Pore Size Distribution Of Membranes Research Articles

Ferric ions mediated defects narrowing of graphene oxide nanofiltration membrane for robust removal of organic micropollutants

Removal of organic micropollutants (OMPs) in the wastewater treatment is greatly important due to their adverse effects on human health and ecosystem. In this work, we provide a new perspective to prepare graphene oxide (GO) nanofiltration (NF) membrane with narrow pore size distribution for robust removal of OMPs. Ferric ions (Fe3+) mediated GO nanosheets are firstly used to prepare GO membrane, then the membrane surface is modified by a targeted coating layer consisting of tannic acid-aminopropyltriethoxysilane (TA-APTES) via their strong affinity to Fe3+, where the larger membrane defects with more Fe3+ would be patched by thicker TA-APTES. Such “speckled” TA-APTES coating can simultaneously enhance antifouling ability and regulate nanochannels of the GO membrane. The resulted GO membrane shows high and steady rejections on various OMPs, even in the long-term operation, cross-flow filtration or under high-pressure. This work proposes an innovative idea for constructing hydrophilic surface and narrow pore size distribution of NF membrane.

Finely tailored pore structure of polyamide nanofiltration membranes for highly-efficient application in water treatment

• PIP has been applied as a structure regulator to enlarge pores of PA NF membranes. • The addition of PIP enhances the permeance by 97.3% with rejection of MO above 98%. • TPC has been deployed for narrowing pore size distribution of the PA NF membranes. • The incorporation of TPC enhances rejection to positive multi-valent ions greatly. • The finely tailored membranes show strong promise in waste water treatment. With fine pore structures and abundant surface charge, polyamide nanofiltration membranes have been widely deployed for separating small active organic molecules and multi-valent ions. However, lack of highly permeable membranes with excellent rejection towards target molecules hampers the widespread application of the polyamide (PA) nanofiltration membranes on a large scale. In current study, we conceive a facile strategy to regulate the molecular structure of polyamide selective layer through introducing piperazine (PIP) or terephthaloyl chloride (TPC) as a structural regulator during the interfacial polymerization between polyethyleneimine (PEI) and trimesoyl chloride (TMC). On the one hand, adding PIP to aqueous solution enlarges the length between the crosslinked networks, thereby enhancing the pure water permeance by 97.3% (to 23.70 L m −2 h −1 bar −1 ). Interestingly, the membranes exhibit excellent performance for dyes separation (rejection greater than 98%) and molecular weight cut-off (MWCO) about 554.34 Da under the optimum separation conditions. On the other hand, the introduction of TPC could assist the formation of crosslinked structures, thereby narrowing the pore size distribution of the membranes. The well-designed membranes reject above 98% PbCl 2 with permeance about 6.36 L m −2 h −1 bar −1 and MWCO below 150 Da under the optimum operation conditions, which is preferable to the state-of-art PA membranes. Excitingly, all of the well-designed membranes demonstrate excellent anti-fouling performances. In summary, with finely tailored pore structure, high permeance and high rejection, and excellent anti-fouling performance, the obtained membranes show strong promise in treating effluence from printing and dyeing industry, and metallurgy and mining industry, respectively.

Characterization of porous polyacrylonitrile membranes by liquid-liquid displacement technique

In this work, series of PAN membranes were prepared by the combined VIPS/NIPS method using different solvents. These membranes were investigated by using liquid-liquid displacement method for membrane pore size distribution and membrane permeance measurements. Wide range of pores size (30-60 nm) and membrane permeance up to 400 L/m2·h·bar were achieved depending on the casting conditions. It was shown that longer exposure in water vapor leads to higher pore size and at the same time makes membrane less permeable due to low asymmetry of porous structure..

Influence of Sodium Hypochlorite Treatment on Pore Size Distribution of Polysulfone/Polyvinylpyrrolidone Membranes.

This work was focused on the study of hypochlorite treatment on the pore size distribution of membranes. To this end, ultrafiltration membranes from a polysulfone/polyvinylpyrrolidone blend with a sponge-like structure were fabricated and exposed to hypochlorite solutions with different active chlorine concentrations for 4 h at ambient temperature. Liquid–liquid displacement and scanning electron microscopy were employed to study the limiting and surface pores, respectively. After treatment with 50 ppm hypochlorite solution at pH = 7.2, a five-fold increase in water permeance up to 1400 L/(m2·h·bar) was observed, accompanied by a 40% increase in the limiting pore sizes and almost a three-fold increase in the porosity. After 5000 ppm treatment at pH = 11.5, a 40% rise in the maximum limiting pore size and almost a two-fold increase in the porosity and permeance was observed, whereas the mean pore size was constant. Apparently, changes in the membrane structure at pH = 11.5 were connected with polyvinylpyrrolidone (PVP) degradation and wash-out, whereas at lower pH and despite lower active chlorine concentration, this process was coupled with polysulfone (PSf) destruction and removal.

Modification of polysulfone ultrafiltration membranes using block copolymer Pluronic F127

The effect of the addition of triblock copolymer polyethylene glycol (PEG)–polypropylene glycol (PPG)–polyethylene glycol (PEG) (Pluronic F127) and polyethylene glycol (PEG-4000, Mn = 4000 g mol−1) to the polysulfone (PSF) casting solution on the membrane structure and performance was studied. The phase state, viscosity and turbidity of PSF solutions in N,N-dimethylacetamide (DMAc) with the addition of block copolymer Pluronic F127 were investigated. It was found that 18–22 wt.% PSF solutions in DMAc with Pluronic F127 content ≥ 5 wt.% feature a lower critical solution temperature (LCST). Membrane structure was investigated using scanning electron and atomic force microcopies. It was revealed that average pore size and pore amount on the surface of the membrane selective layer increase and pore size distribution becomes wider with an increase in Pluronic F127 content in the casting solution. It was found that the average surface roughness parameters of the membrane selective layer for PSF/Pluronic F127 membranes significantly exceed those for PSF/PEG-4000 membranes. It was shown that the increase in the membrane flux and the decrease in polyvinylpyrrolidone (PVP K-30, Mn = 40,000 g mol−1) rejection are a result of the addition of both Pluronic F127 and PEG-4000 into the casting solution. It was revealed that PSF/Pluronic F127 membranes are characterized by higher pressure resistance in ultrafiltration process, a lower total flux decrease during ultrafiltration of bovine serum albumin solutions. The antifouling performance of PSF/Pluronic F127 membranes was found to exceed significantly the antifouling performance of PSF/PEG-4000 membranes.

Antifouling nanocellulose membranes: How subtle adjustment of surface charge lead to self-cleaning property

Membrane fouling is a major issue in wastewater treatment. In this study, a unique class of low fouling nanocellulose-enabled thin film nanofibrous composite (TFNC) ultrafiltration (UF) membranes was fabricated by coating of negatively charged TEMPO-oxidized cellulose nanofibers (CNF) on the porous electrospun polyacrylonitrile (ePAN) substrate. The surface charge density of the nanocellulose barrier layer was controlled by using CNF with different degree of oxidation (DO) and coating area density (AD, g/m2). The morphology, pore size distribution, hydrophilicity and zeta potential of these CNF-TFNC membranes were characterized, all of which exhibited excellent permeation flux (15-61 L m−2h−1 at 0.5 psi), high rejection ratio (>98%), and good antifouling tendency against bovine serum albumin (BSA). The practical antifouling and self-cleaning characteristics of CNF-TFNC membranes were further evaluated using biotreated municipal wastewater. The best performing membrane (CNF with 0.40 AD and 1.80 DO) achieved a near total flux recovery ratio (98 ± 2%) using simple hydraulic flushing. This could be attributed to the strong electrostatic repulsions between the CNF layer and foulants, both of which were negatively charged. Conversely, the commercial polyvinylidene difluoride (PVDF) UF membrane suffered severe fouling decay and very low flux recovery ratio (33 ± 3%). The results indicated the practicality of using charged CNF as a barrier layer for antifouling ultrafiltration membranes in wastewater treatment.

Hierarchically tunable structure of polystyrene-based microfiber membranes for separation and selective adsorption of oil-water

Separation and selective adsorption of oil–water are widely involved in the industrial and marine oil pollution removal. Among the advanced materials, microfiber membrane is a kind of desirable ones. Even so, the effective, low-cost and green fabrication as well as precise structure control of the microfiber and membrane still remains challenging. Herein, a facile approach was proposed to fabricate hierarchically structural membrane with excellent hydrophobicity-lipophilicity via one-step electrospinning. Cellulose acetate (CA), silica nanoparticles (SiO2 NPs) and hydrophobic silica nanoparticles (HSiO2 NPs) were added into polystyrene (PS) solution, which was electrospun into PS-based microfiber membrane with improved fiber porosity and surface roughness but reduced surface energy. The tunable inner-fiber porosity and inter-fiber pore size distribution of PS-CA microfiber membrane were optimized and adopted for oil–water separation with a flux as high as 11,460 L·m−2·h−1 for petroleum ether, while the PS-CA-HSiO2 microfiber membrane was ultra-hydrophobic and promising for oil adsorption. Moreover, five-layer structured membranes were developed by stacking the PS-CA and PS-CA-SiO2 (or PS-CA-HSiO2) microfiber sub-membranes alternately, to further enhance their oil adsorption performance (>160 g/g for high viscosity oils). The current study offered a strategy for the bottom-to-top design of microfiber composite membranes for separation and selective adsorption of oil–water.

Polyimide with half encapsulated silver nanoparticles grafted ceramic composite membrane: Enhanced silver stability and lasting anti‒biofouling performance

To take advantage of Ag NPs‒enhanced membrane properties, how to slow the release of silver ions from membrane surface is the key. In this study, to enhance silver stability, half encapsulated Ag NPs by a loosely polyimide (PI) were covalently grafted onto ceramic membrane (CM) via in-situ reduction during thermal imidization. Various techniques were used to characterize the micro‒structure, pore size distribution, surface tension, and Zeta potential of the polyimide‒silver nanoparticle‒ceramic composite membrane (PI–Ag/CM). The antibacterial activity was assessed with fluorescent imaging method. The stability of silver was evaluated by static immersion and dynamic filtration tests. The anti‒biofouling performance was evaluated using bovine serum albumin (BSA) and E. coli as the model foulants, respectively. The results showed that the Ag NPs with the size of 50–80 nm were uniformly embedded on the surface of the grafted PI, which endowed the PI‒Ag/CM with improved silver stability, antibacterial activity, and anti‒biofouling performance simultaneously. This study demonstrated a new pathway for the modification of CM‒based and other inorganic membranes with lasting anti‒biofouling performance in water treatment.

ZIF-67@Cellulose nanofiber hybrid membrane with controlled porosity for use as Li-ion battery separator

ZIF-67@CNF membranes were prepared and used as Li-ion battery separator to address the inhomogeneous pore distribution problem in CNF membranes. The hybrid membrane exhibited better cycling performance and rate capability. Zeolitic imidazolate framework-67 (ZIF-67) was synthesized on the surface of cellulose nanofibers (CNFs) in methonal to address the problems of unhomogeneous pore size and pore distribution of pure CNF membrane. A combination of Energy Dispersive X-Ray Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) patterns were used to determine the successful synthesis of ZIF-67@CNFs. The size of the ZIF-67 particles and pore size of the ZIF-67@CNF membrane were 50–200 nm and 150–350 nm, respectively. The prepared ZIF-67@CNF membrane exhibited excellent thermal stability, lower thermal shrinkage and high surface wettability. The discharge capacity retention of the Li-ion batteries (LIBs) made with ZIF-67@CNF, glass fiber (GF), CNF and commercial polymer membranes after 100th cycle at 0.5C rate were 88.41%, 86.22%, 83.27%, and 81.03%, respectively. LIBs with ZIF-67@CNF membrane exhibited a better rate capability than these with other membranes. No damage of porous structure or peel-off of ZIF-67 was observed in the SEM images of ZIF-67@CNF membrane after 100th cycle. The improved cycling performance, rate capability, and good electrochemical stability implied that ZIF-67@CNFs membrane can be considered as a good alternative LIB separator.

The Maximal Pore Size of Hydrophobic Microporous Membranes Does Not Fully Characterize the Resistance to Plasma Breakthrough of Membrane Devices for Extracorporeal Blood Oxygenation.

Extracorporeal membrane oxygenation (ECMO) in blood-outside devices equipped with hydrophobic membranes has become routine treatment of respiratory or cardiac failure. In spite of membrane hydrophobicity, significant amounts of plasma water may form in the gas compartment during treatment, an event termed plasma water breakthrough. When this occurs, plasma water occludes some gas pathways and ultimately cripples the oxygenator gas exchange capacity requiring its substitution. This causes patient hemodilution and increases the activation of the patient's immune system. On these grounds, the resistance to plasma water breakthrough is regarded as an important feature of ECMO devices. Many possible events may explain the occurrence of plasma breakthrough. In spite of this, the resistance to plasma breakthrough of ECMO devices is commercially characterized only with respect to the membrane maximal pore size, evaluated by the bubble pressure method or by SEM analysis of membrane surfaces. The discrepancy between the complexity of the events causing plasma breakthrough in ECMO devices (hence determining their resistance to plasma breakthrough), and that claimed commercially has caused legal suits on the occasion of the purchase of large stocks of ECMO devices by large hospitals or regional institutions. The main aim of this study was to identify some factors that contribute to determining the resistance to plasma breakthrough of ECMO devices, as a means to minimize litigations triggered by an improper definition of the requirements of a clinically efficient ECMO device. The results obtained show that: membrane resistance to breakthrough should be related to the size of the pores inside the membrane wall rather than at its surface; membranes with similar nominal maximal pore size may exhibit pores with significantly different size distribution; membrane pore size distribution rather than the maximal pore size determines membrane resistance to breakthrough; the presence of surfactants in the patient's blood (e.g., lipids, alcohol, etc.) may significantly modify the intrinsic membrane resistance to breakthrough, more so the higher the surfactant concentration. We conclude that the requirements of ECMO devices in terms of resistance to plasma breakthrough ought to account for all these factors and not rely only on membrane maximal pore size.

The Method and Analysis of Pore Size Distribution of Gas Separation Membrane by Gas Adsorption Equipment

In the membrane industrial field, from improving the quality of filtration for water treatment, separation technology of medical field, performance improvement of the electrode and separator of the battery, and dust filter, the pore size distribution is very important to maintain its quality. In recent years, research and development of gas separation membrane has been actively researched. For the analysis of ultra–micro pores of Angstrom order, Anton–Paar can offer a more accurate pore size distribution by new analysis technology NLDFT and QSDFT that simulates the behavior of fluid in the pores. The pore size analysis technology and our product line–up that are related to the membrane are introduced in this Journal.

The preparation and characterization of buckypaper made from carbon nanotubes impregnated with chitosan

AbstractBiopolymer chitosan was incorporated into a thin multiwalled carbon nanotube membrane (MWNT buckypaper) via filtration and soaking in 0.1% (w/v) of low‐molecular‐weight (MW) chitosan. The properties of the buckypaper membrane before and after annealing and after soaking were characterized by measurement of their electrical conductivities (19 ± 2 to 42 ± 2 S/cm), contact angles (31 ± 4° to 71 ± 4°), and mechanical properties (tensile strength, small‐ranging between 1.4 ± 0.1 and 4.2 ± 0.7 MPa; Young's modulus: 85 ± 4 to 443 ± 20 MPa). Moreover, the morphological properties, surface area, and permeability toward water of these buckypaper membranes were characterized and compared with corresponding carbon nanotube membranes prepared with Triton X‐100 (Trix) as the surfactant. Scanning electron microscopic (SEM) images and Brunauer, Emmett, and Teller (BET) data of MWNT‐annealing buckypaper membranes revealed that the diameters of their surface pores were significantly higher than that of the corresponding buckypaper membranes soaked in chitosan solution. The solution of chitosan incorporated inside the porous structure of the annealed MWNT membrane led to a significantly reduced surface area and pore size distribution of the composite membrane, revealing that this could be a useful method for desalination.

Preparation of defect free ceramic/Ti composite membranes by surface modification and in situ oxidation

Al2O3 ceramic powder was applied to modify the large pores defects on the surface of the porous metal Ti support, in situ oxidation method was a convenient method to prepare defect free ceramic/Ti composite membranes on this basis. In situ oxidation conditions experimental results show that the best condition for preparing the TiO2-Al2O3/Ti composite membrane is under 800 °C for 2 h, and the microstructure and pore sizes of the TiO2-Al2O3/Ti composite membranes are affected obviously. The thickness and composition of the TiO2/Ti composite membranes are determined by SEM and XRD completely. The pore size distribution of the composite membrane is measured by bubble pressure method, the most probable aperture is about 3.12 µm, while the average pore size of defect free TiO2-Al2O3/Ti is about 3.23 µm. After ultrasonic treatment, the slight weight change of membranes reveals no observable change, which indicates that TiO2-Al2O3/Ti composite membranes maintain a good stability.

Pervaporation membrane based on laterite zeolite-geopolymer for ethanol-water separation

In recent years, the worldwide production of ethanol as a liquid biofuel has reached 27 billion gallons per year. The United States and Brazil are the main producers of ethanol, which account for 58% and 27% of total production, respectively. Ethanol has been known as a leading biofuel and as an additive to gasoline. In the USA, ethanol was produced from corn, from sugarcane in Brazil, and grains in Europe. The price of corn, sugarcane, grains and crude oil (gasoline) have a direct impact on the price of ethanol. The most common purification technique utilized in the ethanol industry is rectification followed by azeotropic distillation. This method is energy consume and its separation capacity is inadequate. Pervaporation system with inorganic membrane has been proposed as a new method for ethanol purification. The main objective of this research is to produce and characterize the performance of inorganic membrane made from a zeolite-geopolymer for pervaporation of ethanol-water separation. Zeolite was produced through geopolymerisation route using laterite as raw material. The aluminous iron type of laterite was dehydroxylated at 750 °C for 4 h to enhance its reactivity in a high alkali environment. The elemental compositions of laterite were examined by using x-ray fluorescence (XRF). The structure, phase and chemical compositions of zeolite-geopolymer were measured by using the x-ray diffraction (XRD) technique. The microstructure of the resulting membrane was investigated by using scanning electron microscopy (SEM). Liquid N2 absorption based on the Brunauer-Emmett-Teller (BET) method was used to determine the pore size distribution of the zeolite-geopolymer membrane. The pervaporation experiment was performed by using two membranes having different compositions (designated as K1 and K2) at temperature 50 °C and 70 °C. The measurement results showed that there are two types of zeolites produced namely sodalite and sodium silicate hexahydrate. The crystalline level of both zeolites is very high and regular in shape based on SEM examination. BET measurements showed that the pore size of K1 ranging from 15 to 900 Å and K2 ranging from 15 to 2000 Å. The results of pervaporation experiments showed that the selectivity of both membranes was very low due to high permeation flux. It is proposed that zeolite-geopolymer membranes should be coated with hydrophobic materials to reduce the hydrophilic properties of geopolymer and hence become more feasible for ethanol purification through pervaporation system.

How Molecular Weight Cut-Offs and Physicochemical Properties of Polyether Sulfone Membranes Affect Peptide Migration and Selectivity during Electrodialysis with Filtration Membranes.

Filtration membranes (FMs) are an integral part of electrodialysis with filtration membranes (EDFM), a green and promising technology for bioactive peptide fractionation. Therefore, it is paramount to understand how physicochemical properties of FMs impact global and selective peptide migration to anionic (A−RC) and cationic (C+RC) peptide recovery compartments during their simultaneous separation by EDFM. In this context, six polyether sulfone (PES) membranes with molecular weight cut-offs (MWCO) of 5, 10, 20, 50, 100 and 300 kDa were characterized and used during EDFM to separate peptides from a complex whey protein hydrolysate. Surface charge, roughness, thickness and surface/pores nature of studied PES membranes were similar with small differences in conductivity, porosity and pore size distribution. Interestingly, global peptides migration to both recovery compartments increased linearly as a function of MWCO. However, peptide selectivity changed according to the recovery compartments and/or the peptide’s charge and MW with an increase in MWCO of FMs. Indeed, in A−RC, the relative abundance (RA) of peptides having low negative charge and MW (IDALNENK and VLVLDTDYK) decreased (45% to 19%) with an increase in MWCO, while the opposite for peptides having high negative charge and MW (TPEVDDEALEK, TPEVDDEALEKFDK & VYVEELKPTPEGDLEILLQK) (increased from 16% to 43%). Concurrently, in C+RC, regardless of MWCO used, the highest RA was observed for peptides having low positive charge and MW (IPAVFK & ALPMHIR). It was the first time that the significant impact of charge, MWCO and pore size distribution of PES membranes on a wide range of MWCO was demonstrated on EDFM performances.

Facile pore size tuning and characterization of nanoporous ceramic membranes for the purification of polysaccharide

Developing nanoporous ceramic membranes with tunable pore structure offers a new paradigm to the precise separation and purification of functional polysaccharides. Here, a facile in-situ chemical deposition method was applied to obtain nanoporous ZrO2 membranes with controllable pore size. A modified rejection curve method based on Poiseuille flow, Ferry's equation, and log-normal distribution was proposed to calculate pore size distribution of membrane. The results showed that with the increase of precursor content from 0 to 20 wt%, the geometric mean diameter of ceramic membranes decreased from 5.9 nm to 3.1 nm, corresponding to a significant decrease of molecular weight cut-off from 15.0 kDa to 3.3 kDa. Still, the pure water permeability was maintained at a high level of about 42 L m−2 h−1·bar−1. Meanwhile, the geometric standard deviation decreased from 1.20 to 1.16, indicating a narrower pore size distribution. The obtained nanoporous ZrO2 membrane performed a high rejection of dextran, while the fructose can be effectively and efficiently separated with a separation factor as high as 11.5, therefore enlarging our choices removing fructose from dextran.

Construction of high selectivity and antifouling nanofiltration membrane via incorporating macrocyclic molecules into active layer

We demonstrated the fabrication of a loose, hydrophilic and antibacterial nanofiltration (NF) membrane with high mono/divalent salt selectivity and antifouling ability. Macrocyclic molecule, primary amination Noria (PANoria), was synthesized firstly. Then the PANoria was taken as a novel aqueous phase monomer alone for thin film composite (TFC) membrane preparation via interfacial polymerization (IP) with trimesoyl chloride (TMC). Consequently, the well-defined pore structure, hydrophilic and antibacterial groups of PANoria could be effectively introduced into active layer of NF membranes. The hydrophilicity, zeta potential and pore size distribution of membranes could be altered by regulating the PANoria concentration or IP reaction time. When the PANoria concentration was 2.0 wt% and IP reaction time was 20 min, the PANoria membranes exhibited outstanding NaCl/Na2SO4 selectivity and the water permeance was 14.5 ± 0.5 L m−2 h−1 bar−1. Furthermore, the flux recovery ratio was more than 95% in the BSA/HA filtration test and the E.coli bacteria killing ratio was more than 92% in the bacteria contact experiment. Therefore, this work provided a viable strategy for fabricating NF membrane with high selectivity and outstanding antifouling ability.

A facile and environmental-friendly strategy for preparation of poly (tetrafluoroethylene-co-hexafluoropropylene) hollow fiber membrane and its membrane emulsification performance

Membrane technology as a highly efficient and powerful tool has been widely used in many industrial still faces toxic organic solvents issues. We developed a facile, efficient and environmental-friendly approach to implement poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) hollow fiber membrane using melt-spinning technique without any solvent and diluent involved in membrane preparation process. In particular, the compound pore-forming agents including polyethylene oxide (PEO) and calcium chloride (CaCl2) were completely water-soluble and obtained by ball milling blending which presented favorable environmental profiles. A series of characterizations were conducted regarding the morphologies, pore size distribution, porosity and hydrophobicity of the prepared membranes. Also, given the advantages of both oleophilicity and hydrophobicity, narrow pore size distribution as well as inherent thermal and solvent resistant, the prepared FEP membranes were used in membrane emulsification system for the first time. The results showed that the FEP membranes with mean pore size of 0.461 μm showed good performance in director membrane emulsification application by reason of its suitable pore size distribution and stable hydrophobic surface of FEP membranes. The obtained emulsion had narrow droplet size distribution and high stability. So these promising results demonstrate that the technique developed in this study is potentially applicable in membrane emulsification process.

Dilute solvent welding: A quick and scalable approach for enhancing the mechanical properties and narrowing the pore size distribution of electrospun nanofibrous membrane

Major limitations to the practical use of nanofibrous membranes in water filtration are their weak mechanical properties and wide pore size distribution. This study describes a quick and scalable method to improve the mechanical properties and narrow the pore size distribution of nanofibrous membranes by welding the nanofibers at their junction points. The welding process involves a simple dilute solvent spraying step followed by heating, requiring only a few minutes. The polymer's solvent was diluted with a non-solvent to avoid excessive dissolution of the nanofibers. With that, the degree of welding can be controlled by the volume fraction of solvent, the heating temperature and heating temperature. Dilute solvent welding enhanced the mechanical properties of the nanofibrous membrane while slightly changed the fiber crystallinity and fiber size distribution. Furthermore, the membrane pore size distribution narrowed with welding while high porosity (~80%) was retained. In membrane distillation (MD) experiments, the welded nanofibrous membrane exhibited more robust MD performance than the pristine nanofibrous membrane with only slight decreases of vapor flux. This technique can be applied universally to treat both nanofibrous flat sheet and tubular membranes made from soluble polymers with their corresponding diluted solvents.

Fabrication of PES/PVP Water Filtration Membranes Using Cyrene®, a Safer Bio-Based Polar Aprotic Solvent

A more sustainable dialysis and water filtration membrane has been developed, by using the new, safer, bio-based solvent Cyrene® in place of N-methyl pyrrolidinone (NMP). The effects of solvent choice, solvent evaporation time, the temperature of casting gel, and coagulation bath together with the additive concentration on porosity and pore size distribution were studied. The results, combined with infrared spectra, SEM images, porosity results, water contact angle (WCA), and water permeation, confirm that Cyrene® is better media to produce polyethersulfone (PES) membranes. New methods, Mercury Intrusion Porosimetry (MIP) and NMR-based pore structure model, were applied to estimate the porosity and pore size distribution of the new membranes produced for the first time with Cyrene® and PVP as additive. Hansen Solubility Parameters in Practice (HSPiP) was used to predict polymer-solvent interactions. The use of Cyrene® resulted in reduced polyvinylpyrrolidone (PVP) loading than required when using NMP and gave materials with larger pores and overall porosity. Two different conditions of casting gel were applied in this study: a hot (70°C) and cold gel (17°C) were cast to obtain membranes with different morphologies and water filtration behaviours.