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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]

[Display omitted] • Over 97 % of FGD gypsum was converted into CaS. • •The reduction is controlled by the phase boundary, which is a typical shrinking sphere reaction. • •The reduction process of S in the FGD gypsum is SO 4 2−-SO 3 2−-S 2 2−-S2−. • •The obtained CaS has a honeycomb structure, which is conducive to the reuse. • The mechanism of reduction roasting of FGD gypsum was proposed. Flue gas desulfurized (FGD) gypsum is produced during the removal of SO 2 from flue gas. The reductive decomposition of FGD gypsum to calcium sulfide (CaS) is a crucial method for resource utilization. This study investigated the reduction roasting behavior and mechanism to enrich and recycle the calcium and sulfur resources in FGD gypsum effectively. Firstly, thermodynamics calculation revealed that the complete reduction of CaSO 4 to CaS is feasible. Experimental results showed that more than 95 % of the FGD gypsum can be reduced to CaS. Subsequently, the kinetic parameters of the reduction process were calculated. The results indicate that the reaction is controlled by the phase boundary, which is a typical shrinking sphere reaction process. Based on the kinetic study, the micromorphological transformation during the reduction process were studied. The results show that the reduction reaction initially starts from the boundary and gradually occurs towards the core. Finally, the reduction roasting mechanism is proposed. The intermediate processes of calcium sulfate reduction behavior were studied through XRD and XPS. The phase conversion and behavior of the main elements S in the process were explored. The results indicate that the process is a step-by-step reduction, and the transformation of S is SO 4 2−-SO 3 2−-S 2 2−-S2−. The reduction product forms a hollowed-out spheroid structure that cannot only effectively enrich Ca and S resources, but also provide advantageous conditions for their subsequent reuse. [ABSTRACT FROM AUTHOR]

Two-dimensional conjugated aromatic polymer with S/P substitutions demonstrated significant balance of H 2 permeance and selectivities over CO 2 /CO/N 2 /CH 4 via the effects of pore size and gas-membrane interaction. [Display omitted] • High cohesive energies confirm high structural stabilities of CAP-1S/CAP-1P. • CAP-1P exhibits almost complete H 2 selectivity with high H 2 permeance. • S/P substitution creates large pore sizes and strong gas-membrane interactions. • The interaction and pore size render efficient H 2 purification jointly. Based on two-dimensional conjugated aromatic polymer (2D-CAP), CAP-1S/CAP-1P monolayers were designed by substituting N with S/P atoms for H 2 purification. By using MD and DFT approaches, the H 2 purification performance and separation mechanisms of CAP-1S/CAP-1P membranes were investigated. Results showed that ultrahigh H 2 permeances of 3.546 × 10−5 and 2.593 × 10−4 mol m−2 s−1 Pa−1 were obtained in CAP-1S/CAP-1P, which were almost 104–105 times larger than the industrially acceptable standard. The selectivities of H 2 over CO 2 /CO/CH 4 /N 2 ranged from 5.719 × 1018 to 3.683 × 1039 in CAP-1S and 4.554 × 1013 to 2.153 × 1033 in CAP-1P. From a statistic viewpoint, the CAP-1S/CAP-1P membranes exhibited complete selectivities of H 2 over CO 2 /CO/CH 4 /N 2. The cohesive energies confirmed the high stabilities of CAP-1S/CAP-1P membranes. The minimum energy pathways, energy profiles, electron density, and charge density difference were analyzed to illustrate the significant impact of precise pore size on the H 2 separation performance. From a statistic mechanics view, the interaction between gases and CAP-1S/CAP-1P membranes indicated that the long-range Coulomb interactions dominated the gas diffusion processes. Results of this work highlighted CAP-1P as a promising H 2 separation membrane and elucidated the promotion mechanism by fine-tunning pore size and interaction between gases and membranes to balance the H 2 permeance and selectivity jointly. [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]