Salt Rejection Research Articles

Engineering multi-level structured electrospun nanofiber Janus membrane for direct contact membrane distillation

The membrane distillation (MD) has been considered as an attractive technique for the desalination and water treatments. However, the membrane with the superhydrophobic surface is still urgently needed for the wide application of MD process. Inspired by nature, the membranes with the highly porous structure have been fabricated by electrospinning to enhance the water vapor permeation in MD process. In this work, a hydrophobic layer with the hierarchical reentrant architecture was fabricated by electrostatically depositing silicon dioxide (SiO2) nanoparticles on the surface of polyvinylidenefluoride electrosprayed layer followed by the fluorination treatment. The properties of hydrophobic layers were evaluated by varying the electrospraying time and SiO2 loading amount. The optimal membrane had a water contact angle value of 145.7° and surface roughness of ∼275 nm, demonstrating a water flux of 21.2 L.m−2.h−1 and superior salt rejection of >99.9 % when 3.5 wt% NaCl solution was used as the feed solution and the temperature difference was set as 40 °C. The membrane showed an excellent operation stability and effective mitigation in scaling and fouling tendency. The prepared membrane could be applied as a good candidate for the MD-based water treatment processes.

Preparation of polysulfone-based nanofiber Janus membrane for membrane distillation containing organic pollutants

Membrane distillation is an emerging wastewater treatment technology that harnesses low-grade heat as an energy source and exhibits potential for complete desalination. Nonetheless, two notable challenges hinder the practical application of this technology: membrane wetting and fouling. To counter these challenges, an innovative anti-fouling Janus membrane with asymmetric wettability was developed through electrospinning. The hydrophobic layer was formed using tetraethyl orthosilicate/polysulfone (PSF), and the superhydrophilic layer was created using polyvinylpyrrolidone (PVP)/PSF. A sensitive adhesion probe was used to assess the anti-fouling performance of the Janus membrane against oil. Molecular dynamics simulation suggested that PVP reduced the adsorption tendency of the membrane for humic acid (HA). Under experimental conditions involving saline water with HA and a saline oil–water emulsion, the non-Janus membrane suffered severe fouling, resulting in rapid water permeate flux decline. However, the Janus membrane demonstrated consistent permeate flux (26.84 LMH and 24.92 LMH) and an impressive salt rejection rate (> 99.99%). This study suggests that the Janus membrane, with its high permeate fluxes and remarkable resistance to fouling and wetting, could be an effective solution for wastewater treatment, with considerable potential for future application.

Sodium chloride solution transport through a carbon nanotube with an embedded carbon nanotube via molecular dynamics simulations

Carbon nanotubes hold significant potential for developing highly efficient desalination membranes. However, achieving both enhanced water transfer rate and salt rejection efficiency simultaneously has been challenging due to the pore size limitation. In this study, we discovered that embedding a carbon nanotube within a large-diameter carbon nanotube enables the simultaneous enhancement of both water transfer rate and salt rejection efficiency. This outcome is attributed to the accelerated water velocity and the blockage of ions entering the narrowed cross-section of the carbon nanotube. These findings have valuable implications for the design of fast water transport membranes with high salt rejection efficiency.

Robust superhydrophobic Poly(vinylidene fluoride) membranes with spherulitic surface morphology against wetting and scaling in membrane distillation

Membrane distillation (MD) offers a theoretically complete interception of salts, presenting a promising desalination pathway for freshwater supply. However, conventional hydrophobic membranes fail to desalinate water containing surfactants or supersaturated gypsum over prolonged periods. To address wetting and scaling challenges, we developed a superhydrophobization methodology for poly (vinylidene fluoride) membranes by in situ controlling spherulitic surface morphology through thermally induced phase separation. The major advantages of this one-step strategy lie in its fluorination-free, template-free, and nanoparticle-free. The as-prepared membranes exhibit a rough morphology and superhydrophobic characters with high air-trapping pockets. They demonstrate stable vapor fluxes and high salt rejections (>99 %) when used in desalination processes for saline water containing 0.6 mM sodium dodecyl sulfate, 0.03 mM cetyltrimethylammonium bromide, or gypsum solution with a saturation index of 1.1. Also, the outstanding anti-wetting and anti-scaling properties were demonstrated using synthetic shale gas wastewater. The formation of an air layer on the integrated spherulitic surface highlights the local kinetic barrier and slippery surface, effectively preventing the attachment of amphiphilic surfactants and mineral ions. Importantly, due to the membrane's structural integrity, the spherulitic surface displays high robustness and minimal impact from abrasion cycles and ultrasonication. This work exemplifies a facile strategy to engineer micro-/nano-spherulitic surface morphology for robust superhydrophobic membranes used in MD desalination.

Utilization of MOF‐enhanced hydrophilic nanocomposite reverse osmosis membrane for desalination with antifouling capabilities

AbstractCellulose acetate (CA) membranes used in reverse osmosis (RO) desalination techniques often face fouling challenges. In this experimental study, the phase inversion method was employed to investigate the incorporation of graphene oxide nanoparticles (GONP) metal–organic frameworks (MOF), into the casting solution for composite CA‐RO membranes. The effects of varying GONP concentrations on fouling resistance and hydrophilicity were evaluated using scanning electron microscopy (SEM), contact angle measurements, and water content analysis. The results demonstrated that the modified CA membrane with 0.05 wt% GONP exhibited improved water permeability (10.3 L/m2 h) and salt rejection (95.8%) compared with the pristine CA membrane. These improvements stem from increased hydrophilicity and reduced fouling. This study's findings suggest that incorporating GONP into the polymeric doped solution can effectively mitigate fouling issues and enhance the performance of RO membranes in desalination applications.Highlights GONP enhances hydrophilicity, reducing fouling in desalination. Effects of varying GONP concentrations were studied. GONP‐CA membrane shows better permeability and salt rejection than pristine. Nanocomposite membranes promise in overcoming fouling in RO membranes.

Investigating Permselectivity in PVDF Mixed Matrix Membranes Using Experimental Optimization, Machine Learning Segmentation, and Statistical Forecasting.

This research examines the correlation between interfacial characteristics and membrane distillation (MD) performance of copper oxide (Cu) nanoparticle-decorated electrospun carbon nanofibers (CNFs) polyvinylidene fluoride (PVDF) mixed matrix membranes. The membranes were fabricated by a bottom-up phase inversion method to incorporate a range of concentrations of CNF and Cu + CNF particles in the polymer matrix to tune the porosity, crystallinity, and wettability of the membranes. The resultant membranes were tested for their application in desalination by comparing the water vapor transport and salt rejection rates in the presence of Cu and CNF. Our results demonstrated a 64% increase in water vapor flux and a salt rejection rate of over 99.8% with just 1 wt % loading of Cu + CNF in the PVDF matrix. This was attributed to enhanced chemical heterogeneity, porosity, hydrophobicity, and crystallinity that was confirmed by electron microscopy, tensiometry, and scattering techniques. A machine learning segmentation model was trained on electron microscopy images to obtain the spatial distribution of pores in the membrane. An Autoregressive Integrated Moving Average with Explanatory Variable (ARIMAX) statistical time series model was trained on MD experimental data obtained for various membranes to forecast the membrane performance over an extended duration.

Photo-Electro-Thermal Textiles for Scalable, High-Performance, and Salt-Resistant Solar-Driven Desalination.

Solar-driven interfacial evaporation is an emerging desalination technology that can potentially relieve the freshwater scarcity issue. To obtain high and continuous evaporation rates for all-weather, chemically engineered structural materials have been widely explored for simultaneous photothermal and electrothermal conversion. However, many previously reported fabrication processes involve poor integration and considerable energy loss. Herein, a scalable photo-electro-thermal textile is proposed to enable high efficiency, long-term salt rejection, and solar-driven desalination. Specifically, the photo-electro-thermal yarns with a core (commercial electric wire)-shell (polypyrrole-decorated Tencel) structure realize the integration of electrothermal and photothermal conversion. The wrapping eccentricity of 1.53mm and pitch of 3Tcm-1 for the electric wire are rationally regulated to achieve a high surface temperature of over 52°C at a 3V DC input. As a result, exceptional and stable evaporation rates of 5.57kgm-2h-1 (pure water) and 4.89kgm-2h-1 (3.5wt.% brine) under 1kWm-2·radiation with a 3V input voltage are realized. Practical application shows that the textiles can achieve high water collection of over 46kgm-2d-1 over the whole day of operation. The constructed photo-electro-thermal textile-based evaporator provides an effective method for commercial and scalable photo-electro-thermal conversion to achieve high-performance and salt-resistant solar-driven desalination.

High-temperature reverse osmosis and molecular separation with robust polyamide-ceramic membranes

Polyamide thin-film composite (TFC) membranes are widely used for reverse osmosis (RO), but most commercial RO membranes have a limited operating temperature of <45 °C. This has constrained the broader applications of RO in industries, where process and water feeds with high temperature >50 °C are common. In this study, robust polyamide-ceramic TFC membranes were developed for high-temperature RO (HT-RO). RO-type polyamide thin-film was successfully synthesized on the inner surface of ceramic tubular membranes via interfacial polymerization. The polyamide-ceramic membranes exhibited excellent thermal stability, maintaining high NaCl rejection (>98 %) and steady water permeability (∼5 LMH/bar) during HT-RO at 70 °C. The molecular weight cut-off (MWCO) of the membranes increased slightly from 90 to 140 Da at 70 °C, and the surface charge played an important role in maintaining the high salt rejection. Long-term stability tests showed that polyamide thin-films may undergo thermal hydrolysis at 80 °C. It was also found that polymeric substrates of flat-sheet RO membranes may experience serious compaction at high temperature, which could subsequently affect the performance and stability of the polyamide layer. The ceramic substrates provide strong support at high temperature, and the highly stable polyamide-ceramic membranes demonstrated huge potential for RO applications under more challenging conditions.

Influences of substrate pore size on the morphology and separation performance of MoS2-interlayered thin-film nanocomposite membranes

Recent studies reveal the enhancement in water permeability for thin-film nanocomposite (TFN) membranes that incorporate an interlayer (TFNi), mainly when developed using substrates with larger pores. Nevertheless, the impact of substrate pore size on the membrane's morphology and separation performance requires further exploration. The study systematically investigates how the pore size of polycarbonate track-etched (PCTE) substrates influences these factors. Findings suggest that larger pores lead to rougher membrane surfaces and higher water permeance by reducing hydraulic transport resistance. However, optimal performance on larger pores requires a thicker MoS2 interlayer, leading to a thinner polyamide layer. Specifically, on PCTE-200 substrates, the MoS2 interlayer made up of large MoS2 nanosheets creates a more tortuous path for water molecules, limiting permeance. Conversely, smaller pores than the MoS2 nanosheets' dimensions obstruct the storage and diffusion of PIP monomers, negatively affecting the polyamide film and salt rejection. These findings underscore the significance of choosing the suitable substrate and adjusting interlayer thickness for creating TFN membranes with desired separation characteristics. The study provides valuable insights into the role of substrate selection and interlayer thickness in TFNi membrane design, offering guidelines for developing high-performance membranes for various separation tasks.

Design and fabrication of porous three‐dimensional Ag-doped reduced graphene oxide (3D Ag@rGO) composite for interfacial solar desalination

Solar-driven interfacial desalination technology has shown great promise in tackling the urgent global water scarcity crisis due to its ability to localize heat and its high solar-to-thermal energy conversion efficiency. For the realization of sustainable saline water desalination, the exploration of novel photothermal materials with higher water vapor generation and photothermal conversion efficiency is indispensable. In the current study, a novel 3D interconnected monolithic Ag-doped rGO network was synthesized for efficient photothermal application. The Ultraviolet–Visible-Near Infrared (UV–Vis-NIR) and FTIR analyses demonstrated that the controlled hydrothermal reduction of GO enabled the restoration of the conjugated sp2 bonded carbon network and the subsequent electrical and thermal conductivity through a significant reduction of oxygen-containing functional groups while maintaining the hydrophilicity of the composite photothermal material. In the solar simulated interfacial desalination study conducted using 3.5 wt.% saline water, the average surface temperatures of the 3D material increased from 27.1 to 54.7 °C in an hour, achieving an average net dark-excluded evaporation rate of 1.40 kg m−2 h−1 and a photothermal conversion efficiency of ~ 97.54% under 1 sun solar irradiance. In the outdoor real-world application test carried out, the surface temperature of the 3D solar evaporator reached up to 60 °C and achieved a net water evaporation rate of 1.50 kg m−2 h−1 under actual solar irradiation. The 3D interwoven porous hierarchical evaporator displayed no salt precipitation over the 54-h period monitored, demonstrating the promising salt rejection and real-world application potential for efficient desalination of saline water.

An investigation of a proposed freezing desalination system integrating sweating effect and a Centrifugal-Based brine rejection technique

Freeze desalination (FD) presents a promising yet underutilized technique for addressing global water scarcity, hindered by challenges such as the necessity for ice crushing and washing. This study introduces an innovative FD system incorporating sweating effects and centrifugal brine rejection, aiming to simplify the process by eliminating these additional steps. We evaluate the impact of key variables including sweating period, centrifugation duration, and rotational velocity on ice quality and process efficiency. Through systematic examination, our findings reveal that the sweating period significantly influences product salinity and salt rejection efficiency, achieving a salinity reduction from 40 ppt to 0.99 ppt with a 95.05 % salt rejection rate. Additionally, the centrifugation method showcased low power consumption, marking a significant advancement towards more sustainable desalination practices. This research not only demonstrates the feasibility of the proposed FD system but also sets the groundwork for future enhancements in the field of desalination technology.

Highly efficient and selective nitrate and Hg(II) removal from wet oxidation flue gas purification wastewater using bifunctional MXene nanofiltration membrane

The wet oxidation process is a promising method for simultaneously removing SO2, NO, and Hg0 from coal-fired flue gas. However, the resource utilization of the resulting wastewater, which is enriched with complex ions such as Hg2+, NH4+, NO3−, and SO42−, remains a significant challenge. To achieve the simultaneous goals of concentrating NH4+/NO3−/SO42− ions, adsorbing and separating Hg2+ ions, and reusing wastewater, a bifunctional MXene composite nanofiltration membrane with large interlayer spacing and excellent electrostatic repulsion was developed. The membrane was prepared by co-depositing MXene nanosheets, carboxylated multi-walled carbon nanotubes (MWCNTs), and sodium dodecyl sulfate (SDS) onto an NF-90 membrane. The resulting MXene-MWCNTs-SDS (MMS-COOH) composite membrane demonstrated exceptional salt rejection of 84.4 % for NO3−, 89.0 % for NH4+, 99.8 % for SO42−, and 99.7 % for Hg2+. After 30 cycles, the membrane structure remained stable, maintaining good reusability, with NH4+ and SO42− rejection still reaching 90.0 %. Moreover, the maximum adsorption capacity for Hg2+ was 2869.6 mg g−1, while the capacities for Cr6+ and Pb2+ were 577.6 and 316.8 mg g−1, respectively. The MMS-COOH composite membrane introduces an innovative method for the benign treatment of wet oxidation flue gas purification wastewater and facilitates the recovery of (NH4)2SO4 and NH4NO3 as fertilizers, holding a promising application prospect.

Fabrication of loose nanofiltration membrane with Laponite nanosheets incorporated into polyamide layer for effective dye/divalent salt separation

Traditional methods for treating textile wastewater face significant challenges when it comes to effectively separating dye/salt mixtures while maintaining high levels of dye recovery and desalination efficiency. In the present study, we proposed a novel loose nanofiltration (LNF) membrane fabricated through the Laponite (Lp) assisted interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC). The unique structure of Lp nanosheets, characterized by exfoliated lamellae, serves to modulate the diffusion rate of PIP during interfacial polymerization, influencing the structural and performance characteristics of the resulting nanofiltration membranes through hydrogen bonding interactions. By controlling the concentration and standing time of Lp nanosheets in the amine aqueous solution, we systematically tailored the surface morphology of the LNF membrane from nodular to convex structures. Additionally, we regulated the thickness of the polyamide layer within a range of 175–276 nm. Due to this well-designed structure and excellent hydrophilicity, the LNF membrane possessed good water permeability (30.7 L/(m2·h·bar)) and superior efficiency in separating dyes from salts. It exhibited exceptional dye rejections (e.g., 99.1 % for Congo Red, 99.4 % for Methyl blue) and low salt rejections (e.g., Na2SO4: 2.73 %, MgCl2: 1.95 %). Besides, the composite membrane displayed favorable anti-fouling properties and operational stability, underscoring its potential in applications.

Design an in-situ anti-bacterial structure of nanofiltration membrane with a novel bisimidazoline aqueous monomer

Bio-fouling is a key issue for the nanofiltration operation. In this study, 1, 2-bis (N-aminoethyl imidazoline) ethane (BAIE) firstly was used as a novel bisimidazoline aqueous monomer to prepare the anti-bacterial nanofiltration (NF) membranes. A novel nanofiltration (BAIE-TMC NF) membrane with in-situ anti-bacterial structure and anti-fouling property was fabricated via interfacial polymerization (IP) with trimesoyl chloride (TMC), basing on a polyethersulfone (PES) substrate. Protonated imidazole endowed the surface of BAIE-TMC NF membrane with weak electronegativity, and its salt rejection sequence was MgSO4 > Na2SO4 > MgCl2 > NaCl > LiCl. Meantime, the BAIE-TMC NF membrane with 0.5 wt% BAIE (M-0.5) exhibited a high rejection for bivalent ions, with a high MgSO4 rejection (94.7 %). Notably, BAIE-TMC NF membrane containing an in-situ anti-bacterial imidazole structure showed significant anti-fouling and anti-bacterial properties. After BSA or HA filtration process, the flux recovery rates of all BAIE-TMC NF membranes were higher than 95 %, and M-0.5 exhibited high inhibition performance against Escherichia coli (98.5 %) and Staphylococcus aureus (98.4 %). Furthermore, M-0.5 exhibited excellent long-term separation stability during the three weeks separation experiment. BAIE can serve as an effective aqueous monomer for fabricating in-situ anti-bacterial and anti-fouling NF membrane to achieve the rejection of organic pollutant and bivalent ions.

Low Fouling Polyelectrolyte Layer-by-Layer Self-Assembled Membrane for High Performance Dye/Salt Fractionation: Sequence Effect of Self-Assembly.

Layer-by-layer (LbL) self-assembly of oppositely charged polyelectrolytes (PEs) is usually performed on a conventional ultrafiltration base substrate (negative zeta potential) by depositing a cationic PE as a first layer. Herein, we report the facile and fast formation of high performance molecular selective membrane by the nonelectrostatic adsorption of anionic PE on the polyvinylidene fluoride (PVDF, zeta potential -17 mV) substrate followed by the electrostatic LbL assembly. Loose nanofiltration membranes have been prepared via both concentration-polarization (CP-LbL, under applied pressure) driven and conventional (C-LbL, dipping) LbL self-assembly. When the first layer is poly(styrene sodium) sulfonic acid, the LbL assembled membrane contains free -SO3- groups and exhibits higher rejection of Na2SO4 and lower rejection of MgCl2. The reversal of salt rejection occurs when the first layer is quaternized polyvinyl imidazole (PVIm-Me). The membrane (five layers) prepared by first depositing PStSO3Na shows higher rejection of several dyes (97.9 to >99.9%), higher NaCl to dye separation factor (52-1800), and higher dye antifouling performance as compared to the membrane prepared by first depositing PVIm-Me (97.5-99.5% dye rejection, separation factor ∼40-200). However, the C-LbL membrane requires a longer time of self-assembly or higher PE concentration to reach a performance close to the CP-LbL membranes. The membranes exhibit excellent pressure, pH (3-12), and salt (60 g L-1) stability. This work provides an insight for the construction of low fouling and high-performance membranes for the fractionation of dye and salt based on the LbL self-assembly sequence.

Tailoring polyamide membranes via dynamic interfacial manipulation with functional Fe3O4 nanoparticles for elevated Nanofiltration performance

This study investigates the enhancement of thin-film-composite polyamide (TFC-PA) membranes for nanofiltration (NF) by conducting direct interfacial polymerization (IP) at a substrate-free water/n-hexane interface. Fe3O4 nanoparticles, stabilized with surfactants sodium laurate (SL) and hexadecyltrimethylammonium bromide (CTAB), were employed to dynamically influence the diffusion of piperazine (PIP) monomers. The incorporation of these nanoparticles enabled the modulation of the IP process, yielding membranes with distinct morphologies and performance characteristics. Specifically, membranes with SL-stabilized Fe3O4 (SLF) demonstrated enhanced cross-linking and superior salt rejection capabilities for divalent cations, with MgCl2 and CaCl2 rejection rates notably increasing to 95.5 % and 93.4 % respectively. Conversely, CTAB-stabilized Fe3O4 (CTABF) membranes, characterized by smoother surfaces and a looser structure, exhibited increases in water permeance up to 140 % relative to controls, but with a significant reduction in salt rejection efficacy as nanoparticle concentration increased. This study highlights the crucial impact of surfactant-stabilized nanoparticle modifications in manipulating the IP process and tailoring the filtration properties of PA membranes, offering promising avenues for optimizing NF membrane technology.

Exploring mass transfer mechanisms in reverse osmosis membranes: A comparative study of SDM and DSPM-DE models

Thin-film composite reverse osmosis (RO) membranes have dominated desalination technology for decades, with the solution diffusion model (SDM) serving as the gold standard for interpreting mass transfer phenomena since its inception. However, debates still persist regarding the effect of charge on separation performance, owing to the SDM's inability to explore membrane charge. In this study, polyethyleneimine (PEI) was utilized to modify the surface of a commercial seawater desalination membrane (SW30, Dupont Company), imparting regulatable charge properties based on the solution pH. The separation performance of the modified RO membrane was experimentally validated under varying NaCl feed salinities. Specifically, the Donnan-steric pore model with dielectric exclusion (DSPM-DE), known as a charge-responsive model, was employed and juxtaposed with SDM to authenticate the experimental findings. The results indicated that the dielectric effect primarily governed ion distribution (Na+ and Cl−) within the membrane, followed by the steric effect, and ultimately, the Donnan effect. Consequently, DSPM-DE aligned well with the observed salt rejection only when the membrane was strongly charged (that is, under acidic or alkaline conditions), but performed poorly in the neutral state. This observation, rarely revealed in previous research, stems from conventional desalination membranes being negatively charged in most natural water environments. Conversely, the SDM aligned well with the experimental data because it solely considered the solutes' solubility parameters and diffusion coefficient, independently of the surface charge of the desalination membranes. Given the extensive research on surface modification, our study demonstrates the limited influence of charge effects on the selective enhancement of RO membranes.

Built-in Electric Fields in Heterostructured Lamellar Membranes Enable Highly Efficient Rejection of Charged Mass.

Separation membranes with homogeneous charge channels are the mainstream to reject charged mass by forming electrical double layer (EDL). However, the EDL often compresses effective solvent transport space and weakens channel-ion interaction. Here, built-in electric fields (BIEFs) are constructed in lamellar membranes by assembling the heterostructured nanosheets, which contain alternate positively-charged nanodomains and negatively-charged nanodomains. We demonstrate that the BIEFs are perpendicular to horizontal channel and the direction switches alternately, significantly weakening the EDL effect and forces ions to repeatedly collide with channel walls. Thus, highly efficient rejection for charged mass (salts, dyes, and organic acids/bases) and ultrafast water transport are achieved. Moreover, for desalination on four-stage filtration option, salt rejection reaches 99.9 % and water permeance reaches 19.2 L m-2 h-1 bar-1. Such mass transport behavior is quite different from that in homogeneous charge channels. Furthermore, the ion transport behavior in nanochannels is elucidated by validating horizontal projectile motion model.

Electrospun bio-polymeric nanofibrous membrane for membrane distillation desalination application

Polylactic acid (PLA) has been explored as a sustainable material for membrane distillation (MD) membranes using electrospinning for the first time. Adjusting the electrospinning parameters of PLA nanofiber, such as concentration, voltage, collector distance, humidity, and flow rate, resulted in uniformly distributed and smaller nanofibrous structures. Heat treatments were also performed to enhance the tackiness and fusibility of the fibers within the nanofibrous structure, optimizing the pore size, hydrophobicity, and surface roughness of the PLA membranes. The hierarchical structure of the PLA membranes improved the liquid entry pressure (LEP) and mechanical strength by 320 % and 230 %, respectively. The membrane characteristics were assessed in terms of porosity, pore size, surface roughness, and contact angle, which determined the impact of the wettability of the membrane under different conditions. The results showed that under certain constraints, PLA membranes could be effectively used in the air gap membrane distillation (AGMD) process, achieving a permeated flux of ~2 kg/m2h and a salt rejection of 99 %. However, PLA-based nanofibrous membranes are unsuitable for MD applications at feed temperatures above 60 °C and a flow rate of 60 LHP. This study provides a strong basis for developing and manufacturing eco-friendly bio-based nanofibers materials for desalinating saltwater.

Eco-Friendly Superhydrophobic Modification of Low-Cost Multi-Layer Composite Mullite Base Tubular Ceramic Membrane for Water Desalination

This study aimed to investigate and develop a cost-effective and superhydrophobic ceramic membrane for direct contact membrane distillation (DCMD) applications. Two types of mullite-based composite membranes were prepared via extrusion and sintering techniques. To create a small and narrow pore diameter distribution on the membrane surface, the dip-coating technique with 1 µm alumina was employed. The hexadecyltrimethoxysilane eco-friendly grafting agent was adopted to modify low-cost multilayer mullite-based composite membranes, transforming them from hydrophilic to superhydrophobic. The prepared membranes were characterized via field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), liquid entire pressure (LEP), contact angle, atomic force microscopy (AFM), porosity, and membrane permeability. The results of the prepared membranes validate the appropriateness of the material for membrane distillation applications. The optimized membrane, with a contact angle of 160° and LEP = 1.5 bar, was tested under DCMD using a 3.5 wt.% sodium chloride (NaCl) synthetic solution and Persian Gulf seawater as a feed. Based on the acquired results, an average permeate flux of 3.15 kg/(m2·h) and salt rejection (R%) of 99.62% were found for the 3.5 wt.% NaCl solution. Moreover, seawater desalination showed an average permeate flux of 2.37 kg/(m2·h) and salt rejection of 99.81% for a 20-h test without any pore wetting. Membrane distillation with a hydrophobic membrane decreased the turbidity of seawater by 93.13%.