High Liquid Entry Pressure Research Articles

Superhydrophobic nanofiber membranes with 3D-network reinforced pore structure for membrane distillation

Electrospun nanofiber membranes (ENMs) have garnered significant attention among researchers for membrane distillation (MD) in treating high-salinity wastewater due to their high water flux and low mass transfer resistance. However, a significant challenge in using ENMs for MD is membrane wetting, which results from the deformation of their weakly randomly overlaid nanofibers structure due to water flow shear forces. Herein, we focused on the membrane's structure and successfully prepared superhydrophobic nanofiber membranes with 3D-network reinforced pore structure by immersing PVDF ENMs in a mixed solution of polydimethylsiloxane (PDMS) and titanium dioxide nanoparticles (TNPs) after a hot-pressing treatment for impregnation and coating. The resulting membrane exhibits exceptional properties, including a high water contact angle (WCA) of 160.3°, a high liquid entry pressure (LEP) of 1.57 bar, and sustained structural integrity with an unchanged pore size distribution even after 5 h of water scouring. These characteristics contribute to a water flux of 39.3 kg·m−2·h−1 and an unexpectedly long durability of up to 102 h, along with an outstanding salt rejection exceeding 99.99 %. Moreover, the membrane demonstrates stable water flux and resistance to wetting when processing a 3.5 wt% NaCl solution containing 0.1 mM sodium dodecyl sulfate (SDS), underscoring its significant potential for MD applications.

Fabrication of hydrophobic bi-layer fiber-aligned PVDF/PVDF-PSF membranes using green solvent for membrane distillation

Green high-flux poly(vinylidene fluoride) (PVDF) membranes with hydrophobic properties are beneficial for membrane distillation (MD). In this study, PVDF and polysulfone (PSF) polymer powders were dissolved in PolarClean to form immiscible polymer solutions. After casting the PVDF-PSF membranes and inducing a phase inversion procedure in water, a high-porosity fiber aligned PVDF-PSF membrane was obtained. The PVDF-PSF membranes also exhibited high tensile strength and satisfactory vapor flux. However, the surface hydrophobic properties were relatively poor and the surface pore sizes were large. Therefore, a PVDF/PolarClean/propylene glycol (PG) solution was used to construct rough PVDF nanoparticles (NPs) on the PVDF-PSF membrane surface. The PVDF NPs decreased the membrane pore size and increased the surface roughness. The resulting membrane exhibited a highly hydrophobic membrane surface and a higher liquid entry pressure than the pristine PVDF-PSF membrane. In addition, the whole process did not contain any toxic solvents and the stability of the PVDF/PVDF-PSF membrane was satisfactory after ultrasonic treatment. In the desalination of saline water containing 3.5 wt% and 12 wt% NaCl solutions, the resulting membrane showed a high water flux, with a rejection rate higher than 99.99 % after 120 h. This study provides important guidance for polymer membranes for MD.

Surface Modification of UiO-66 on Hollow Fibre Membrane for Membrane Distillation.

The hydrophobicity of metal-organic frameworks (MOFs) is critical in enhancing the separation process in membrane distillation. Herein, a new superhydrophobic University of Oslo 66 (UiO-66) MOFs was successfully constructed on the top of alumina hollow fibre (AHF) membrane for desalination purposes. The fabrication methodology of the membrane involved in situ growth of pure crystalline UiO-66 on top of AHF and post-synthetic modification by fluorosilane grafting. The resultant membrane was characterised to study the physicochemical properties of the pristine and modified membrane. A superhydrophobic UiO-66 with a contact angle of 163.6° and high liquid entry pressure was obtained by introducing a highly branched fluorocarbon chain while maintaining its crystallinity. As a result, the modified membrane achieved 14.95 L/m2∙h water flux and 99.9% NaCl rejection with low energy consumption in the direct contact membrane distillation process. Furthermore, the high surface energy contributed by UiO-66 is maximised to produce the maximum number of accessible sites for the grafting process. The synergistic effect of surface hydrophobicity and porous UiO-66 membrane in trapping water vapour shows great potential for desalination application.

Superhydrophobic composite asymmetric electrospun membrane for sustainable vacuum assisted air gap membrane distillation

Membrane distillation (MD) relies on superhydrophobic membranes that must achieve the competing goals of high liquid entry pressure (LEP) and high permeability. In this study, we developed the first superhydrophobic composite electrospun asymmetric membrane using fluorinated graphite (FG). We also provided among the first comparisons of the relative benefits of membrane asymmetry and composite coatings via 3D electrospinning and spraying. FG particles increased the roughness and reduced the zeta potential of the membranes. Superhydrophobic composite membranes had a contact angle of 157° (sliding angle of 7°) and an LEP of 327 kPa. Long-term MD testing revealed that FG particles could increase MD's sustainability while decreasing membrane wetting. Vacuum-assisted air gap membrane distillation (V-AGMD) showed that the composite asymmetric membrane outperformed the non-asymmetric version (composite nanofiber) membrane by 21 % in average water flux and 25 % in average thermal efficiency because of the asymmetric structure of the membrane. The numerical model developed for the V-AGMD system also successfully predicted the water flux generated experimentally from the composite nanofiber and composite asymmetric membranes. Our results confirmed that electrospun asymmetric FG membranes with high contact angle, low sliding angle, high permeability, and high gained output ratio (GOR) would be promising candidates for sustainable MD.

Electrosprayed CNTs on Electrospun PVDF-Co-HFP Membrane for Robust Membrane Distillation.

In this investigation, the electrospraying of CNTs on an electrospun PVDF-Co-HFP membrane was carried out to fabricate robust membranes for the membrane distillation (MD) process. A CNT-modified PVDF-Co-HFP membrane was heat pressed and characterized for water contact angle, liquid entry pressure (LEP), pore size distribution, tensile strength, and surface morphology. A higher water contact angle, higher liquid entry pressure (LEP), and higher tensile strength were observed in the electrosprayed CNT-coated PVDF-Co-HFP membrane than in the pristine membrane. The MD process test was conducted at varying feed temperatures using a 3.5 wt. % simulated seawater feed solution. The CNT-modified membrane showed an enhancement in the temperature polarization coefficient (TPC) and water permeation flux up to 16% and 24.6%, respectively. Field-effect scanning electron microscopy (FESEM) images of the PVDF-Co-HFP and CNT-modified membranes were observed before and after the MD process. Energy dispersive spectroscopy (EDS) confirmed the presence of inorganic salt ions deposited on the membrane surface after the DCMD process. Permeate water quality and rejection of inorganic salt ions were quantitatively analyzed using ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS). The water permeation flux during the 24-h continuous DCMD operation remained constant with a >99.8% inorganic salt rejection.

A novel janus membrane modified by MXene for enhanced anti-fouling and anti-wetting in direct contact membrane distillation

Membrane fouling and wetting limit the applications of membrane distillation (MD) for wastewater treatment, especially when treating the wastewater with a high concentration of low surface tension substances such as oil and surfactants. In this paper, virgin polyvinylidene fluoride (PVDF) membrane was modified by polydimethylsiloxane (PDMS) to enhance anti-wetting ability. Then a thin polydopamine (PDA) layer was coated as a reaction platform for further modification. Polyethyleneimine (PEI) was cross-linked with PDA to form a uniform and stable layer, through hydrogen bonds and electrostatic interaction to immobilize hydrophilic MXene, which formed a Janus MXene-PVDF membrane. The MXene layer was the key for superoleophobicity and high liquid entry pressure (LEP) of membrane, capable of mitigating membrane fouling and wetting when dealing with low surface tension wastewater (LSTW). From the experiments results, pristine PVDF membrane showed severe fouling and wetting with flux decline and salt leakage during treatment of LSTW (surfactants containing water, oil-in-water emulsion and sodium dodecyl sulfate stabilized oil-in-water emulsion). However, under the same conditions, the Janus MXene-PVDF membrane exhibited remarkably stable flux (9.3 kg m−2h−1, 9.1 kg m−2h−1, 10.2 kg m−2h−1) and salt rejection (almost 99.9%) after 15 h operation. Excellent fouling and wetting resistance of MXene-PVDF membrane was mainly attributed to its superhydrophilic and superoleophobic top surface (in-air water contact angle: 30.2°, under-water oil contact angle: 169.9°) and hydrophobic substrate (in-air water contact angle: 130.8°), together with high LEP value (91.1 Kpa). This study provides a viable route to fabricated a Janus membrane with outstanding fouling and wetting resistance for LSTW, oily wastewater and it has great potential for sewage treatment in the future.

Hydrophobic PVDF-HNT membrane for oxytetracycline removal via DCMD: The influence of fabrication parameters on permeability, selectivity and antifouling properties

Halloysite nanotube (HNT) was incorporated in poly(vinylidene fluoride) (PVDF) membrane to remove contaminants of emerging concern (CEC) known as oxytetracycline (OTC), which is extensively used in the aquaculture industry. The presence of HNT in the PVDF matrix has improved the characteristics and separation of the pristine membrane. This study evaluated the effectiveness of low concentration of HNT loading for treating OTC molecules via direct contact membrane distillation (DCMD), which produced high flux recovery after ethanol cleaning. The performance of PVDF-HNT (PHNT) membrane with 0.5 % HNT loading was compared using immersion time of 5 and 15 s. Further improvement was carried out by reducing 500 μm of the membrane thickness to 250 and 100 μm. The wetting characteristics were determined to achieve the desired properties of DCMD membrane and gain insights into the antifouling mechanism of PHNT membrane. The modified membrane using 5 s immersion time obtained a high liquid entry pressure and contact angle (CA) of 2.13 bar ±0.34 and 140° ± 3.10, respectively. This membrane had removed 95 % of OTC molecules with a permeate flux of 5.52 L/m2h. A 38.4 % increment in flux permeation with 98 % removal was obtained after reducing the membrane thickness to 250 μm (7.64 L/m2h). The total and irreversible flux decline of this membrane was significantly low; as a result, the flux recovery obtained above 90 % after ethanol cleaning including for membrane regeneration and long-term operation investigation. OTC removal from the feed solution improved from 98 % to 100 % after the regeneration and long-term operation.

Omniphobic membrane via bioinspired silicification for the treatment of RO concentrate by membrane distillation

Membrane distillation (MD) is promising for the reclamation of reverse osmosis (RO) concentrate ascribed to the advantages of moderate membrane fouling, space-saving and theoretical 100% rejection to non-volatile substances. However, wetting issues remain great challenges for the hydrophobic porous membrane in the treatment of industrial wastewater by MD. In this study, a novel omniphobic membrane is developed via bioinspired silicification and fluorosilanization. The effects of polydopamine/polyethylenimine (PDA/PEI) co-deposition and silicification time on the morphology, pore structure, wettability and separation performance of the membrane are systematically investigated. The results show that the membrane surface is evenly covered by a rough silica layer after bioinspired silicification. The omniphobic membrane exhibits excellent anti-wetting properties with high liquid entry pressure (326.4 kPa) and contact angles to liquids with various surface tensions such as water (162.50°), diiodomethane (149.20°), mineral oil (135.97°), etc. The omniphobic modification has little effect on the pore structure but increases the mechanical strength of membranes significantly. The MD operation results reveal that the virgin membrane is rapidly wetted by a feed solution of 0.1 mM sodium dodecyl sulfate (SDS) in 35 g/L NaCl, while the omniphobic membranes maintain stable MD performance over a 420 min operation against the feed with a SDS concentration of up to 0.3 mM. The omniphobic membrane shows a superior separation performance in the treatment of RO concentrates from dyeing and printing industry without wetting and fouling observed. Meanwhile, high rejections to salts, SDS, metals, water quality indexes (COD, TOC, TN, NH3–N) and organic matters are achieved, demonstrating a high efficiency of the omniphobic membrane for the reclamation of RO concentrates.

Efficient Estimation of Permeate Flux of Asymmetric Ceramic Membranes for Vacuum Membrane Distillation.

Ceramic membranes have the advantages of high mechanical strength and thermal stability and are promising candidates for membrane distillation. Ceramic membranes are generally designed to have a multilayer structure with different pore sizes to create a high liquid entry pressure and obtain a high permeability. However, these structural characteristics pose significant difficulties in predicting permeate flux in a ceramic membrane contactor for vacuum membrane distillation (VMD). Here, a modeling approach was developed to simulate the VMD process and verified by comparing the simulated results with the experimental data. Furthermore, correlations are proposed to simplify the calculations of permeate flux for VMD using asymmetric ceramic membranes by assuming those multilayers to be an effectively quasi-symmetric layer and by introducing a correction factor. The simulation results indicated that this simplified correlation was effective and enabled a quick estimation of the effect of membrane parameters on permeate flux.

Effect of non‐solvent on the synthesis of polyvinylidene fluoride membranes for vacuum membrane distillation desalination

AbstractThe need for freshwater boosted the research for alternative technologies with a cleaner and more efficient approach. Membrane distillation (MD) stands out due to its efficiency in purifying aqueous solutions and easy operation. Thus, this work aims at developing and characterizing polyvinylidene fluoride membranes using the non‐solvent phase inversion (NIPS) methodology for the MD process. Distilled water and ethanol (at different proportions) were tested as non‐solvent and N'N'‐dimethylformamide as solvent. The morphology, crystallinity, and porosity of each sample were determined. The utilization of ethanol as non‐solvent produced more hydrophobic membranes with higher liquid entry pressure. Scanning electron microscope analysis showed that different proportions of water and ethanol changes the morphology of the resulting membrane, with clear influence on the formation of macrovoids. The samples crystallinity was over 54% and the porosity, over 55%. The sample with best results in the vacuum MD process prpesented an average of over 98% of salt retention during a period of 6 h. This work shows the beneficial influence ethanol as non‐solvents for the preparation of PVDF membranes for the process of hydrophobic vacuum MD.

Experimental study and numerical optimization for removal of methyl orange using polytetrafluoroethylene membranes in vacuum membrane distillation process

One of the most water-intensive and environment polluting anthropogenic industries is the textile industry. Amongst textile dyes, methyl orange (MO) is an extensively used anionic azo dye that is toxic to the environment. In this study, the effect of various process parameters was studied for different operating conditions (mass flow rate, vacuum pressure, inlet feed temperature, dye concentration) to remove MO from synthetic wastewater in the vacuum membrane distillation (VMD) process. We determined the optimum conditions for operating variables using response surface methodology (RSM) and developed a regression model to describe permeate flux, dye rejection and specific energy consumption. The optimum operating parameters from the RSM study were bulk feed temperature: 70 °C, mass flowrate: 40 kg h−1, dye concentration: 60 mg l−1 and vacuum pressure: 720 mm Hg. For the optimized input process parameters, the experimentally observed values were permeate flux: 19.60 ± 1.03 l m−2 h−1, dye rejection: 99.80 ± 0.07%, and SEC: 2.04 ± 0.11 kW h m−3. Furthermore, for these optimized conditions, a 3D CFD model was developed to gain insight into the membrane module's thermal, velocity, and concentration field. The evaporation of feed at the membrane surface on the feed side and condensation of vapours at the membrane surface on the permeate side was captured in this model. The permeate flux profile and dye rejection for various cycles of VMD operation with intermittent washing were also performed to study the fouling behaviour of the membrane. The membrane's surface fouling was analyzed using SEM and FT-IR analysis. The SEM analysis of the fouled membrane indicated that the dye deposition was not severe due to high hydrophobicity, high liquid entry pressure, and high pore wetting resistance of the PTFE membrane. The FT-IR analysis showed that the fouled PTFE membrane sufficiently retained its initial structure and property.

Membrane Distillation: Experimental evaluation of Liquid Entry Pressure in commercial membranes with textile dye solutions

In Membrane Distillation, the Liquid Entry Pressure (LEP) determination is crucial to ensure permeate quality. While the process has been increasingly applied to dyeing wastewater, the influence of dye class on LEP has not been evaluated yet. In the present work, the experimental evaluation of LEP was carried out with four classes of textile dyes (reactive, disperse, acid, and direct) and the three commercial membranes most used (PTFE, PP, and PVDF). The influence of dye class on LEP was associated with analyses as liquid surface tension, ATR-FTIR spectroscopy, and degree of liquid absorption. Acid and direct classes presented a higher tendency to membrane wetting due to the very low LEP values. On the other hand, reactive and disperse dye classes maintained high LEP values throughout the tests for the PTFE and PVDF membranes. The PP membrane showed lower LEP values, intermediate liquid absorption, and the highest permeate flux. The wetting phenomenon was avoided due to the high LEP values observed for reactive and disperse dyes, indicating that commercial membranes are potential candidates for implantation on an industrial scale, which can speed up the MD commercialization process in the textile industry.

Superhydrophobic modification of electrospun nanofibrous Si@PVDF membranes for desalination application in vacuum membrane distillation

Superhydrophobic nanofibers have received prominent attention owing to their exceptional properties and researchers are focused on developing high-performing MD membranes. Herein, we fabricate superhydrophobic electrospun nanofibrous membranes using polyvinylidene fluoride (PVDF) solutions with silica nanoparticles (0 wt% to 6 wt%) to create multiscale (or hierarchical) surface roughness. For superhydrophobicity, the composite membranes (Si@PVDF) were subjected to a two-step modification that included acid pre-treatment and silanization with fluoroalkylsilane (FAS) compound of low surface energy. The acid pre-treatment enhances the hydroxyl group of SiO2 nanoparticles and create active sites in abundance for silanization. The modified membranes (FAS-Si@PVDF-A) having 6 wt% SiO2 showed excellent wetting resistance with water contact angle (WCA) up to 154.6 ± 2.2°, smaller average pore size of 0.27 ± 0.3 μm, and high liquid entry pressure (LEP) of 143 ± 4 kPa. It was observed, increasing silica content decreased the fiber diameter and average pore size and increased WCA and LEP of modified membranes. The modified superhydrophobic membranes gave stable permeate flux, exhibited strong wetting resistance and excellent salt rejection in vacuum membrane distillation (VMD) test. The optimal FAS-Si@PVDF-A membrane (6 wt% SiO2) of thickness 98 ± 5 μm produced a stable permeate flux of more than 11.5 kg m−2 h−1 and salt rejection as high as 99.9% after 22 h of continuous operation using NaCl solution (3.5 wt%) as feed. Therefore, this modification provided superhydrophobic membranes possessing robust anti-wetting properties with significant permeability and has encouraging application in membrane distillation for desalination.

Analysis of Polyvinylidene Fluoride Membranes Fabricated for Membrane Distillation.

The optimization of the properties for MD membranes is challenging due to the trade-off between water productivity and wetting tendency. Herein, this study presents a novel methodology to examine the properties of MD membranes. Seven polyvinylidene fluoride (PVDF) membranes were synthesized under different conditions by the phase inversion method and characterized to measure flux, rejection, contact angle (CA), liquid entry pressure (LEP), and pore sizes. Then, water vapor permeability (Bw), salt leakage ratio (Lw), and fiber radius (Rf) were calculated for the in-depth analysis. Results showed that the water vapor permeability and salt leakage ratio of the prepared membranes ranged from 7.76 × 10−8 s/m to 20.19 × 10−8 s/m and from 0.0020 to 0.0151, respectively. The Rf calculated using the Purcell model was in the range from 0.598 μm to 1.690 μm. Since the Rf was relatively small, the prepared membranes can have high LEP (more than 1.13 bar) even at low CA (less than 90.8°). The trade-off relations between the water vapor permeability and the other properties could be confirmed from the results of the prepared membranes. Based on these results, the properties of an efficient MD membrane were suggested as a guideline for the membrane development.

Desalination by direct contact membrane distillation using a superhydrophobic nanofibrous poly (methyl methacrylate) membrane

A practical, high-productive and superhydrophobic nanofibrous membrane was firstly introduced for membrane distillation (MD) process using poly (methyl methacrylate) (PMMA) and the electroblowing process. Wrinkled PMMA nanofibers demonstrated nano/micro-structure improving hydrophobicity greatly. Direct contact membrane distillation (DCMD) performance of the cold-pressed nanofibrous PMMA membrane was assessed using 35 and 150 g/L saline feed waters for 24 h and the results were compared with commercial polytetrafluoroethylene (PTFE) and polypropylene (PP) membranes. The PMMA membrane exhibited highest permeate flux (41.04 and 35.94 kg/m2 h for 35 and 150 g/L feeds, respectively) with stable electrical conductivity (EC) (˂ 5 μS/cm) resulting from superhydrophobicity (164.2°) and high liquid entry pressure (LEP) of 227.3 kPa. Although the commercial membranes presented good DCMD performance for 35 g/L feed, partial pore wetting with final EC of 11.93 and 17.62 μS/cm was measured for the PTFE and PP membranes using 150 g/L feed, respectively. The nanofibrous PMMA membrane is a promising applicant for conducting promising desalination using the DCMD process considering high production rate, simplicity of fabrication process and cost-effectiveness.

Fabrication of superhydrophobic PDTS-ZnO-PVDF membrane and its anti-wetting analysis in direct contact membrane distillation (DCMD) applications

Membrane distillation (MD) is an emerging water treatment technology suitable for hypersaline wastewater. However, membrane wetting is a primary obstacle to restrict its widespread industrial use. In this study, a superhydrophobic nanofibrous membrane (labeled as FZP) with high water contact angle of 162.3° and sliding angle of 9.8° was fabricated through fluorinating of zinc oxide (ZnO) blended electrospun polyvinylidene fluoride (PVDF) membrane. In comparison with neat and ZnO blended PVDF (ZP) nanofibrous membranes, FZP membrane has much better anti-wetting property due to its superhydrophobicity and higher liquid entry pressure (LEP) value when desalinating both pure NaCl solution and NaCl solutions with low-surface-tension sodium dodecyl sulfate (SDS) and sparingly soluble salt CaSO4. LEP values of membranes for SDS and CaSO4 contained feed solutions were calculated to be smaller than that for pure NaCl solution, accelerating the occurrence of membrane wetting. Temperature gradient across the membrane and Gibbs free energies of CaSO4 heterogeneous nucleation were further calculated to elucidate the wetting mechanism. Our results provide valuable insights for better developing superhydrophobic membrane and understanding its anti-wetting property in MD process.

Crosslinked PVDF based hydrophilic-hydrophobic dual-layer hollow fiber membranes for direct contact membrane distillation desalination: from the seawater to oilfield produced water

Crosslinked polyvinylidene fluoride (PVDF) based hydrophilic-hydrophobic dual-layer hollow fiber membranes were fabricated for direct contact membrane distillation (DCMD). PVDF/ammonia/water dope solution was formulated with a spinning process delay of 9 days for the formation of a mechanically robust and hydrophobic crosslinked PVDF outer layer, and polyethylene glycol 6000 (PEG-6000) was introduced to create a thick hydrophilic PVDF/PEG-6000 inner layer. The influences of ammonia/water contents and the spinning process delay on the membrane morphology were studied. The DCMD performances were investigated using both simulated seawater and actual oilfield produced water as the feed solutions. The incorporation of ammonia/water mixture allowed a slow PVDF crystallization in the dope solution during the 9 days of spinning process delay. The obtained membrane DN2H2-9 showed contact angles of 133.6° and 47.1°on the surfaces of the crosslinked PVDF outer layer and PVDF/PEG-6000 inner layer, respectively. The membrane DN2H2-9 showed a superior permeate water flux of 97.6 kg m−2 h−1 and an energy efficiency of 92.8% to desalinate a 3.5% NaCl solution. The result from a 200 h continuous DCMD operation revealed a stable permeate water flux and more than 99.9% of salt rejection, which was attributed to a relatively high liquid entry pressure (LEP) of 1.95 bar and the simultaneously enhanced mechanical strength of the membrane. The membrane DN2H2-9 also demonstrated promising DCMD performance in the desalination of the real oilfield produced water with a high total dissolved solids (TDS), including almost 100% of permeate water recovery and more than 99.9% of salt rejection in 72 h of operation.

Enhancing membrane hydrophobicity using silica end-capped with organosilicon for CO2 absorption in membrane contactor

Silica nanoparticles (SiNPs) modified with hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDCS) and polydimethylsiloxane (PDMS) were used to fabricate mixed matrix membranes (MMMs) for carbon dioxide (CO2) absorption. It is vital for membrane contactors to be hydrophobic in order to avoid membrane wetting. Of the three functionalised SiNPs, the one treated with HMDS, dubbed TS-530, was well-dispersed within the polyvinylidene fluoride (PVDF) polymer matrix, producing a membrane with high porosity and liquid entry pressure of 77.57% and 7.51 bar, respectively. In addition to higher resistance to membrane wetting, the PVDF/TS-530 MMM also demonstrated superior thermal and mechanical stability. Although the CO2 absorption flux of the MMMs could not rival the 2.84 × 10−4 mol/m2s flux of the neat PVDF membrane, all three SiNPs/PVDF MMMs had demonstrated better selectivity. The MMM with TS-530 SiNPs had reported a CO2 absorption flux of 1.91 × 10−4 mol/m2s as well as the best selectivity of 22.5; over three times higher selectivity than the neat membrane.

Recent Developments in Nanomaterials-Modified Membranes for Improved Membrane Distillation Performance.

Membrane distillation (MD) is a thermally induced membrane separation process that utilizes vapor pressure variance to permeate the more volatile constituent, typically water as vapor, across a hydrophobic membrane and rejects the less volatile components of the feed. Permeate flux decline, membrane fouling, and wetting are some serious challenges faced in MD operations. Thus, in recent years, various studies have been carried out on the modification of these MD membranes by incorporating nanomaterials to overcome these challenges and significantly improve the performance of these membranes. This review provides a comprehensive evaluation of the incorporation of new generation nanomaterials such as quantum dots, metalloids and metal oxide-based nanoparticles, metal organic frameworks (MOFs), and carbon-based nanomaterials in the MD membrane. The desired characteristics of the membrane for MD operations, such as a higher liquid entry pressure (LEPw), permeability, porosity, hydrophobicity, chemical stability, thermal conductivity, and mechanical strength, have been thoroughly discussed. Additionally, methodologies adopted for the incorporation of nanomaterials in these membranes, including surface grafting, plasma polymerization, interfacial polymerization, dip coating, and the efficacy of these modified membranes in various MD operations along with their applications are addressed. Further, the current challenges in modifying MD membranes using nanomaterials along with prominent future aspects have been systematically elaborated.

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.