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Molecular dynamics simulation was applied to test and evaluate the ability of several models of carbon dioxide on predicting thermodynamics and transport properties. Firstly, we compared the liquid-vapor coexist curves of seven kinds of carbon dioxide models by molecular dynamics simulations. It was found that the Cygan_flex model and EPM2 model were more accurate than the others. Then we investigated the structural properties of carbon dioxide using NPT ensemble molecular dynamics simulation. The fluid became less dense with the increasing temperature. Thirdly, the self-diffusion coefficients were studied at temperature and pressure up to 600 K and 80 MPa, respectively. The results showed that the self-diffusion coefficient decreased with the increasing pressure and increased with increasing temperature. Finally, we calculated the thermal conductivity of carbon dioxide at 250 K using EPM2_flex model, Cygan_flex model and TraPPE_flex model. So, we should pay attention to the selection of appropriate carbon dioxide models to obtain different carbon dioxide properties. • We reproduced the liquid-vapor coexist curve for seven carbon dioxide models. • Self-diffusion coefficient and thermal conductivity of carbon dioxide are obtained. • Choose appropriate carbon dioxide model for different carbon dioxide properties. [ABSTRACT FROM AUTHOR]

Global warming due to greenhouse gas emissions has continuously threatened the climate and environment. Zirconium-based metal-organic frameworks (Zr-MOFs) with Zr 6 inner cores represent a subfamily of nanoporous materials with good physicochemical stabilities, showing significant prospects for practical applications in gas separation. A molecular simulation study is reported here to investigate the membrane separation of CO 2 /N 2 and CO 2 /CH 4 mixtures in five Zr-MOFs (Zr-fum, UiO-66, DUT-52, Zr-cca, UiO-67) with similar ligand in their structures and different pore-limiting diameter (PLD) ranging from 0.36 nm to 0.59 nm. The gas permeation and separation performance are evaluated with the concentration gradient-driven molecular dynamics (CGD-MD) method. The results show that the separation of both gas mixtures is dominated by the preferential sorption of CO 2 over N 2 and CH 4 , respectively. Meanwhile, the PLD of MOFs is also a significant factor governing permeation. MOFs with a larger PLD have a higher permeability and a lower selectivity for CO 2 /N 2 and CO 2 /CH 4 separation. Free-energy profiles were calculated to describe the insights into CO 2 separation, that the larger PLD can cause a lower energy barrier when gases transport through the pore of MOFs. The results were compared with the grand canonical Monte Carlo and equilibrium molecular dynamics (GCMC + EMD) approach, a traditional method to predict gas adsorption and diffusion in MOFs. As the GCMC+EMD approach neglected the interaction between components and potential mass transfer resistance at the surface of the membranes, the results obtained from the CGD-MD method in this work are more reliable. This study provides microscopic insights into CO 2 separation in Zr-MOF membranes and suggests their potential use for gas separation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Double transition metal atoms on GDY break the scaling relationship. • Machine learning speeds up the screening catalysts and reveals the descriptors. • Relations of intermediate adsorption energies aid catalyst selection in deep CO 2 RR. • GDY-based catalysts with strong CO binding exhibit high selectivity towards CH 4. Electrochemical CO 2 reduction reaction (CO 2 RR) has become a promising application in addressing energy challenges and environmental crises. However, the scaling relationship between the reaction intermediates constrains the successful deep reduction of CO 2. Dual-metal-site catalysts (DMSCs) have emerged as potential electrocatalysts for CO 2 RR by breaking the scaling relationship due to their more adaptable active sites. Herein, this study aims to investigate the correlation between the adsorption energies of essential intermediates in CO 2 RR catalysis with double transition metal atoms anchored on graphdiyne monolayer (TM 1 -TM 2 @GDY) through machine-learning (ML) assisted density functional theory (DFT) calculations. The results reveal the important descriptors of CO 2 RR catalyzed by TM 1 -TM 2 @GDY, and demonstrate that the heteronuclear TM 1 -TM 2 @GDY have great potential for deep CO 2 reduction. Especially, Co-Mo@GDY and Co-W@GDY show low limiting potential (-0.60 V and −0.39 V, respectively) and high selectivity on the reaction from CO 2 to CH 4 based on the free energy diagrams. This study indicates that the two TM atoms on GDY act cooperatively for the catalysis of CO 2 RR. Notably, utilizing ML eliminates the need to calculate all transition metal combinations by DFT, which is a great boost in quickly investigating catalytic performance and high screening for excellent catalysts. [ABSTRACT FROM AUTHOR]

Membrane separation technology has been widely used in the separation and capture of CO 2 to reduce carbon emissions. The performances of facilitated hybrid membranes (FHMs) can be improved by properly adding metal-organic framework (MOF)-based nanoparticles (NPs) and modifying polymers to the polymer matrix. Grafting and blending methods are widely used to introduce modifying polymers to improve the compatibility between NPs and the polymer matrix, and the performance of FHMs for CO 2 separation. However, the separation performance of FHMs decreases significantly when the long chains of the polymer infiltrate into the pores of the MOF at the interface between the modifying polymer and MOF. To in-depth understand the nano-scale polymer-NPs interfacial interaction mechanism of the grafting and blending methods, we herein employed molecular dynamic (MD) simulation method combined with experiments to investigate the interface between NPs of Cu-MOF (Cu-BDC) and four commonly used modifying polymers (PEG, polyethylene glycol; PEI, polyethylenimine; PVA, polyvinyl alcohol; PPy, polypyrrole) with PVDF (polyvinylidene difluoride) as the polymer matrix. The results showed that the blending method for modification can effectively avoid the polymer blockage in Cu-BDC pores by using four modifying polymers, while the grafting method caused polymer infiltration for PEG and PEI. The relationship between the polymer diameter and the pore limiting diameter (PLD) of the Cu-BDC was evaluated to analyze the polymer infiltration effect. FHMs of Cu-BDC/PEG@PVDF were synthesized based on the MD simulation results, which showed excellent CO 2 separation performance due to the good compatibility between the Cu-BDC and the modified matrix polymer. This work offers an insight in nano-scale into the interface design between the MOF and the polymer for FHMs separating CO 2. [Display omitted] • The interface interaction between MOF and modifying polymers was studied by molecular dynamics. • Using blending method to avoid the modifying polymer (PEG and PEI) infiltrating into MOF(Cu-BDC) pores. • The compatibility between modified matrix polymer and MOF was improved. • Cu-BDC/PEG@PVDF was synthesized and exhibited good performance for CO 2 separation. [ABSTRACT FROM AUTHOR]

Facilitated transport mixed matrix membranes (FTMMMs) separation technology has shown advantages in improving CO 2 recycling efficiency and reducing the environmental impacts associated with carbon emission. The design of FTMMMs is highly dependent on the selection of a compatible combination of polymer and filler. Herein, a novel grafted nanoparticles (GNPs) filler UiO-66-NM@PEG with multiple groups prone to hydrogen bond was designed to alleviate the phase separation and performance degradation caused by filler/polymer poor compatibility. In the GNPs configuration, by employing the coexistence strategy of coupling reaction and covalent bonds, maleic anhydride (MAH) was coupled with the amino group on UiO-66-NH 2 without clogging or cracking, and the generated carboxyl groups can be cross-linked with the hydroxyl groups on the poly (ethylene glycol) (PEG) by covalent bonds. The UiO-66-NM@PEG demonstrated excellent interface compatibility between the filler and matrix phase of UiO-66-NM@PEG/PVDF, which was further convinced by molecular modelling. The resultant UiO-66-NM@PEG/PVDF achieved a simultaneous enhancement of gas permeability (537.6 Barrer) and ideal CO 2 /N 2 selectivity (47.8), which surpassed Robenson upper bound. Moreover, the UiO-66-NM@PEG/PVDF has a lasting sustainability over 960 h (40 days), and a valid anti-acid/alkali corrosion resistance in harsh environments. More importantly, UiO-66-NM@PEG can also be well mixed with other mixture matrices such as hydroxy-terminated polydimethylsiloxane (PDMS) and polyether-block-polyamide copolymer (PEBAX) to promote permeability/ideal selectivity up to (724.1 Barrer/21.1) and (307.4 Barrer/31.4). We thus concluded that this rational-design GNPs approach provides a general toolbox for controllable engineering in GNPs whereby enhanced favorable filler/matrix compatibility in FTMMMs with optimized CO 2 /N 2 separation properties. By the means of covalent "bridge-crosslinking", the UiO-66-NM@PEG/PVDF FTMMM with favorable phase compatibility between filler/matrix displayed excellent gas separation performance. [Display omitted] • A novel grafted filler UiO-66-NM@PEG was synthesized via Covalent "Bridge-crosslinking" strategy. • The membrane showed excellent sustainability over 40 days and corrosion resistance. • UiO-66-NM@PEG exhibited favorable filler/matrix compatibility in other two matrices. • The performance of UiO-66-NM@PEG/PVDF surpassed Robenson upper bound. [ABSTRACT FROM AUTHOR]