Membrane Wetting Research Articles

Preparation of 4-methyl-1-pentene membranes via non-solvent induced phase separation (NIPS)

Poly 4-methyl-1-pentene (PMP) membranes are often used in gas separation and membrane oxygenators in extracorporeal membrane oxygenation (ECMO). Considering the high energy consumption of thermally induced phase separation (TIPS) method, in this article, PMP membranes were prepared via non-solvent induced phase separation (NIPS) under wide preparation conditions. The phase separation behavior of PMP/cyclohexane/alcohol system, effects of non-solvent additive in casting solution, evaporation temperature (0 ℃ − 60 ℃), evaporation time and coagulation temperature (-10 ℃ − 20 ℃) on the membrane structure and air permeability of PMP membranes were studied. The results showed that, the addition of appropriate amount of non-solvent to the casting solution effectively improved the air permeability. The evaporation step at low temperature led to robust membranes with high air permeability. Extending the evaporation time of the wet membranes increased the mechanical strength and air permeability. The lower coagulation temperature also contributed to a higher air permeability. The prepared PMP membranes showed great promises for applications in membrane oxygenators.

Performance and implications of forward osmosis-membrane distillation hybrid system for simultaneous treatment of different real produced water streams

This study investigates the simultaneous treatment of different real produced water streams using forward osmosis-membrane distillation (FO-MD) hybrid system. The water–oil separator outlet (WO) was used simultaneously as FO draw solution (DS) and MD feed solution (FS). The FO process generated stable average fluxes of 13.6 L/m2/h and 15.8 L/m2/h with desalter effluent (DE) and wash water (WW) as FO feed streams, while MD produced 13.2 L/m2/h and 11 L/m2/h, respectively. Monovalent ions induced internal concentration polarization and CaSiO3 colloidal scaling on the support layer reduced the FO flux. Further FO flux reduction was caused by CaSO4 and NaCl crystals on the active layer. Moreover, CaSO4 created partial pore covering while oil and grease depicted pore clogging of the MD membrane, which decreased the MD flux. Volatile fatty acids and organic nano pollutants reached MD permeate and FO FS. Humic acid scaling was fully recovered by ethylenediaminetetraacetic acid by masking calcium ions and reducing the pH. No membrane wetting was observed in the system. No bacteria were found in real streams as analyzed with Epifluorescence microscopy, eliminating the potential of microbial fouling. The hybrid system showed > 93 % removal of oil, inorganics and organics, making the permeate quality excellent for re-injection or industrial reuse. The FS streams were concentrated by 77–84 % resulting in smaller disposal volumes. No utilization of chemicals and water makes this hybrid concept practical and sustainable. The findings of this study can serve as design criteria for future onsite pilot plant applications.

Wetting of photoplasmonic PVDF/silver membranes in photothermal membrane distillation: Identification of wetting mechanisms and comparison of wetting dynamics

Photothermal membrane distillation (PMD) is a promising configuration of membrane distillation (MD), which can overcome the temperature polarization problem and allows using solar thermal energy. However, the effect on wetting of the incorporation of plasmonic nanoparticles (NPs) into a membrane is still unknown. This paper aims supporting the development of photoplasmonic membranes for PMD, by studying their wetting in vacuum MD operation, thanks to two methods recently developed in our group: the ex-situ detection of dissolved tracer intrusion (DDTI) and an in-operando optical method. Different composite membranes with Ag-NPs included in PVDF were elaborated by phase-inversion for checking if the proportion of NPs influences membrane wetting. This study demonstrates the importance of considering wetting in the earlier stages of the development of new membranes. Indeed, whatever the NP load, at global scale partial wetting was detected and the pore wetting ratio increased with the NP load, whereas the PVDF membrane remained un-wetted. Wetting dynamics was highly impacted by the presence of NPs and wetting occurred faster with increasing NP load, thus reducing the duration of the MD operation for the highest load. For limiting short-term wetting, a limited proportion of Ag-NPs (≤25 %) is recommended to membrane manufacturers or developers.

Comparison of omniphobic membranes and Janus membranes with a dense hydrophilic surface layer for robust membrane distillation

Membrane wetting, fouling, and scaling are three prominent challenges that limit membrane distillation (MD) applications. To overcome these challenges, novel MD membranes including omniphobic membranes and Janus membranes with a dense hydrophilic surface layer have been developed. In this study, we fabricated an omniphobic membrane and a Janus membrane composed of a dense polyvinyl alcohol (PVA) surface layer and a polyvinylidene fluoride (PVDF) substrate. The two membranes have been compared in MD experiments with different feeds. Furthermore, the working mechanisms of the two membranes have been elucidated. As a result, neither the omniphobic MD membrane nor the Janus MD membrane can resolve all three challenges at the same time. Specifically, both the omniphobic MD membrane and Janus MD membrane can resist wetting but via different working mechanisms. From breakthrough pressure (BP) determinations with an ethanol-water mixture (i.e., a low-surface-tension liquid), the omniphobic MD membrane resists wetting as its LEP (82.0 ± 9.2 kPa) is larger than the transmembrane pressure in the MD operation, while the Janus MD membrane resists wetting because the huge capillary pressure (550 ± 50 kPa) in the dense hydrophilic surface layer retains the wetting solution. The omniphobic MD membrane is prone to oil fouling because of the strong underwater hydrophobic attraction between the membrane surface and the mineral oil droplets, while the Janus MD membrane can substantially mitigate fouling due to the lack of attraction between the mineral oil droplets and the hydrophilic membrane surface. The omniphobic MD membrane exhibits outstanding scaling resistance because minerals can hardly precipitate and/or crystalize on the membrane surface, while the Janus MD membrane was susceptible to scaling due to the precipitation and/or crystallization of minerals inside the hydrophilic surface layer. Therefore, the selection of MD membranes should depend on the feed constituents. Overall, our study provides important guidelines for the future development of robust MD membranes.

Reducing the Wettability of Porous Polymeric Membranes in Membrane Contactors: An Overview on the Methods and Their Effective Parameters

Reducing the Wettability of Porous Polymeric Membranes in Membrane Contactors: An Overview on the Methods and Their Effective Parameters

Tannic acid-mediated interfacial layer-by-layer self-assembly of nanofiltration membranes for high-efficient dye separation

Layer-by-layer (LBL) self-assembly is believed as a simple and versatile strategy to fabricate wastewater purification membranes, whose separation efficiency is highly dependent on the stability of the self-assembly membranes. In this work, a composite nanofiltration membrane was prepared using carboxyl-functionalized poly (arylene ether nitrile) (CPEN) as the substrate, on which the cross-linked nanostructures derived from tannic acid (TA), metal ions, and bovine serum albumin (BSA) were immobilized via the layer-by-layer self-assembly. Particularly, several interfacial interactions, including hydrogen bonding, metal ions coordination, and hydrophobic interaction, were explored to manipulate the surface structures, wettability, and pore morphology of composite membranes. Consequently, the optimized membrane exhibited a low pressure (0.09 MPa) driven dye permeability of 52.04 L m−2 h−1 bar−1, as well as a high rejection rate for Congo Red (CR ∼ 99.9%) and Methylene Blue (MLB ∼ 99.8%), respectively. Thanks to the stable separation performance, structural stability, and dye removal, the protocol reveals in the current work would open new ways for the fabrication of water purification membranes.

Developed applicability of a bacterial cellulose matrix as a gelling substitute for plant tissue culture media

Bacterial cellulose (BC) is a natural biodegradable, eco-friendly fiber, lying within the nanoscale range. It is reputable for its various physical and chemical qualities, like high hydrophilicity, immense crystallinity, ease of sterility, being toxin-free, and extremely pure. Adding to its wide applicability in different fields, this study evaluated the applicability of a developed gelling substitute for plant tissue culture media. The BC matrix was characterized under the acronym PLATIBACGEL (PLAnt TIssue Culture BActerial Cellulose GEL), formed by Komagataeibacter hansenii AS.5, preisolated from rotten apple waste. Scanning electron microscope, Fourier-transform infrared, X-ray diffractometer, and tensile strength analyses confirmed the formation of purified, porous, and heterogeneous densely packed multiple network polymers possessing cellulose properties. The water holding capacity (WHC) values of wet and dried BC membranes were 9179% and 226.9%, respectively, and the water absorption rate (WAR) of dry BC membranes was higher than that of wet membranes. Using BC as a tissue culture gelling agent, six genotypes from tomato and wheat seeds were cultured in vitro, for guaranteeing explant genetic diversity, over seven treatments. Treatment 5, included PLATIBACGEL as the main constituent, improved and sustained all in vitro seed germination, root penetration, and plant support. Likewise, repeated tomato micropropagation subcultures were successful. Results demonstrated applying PLATIBACGEL as a promising, reusable, cheap, and reliable alternative plant micropropagation media gelling agent. Wherefore, plant cellular developers and tissue-culturists can utilize bio-polymers like BC for better understanding plant cell response to different in vitro culturing conditions, with expected beneficial returns on gelling agents industry and markets as well.Graphical abstract

Improvement of membrane hydrophobicity by one-step electrospraying for water recovery from textile dye solutions by membrane distillation

Membrane distillation is an upcoming technology for water recovery from industrial effluents. However, inherent operational phenomena, such as membrane wetting, compromise its functioning with complex solutions. Membrane modification can be a key to mitigating membrane gaps. Herein, a polypropylene membrane was physically modified via one-step electrospraying using a polymeric blend of polydimethylsiloxane and polyvinylidene fluoride. The main goal was to improve membrane hydrophobicity and enhance DCMD performance with four dye classes (Reactive, Disperse, Direct, and Acid). Polymer reticulation and polymer concentration in dope solution were studied, affecting membrane hydrophobicity. The modification improved the water contact angle by 20% after 90 min under the spray containing 2% PVDF and 6% PDMS-cured. The modified PP membrane reached contact angles of 148.38 ± 2.36° and 151.5 ± 6.18° for direct and acid dyes, respectively. The modified layer increased the membrane thickness by 3 µm without significant porosity alterations, amplifying the pH range where membranes assume negative charges. Stable permeate fluxes on a DCMD operation were reached, varying between 29.7 and 44.85 L m−2 h−1, and the rejection rate increased to 6%. The modification enhanced the membrane performance with textile dye solutions, enabling MD operation to water reclamation from textile effluents.

LIB 습식분리막 열손상에 따른 발화위험성에 관한 연구

LIB-related fires are continuously increasing due to the increase in personal transportation means and the commercialization of electric vehicles. Among the LIB components, the separation membrane is the most important key material for stability, and there is a problem in that it is lost at the scene of a fire and cannot confirm its shape. Accordingly, fire statistics and cases were analyzed, and the experimental outline was established through theoretical consideration of the wet separation membrane, which is the most used as a personal transportation means. As for the experimental method, we conducted a study on the shrinkage rate and tensile strength of the wet separator according to thermal damage for each temperature change with five experimental variables using the wet separator, which plays an important role in the stability of the battery components, as a sample. Through this, the change in shrinkage rate and mechanical properties of the wet separator were derived to understand the fire of lithium-ion batteries caused by damage to the wet separator and to contribute to the fire investigation analysis technique.

Development of highly permeable self-standing nanocomposite sulfonated poly ether ketone membrane using covalent organic frameworks

This study developed a new symmetric and ultrathin membrane by incorporating Schiff base network-1 (SNW-1), which are covalent organic framework (COF) nanoparticles, as fillers in the sulfonated poly ether ketone (SPEK) matrix to improve forward osmosis (FO) performance. The amine-rich and porous SNW-1 nanoparticles enhanced the surface wettability of the SPEK membranes and offered additional passages for the water molecules' transport, which assisted in the elevation of membrane water flux. The modified membrane loaded with 20 wt% SNW-1 (COF-20) exhibited the best performance with a significantly higher water flux (28.5 L m−2 h−1) and lower specific reverse solute flux (SRSF, 0.05 g L−1) than that of the unmodified SPEK (COF-0) membrane (water flux of 12 L m−2 h−1 and SRSF of 0.16 g L−1) when experimented with deionized water and 1 M Na2SO4 as feed and draw solutions, respectively. The impressive FO performances of nanocomposite SPEK membranes suggest that SNW-1 nanoparticles could be used as fillers for improving the SPEK membrane's performance in the FO application.

Durable superhydrophobic polyvinylidene fluoride membranes via facile spray-coating for effective membrane distillation

Membrane wetting and fouling substantially limits application and deployment of membrane distillation process. Designing high-performance superhydrophobic membranes offers an effective solution to solve the challenge. In this work, a highly durable superhydrophobic surface (water contact angle of 170.8 ± 1.3°) was constructed via a facile and rapid spray-coating of extremely hydrophobic SiO2 nanoparticles onto a porous polyvinylidene fluoride (PVDF) substrate for membrane distillation. The superhydrophobic membrane coated by fluorinated SiO2 nanoparticles exhibited a superior physicochemical stability in a wide range of extreme environments (i.e., NaOH, HCl, hot water, rust water, humic acid solution, ultrasonication, and high-speed water scouring). During 8-h continuous membrane distillation desalination experiment, the coated superhydrophobic membrane experienced a consistently stable water vapor flux (ca. 19.1 kg·m−2·h−1) and desalination efficiency (99.99 %). Additionally, such a stable superhydrophobicity endowed the spray-coated PVDF membrane to overcome membrane wetting and fouling during membrane distillation of highly saline solutions containing foulants (i.e., humic acid and rust). Results reported in this study provides a useful concept and strategy in facile construction of robust superhydrophobic membranes via spray-coating for effective membrane distillation.

Tailoring pore size and interface of superhydrophobic nanofibrous membrane for robust scaling resistance and flux enhancement in membrane distillation

Electrospun nanofibrous membrane with ultrafine nanofibers, high porosity, and interconnected pores has attracted significant attention in high-flux membrane distillation (MD). However, the comparatively large pore size and low liquid entry pressure (LEP) of nanofibrous membranes often result in severe membrane scaling and wetting. In this work, superhydrophobic nanofibrous membranes with tailored membrane pore size and interface were successfully fabricated via sequential electrospinning and electrospraying approaches. Results revealed that the decreased membrane pore size and increased interface evaporation area could synchronously mitigate membrane scaling and improve water flux. Besides, the water recovery of the membrane could be further increased with the aid of antiscalant, e.g., polymer polyacrylic acid, toward treating a nearly saturated gypsum solution. The excellent concentration performance was attributed to the cooperation of the antiscalant that inhibits the nuclei formation and the engineered surface that reduced the adhesion between the membrane interface and gypsum crystals. Notably, the resultant membrane also showed a high initial flux of ∼40 L m−2 h−1 and high salts rejection efficiency of ∼100% in a continuous concentration process for over 100 h. Our study provides a promising methodology for preparing novel membrane surfaces to treat hypersaline wastewaters meeting the minimal/zero liquid charge target.

High-Efficiency Water Recovery from Urine by Vacuum Membrane Distillation for Space Applications: Water Quality Improvement and Operation Stability.

Water recovery by membrane distillation (MD) is an attractive alternative to existing urine treatment systems because it could improve the water recovery rate and reliability in space missions. However, there are few studies of urine MD, particularly on the removal of the remaining contaminants from distillate water and the assessment of its long-term performance. In this study, the influences of various operation parameters on distillate water quality and operation stability were investigated in batch mode. The low pH of feedstock reduced the conductivity and total ammonium nitrogen (TAN) in distillate water because the low pH promoted the ionization of ammonia to ammonium ions. However, the low pH also facilitated the formation of free chlorine hydride, which resulted in the minor deterioration of the conductivity in the distillate due to the increasing volatility of chlorine hydride in the feedstock. Thirty batches of vacuum membrane distillation (VMD) experiments demonstrated that the permeate flux and the distillate water quality slightly decreased due to the small range of membrane wetting but still maintained an over 94.2% and 95.8% removal efficiency of the total organic carbon (TOC) and TAN, and the conductivity was <125 μs cm−1 in the distillate water after 30 test batches. VMD is a feasible option for urine treatment in space missions.

Integration of catalytic wet peroxidation and membrane distillation processes for olive mill wastewater treatment and water recovery

The degradation of organic matter present in olive mill wastewater (OMW) and the recovery of water were studied by the integration of catalytic wet peroxidation (CWPO) and direct contact membrane distillation (DCMD) for the first time. The oxidation step was performed in a fixed–bed reactor (FBR) working in continuous mode (pH0 = 4.0 ± 0.2, 60 °C, Q = 0.75 mL/min, [H2O2]/[COD]feed = 2.3 ± 0.1 gH2O2/gO2). Samples of OMW diluted by 5–and 7.5–fold were used (OMW–5× and OMW–7.5×, respectively), corresponding to inlet chemical oxygen demand (COD) values of 3562 ± 68 and 2335 ± 54 mg/L, total phenolic content (TPh)of177 ± 17 and 143 ± 7 mgGAeq/L, and total organic carbon (TOC) of 1258 ± 63 and 842 ± 45 mg/L, respectively. The FBR was loaded with 2.0 g of a Fe–activated carbon derived–catalyst, prepared by using olive stones as the precursor, in line with a circular economy model approach. The catalyst was selected based on the activity and stability towards polyphenolic synthetic solutions shown in previous works of the team, while actual OMW samples were used in this work. CWPO–treated samples of OMW allowed the operation of the DCMD unit at higher fluxes than with the analogous untreated ones, also showing higher rejections of organic matter from the feed solution upon DCMD, highlighting the beneficial effect of this novel configuration. Using a pre-treated sample of OMW–7.5× as feed solution (Q = 100 mL/min, Tpermeate≈18 °C, Tfeed≈66 °C), the produced permeate water stream presented several parameters well–below the legislated thresholds required for direct discharge for crops irrigation, including total suspended solids (TSS < 10 mg/L), TPh (<0.01 mgGAeq/L), biochemical oxygen demand (BOD5 < 40 mg/L), and dissolved Fe (<0.06 mg/L). Moreover, the resulting concentrated OMW–retentate streams could be recirculated to the FBR and maintain the same removal efficiencies obtained previously, despite the increased initial organic loadings of the retentate after DCMD.

UiO-66-NH2/PVA composite Janus membrane with a dense hydrophilic surface layer for strong resistance to fouling and wettability in membrane distillation

Polytetrafluoroethylene (PTFE) hydrophobic membranes used in direct contact membrane distillation (DCMD) processes were prone to fouling and wetting by oil and surfactants, which hampered their broad industrial application. In this work, a new Janus composite membrane was developed by modifying UiO-66-NH2 with polyvinyl alcohol (PVA) as a cross-linking agent and immobilizing the modified UiO-66-NH2 on the PTFE membrane by vacuum filtration. By tuning the ratio of PVA to MOF, an optimally proportioned Janus membrane was obtained, and its performance was tested in DCMD experiments through the use of a sodium chloride feed solution containing hexadecane and sodium dodecyl sulfate. The top layer of this Janus membrane exhibited underwater oleophobicity (130.1 ± 0.96°) and hydrophilicity in the air (54.0 ± 0.92°), while the bottom layer is hydrophobic (132.3 ± 0.97°). Compared to the pristine PTFE membrane, the modified Janus membrane demonstrated promising resistance to both membrane fouling and wetting of oils and surfactants. The desalination rate of 99.99% was still achieved within 24 h with the conductivity remaining lower than 10 μS/cm and the flux maintained at 21.3 L/(m2·h). As a result, the Janus composite membrane developed in this study was shown to be a prospective alternative for treating wastewater containing oily substances and surfactants in a resourceful manner.

Preparation and Modification of PVDF Membrane and Study on Its Anti-Fouling and Anti-Wetting Properties

Membrane distillation (MD) has unique advantages in the treatment of high-salt wastewater because it can make full use of low-grade heat sources. The high salinity mine water in western mining areas of China is rich in Ca2+, Mg2+, SO42− and HCO3−. In the MD process, the inorganic substances in the feed will cause membrane fouling. At the same time, low surface tension organic substances which could be introduced in the mining process will cause irreversible membrane wetting. To improve the anti-fouling and anti-wetting properties of the membrane, the PVDF omniphobic membrane in this paper was prepared by electrospinning. The water contact angle (WCA) can reach 153°. Direct contact membrane distillation (DCMD) was then used for treating high-salinity mine water. The results show that, compared with the unmodified membranes, the flux reduction rate of the omniphobic membrane was reduced by 34% in 20 h, showing good anti-fouling property. More importantly, the omniphobic membrane cannot be wetted easily by the feed containing 0.3 mmol/L SDS. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory was used to analyze the free energy of the interface interaction between the membrane and pollutants, aiming to show that the omniphobic membrane was more difficult to pollute. The result was consistent with the flux variation in the DCMD process, providing an effective basis for explaining the mechanism of membrane fouling and membrane wetting.

Confounding Effect of Wetting, Compaction, and Fouling in an Ultra-Low-Pressure Membrane Filtration: A Review.

Ultra-low-pressure membrane (ULPM) filtration has emerged as a promising decentralized water and wastewater treatment method. It has been proven effective in long-term filtration under stable flux without requiring physical or chemical cleaning, despite operating at considerably lower flux. The use of ultra-low pressure, often simply by hydrostatic force (often called gravity-driven membrane (GDM) filtration), makes it fall into the uncharted territory of common pressure-driven membrane filtration. The applied polymeric membrane is sensitive to compaction, wetting, and fouling. This paper reviews recent studies on membrane compaction, wetting, and fouling. The scope of this review includes studies on those phenomena in the ULPM and how they affect the overall performance of the system. The performance of GDM systems for water and wastewater treatment is also evaluated. Finally, perspectives on the future research direction of ULPM filtration are also detailed.

Study of Wettability of Polyethylene Membranes for Food Packaging

In this study, the wettability of PET membranes (prepared with different pore sizes) treated by UV irradiation, thermal annealing or doping with metal nanoparticles was investigated. The wettability was studied using the contact angle method based on the optical microscopy. The membranes were analyzed before and after pore etching, and after each applied treatment. It turned out that membranes with different pore sizes exhibit different wetting behavior. Of particular interest are membranes with 0.53 μm pores. When pristine, they show high hydrophobicity (a high contact angle), but after treatment (some of which can be considered as an accelerated aging), their wetting characteristics swap between a hydrophobic and hydrophilic state. Interactions between packaging material and food and the external environment through fine control of wettability could have a major impact on maintaining product quality.

Graphene-Coated PVDF Membranes: Effects of Multi-Scale Rough Structure on Membrane Distillation Performance.

Graphene-coated membranes for membrane distillation have been fabricated by using a wet-filtration approach. Graphene nanoplatelets have been deposited onto PVDF membrane surfaces. Morphology and physicochemical properties have been explored to evaluate the changes in the surface topography and related effects on the membrane performance in water desalination. The membranes have been tested in membrane distillation plants by using mixtures of sodium chloride and humic acid. The multi-scale rough structure of the surface has been envisaged to amplify the wetting and fouling resistance of the graphene-coated membranes so that a better flux and full salt rejection have been achieved in comparison with pristine PVDF. Total salt rejection and an increase of 77% in flux have been observed for coated membrane with optimized graphene content when worked with NaCl 0.6 M (DCMD, ΔT ≈ 24 °C) over a test period of 6 h. The experimental findings suggest these novel graphene-coated membranes as promising materials to develop functional membranes for high-performing water desalination.

Aquaporin-Inspired CPs/AAO Nanochannels for the Effective Detection of HCHO: Importance of a Hydrophilic/Hydrophobic Janus Device for High-Performance Sensing.

Probe reactivity has long been considered to play a key role in artificial nanochannel sensors, but systematic studies of membrane wettability on detection performance are currently lacking. Inspired by biological aquaporins, we developed an effective strategy to regulate the hydrophilic/hydrophobic balance by the controllable in situ assembly of coordination polymers (CPs) using BDC-NH2 on anodic aluminum oxide (AAO) nanochannels to promote HCHO detection. We found that the hydrophobic/hydrophilic balance in CP/AAO heterosomes plays significant roles in the effective detection of HCHO. The hydrophobic AAO barrier layer is necessary to support the confinement effect, while the hydrophilic CP surface is favorable for HCHO to access the channels and then condense with the responsive amine to generate a new imine. The optimized CP/AAO Janus device shows excellent performance in the quantitative analysis of HCHO over a wide range from 100 pM to 1 mM by monitoring the rectified ionic current.