Membrane Flux Research Articles

Double-drying 3D lamellar-structured aerogel membrane for efficient oil-water separation and long-lasting antibacterial activity

Conventional oil-water separation membranes are difficult to establish a trade-off between membrane flux and separation efficiency, and often result in serious secondary contamination due to their fouling issue and non-degradability. Herein, a double drying strategy was introduced through a combination of oven-drying and freeze-drying to create a super-wettable and eco-friendly oil-water separating aerogel membrane (TMAdf). Due to the regular nacre-like structures developed in the drying process and the pores formed by freeze-drying, TMAdf aerogel membrane finally develops regularly arranged porous structures. In addition, the aerogel membrane possesses excellent underwater superoleophobicity with a contact angle above 168° and antifouling properties. TMAdf aerogel membrane can effectively separate different kinds of oil-water mixtures and highly emulsified oil-water dispersions under gravity alone, achieving exceptionally high flux (3693 L·m−2·h−1) and efficiency (99 %), while being recyclable. The aerogel membrane also displays stability and universality, making it effective in removing oil droplets from water in corrosive environments such as acids, salts and alkalis. Furthermore, TMAdf aerogel membrane shows long-lasting antibacterial properties (photothermal sterilization up to 6 times) and biodegradability (completely degraded after 50 days in soil). This study presents new ideas and insights for the fabrication of multifunctional membranes for oil-water separation.

Graphene oxide nanofiltration membrane for efficient dye separation by β-FeOOH intercalation and dopamine surface modification

Graphene oxide (GO) membranes have been extensively studied for the separation and purification of dye wastewater. Improving the stability, permeability and self-cleaning ability of these materials is urgently needed for the purification of complex dye wastewater. In this study, we developed a simple and effective method to insert ternary β-iron hydroxide (β-FeOOH) between GO nanosheets and modify the membrane surface with dopamine hydrochloride (PDA) to solve this problem. The pure water flux of the composite membrane was 9 times higher than that of the pure GO membrane (92.82 L m−2h−1), and the rejection of dye molecules larger than 400 Da was consistently greater than 99 %. The PDA/GO-β-FeOOH2 composite membrane was operated for 50 h (with xenon lamp irradiation to clean the membrane surface) with a flux of 34.98 L m−2h−1 and a rejection rate consistently higher than 98.5 %.

Investigation of photocatalytic and visible light self-cleaning performance of 2D/2D g-C3N4-ZrO2 based PES/PDA membranes for organic contaminants degradation

This study fabricated a novel photocatalytic, self-cleaning membrane by depositing a 2D-2D g-C3N4/ZrO2 photocatalyst on polydopamine-coated polyethersulfone. The morphologies and surface chemistry of the membranes were studied through FESEM-EDX, AFM, and XPS. The results showed the satisfactory binding stability of the photocatalyst on the polyethersulfone/polydopamine. Also, depositing of the photocatalyst on the polyethersulfone/polydopamine strongly enhanced hydrophilicity. The optimized photocatalytic membrane (39.68 Lm2h) had a substantially higher water flux than polyethersulfone (13.61 Lm2h) and polyethersulfone/polydopamine (19.42 Lm2h). The photocatalytic membranes showed high dye removal and protein rejection rates. The flux recovery ratio was 83.32 % after 30 min of visible-light exposure. The conversion of irreversible contaminants into reversible ones under visible-light demonstrated the self-cleaning nature of the membrane. In addition, the photocatalytic membrane showed substantial stability in the vibration and shear force tests. Therefore, the polyethersulfone/polydopamine/(g-C3N4/ZrO2) membrane is a promising candidate for removing organic contaminants from water due to high rejection, water flux rate, and satisfactory stability. This study not only proposed an efficient methodology to fabricate a novel photocatalytic self-cleaning membrane with high stability but also provided further insights into the effects of the 2D structure of photocatalyst on the flux and photocatalytic degradation performance of such membranes.

Preparation of PVDF-nSiO2/PVSQ high-flux composite membrane by chemical grafting and separation of composite brine by membrane distillation

The large-scale application of membrane distillation (MD), an important method for desalting seawater, is limited due to membrane fouling. In this study, ethyl orthosilicate (TEOS) was polymerized to obtain different nSiO2 particles. Vinyl triethoxysilane (VTES) was hydrolysed and polycondensation was used to produce spherical polyethylene-sesquioxane (PVSQ) microparticles, which were modified to construct micro/nano particles. Then grafted on the surface of polyvinylidene fluoride (PVDF) composite membrane. The low-surface-energy hydrophobic groups present on the surfaces of the vinyl and ethoxy particles greatly enhanced the membrane hydrophobicity. The particle size of nSiO2 can change the properties of the membrane. The separation performance of the membrane was tested by direct contact membrane distillation (DCMD). In the separation of a constant concentration of feed solution (3.5 wt% NaCl), the membrane flux was relatively stable at 23.8 kg·m−2·h−1, and the salt interception rate reached 99.99 %. In the subsequent separation of a salt/humic acid solution, the flux remained stable and the good anti-fouling performance indicating that this system outperformed the unmodified membrane. Finally, the effect of different cations on the water diffusivity was studied using a molecular simulation method. Both Ca2+ and Mg2+ reduced the diffusion coefficient of water. However, when these two ions were present simultaneously, Ca2+ inhibited the binding of Mg2+ to water, and the diffusion coefficient of water increased. This study provides a novel approach for preparing hydrophobic membranes for the separation of complex brines.

Enhancement of antifouling and mechanical properties of polysulfone membrane using zwitterionic biphenyl polyimide as additive

Biphenyl polyimides, which are known by its excellent heat resistance and mechanical properties, were synthesized by adjusting the molar ratio of monomers, followed by end-functionalized with zwitterionic group via reaction with 1,3-propanesultone. The zwitterionic sulfobetaine biphenyl polyimide (z-biph-PI) copolymers with different hydrophobic chain lengths were employed as the additive for the preparation of polysulfone (PSf) membrane. X-ray photoelectron spectrometry (XPS) measurement on membrane surfaces revealed that the sulfobetaine groups of z-biph-PI migrated toward water in the membrane formation process, during which a large amount of porous, narrow and densely packed pores were created as illustrated in scanning electron microscopy (SEM) images. Therefore, the incorporation of z-biph-PI simultaneously enhanced the pure water flux and protein rejection ratio of membranes, overcoming the trade-off effects between permeability and selectivity. The adsorption of bovine serum albumin decreased from ∼47.7 μg/cm2 for the pristine membrane to a minimum of ∼12.4 μg/cm2 for the blend membrane. More importantly, the tensile strength and elongation at break were also simultaneously improved due to the unique mechanical property of biph-PI and the strong π-π interaction between biphe-PI and PSf. Meanwhile, the blend membrane exhibited excellent filtration and thermal stability. All these characteristics of the blend membrane made it promising in ultrafiltration application.

1,3-Dioxolane production via reactive distillation combined with vapor permeation: Experiments and modelling

To overcome the problem of difficult separation of the 1,3-dioxane (DOL)–H2O azeotrope in the production of DOL, a new process via reactive distillation (RD) combined with vapor permeation (VP) was established. The reliability of the RD model has been reported in the literature. The VP membrane used an Aspen Custom Modeler (ACM) self-built model, with the permeation parameters of H2O, DOL, and formaldehyde (FA) in the membrane flux equation fitted through the H2O-DOL-FA dehydration experiments by NaA zeolite membrane. The results showed that the relative error between the mass of H2O in a series of permeates in experiments and simulated by the VP model was mainly within 20%, and R2 is 0.94. For DOL and FA, which have very small permeation, the value was within 50%, implying the reliability of the VP model. On this basis, a two-dimensional VP model was established. Finally, a new RD-VP-D process for producing DOL was designed. The VP was used to overcome the azeotropic point of DOL and H2O by dehydration. Then 99.9 wt% DOL can be obtained at the bottom of the subsequent DOL purification column, with DOL- H2O azeotrope at the top recycled back to the VP membrane. The effects of the degree of VP dehydration and column pressure on membrane area, reboiler duty, and TAC were investigated, meanwhile introducing a new concept: logarithmic mean partial-pressure difference (LMPD). Under the optimal parameter, TAC was reduced by 20.0% compared with the process reported in the literature, and CO2 emissions were reduced by 35.8%.

A A Novel Poly (vinylidene) Fluoride/TiO2/Spent Bleaching Earth for Enhancing Hydrophilic Hollow Fibre Membrane

Nowadays, polymer as the raw material has been utilized in the development of Hollow Fibre (HF) membranes. PVDF is a commonly used for HF membrane material. However, it has hydrophobicity properties and lead membrane becomes low permeability and fouling. Therefore, to avoid these membranes problems, the incorporation of inorganic nanoparticles into PVDF membranes matrix is necessary to be applied for significantly improving PVDF membranes performance. This study investigates the characteristics and performance of PVDF-TiO2 HF membranes using spent bleaching earth (SBE) as a promising material from industrial waste as a renewable inorganic nanoparticle. This novel PVDF-TiO2-SBE HF membrane was fabricated using the subsequent steps: The preparation process incorporates SBE revival through solvent extraction and thermal treatment alongside the wet spinning technique for membrane fabrication. The Fourier transform infrared (FTIR) functional groups, scanning electron microscope (SEM) morphology, water contact angle and pure water flux performance were investigated to specifically understand the performance of this typical HF membranes. The IR results show that Si-O-Si groups were found in the membrane matrices due to the addition of SBE material. The addition of TiO2-SBE particles also indicate a sandwich (sponge-finger-like) morphological structure on the cross-sectional, a rough and porous surface structures. The hydrophilic properties of the HF membrane and pure water flux performance are determined by the composition of the TiO2-SBE mixture added as an additive material. The minimum contact angle found at 74.33°, while the water flux is 5.81 kg.m-2.h-1 on the identical HF membrane. Accordingly, this approach significantly enhances the properties of the pure PVDF HF membrane.

Laminated graphene oxide and hydrotalcite membranes via alternating spray-deposition with stable desalting performance

Laminated graphene oxide (GO) membrane has great potential for desalination, but achieving good stability in salt retention and water permeation is still a challenge. The “compact” sieving structure and the “loose” permeating structure of the GO membranes offer synergetic effects for high-performance desalination. Here, a composite desalination membrane involving two two-dimensional layered nanomaterials with opposite charges has been reported. The multi-layered GO (MLGO) and hydrotalcite (HT) were then alternated in a spray-coating on a PDA-modified substrate to construct multiple structures. Different assembly regions were identified by in-situ morphology monitoring, which showed that MLGO and HT were connected by electrostatic attractions. Also, the composite membrane showed high salt retention, permeability and long-term performance stability. The water flux of the composite membrane increased from 2.8 L m−2 h−1 bar−1 to 3.6–5.2 L m−2 h−1, which was due to the increases in the interlayer spacing distances and the introduction of new permeable spaces. After a 400 h continuous filtration test, the Na2SO4 retention remained stable. The water fluxes were in the range of 2.0–3.0 L m−2 h−1 bar−1, which corresponded to an increase by 42.9 %–114.3 % in comparison with the pure MLGO membrane. As compared with the MLGO membrane, molecular dynamics (MD) simulations revealed that more water molecules passed through the MLGO-HT membrane with a shorter pathway length and higher speed than MLGO membrane. The present study demonstrated the potential of a composite with 2D materials for desalination applications.

Impact of Colloidal Drug-Rich Droplet Size and Amorphous Solubility on Drug Membrane Permeability: A Comprehensive Analysis

This study aimed to investigate the impact of amorphous solubility and colloidal drug-rich droplets on drug absorption. The amorphous solubility of cilnidipine (CND) in AS-HF grade of hypromellose acetate succinate (HPMC-AS) solution was significantly reduced compared to that in non-polymer solution due to AS-HF partitioning into the CND-rich phase. In contrast, AS-LF grade of HPMC-AS has minimal effect on the amorphous solubility. The size of colloidal CND-rich droplets formed in the CND-supersaturated solution was less than 100 nm in the presence of AS-HF, while 200–450 nm in the presence of AS-LF. When the CND concentrations were near the amorphous solubility, CND membrane flux was reduced in the presence of AS-HF due to the decrease in the amorphous solubility of CND. However, the CND flux increased with the increase in CND-rich droplets, especially in the AS-HF solution. The size reduction of the CND-rich droplets led to their effective diffusion into the unstirred water layer, enhancing CND flux. In higher CND concentration regions, the CND flux became higher in the AS-HF solution than in the AS-LF solution. Thus, it is essential to elucidate the drug concentration-dependent impact of the colloidal drug-rich droplets on the drug absorption performance to optimize supersaturating formulations.

Synergistic Interaction of Ionic Liquid Grafted Poly(vinylidene Fluoride) and Carbon Nanotubes to Construct Water Treatment Membranes with Multiple Separation Properties.

In this study, the dual strategy of 1-butyl-3-vinylimidazolium bromide ionic liquid (IL) grafting and carbon nanotubes (CNTs) nanocomposition was applied to modify poly(vinylidene fluoride) (PVDF)-based membranes. The highly hydrophilic/oleophobic and fouling-resistant PVDF-g-IL/CNTs membranes with excellent separation efficiency were obtained by the nonsolvent-induced phase separation method with ethanol-water mixed solution as the coagulation bath. The grafted IL not only generated hydrophilic groups on PVDF chains but also acted together with the CNTs to induce the formation of hydrophilic β-crystalline phase of PVDF, which significantly improved the hydrophilicity and pore structure of the modified PVDF membranes. As a result, the pure water flux of the optimal membrane increased up to 294.2 L m-2 h-1, which was 5.2 times greater than that of the pure PVDF membrane. Simultaneously, the electrostatic interaction of the positive IL and the integration of CNTs enhanced adsorption sites of the membranes, producing exceptional retention and adsorption of dye wastewater and oil-water emulsion. This study presents a straightforward and efficient approach for fabricating PVDF separation membranes, which have potential applications in the purification of various polluted wastewater.

AFM Analysis of Polymeric Membranes Fouling

This work represents a part of a larger work, aimed at evaluating the fouling behavior of different flat polymeric membranes for low-pressure applications when placed in contact with industrial wastewater (IWW). To design and understand the operation of a membrane process it is essential to know the fouling mechanisms. Commercial PVDF and PS membranes were tested under static conditions. The reduction in membrane flux was calculated, before and after the fouling tests. Parameters such as membrane material, pore size, solids concentration, particle size, pH, temperature, flow rate, and pressure were studied to identify the fouling behavior of the membrane. The strong adhesion of organic molecules on the membrane surface develops a resistance to pore blockage which allows a significant decrease in the flow of clean water. It is important to note that membranes of the same material, PVDF, but with different pore size (0.2 and 0.5 mm), and membranes of different materials, PVDF and PS, but with the same pore size (0.2 mm) were tested to study the trend of surface fouling to predict it and/or design surface modifications of the membranes employed. A morphological analysis of the membranes was carried out to understand the fouling mechanism, the fouling times, and the nature of the block that determines the reduction of flow through the membrane itself. Roughness measurements reveal that roughness goes up to 120 minutes of immersing time in wastewater, but after 4 hours it returns to initial value but with a significant decrease of flux to water. Understanding the relationship between flux decline, morphology, and roughness role is key to preventing fouling and studying a valid method to clean the membrane.

Pilot scale fabrication of low fouling seawater desalination thin film composite reverse osmosis membrane

We report the pilot scale fabrication of thin film composite seawater reverse osmosis membrane (TFC-SW-RO) with low fouling propensity and improved permeate flux. In situ incorporation of poly(ethylene glycol) (PEG) into the polyamide (PA) network simultaneously improves the permeate flux (effect of hydrophilic channels) and antifouling property of the membrane. The PEG chains exhibit good stability during desalination of SW (NaCl = 33,000 mg L−1, applied pressure = 55.2 bar). The mechanism of PEG stabilization into the PA layer has been elucidated on the basis of hydrogen bond formation between ether linkage of PEG and carboxylic acid group of the PA network as well as steric hindrance posed by the network. The TFC-SW-RO membrane (no PEG) in several 100 m2 batches show pure water permeance of 1.4 L m−2 h−1 bar−1 and 98.5–98.8 % NaCl rejection during SW desalination. On the other hand, TFC-SW-RO-PEG shows pure water permeance of 2.2 L m−2 h−1 bar−1 with marginal drop in NaCl rejection (98.4–98.6 %). The TFC-SW-RO-PEG membrane exhibits improved antifouling (flux recovery ratio = 87 %) property during desalination of SW as compared to that of the pristine membrane (flux recovery ratio = 67 %). This work provides an important strategy for the fabrication of SW TFC RO membrane with improved performance.

Deciphering two-dimensional calcium fractional diffusion of membrane flux in neuron

Deciphering two-dimensional calcium fractional diffusion of membrane flux in neuron

Predicting water flux and reverse solute flux in forward osmosis processes using artificial neural networks (ANN) modelling with structural parameters

Artificial neural network (ANN) has gained increasing attention in modelling wastewater treatment processes because it harnesses historical datasets to uncover relationships between input and output data, enabling accurate predictions without the need for complex equations. However, there are few ANN studies that simultaneously predict both water flux (Jw) and reverse solute flux (Js) in the forward osmosis (FO) process. In this work, we present an ANN model designed with only eight input variables, introducing the rarely explored membrane structural parameter (S) as an input variable for the first time. Through the optimisation of hidden layers, neuron counts, and the combination of activation functions, the ANN model achieved high R-squared values of 94.6 % and 95.2 % for Jw and Js prediction, respectively. To assess the model’s versatility across different scenarios, the application scope of the model was further evaluated using three distinct membrane types (namely, substrate-modified, active layer-modified and interlayer-modified). Results demonstrated the ANN model’s capacity to accurately predict the water flux of the substrate-modified membranes. Remarkably, even though the interlayer-modified and active layer-modified membranes were not part of the model’s training, the ANN model still exhibited relative accuracy, effectively capturing the modifications made through the structural parameter input. Compared with the solution diffusion (SD) model, the ANN model showed promising potential as a simplified yet powerful tool to predict the water flux in FO processes. Its capability to deliver accurate results with fewer complexities makes it an attractive choice for the modelling of FO processes.

#1351 Assessment of safety and efficacy of expanded hemodialysis in comparison to HDF

Abstract Background and Aims In end-stage kidney disease, solutes with a wide spectrum of molecular weight, called uremic toxins, are retained due to impaired kidney cleansing capacity. Particularly, the retention of toxins in the middle molecular weight range 15–45 kDa might negatively affects multiple organ systems and metabolic pathways. The removal of such large uraemic toxins is still a challenge. HDF has produced some results although large convective volume, optimal vascular access to increase the blood flow rate and strict water quality management are required. Medium Cut-Off, high Retention Onset membrane have been recently developed introducing the concept therapy called “expanded haemodialysis” (HDx). Furthermore, vitamin E-coated membrane has potential beneficial effects on inflammation and oxidative stress. Method A prospective longitudinal single-center study was conducted for 3 months among 18 chronic haemodialysis patients. Patients were randomly assigned into either HDF with high flux membrane or HDx with Theranova or ViE-X membrane. The primary goal was to assess albumin loss among the three types of dialyzers. Secondary goals included assessment of depurative efficacy for uraemic toxins and clinical outcomes. Throughout the treatment, a proportional part of the dialysis fluid was collected to quantify albumin loss. Blood samples were taken before and after dialysis session in order to calculate the Removal Ratio and at two different intradialytic timepoints from arterial and venous line of the circuit in order to calculate instantaneous clearance. Results Mean albumin loss was significantly higher in patients undergoing HDx with Theranova membrane (ANOVA, p<0.001) without any difference in serum albumin concentration among the three groups. Instantaneous clearance of small and middle molecules was significantly higher in patients undergoing HDF, but we didn't find differences in removal ratio. Reduction of Erythropoietin resistance index was observed in patients treated with ViE-X membrane but it was related to their lower dialysis vintage. Conclusion HDx with Theranova membrane was associated with higher albumin loss without any effect on pre-dialysis serum albumin. Moreover, patients treated Theranova membrane, in the presence lower Qb, lower convective dose and lower instantaneous clearance reached same dialysis efficacy compared to HDF.

Preparation and properties of asymmetric inverse opal-like microfiltration membranes

Most types of commercially available MF membranes suffer limited separation performances due to huge deviations in pore size and low porosity. In view of this, a new and facile assembly strategy was proposed to prepare an asymmetric inverse opal (IO) like microfiltration (MF) membrane with ordered pore structure, high porosity and large water flux, which is a composite of a disordered layer with three-dimensional pore structures made by dissolved N, N-dimethylformamide (DMF) and an ordered layer with uniform pore size by using a sacrificial template method. The effects of SiO2 microsphere size and DMF treatment on the structure and properties have been investigated. Different DMF treatment times can significantly change the asymmetric structure distribution of MF membrane and further affect the permeability. The water flux of the asymmetric membrane increases with the DMF infiltration time. Based on the SiO2 microsphere template size of 494 nm and the DMF treatment time of 90 s, the porosity and pure water flux can reach 78 % and 1810 L/m2h, respectively. The membrane retains the IO-like structure layer with uniform pore size, and features excellent retention (almost 100 %) for SiO2 microspheres, indicating the great potential of asymmetric IO-like MF membranes for membrane separation applications.

In situ cleaning of foulants by gas scouring on the membrane-electrode in an electro-membrane bioreactor

Low-maintenance membrane cleaning is essential for the stable operation of membrane bioreactors. This work proposes an in-situ electrical-cleaning method using an electro-MBR. When the applied bias was transiently increased, the membrane flux recovered rapidly because of the scouring effect from gas evolution reactions. The exfoliation of the cake layer induced by gas scouring played a major role in mitigating membrane fouling, recovering the transmembrane pressure (TMP) by 88.6 % under optimal conditions. Membrane modules did not require replacement during the operation period due to the efficacy of electrical cleaning, with the TMP varying between 37.5 % and 62.5 % of the ultimate pressure requiring change of the membrane modules. Despite the increase in power consumption of 0.66 Wh·m−3 due to the additional applied bias, there was no need for chemical additives or manual maintenance. Therefore, the electrical cleaning method enhanced the service life and reduced the maintenance costs of the electro-MBR.

Effects of hydrogen bond donors on PVDF membrane modification using choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) were investigated as promising candidates in modifications towards hydrophobic polyvinylidene fluoride (PVDF) membranes based on its hydrophilic and hygroscopic properties. Five choline chloride-based DESs with various hydrogen bond donor (HBD) components were investigated as PVDF membrane modifiers by blending it with the membrane dope solution at 2 wt%. The incorporation of DESs appeared to influence the structure and morphology of the membranes, where macrovoid formations were suppressed and the formation of thin, densely porous skin layers were promoted as observed through SEM imaging. DES incorporation showed effects in contact angle reduction of the PVDF membranes from 90.22° to 60.07°, indicating hydrophilic modifications. Additionally, modifications with DESs yielded improvements in membrane flux (62.49 L/m2·h using glycerol-HBD) and protein solute rejection (74.62 % using glucose-HBD), though the overall tensile strength of the membranes were decreased from 4.24 MPa to the lowest value of 2.92 MPa. Ultimately, DESs were shown to be significant pore-forming agents in altering the morphology of PVDF membranes, and improving the thermal stability. Among the five tested DESs, PVDF modified with glycerol-HBD DES yielded the best membrane parameters and performances. DESs were demonstrated as prospective membrane modifiers in inducing hydrophilicity and influencing membrane morphology.

Optimizing reverse osmosis desalination from brackish waters: Predictive approach employing response surface methodology and artificial neural network models

A mathematical model frame has been developed to optimize the performance of reverse osmosis (RO) desalination in brackish waters with medium to high salt concentrations using response surface methodology (RSM) and artificial neural network (ANN), specifically catered towards efficiently operating RO desalination systems. The RSM model aims at predicting RO performance with second-order polynomials based on 15 experimental datasets. Inputs for RSM model include feed TDS concentration, feed water flow rate, and concentration-to-desalination ratio, while the outputs consider rejection, membrane flux, performance index, and specific energy consumption. The Genetic Algorithm optimized back-propagation Neural Network was employed to update network weights and biases, leading to an optimal ANN network structure of 3–10-4. A ratio of 70 % training, 15 % validation, and 15 % test data was chosen to establish an ANN model that predicts the performance of RO desalination. The ANN model demonstrated significantly higher prediction accuracy than the RSM model, with impressive correlation coefficients of 0.9936 for the performance index and 0.9932 for SEC prediction, and low RMSE of 0.85 for rejection. To maximize the performance index and minimize specific energy consumption, a two-step optimization method was further set up by applying the RSM model to initially determine optimal process conditions followed by the ANN model to enhance the accuracy of performance forecasts. Optimal process conditions were proposed for specific feed TDS scenarios, which involved setting a feed TDS concentration limit to meet drinking water standards.

Preparation and modification of PVDF membrane via VIPS method for membrane distillation

Membrane distillation (MD) is a promising technology for treating high-salinity mine water. However, MD membranes are known to have low membrane flux and are prone to fouling. In this study, we used the cost-effective and controllable vapor-induced phase separation (VIPS) technology to prepare polyvinylidene difluoride (PVDF) membranes, replacing the traditional immersion precipitation method and optimizing the membrane structure by including LiCl and acetone as porogen in the casting solution. The results showed that the membrane prepared using the VIPS method exhibited a highly open interconnected porous surface. Unlike traditional MD membranes with a dense epidermal layer and large finger-like pores, these optimized membranes had a symmetrical and uniform internal structure, leading to a high flux of 8.62 kg·(m2·h)−1 during direct contact membrane distillation testing. Different porogens produced varied results on the VIPS process and varying effects on membrane structure. The use of LiCl promoted the formation of PVDF β-phase, resulting in a decrease in the number of spherical nodules on the membrane surface, as well as improved density and smoothness. Consequently, this reduced fouling risk during membrane distillation while slightly decreasing membrane flux. On the other hand, acetone rapidly evaporated during the VIPS process, facilitating pre-gelatinization and α-phase formation of PVDF. This concurrent effect effectively restricted excessive nodule growth on the membrane surface, endowing the membrane with antifouling capabilities while preserving high flux.