Improved Filtration Performance Research Articles

Direct Membrane Filtration (DMF) of municipal wastewater – A study on the prevention and remediation of fouling

Direct membrane filtration (DMF) has gained a lot of attention in recent years because of its potential to treat low-strength and low temperature wastewater, where biological based treatments are inefficient. However, fouling is a major concern which keeps this technique from being more widely used. The main aim of this study was to investigate membrane fouling, its mitigation approaches and the organic/nutrient retention during DMF of municipal wastewater by adjusting operational parameters and pretreating the sewage. In a laboratory-scale setup employing crossflow to mitigate fouling, both ultrafiltration and microfiltration membranes were utilized. Physicochemical pre-treatment of sewage with polyaluminum chloride and polyamide significantly inhibited membrane fouling and improved organics/nutrient retention. Subsequent experiments with physiochemically pre-treated sewage, using microfiltration and ultrafiltration separately, revealed that (i) an increase in crossflow velocity from 1 to 2 m s −1 improved filtration performance by reducing irreversible fouling, (ii) elevating transmembrane pressure from 0.18 to 0.4 bar increased both reversible and irreversible fouling, and (iii) periodic relaxation increased the extent of irreversible fouling, contributing to higher overall fouling in ultrafiltration. When employing DMF for sewage concentration, ultrafiltration demonstrated superior filtration performance and organics retention compared to microfiltration. Furthermore, through pre-precipitation and microsieving (100 μm) followed by DMF with ultrafiltration membranes, a remarkable removal efficiency of 92 % for chemical oxygen demand (COD), 98 % for total phosphorus (TP), and 100 % for total suspended solids (TSS) was achieved. By cleaning the fouled membranes using an alkaline cleaning solution (Ultrasil-10) at 50 °C, combined with a crossflow of 1 m s−1, the permeability was completely restored. Overall, this study demonstrates that by optimizing operational settings and cleaning conditions, a sustainable DMF process for wastewater treatment with controlled membrane fouling and improved resource recovery can potentially be developed for upscaling. Short abstractThis study investigated the effectiveness of direct membrane filtration for municipal wastewater treatment. It was found that physicochemical pre-treatment with polyaluminum chloride and polyamide significantly reduced membrane fouling and improved nutrient retention. Ultrafiltration membranes demonstrated superior performance and nutrient retention compared to microfiltration membranes. By optimizing operational parameters and cleaning conditions, a sustainable direct membrane filtration process with controlled fouling and improved resource recovery can be developed for wastewater treatment.

Membrane fouling mechanisms in the presence of microplastics and organic matter: The unexpected mitigating role of Ca2+

Ultrafiltration (UF) is demonstrated to be highly effective in the removal of microplastics (MPs), but the presence of coexisting foulants introduces significant uncertainties into the associated membrane fouling behaviors. In this study, membrane fouling mechanisms were investigated when MPs, represented by polystyrene (PS), coexisted with typical organic foulants (sodium alginate, SA) and inorganic ions (Ca2+). Fouling tests revealed that the order of Ca2+ addition significantly impacted the fouling behavior of the SA-PS combined foulants. Specifically, the specific filtration resistance (SFR) was reduced by 40.82 % in the SA-PS-Ca2+ foulants and by 90.92 % in the SA-Ca2+-PS foulants, compared to the SA-PS foulants. X-ray photoelectron spectroscopy and density functional theory calculations indicated that sufficient cross-linking of Ca2+ with SA molecular chains in the SA-Ca2+-PS foulants, forming a large-scale 3D network that encapsulated more PS particles and resulted in larger flocs than those found in the SA-PS-Ca2+ foulants. According to extended Flory-Huggins theory, the improved filtration performance of the SA-PS combined foulants was due to substantial changes in chemical potential during their transition from gel to flocs upon Ca2+ addition. Furthermore, interfacial thermodynamic analyses suggested that increased repulsion between SA-Ca2+-PS foulants and between them and the membrane led to a looser fouling layer, significantly mitigating membrane fouling. This study elucidates the fouling mechanisms in the presence of MPs and other foulants from the perspectives of energy changes and molecular structures, providing novel insights for developing strategies to mitigate membrane fouling.

Impact of pH, ionic strength, and operating conditions on capture mechanisms in nanoparticle filtration

Filtration of biopharmaceutical streams can be complex due to the variety of components in the stream and their interactions among themselves and with the filter pore surfaces. This work used a variety of measurements to study the filtration of model silica nanoparticles through asymmetric hydrophilized polyethersulfone (mPES) membrane in solutions covering a range of pH and ionic strengths. Measurements included particle size, particle concentration, zeta potential, particle-particle and particle-membrane surface intermolecular forces. These measurements were used to rationalize observed particle capture behavior under various filtration conditions. We found that increasing ionic strength and decreasing pH resulted in higher particle aggregation and higher particle retention due to adsorption of model silica nanoparticles to the membrane and sieving of aggregates within the membrane. In addition, captured particles can be eluted from the membrane in some cases, depending on the operating conditions, extent of particle loading, buffer flush pressure, and buffer pH and conductivity conditions. These findings provide insight into methods to improve filtration performance and particle capture or release, including product recovery, in filtration processes.

Comparison of 2D and 3D materials on membrane modification for improved pressure retarded osmosis (PRO) process

Pressure retarded osmosis (PRO) is a sustainable process that convert Gibbs free energy to osmotic energy by mixing two solutions of different salinities. The main challenges in the design of PRO membranes are obtaining a membrane with high water permeability and low salt permeability but also very high mechanical strength because the PRO process involves high pressure on the draw solution. Commercially available RO membranes with potential utility in a PRO system exhibit a high salt rejection rate but low water permeability and mechanical stability. Surface modification is a promising strategy for tuning the fundamental properties of the membranes (e.g. hydrophilicity, surface charge and thickness) that can improve the filtration performance of the membranes. The coating layer can also improve the mechanical stability of the membranes. Therefore, in this work, various types of modification materials were applied to the commercial available RO membranes to enhance their performance.With the assistance of hydrophilic materials (e.g. polydopamine – PDA), filtration performance of the membranes can be increased through membrane modification by 2D materials with high charge intensities (e.g. polyelectrolytes and graphene oxides) and by 3D mesoporous materials (e.g. zeolites), which increases the thickness of the membrane that can be beneficial in mechanically reinforcing the membrane. In this work, we modified commercial RO membrane with PDA, polyelectrolytes, graphene oxide and zeolites (ZSM-5). Improved filtration performance (increased water permeability and maintained salt permeability) of the modified membrane was observed. Tensile tests showed enhanced mechanical strength of the modified membranes, especially following 3D zeolites modification (up to 35 % of higher tensile strain was reported). Interestingly, a lower concentration of PDA (2 mg/mL) and zeolites resulted in higher mechanical strength of the modified membranes. Such results were likely due to a more homogenous coating layer when a low modifier concentration was applied. The thin and uniform layer can better absorb energy when membranes are under high pressure.

Copper Nanoparticles Coupled with Fine-Powdered Active Carbon-Modified Ceramic Membranes for Improved Filtration Performance in a Membrane Bioreactor

Membrane fouling is a key factor limiting the application of a membrane bioreactor (MBR), and membrane-surface modification holds the potential to control membrane fouling and solves this problem. In the research, novel nanocomposite membranes were designed and fabricated using antimicrobial copper nanoparticles (CuNPs) coupled with powdered active carbon (PAC) to mitigate membrane fouling. The successful coating was confirmed by SEM, XRD, and FTIR analysis. Compared with a pristine membrane, the functionalization of CuNPs and PAC improved the hydrophilicity of the modified membrane but led to a lower permeate flux. The result of antimicrobial adhesion experiments showed that the modified M-CuOC displayed high antibacterial activity with the bacteria count decreased by 72%. In MBR operation, the modified M-CuOC leads to the removal efficiency of chemical oxygen demand (COD) increasing to 93%, with better filtration performance under a lower TMP rise. The fouling-resistance analysis demonstrated that, although the intrinsic membrane resistance of modified M-CuOC slightly increased, the reversible and irreversible fouling resistances obviously decreased by 45% and 90%. Moreover, the membrane flux recovery efficiency of the modified M-CuOC also increased by 35%. Overall, these results indicated that, in addition to an improvement in antifouling performance, the functionalization of CuNPs and PAC also enhanced the membrane flux recovery efficiency, revealing a good antifouling potential in a practical application.

Manufacture and filtration performance of glass filters made from capillary suspensions

This research highlights the potential of capillary suspensions in tailoring the properties of glass filters and improving filtration performance. Borosilicate glass 3.3 filters fabricated in a wet processing route based on capillary suspensions were developed. Their filter properties and filtration performance as well as control of shrinkage and porosity gradients during sintering were investigated. The use of capillary suspensions significantly reduced green body shrinkage. Long residence times and spatially inhomogeneous heat transfer during sintering favored the formation of porosity gradients. Pore size, porosity, permeability and flexural strength of the filters could be tailored by adjusting capillary suspension composition and sintering conditions. Glass filters with particularly high permeability and small pore sizes were successfully developed. Filtration experiments with Oenococcus oeni and polystyrene spheres (diameter ≈ 1 μm) were conducted, showing that filtration efficiency and flux depend on pore size and open porosity. Crack-free asymmetric glass membranes with improved filtration performance were developed. Compared to dry processed commercial benchmark filters, the capillary suspension-based filters made from the same glass powder had higher pore sizes and permeability. At similar pore size and porosity, filters based on capillary suspensions showed significantly higher filtrate flux than the commercial benchmarks due to a more uniform pore structure.

Increasing Performance of Spiral-Wound Modules (SWMs) by Improving Stability against Axial Pressure Drop and Utilising Pulsed Flow.

Spacer-induced flow shadows and limited mechanical stability due to module construction and geometry are the main obstacles to improving the filtration performance and cleanability of microfiltration spiral-wound membranes (SWMs), applied to milk protein fractionation in this study. The goal of this study was first to improve filtration performance and cleanability by utilising pulsed flow in a modified pilot-scale filtration plant. The second goal was to enhance membrane stability against module deformation by flow-induced friction in the axial direction ("membrane telescoping"). This was accomplished by stabilising membrane layers, including spacers, at the membrane inlet by glue connections. Pulsed flow characteristics similar to those reported in previous lab-scale studies could be achieved by establishing an on/off bypass around the membrane module, thus enabling a high-frequency flow variation. Pulsed flow significantly increased filtration performance (target protein mass flow into the permeate increased by 26%) and cleaning success (protein removal increased by 28%). Furthermore, adding feed-side glue connections increased the mechanical membrane stability in terms of allowed volume throughput by ≥100% compared to unmodified modules, thus allowing operation with higher axial pressure drops, flow velocities and pulsation amplitudes.

Development of an automatic and object-oriented method for spacer design in the spiral wound nanofiltration modules to comprehensively enhance filtration performance

Adjustment of feed spacers holds the potential to effectively address the inherent trade-off between permeate flux, anti-fouling capabilities, and feed channel pressure (FCP) drop, consequently enhancing the filtration performance of spiral wound modules (SWM). In this study, a novel automated spacers design approach based on response surface methodology and multi-objective genetic algorithm was successfully developed and experimentally verified, for the first time. By establishing the correlation between spacer parameters and key performance parameters of nanofiltration SWM (average wall shear, specific energy consumption, etc.), the design method facilitated the screening and optimization of the optimal spacer parameters by manipulating the variables spacer parameters to locally modify the spacer shapes and then to improve filtration performance. Subsequent simulations and experiments both demonstrated that, in contrast to the traditional spacer, the optimized spacer exhibited remarkable efficacy in striking a balance between membrane performance and energy consumption. Specifically, flux attenuation was reduced by 8 %, and minimum wall shear increased by 57.9 %, resulting in a significant reduction in membrane fouling. This report presents a small-scale and practical approach to spacer's local design, offering a valuable solution to address the inherent constraints posed by the interplay among permeation, anti-fouling, and FCP drop.

Airfoil-shaped filament feed spacer for improved filtration performance in water treatment

Optimal spacer design enhances the filtration performance in spiral-wound modules by controlling the local hydrodynamics inside the filtration channel. A novel airfoil feed spacer design fabricated using 3D-printing technology is proposed in this study. The design is a ladder-shaped configuration with primary airfoil-shaped filaments facing the incoming feed flow. The airfoil filaments are reinforced by cylindrical pillars supporting the membrane surface. Laterally, all the airfoil filaments are connected by thin cylindrical filaments. The performances of the novel airfoil spacers are evaluated at Angle of Attack (AOA) of 10° (A-10 spacer) and 30° (A-30 spacer) and compared with commercial (COM) spacer. At fixed operating conditions, simulations indicate steady-state hydrodynamics inside the channel for A-10 spacer, while an unsteady state is found for A-30 spacer. Numerical wall shear stress for airfoil spacers is uniformly distributed and has a higher magnitude than the COM spacer. A-30 spacer design is the most efficient in ultrafiltration process with enhanced permeate flux (228%) and reduced specific energy consumption (23%) and biofouling development (74%) as characterized by Optical Coherence Tomography. Results systematically demonstrate the influential role of airfoil-shaped filaments for feed spacer design. Modifying AOA allows localized hydrodynamics to be effectively controlled according to the filtration type and operating conditions.

Influence of pulsed and alternating flow on the filtration performance during skim milk microfiltration with flat-sheet membranes

Control of deposit formation during skim milk microfiltration (MF) remains challenging, particularly in membranes with spacer nets between membrane layers like flat-sheet and spiral-wound membranes, due to the extensive occurrence of flow shadows behind spacer filaments. One approach to improve process control and efficiency is applying pulsed or alternating flow, which creates regular fluctuations in shear stress, pressure and, for alternating flow, in flow direction. This study assessed the effects of these alternative flow types and compared them to conventional steady crossflow on deposit formation and filtration performance. Flux and protein permeation were monitored during filtration. After filtration, the membranes were removed and deposited proteins stained by Coomassie-blue. The visual analysis of the stained membranes confirmed that the alternative flow types improved access to flow shadows behind spacer filaments by causing a significantly reduced deposition or enhanced removal. Consequently, the reduced deposit formation with pulsed and alternating flow led to enhancements in the steady-state whey protein mass flow by > 8% and > 37% over any steady flow conditions. Considering the flow-specific pump energy demands, pulsed and alternating flow not only improved filtration performance, but also reduced specific energy consumption relative to whey protein mass transfer by > 60%.

Improved water purification by PVDF ultrafiltration membrane modified with GO-PVA-NaAlg hydrogel

This work presents a modified polyvinylidene fluoride (PVDF) ultrafiltration membrane blended with graphene oxide-polyvinyl alcohol-sodium alginate (GO-PVA-NaAlg) hydrogel (HG) and polyvinylpyrrolidone (PVP) prepared by the immersion precipitation induced phase inversion approach. Characteristics of the membranes with different HG and PVP concentrations were analyzed by field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), contact angle measurement (CA), and Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The FESEM images showed an asymmetric structure of the fabricated membranes, and possessing a thin dense layer over the top and a layer finger-like. With increasing HG content, membrane surface roughness increases so that highest surface roughness for the membrane containing 1wt% HG is with a Ra value of 281.4 nm. Also, the contact angle of the membrane reaches from 82.5° in bare PVDF membrane to 65.1° in the membrane containing 1wt% HG. The influences of adding HG and PVP to the casting solution on pure water flux (PWF), hydrophilicity, anti-fouling ability, and dye rejection efficiency were evaluated. The highest water flux reached 103.2 L/m2 h at 3 bar for the modified PVDF membranes containing 0.3 wt% HG and 1.0wt% PVP. This membrane exhibited a rejection efficiency of higher than 92%, 95%, and 98% for Methyl Orange (MO), Conge Red (CR), and Bovine Serum Albumin (BSA), respectively. All nanocomposite membranes possessed a flux recovery ratio (FRR) higher than bare PVDF membranes, and the best anti-fouling performance of 90.1% was relevant to the membrane containing 0.3 wt% HG. The improved filtration performance of the HG-modified membranes was due to the enhanced hydrophilicity, porosity, mean pore size, and surface roughness after introducing HG.

Preparation and Characterization of PVDF-TiO2 Mixed-Matrix Membrane with PVP and PEG as Pore-Forming Agents for BSA Rejection.

Polymeric membranes offer straightforward modification methods that make industry scaling affordable and easy; however, these materials are hydrophobic, prone to fouling, and vulnerable to extreme operating conditions. Various attempts were made in this study to fix the challenges in using polymeric membranes and create mixed-matrix membrane (MMMs) with improved properties and hydrophilicity by adding titanium dioxide (TiO2) and pore-forming agents to hydrophobic polyvinylidene fluoride (PVDF). The PVDF mixed-matrix ultrafiltration membranes in this study were made using the non-solvent phase inversion approach which is a simple and effective method for increasing the hydrophilic nature of membranes. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) as pore-forming chemicals were created. Pure water flux, BSA flux, and BSA rejection were calculated to evaluate the mixed-matrix membrane's efficiency. Bovine serum albumin (BSA) solution was employed in this study to examine the protein rejection ability. Increases in hydrophilicity, viscosity, and flux in pure water and BSA solution were achieved using PVP and PEG additives. The PVDF membrane's hydrophilicity was raised with the addition of TiO2, showing an increased contact angle to 71°. The results show that the PVDF-PVP-TiO2 membrane achieved its optimum water flux of 97 L/(m2h) while the PVDF-PEG-TiO2 membrane rejected BSA at a rate greater than 97%. The findings demonstrate that use of a support or additive improved filtration performance compared to a pristine polymeric membrane by increasing its hydrophilicity.

Preparation and characterization of fiber braided tube reinforced polyethylene hollow fiber membranes via thermally induced phase separation

In wastewater treatment applications, mechanical strength of the membranes often cannot meet practical requirements due to the disturbance of aeration flow or the damage of high-pressure cleaning. In this work, fiber braided tube reinforced polyethylene (BR PE) hollow fiber membranes with desirable filtration performance and high tensile strength were successfully prepared via fiber braided tube reinforcement (BR) and thermally induced phase separation (TIPS) methods. Especially, the effect of heat treatment temperature on structure and properties of the membranes was discussed. The results exhibited that tensile strength and interfacial bonding state between the surface separation layer and the fiber braided tube reinforcement were improved with the increase of heat treatment temperature. While the heat treatment temperature was 130 °C, BR PE hollow fiber membranes exhibited favorable interfacial bonding state, and tensile strength was up to 204.4 MPa, which was significantly higher than that of previously reported PE membranes. Moreover, the increase of heat treatment temperature could decrease the membrane pore size and improve filtration performance. Comprehensive consideration, the optimal heat treatment temperature of BR PE hollow fiber membranes was 110 °C. This work can provide scientific and practical basis for large-scale development of BR hollow fiber membranes with good comprehensive performance.

Synthesis of co-polyamide reverse osmosis membrane constituting a linear aliphatic triamine and m-phenylenediamine for enhanced desalination performance

The improvement in the overall efficiency of membranes (especially reverse osmosis, RO) is limited by the tradeoff between salt rejection and permeate flux. To overcome this tradeoff, an RO membrane with a co-polyamide active layer was fabricated using a mixture of an aliphatic amine Bis(3-aminopropyl)amine (BAPA) and an aromatic amine m-phenylenediamine (MPD). Interfacial polymerization (IP) was carried out by crosslinking the amine mixture with trimesoyl chloride (TMC) on a polysulfone (PSf) support leading to a co-polyamide (Co-PA) membrane. A control polyamide membrane (PA) was also fabricated from conventional monomers of MPD and TMC. The Co-PA membrane showed significantly improved filtration performance when compared to the MPD conventional membrane; the permeate flux increased by 70 % while having comparable salt rejection. Furthermore, the Co-PA membrane showed better fouling resistance toward alginate (a model polysaccharide foulant), retaining 80 % of its initial flux, which was almost completely reversible. The lesser fouling tendency of the Co-PA membrane was ascribed to its reduced surface roughness and lower negative charge compared to the control sample. Long-term stability tests with a 2000 ppm NaCl feed revealed that both membranes maintained a constant performance for 72 h of continuous operation.

Crystal Engineering in Antisolvent Crystallization of Rare Earth Elements (REEs)

Antisolvent crystallization is a separation technology that separates the solute from the solvent by the addition of another solvent, in which the solute is sparingly soluble. High yields are achieved by using higher antisolvent-to-aqueous ratios, but this generates higher supersaturation, which causes excessive nucleation. This results in the production of smaller particles, which are difficult to handle in downstream processes. In this work, the effect of varying the organic (antisolvent)-to-aqueous (O/A) ratio and seed loading on the yield, particle size distribution, and morphology of neodymium sulphate product, during its recovery from an aqueous leach solution using antisolvent crystallization, was investigated. A batch crystallizer was used for the experiments, while ethanol was used as an antisolvent. Neodymium sulphate octahydrate [Nd2(SO4)3.8H2O] seeds were used to investigate the effect of seed loading. It was found that particle sizes increased as the O/A ratio increased. This was attributed to the agglomeration of smaller particles that formed at high supersaturation. An O/A ratio of 1.4 resulted in higher yields and particles with a plate-like morphology. The increase in yield was attributed to the increased interaction of ethanol molecules with the solvent, which reduced the solubility of neodymium sulphate. Increasing the seed loading resulted in smaller particle sizes with narrow particle size distribution and improved filtration performance. This was attributed to the promotion of crystal growth and suppression of agglomeration in the presence of seeds.

Multifunctional Filter Membranes Based on Self-Assembled Core-Shell Biodegradable Nanofibers for Persistent Electrostatic Filtration through the Triboelectric Effect.

The massive production of polymer-based respiratory masks during the COVID-19 pandemic has rekindled the issue of environmental pollution from nonrecyclable plastic waste. To mitigate this problem, conventional filters should be redesigned with improved filtration performance over the entire operational life while also being naturally degradable at the end. Herein, we developed a functional and biodegradable polymeric filter membrane consisting of a polybutylene adipate terephthalate (PBAT) matrix blended with cetyltrimethylammonium bromide (CTAB) and montmorillonite (MMT) clay, whose surface properties have been modified through cation exchange reactions for good miscibility with PBAT in an organic solvent. Particularly, the spontaneous evolution of a partial core-shell structure (i.e., PBAT core encased by CTAB-MMT shell) during the electrospinning process amplified the triboelectric effect as well as the antibacterial/antiviral activity that was not observed in naive PBAT. Unlike the conventional face mask filter that relies on the electrostatic adsorption mechanism, which deteriorates over time and/or due to external environmental factors, the PBAT@CTAB-MMT nanofiber membrane (NFM)-based filter continuously retains electrostatic charges on the surface due to the triboelectric effect of CTAB-MMT. As a result, the PBAT@CTAB-MMT NFM-based filter showed high filtration efficiencies (98.3%, PM0.3) even at a low differential pressure of 40 Pa or less over its lifetime. Altogether, we not only propose an effective and practical solution to improve the performance of filter membranes while minimizing their environmental footprint but also provide valuable insight into the synergetic functionalities of organic-inorganic hybrid materials for applications beyond filter membranes.

Improving properties of thin film nanocomposite membrane via temperature-controlled interfacial polymerization for nanofiltration process

Research on the effect of interfacial polymerization (IP) temperature during polyamide layer synthesis is lacking, especially for thin film nanocomposite (TFN) nanofiltration membrane. Typically, polyamide composite membranes are fabricated at room temperature, ignoring the potential impact of reaction temperature. In this work, we varied the organic solvent temperature to study its impacts on the properties of TFN membrane containing surface-functionalized graphene oxide (GO) for nanofiltration process. A more cross-linked and rougher polyamide layer could be formed at 55 °C due to higher reaction kinetics and more volatile IP reaction. This membrane exhibited excellent Na2SO4 rejection (99 %) with a water-salt permselectivity ratio of 11.0, i.e., >2 folds compared to the commercial membrane (4.88). However, its rougher surface resulted in a higher protein adhesion even with the enhanced antifouling property brought by GO hydrophilicity. In comparison, the TFN membrane developed at 0 °C displayed very thin yet smooth polyamide layer, resulting in a higher water flux and improved antifouling performance. Furthermore, the TFN membrane demonstrated stable filtration performance for 12 h and GO nanosheets were still well accommodated within selective layer after testing. Overall, the improved filtration performance and reduced protein adsorption demonstrated the feasibility of IP temperature variation in TFN membrane fabrication.

Improved filtration performance of polyvinylidene fluoride nanocomposite membranes embedded with deep eutectic solvent: Application towards MBR

Herein, high-performance polyvinylidene fluoride (PVDF) nanocomposite membranes were established by including a functional agent, Choline chloride (ChCl):1,5-Diphenylcarbazide (DPC) -based deep eutectic solvent (DES), into the phase inversion process, allowing the membrane structure to be tailored owing to the synergetic impact between DES components in the phase inversion process. The physicochemical properties of DES and membranes were characterized employing techniques including FTIR spectroscopy, TGA, SEM, EDX, XPS, AFM, and contact angle measurement. The membranes' performance was evaluated using milk powder solution and membrane bioreactor (MBR) effluent filtration experiments, as well as a systemic study of the impacts of varying DES loadings. The incorporation of DES into the membrane matrix enhanced the porous structure and hydrophilicity of the membranes, contributing to the enhanced water permeability (pure water flux of 215.98 ± 4.32 kg·m−2·h−1), high selectivity (removal of >99 %), and remarkable antifouling property (FRR of 98.26 %) of the resultant membranes. The long-term filtration results ample substantiated that DES could potentially be used as a modifying agent.

Multifunctional membranes for lipidic nanovesicle capture

Tangential flow filtration membrane systems are employed for the isolation and concentration of extracellular vesicles. However, interfacial interactions between the membrane surface and species influence the flux and membrane performance. Here we propose a strategy aimed at introducing functional ligands over the membrane surface to improve the separation process through combined size-exclusion and affinity-based mechanisms, avoiding the binding of contaminants and other non-target molecules. Polysulfone membranes were modified by a nanometric coating of differently functionalized copolymers with the dual purpose of limiting non-specific interactions while promoting the chemoselective conjugation of a membrane-sensing peptide ligand (BPt) for lipid nanovesicles capture. Copoly azide polymer coating positively affects the physico-chemical properties of the membrane, improving filtration performance and antifouling capacity. A decrease of the flux decline ratio from 38.7 ± 3.9% to 21.2 ± 2.4% and an increase of the ratio of protein permeate concentration (Cp) to the respective feed concentration (Cf) to values of 0.97 was measured after coating the membrane with c-(DMA-N3-BP-MAPS) highlighting its capability to reduce protein adsorption. In addition, the BPt-functionalized membrane displayed a high capturing efficiency towards synthetic liposomes which, notably, can be promptly released upon mild treatment with a divalent cation solution. Overall, our work integrates conventional TFF principles with affinity-based isolation, broadening TFF perspective applications.

Electrospun PAN-HNTs composite nanofiber membranes for efficient electrostatic capture of particulate matters

The fine particulate matter (PM) pollution has become a serious concern to public health. As the core part of PM air filters, high-performance electrostatic nanofiber membranes are urgently needed. However, the existing air filters remain challenging to further decrease the pressure drop to improve the wearer comfort. On the other hand, the rapidly disappearing static electricity of the existing electrostatic nanofiber inevitably gives rise to a relatively short service life. Here, we demonstrate a novel and enhanced electrostatic nanofiber membrane by introducing the halloysite nanotubes (HNTs) to the traditional electrospun PAN nanofiber membrane. The optimal PAN-HNTs nanofiber membrane shows a high removal efficiency of 99.54%, a low pressure drop of 39 Pa, and a high quality factor of 0.89 Pa−1. This greatly improved filtration performance can be attributed to the increased surface area and diameter of nanofiber after introducing the HNTs as additives with suitable doping concentrations. More importantly, compared with the pure PAN nanofiber membrane, the electrostatic capacity of the PAN-HNTs nanofiber membrane is significantly enhanced, which is confirmed by the leaf electroscope. After introducing the HNTs as additives, the surface of the PAN-HNTs nanofiber membrane becomes hydrophilic, which benefits for preventing foulants from attaching to the surface. We anticipate that the PAN-HNTs nanofibers as high-performance membrane air filters will bring great benefits to public health.