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[Display omitted] Excessive CO 2 emissions have contributed to global environmental issues, driving the development of CO 2 capture adsorbents. Among various candidates, metal–organic frameworks (MOFs) are considered the most promising due to their unique microporous structure. Herein, a series of partially interpenetrated MOFs named UPC-XX were built to investigate the continuous enhancement in CO 2 capture performance via synergistic effects from functional group, pore size, and steric-hindrance using theoretical calculations. It's showed that the introduction of functional groups improved the structure polarity and created more adsorption sites, thus, enhanced CO 2 capture capacity. The pore size modification augments the exposure of adsorption sites to mitigate the negative impact of pore space and surface area reduction caused by the introduction of functional groups, thereby further increasing the CO 2 capture capacity. The steric-hindrance effect optimized the adsorption sites distribution, which hasn't been considered in the previous two regulation strategies, thus, further increased the CO 2 capture capacity. The results underscore UPC-MOFs as outstanding adsorbent materials, among the UPC-MOFs, UPC-OSO 3 -steric exhibited the highest CO 2 capture capacity of 12.69 mmol/g with selectivities of 1142.41 (CO 2 over N 2) and 507.42 (CO 2 over CH 4) at 1.0 bar, 298 K. And the synergistic effect mechanisms of functional group, structure size, and steric hindrance were elucidated through theoretical calculations analyzing pore characteristics, gas distribution, isosteric heat, and van der Waals/Coulomb interactions. [ABSTRACT FROM AUTHOR]

The CO 2 capture and separation performance is enhanced by the improved structural polarity and additional adsorption sites created by anchoring alkali metal Li/Na/K. And the increase shows a positive correlation with AM concentration. Specially, UPC-6Li presents the best CO 2 capture capacity of 221.64 cm3 cm−3, along with the CO 2 over N 2 /CH 4 selectivity of 308/206, among UPC-AMs. [Display omitted] • CO 2 capture and separation performance were evaluated in 2D-COFs anchored by different concentration alkali metal (Li, Na, and K). • UPC-6Li exhibited the best CO 2 capture capacity of 221.64 cm3 cm−3 and CO 2 over N 2 /CH 4 selectivity of 308/206. • Improved structural polarity and additional metal adsorption sites are the main reasons for optimized performance. The development of advanced adsorbents with high CO 2 capture and separation performances is essential for decreasing atmospheric CO 2 concentration. Herein, grand canonical Monte Carlo and density functional theory were employed to investigate the adsorption and separation properties of CO 2 , N 2 , and CH 4 in 2D covalent organic framework (COFs) anchored by alkali metal (AMs) Li, Na, and K (UPC-nAMs, n = 3 or 6) at 298 K and 0–1.0 bar. The anchoring of AMs formed favorable adsorption sites, endowing UPC-nAMs with better CO 2 capture and separation performances. This effect was more evident with an increase in Li/Na/K concentration. The CO 2 adsorption capacity of UPC-6Li/Na/K was ∼ 221.64, 188.28, and 140.50 cm3 cm−3. The smaller atomic size of Li occupied less adsorption space, resulting in the highest CO 2 capture capacity of 221.64 cm3 cm−3 with selectivity of 308/206 over N 2 /CH 4 in UPC-6Li at 298 K and 1.0 bar. Structural stability, pore characteristics, isothermal adsorption heat, van der Waals and Coulomb interactions, gas distribution density, adsorption configuration, and gas radial distribution function were analyzed to identify the intrinsic mechanism of anchoring Li/Na/K to improve CO 2 capture and separation performances. [ABSTRACT FROM AUTHOR]

Abstract The structure-activity relationship of eleven diamines and MEA was investigated in order to provide guidance for the selection of the potential CO 2 capture absorbent. The effects of methyl, ethyl, hydroxyl groups, and distance between N groups in molecular structures were evaluated experimentally by using the rapid fast screening method and computed by Gaussian 09. Experimental results revealed that the proper number of methyl groups and ethyl groups on N atom could improve the absorption rate as well as the cyclic CO 2 capacity, and the addition of a hydroxyl group actually achieved a lower energy requirement (i.e. cyclic CO 2 capacity) for solvent regeneration with the decreasing stability of carbamate. In addition, the diamine with a hydroxyl group is more favorable for good stability in regeneration process, which addresses the problem of solvent loss in the application of diamines. Chain length extension from C 2 to C 3 can result in the poorer stability of the carbamate and lower energy requirement for amine regeneration. Thus, the lowest energy consumption (i.e. CO 2 cyclic capacity) was then achieved by aqueous 2-((2-aminoethyl)amino)ethanol (AEEA) solution, presenting it can be considered as an alternative or a potential absorbent for post-combustion CO 2 capture. Furthermore, the relative free energies of the tested diamines were computed by the Gaussian software for validating the stability of the carbamate formation, the order of which is in accordance with the order of the cyclic CO 2 capacity for all tested amines, indicating the experimental conclusion can be reliable. Highlights • The structure-activity relationship of eleven diamines was investigated. • A methyl group or an ethyl group on the N atom can enhance cyclic CO 2 capacity. • The hydroxyl group in the amine is more favorable for lower energy consumption. • The Gibbs free energies of tested diamines and carbamates were computed. [ABSTRACT FROM AUTHOR]

Highlights • A novel method of high-efficiency amine selection was proposed for CO 2 capture. • Reaction energy of Δ r G m and Δ r H m was applied to evaluate amine absorbents. • The EAE and MAE were selected as the promising absorbents for CO 2 removal. • Eleven amine solutions were investigated by the rate-based screening method. • The acid dissociation constants of eleven amines were determined at 293–333 K. Abstract In this work, a novel method in terms of reaction energy was proposed to evaluate the potential amine absorbents for post-combustion CO 2 capture, including two key parameters, i.e. the molar Gibbs energy change (Δ r G m) of proton combination with amine and the molar reaction enthalpy (Δ r H m) of protonated amine dissociation into amine and proton, which are calculated by the Van't Hoff equation. Firstly, the equilibrium acid dissociation constant (K a) of seven primary and secondary amines were experimentally determined at 293–323 K. The calculated Δ r G m and Δ r H m values obtained by the novel method indicated that the 2-(ethylamino)ethanol (EAE) and 2-(methylamino)ethanol (MAE) were the alternative promising absorbents among the seven tested amines, with a relatively low Δ r G m of about −57.0 kJ/mol and Δ r H m of 49.7 kJ/mol. In addition, seven amine solutions with molar concentration of 2.5 M and 5.0 M were investigated by the rate-based fast screening method to validate the reliability and applicability of the novel method. The comprehensive comparison of the absorption rate, desorption rate, CO 2 equilibrium solubility and cyclic capacity, also demonstrated the same conclusion that EAE and MAE solutions presented good CO 2 capture performances. The 2.5 M and 5.0 M EAE solutions obtain the highest energy efficiency for CO 2 capture with the highest cyclic capacity, which is about 52.9% and 32.3% higher than those of Monoethanolamine (MEA) solution, respectively. Additionally, the structure-activity analysis of seven amines suggested that the addition of hydroxyl group can obviously decrease the absorption rate and energy consumption of amine solution for CO 2 removal, the alkyl group addition on or close to amino group with steric hindrance is favorable for the CO 2 capture performance, while the addition of methyl group on amine molecular without steric hindrance can reduce the CO 2 cyclic capacity. What's more, four tertiary amines were also investigated by using these two approaches, and the compared results further validated the accuracy and applicability of the proposed novel method. [ABSTRACT FROM AUTHOR]

• The models of H e C O 2 - M E A / 1 D M A 2 P and α e q were constructed. • Mass transfer performance of MEA/1DMA2P solution was comprehensively investigated. • An integrative K G a v was established by embedding and α e q model. • The effect of y A ⁎ on K G a v was considered based on the H e C O 2 - M E A / 1 D M A 2 P data. • y CO 2 , o u t were correlated by using new K G a v models. In order to establish an integrative mass transfer coefficient (K G a V) model for CO 2 absorption into blended monoethanolamine (MEA)/1-dimethylamino-2-propanol (1DMA2P) solution in packed column, the models of CO 2 Henry's law constants (He CO₂-MEA/1DMA2P) and the equilibrium CO 2 solubility (α eq) were constructed. The experimental produced data can be reasonably analyzed. In this work, the Arrhenius equation was employed to fit the values of He CO₂-MEA/1DMA2P at different temperature with AARD of 4.06%; the Kent-Eisenberg prediction model and empirical polynomial prediction model were used to predict the data of α eq under different CO 2 partial pressures and temperatures with AARDs of 2.64% and 0.83%, respectively; the empirical K G a V model proposed by Li, the empirical K G a V model proposed by Aroonwilas and new K G a V model were used to correlate the average values of K G a V with AARDs of 14.36%, 12.44% and 9.03%, respectively; the model for outlet CO 2 concentration (y CO₂,out) in packed column was developed with AARD of 15.97%. Moreover, the heat of CO 2 absorption in 6 kmol/m3 MEA/1DMA2P solution was estimated by Gibbs-Helmholtz equation which gave a value of −39.8 kJ/mol. The results show that the blended MEA/1DMA2P solution has advantages that make it a potential absorbent for CO 2 capture. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are emerging adsorbent materials for CO2 capture and separation due to their tunable pore size, periodic permutation, and chemical thermal stability. Herein, four functionalized 3D COF‐300s (COF‐300‐X, X = –SO3H, –NO2, –OH, and –NH2) for CO2 adsorption and separation are studied by using density functional theory and grand canonical Monte Carlo simulation. The results show that four functionalized COF‐300s could create a feasible environment for CO2 adsorption with high accessible surface area, suitable pore size, and high porosity. The CO2 adsorption capacity in COF‐300s could be significantly improved by functionalization. In comparison, the best performing COF‐300‐SO3H shows a superior CO2 adsorption capacity of 6.23 mmol g−1 and a high CO2/N2 selectivity of 393 at 298 K and 100 kPa. The adsorption heat and interaction analyses demonstrate that the CO2 affinity in COF‐300s is enhanced by the introduction of polar functional groups, which renders great CO2 adsorption and separation performances. The gas distribution shows that the adsorption sites are concentrated near the functional groups and the distribution of CO2 in COF‐300‐SO3H has a characteristic of multilayer adsorptions. This work highlights COF‐300‐SO3H as an outperforming adsorbent candidate for CO2 capture and separation. [ABSTRACT FROM AUTHOR]

Understanding the internal mechanism of CO2 adsorption and separation of COF adsorbent materials is of great significance for high-efficiency carbon capture and storage (CCS). Herein, polyarylether-based covalent organic frameworks (PAE-COFs) structures with functionalized –CN, –COOH, and –C(NH2)NOH groups were evaluated for CO2 adsorption and separation over N2 by using grand canonical Monte Carlo (GCMC) simulation and density functional theory (DFT). Our calculation results showed that the adsorption and separation performance of CO2 in COF frameworks was related to the physical characteristics of pores, the types of gas molecules, and the interaction between COFs and gas molecules. JUC-505 modified by –CN functional group provided a feasible microporous environment with moderate specific surface area and porosity, presenting a high CO2 adsorption capacity of 5.14 mmol/g at 273 K and 1 bar. The PAE-COFs structures had good CO2/N2 separation performance, in which the CO2/N2 selectivity of JUC-505-COOH reached up to 90 at 273 K and 1 bar. Interactions analysis showed that the van der Waals and Coulomb interactions between CO2 and the framework were significantly stronger than those between N2 and the framework. Therefore, CO2 had a higher adsorption heat, which led to the larger adsorption capacity and the high selectivity of CO2 over N2. The gas radial distribution functions and 2D density distribution displayed that the CO2 adsorption corresponded to a multi-layer adsorption in frameworks, leading to the high performances of PAE-COFs for CO2 capture and separation. [ABSTRACT FROM AUTHOR]

By regulating the doping number of Li atoms in graphdiyne (GDY), the adsorption site of the structure is increased and the interaction between gas and skeleton is enhanced, thus creating a favorable environment for CO 2 adsorption. Li-GDYs have ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. [Display omitted] • Three structures with different Li doping types are screened. • Li-GDYs exhibit an ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. • Li doping has a more pronounced effect on enhancing the CO 2 − Li-GDYs interaction. • Gas distribution analyses demonstrate Li doping provides more adsorption sites. The development of CO 2 adsorbents with high adsorption and separation performances is important to solve severe environmental problems. Herein, two-dimensional graphdiyne acetylene rings doped with different concentrations of lithium atoms (1/2/6Li-GDYs) were introduced as potential adsorbents for CO 2 capture and separation by using Grand Canonical Monte Carlo and Density Functional Theory methods. According to the structure analysis, Li atoms could stably bind to GDY with a binding energy of 1.04 – 2.77 eV/atom; 1/2/6Li-GDYs had high cohesive energy of 7.02 – 7.54 eV/atom. Electronic structure analysis confirmed the large charge transfer and strong interaction between Li atoms and GDY. The pore physical properties of Li-GDYs indicated that the pore volume, porosity, and pore size provided a favorable environment for CO 2 adsorption. Among Li-GDYs, 2/6Li-GDYs exhibited an ultra-high CO 2 adsorption capacity of 11.91 mmol/g at 298 K and 100 kPa, and was superior to other metal-modified adsorbents. The CO 2 /N 2 selectivity in 1/2/6Li-GDYs reached ∼ 168, ∼311, and ∼ 1021 at 298 K and 100 kPa. Gas distribution analysis revealed a broad CO 2 distribution consisting of multilayer adsorption peaks around Li and adjacent C atoms, illustrating the significant effect of Li and Li-connected C atoms on CO 2 adsorption. Interaction analysis showed that Li doping enhanced the CO 2 -framework interaction more significantly than the N 2 -framework interaction, resulting in ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. The results of this work highlight 1/2/6Li-GDYs as ultrahigh-performance adsorbent materials for CO 2 adsorption and separation over N 2. [ABSTRACT FROM AUTHOR]

• The equilibrium CO 2 solubility of EMAB with designed structures was measured. • The pKa, reaction kinetics, and heat of CO 2 absorption of EMAB were evaluated. • Two novel models, i.e. Fugacity-activity and Extended C f model, are established. • EMAB is a potential CO 2 capture agent for use in amine-based PCC technology. The aim of this project was to develop a thermodynamic model for the vapour-liquid equilibrium of an amine-water-carbon dioxide system and to evaluate the CO 2 capture performance of aqueous EMAB solution. The structurally modified tertiary amine 4-(ethyl-methyl-amino)-2-butanol (EMAB) was chosen because of its molecular structure-activity relationship. Measurements were made of its equilibrium CO 2 solubility, viscosity, dissociation constant, and second-order reaction rate constant, and the heat of absorption was then calculated. Additionally, the novel semi empirical model (Extended C f model) and the novel rigorous thermodynamic model (fugacity-activity model) which take into consideration the association of the partial molar property and the equation of state were developed to predict the equilibrium CO 2 solubility. The models can provide reasonable prediction results with AARDs of 2.3% and 3.68%, respectively. Furthermore, the thermodynamic and dynamic properties of EMAB were analyzed and evaluated by a comprehensive method and compared with some new tertiary amines and traditional commercial amines. The study concludes that EMAB has good CO 2 capture performance and is expected to be one of the most promising alternative amines for post combustion CO 2 capture technology. [ABSTRACT FROM AUTHOR]

By regulating the doping site and concentration of Li atoms in β1-Graphyne, more charges accumulate on the surrounding C atoms and the gas-framework interaction increase, thus creating a favorable environment for CO 2 adsorption and an ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity in Li-β1-GYs. [Display omitted] • Li-β1-GYs exhibit an ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. • Li doping has a more pronounced effect on enhancing the CO 2 −Li-β1-GYs interaction. • Gas distribution analyses demonstrate Li doping provides more adsorption sites. The selective CO 2 adsorption is of great significance to many energy and environment-related processes. Herein, CO 2 /N 2 adsorption and separation in Li-doped 2D graphyne allotrope (β1-GY) were studied by using grand canonical Monte Carlo simulation and density(GCMC) functional theory approaches(DFT). The results showed that Li atoms were stably combined with β1-GY and the binding energy was −2.85−−3.60 eV, which ensured the structural stability of Li-doped β 1 -graphyne (Li-β1-GY) for CO 2 /N 2 adsorption and separation. Different Li doping types were evaluated, and five Li-β1-GY structures were screened, including the a, b, c, ac, and bc structures. Li doping provided more adsorption sites and improved the CO 2 adsorption performance. Among all Li-β1-GYs, the ac structure showed the best CO 2 adsorption performance. The CO 2 adsorption capacity of ac structure reached 11.10 mmol−1 g−1 at 298 K and 100 kPa, which was higher than the well-known metal–organic framework Mg-MOF-74 (∼8.60 mmol−1 g−1) under the same condition. At 298 K and 100 kPa, the CO 2 /N 2 selectivity reached 354. The gas distribution confirmed that CO 2 was adsorbed around the Li and C atoms and demonstrated the significant improvement of C atoms around Li atoms on the CO 2 adsorption. The interaction analyses showed that Li doping enhanced the CO 2 -framework interaction more distinctively than the N 2 -framework interaction, leading to an ultra-high CO 2 adsorption capacity and CO 2 /N 2 selectivity. Results of this work highlighted Li-β1-GYs as promising materials for CO 2 /N 2 adsorption and separation. [ABSTRACT FROM AUTHOR]