Solvent Flux Research Articles

How Irregular Geometry and Flow Waveform Affect Pulsating Arterial Mass Transfer.

Alzheimer's disease is a progressive degenerative condition that has various levels of effect on one's memory. It is thought to be caused by a buildup of protein in small fluid-filled spaces in the brain called perivascular spaces (PVS). The PVS often takes on the form of an annular region around arteries and is used as a protein-clearing system for the brain. To analyze the modes of mass transfer in the PVS, a digitized scan of a mouse brain PVS segment was meshed and used for computational fluid dynamics (CFD) studies. Tandem analyses were then carried out and compared between the mouse PVS section and a cylinder with commensurate dimensionless parameters and hydraulic resistance. The geometry pair was used to first validate the CFD model and then assess mass transfer in various advection states: no-flow, constant flow, sinusoidal flow, sinusoidal flow with zero net solvent flux, and an anatomically correct asymmetrical periodic flow. Two mass transfer situations were considered, one being a protein build-up and the other being a protein blend-down using a multitude of metrics. Bulk arterial solute transport was found to be advection-controlled. The consideration of temporal evolution and trajectories of contiguous protein bolus volumes revealed that flow pulsation was beneficial at bolus break-up and that additional local wall curvature-based geometry irregularities also were. Using certain measures, local solute peak concentration blend-down appeared to be diffusion-dominated even for high Peclet numbers; however, bolus size evolution analyses showed definite advection support.

Convective Instability Driven by Diffusiophoresis of Colloids in Binary Liquid Mixtures.

In a binary fluid mixture, the concentration gradient of a heavier molecular solute leads to a diffusive flux of solvent and solute to achieve thermodynamic equilibrium. If the solute concentration decreases with height, the system is always in a condition of stable mechanical equilibrium against gravity. We show experimentally that this mechanical equilibrium becomes unstable in case colloidal particles are dispersed uniformly within the mixture and that the resulting colloidal suspension undergoes a transient convective instability with the onset of convection patterns. By means of a numerical analysis, we clarify the microscopic mechanism from which the observed destabilization process originates. The solute concentration gradient drives an upward diffusiophoretic migration of colloids, in turn causing the development of a mechanically unstable layer within the sample, where the density of the suspension increases with height. Convective motions arise to minimize this localized rise in gravitational potential energy.

Molecular simulations of organic solvent transport in dense polymer membranes: Solution-diffusion or pore-flow mechanism?

We employed non-equilibrium molecular dynamics simulations and theoretical predictions to elucidate organic solvent and water transport mechanisms in dense polymer membranes. Our study investigated the transport of water and 14 organic solvents across 16 dense polymer membranes with varying fractional free volumes. Simulations demonstrated that the dependence of organic solvent or water flux on applied pressure exhibited minimal deviation from linearity, contrary to the prediction of a “ceiling flux” at high pressures, based on the solution-diffusion model. Notably, our findings underscore the paramount influence of solvent size and membrane pore size on solvent permeance, significantly diverging from the solvent solubility-based predictions of the solution-diffusion model. Overall, our results agree with the solution-friction model for characterizing water and organic solvent transport in dense polymer membranes such as reverse osmosis and organic solvent nanofiltration. These fundamental insights into the transport mechanisms of water and organic solvents offer molecular-level guidance for designing next-generation high-performance polymer membranes for various separation applications.

Accurate prediction of solvent flux in sub-1-nm slit-pore nanosheet membranes.

Nanosheet-based membranes have shown enormous potential for energy-efficient molecular transport and separation applications, but designing these membranes for specific separations remains a great challenge due to the lack of good understanding of fluid transport mechanisms in complex nanochannels. We synthesized reduced MXene/graphene hetero-channel membranes with sub-1-nm pores for experimental measurements and theoretical modeling of their structures and fluid transport rates. Our experiments showed that upon complete rejection of salt and organic dyes, these membranes with subnanometer channels exhibit remarkably high solvent fluxes, and their solvent transport behavior is very different from their homo-structured counterparts. We proposed a subcontinuum flow model that enables accurate prediction of solvent flux in sub-1-nm slit-pore membranes by building a direct relationship between the solvent molecule-channel wall interaction and flux from the confined physical properties of a liquid and the structural parameters of the membranes. This work provides a basis for the rational design of nanosheet-based membranes for advanced separation and emerging nanofluidics.

COF-anchored design of nanoporous graphene membranes for ultrafast and selective organic separation

Nanoporous graphene has attracted extensive attention as a type of disruptive membrane materials for organic separation. However, the fabrication of an ideal graphene membrane with high permeability and selectivity remains challenging due to the inevitable non-selective defects. Here, a strategy based on synergetic effect of graphene membranes and covalent organic framework (COF) nanounits is developed. Atomically thin nanoporous graphene provides high solvent flux and stability. To prevent the leakage from inevitable non-selective pores in graphene without sacrificing flux, porous COF nanounits are directly anchored at the defective sites. The fabricated membranes exhibit record-high solvent flux of 49.81 L m−2 h−1 (1–2 orders of magnitude higher than that of state-of-the-art membranes), and relatively low reverse solute flux of 1.69 g m−2 h−1 in organic solvent forward osmosis (OSFO) process. The strategy we proposed gives dramatic impetus to the development of OSFO and other membrane separation processes.

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.

Solvent-resistant crosslinked polybenzimidazole membrane for use in enhanced molecular separation

In molecular separation using membranes, enhanced parameters, such as an increased flux and selectivity, are required for efficiency. Additionally, in molecular separation using solvents, solvent resistance is critical in preventing solvent-induced damage. However, most membranes lack resistances to specific harsh solvents, and simultaneously enhancing solvent flux and selectivity performance, which exhibit a trade-off relationship, is challenging. In this study, a high-performance solvent-resistant polybenzimidazole (PBI) membrane is fabricated via chemical crosslinking with divinyl sulfone (DVS). The membrane consists of porous finger-like support and dense skin layers, and the uniform DVS crosslinking of the PBI membrane is confirmed via chemical analysis. The DVS-crosslinked PBI membrane exhibits a superior solvent stability and separation performance, with an ethanol permeance and molecular weight cut-off of 5.88 L m−2 h−1 bar−1 and 483 g mol−1, respectively. These values represent an enhanced permeance and rejection performance compared to those of the pristine membrane. The DVS-crosslinked PBI membrane also displays a long-term stability in mepenzolate bromide separation over 72 h.

Towards green membranes: Repurposing waste polypropylene with a single plant-based solvent via tandem spin-casting and annealing

A key aspect of advancing sustainable membrane technology is to source eco-friendly polymers, such as recycled plastic waste, use renewable plant-based solvents, and limit the number of solvents used in dissolution-precipitation processes. In this study, we upcycle polypropylene PP waste into bi-layered microporous superhydrophobic membranes using a single plant-based solvent, Cymene, through tandem spin-casting and annealing. The surface roughness and hydrophobicity of the top layer enhance selectivity, while the presence of micropores ensures efficient liquid passage and high permeability. The microporous bottom layer serves as a substrate for the top layer, providing structural support. Various annealing conditions were employed to optimize hydrophobicity, roughness, porosity and strength of as-prepared membranes, yielding high permeance and outstanding separation efficiency. The fabricated membranes were subjected to oil–water emulsion separations, demonstrating a contact angle exceeding 155° and a surface roughness of 123 nm, resulting in an organic solvent flux of 14,000 Lm-2h−1 with a 96 % water rejection. Tensile strength and strain % were found to be 13–28 MPa and 20–27 %, respectively. This research provided access to environmentally friendly membranes, adding value to plastic waste with potential benefits to both the polymer and membrane industries as they transition towards a circular economy.

Organic-inorganic hybrid two-dimensional membranes with enhanced solvent flux and stability

Two Dimensional membranes, which are usually constructed by inorganic nanosheets, have shown great potentials in efficient separation of low-molecular-weight chemicals. In this study, a novel type of organic–inorganic hybrid two-dimensional membrane is designed and prepared by co-assembly of a two-dimensional organic building block, Dopa thin-walled microcapsule, and a typical inorganic nanosheet, MXene. The introduction of MXene not only increases the distance between adjacent Dopa microcapsules and improves the solvent flux of the membrane, but also improves the structural stability by modulating the chelation strength of MXene with the Dopa microcapsules. The optimal Dopa/MXene composite membrane shows good performance in the field of organic solvent nanofiltration (OSN), with a flux of 723 L m−2 h−1 bar−1 for methanol and reactive black rejection of more than 90%. All the Dopa/MXene hybrid membranes show better stability than MXene lamellar membranes and MXene/Dopa hybrid membranes (where Dopa microcapsule is inserted into MXene membrane), demonstrating the advantages of organic species in enhancing interfacial adhesion. More interestingly, since the chelation between Dopa and MXene mainly depends on the presence of TiO2 in MXene, the oxidation of MXene, which often raises concerns of instability, herein is found to further increase the rejection and stability of Dopa/MXene hybrid membranes with only slight decrease of solvent flux.

Continuous purification of drugs by ionic liquid-drawn organic solvent forward osmosis and solute recovery

Classical purification of pharmaceuticals is energy-intensive and employs toxic solvents that are discarded, calling for more sustainable methods. Here, we purified tetracycline by organic solvent forward osmosis using ionic liquids. Results show the osmotic enrichment of feed solutions containing different concentrations of tetracycline in methanol. The solvent flux during the filtration process is mainly influenced by solvent properties, such as molecular size, viscosity, polarity, and the solvent–membrane interaction. We evaporated the diluted draw solution to recover the draw solute for reuse. Overall ionic liquids appear as suitable draw solutes for organic solvent forward osmosis for pharmaceutical compound enrichment with draw solute recovery and reuse.

Preparation of organic solvent forward osmosis membranes using a thermally facilitated strategy for the separation of alcohols and pharmaceuticals

Organic solvent forward osmosis (OSFO) process is a potential method for separating pharmaceuticals from organic solvents due to its low energy consumption and without external pressure requirements. However, OSFO process is limited in practical application due to low solvent flux. Here we reported the use of organic solvent pressure-assisted osmosis (OSPAO) process, which is a novel OSFO operation with increases a driving force (≤1 bar) in the same direction as solvent flow, enhancing solvent flux by combining osmotic pressure driving force with external hydraulic pressure. This work highlights a thermal facilitated simultaneous phase-inversion and crosslinking (T-SIM) strategy, which facilitates crosslinking degree and reduces preparation time and multi-step operations of solvent-resistant polyimide (PI) substrates. The temperature and extended time during the T-SIM strategy can more effectively controlling the physicochemical property and surface pore structures of solvent-resistant PI substrates. The morphological and physicochemical changes of the solvent-resistant PI substrates were observed by SEM, AFM, XPS, TG, contact angle and ATR-FTIR spectroscopy. Polyamide (PA) membranes were produced on the solvent-resistant PI substrates using an interfacial polymerization (IP) process, which led to the creation of defect-free PA layers with “ridge-and-valley” patterns. The methanol flux of 9.65 L m-2h−1 (LMH) and oxytetracycline (OTC) rejection of > 91% under the organic solvent nanofiltration test were achieved for the optimized T-SIM120 membrane, while the ethanol flux of 7.24 LMH and OTC rejection higher than 97% were observed under the OSPAO test. Additionally, DMF activation improved membrane permeance, the maximum ethanol flux of the T-SIM120 membrane after 2 h DMF activation reached 8.27 LMH under 1 bar during the OSPAO process and OTC rejection > 97%. The OSPAO process in this work demonstrated higher ethanol flux compared to the OSN process, lower Js/Je and enhanced OTC rejection compared to the OSFO process. Then the unique characteristic makes OSPAO process a desirable technology for solvent recovery in the pharmaceutical industry.

Thermo-Osmosis in Charged Nanochannels: Effects of Surface Charge and Ionic Strength.

Thermo-osmosis refers to fluid migration due to the temperature gradient. The mechanistic understanding of thermo-osmosis in charged nano-porous media is still incomplete, while it is important for several environmental and energy applications, such as low-grade waste heat recovery, wastewater recovery, fuel cells, and nuclear waste storage. This paper presents results from a series of molecular dynamics simulations of thermo-osmosis in charged silica nanochannels that advance the understanding of the phenomenon. Simulations with pure water and water with dissolved NaCl are considered. First, the effect of surface charge on the sign and magnitude of the thermo-osmotic coefficient is quantified. This effect was found to be mainly linked to the structural modifications of an aqueous electrical double layer (EDL) caused by the nanoconfinement and surface charges. In addition, the results illustrate that the surface charges reduce the self-diffusivity and thermo-osmosis of interfacial liquid. The thermo-osmosis was found to change direction when the surface charge density exceeds -0.03C · m-2. It was found that the thermo-osmotic flow and self-diffusivity increase with the concentration of NaCl. The fluxes of solvent and solute are decoupled by considering the Ludwig-Soret effect of NaCl ions to identify the main mechanisms controlling the behavior. In addition to the advance in microscopic quantification and mechanistic understanding of thermo-osmosis, the work provides approaches to investigate a broader category of coupled heat and mass transfer problems in nanoscale space.

Ultrathin organic solvent nanofiltration membrane with polydopamine-HKUST-1 interlayer for organic solvent separation

Polydopamine (PDA) and metal-organic skeleton HKUST-1 were co-deposited on the base membrane of hexamethylenediamine (HDA)-crosslinked polyetherimide (PEI) ultrafiltration membrane as the interlayer, and high-throughput organic solvent nanofiltration membrane (OSN) was prepared by interfacial polymerization and solvent activation reaction. The polyamide (PA) layer surface roughness from 28.4 nm in PA/PEI to 78.3 nm in PA/PDA-HKUST-10.6/PEI membrane, reduced the thickness of the separation layer from 79 to 14 nm, and significantly improved the hydrophilic, thermal and mechanical properties. The flux of the PA/PDA-HKUST-10.6/PEI membrane in a 0.1 g/L Congo Red (CR) ethanol solution at 0.6 MPa test pressure reached 21.8 L/(m2·hr) and the rejection of CR was 92.8%. Solvent adsorption test, N, N-dimethylformamide (DMF) immersion experiment, and long-term operation test in ethanol showed that the membranes had high solvent tolerance. The solvent flux test demonstrated that, under the test pressure of 0.6 MPa, the flux of different solvents ranked as follows: methanol (56.9 L/(m2·hr)) > DMF (39.6 L/(m2·hr)) > ethanol (31.2 L/(m2·hr)) > IPA (4.5 L/(m2·hr)) > N-hexane (1.9 L/(m2·hr)). The ability of the membranes to retain dyes in IPA/water dyes solution was also evaluated. The flux of the membrane was 30.4 L/(m2·hr) and the rejection of CR was 91.6% when the IPA concentration reached 50%. This OSN membrane-making strategy is economical, environment-friendly and efficient, and has a great application prospect in organic solvent separation systems.

The Revised Starling Hypothesis: Modeling the impact of the glycocalyx on vascular refilling during ultrafiltration in humans

The glycocalyx lines systemic capillaries and influences the distribution of osmotic forces across the capillary between the intravascular and interstitial compartments. By creating a pericapillary space between the capillary and the interstitium with a low osmotic pressure, the predicted and measured water flux at the distal end of systemic capillaries is outward under physiological conditions – contrary to the prediction of the traditional Starling model of capillary fluid transport. This has led to a ‘revised’ Starling model in which the predicted the movement of water from the capillary into the interstitium is consistently outward, and the return of water from the interstitial compartment necessary to maintain intravascular volume occurs nearly exclusively through the lymphatic system. We developed a methematicl model of the revised Starling Hypothesis that is applicable to the whole body in the special circumstance of hemodialysis, where the contributions of renal function to blood volume regulation may be ignored, and the total input and output of water and solutes are controlled and measured as part of the process of hemodialysis. We created a revised, two compartment (vascular+interstitial space), Starling model using the quantitative model of Facchini et al. (Microvasc. Res. 94:52-63, 2014) that describes capillary transport through the glycocalyx (albeit as normalized dimensionless values). We modelled the return of interstitial water to the vascular space through lymphatic flow based on the interstitial pressure (Possenti et al., Micro. Vasc. Res. 122:101-110, 2019), and we estimated the interstitial pressure based upon the formulation of Chapple et al. (Comp. Meth, and Prog. In Biomed. 41: 33-54,1993). We used the two-compartment model (intravascular and extravascular spaces) developed by de los Reyes et al. (J. Theoret. Biol. 390:146-155, 2016) to analyze transcapillary fluxes based on the traditional Starling model, and we embedded the description of fluxes across glycocalyx developed by Facchini et al. to decribe the fluxes of solutes and water across the glycocalyx and peri-glycocalyx/sub-capillary space and added control of lymphatic function within this two-compartment model to create a revised Starling model. The traditional and revised models were evaluated using data from periods of ultrafiltration in which the hematocrit (Crit-line), body weight and measured fluid input or ultrafiltrate removed were measured, and we compared the predicted fluxes of solvent and solutes across the capillary and through the lymphatic system between the traditional and revised Starling models. The two models lead to dramatically different predictions—all of the fluid transported out of the capillary must come back via the lymphatics according to the revised Starling model. This places vital importance upon the lymphatic flow during vascular refilling when blood volume is reduced and must be repleted to maintain stable cardiac function. Partially funded by the Renal Research Institute This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Covalent organic frameworks based membranes for separation of azeotropic solvent mixtures by pervaporation

Pervaporation of organic-organic mixtures has shown great potential as a replacement for conventional distillation processes, particularly when dealing with azeotropes and liquids with similar boiling points that are difficult to separate. However, the lack of high-performing membranes that can consistently provide reliable selectivity and high production rates has been a major hurdle in this field. Here, we used an in-situ growth method to prepare two prototypes of imine-linked COFs, i.e., COF-LZU1 and COF-300 membranes for separating azeotropic mixtures of polar/non-polar solvent, i.e., acetone/n-hexane, acetone/cyclohexane and methanol/benzene. The composite membranes comprising a continuous and defect-free COF layer on a ceramic hollow fibre substrate demonstrate high solvent fluxes of acetone and methanol, up to 20.0 and 4.9 kg m−2h−1, respectively. The preferential permeation of polar solvents through polar imine-linked nanochannels leads to a high separation factor of the studied mixtures: 30 for acetone/n-hexane, 13.4 for acetone/cyclohexane and 4.3 for methanol/benzene systems. Combined with good stability in solvent systems, our results have proved a technical feasibility of using COF-based membranes for separation of azeotropic solvent mixtures.

Molecular simulation study of 2D MXene membranes for organic solvent nanofiltration

MXene membranes has emerged as promising membrane materials due to their rigid lamellar structure and easily functionalized terminal groups. Understanding the mechanism of solvent transportation through MXene membrane at the microscopic level is significant for the development of new MXene based membranes. In this study, MXene membranes with different interlayer d-spacings (e.g., 0.9 nm, 1.45 nm, 2.0 nm, and 2.5 nm) are investigated for organic solvent nanofiltration (OSN) of four solvents (e.g., acetone, acetonitrile, methanol, and ethanol) and a model solute (Nile red). In membrane with the d-spacing of 0.9 nm, the solvent fluxes are regulated by the arrangements of solvents in the membrane. An ordered orientation and arrangement of solvent would result in a high flux. At this time, the solvent arrangement is dominated by the interaction energies between the solvent and membrane surface. When the d-spacing is larger than 1.45 nm, the solvent property (e.g., viscosity) plays the dominant role in flux determination. Compared with reported membranes, a substantially higher solvent flux can be achieved through the 2D MXene lamellar membranes. The solute rejections are controlled by a size-sieving mechanism, and 100% rejection of Nile red could be obtained in MXene membranes with 0.9 and 1.45 nm d-spacings. From the bottom-up, this work reveals the key governing factors that dominate the solvent permeation and solute rejection of 2D MXene lamellar membranes, and would also promote the development of new OSN membranes.

Imparting Outstanding Dispersibility to Nanoscaled 2D COFs for Constructing Organic Solvent Forward Osmosis Membranes.

In the context of thin-film nanocomposite membranes with interlayer (TFNi), nanoparticles are deposited uniformly onto the support prior to the formation of the polyamide (PA) layer. The successful implementation of this approach relies on the ability of nanoparticles to meet strict requirements regarding their sizes, dispersibility, and compatibility. Nevertheless, the synthesis of covalent organic frameworks (COFs) that are well-dispersed, uniformly morphological, and exhibit improved affinity to the PA network, while preventing agglomeration, remains a significant challenge. In this work, a simple and efficient method is presented for the synthesis of well-dispersed, uniformly morphological, and amine-functionalized 2D imine-linked COFs regardless of the ligand composition, group type, or framework pore size, by utilizing a polyethyleneimine (PEI) shielded covalent self-assembly strategy. Subsequently, the as-prepared COFs are incorporated into TFNi for the recycling of pharmaceutical synthetic organic solvents. After optimization, the membrane exhibits a high rejection rate and a favorable solvent flux, making it a reliable method for efficient organic recovery and the concentration of active pharmaceutical ingredient (API) from the mother liquor through an organic solvent forward osmosis (OSFO) process. Notably, this study represents the first investigation of the impact of COF nanoparticles in TFNi on OSFO performance.

Metal ion-catalyzed interfacial polymerization of functionalized covalent organic framework films for efficient separation

Covalent organic frameworks (COFs), with high porosity, uniform and tunable pore size, which are advantageous to prepare defect-free membranes with high separation performance and high permeability, and have achieved efficient applications in the field of separation membranes in numerous directions. According to our knowledge, the transition metal ion (Cu2+) which is used in Schiff base condensation reaction has been rarely described. Herein, we report the interfacial polymerization of ternary amines and binary aldehyde monomers via the catalyst Cu(ClO4)2·6H2O. In this work, we report the fabrication of covalent organic framework films from four different functional structure monomers by using the transition metal ion-catalyzed interfacial polymerization at room temperature. The four as-synthesized films are flexible, continuous, defect-free and have large areas, which have excellent performance in the direction of dye separation as well as solvent penetration. After the COF films were transferred to the polyethersulfone support, the composite films exhibited enhance the rejection of methylene blue (98.43%), high-water flux (81.46 L m−2 h−1 bar−1) and solvent flux (ethanol (13.03 L m−2 h−1 bar−1), acetonitrile (50.38 L m−2 h−1 bar−1)). The large area, tunable pore size, and tailored molecular composite membranes show potential for nanofiltration applications.

In-Situ EC-AFM Study of Electrochemical P-Doping of Polymeric Nickel(II) Complexes with Schiff base Ligands

Conductive electrochemically active metallopolymers are outstanding materials for energy storage and conversion, electrocatalysis, electroanalysis, and other applications. The hybrid inorganic–organic nature of these materials ensures their rich chemistry and offers wide opportunities for fine-tuning their functional properties. The electrochemical modulation of the nanomechanical properties of metallopolymers is rarely investigated, and the correlations between the structure, stiffness, and capacitive properties of these materials have not yet been reported. We use electrochemical atomic force microscopy (EC-AFM) to perform in-situ quantitative nanomechanical measurements of two Schiff base metallopolymers, poly[NiSalphen] and its derivative that contains two methoxy substituents in the bridging phenylene diimine unit poly[NiSalphen(CH3O)2], during their polarization in the electrolyte solution to the undoped and fully doped states. We also get insight into the electrochemical p-doping of these polymers using electrochemical quartz crystal microgravimetry (EQCM) coupled with cyclic voltammetry (CV). Combined findings for the structurally similar polymers with different interchain interactions led us to propose a correlation between Young’s modulus of the material, its maximum doping level, and ion and solvent fluxes in the polymer films upon electrochemical oxidation.

Calcium-alginate/HKUST-1 interlayer-assisted interfacial polymerization reaction enhances performance of solvent-resistant nanofiltration membranes

This study aimed to further enhance the solvent stability and flux of organic solvent-resistant nanofiltration (OSN) membranes. Based on hexane diamine cross-linked polyetherimide (PEI) ultrafiltration membranes, in-situ calcium alginate (CaAlg) hydrogel doped with HKUST-1 was constructed as an interlayer, and then the OSN membrane with an integral covalent bond structure was constructed from interfacial polymerization reaction and NN dimethylformamide (DMF) activation. The membrane showed ultra-thinness (polyamide (PA) layer thickness reduced from 97 to 11 nm), large surface area (surface roughness increased from 75.6 to 113 nm), high hydrophilicity (water contact angle reduced from 60.1° to 54.45°), and negative charge. The CaAlg-HKUST-1 interlayer limited the piperazine diffusion rate by hydrogen bonding and covalent bonding, etc., reduced the thickness of the PA layer, and linked the base membrane and the PA layer by its internal integral covalent bonding, which effectively enhanced the structural stability of the OSN membrane. The PA/CaAlg-HKUST-16/PEI membrane achieved a flux of 29.4 L·m−2·h−1 in ethanol and a rejection of 94.7 % in 0.1 g·L-1 methyl blue. Different dye rejection tests, solvent flux tests, DMF and acetone immersion tests, fouling resistance tests, and continuous operation tests show PA/CaAlg-HKUST-16/PEI membrane has better solvent resistance, dye separation performance, and stable membrane flux. Hence, it has great application prospects in the fields of organic solvents and other types of wastewater treatment.