Recent advances in dual-filler mixed matrix membranes

Mixed matrix membranes (MMMs) have been widely developed as an attractive solution to overcome the drawbacks found in most polymer membranes, such as permeability-selectivity trade-off and low physicochemical stability. Numerous fillers based on inorganic, organic, and hybrid materials with various structures including porous or nonporous, and two-dimensional or three-dimensional, have been used. Demanded to further improve the characteristics and performances of the MMMs, the use of dual-filler instead of a single filler has then been proposed, from which multiple effects could be obtained. This article aims to review the recent development of MMMs with dual filler and discuss their performances in diverse potential applications. Challenges in this emerging field and outlook for future research are finally provided.

Discovery of Innovative Polymers for Next-Generation Gas-Separation Membranes using Interpretable Machine Learning

Polymer membranes perform innumerable separations with far-reaching environmental implications. Despite decades of research on membrane technologies, design of new membrane materials remains a largely Edisonian process. To address this shortcoming, we demonstrate a generalizable, accurate machine-learning (ML) implementation for the discovery of innovative polymers with ideal separation performance. Specifically, multitask ML models are trained on available experimental data to link polymer chemistry to gas permeabilities of He, H2, O2, N2, CO2, and CH4. We interpret the ML models and extract chemical heuristics for membrane design, through Shapley Additive exPlanations (SHAP) analysis. We then screen over nine million hypothetical polymers through our models and identify thousands of candidates that lie well above current performance upper bounds. Notably, we discover hundreds of never-before-seen ultrapermeable polymer membranes with O2 and CO2 permeability greater than 104 and 105 Barrer, respectively. These hypothetical polymers are capable of overcoming undesirable trade-off relationship between permeability and selectivity, thus significantly expanding the currently limited library of polymer membranes for highly efficient gas separations. High-fidelity molecular dynamics simulations confirm the ML-predicted gas permeabilities of the promising candidates, which suggests that many can be translated to reality.

Discovery of Innovative Polymers for Next-Generation Gas-Separation Membranes using Interpretable Machine Learning

Polymer membranes perform innumerable separations with far-reaching environmental implications. Despite decades of research on membrane technologies, design of new membrane materials remains a largely Edisonian process. To address this shortcoming, we demonstrate a generalizable, accurate machine-learning (ML) implementation for the discovery of innovative polymers with ideal separation performance. Specifically, multitask ML models are trained on available experimental data to link polymer chemistry to gas permeabilities of He, H2, O2, N2, CO2, and CH4. We interpret the ML models and extract chemical heuristics for membrane design, through Shapley Additive exPlanations (SHAP) analysis. We then screen over nine million hypothetical polymers through our models and identify thousands of candidates that lie well above current performance upper bounds. Notably, we discover hundreds of never-before-seen ultrapermeable polymer membranes with O2 and CO2 permeability greater than 104 and 105 Barrer, respectively, orders of magnitude higher than currently available polymeric membranes. These hypothetical polymers are capable of overcoming undesirable trade-off relationship between permeability and selectivity, thus significantly expanding the currently limited library of polymer membranes for highly efficient gas separations. High-fidelity molecular dynamics simulations confirm the ML-predicted gas permeabilities of the promising candidates, which suggests that many can be translated to reality.

Study of the structural and electrical properties of the PVA–NH4SCN membrane for its application in electric double layer capacitors

The PVA–NH4SCN polymer membranes were prepared by simple solution casting technique by passing ultrasound waves during the preparation. The polymer membranes were subjected to X-ray diffraction analysis and scanning electron microscopy. The X-ray diffraction pattern confirmed the incorporation of a salt into the polymer matrix. The scanning electron microscopy images showed the morphological changes of the polymer membrane. The polymer electrolyte (designated as UPVA20) incorporated with the 20 wt.% of the salt had the highest electrical conductivity in the order of 10–4 S cm–1. It was concluded from the dielectric, tangent and modulus spectra that the UPVA20 membrane was good at its properties. Thus, electric double layer capacitor was constructed with UPVA20 membrane as the separator. The capacitance value of the electric double layer capacitor determined from cyclic voltammetry was found to be 1652 mF g–1. The ultrasound assisted preparation of polymer membranes were good at performance when compared with the polymer membranes of ultrasound unassisted preparation. Among all the polymer electrolytes, UPVA20 polymer membrane had high conductivity, potential stability and capacitance.

Epoch-Making Discovery for CO2 Characteristics: “Pseudo Osmosis” in the Gas Phase

Recently, unprecedented torrential rains have deluged the globe, resulting in disastrous floods. These disasters were caused by climate changes because of an increase in carbon dioxide (CO2) concentration in the atmosphere since the industrial revolution. Therefore, atmospheric accumulation of CO2 should be reduced to avoid a future climate crisis. Many methods to fix CO2 have been developed, but a practical method has not been established, except for the method using amines based on moderate plant constructions. However, the membrane method has not yet been established because of the conflicting relationship between penetrability and specificity, although membrane technology can be used for CO2 separation. Epoch-making discoveries for CO2 characteristics have been presented as follows: 1) the high penetrability of CO2 in the gas phase caused “pursued osmosis” against polymer elasticity; 2) highly penetrable CO2 passed through polymer membranes such as authentic polymers and natural cellulose, whereas neither O2 nor N2 penetrates these polymers examined; 3) CO2 is absorbed by plastics; 4) H2 and CH4 gases penetrate through polymer membranes, but their penetration was completely blocked in the presence of water; and 5) using a polytunnel made of polymer sheets (an artificial forest or positive green house), which allows CO2 penetration, instead of hard chamber, steel, or plastic could be cost effective. Therefore, polymer membranes could be practically and economically useful for CO2 separation from the exhaust gas and atmosphere.

Efficient Recovery of Noble Metal Ions (Pd2+, Ag+, Pt2+, and Au3+) from Aqueous Solutions Using N,N'-Bis(salicylidene)ethylenediamine (Salen) as an Extractant (Classic Solvent Extraction) and Carrier (Polymer Membranes)

This paper presents the results of the first application of N,N'-bis(salicylidene)ethylenediamine (salen) as an extractant in classical liquid–liquid extraction and as a carrier in membrane processes designed for the recovery of noble metal ions (Pd2+, Ag+, Pt2+, and Au3+) from aqueous solutions. In the case of the utilization of membranes, both sorption and desorption were investigated. Salen has not been used so far in the sorption processes of precious metal ions. Recovery experiments were performed on single-component solutions (containing only one type of metal ions) and polymetallic solutions (containing ions of all four metals). The stability constants of the obtained complexes were determined spectrophotometrically. In contrast, electrospray ionization high-resolution mass spectrometry (ESI-HRMS) was applied to examine the elemental composition and charge of the generated complexes of chosen noble metal ions and salen molecules. The results show the great potential of N,N'-bis(salicylidene)ethylenediamine as both an extractant and a carrier. In the case of single-component solutions, the extraction percentage was over 99% for all noble metal ions (molar ratio M:L of 1:1), and in the case of a polymetallic solution, it was the lowest, but over 94% for platinum ions and the highest value (over 99%) for gold ions. The percentages of sorption (%Rs) of metal ions from single-component solutions using polymer membranes containing N,N'-bis(salicylidene)ethylenediamine as a carrier were highest after 24 h of the process (93.23% for silver(I) ions, 74.99% for gold(III) ions, 69.11% and 66.13% for palladium(II) and platinum(II) ions, respectively), similar to the values obtained for the membrane process conducted in multi-metal solutions (92.96%, 84.26%, 80.94%, and 48.36% for Pd(II), Au(III), Ag(I), and Pt(II) ions, respectively). The percentage of desorption (%Rdes) was very high for single-component solutions (the highest, i.e., 99%, for palladium solution and the lowest, i.e., 88%, for silver solution), while for polymetallic solutions, these values were slightly lower (for Pt(II), it was the lowest at 63.25%).