Accelerating Solvent Selection for Type II Porous Liquids

Accelerating Metal-Organic Framework Selection for Type III Porous Liquids by Synergizing Machine Learning and Molecular Simulation

MOF-based type III porous liquids, comprising porous MOFs dissolved in a liquid solvent, have attracted increasing attention in carbon capture. However, discovering appropriate MOFs to prepare porous liquids was still limited in experiments, wasting time and energy. In this study, we have used the density functional theory and molecular dynamics simulation methods to identify 4530 MOF candidates as the core database based on the idea of prohibiting the pore occupancy of porous liquids by the solvent, [DBU-PEG][NTf2] ionic liquid. Based on high-throughput molecular simulation, random forest machine learning models were first trained to predict the CO2 sorption and the CO2/N2 sorption selectivity of MOFs to screen the MOFs to prepare porous liquids. The feature importance was inferred based on Shapley Additive Explanations (SHAP) interpretation, and the ranking of the top 5 descriptors for sorption/selectivity trade-off (TSN) was gravimetric surface area (GSA) > porosity > density > metal fraction > pore size distribution (PSD, 3.5-4 Å). RICBEM was predicted to be one candidate for preparing porous liquid with CO2 sorption capacity of 20.87 mmol/g and CO2/N2 sorption selectivity of 16.75. The experimental results showed that the RICBEM-based porous liquid was successfully synthesized with CO2 sorption capacity of 2.21 mmol/g and CO2/N2 sorption selectivity of 63.2, the best carbon capture performance known to date. Such a screening method would advance the screening of cores and solvents for preparing type III porous liquids with different applications by addressing corresponding factors.

Rational Design of Porous Ionic Liquids for Coupling Natural Gas Purification with Waste Gas Conversion

Removal of trace impurities for natural gas purification coupled with waste gas conversion is highly desired in industry. We here report a type of porous ionic liquids (PILs) that can realize the continuous flow separation of CH4 /CO2 /H2 S and the conversion of the captured H2 S to useful products. The PILs are synthesized through a step-by-step surface modification of ionic liquids (ILs) onto UiO-66-OH nanocrystals. The introduction of free tertiary amine groups on the nanocrystal surface endows these PILs with an exceptional ability to enrich H2 S from CO2 and CH4 with impressive selectivity, while the permanent pores of UiO-66-OH act as containers to store an exceptionally higher amount of the selectively captured H2 S than the corresponding nonporous ILs. Simultaneously, the tertiary amines as dual functional moieties offer effective catalytic sites for the conversion of the H2 S stored in PILs into 3-mercaptoisobutyric acid, a key intermediate required for the synthesis of Captopril (an antihypertensive drug). Molecular dynamics, density functional theory calculations and Grand Canonical Monte Carlo simulations help understand both the mechanisms of separation and catalysis performance, confirming that the tertiary amines as well as the permanent pores in UiO-66-OH play vital roles in the whole procedure.

Thermodynamic Evidence for Type II Porous Liquids

Porous liquids are an emerging class of microporous materials where intrinsic, stable porosity is imbued in a liquid material. Many porous liquids are prepared by dispersing porous solids in bulky solvents; these can be contrasted by the method of dissolving microporous molecules. We highlight the latter "Type II" porous liquids-which are stable thermodynamic solutions with demonstrable colligative properties. This feature significantly impacts the ultimate utility of the liquid for various end-use applications. We also describe a facile method for determining if a Type II porous liquid candidate is "porous" based on assessing the partial molar volume of the porous host molecule dissolved in the solvent by measuring the densities of candidate solutions. Conventional CO₂ isotherms confirm the porosity of the porous liquids and corroborate the facile density method.