MARTINI-Based Force Fields for Predicting Gas Separation Performances of Metal–Organic Framework/Polymer Composites

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Although polyvinyl alcohol (PVA) membranes are commonly used for CO2 separation, there is still large development space in mechanical properties and high selectivity of the gas separation process. In this study, the gas separation performance and mechanical properties of the (PVA/Cu2+) substrate membranes were improved by introducing polyamidoamine (PAMAM). PAMAM had an important effect on the gas adsorption and separation performance of the membrane. In addition, the gas adsorption and separation properties of the PVA/Cu2+/PAMAM membrane (PPCm) were analyzed and studied when the inlet gas pressure and the species of mixed gases were variable. The results showed that the crystallinity and mechanical properties of the membrane with the PAMAM had been significantly improved. Young’s modulus of PPCm with 30% PAMAM was 132% higher than that of the PVA/Cu2+ composite membrane without PAMAM. In addition, efficient separation efficiency and high selectivity of the gas separation process were observed. The separation factors of the PPCm for CO2/H2 and CO2/N2 were about three times higher than that of the PVA/Cu2+ substrate membranes. These results suggested that the introduction of PAMAM was promising for CO2 separation and permeance.

Mixed matrix membranes (MMMs) are hybrid membranes, which have been intensively studied and expected to overcome the drawbacks of both polymeric and inorganic counterparts. In fact, MMMs are still facing great challenges, mostly due to the poor compatibility and adhesion between the fillers and polymer matrix, which considerably reduce MMMs separation performance. To address that issue, the work in this thesis focus on modification methods in order to improve the interfacial adhesion between polymer/fillers in the MMMs and consequently enhance the gas separation efficiency of the MMMs.In the first part of experiment, a non-porous nano-size filler, nanodiamond (ND) was introduced into Pebax copolymer to fabricate the MMM. While being promising filler, the non-porous structure and susceptible to agglomeration of ND are still the issues in gas separation membrane. This chapter proposes an efficient approach as grafting polyethyleneimine (PEI) onto the surface of ND before embedding into the polymer matrix to fabricate the MMMs for CO2/N2 separation. The presence of PEI layer on ND surface significantly improved the interfacial adhesion and dispersion of ND in the Pebax matrix, which were clearly indicated by SEM and FIB-SEM observation. The improvement of interfacial interaction led to the increment in CO2/N2 selectivity compared to the pristine polymer membranes and the non-PEI MMMs as well. The CO2/N2 selectivity of the Pebax/oxND-PEI 0.5 wt.% increased 25% compared to the neat polymer and 43.66% compared to the Pebax/oxND. This chapter has contributed to a simple but effective method to improve the dispersion of the non-porous nanofiller, as well as enhance the gas separation performance of the MMMs.The next chapter studied the effects of different morphologies of filler on the dispersion, interfacial interaction and gas separation performance of the MMMs. Three types of filler morphologies: conventional polyhedral (P-ZIF), nanorod (R-ZIF) and leaf-shaped nanosheet (L-ZIF) were introduced and investigated. The change in morphology can alter the interfacial interaction between polymer and fillers due to the different aspect ratio and surface structure. The L-ZIF and R-ZIF showed better compatibility with the 6FDA-durene polymer matrix compared to the polyhedral ZIF. L-ZIF improved the gas selectivity of CO2/N2 (30.3%), CO2/CH4 (40%) compared to the neat polymer, while the R-ZIF enhance the CO2 permeability (41%) with comparable gas selectivity to the neat polymer. This chapter's results suggested that the nanorod and nanosheet morphologies are more effective in enhancing the interfacial adhesion between polymer/filler and contributed to the guidance in filler morphology selection to achieve improved gas separation performance.In the following chapter, ZIF nanorod (R-ZIF) was further investigated as the filler and was coated with two types of ILs before incorporated in the the 6FDA-durene matrix. In the previous chapter, while showing compatibility with the 6FDA-durene matrix at low filler loading (10 wt.%), R-ZIF still formed aggregates in the membrane at high loading (20 wt.%) which decrease the gas separation performance of the MMMs. The ionic liquid decoration improved the interfacial interaction between R-ZIF and the polymer matrix leading to the enhancement in gas separation performance of the PR/IL MMMs which was intensively investigated by conventional SEM, FTIR, single and mix gas tests. The most significant improvements were the increment of 50% in CO2/CH4 selectivity, while maintaining the CO2 permeability of the 10 wt.% R-ZIF/IL MMM. The improvement in gas separation efficiency of the IL-incorporated MMMs compared to the non-IL MMMs was still observed even at high loading of filler (20 wt.%). The contribution in this part is to confirm that IL-decoration is an effective approach to enhance the interfacial issues and improve the gas separation efficiency of the MMMs.In the last experiment section, micron size polyhedral shape ZIF (P-ZIF) was coated with 3 different ILs and dispersed in 6FDA-durene matrix to prepare the MMMs. As investigated in previous experiment section, P-ZIF exhibited the worst interfacial interaction with the polymer matrix among 3 different morphologies. Thus, it is more challenging to obtain excellent filler/polymer contact between micron-sized P-ZIF and polymer matrix and achieve improvement in gas separation efficiency. Acting as the interfacial binder, IL layer has effectively reduced the non-selective interfacial voids in the MMM and enhanced the polymer/P-ZIF adhesion. The vol.% of interfacial voids of the pristine PZ MMM has been reduced from 1.17% to 0.35%, 0.33% and 0.49% with the PZ/IL1, PZ/IL2 and PZ/IL3 MMM, respectively, leading to a significant improvement in gas separation performance, particularly with the CO2/CH4 separation performance surpassing the 2008 upper bound. Additionally, the PZ/IL MMMs also showed enhancement in gas separation performance for the CO2 - CH4 mix gas (50:50) compared to the non-IL MMMs and the neat polymer membrane. The contribution of this chapter is that it further evidenced the effectiveness of using IL as a interfacial binder to minimize the interfacial defects in MMMs as well as enhance the gas separation performance in both ideal and real conditions.

Poly(ionic liquid) (PIL)-based block copolymers are of particular interest as they combine the specific properties of PILs with the self-assembling behaviors of block copolymers, broadening the range of potential applications for PIL-based materials. In this work, three particle brushes: SiO2-g-poly(methyl methacrylate) (PMMA), SiO2-g-PIL, and SiO2-g-PMMA-b-PIL were prepared through surface-initiated atom transfer radical polymerization. Unlike the homogeneous homopolymer particle brushes, the block copolymer particle brush SiO2-g-PMMA-b-PIL exhibited a bimodal chain architecture and unique phase-separated morphology, which were confirmed by size-exclusion chromatography and transmission electron microscopy. In addition, the influence of the introduction of the PMMA segment on the gas separation and mechanical performance of the PIL-containing block copolymer particle brushes were investigated. A significant improvement of Young's modulus was observed in the SiO2-g-PMMA-b-PIL compared to the SiO2-g-PIL bulk films; meanwhile, their gas separation performances (CO2 permeability and CO2/N2 selectivity) were the same, which demonstrates the possibility of improving the mechanical properties of PIL-based particle brushes without compromising their gas separation performance.

An investigation on the effects of both amine grafting and blending with biodegradable chitosan membrane for CO2 capture from CO2/N2 gas mixtures

In recent years, mixed matrix membranes (MMMs) have received worldwide attention for their potential to offer superior gas permeation and separation performance involving CO2 and CH4. However, fabricating defect-free MMMs still remains as a challenge where the incorporation of fillers into MMMs has usually led to some issues including formation of undesirable interfacial voids, which may jeopardize the gas separation performance of the MMMs. This current work investigated the incorporation of zeolite RHO and silane-modified zeolite RHO (NH2–RHO) into polysulfone (PSf) based MMMs with the primary aim of enhancing the membrane’s gas permeation and separation performance. The synthesized zeolite RHO, NH2–RHO, and fabricated membranes were characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared-attenuated total reflection (FTIR-ATR), thermogravimetric analysis (TGA) and field emission scanning election microscopy (FESEM). The effects of zeolite loading in the MMMs on the CO2/CH4 separation performance were investigated. By incorporating 1 wt% of zeolite RHO into the MMMs, the CO2 permeability and ideal CO2/CH4 selectivity slightly increased by 4.2% and 2.7%, respectively, compared to that of a pristine PSf membrane. On the other hand, a significant enhancement of 45% in ideal CO2/CH4 selectivity was attained by MMMs incorporated with 2 wt% of zeolite NH2-RHO compared to a pristine PSf membrane. Besides, all MMMs incorporated with zeolite NH2-RHO displayed higher ideal CO2/CH4 selectivity than that of the MMMs incorporated with zeolite RHO. By incorporating 1–3 wt% zeolite NH2-RHO into PSf matrix, MMMs without interfacial voids were successfully fabricated. Consequently, significant enhancement in ideal CO2/CH4 selectivity was enabled by the incorporation of zeolite NH2–RHO into MMMs.

Two-dimensional (2D) nanomaterials are an emerging platform with unique structural and physiochemical properties attracted intense interest in developing high-performance gas and liquid separation membranes. This review provides an overview on the latest breakthrough studies in the fabrication of 2D nanomaterials membranes including atomically thin membranes, laminar and mixed matrix membranes. Especially, we focus on structural features, permeation mechanism as well as gas and liquid separation performance of 2D nanomaterials membranes. Additionally, we highlighted the unique role of 2D nanomaterials in mitigating plasticization and physical aging phenomena in polymer-based membranes. Finally, we underline current challenges and future prospects of this intriguing materials platform for developing next generation of membranes.Highlights• Physiochemical properties and synthesis approaches of various 2D nanomaterials are highlighted• Latest breakthrough achievements in developing large area atomically thin graphene membranes are presented• Gas separation, water and organic solvent permeation performance, and ion sieving properties of 2D materials-based membranes are summarized• Role of 2D nanomaterials in mitigating plasticization, physical aging and fouling of polymer-based membranes are highlighted

Membrane based gas separation process technology has been recognized as one of the most efficient and advanced unit operation for gas separation. One of the problems in membrane gas separation is membrane performance. This paper explores the application of cellulose acetate (CA) membrane for natural gas purification and separation by improving its permeability and selectivity. The main interest in this research is to study the effect of quench medium on the gas separation performance towards its physical characteristics and gas separation performance of CA membrane. Cellulose acetate polymer was dissolved in n- methyl-2-pyrrolidone solvent and casted onto a glass plate using a pneumatically controlled casting system with fixed shear rate and solvent evaporation times. The parameter varied was the non-solvent used as quench medium during membrane post treatment that were methanol and n-hexane. The different quench media as post treatment affected the O2 and N2 gas permeation and O2/N2 selectivity as well as the tensile strength of the flat sheet asymmetric membrane. Combination of methanol and n-hexane as quench media gave the best result than the other steps. This solvent exchange step influenced the morphology by producing thin skin layer and thus gives better gas separation performance than other steps

Theoretical investigation of gas separation in functionalized nanoporous graphene membranes

The unique high surface area and tunable cavity size endow metal-organic cages (MOCs) with superior performance and broad application in gas adsorption and separation. Over the past three decades, for instance, numerous MOCs have been widely explored in adsorbing diverse types of gas including energy gases, greenhouse gases, toxic gases, noble gases, etc. To gain a better understanding of the structure-performance relationships, great endeavors have been devoted to ligand design, metal node regulation, active metal site construction, cavity size adjustment, and function-oriented ligand modification, thus opening up routes toward rationally designed MOCs with enhanced capabilities. Focusing on the unveiled structure-performance relationships of MOCs towards target gas molecules, this review consists of two parts, gas adsorption and gas separation, which are discussed separately. Each part discusses the cage assembly process, gas adsorption strategies, host-guest chemistry, and adsorption properties. Finally, we briefly overviewed the challenges and future directions in the rational development of MOC-based sorbents for application in challenging gas adsorption and separation, including the development of high adsorption capacity MOCs oriented by adsorbability and the development of highly selective adsorption MOCs oriented by separation performance.

Polymers of intrinsic microporosity (PIMs), with an interconnected microporous network, high surface area, and structural diversity, have attracted great interest in developing diverse materials for various applications in the fields of environmental remediation, gas and liquid separation, sensors, and energy. Solution-processable PIMs can be transformed into various robust functional materials, including films, membranes, coatings, and fibers, that can be applied to address different industrial challenges. Since the first PIM synthesis, great strides have been made in expanding the structural diversity of PIMs by designing fine-tuned PIMs for various applications. This review provides a general overview of PIMs, from their synthesis to their involvement in state-of-the-art applications such as water and air filtration, gas and liquid separation, catalysis, sensing, and energy applications, during the last decade. Several PIMs have exhibited outstanding performance in oil adsorption, gas separation, and catalysis. In this context, PIMs’ functionality and porosity are key parameters that must be controlled to tailor PIMs for broader applications. Overall, this review provides a comprehensive overview of PIMs from chemistry to applications and highlights the challenges and prospects of the next generation of PIM-based functional materials that will open new avenues for adsorption, gas separation, and filtration applications.

ABSTRACTCarboxylated carbon nanotubes (C or cCNTs) were incorporated in polyethersulfone hollow fiber membranes (P HFMs) to improve the gas separation performance, i.e., pure gas permeability and ideal gas selectivity. The developed CP HFMs showed the remarkable improvement in thermal stability and mechanical strength as compared to that of the pristine P HFMs. The pure gas permeability of CO2, CH4, O2, and N2 gases for the HFMs were measured at 3 bar feed pressure and room temperature. It was observed that the presence of cCNTs in HFMs significantly improved the CO2 and O2 permeability for CP HFMs by 10.8-and 11.7- fold, respectively, as compared to that measured for P HFMs. Furthermore, the ideal gas selectivity for CO2/CH4, O2/N2, and CO2/N2 gas pairs for CP HFMs was also remarkably enhanced by almost 8.6-, 10.7-and 9.9-times, respectively, as compared to that measured for P HFMs. CP HFMs exhibited gas separation performance better than or comparable to that of the literature-reported CNTs-based membranes. Remarkably, the gas separation performance of CP HFMs crossed Robeson’s 2008 upper bound curve for O2/N2 gas-pair and was almost closer to the upper bound curves drawn by Robeson in 2008 for CO2/CH4 and CO2/N2 gas pairs. The improved separation performance can be attributed to the presence of cCNTs in HFMs. Thus, the results obtained in this study clearly showed that the CP HFMs can potentially be used as a membrane material for the industrially relevant gas separations.

In-situ growth of zeolitic imidazolate framework-67 nanoparticles on polysulfone/graphene oxide hollow fiber membranes enhance CO2/CH4 separation

Blend membranes consisting of two polymer pairs improve gas separation, but compromise mechanical and thermal properties. To address this, incorporating titanium dioxide (TiO2) nanoparticles has been suggested, to enhance interactions between polymer phases. Therefore, the objective of this study was to investigate the impact of TiO2 as a filler on the thermal, surface mechanical, as well as gas separation properties of blend membranes. Blend polymeric membranes consisting of polyetherimide (PEI) and polyvinyl acetate (PVAc) with blend ratios of (99:1) and (98:2) were developed via a wet-phase inversion technique. In the latter, TiO2 was incorporated in ratios of 1 and 2 wt.% while maintaining a blend ratio of (98:2). TGA and DSC analyses were used to examine thermal properties, and nano-indentation tests were carried out to ascertain surface mechanical characteristics. On the other hand, a gas permeation set-up was used to determine gas separation performance. TGA tests showed that blend membranes containing TiO2 had better thermal characteristics. Indentation tests showed that TiO2-containing membranes exhibited greater surface hardness compared to other membranes. The results of gas permeation experiments showed that TiO2-containing membranes had better separation characteristics. PEI-PVAc blend membranes with 2 wt.% TiO2 as filler displayed superior separation performance for both gas pairs (CO2/CH4 and CO2/N2). The compatibility between the rubbery and glassy phases of blend membranes was improved as a result of the inclusion of TiO2, which further benefited their thermal, surface mechanical, and gas separation performances.

A large number of metal organic frameworks (MOFs) synthesized to date have nodes with a Zn metal, and a detailed understanding of their gas separation efficiency upon metal exchange is needed to pave the way for designing the next generation of MOFs. In this work, we implemented a protocol to identify MOFs with Zn nodes out of 10,221 MOFs and classified them into two main groups. Depending on the pore properties and adsorption selectivities, two MOFs from IRMOFs and two MOFs from ZnO-MOFs were selected. The metal atom (Zn) of the selected four MOFs was exchanged with eight different metals (Cd, Co, Cr, Cu, Mn, Ni, Ti, and V), and 32 different metal-exchanged MOFs (M-MOFs) were obtained. By performing grand canonical Monte Carlo simulations, we investigated the influence of the metal type on the CO2/H2 and CO2/CH4 separation performances of these 32 M-MOFs. Physical properties of the MOFs such as the pore size and surface area, and chemical properties such as the partial charges of the atoms in the framework were investigated to understand the effect of metal exchange on the gas adsorption and separation performances of materials. Exchange of Zn with V and Cr led to a remarkable increase in the CO2 uptakes of selected MOFs and these increases were reflected on the adsorption selectivity, working capacity, and the adsorbent performance score of MOFs. The exchange of Zn with V increased the selectivity of one of the MOFs from 119 to 355 and the adsorbent performance score from 70 to 444 mol/kg, while for another MOF, exchange of Zn with Cr increased the selectivity from 161 to 921 and the adsorbent performance score from 162 to 1233 mol/kg under the condition of vacuum swing adsorption. The molecular level insights we provided to explain the improvement in the gas separation performances of M-MOFs will serve as a guide to design materials with exceptional CO2 separation performances.