Novel sulfonated poly(ether ether ketone)/triphenylamine hybrid membrane for vanadium redox flow battery applications

A novel sulfonated poly(ether ether ketone)/triphenylamine hybrid membrane with various triphenylamine loadings (1%, 2% and 5%) has been successfully fabricated. Optimum triphenylamine loading was confirmed by exploring the physicochemical properties and morphology of different membranes. The hybrid membrane exhibited lower vanadium permeability than pristine SPEEK membranes due to the acid–base interaction between amine groups and sulfonated groups. Introduction of triphenylamine also improved the proton conductivity because the nitrogen atom of triphenylamine can be protonated and contribute to the proton transfer. As the result, the hybrid membrane demonstrated higher ion selectivity compared with SPEEK and Nafion115 membranes. The VRFB single cell with SPEEK/TPAM-1% membrane showed better performance compared to a Nafion115 membrane at the current density of 60 mA cm⁻². The SPEEK/TPAM hybrid membrane has great potential for VRFB application.

The novel TPAM hybrid membrane exhibited both lower vanadium permeability and higher proton conductivity than pristine SPEEK membrane.     

The spirobichroman-based polyimides with different side groups: from structure–property relationships to chain packing and gas transport performance

Spirobichroman-based polymers with high gas permeability and selectivity are promising for their applications as membranes in gas separation. In this study, three spirobichroman-based polyimides (PIs; 6FDA-FH, 6FDA-DH, and 6FDA-MH) were synthesised by the polyreaction between diamines containing different substituents (benzene ring, pyridine ring, and methyl group) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The physical properties, gas transport behaviour, d-spacing, dihedral angle of molecules, and fractional free volume of the PIs were investigated through experiments and molecular simulations. The PIs exhibited excellent thermal stability and good solubility in common organic solvents. The gas permeability of the PIs was investigated; the results highlighted the critical role of the substituents in the enhancement of the gas separation performance of polymer membranes. Detailed analysis of the PIs showed that 6FDA-FH exhibits the highest gas permeability. This can be ascribed to the loose packing of the polymer chain owing to the increased dihedral angle between the two planes. However, the methyl substituent in 6FDA-MH disrupts the polymer chain packing rather than changing the dihedral angle between the two planes, thus enhancing the gas permeability of 6FDA-MH. Furthermore, 6FDA-DH exhibited the highest CO₂/CH₄ selectivity, which is attributed to the CO₂ affinity of the polymer containing the pyridine unit.

Effect of substituents on the dihedral angle and chain packing plays a critical role in the enhancement in the gas separation performance of polymer membranes.     

Effects of critical interfacial shear strength between a polymer matrix and carbon nanotubes on the interphase strength and Pukanszky's “B” interphase parameter

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs. A suggested model and a developed Pukanszky model for tensile strength of nanocomposites are combined to develop the equations for “B” and interphase strength. Many experimental data for various samples confirm the models. The impacts of all parameters on the “B” and interphase strength are explained to approve the developed equations. The contour plots display the same trends for the roles of all parameters in the “B” and interphase strength. Low “τ_c”, high “τ”, thin and large CNTs as well as a dense interphase are ideal to obtain the high levels for “B” and interphase strength. Among the studied parameters, CNT size largely controls the “B” and interphase strength, while the waviness and strength of CNTs play insignificant roles.

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs.     

ZIF-95 as a filler for enhanced gas separation performance of polysulfone membrane

Metal–organic frameworks (MOFs) are found to be promising porous crystalline materials for application in gas separation. Considering that mixed matrix membranes usually increase the gas separation performance of a polymer by increasing selectivity, permeability, or both (i.e., perm-selectivity), the zeolitic imidazole framework-95 (ZIF-95) MOF was dispersed for the first time in polysulfone (PSF) polymer to form mixed matrix membranes (MMMs), namely, ZIF-95/PSF. The fabricated ZIF-95/PSF membranes were examined for the separation of various gases. The characterization of solvothermally synthesized ZIF-95 was carried out using different analyses such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), porosity measurements, etc. ZIF-95 was mixed with PSF at 8%, 16%, 24%, and 32% weight percent to form different loading MMMs. SEM analysis of membranes revealed good compatibility/adhesion between the MOF and polymer. The permeability of He, H₂, O₂, CO₂, N₂, and CH₄ were measured for the pure and composite membranes. The ideal selectivity of different gas pairs were calculated and compared with reported mixed matrix membranes. The maximum increases in permeabilities were observed in 32% loaded membrane; nevertheless, these performance/permeability increases were at the expense of a slight decrease of selectivity. In the optimally loaded membrane (i.e., 24 wt% loaded membrane), the permeability of H₂, O₂, and CO₂ increased by 80.2%, 78.0%, and 67.2%, respectively, as compared to the pure membrane. Moreover, the selectivity of H₂/CH₄, O₂/N₂, and H₂/CO₂ gas pairs also increased by 16%, 15%, and 8% in the 24% loaded membrane, respectively.

Metal–organic frameworks (MOFs) are found to be promising porous crystalline materials for application in gas separation.     

Piperazinium-mediated crosslinked polyimide-polydimethylsiloxane (PI-PDMS) copolymer membranes: the effect of PDMS content on CO2 separation

We synthesized copolymers consisting mostly of physically stable rigid polyimide (PI) and a low content of highly permeable rubbery polydimethylsiloxane (PDMS), that were crosslinked by CO₂-philic ionic piperazinium groups attached to the side chains of the copolymers. These crosslinked copolymers (xPI-PDMSs) were fashioned into membranes that showed very high levels of thermochemical stability and excellent CO₂ separation performance (P_CO2 of 799 Barrer and CO₂/N₂ permselectivity of 15.7). The inclusion of the piperazinium groups not only endowed these xPI-PDMS membranes with increased selectivity for CO₂, but also good resistance to CO₂ plasticization. The effect of PDMS content on morphology and CO₂ separation properties of xPI-PDMS was also investigated.

Polyimide-polydimethylsiloxane copolymer membranes crosslinked with piperazinium were prepared for high performance CO₂ separation.     

Synergistic effects of zeolite imidazole framework@graphene oxide composites in humidified mixed matrix membranes on CO2 separation

In this study, composite nanosheets (ZIF-8@GO) were prepared via an in situ growth method and then incorporated into a polyimide (PI) matrix to fabricate mixed matrix membranes (MMMs) for CO₂ separation. The as-prepared MMMs were characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA) and water uptake measurements. Water uptake measurements establish the relationship between the gas permeability and water uptake of membranes and an increase in the water uptake contributes to the CO₂ permeability owing to an increase in the CO₂ transport channels. The MMMs exhibit excellent CO₂ permeability in when compared with an unfilled PI membrane in a humidified state. The ZIF-8@GO filled membranes can separate CO₂ efficiently due to the ZIF-8@GO nanocomposite materials combining the favorable attributes of GO and ZIF-8. First, the high-aspect ratio of the GO nanosheets enhances the diffusivity selectivity. Second, ZIF-8 with a high surface area and microporous structure is beneficial to the improvement of the CO₂ permeability. Third, ZIF-8@GO possesses synergistic effects for efficient CO₂ separation. The MMM with 20 wt% ZIF-8@GO exhibits the optimum gas separation performance with a CO₂ permeability of 238 barrer, CO₂/N₂ selectivity of 65, thus surpassing the 2008 Robeson upper bound line.

In this study, composite nanosheets (ZIF-8@GO) were prepared via an in situ growth method and then incorporated into a polyimide (PI) matrix to fabricate mixed matrix membranes (MMMs) for CO₂ separation.     

Fabrication of a PVDF membrane with tailored morphology and properties via exploring and computing its ternary phase diagram for wastewater treatment and gas separation applications

We report a simple approach for tailoring the morphology of poly(vinylidene fluoride) (PVDF) membranes fabricated using a nonsolvent induced phase separation (NIPS) method that sustains both the hydrophilic and hydrophobic properties. Various membrane structures, i.e. skin layers and whole membrane structures as well, were obtained via an experimental method based on the obtained and computed ternary phase diagram. The nonsolvent interactions with polymer solution resulted in the different forms and properties of a surface layer of fabricated membranes that affected the overall transport of solvent and nonsolvent molecules inside and outside the bulk of the fabricated membranes. The resulting morphology and properties were confirmed using the 3D optical profiler, SEM, FT-IR and XRD methods. The effect of binary interaction parameters on the morphology of the fabricated membranes and on their separation performance was tested using water/oil mixture and gas separation. Both hydrophobic and hydrophilic properties of PVDF showed the excellent durable separation performance of the prepared membranes with 92% of oil separation and the maximum flux of 395 L h⁻¹ m⁻² along with 120 min of long-term stability. CO₂ separation from H₂, N₂, CH₄ and SF₆ gases was performed to further support the effect of tuned PVDF membranes with different micro/nanostructured morphologies. The gas performance demonstrated ultrahigh permeability and a several-fold greater than the Knudsen separation factor. The results demonstrate a facile and inexpensive approach can be successfully applied for the tailoring of the PVDF membranes to predict and design the resulting membrane structure.

We report a simple approach for tailoring the morphology of poly(vinylidene fluoride) (PVDF) membranes fabricated using a nonsolvent induced phase separation (NIPS) method that sustains both the hydrophilic and hydrophobic properties.     

Light-responsive metal–organic framework sheets constructed smart membranes with tunable transport channels for efficient gas separation

Exploring a new type of smart membrane with tunable separation performance is a promising area of research. In this study, new light-responsive metal–organic framework [Co(azpy)] sheets were prepared by a facile microwave method for the first time, and were then incorporated into a polymer matrix to fabricate smart mixed matrix membranes (MMMs) applied for flue gas desulfurization and decarburization. The smart MMMs exhibited significantly elevated SO₂(CO₂)/N₂ selectivity by 184(166)% in comparison with an unfilled polymer membrane. The light-responsive characteristic of the smart MMMs was investigated, and the permeability and selectivity of the Co(azpy) sheets-loaded smart MMMs were able to respond to external light stimuli. In particular, the selectivity of the smart MMM at the Co(azpy) content of 20% for the SO₂/N₂ system could be switched between 341 and 211 in situ irradiated with Vis and UV light, while the SO₂ permeability switched between 58 Barrer and 36 Barrer, respectively. This switching influence was mainly ascribed to the increased SO₂ adsorption capacity in the visible light condition, as verified by adsorption test. The CO₂ permeability and CO₂/N₂ selectivity of MMMs in the humidified state could achieve 248 Barrer and 103.2, surpassing the Robeson''s upper bound reported in 2019.

New light-responsive MOF sheets were synthesized to fabricate a smart membrane, which displays switchable gas separation performance stimulated with UV-Vis light.     

Estimation of the tensile modulus of polymer carbon nanotube nanocomposites containing filler networks and interphase regions by development of the Kolarik model

In this paper, the Kolarik model for the tensile modulus of co-continuous blends based on cross-orthogonal skeleton structures is simplified and developed for polymer/carbon nanotube (CNT) nanocomposites assuming continuous CNT networks in the polymer matrix and the reinforcing and percolating efficiencies of the interphase. For this purpose, the Ouali model for the modulus of nanocomposites above the percolation threshold is linked with the Kolarik model and the interphase percolation is considered with the excluded volume of the nanoparticles. In addition, the simplified Kolarik model is developed with the interphase as a new phase surrounding the nanofiller. A good agreement between the experimental data and the predictions is observed in the samples containing interphases and filler networks, while the developed model cannot estimate the modulus in the absence of interphases and network structures. The developed model demonstrates the effects of all the parameters on the modulus. The interphase parameters more significantly affect the modulus compared to the concentration and modulus of the filler, demonstrating the importance of the interphase properties.

The Kolarik model for the tensile modulus of co-continuous blends is developed for polymer/carbon nanotube (CNT) nanocomposites assuming continuous CNT networks and the reinforcing and percolating efficiencies of the interphase.     

CO2 conversion into methanol under ambient conditions using efficient nanocomposite photocatalyst/solar-energy materials in aqueous medium

A promising route to solve the CO₂ issue is its photocatalytic back-conversion to H-based solar fuels/chemicals, particularly methanol – being widely used as a strategic material in chemical/energy-related industries. Herein, the authors address this globally interesting problem and demonstrate how through an effortless hydrothermal route and using earth-abundant elements, two efficient carbon nanotube (CNT)-based heterojunction photocatalyst/solar-energy materials, viz. CNT/NiO and CNT/NiO/Fe₂O₃ are synthesized and employed for methanol production. The investigations revealed that both binary and ternary composites could selectively (≥93%) produce methanol using CO₂ feed in aqueous medium. Moreover, a higher performance (energy efficiency: 1.81%) was witnessed for the ternary photocatalyst. From a catalytic standpoint, the superior activity of the CNT/NiO/Fe₂O₃ photocatalyst was discussed in detail in terms of its larger surface area, higher absorption of incident light, better charge separation/transfer, and generation of greater photo-voltage/current to effectually split the water medium and achieve the photoconversion process. A mechanistic scheme was finally proposed for the production of methanol and methane, as liquid and gas phase products, respectively.

CNT-based nanocomposite photocatalyst/solar-energy materials serving as in situ hydrogen generators for selective conversion [hydrogenation] of CO₂ into methanol: a mechanistic/photoelectrochemical outlook.     

Predicting the electrical conductivity in polymer carbon nanotube nanocomposites based on the volume fractions and resistances of the nanoparticle,interphase, and tunneling regions in conductive networks

Some limited models have been suggested to determine the conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNTs). However, earlier models (e.g., the Kovacs model) cannot properly consider the roles of the interphase regions or tunneling properties on the percolation threshold and subsequent conductivity of PCNTs. In this paper, the Kovacs model is further developed by assuming that the CNT, interphase, and tunneling regions are separate phases. Also, some simple equations are provided to calculate the percolation threshold as well as the volume fractions and resistances of the CNT, interphase, and tunneling regions in conductive networks. The experimental conductivity results for several samples are compared with the predictions of the developed model. In addition, the calculations of the developed model at different parameter levels are explained and justified. The conductivity calculations show good agreement with the experimental data. Moreover, the developed model reasonably explains the roles of the different parameters on the conductivity. For example, long, thin, and straight CNTs efficiently improve the conductivity because they form large networks in the nanocomposites. Additionally, a thick interphase enlarges the conductive networks, resulting in a desirable conductivity. The conductivity of PCNTs only depends on the tunneling resistance; this is the case because the poor resistance/significant conductivity of the CNT and interphase regions do not influence the conductivity. The developed equations can replace conventional approaches for predicting the conductivity of nanocomposites.

Some limited models have been suggested to determine the conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNTs).     

A windowed carbon nanotube membrane for CO2/CH4 gas mixture penetration separation: insights from theoretical calculation

A new class of species-permselective molecular sieves with functionalized nanowindows has been prepared by modifying the armchair single-walled carbon nanotubes (SWNTs) of a pillared graphene membrane, namely windowed carbon nanotube membrane. The mechanism and characteristics of the windowed carbon nanotube membrane for the selective separation of the CO₂/CH₄ gas mixture are comprehensively and deeply studied. Selective gas separation has a great dependence not only on the interaction of the gas adsorbing on the graphene membrane and inside the CNT channel but also with the energy barrier for the gas diffusing through the nanowindow. In all the functional nanowindows investigated, CH₄ is completely rejected by the N/F-modified nanowindows while maintaining extremely high CO₂ permeability. The CO₂ permeance of the nanowindows is as high as 10⁹ GPU. It emerged that these windowed carbon nanotube membranes are efficient species-selective molecular sieves possessing excellent CO₂/CH₄ selectivity and brilliant CO₂ capture capability.

Final snapshot of the CO₂/CH₄ gas mixture separating through the windowed carbon nanotube membrane.     

3D printed MOF-based mixed matrix thin-film composite membranes

MOF-based mixed-matrix membranes (MMMs) have attracted considerable attention due to their tremendous separation performance and facile processability. In large-scale applications such as CO₂ separation from flue gas, it is necessary to have high gas permeance, which can be achieved using thin membranes. However, there are only a handful of MOF MMMs that are fabricated in the form of thin-film composite (TFC) membranes. We propose herein the fabrication of robust thin-film composite mixed-matrix membranes (TFC MMMs) using a three dimensional (3D) printing technique with a thickness of 2–3 μm. We systematically studied the effect of casting concentration and number of electrospray cycles on membrane thickness and CO₂ separation performance. Using a low concentration of polymer of intrinsic microporosity (PIM-1) or PIM-1/HKUST-1 solution (0.1 wt%) leads to TFC membranes with a thickness of less than 500 nm, but the fabricated membranes showed poor CO₂/N₂ selectivity, which could be attributed to microscopic defects. To avoid these microscale defects, we increased the concentration of the casting solution to 0.5 wt% resulting in TFC MMMs with a thickness of 2–3 μm which showed three times higher CO₂ permeance than the neat PIM-1 membrane. These membranes represent the first examples of 3D printed TFC MMMs using the electrospray printing technique.

An electrospray 3D printing approach for fabricating thin-film composite mixed-matrix membranes (TFC MMM) with a thickness of 2–3 μm.     

Selective CO2 adsorption and bathochromic shift in a phosphocholine-based lipid and conjugated polymer assembly

We assemble a film of a phosphocholine-based lipid and a crystalline conjugated polymer using hydrophobic interactions between the alkyl tails of the lipid and alkyl side chains of the polymer, and demonstrated its selective gas adsorption properties and the polymer''s improved light absorption properties. We show that a strong attractive interaction between the polar lipid heads and CO₂ was responsible for 6 times more CO₂ being adsorbed onto the assembly than N₂, and that with repeated CO₂ adsorption and vacuuming procedures, the assembly structures of the lipid-polymer assembly were irreversibly changed, as demonstrated by in situ grazing-incidence X-ray diffraction during the gas adsorption and desorption. Despite the disruption of the lipid structure caused by adsorbed polar gas molecules on polar head groups, gas adsorption could promote orderly alkyl chain packing by inducing compressive strain, resulting in enhanced electron delocalization of conjugated backbones and bathochromic light absorption. The findings suggest that merging the structures of the crystalline functional polymer and lipid bilayer is a viable option for solar energy-converting systems that use conjugated polymers as a light harvester and the polar heads as CO₂-capturing sites.

Assembly films of a phosphocholine-based lipid and a crystalline conjugated polymer had significant CO₂ selective adsorption and light absorption due to the attractive interaction of CO₂ with exposed polar lipid heads and enhanced morphologies.     

Modeling the effect of interfacial conductivity between polymer matrix and carbon nanotubes on the electrical conductivity of nanocomposites

This article presents the role of interfacial conductivity between the polymer matrix and nanoparticles in the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNT) by simple equations. In this methodology, CNT size, CNT conductivity, CNT waviness and interfacial conductivity express the effective length and effective concentration of CNT in PCNT. Additionally, the percolation threshold and the percentages of CNT in the conductive networks are defined by the above mentioned terms. Finally, a simple model is developed to suggest the electrical conductivity of PCNT by CNT dimensions, CNT conductivity, CNT waviness, interphase thickness, interfacial conductivity and tunneling distance. The developed model is applied to show the roles of all parameters in the conductivity. Also, the experimental levels of percolation threshold and conductivity for several samples are compared to the predictions to validate the developed equations. The interfacial conductivity directly controls the electrical conductivity of nanocomposites. In addition, thick interphase, low waviness and short tunneling distance increase the conductivity. Moreover, the predictions show good agreement with the experimental measurements, providing evidence in support of the developed equations.

This article presents the role of interfacial conductivity between the polymer matrix and nanoparticles in the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNT) by simple equations.     

Superior performance of surface-treated NaX@Pebax-1657 membranes for O2/N2 separation

In this study, the performances of mixed matrix composite membranes (MMCMs) containing surface-treated NaX nanocrystals (ST-NaX-NCs) were experimentally and theoretically investigated for O₂/N₂ separation. For this purpose, the MMCMs were fabricated by the casting solution method and characterized by various analyses. The results reveal that there is a robust interaction between the polymer chains and the ST-NaX-NCs, and that the ST-NaX fillers are uniformly dispersed in the polymer matrix. The incorporation of ST-NaX-NCs alters the PEBAX polymer chain packing arrangement resulting in decreased membrane transport behavior for both O₂ and N₂ gases. The MMCM containing 16.7% wt ST-NaX-NCs has drastically enhanced air separation properties, with a selectivity that is increased to 204% of that of the neat membrane. Moreover, the Lewis–Nielsen model was modified by considering non-ideal effects in mixed matrix membranes, like the clogging of filler pores and polymer chain hardening around the nanocrystals, to predict the gas permeation behavior through the MMCMs. The comparison of the experimental and model results reveals that the modified model can accurately predict the gas permeability and selectivity through the MMCMs.

In this study, the performances of mixed matrix composite membranes (MMCMs) containing surface-treated NaX nanocrystals (ST-NaX-NCs) were experimentally and theoretically investigated for O₂/N₂ separation.     

A study on fabrication of PVDF-HFP/PTFE blend membranes with controllable and bicontinuous structure for highly effective water-in-oil emulsion separation

In this study, poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP)/polytetrafluoroethylene (PTFE) blend membranes for water-in-oil emulsion separation were prepared via a thermally induced phase separation (TIPS) method using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as a mixed diluent. The effects of PTFE content on the obtained membranes'' structure and properties were studied. The results showed that the surface structure of the obtained membranes without addition of PTFE particles was denser and the surface pores got smaller. The porosity, pore size and hydrophobicity obviously increased with the increase in PTFE content. However, the breaking elongation and breaking strength decreased with the increase of PTFE content. When the PTFE content was 10 wt%, the obtained membrane showed the highest separation efficiency for different kinds of water-in-oil emulsions. In addition, the antifouling performance of the obtained membranes was also studied for many times of reuse. This paper introduces an effective and facile method to prepare hydrophobic–oleophilic membranes for water-in-oil emulsion separation.

PVDF-HFP/PTFE blend membranes were prepared for the first time via TIPS method with DBP and DOP as mixed diluent and PTFE as the blending polymer. The obtained membranes could separate different water-in-oil emulsions effectively.     

Introducing hydrophilic ultra-thin ZIF-L into mixed matrix membranes for CO2/CH4 separation

Mixed matrix membranes (MMMs) were developed by mixing hydrophilically modified two-dimensional (2D) imidazole framework (named as hZIF-L) flakes into a Pebax MH 1657 (Pebax) matrix, and designed to separate carbon dioxide/methane (CO₂/CH₄) mixtures. The hZIF-L flakes were important for increasing the effectiveness of the MMMs. First, the tannic acid (TA) etched hZIF-L flakes have a large number of microporous (1.8 nm) and two-dimensional anisotropic transport channels, which offered convenient gas transport channels and improved the permeability of CO₂. Second, the TA molecules provide the surface of the ZIF-L flakes with more hydrophilic functional groups such as carbonyl groups (C O) and hydroxyl groups (–OH), which could effectively prevent non-selective interfacial voids and filler agglomeration in the Pebax matrix, and also presented strong binding ability to water and CO₂ molecules. The satisfactory interface compatibility and affinity with the CO₂ molecule promoted its permeability, solubility, and selectivity. As a result, the MMMs exhibited the highest performance of gas separation with the hZIF-L flake weight content of 5%, at which the CO₂ permeability and CO₂/CH₄ selectivity were 502.44 barrer and 33.82 at 0.2 MPa and 25 °C, respectively.

Schematic diagram of CO₂ transfer in Pebax/hZIF-L mixed matrix membranes.     

Effects of mesoporous silica particle size and pore structure on the performance of polymer-mesoporous silica mixed matrix membranes

The fabrication of mixed matrix membranes (MMMs) has been regarded as an effective and economic approach to enhance the gas permeability and selectivity properties of conventional polymeric membranes for gas separation applications. However, the poor compatibility between polymeric matrix and inorganic filler in MMMs could lead to the generation of interfacial defects resulting in reduced gas selectivity. In this work, with the aim of studying the effect of particle size and pore structure of the filler on the performance of the resultant MMMs, nano/micro sized spherical mesoporous silicas with 2D/3D pore structure (MCM-41 and MCM-48) were synthesized and selected as fillers for the preparation of polydimethylsiloxane (PDMS)-based MMMs. The separation properties of the membranes prepared were characterized by permeability measurements for nitrogen and organic vapors (C₃H₆ and n-C₄H₁₀). Compared with microsized particles, nanosized fillers have better dispersion in the polymer matrix which could minimize the formation of non-selective microvoids around the particles, leading to higher vapor/N₂ ideal selectivities of the MMMs, even at the high loading (15 wt%). Moreover, due to the conventional random packing orientation of the particles in the polymer, vapor permeation was severely hindered in the MMMs fabricated from mesoporous silica with 2D pore channels. The interface morphologies and gas diffusion paths in the MMMs have also been proposed. With an optimum loading of nanosized MCM-48 (3D pore structure), the vapor permeabilities and vapor/N₂ ideal selectivities of the MMMs were shown to increase simultaneously, compared with the neat polymer membrane.

The effects of filler particle size and pore structure on the gas separation performance of mixed matrix membranes were comprehensively investigated via elaborate synthesis of mesoporous silicas.     

Synthesis and characterization of new polyimides from diphenylpyrene dianhydride and ortho methyl substituted diamines

Three new polyimides were synthesized via one-step polycondensation from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF). The effect of diamine structure in DPPD based polyimides'' physical, thermal, mechanical and gas transport properties has been studied. The polyimide structure was confirmed by FTIR and ¹H NMR. All polymers show high thermal stability with decomposition temperatures above 493 °C, and glass transition temperatures above 336 °C. Changes in packing density of polyimide membranes were assessed by wide angle X-ray diffraction and correlated to fractional free volume FFV. Polyimides based on rigid DPPD dianhydride exhibited an improved gas permeability and selectivity when ortho methyl substituents are present in the diamine used for polyimide synthesis. DPPD-MBDAM polyimide showed the best gas productivity values with 565 barrer CO₂ permeability and a selectivity of 16 for CO₂/CH₄.

Three new polyimides were synthesized from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF).