the one with the highest CO2 adsorption. According to the statistical analyses conducted, the evaluated models Langmuir, Freundlich, and Redlich-Peterson presented good fits to the experimental data. However, the Redlich-Peterson model showed the lowest values for the residual variance, which were of the order of 0.001 or less in all cases based on the CO2 adsorption isotherms on the studied activated carbons. However, the carbons obtained by defatting showed favorable hydrophilic behavior along with adsorption capacities in the bioremediation process and affinity towards of this GHG.

Soft and diffusion-controlled Sr-MOF for efficient separation of H2O/D2O

Heavy water (D2O) electrolysis is the primary technology for D2 production, playing an irreplaceable role in fields such as nuclear fusion research and isotope tracing. However, the inherent similarity in chemical properties between H2O and D2O (with only a 1.4 °C difference in boiling points) poses significant challenges to their separation. Furthermore, the extremely low natural abundance of D2O (0.015 %) increases the difficulty and cost of separation, while traditional electrolysis and distillation techniques are highly energy intensive. Therefore, there is an urgent need to develop novel adsorbents for efficient and environmentally sustainable H2O/D2O separation. Herein, we used polydentate ligand 2, 5-dihydroxyterephthalic acid (DOBDC) and its derivatives 4,4́-(anthracene-9,10-diyl) bis (2-hydroxybenzoic acid (ABHB) as raw materials to prepare two novel high coordination Sr-MOFs namely IPE-1 and IPE-2, respectively. These MOFs were applied for efficient separation of H2O and D2O at room temperature. X-ray diffraction results reveal that one Sr atom in IPE-1 is coordinated with 9 oxygen atoms. This high coordination number results in the formation of ultra-small rectangular pores of approximately 2.5 Å. Adsorption isotherms of N2, CO2, H2O, and D2O indicate that the ultramicroporous structure of IPE-1 precludes efficient diffusion of CO2 and H2O molecules into the MOF channels. In contrast, the activated IPE-2 exhibits good CO2, H2O, and D2O uptake capacities of 3 mmol/g, 8.38 mmol/g, and 6.51 mmol/g at 298 K, respectively. The Qst values and Ksap values of H2O and D2O indicate that the adsorption rates of H2O were much higher than D2O under 0.2 < P/P0 < 0.7, with a calculated ratio of approximately 1.26. This study not only provides appealing MOFs materials for efficient H2O/D2O separation at room temperature but also provides a new avenue for preparing adsorbents with high stability and high separation performance.

CO2 Adsorption by CMK-3 at Low Temperatures and High Pressure to Reduce the Greenhouse Effect.

In this study, the maximum CO2 capture capacity of an ordered mesoporous carbon (CMK-3) was evaluated at high pressure (35 atm) and several temperatures (0, 10, 20, and 35 °C). CMK-3 was synthesized with the hard template method (silica SBA-15) using furfuryl alcohol and toluene as carbon sources. The CO2 adsorption isotherms were fitted to the following adsorption theories: Freundlich, Langmuir, Sips, Toth, Dubinin-Radushkevich, and Temkin. The maximum capture capacity (726.7 mg·g-1) was achieved at 0 °C and 34 atm. The results of the study of successive adsorption-desorption cycles showed that multi-cycle reversible gas capture processes could be used in optimal temperature and pressure conditions. It was determined that 0.478 g of CMK-3 would be required to reduce the CO2 concentration in 1 m3 of air to pre-industrial levels (280 ppm). The obtained results may contribute to technological developments for the mitigation of human impacts on the environment through the capture of atmospheric CO2.

Highly stable mesoporous Co/Ni mixed metal-organic framework [Co/Ni(μ3-tp)2(μ2-pyz)2] for Co (II) heavy metal ions (HMIs) remediation

A bimetallic cobalt/nickel-based metal-organic framework (MOF), [Co/Ni(μ3-tp)2(μ2-pyz)2], denoted as Co/Ni-MOF, has been successfully prepared by a hydrothermal method. The MOF was prepared by incorporating mixed O− and N− donor ligands, specifically terephthalic acid (tp) and pyrazine (pyz). The Mesoporous Co/Ni-MOF was comprehensively characterized using various analytical methods such as XRD, BET, FT-IR, TGA (23 % char yields), SEM, and EDS analyses. The synthesized mesoporous Co/Ni-MOF was then used to absorb Co (II) from aquatic areas efficiently. Several critical parameters, such as the beginning Co (II) concentration (25–150 mg/L), the effect of pH (2–10), the duration of time (5–30 min), and the amount of adsorbent (0.003–0.02 g), were systematically investigated. Remarkably, the Mesoporous Co/Ni MOF displayed a significant adsorption capacity of 372.66 mg g−1 in the optimum conditions, including pH = 6, amount of adsorbent = 0.003 g, duration of time = 25 min, and beginning Co (II) concentration = 150 mg/L. Adsorption data from the experimental studies of the mesoporous Co/Ni MOF are matched based on the non-linear pseudo-first-order (PSO) kinetic model (R2 = 0.9999), and a chemical process is suggested for chemisorption. Furthermore, the adsorption isotherms of Co (II) heavy metal ions (HMIs) are an excellent fit with the non-linear Temkin, indicating that they explain the sorbent/sorbate interactions concerning the heat of adsorption. It is evident from the thermodynamic parameters that adsorption is a spontaneous and favorable exothermic process. These results highlight the promising adsorption performance and potential applications of the mesoporous Co/Ni-MOF as an effective adsorbent for Co (II) elimination from aquatic areas. Four-cycle regeneration studies were the most effective for the Co (II) under study.

Adsorption study of CO2/CH4 and CO2/N2 binary mixtures on titanosilicates ETS-10 and SrETS-10; industrial application aspects

Despite the outstanding features of the titanosilicate ETS-10 and some studies done on CO2 adsorption so far, there is a lack of coherent information to evaluate its potential industrial application in CO2 separation from natural gas and flue gas. In this work, ETS-10 and SrETS-10 were synthesized and characterized by PXRD, SEM, DTA, EDX, and BET. Pure gas adsorption isotherms of CO2, CH4, and N2 at 298 K were obtained by the constant-volume method. The obtained adsorption data were fitted with Langmuir and UNILAN isotherm models. The CO2/CH4 selectivity (yCO2 = 0.05) predicted by Ideal Adsorption Solution Theory (IAST) was 67.54 and 35.65 for ETS-10 and SrETS-10, respectively, while the CO2/N2 selectivity (yCO2 = 0.04) was 94.64 and 99.94. The Pseudo-Nth-Order (PNO) and micropore diffusion model were used to evaluate the CO2 adsorption kinetics and diffusivity of the adsorbents. The results showed that both ETS-10 and SrETS-10 exhibited fast kinetics for CO2 adsorption, but SrETS-10 had a slightly smaller diffusion coefficient (DC/rC2 = 0.01494 and 0.01458 s−1 for ETS-10 and SrETS-10, respectively) resulting in a slower adsorption rate than ETS-10. The regenerability of ETS-10 and SrETS-10 was studied and it was found that for ETS-10 about 79.07% and 96.32% of the capacity can be regenerated by applying vacuum and heating, respectively and also 79.67% of the SrETS-10 capacity can also be regenerated by applying vacuum. From the results of this work with an approach of industrial application, it was concluded that ETS-10 and SrETS-10 can be used in a combined PSA and TSA process for CO2 separation.

Effective heat transfer associated with CO2 and CH4 adsorption on HKUST-1 metal-organic framework deposited in situ on heat exchanger

The aim of this study was to analyze the heat transfer properties a copper heat exchanger with the in situ synthesized HKUST-1 metal-organic framework (MOF). For this purpose, a dedicated reactor was constructed to enable the direct measurements of heat of adsorption of CO2 and CH4, that accompanies the dynamic course of these processes. In parallel, CO2 and CH4 adsorption isotherms were determined at various temperatures and the heat of adsorption was calculated by an indirect method. Temperature changes on the heat exchanger as a result of cyclic adsorption/desorption processes of CO2 and CH4 on the HKUST-1 layer were registered, and the results of adsorption heat by direct and indirect methods were compared. Comparing the results of indirect and direct measurements of temperature changes accompanying CO2 adsorption, a difference of 19 % was obtained. In the case of CH4 adsorption, the results obtained by the two methods differed by 22 %. Based on the experimental results, it was proven that HKUST-1 synthesized in situ on a copper heat exchanger has improved heat transfer properties. The proposed concept of MOF layer on heat exchanger allows for efficient thermal stimulation of sorption processes and simultaneous MOF regeneration while minimizing the thermal energy supplied to the system.

Transforming a mixture of real post-consumer plastic waste into activated carbon for biogas upgrading

Plastic waste management is a current environmental issue that demands potential solutions since complete mechanical recycling is limited to the complexity and feasibility regarding the quality and purity of plastic waste. Pyrolysis has emerged as a reasonable solution for the recycling of those fractions that are not further suitable for recycling. Although the implementation of this technology is mature, the generated solid fraction or char has not been completely inserted in the closed loop of plastic recycling. This work explores the possibility of using the carbonaceous char as a precursor for the preparation of porous activated carbons for environmental application as CO2 adsorbent and biogas upgrading. The effect of the pyrolysis temperature (450 or 500 ºC) on the obtained chars has been assessed for the benefits in the second stage of chemical activation, exploring the possibility of the use of diverse chemical agents. The composition, textural, and surface properties of the porous materials were characterized. N2 isotherms showed that the char prepared at 500 ºC provided the best textural properties with a performance of K2CO3 ∼ KOH > Na2CO3 > NaOH > ZnCl2 > FeCl3. Isotherms of CO2 adsorption showed that the activation with K2CO3 displayed the best uptake (130.2 mg g−1 at 273 K), closely followed by KOH (125.0 mg g−1 at 273 K), also confirmed by dynamic tests in a fixed bed column configuration. The uptake was well correlated with the ultramicropore volume and the oxygenated functional groups. The CO2 and CH4 adsorption were studied either in static or dynamic assays. The behavior of the sample activated with K2CO3 was studied in detail in column tests, suggesting that the activated material exhibits promising behavior for biogas upgrading.

Enhancing CO2 adsorption capacity and selectivity of UiO-67 through external ligand modification

To address the escalating issue of CO2 pollution, the development of innovative CO2 adsorbents has been necessitated, leading to the exploration of UiO-67-based materials. In this study, UiO-67 was synthesized with meticulous selection of the appropriate modulators in optimal ratios. Subsequently, 4-iodopyrazole, a ligand distinguished by its local electric fields and polar sites, was incorporated to fabricate UiO-67-I. This novel material underwent examination employing techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) analysis. The adsorption rates of gases including CO2, CH4, and N2 were measured at various temperatures. Utilizing the ideal adsorbed solution theory (IAST) and the Clausius-Clapeyron equation, the selectivity of CO2 against CH4 and N2 was calculated, along with the CO2 adsorption isotherms. Remarkably, UiO-67-I(50) demonstrated a CO2 adsorption capacity of 1.84 mmol/g at 298 K and 1 bar, representing a significant enhancement attributable to the ligand's enhanced local electric fields and polar sites. The selectivities for CO2 over CH4 and CO2 over N2 were determined to be 14.2 and 84.6, respectively, under these conditions. Moreover, UiO-67-I(50) proved effective in the separation of CO2 from N2 under dynamic flow conditions, showcasing its potential for practical application in gas separation.

Исследование адсорбционного разделения газовых смесей в условиях нестационарности

The influence of the initial concentration, rate and temperature of adsorption on the adsorption separation of gas mixtures (CO2, CH4, N2, H2S) is investigated. Components: N2 – 5%, H2S – 5%, CO2 – 5% and CH4 – 85%. And as an adsorbent granule of clinoptilolite of irregular shape were used. Isothermal adsorption of CO2 was obtained at different temperatures (293, 313, and 323 K). The obtained isotherms of CO2 adsorption showed that with an increase in temperature, the adsorption of CO2 decreased. The type of isotherms corresponds to Langmuir. The output curves of gas mixture adsorption depending on the gas flow rate and various main components of CO2 were also experimentally studied. The output curves of the adsorption of the CO2 component were studied at various gas flow rates of 20, 50, and 80 mL/min. Equilibrium time increases with a decrease in the gas flow rate. Output curves were also obtained depending on the initial CO2 concentrations of 5%, 10% and 20%. It was determined that with a decrease in the initial concentration of CO2, the equilibrium time also increases. Gas mixture components sorbed downwards: H2S→CO2→CH4→N2. The resulting system of model equations describing the adsorption separation of gas mixtures in a fixed adsorbent layer represents a complete mathematical model of the process under unsteady conditions. The obtained regularities of the process of adsorption of gas mixtures testify to the fact that the process takes place under non-stationary conditions. The proposed models for the optimal design of industrial absorbers can be used for adsorption separation of gas mixtures in the conditions of their unsteady flow.

Physicochemical Properties, Equilibrium Adsorption Performance, Manufacturability, and Stability of TIFSIX-3-Ni for Direct Air Capture of CO2.

The use of adsorbents for direct air capture (DAC) of CO2 is regarded as a promising and essential carbon dioxide removal technology to help meet the goals outlined by the 2015 Paris Agreement. A class of adsorbents that has gained significant attention for this application is ultramicroporous metal organic frameworks (MOFs). However, the necessary data needed to facilitate process scale evaluation of these materials is not currently available. Here, we investigate TIFSIX-3-Ni, a previously reported ultramicroporous MOF for DAC, and measure several physicochemical and equilibrium adsorption properties. We report its crystal structure, textural properties, thermal stability, specific heat capacity, CO2, N2, and H2O equilibrium adsorption isotherms at multiple temperatures, and Ar and O2 isotherms at a single temperature. For CO2, N2, and H2O, we also report isotherm model fitting parameters and calculate heats of adsorption. We assess the manufacturability and process stability of TIFSIX-3-Ni by investigating the impact of batch reproducibility, binderless pelletization, humidity, and adsorption-desorption cycling (50 cycles) on its crystal structure, textural properties, and CO2 adsorption. For pelletized TIFSIX-3-Ni, we also report its skeletal, pellet, and bed density, total pore volume, and pellet porosity. Overall, our data enable initial process modeling and optimization studies to evaluate TIFSIX-3-Ni for DAC at the process scale. They also highlight the possibility to pelletize TIFSIX-3-Ni and the limited stability of the MOF under humid and oxidative conditions as well as upon multiple adsorption-desorption cycles.

Evaluation of methane adsorption isotherms at ambient temperature on carbon materials from NLDFT pore size analysis derived from standard N2 and CO2 adsorption isotherms

In this paper, we attempt to estimate CH4 adsorption on carbon materials based on the pore size distribution (PSD) characteristics evaluated from standard nitrogen and carbon dioxide adsorption isotherms using the nonlocal density functional theory (2D-NLDFT), or more precisely, its two-dimensional version (2D-NLDFT). The PSDs of the carbons were calculated by the simultaneous fit of the NLDFT models to the corresponding N2 and CO2 adsorption data. This method is referred to in the literature as the dual gas analysis method which is implemented in SAIEUS software. Essential features of carbon PSDs affecting the shapes of methane adsorption isotherms measured at ambient temperature were identified as related to micro and mesopores carbon structure. We discuss how different micro and mesopore size ranges contribute to methane adsorption isotherms in the low and higher-pressure ranges. The results of the present study may serve as guidance for selecting and designing suitable carbon materials for practical applications such as PSA recovery of CH4 from its mixtures or for methane storage.

Synthesis of biomass combustion fly ash derived zeolites for CO2 adsorption: Optimisation of hydrothermal synthetic pathway

Industrial biomass combustion fly ash has been investigated as a precursor for zeolites with a view to evaluate the potential for adsorption of CO2. The synthesis methodology has been optimised via Design of Experiment by employing a Taguchi L9 array. Three variables were identified as statistically significant, the crystallisation temperature, crystallisation time and the liquid to solid ratio. Analysis of the main effects revealed an optimum set of conditions which produced a sample with the highest adsorption capacity of those prepared, 1.84 mmol g−1 at 50 °C. This was a result of the conversion of the as-received fly ash into type A (LTA) and type X (FAU) zeolites after alkaline fusion with NaOH and hydrothermal treatment. The enthalpy of adsorption was estimated at -40.2kJmol−1 and was shown to be dependent on surface coverage; the isosteric enthalpy of adsorption at zero coverage was -86 kJ mol−1. The working capacity of the adsorbent was maintained at 85 % of the first adsorption uptake after a total of 40 cycles in a simulated temperature swing adsorption process (50 °C/150 °C adsorption/desorption). The equilibrium and kinetic CO2 adsorption isotherms are presented and modelled through non-linear regression to reveal the adsorption mechanisms demonstrated by the fly ash-derived zeolites. Significant heterogeneity exists within the multi-phase zeolite which presents both micro and mesoporosity. The developed adsorbent presents a feasible route to valorisation of biomass combustion fly ash with good potential for application in the separation of CO2.

Carbon foams for CO2 adsorption: Synthesis, characterization and application

Carbon foams from phenolic resins of the resol and novolac type were synthesized and characterized, based on different experimental parameters and characterization techniques; with the objective of studying the synthesis process of carbon foams, their physicochemical characteristics, their CO2 adsorption capacities, and the influence that the different parameters applied in the synthesis process may have on the characteristics and adsorption capacity of each foam. The parameters applied in the synthesis of the carbon foams included the use of three different catalysts (sodium hydroxide, ammonia and oxalic acid), two foaming agents (n – pentane and dichloromethane) and two carbonization temperatures (600 and 800 °C).); and the characterization techniques used were CO2 adsorption isotherms, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy with X-ray scattering spectroscopy (SEM). – EDS). It is obtained that the highest adsorption capacities were obtained using sodium hydroxide as catalyst, and a carbonization temperature of 600 °C, this is reflected in the theoretical model of adsorption isotherms being the one that best describes the process of CO2 adsorption from carbon foams the Tóth model; with a maximum adsorption capacity (Qmax) higher than 50 cm3/g, up to 103 cm3/g.

Directly synthesized high-silica CHA zeolite for efficient CO2/N2 separation

Carbon dioxide capture is an effective method to mitigate climate change. Highly CO2-selective and highly moisture-resistant absorbent is essential for energy-efficient carbon capture by absorption. Herein, a highly CO2-selective and high-silica CHA zeolite in a pure lithium form (Li-SSZ-13) was synthesized using a direct synthesis method for the first time. The effects of gel n(SiO2)/n(Al2O3) ratio, gel n(SiO2)/n(Li2O) ratio and synthesis time on the crystallinity, yield, micropore volume and CO2 loading of the crystals were systematically investigated. The adsorption isotherms of CO2 and N2 were measured for directly synthesized Li-SSZ-13, conventional Na-SSZ-13 and ion-exchanged Li-Na-SSZ-13 zeolites. The dynamic breakthrough adsorption properties were measured for Li-SSZ-13 in comparison with Na-SSZ-13 and Li-Na-SSZ-13. The obtained Li-SSZ-13 exhibited a high CO2 adsorption capacity of 4.48 mmol/g and a high CO2/N2 IAST selectivity of 310 at 100 kPa and 273 K, which were 45.0% and 441% higher than Na-SSZ-13 zeolite, 24.8% and 179% higher than Li-Na-SSZ-13 zeolite, respectively. It suggests that directly synthesized Li-SSZ-13 zeolite has great potential for efficient CO2 capture from flue gas.

Synthesis, characterization, hysteretic two-step CO2 adsorption, and fluorescence properties of two isoreticular mixed-ligand pillared-layer frameworks

Two isostructural and isomorphrous metal–organic frameworks (MOFs), namely [Zn2(Brtpt)2 (bpBTD)]n (1) and {[Zn2 (ntpt)2 (bpBTD)]∙solvent}n (2), where bpBTD = bis(pyridin-4-yl)benzothiadiazole, H2Brtpt = 2-bromoterephthalic acid, H2ntpt = 2-nitroterephthalic acid, with thermal stability of 355 °C for 1 and 265 °C for 2 were hydro (solvo)thermally synthesized in DMF/H2O media at 100 °C. Single-crystal X-ray diffraction analysis revealed that 1 and 2 both possess 2-fold interpenetrating pillared-layer frameworks showing pcu net topology with the point symbol of 41,263. The sufficient extra-framework void spaces are approximately 30.1 % for 1 and 32.0 % for 2 with open channels along the b axis, where the window sizes are ca. 5.51 × 3.15 Å2 in edge for the former and ca. 5.47 × 3.44 Å2 and 3.12 × 3.44 Å2 in edge for the latter. Gas adsorption isotherms revealed that thermally activated 1 and 2 both hardly adsorb N2 with very low N2 uptakes at 77 K. Comparably, the CO2 adsorption isotherms of thermally activated 1 and 2 both revealed gate-opening (two-step) sorption behaviors with an apparent hysteretic adsorption–desorption process, where the maximum uptakes are 135.4 and 171.5 cm3 g−1 STP for 1 and 2, respectively, at 195 K and P/P0 = 1. Photoluminescence studies showed that 1 and 2 both emitted bpBTD-dominated ligand-centered emissions, being as cyan and pearl aqua color fluorescence centered at λem = 467 and 495 nm, respectively, in solid-state and as cyan color fluorescence centered at λem = 455 and 458 nm, respectively, in H2O suspensions.