Liquid Entry Pressure Of Water Research Articles

Engineered eco-friendly composite membranes with superhydrophobic/hydrophilic dual-layer for DCMD system

Considerable advancements have been made in the development of hydrophobic membranes for membrane distillation (MD). Nonetheless, the environmentally responsible disposal of these membranes poses a critical concern due to their synthetic composition. Herein, an eco-friendly dual-layered biopolymer-based membrane was fabricated for water desalination. The membrane was electrospun from two bio-polymeric layers. The top hydrophobic layer comprises polycaprolactone (PCL) and the bottom hydrophilic layer from cellulose acetate (CA). Additionally, silica nanoparticles (SiO2 NPs) were electrosprayed onto the top layer of the dual-layered PCL/CA membrane to enhance the hydrophobicity. The desalination performance of the modified PCL-SiO2/CA membrane was compared with the unmodified PCL/CA membrane using a direct contact membrane distillation (DCMD) unit. Results revealed that silica remarkably improves membrane hydrophobicity. The modified PCL-SiO2/CA membrane demonstrated a significant increase in water contact angle of 152.4° compared to 119° for the unmodified membrane. In addition, PCL-SiO2/CA membrane has a smaller average pore size of 0.23 ± 0.16 μm and an exceptional liquid entry pressure of water (LEPw), which is 3.8 times higher than that of PCL/CA membrane. Moreover, PCL-SiO2/CA membrane achieved a durable permeate flux of 15.6 kg/m2.h, while PCL/CA membrane showed unstable permeate flux decreasing approximately from 25 to 12 kg/m2.h over the DCMD test time. Furthermore, the modified PCL-SiO2/CA membrane achieved a high salt rejection value of 99.97% compared to a low value of 86.2% for the PCL/CA membrane after 24 h continuous DCMD operation. In conclusion, the proposed modified PCL-SiO2/CA dual-layer biopolymeric-based membrane has considerable potential to be used as an environmentally friendly membrane for the MD process.

High-performance electrospun polystyrene-based nanofiber membrane for efficient SO2 capture

It is essential to design a stable membrane material to solve the pollution produced by SO2 emissions. This study aims to fabricate polystyrene (PS) nanofiber membranes, which are applied for flue gas desulfurization. PS nanofiber membranes are fabricated via electrospinning with porous polypropylene (PP) membrane as the support and high hydrophobic PS as the main membrane material. The modified membranes are characterized by scanning electron microscopy, true color confocal microscopy and other analyticalmethods, and the effects of mixed solvent ratio and polymer concentration on the desulfurization performance and on the stability of PS nanofiber membranes are investigated. The results suggest that an optimum hydrophobicity of PS nanofiber membrane is obtained with a water contact angle of 145°, when the polymer concentration is 5 %. The average pore size of PS nanofiber membrane is 1.56 μm, and the liquid entry pressure of water (LEPw) is 0.26 bar and the roughness of membrane is 5.674 μm. The desulfurization performance of the PS nanofiber membrane is better than that of the PP membrane. The SO2 absorption flux of the modified membranes keeps at 7.2 × 10−4 to 7.6 × 10−4 mol·m−2·s−1 during 5 h operating, and SO2 removal efficiency is up to 50 %, which potentially makes contributions to air pollution reduction.

Enhanced permeability and stability of PVDF hollow fiber membrane in DCMD via heat-stretching treatment

Membrane distillation (MD) demonstrates excellent desalination application potential for high salt concentration wastewater. However, keeping the membrane flux and rejection high during long-term operation remains one of the critical challenges. In this work, a heat-stretching treatment method was proposed to improve the structure of polyvinylidene fluoride (PVDF) hollow fiber membrane and enhance its stability in the MD process. The membrane's pore size decreased after a heat-stretching treatment in water at 120 °C for 1 h. However, the liquid entry pressure of water (LEPw) value and membrane strength increased significantly, making it less prone to pore deformation during the drying or MD process and thus improving the membrane flux and stability in the MD process. The heat-stretching treatment made the PVDF chain arrangement more compact and oriented, avoiding shrinkage in the length direction. Besides stretching, the shrinkage of hollow fiber can be constricted by the combinedeffects of pore filling and stretching due to water or glycerol filling in the membrane pores, thus eliminating the capillary stress caused by liquid evaporation during the air-drying. Consequently, the heat-stretching treatment broke the trade-off between high permeate flux and high stability in the MD process.

Hydrophobic silica sand ceramic hollow fiber membrane for desalination via direct contact membrane distillation

A porous hollow fibre ceramic membrane derived from a low-cost natural material (silica sand) and fabricated by combine phase inversion and sintering technique followed by fluoroalkylsilane (FAS17) grafting to improve its hydrophobicity is reported in this study. Prior to the subjection of the silica sand ceramic hollow fibre membrane (SSCHFM) to a desalination performance test via direct contact membrane distillation (DCMD), characterization studies were performed on the SSCHFM before and after grafting using different characterization techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), 3-points bending, water liquid entry pressure (LEPw), and water contact angle measurement. Mercury porosimetry analysis (MIP) was also used to determine the pore size distribution and porosity of the SSCHFM. The grafting process caused an increasing of the contact angle from 0° to 142.5° ± 2.0, and LEPw value of (2.6 ± 0.4 bar) was achieved. AFM images showed an increment in the surface roughness of the grafted SSCHFM from 0.305 µm to 0.375 μm, with a slight decrease in the average pore size and porosity from 0.17 µm and 17% to 0.12 µm and 14.7% respectively. After the grafting process, the performance of the membrane in DCMD was evaluated on a salt solution for 32 h at different NaCl concentrations (8,16, 24, 32 and 40) g/L, feed flow rates and feed temperatures. The results showed a decrease in the permeate flux at increasing feed concentration, but the reverse was at higher feed flow rates and feed temperatures. The surface-modified membrane recorded a water flux value of 35 kg/m2.h and 100% salt rejection. The results indicate that the hydrophobic hollow fibre ceramic membranes derived from silica sand have significant potential to be developed for membrane distillation application in water purification and reclamation.

Double layer PVDF blends PVDF‐HFP membrane with modified ZnO nanoparticles for direct contact membrane distillation (DCMD)

AbstractIn this work, the double layer (DL) polyvinylidene fluoride (PVDF) blends polyvinylidene hexafluoropropylene (PVDF‐HFP) membrane is prepared via the double casting phase inversion (DCPI) method. The PVDF blended PVDF‐HFP incorporation with ZnO nanoparticles is cast on the top layer of the membrane. The morphology of the fabricated membrane displays two layers of the membrane with different morphology, where the top layer is dense and no macrovoid form. Furthermore, the water contact angle increase due to the increment of perfluorinated polymer content in the top layer, which is 147°. Besides, the liquid entry pressure of water (LEPw) is 0.76 bar with average pore size of the top surface is 0.24 μm, while the bottom surface is 8 μm. The porosity of the DL PVDF blends PVDF‐HFP membrane do not have significant changes compared to the single layer (SL) membrane, with 87%. A stable flux of 6.14 L/m2h was achieved over the 6 h of operation of direct contact membrane distillation (DCMD) lab‐scale unit. The DL membrane removes almost 99% salt.

A well-designed polystyrene/polycarbonate membrane for highly saline water desalination using DCMD process

A novel porous polycarbonate (PC) membrane was fabricated using ethanol as non-solvent deploying immersion-precipitation process. To further increase surface hydrophobicity, polystyrene (PS) microbeads were sprayed on PC support using an air-assisted electrospraying process. Due to the micro/nano roughness of the PS layer, the formed dual-layer PS/PC membrane possessed outstanding wetting resistance over the neat PC membrane. The water contact angle (WCA) of the neat PC and PS/PC membranes was measured as 95.2 and 155.1°, respectively. Liquid entry pressure of water represented a considerable enhancement of 84.6% compared to the neat membrane. Direct contact membrane distillation (DCMD) evaluation was performed using the fabricated and commercially available polytetrafluoroethylene (PTFE) membranes. Using concentrated saline water as feed (150 g/L), only PS reinforced PC (PS/PC) membrane showed nonwetting capability with stable DCMD performance during continuous long-term DCMD evaluation. Superhydrophobicity of PS/PC not only diminished pore wetting but also increased permeate flux considerably (45.9%↑) to produce high-quality permeate flux (˂4.6 μS/cm). Considering these attributes, using the low-cost PC polymer along with the high-productive air-assisted electrospraying process is a facile route to fabricate decent membranes for the membrane distillation (MD) process.

A study on the mechanism of pore formation through VIPS-NIPS technique for membrane fabrication

In this research, the pore formation mechanism of the membranes through the vapor-induced phase separation (VIPS) technique is studied. Polyvinylidene Fluoride (PVDF) microfiltration membranes are successfully fabricated by a combination of the vapor-induce phase separation (VIPS) and non-solvent-induced phase separation (NIPS), known as VIPS-NIPS method, and the influence of exposure time is investigated on the characteristics of the fabricated membranes. The membranes are characterized by scanning electron microscope (SEM) images, porosity, maximum pore radius, pore size distribution (PSD), liquid entry pressure of water (LEPw), mechanical strength, and flux of ethanol through the membrane. The results demonstrated the pore radius of the membranes increased, then decreased, and then increased again by increasing the exposure time. The narrowest pore size distribution was obtained for the membranes when the polymeric film was exposed to the humid environment for five minutes. The pore size distribution results confirmed the four-step mechanism for pore formation in the VIPS process. The nucleation points are formed on the membrane surface in the VIPS step. At low exposure times, the number of nuclei is low and they grow in the coagulation bath and form large pores. By increasing the exposure time, the number of nuclei is increased and reaches a maximum value. At this point, the growth of nuclei in the coagulation bath is minimum and results in a membrane with a smaller pore radius. Afterward, by increasing the VIPS time, the nuclei become larger and join each other to make larger pores, therefore, a wider pore size distribution with a larger average pore radius of the membrane would be expected.

Fabrication of a superhydrophobic mixed matrix PVDF-SiO2-HDTMS hollow fiber membrane for membrane contact carbon dioxide absorption

In order to obtain high performance polyvinylidene fluoride (PVDF) hollow fiber membrane for post combustion carbon dioxide (CO2) capture from flue gas by membrane contact absorption technology, a novel mixed matrix membrane fabrication process was proposed in this study. The mixed matrix PVDF-SiO2 (silicon dioxide)-HDTMS (hexadecyltrimethoxysilane) hollow fiber membranes fabricated via this process exhibit super-hydrophobicity on the outer surface and high mechanical strength. Among the membranes, the PVDF-SiO2(1.5)-HDTMS membrane exhibited the highest CO2 absorption performance, which was due to its excellent properties. It had water and diethanolamine (DEA, 1 mol/L) contact angles of 159.3° and 157.5°, respectively. Tensile strength, elongation at break, and LEPW (liquid entry pressure of water) of it were 3.2 × 106 Pa, 35.0%, and 9.0 × 105 Pa, respectively. The CO2 absorption flux of PVDF-SiO2(1.5)-HDTMS membrane attained 2.39 × 10−3 mol‧m−2‧s−1, which was 7.2% and 141.4% higher than that of the PVDF-HDTMS-1.5 and PVDF membranes, respectively. Moreover, CO2 absorption flux of the PVDF-SiO2(1.5)-HDTMS membrane decreased only 3% after twenty days of continuous operation. Highlighted by the outstanding performance in membrane contact CO2 absorption, the PVDF-SiO2(1.5)-HDTMS membrane shows great potential in the application of membrane contact absorption for post-combustion CO2 capture.

Tuning poly(vinyl chloride) membrane morphology to suit vacuum membrane distillation: Focusing on membrane preparation process based on phase separation

Nowadays, water scarcity is a paramount concern all over the world. Water desalination has been proposed as an applicable solution to face this problem. In this work, water desalination based on distillation technique using Poly(vinyl chloride) (PVC) membrane was considered. PVC membranes were fabricated via nonsolvent-induced phase separation (NIPS). Parameters involved in membrane production process were changed to tune the PVC membrane morphology for vacuum membrane distillation (VMD). These parameters include (1) polymer concentration in casting dope, (2) exposure of cast solution to the water vapor before immersing in nonsolvent bath, (3) addition of a hydrophilic polymer such as polyvinyl pyrrolidone (PVP) with different concentrations to the casting dope and (4) casting thickness. It was shown that the investigated parameters significantly affect the morphology and VMD performance of the PVC membranes. Additionally, enough evidence was provided to demonstrate that PVC concentration in the casting dope is the parameter using which PVC membrane morphology can be easily and effectively tuned to suit the VMD. Utilizing appropriate PVC concentrations, membranes with a suitable combination of both macrovoids and cellular pores can be produced. Note that although macrovoids are beneficial to enhance membrane flux, they adversely influence the membrane liquid entry pressure of water (LEP w ). An optimum LEP w is essential to resist against membrane wetting and achieve a high flux and long-term performance during the VMD. Therefore, the length and density of macrovoids within the membrane structure must be optimized to obtain a membrane, which is suitable for the VMD. It can be best achieved by changing the PVC concentration in the casting dope. The influence of VMD operational parameters on the performance of PVC membranes produced using a casting solution with appropriate PVC concentration was further investigated. It was shown that in spite of the feed salt concentration, the temperature and flow rate of feed solution positively affect membrane flux while the salt rejection remains unchanged. • Tuning the PVC membrane morphology to suit VMD is comprehensively explored. • The appropriate PVC membrane morphology for VMD is disclosed. • For VMD, membrane morphology can be best tuned by changing solution concentration.

Hierarchical Janus membrane via a sequential electrospray coating method with wetting and fouling resistance for membrane distillation

Membrane wetting and fouling issues are two major obstacles which hinder the practical application of membrane distillation (MD). In this study, a sequential electrospray method was introduced to impart a dual-layered superhydrophilic/superhydrophobic Janus skin onto a commercial polyvinylidene fluoride (PVDF) substrate. The bottom superhydrophobic layer was obtained by incorporating octaphenylsilsesquioxane (POSS) nanoparticles into PVDF carriers to construct a POSS@PVDF multiscale rough surface via electrospraying. At the same time, the top hierarchical-structured hydrophilic coating was composed of PAN beaded nanofilaments, rendering an intriguing in-air hydrophilicity and underwater superoleophobicity which benefited from the loose packing state of the interconnected beads and nanofibers. Further, this Janus skin exhibited good integrity and strong adhesion with the substrate, and due to its underlying superhydrophobicity and slightly decreased pore size, the hierarchical Janus membrane possessed a greatly enhanced liquid entry pressure of water (LEPw). Once applied in the MD process, with soybean-oil-in-saline-water emulsions as feed, this Janus membrane exhibited stable and excellent desalination performance with a high flux and nearly perfect salt rejection, whereas both the commercial and superhydrophobic membranes failed from oil contaminating. This suggests the remarkable simultaneous anti-wetting and anti-fouling property of Janus membranes, which possess great potential in water reclamation for challenging hypersaline oily wastewaters.

Membrane distillation & pressure retarded osmosis hybrid system using thermally rearranged nanofibrous membranes

To increase the efficiency of a closed-loop hybrid system consisting of membrane distillation (MD) and pressure retarded osmosis (PRO) processes, thermally rearranged nanofibrous membranes (TR-NFMs) via electrospinning were proposed in this study. Two fluorine-based modifications were performed on TR-NFMs to optimize their affinity with water. Hydrophobicity of TR-NFM was enhanced by atmospheric plasma coating (TR-NFM-Rx) to increase liquid entry pressure of water (LEPw) for MD applications. On the other hand, for PRO applications, gas-phase direct fluorination was applied on TR-NFM (TR-NFM-Fx) to improve its hydrophilicity by replacing the C–H bond of a TR polymer with a C–F bond. Before measuring the performance of the hybrid system, the MD performance was calculated from the mass transfer model based on the temperature and concentration of the solution to confirm the operating conditions of the MD-PRO hybrid system. The resulting TR-NFM-R40 showed an excellent water flux of 51.5 L/m2 hr at 70 °C despite a 3 M NaClaq operating solution that is unfavorable for MD performance. In the PRO process, thin film composite membrane (TR-TFC-F5) also exhibited outstanding power density of 120 W/m2 at 27 bar using 3 M NaClaq and D.I. water as operating and feed solutions, respectively. During 180 h continuous operation of MD-PRO hybrid system, the resulting average power density was about 90 W/m2 and average MD water flux was about 45–50 L/m2 hr at 70 °C using 3 M NaClaq operating solution. In conclusion, the developed TR membranes for MD-PRO hybrid system provides an insight into the future of energy harvesting technology.

Superhydrophobic ceramic hollow fibre membranes for trapping carbon dioxide from natural gas via the membrane contactor system

The membrane contactor system is one of the most important technologies to trap CO2 from natural gas. To apply this technology, hollow fibre membranes with a superhydrophobic surface must be used, where membranes were prepared from kaolin clay through the phase inversion/sintering technique and modified by three types of fluoroalkylsilane (FAS) molecules (C6, C8, C10) at different immersion times (6, 24, 48,72 h) to capture CO2 from natural gas via contacting the gas-liquid system. The kaolin was chosen due to its abundant availability at an affordable price as well as the high amount of the hydroxyl (OH) group in the surface which easily reacts with FAS during the grafting process. Superhydrophobicity was distinguished by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), liquid entry pressure of water (LEPw) measurement, and contact angle (CA). The lowest pore size of the grafted membrane obtained for C8 was about 1.32 μm; it was considered the perfect target for high membrane resistance. The chosen superhydrophobic kaolin membrane was tested for carbon dioxide (CO2) capture via the membrane contactor system. With increasing time of immersion, the hydrophobicity phenomena rose gradually until superhydrophobicity property was obtained. Forty-eight hours was proven as sufficient time to obtain the desired superhydrophobicity property to avoid wetting pores of the membranes. Besides, the perfect type of FAS for separating CO2 was C8 based on the sufficient LEPw and contact angle. The reduction of pH was observed after testing the performance of using a membrane contactor to separate CO2 by using water as absorbent where pH value decreased from 6.6 to 4.3 within 1 h, which concludes the success of the gas-liquid system into removing CO2 from natural gas.

Evaluation of a novel and highly hydrophobic acrylonitrile-butadiene-styrene membrane for direct contact membrane distillation: Electroblowing/air-assisted electrospraying techniques

Novel nanofibrous membranes were fabricated from acrylonitrile-butadiene-styrene (ABS) polymer using electroblowing process. Air-assisted electrospraying was applied to produce highly hydrophobic surfaces. The ABS membranes were coated using a dope solution including 6 wt% polystyrene (PS) in dimethylformamide. The beaded structure mounted on the hot-pressed ABS support layer demonstrated extremely rough character with a hierarchical structure. The water contact angle was significantly enhanced from 137.9 to 157.8°. Moreover, the liquid entry pressure of water (LEP) of the fabricated ABS membranes was incredibly improved 4.1 times compared to the neat one. By using high saline (250 g/L) and low surface tension (up to 2 mM sodium dodecyl sulfate) feeds, the well-modified membrane showed excellent direct contact membrane distillation (DCMD) performance with stable permeate flux and salt rejection factor due to high LEP value and sufficient hydrophobicity. Combining low-cost ABS and PS polymers with the productive electroblowing/air-assisted electrospraying process can pave the way for fabricating more robust membrane distillation (MD) membranes with anti-scaling/wetting properties.

Constructing superhydrophobic surface of PES/PES-SiO2 mixed matrix membrane contactors for efficient SO2 capture

Obtaining high SO2 absorption flux for membrane contactor is noticeably vital for fule gas desulfurization, and superhydrophobic surface is essential to reach excellent desulfurization performance. The development of a generic and low budget strategy for membrane contactors preparation is important in indisturial application. In this study, a superhydrophobic polyethersulfone-silica (PES/PES-SiO2) gas-liquid membrane contactor is fabricated using a facile spin coating method. PES substrate is prepared by a facile non-solvent induced phase separation (NIPS), and then the superhydrophobic surface of PES/PES-SiO2 is formed on the PES substrate by spin coating method. The solubility parameters of mixed solvent, PES concentration, and SiO2 content are regulated to investigate the morphology of membrane contactors. On one hand, the surface structure of MMMCs is regulated, and constructs lotus-leaf like morphology, which noticeably elevate surface roughness. On the other hand, SiO2 nanoparticles enhance hydrophobic characteristic with water contact angle 159° and anti wetting resistance with liquid entry pressure of water (LEPw) 1.389 bar. Moreover, the SiO2 nanoparticles help to significantly improve the stability of desulfurization performance, which is much higher than PES control membrane after 12 h test. The SO2 absorption fluxes and SO2 removal efficiencies are 1.24 × 10−3 mol·m−2·s−1 and 63.8%, respectively. Besides, the membrane phase transfer coefficient (Km) and membrane phase transfer resistance (H/Km) are explored.

Treatment of dye wastewater by direct contact membrane distillation using superhydrophobic nanofibrous high-impact polystyrene membranes

A superhydrophobic and nanofibrous high-impact polystyrene (HIPS) membrane was fabricated using electroblowing technique. The neat HIPS membrane was then subjected to the hot-pressing process to increase mechanical strength, narrowing pore size distribution, and also improving liquid entry pressure of water (LEP). The membrane characteristics (surface morphology, hydrophobicity, LEP, porosity, as well as mechanical properties) and direct contact membrane distillation (DCMD) performance (permeate flux and dye rejection factor) of the fabricated membranes were assessed using synthetic disperse dye solutions (0.4, 0.8 and 1.2 g/L) under constant DCMD condition. HIPS membranes maintained their durability even after operating at the highest concentration. The obtained results demonstrated that the dye removals were higher than 99.8% when different concentrations of dye were used as the feed. The permeate flux decline and surface fouling were increased by increasing the feed concentration. However, the surface contact angle of membranes subjected to DCMD tests was still in the range of hydrophobic surface (˃ 90°). Given these attributes, nanofibrous HIPS membrane can be considered as a potential alternative for membrane distillation in dying water treatment. Furthermore, DCMD can utilize the high temperature of dyeing baths as a viable heat source.

Effect of ZnO nanoparticles loading in double‐layer polyvinylidene fluoride membrane for desalination via direct contact membrane distillation

AbstractIn this study, double‐layer flat sheet membranes consist of nanocomposite polyvinylidene fluoride (PVDF)–ZnO layer on the top, whereas pristine polymeric PVDF on the bottom was fabricated via the double‐casting phase inversion (DCPI) method. The nanocomposite layer was prepared by loading 0.5%, 1.0%, 1.5% and 2.0% of ZnO nanoparticles. The morphology of the membranes changed as ZnO nanoparticles were introduced in the top layer, where the structure is more rigid and porous than the bottom layer. The increment concentration of nanoparticles in the top layer of the double‐layer membrane gives an effect in increasing of water contact angle slightly, which is from 136° to 140°. Furthermore, the liquid entry pressure of water (LEPw) decreases gradually from 0.69 to 0.4 bar with a high concentration of ZnO due to the presence of large pores. The increment concentration of ZnO nanoparticles also resulted in high porosity and reduced pore size, which reduce the resistance of water vapour to pass through the pores as well as enhancing the performance of membrane distillation (MD). Direct contact membrane distillation (DCMD) experiments were carried out to evaluate the efficiency of the fabricated double‐layer membrane in the desalination of seawater from fish farm water for 6‐h operation. The optimal double‐layer membrane with 0.5% ZnO nanoparticles loading maintained a stable flux of 9.42 L/m2h with 99.9% salt rejection and has antifouling properties. The results indicated that the fabricated double‐layer membrane via the DCPI method fulfils the required properties for MD application with excellent salt rejection.

Preparation of ECTFE porous membrane with a green diluent TOTM and performance in VMD process

In order to mitigate the harm of solvent volatilization during thermally induced phase separation (TIPS), more and more green solvents/diluents were developed, produced and applied in the membrane field. In this paper, trioctyl trimellitate (TOTM), an environmentally friendly diluent with high boiling point and low vapor pressure, was firstly introduced to prepare porous membranes, especially hydrophobic poly(ethylene-chlorotrifluoroethylene) (ECTFE) membranes by TIPS. Effects of ECTFE content on the membrane properties, including morphology, pore size distribution, porosity, liquid entry pressure of water (LEPw), water contact angle (WCA) and mechanical properties were characterized. Then the prepared ECTFE membranes were tested in vacuum membrane distillation (VMD). Phase diagram of this new ECTFE/TOTM binary system presented the existence of liquid-liquid (L-L) phase separation region when the ECTFE content was below 40%. The characterization results showed that the 15 wt% ECTFE membranes presented the continuous structure without the production of dense layer, but as the further increasing of polymer content, the spherulite structure began to be observed and surface became denser. Significantly, all the prepared ECTFE membranes exhibited excellent hydrophobicity. The liquid entry pressure of water (LEPw) and water contact angle (WCA) of 20 wt% ECTFE membranes reached 0.42 MPa and 139.9°, respectively. Moreover, in VMD, the prepared membranes exhibited high permeability (permeation flux was 23.09 kg/(m2.h)) and separation (salt rejection was 99.9%) performance. The above results show that the prepared ECTFE membrane showed promising stability performance in long-term operation of VMD for concentration of salt solution.

Superhydrophobic (polyvinylidene fluoride-co-hexafluoropropylene)/ (polystyrene) composite membrane via a novel hybrid electrospin-electrospray process

A novel hybrid electrospin-electrospray process was introduced to manipulate the membrane hierarchical structure towards enhanced surface superhydrophobicity and structural integrity. In this study, the two-nozzle mode was used to simultaneously electrospin PH (polyvinylidene fluoride-co-hexafluoropropylene) fibers and electrospray PS (polystyrene) beads to prepare a PH-PS composite membrane, during which fibers and beads alternatingly deposited and entangled together on the collector. Upon using the optimized PS solvent and PS content, the optimal PH-PS membrane exhibited superhydrophobicity (water contact angle of 157.6°) and good structural integrity, benefiting from the combination of the tough PH network and the interspersed porous irregular PS beads, as well as their homogeneous blending and good adhesion during this advantageous hybrid electrospin-electrospray process. In addition to superhydrophobicity, the PH-PS composite membrane was also endowed with a uniform pore distribution and high porosity, leading to a greatly enhanced liquid entry pressure of water (LEPw). Once applied in the direct contact membrane distillation (DCMD) process, it showed high desalination robustness and excellent anti-wetting performance with stable flux and high salt rejection under harsh feed conditions, providing great potential in practical desalination applications.

Application of electrospun nanofibrous amphiphobic membrane using low-cost poly (ethylene terephthalate) for robust membrane distillation

Although with great potential, membrane distillation (MD) is still far from satisfaction due to deficiency of ideal membranes with low cost and high performance. In this work, electrospun nanofibrous membranes (ENMs) fabricated using polyethylene terephthalate (PET) derived from recycled Coca Cola plastic bottles were evaluated in direct contact (DC) MD application. Heat-pressing was used to tune physicochemical properties of PET ENMs to get them better qualified for MD. Effect of heat-pressing on membrane structure and properties was emphasized. The preferred PET ENMs with nanofiber diameter of 517 nm exhibited high porosity of 77 %, high hydrophobicity with contact angle of ≥130°, and high liquid entry pressure of water (LEPw) of 49.8 kPa. The optimized PET ENMs displayed permeation of about 11−23 L m−2 h-1 (LMH) with varied temperature differences and salt rejection of 99.9 %. Stable permeation was noticed in the long-run membrane operation without significant permeation loss. Finally, 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (FAS) was used to modify the surface of membrane to enhance their antiwetting capability against the oil. Surface modification rendered excellent endurance to the membrane even with addition of 0.3 M Sodium Dodecyl Sulfate (SDS, a model surfactant) while the pristine membrane failed to work once the SDS was added. This work paves the way for developing a low-cost and acceptable industrial-grade membrane with great potential in DCMD applications.

The performance of polyvinylidene fluoride - polytetrafluoroethylene nanocomposite distillation membranes: An experimental and numerical study

Supported flat sheet polyvinylidene fluoride - polytetrafluoroethylene (PVDF-PTFE) nanocomposite membranes were fabricated for this study using the phase inversion process. Several characterization methods, such as scanning electron microscopy, atomic force microscopy, attenuated total reflectance - Fourier transform infrared spectroscopy, water contact angle, and liquid entry pressure of water (LEPw) measurements, were carried out on the prepared membranes, and vacuum membrane distillation (VMD) experiments were then applied to test membrane permeabilities. The cooperation of PTFE was demonstrated to have great potential in enhancing the permeate flux of PVDF membranes while maintaining an acceptable LEPw value. At a feed temperature of 30 °C and vacuum pressure 97.54 kPa, the VMD pure water permeates flux of the prepared nanocomposite membrane embedded with 40 wt% PTFE was 5.61 kg/m2·h, while that of pure PVDF membrane was 0.71 kg/m2 h. The salt rejection results of the prepared nanocomposite membranes were all above 99.9%. These results indicate the applicability of the PVDF-PTFE nanocomposite membranes supported on non-woven polyester fiber for desalination.