Organic Solvent Nanofiltration Research Articles

Fabrication of Coffee-ring Nanostructured Membranes for Organic Solvent Nanofiltration.

Organic solvent nanofiltration (OSN) plays important roles in pharmaceutical ingredients purification and solvent recovery. However, the low organic solvent permeance under cross-flow operation of OSN membrane hampers their industrial applications. Herein, we report the construction of coffee-ring structured membrane featuring high OSN permeance. A water-insoluble crystal monomer that dissolved in EtOH/H2O mixed solvent was designed to react with trimesoyl chloride via interfacial polymerization. Owing to the diffusion of EtOH to n-hexane, coffee-ring nanostructure on the support membrane appeared, which served as the template for construction of coffee-ring structured membrane. The optimal nanostructured membrane demonstrated 2.6-fold enhancement in the effective surface area with reduced membrane thickness. Resultantly, the membrane afforded a 2.7-fold enhancement in organic solvent permeance, e.g., ~ 13 LMH/bar for MeOH, without sacrificing the rejection ability. Moreover, due to the rigid monomer structure, the fabricated membrane shows distinctive running stability in active pharmaceutical ingredients purification and the ability for concentration of medicines.

New strategy for structure rearrangement of thin-film composite (TFC) polyamide (PA) membranes and offering potential use in both aqueous and organic solvents

The purity of sodium hexafluorophosphate (NaPF6) is crucial for the preparation of electrolytes in manufacturing. We propose a simple process in order to induce membrane structure rearrangement process (SRP) by activating thin-film composite (TFC) membranes with polyamide (PA) structure and explore their potential green recycling application in concentrating sodium-ion batteries (SIBs) electrolyte. The method utilizes a solution containing polar aprotic solvent as the soaking and activating solution to swell and disintegrate the loosely cross-linked PA layer, and a non-solvent solidification solution complete the SRP, enhancing the permeability of the PA layer while maintaining high rejection rates for divalent ions. Subsequently, during the further treatment of the membrane surface in structure rearrangement, tert-butanol (TBA) is introduced into the aqueous solution to reconstruct the surface PA layer, further improving the permeability. The optimal D8010T10 achieved a permeation flux of 24.2 L m−2 h−1·bar−1, with rejection rates for sodium sulfate (Na2SO4), magnesium chloride (MgCl2), and magnesium sulfate (MgSO4) reaching 94.7 %, 98.4 %, and 99.1 % respectively. And the mechanism of SRP with different solvent is analyzed and explained through dissipative particle dynamics (DPD) simulations. This study provides a commercially viable approach for manufacturing high-performance membranes. The D8010T10 membrane achieves more than 90 % separation efficiency for sodium hexafluorophosphate (NaPF6) dissolved in different solvents, providing a potential solution for the concentration and recovery of NaPF6 in lab-scale, verified its potential use in the organic solvent nanofiltration (OSN) and a path way for waste membrane recycling and degrading use in the industry.

Ultramicroporous cardo-pendant polyamide nanofilms for enhanced organic solvent nanofiltration

Permeable, selective, and stable polymeric membranes are essential for efficient molecular separation in organic solvents. Polymers of intrinsic microporosity (PIMs) with rigid and twisted chain structures offer abundant pores for high solvent permeability and are emerging as an ideal membrane material. However, guaranteeing high separation selectivity and stability is challenging owing to the wide pore size distribution and low swelling resistance in organic solvents. In this work, we developed intrinsically ultramicroporous polyamides (PAs) with cardo-pendant groups to create crosslinking, ultrathin, and defect-free nanofilms for organic solvent nanofiltration. The molecular simulation confirmed the pivotal role of cardo-pendant group structures in the amine monomers and exhibited their effect in creating pore channel structures within the PAs. Distinctive rigid fluorenyl-based cardo-pendant groups were introduced in amine monomers to finely tailor the packing of PA chains for high ultramicroporosity and a finely tuned pore size. We further achieved the growth of such PAs using a cyclic deposition strategy, in-situ generating highly crosslinking nanofilms with an ultralow thickness of 23–36 nm without structure relaxation. As such, the typically-designed PA membranes demonstrated high and stable solvent permeance (e.g., 18 L m−2 h−1 bar−1 for methanol) and high solute rejection (up to 95 % rejection of 306 Da Azure I), which is superior to its counterparts and current PIM membranes, presenting a new perspective for efficient organic solvent nanofiltration.

Combined effect of polyelectrolyte assisted interfacial polymerization and tannic acid protective surface modification to boost organic solvent nanofiltration performance

Organic solvent nanofiltration (OSN) is an effective technology for separating solute with molecular weight of 200–1000 Da (Da) from organic solvents. However, as the core of this technology, most of OSN membranes exhibit a low solvent permeance. Herein, a highly permeable OSN membrane was prepared via a poly (sodium 4-styrenesulfonate) (PSSNa)-assisted interfacial polymerization reaction using ultra-low content of aqueous monomer solution, followed by a protective modification using tannic acid (TA) grafting onto the nascent polyamide surface, and a post chemical crosslinking treatment as well as an activation treatment. PSSNa manipulates the diffusion and distribution of the m-Phenylenediamine monomers, leading to a looser and thinner polyamide layer. TA molecules successfully reacted with the remaining acyl chloride groups on the nascent polyamide layer surface and formed ester, thus preventing the surface from subsequent crosslinking reaction and also making the selective layer looser, which is beneficial for solvent permeation. Moreover, the TA modification makes the surface more hydrophilic, thus further helps to improve the solvent permeance of OSN membrane. The optimal membrane possesses an excellent ethanol permeance of 71.5 L m−2 h−1 MPa−1, an increment of 41.6 % as compared with the baseline OSN membrane, while keeping a rejection of 98.2 % for rhodamine B (RDB). Meanwhile, the surface of optimal membrane is ultra-smooth, with an average roughness of 4.4 nm, which is much beneficial for antifouling. Moreover, the OSN membrane possesses a brilliant durability performance, with only a 1.5 % decrease of the RDB rejection after being immersed in N, N-Dimethylformamide (DMF) at room temperature for 115 d, and only a further 0.3 % decrease of the RDB rejection after being further immersed in DMF at 80 °C for another 11 d, indicating its superior solvent resistance, which makes it a promising candidate for treating organic solutions from pharmaceutical and textile industries.

Covalent organic framework membranes modified by end-capping monomers for organic solvent nanofiltration

Covalent organic frameworks (COFs) with excellent solvent stability, high porosity, and well-designed pore size, are competitive candidates for organic solvent nanofiltration (OSN). To manipulate their structures, pre-synthetic and post-synthetic modifications are commonly used. Nevertheless, pre-synthetic modifications may alter the stacking fashion of COF nanosheets; post-synthetic modifications are constrained by limited pre-functionalities and can hardly achieve complete conversion. In contrast, defect engineering is a facile method to modify the structure of COFs through defects generated by the breakage of linkages or the usage of end-capping molecules. In this study, we adopted defect engineering to improve the OSN performance of TpPa-COF membranes constructed of 2,4,6-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa) monomers with end-capping molecules—aniline (An). The membrane synthesized with 30 percent of An molecules (TpPaAn-30/HPAN membrane) maintained a continuous COF layer with a thickness of ∼20 nm but lower density or more free channels, compared to the control membrane. The optimized TpPaAn-30/HPAN membrane had improved permeance for various organic solvents (e.g., 31.8 L m−2 h−1 bar−1 for methanol, fourfold of the control membrane) but maintained rejection towards methyl blue (>90 %). It also allowed the passage of rhodamine B but blocked methyl blue when filtrating a mixed-dye methanolic solution. Herein, the usage of end-capping monomers is proven to be an efficient method to introduce transport channels and improve the separation performance of COF membranes.

Polyamide thin-film composite membranes with enhanced interfacial stability for durable organic solvent nanofiltration

Polyamide thin-film composite (TFC) membranes present a promising option for organic solvent nanofiltration (OSN) due to their superior advantages in facile fabrication and high separation efficiency. However, existing TFC-based OSN membranes are heavily limited by their weak interfacial stability in organic solvents, because many solvent-resistant porous supports are hydrophobic and have poor interfacial compatibility to polyamide. Herein, we report a polyamide TFC membrane with enhanced interfacial stability and durable OSN performance, by multifunctional surface modification and in-situ interfacial polymerization on a hydrophobic and solvent-resistant polypropylene substrate. Distinct from nascent ones, the polypropylene substrates modified by tannic acid/aminopropyltriethoxysilane coating possess excellent hydrophilicity and more functional groups, in which the former allows for the in-situ synthesis of integral polyamide layers via interfacial polymerization and the latter greatly enhances the binding strength between the polyamide layer and PP substrate by 30 times. With this method, the TFC membranes exhibit excellent thermal stability in 80 °C dimethylformamide solution. Meanwhile, the TFC membranes display high ethanol permeance (9.2 L m−2 h−1 bar−1) and acid fuchsin rejection (98.5 %), outperforming the performance of most OSN membranes reported. This straightforward method, robust structural stability, and extraordinary performance make the TFC membranes a step closer to commercial OSN membranes.

In-situ construction of covalent organic frameworks membrane via interfacial polymerization and crosslinking modification using trimesoyl chloride for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a modern technology for separating and purifying organic solvents. It has the advantages of both low energy consumption and low environmental pollution. In this work, we utilized an oligomer triggered interfacial polymerization (OT-IP) method and followed by a post-IP modification using trimesoyl chloride (TMC) to synthesize a kind of covalent organic frameworks (COFs)/TMC membrane. This process involves pre-mixing both COFs monomers in a same organic solvent to form oligomers, followed by conducting an IP reaction at the interface between the organic solvent phase and an aqueous phase solution containing acetic acid as a catalyst. Subsequently, a surface modification is conducted using TMC n-hexane solution, which effectively manipulates the surface hydrophilicity, average size, solute rejection, solvent permeance and solvent resistance of the membrane. Afterward, crosslinking and solvent activation are performed to improve its solvent resistance and separation permeance. The optimized OSN membrane exhibits an ethanol permeance of 72.5 L m−2h−1 MPa−1 with an RDB rejection of 98.4 %. Its surface roughness is as low as 3.4 nm. Furthermore, it has high permeance for both polar solvents (MeOH permeance of 176.7 L m−2h−1 MPa−1) and weakly polar solvents (EtOAc permeance of 183.0 L m−2h−1 MPa−1). Moreover, the optimized OSN membrane demonstrates excellent solvent resistance and excellent catalyst recovery performance. Therefore, this work presents a promising avenue for the application of COFs in OSN membranes.

Ca2+, Fe3+ co-crosslinked tannic acid-bridged sodium alginate gel membrane for organic solvent nanofiltration

It is necessary to prepare a nanofiltration membrane with high permeation flux that can be used in the field of organic solvents. Gel membranes have a high solvent permeation flux, but their chained macromolecular structure is often unstable. In this study, tannic acid-bridged sodium alginate (TAx-Ca/FeSA) organic solvent nanofiltration (OSN) membranes were prepared by the phase transition method using aqueous Ca2+ and Fe3+ solutions as cross-linking agents. TA can interact with SA through hydrogen bonding hydrophobic bonding and other interactions to form an interpenetrating three-dimensional network structure. Compared with Ca/FeSA membrane, the average pore size of TA0.125-Ca/FeSA membrane was reduced from 1.03 nm to 0.74 nm, and the porosity was increased from 47.62 to 59.2 %. In addition, the TA0.125-Ca/FeSA membrane has the characteristics of a negative charge, super hydrophilicity, and high mechanical properties, exhibits a high permeation flux of 48.97 L·m−2·h−1·bar−1 with a rejection of 96.25 % for Congo red ethanol solution, has excellent solvent resistance, stain resistance, and self-cleaning ability. The TA0.125-Ca/FeSA membrane was demonstrated to have great potential for application in the fields of purification and solvent recovery.

Tunable 2D Conjugated Porous Organic Polymer Films for Precise Molecular Nanofiltration and Optoelectronics.

Structural design of 2D conjugated porous organic polymer films (2D CPOPs), by tuning linkage chemistries and pore sizes, provides great adaptability for various applications, including membrane separation. Here, four free-standing 2D CPOP films of imine- or hydrazone-linked polymers (ILP/HLP) in combination with benzene (B-ILP/HLP) and triphenylbenzene (TPB-ILP/HLP) aromatic cores are synthesized. The anisotropic disordered films, composed of polymeric layered structures, can be exfoliated into ultrathin 2D-nanosheets with layer-dependent electrical properties. The bulk CPOP films exhibit structure-dependent optical properties, triboelectric nanogenerator output, and robust mechanical properties, rivaling previously reported 2D polymers and porous materials. The exfoliation energies of the 2D CPOPs and their mechanical behavior at the molecular level are investigated using density function theory (DFT) and molecular dynamics (MD) simulations, respectively. Exploiting the structural tunability, the comparative organic solvent nanofiltration (OSN) performance of six membranes having different pore sizes and linkages to yield valuable trends in molecular weight selectivity is investigated. Interestingly, the OSN performances follow the predicted transport modeling values based on theoretical pore size calculations, signifying the existence of permanent porosity in these materials. The membranes exhibit excellent stability in organic solvents at high pressures devoid of any structural deformations, revealing their potential in practical OSN applications.

Scalable, Interfacially Synthesized, Covalent-Organic Framework (COF)-Based Thin-Film Composite (TFC) Hollow Fiber Membranes for Organic Solvent Nanofiltration (OSN).

Covalent organic frameworks have great potential for energy-efficient molecular sieving-based separation. However, it remains challenging to implement COFs as an alternative membrane material due to the lack of a scalable and cost-effective fabrication mechanism. This work depicts a new method for fabricating a scalable in situ COF hollow fiber (HF) membrane by an interfacial polymerization (IP) approach at room temperature. The 2D COF film was constructed on a polyacrylonitrile HF substrate using aldehyde (1,3,5-trimethylphloroglucinol, Tp) and amine (4,4'-azodianiline (Azo) and 4,4',4″-(1,3,5-triazine- 2,4,6-triyl) trianiline (Tta)) as precursors. The COF membrane on the PAN substrate showed 99% rejection of Direct red-80 with remarkable solvent permeance. The rejection analysis revealed that the structural aspects of the solute molecule play a major role in rejection rather than the molecular weight. We further optimized the precursor concentrations to improve the permeation performance of the resulting membrane. The durability study reveals excellent stability of the membrane toward organic solvents. This study also demonstrated the easy scalability of the membrane fabrication approach. The approach was further extrapolated to fabricate a cation-based COF membrane. These charged membranes exhibited an enhanced rejection performance. Finally, this approach can facilitate industrially challenging molecular sieving applications using COF-based membranes.

Integrated membrane process for pretreating and desolventizing hexane-soybean oil miscella – A pilot plant study

The study aimed to develop a membrane desolventizing technology for solvent recovery in vegetable oil extraction. Pretreatment of crude miscella is a prerequisite for an organic solvent nanofiltration (OSN) based desolventizing process. Solvent-resistant ultrafiltration (SRUF) membrane employed in micelle-enhanced ultrafiltration (MEUF) of hexane-crude soybean oil miscella displayed high phospholipids (PL) rejection (98.5%) and productivity (∼28 L/m2/h), accompanied with a moderate oil rejection (∼22%). The PL-rich retentate fraction was alkali-treated to recover the oil in the stream (8.8%). This complementary pretreatment approach met the quality requirements and maximized the yield of treated oil (>98%) while reducing the chemicals in the process. A subsequent two-stage desolventizing of MEUF-treated miscella with solvent-resistant nanofiltration (SRNF) membrane reduced the oil-in-permeate to 1.37%, achieving the set recycling criteria (<2%). The results obtained from the pilot scale study (batch size 40 kg of crude miscella) revealed that the MEUF met the pretreatment requirements, and the subsequent OSN process recovered ∼63% of hexane through a non-thermal route for recycling in the extraction process. The pilot-scale evaluation demonstrated the technical feasibility of the proposed membrane desolventizing process employing indigenous spiral-wound SRUF and SRNF membrane modules.

Liquid- liquid (Cyclohexanone: Cyclohexanol) separation using augmented tight nanofiltration membrane: A sustainable approach

Organic solvent nanofiltration (OSN) is an incipient technology in the field of organic liquid-liquid separation. The incomplete separations and complexity involved in these, forces many organic liquids to be released as effluents and the adverse effects of these on environment is enormous and irreparable. The work prominences on the complete separation of industrially significant cyclohexanone: cyclohexanol (keto-alcohol oil) and heptane: toluene mixtures. The separations of these above-mentioned organic liquid mixtures were carried out using the fabricated Lewis acid modified graphitic carbon nitride (Cu2O@g-C3N4) incorporated polyvinylidene difluoride (PVDF) composite membranes. These fabricated membranes showed a separation factor of 18.16 and flux of 1.62 Lm−2h−1 for cyclohexanone: cyclohexanol mixture and separation of heptane and toluene mixture (with heptane flux of 1.52 Lm−2h−1) showed a separation factor of 9.9. The selectivity and productivity are based on the polarity and size of the organic liquids. The role of Cu2O@g-C3N4 is influencing the pore size distribution, increased divergence from solubility parameters, polarity, solvent uptake and porosity of the composite membranes. The developed composite membranes are thus envisioned to be apt for a wide range of liquid-liquid separations due to its implicit nature.

Investigating the impact of metal ion variations in terephthalate metal–organic frameworks on the organic solvent nanofiltration performance of mixed matrix membranes

Nano-fillers integrated into mixed matrix membranes (MMMs) present promising alternatives for organic solvent nanofiltration (OSN). In this work, our objective is to enhance OSN performance by incorporating terephthalate metal-organic frameworks (M-BDC, where M = Zr or Cu) into a P84 matrix to fabricate M-BDC/P84 composite MMMs. This work focuses on the influence of metal cluster variation on particle size, pore size distribution, and specific surface area of M-BDC, while systematically investigating the impact of M-BDC addition on OSN performance and underlying separation mechanisms. The synthesized membranes underwent comprehensive characterization using SEM, XRD, ATR-FTIR, contact angle, zeta potential, and thermogravimetric analysis. Significantly, all MMMs exhibited superior permeance and methyl blue (MB) rejection compared to P84 membranes. This enhancement is attributed to the improved interfacial contact between M-BDC and P84, as well as their effective dispersion within the membrane matrix. Interestingly, comparative analysis between Cu-BDC/P84 and Zr-BDC/P84 MMMs revealed the latter's superior permeance, attributed to its larger pore size and surface area. The resulting MMMs demonstrated outstanding MB rejection (>96.7%) with ethanol permeance of 21.5 and 19.0 LMH/Bar for Zr-BDC/P84 and Cu-BDC/P84 MMMs, respectively. Furthermore, the stable performance of M-BDC-based MMMs during prolonged MB/ethanol operation underscores their potential significance in the field of OSN, providing valuable insights for future membrane design and application.

Organic Solvent Nanofiltration in Pharmaceutical Applications.

Separation and purification in organic solvents are indispensable procedures in pharmaceutical manufacturing. However, they still heavily rely on the conventional separation technologies of distillation and chromatography, resulting in high energy and massive solvent consumption. As an alternative, organic solvent nanofiltration (OSN) offers the benefits of low energy consumption, low solid waste generation, and easy scale-up and incorporation into continuous processes. Thus, there is a growing interest in employing membrane technology in the pharmaceutical area to improve process sustainability and energy efficiency. This Review comprehensively summarizes the recent progress (especially the last 10 years) of organic solvent nanofiltration and its applications in the pharmaceutical industry, including the concentration and purification of active pharmaceutical ingredients, homogeneous catalyst recovery, solvent exchange and recovery, and OSN-assisted peptide/oligonucleotide synthesis. Furthermore, the challenges and future perspectives of membrane technology in pharmaceutical applications are discussed in detail.

Hollow Fiber Membrane Modification by Interfacial Polymerization for Organic Solvent Nanofiltration

Hollow Fiber Membrane Modification by Interfacial Polymerization for Organic Solvent Nanofiltration

Lamellar structured GO-Melamine nanocomposite membranes with varying d-spacing for efficient organic solvent nanofiltration (OSN)

There is a lot of research being done on GO lamellar 2D membranes for separating organic solvents and dyes. These membranes are highly sought-after due to their exceptional characteristics. However, existing challenges include inadequate solvent permeability and limited dye rejection capacity due to swelling of membranes. In this study, we proposed a novel technique that employs low-pressure assisted filtration to fabricate nanocomposite membranes using GO and melamine. Remarkably, these composite membranes exhibited outstanding separation performance for dyes (≥99.06 %) in organic solvents, regardless of their positive or negative charges or when present in mixtures. The optimum GO-M0.02 nanocomposite membrane exhibits impressive organic solvent flux (J), attaining a value as high as 50.8 L/m2h (acetone), which is 6.57 times greater than that of the pure GO membrane. Furthermore, these GO-Melamine nanocomposite membranes showed excellent durability against both common and harsh organic solvents, and the flux of solvents through the GO-M0.02 nanocomposite membrane remained almost unchanged even after being immersed in methanol for up to one week. Additionally, the membrane exhibited consistent solvent flux and rejection rates for methyl green during continuous filtration. These results highlight the exceptional stability and immense potential of GO-melamine nanocomposite membranes for real organic solvent nanofiltration.

Preparation of highly efficient nanofiltration membranes resistant to organic solvents by adjusting zinc oxide nanoparticle-loaded attapulgite

Zinc oxide nanoparticle-loaded attapulgite was successfully added to the polyamide layer for the preparation of high-efficiency organic solvent nanofiltration membranes. The addition of zinc oxide nanoparticle-loaded attapulgite to the aqueous monomer regulates the diffusion rate of interfacial polymerization, generating a thin and loosely packed polyamide layer. In addition, the abundant hydrophilicity of the nanoparticles lays the foundation for increased polar solvent permeation. The organic solvent nanofiltration membrane with the best performance exhibited an optimum methanol permeability of 13.19 L m−2h−1 bar−1, which was 1.54 times higher than that of the unadded membrane. Meanwhile, the optimum membrane consistently rejected more than 99.40 % of Evans blue dye, and the rejection rates of different dyes were consistent with the size-sieving effect. Furthermore, the permeation capacities of the membranes were evaluated using organic solvents with different polarities, viscosities, and molecular diameters, and the permeability of acetonitrile reached 16.98 L m−2h−1 bar−1. In addition, the optimum membranes retained excellent rejection capacity after soaking in the strongly polar solvent N, N-dimethylformamide (DMF) for 10 days at room temperature.

Construction of ultrathin and microporous polyesteramide nanofilms for efficient organic solvent nanofiltration (OSN) using diacyl chloride

The integration of high permeability and exceptional selectivity, thereby overcoming the conventional “trade-off” effect, remains a persistent challenge for the practical implementation of organic solvent nanofiltration (OSN) membranes. Herein, at the molecular level of design, we utilized the 5,5′-diamino-2,2′-biphenol (amino-BIPOL) and diacyl chloride as IP monomers to prepare OSN membranes with high perm-selectivity. The amino-BIPOL, a contorted biphenol molecule with four reactive sites, serves as a molecular-level unit to hinder efficient packing of polymer chains and induce the formation of interconnected micropores in the resulting polyesteramide layers. By employing diacyl chloride terephthaloyl dichloride (TPC) and isophthaloyl dichloride (IPC) as the oil-phase cross-linker, two kinds of TFC membranes were prepared. The resulting membranes both present smooth surface morphology, with ultrathin and high microporous selective layer allowing for efficient mass transfer. Specifically, the methanol permeance of amino-BIPOL/TPC and amino-BIPOL/IPC membrane reaches up to 15.1 and 15.6 LMH/bar, while maintaining a molecular weight cut-off (MWCO) value of 300 and 373 Da, respectively. Overall, this work illustrates the different oil-phase cross-linkers will result in diverse nanofilm microstructure and thus with distinct perm-selectivity properties, offering new insights for the design and modification of advanced OSN membranes.

Theory of expansion and compression of polymeric materials: Implications for membrane solvent flow under compaction

We extend the classical Flory-Rehner theory for the expansion and compression of porous materials such as cross-linked polymer networks and membranes. The theory includes volume exclusion, affinity with the solvent, and finite stretching of the polymer chains. We also modify this equilibrium theory, which applies to equal expansion of a material in all directions, to the situation where a material can only expand in a single direction, as is the case when a thin polymer layer is tightly bound to a support structure. We further extend this equilibrium model to the case where a pressure is applied across a thin polymer layer, such as a membrane, and liquid flows across the membrane. The theory describes how in the direction of liquid flow the membrane is increasingly compacted and becomes less porous, and this effect increases when the applied pressure goes up. We present results of example calculations for a thick membrane showing significant changes in compaction across its thickness, and a thin membrane where compaction due to flow is minor. Lastly, we model the dynamics of the change in size of a porous material in time after a step change in the solvent-polymer attraction parameter, which may be relevant, for instance, when the attraction parameter is highly temperature-dependent, and we change the temperature. The developed theory has direct implications for pressure-driven membrane separation processes ranging from reverse osmosis to organic solvent nanofiltration.

Simulation insights into the spirobifluorene aryl diamine (SBAD-1)/porous organic cage mixed-matrix membranes for organic solvent nanofiltration

Mixed-matrix membranes (MMMs) have emerged as promising materials for organic solvent nanofiltration (OSN) applications due to their potential to synergize polymer and porous nanomaterials. Theoretically understanding the role of nanofillers within MMMs in determining the OSN performance is crucial for the development of new MMMs. In this work, the molecular simulations are performed to investigate the swelling process and OSN performance of the spirobifluorene aryl diamine (SBAD-1)/porous organic cage (POC) MMMs. Three POCs (i.e., CC3, CC5, and CC17) and three organic solvents (i.e., methanol, acetonitrile, and acetone) are studied. The pure SBAD-1 and pure POC membranes are also constructed for comparison. Results show that the attractive interactions between SBAD-1 and POC can restrict the flexibility of polymer chains, and thereby decrease the dilation of polymer matrix and also the porosity of swollen MMM. Based on this, the solvent resistant property and dye rejection would be well enhanced. Moreover, compared with pure SBAD-1 and pure POC membranes, the solvent permeabilities through swollen MMMs are found to drop due to the blockage of POC pores by SBAD-1 chains and the smaller porosity in membrane. This work reveals the pivotal role of interaction between SBAD-1 and POC in the swelling and OSN performance of SBAD-1/POC MMMs, and would provide theoretical support for the development of MMMs for OSN applications.