Salt Rejection Research Articles

Comparison of 2D and 3D materials on membrane modification for improved pressure retarded osmosis (PRO) process

Pressure retarded osmosis (PRO) is a sustainable process that convert Gibbs free energy to osmotic energy by mixing two solutions of different salinities. The main challenges in the design of PRO membranes are obtaining a membrane with high water permeability and low salt permeability but also very high mechanical strength because the PRO process involves high pressure on the draw solution. Commercially available RO membranes with potential utility in a PRO system exhibit a high salt rejection rate but low water permeability and mechanical stability. Surface modification is a promising strategy for tuning the fundamental properties of the membranes (e.g. hydrophilicity, surface charge and thickness) that can improve the filtration performance of the membranes. The coating layer can also improve the mechanical stability of the membranes. Therefore, in this work, various types of modification materials were applied to the commercial available RO membranes to enhance their performance.With the assistance of hydrophilic materials (e.g. polydopamine – PDA), filtration performance of the membranes can be increased through membrane modification by 2D materials with high charge intensities (e.g. polyelectrolytes and graphene oxides) and by 3D mesoporous materials (e.g. zeolites), which increases the thickness of the membrane that can be beneficial in mechanically reinforcing the membrane. In this work, we modified commercial RO membrane with PDA, polyelectrolytes, graphene oxide and zeolites (ZSM-5). Improved filtration performance (increased water permeability and maintained salt permeability) of the modified membrane was observed. Tensile tests showed enhanced mechanical strength of the modified membranes, especially following 3D zeolites modification (up to 35 % of higher tensile strain was reported). Interestingly, a lower concentration of PDA (2 mg/mL) and zeolites resulted in higher mechanical strength of the modified membranes. Such results were likely due to a more homogenous coating layer when a low modifier concentration was applied. The thin and uniform layer can better absorb energy when membranes are under high pressure.

Thin film nanocomposite nanofiltration with tannic acid-Fe(III) complexes functionalized Ti3C2Tx for enhanced divalent-salinity-water separation with a superior durability

Incorporating nanomaterials for a thin film nanocomposite (TFN) layer has been verified effective to improve the separation performance of nanofiltration (NF) membranes, whereas the poor compatibility between nanomaterials and polyamide (PA) matrix leads to a decrease in the salt rejection and pollution resistance. In this study, inspired by a new interface-bridging idea, Ti3C2Tx was bonded with tannic acid-Fe(III) (TA-Fe(III)) complexes, and then incorporated into a PA matrix for the first time to obtain a novel TFN NF membrane. The introduction of TA-Ti3C2Tx was found to effectively reduce the diffusion of piperazine, and thus result in the induction of a thinner, lower roughness, more hydrophilic, and defect-free PA layer. With the addition of 0.015 wt% TA-Ti3C2Tx, the TFN membrane obtained the highest water permeability of 12.17 L m−2 h−1 bar−1, almost twice that of the pristine membrane, with a high Na2SO4 rejection above 97 %. In addition, the TA-Ti3C2Tx-filled TFN membranes were verified to exhibit excellent antifouling performance and pressure resistance with a high durability, which is crucial for the practical application in salinity water treatment. This study provides an effective strategy to tailor the interfacial microstructural of nanoparticle-filled NF membranes for superior divalent-salinity-water separation.

Beads-on-string structural nanofiber membrane with ultrahigh flux for membrane distillation

Membrane distillation (MD) is a promising technology among various desalination processes. However, the membrane used in MD is still problematic due to its low permeability and tendency to become wet. In this work, we fabricated a novel electrospun nanofiber membrane (ENM) with micro-nano structures resembling beads on a string to enhance water flux and anti-wetting properties in MD desalination. The composite ENM consists of a heat-conducting top layer made of polyvinylidene fluoride co-hexafluoropropylene (PH) nanofibers embedded with carbon sphere (CS) nanoparticles and a heat-insulating support layer made of pH nanofibers. The PH/CS top layer with beads-on-string micro-nano structures can not only provide a rough surface to elevate anti-wetting property of the membrane, but also create a maximum temperature difference inside the membrane to improve mass transfer of water vapor. The PH/CS composite ENMs acquired the highest water flux of ∼ 71.3 L m−2 h−1 at a temperature difference of 40 °C, and its salt rejection rate for a 3.5 wt% NaCl solution was higher than 99.9% in direct contact membrane distillation. Meanwhile, the composite ENM exhibited long-term stability of 5100 min. Our work presents a novel composite ENM with great potential for promoting water flux and anti-wetting properties towards MD desalination.

Exploration of a two-stage polymerization mechanism in construction of dense polyester membranes for drinking water treatment

Due to the relatively low reactivity of hydroxyls with acyl chloride groups, the synthesized polyester (PE) membranes commonly have loose structures, only capable of removing large-molecule organics with low rejection of inorganic salts. In this study, the pore size reduction of the synthesized PE membrane was successfully achieved by optimizing the interfacial polymerization (IP) reaction between erythritol and trimesoyl chloride (TMC). The optimized membrane was able to maintain a high xylose rejection (∼60 %) and acceptable water permeance (7.85 L m−2 h−1 bar−1), which was suitable for drinking water treatment. Through comprehensive characterizations, a two-stage membrane formation process was demonstrated regarding the reaction between aqueous monomers with different reactive functional groups and TMC. The highly reactive primary hydroxyls more preferentially participated in the initial reaction stage, leading to a linear cross-linking pattern of polyester. When the molecular diffusion was inhibited, the participation of secondary hydroxyls made the reaction proceed toward partial or full cross-linking. The distinct roles of the two kinds of hydroxyl groups were further verified by the energy barrier differences obtained by density functional theory (DFT) calculation. The exploration of membrane-optimized preparation and formation mechanisms can promote the structural regulation and tailored synthesis of PE membranes for various applications.

A non-substrate-specific technique of antifouling and antiwetting Janus membrane fabrication for membrane distillation

Although Janus membranes (comprising a hydrophilic antifouling layer on a wetting-resistant membrane substrate) have shown promise in sustainable membrane distillation (MD) processes for treating industrial wastewaters, most fabrication methods are substrate-specific and lack a universal technique for robust Janus MD membranes. Here, we present a non-substrate-specific technique using polydopamine-assisted, surface-initiated atom-transfer radical-polymerization (ATRP) that grafts a zwitterionic polymer layer onto any wetting-resistant substrate. We first prepare a model omniphobic substrate by surface fluorination of a quartz fiber mat, followed by polydopamine-assisted ATRP to complete Janus membrane fabrication. The grafting of zwitterionic polymer layer with a tunable thickness (∼1–10 μm) on one side of the membrane surface, while preserving the omniphobicity of the membrane substrate, is demonstrated. The binding robustness of the two layers of disparate wettability is then shown. An excellent antifouling functionality of the Janus membrane is confirmed by complete oil detachment in a static oil-fouling test, and by the stable desalination with nearly perfect salt rejection (> 99 %) in direct contact MD using a surfactant-stabilized, crude oil-in-brine emulsion, as simulated high-salinity industrial wastewater feed. Finally, we apply our modification technique to other lab-fabricated as well as commercial non-wetting substrates to demonstrate its universal applicability for Janus membrane fabrication.

Enhanced separation performance of composite nanofiltration membranes via electrostatic air spray PSS/PEI interlayer

Thin-film composite (TFC) membranes with an interlayer were prepared extensively for desalination, but the hydrophilicity and permeability were not well improved. In this work, a smooth and hydrophilic interlayer was constructed by electrostatic air spray deposition (EASD) of poly (sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI) on the polyethersulfone substrate and an ultra-thin separation layer was prepared using interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) to acquire high-performance composite nanofiltration (NF) membranes. The polymer solution was atomized into tiny particles under a high-pressure electrostatic air spray effect, facilitating the deposition of PSS/PEI with good homogeneity and enabling a denser and smoother interlayer surface. The introduction of PSS/PEI enhanced the hydrophilicity of TFC membranes and increased the repulsion of divalent cations to improve the salt rejection. The impacts of PEI concentration and EASD time on the separation performance of NF membrane were explored. The optimized TFC-3 NF membrane had a permeate flux of 74.5 ± 1.6 L·m−2·h−1 under 0.5 MPa, which was 2.5 times higher than the water flux of conventional TFC-0 membrane, while retaining up to 99.2 ± 0.5 % of Na2SO4. This work provides a prospective strategy to develop high-performance TFC membranes with great extensive progress for seawater purification.

Regulation of interfacial polymerization by organic base for high-permselective nanofiltration

In the synthesis of the polyamide nanofiltration (NF) membrane, the hydrogen chloride is a by-product generated at the organic interface from interfacial polymerization, which reduces the reactivity of amine monomers due to protonation. Herein, a strategy of addition of an organic base in the organic phase to neutralize the H+ was reported. The performances of the membranes produced using three organic bases with different chain lengths were explored. The results showed that the organic base neutralized the H+ and promoted the rate of interfacial condensation reaction, which facilitated the formation of a dense and thin polyamide layer. Moreover, compared to control membrane, the membrane modified by organic base exhibited higher water permeance without sacrificing salt rejection. Higher diffusion rate of HCl through PES substrate compared to NF membrane indicated that HCl diffusion was mainly affected by the resistance of polyamide layer. Molecular simulations demonstrated that triethylamine (TEA) has lower energy barrier of neutralization and higher reaction heat in comparison with tripropylamine and N, N-diisopropylethylamine. The TEA modified membrane thereby displayed a permeance up to 24.3 L h−1 m−2 bar−1 and Na2SO4 rejection of 98.8 %. This work provided a promising strategy for the regulation of interfacial polymerization in achieving high-permselective nanofiltration.

Development of an improved deep network model as a general technique for thin film nanocomposite reverse osmosis membrane simulation

Due to the complexity of the inherent trade-off between water permeability and salt rejection in thin film nanocomposite reverse osmosis membranes (TFN-ROMs), conventional methods have not performed satisfactorily in predicting the performance of TFN-ROMs. In this study, to address the limitations of traditional machine learning in predicting the performance of TFN-ROMs, we developed a three-component residual artificial neural network (R-TNN) and learned from membrane properties, nanoparticle properties, and membrane performance to capture the complex trade-off between water permeability and salt rejection of TFN-ROMs. The coefficients of determination of the trained R-TNN model for relative salt passage (RSP) and relative water permeability (RWP) of TFN-ROMs were 0.910 ± 0.028 and 0.739 ± 0.028, respectively, which showed good performance compared to fully-connected neural network and conventional machine learning models even with small sample data. Meanwhile, subsequent ablation experiments conducted verified that the improvement of the R-TNN model is practical and effective. In addition, we conducted data scale experiments, which showed that the R-TNN model has the potential to become a generalized technical framework for the initial informationization era and the future big data era. Subsequently, we employed the partial dependence plot to mechanistically interpret the model. Specifically, we observed a positive correlation between nanoparticle size and both RWP and RSP, while the loading of nanoparticles initially promoted and later inhibited these performances. The validated R-TNN model can better learn the inherent trade-off between salt rejection and water permeability of TFN-ROMs, which implies that this study can provide decision support for the fabrication of membranes with more outstanding performances, which greatly contributes to the promising applications of TFN-ROMs.

Preparation of ‘Extended Range’ thin-film nanocomposite reverse osmosis membrane with excellent permeability and selectivity

Thin-film nanocomposite (TFN) membrane possesses great potential in breaking through the ‘trade-off’ effect, in which nanomaterials are incorporated in the polyamide layer to improve the membrane structure as well as provide extra lower-resistance water channel. However, the aggregation of nanoparticles under high loading concentration always induces decline of salt rejection though higher water flux can be achieved. Inspired by the concept of ‘Extended Range Electric Vehicles’, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes were selected as the extended range materials to make up the defects of TFN membranes that excess palygorskite (Pal) brought in present study. The results showed that 1.3 mg/ml loading concentration of Pal led to dramatic decline of NaCl rejection from 99.3 % to 96.8 % though 63.1 % flux enhancement achieved compared to thin-film composite (TFC) membranes. Incorporation of 0.008 mg/ml DOPC liposomes brought further 55.5 % flux enhancement compared to TFN-Pal1.3 membrane and total 153.6 % increment compared to TFC membranes (1.98 → 5.02 L/m2·h·bar). Most importantly, the NaCl rejection of TFN-Pal1.3-DOPC0.008 membranes reverted to 99.1 % and the flux recovery rate increased to 92 %. This study provides novel method for increasing the loading concentration of nanoparticles in the selective layer combined with better dispersion, and demonstrates the feasibility of the concept of ‘Extended Range’ TFN reverse osmosis (RO) membrane.

Triphosgene crosslinked lignin-based loose nanofiltration membrane with high dye/salt separation performance, anti-fouling, and bactericidal property

Abstract A high-performance lignin-based loose nanofiltration membrane is fabricated using quaternized lignin as a novel raw material and triphosgene as a crosslinker. It has high pure water permeance (33.8 L m−2 h−1 bar−1), dye rejections, and low salt rejections during the separation of dye/salt mixtures. The quaternary ammonium functional groups endow the membrane with excellent antibacterial properties. It also has satisfactory dye-fouling resistance and separation-performance stability. Triphosgene plays an important role in optimizing the membrane structure and enhancing permeability.

Optimisation of direct contact membrane distillation to enhance brackish water desalination and study polyvinylidene fluoride (PVDF) membrane performance

This study explores the optimisation of operational parameters in direct contact membrane distillation (DCMD) for brackish water desalination using polyvinylidene fluoride (PVDF) membranes. Central composite design (CCD) identified optimal conditions, and quadratic regression models demonstrated a strong correlation (R2 values: 0.98 for salt rejection, 0.99 for permeate flux) between operational factors and membrane performance. Artificial neural network (ANN) models surpassed Response Surface Methodology (RSM) in predictability for permeate flux and salt rejection. Multi-objective Genetic Algorithm (MOGA) optimisation yielded a pareto optimal solution, revealing two sets of conditions: one maximising permeate flux (21.40 L/m2 h) with 44.75 LPH feed flowrate and the other achieving 100 % salt rejection with 52.48 LPH feed flowrate. Optimising DCMD for flexible water desalination, this study positions it as a promising, sustainable technique, providing practical large-scale implementation guidance. Addressing limitations is key to widespread adoption as a cost-effective freshwater production method.

Superhydrophilic carbon@halloysite nanotube decorated sponge composites for high efficiency solar steam generation and cleanup of crude oil

Three dimensional composite evaporators have now widely been used for solar driven steam generation. However, some issues such as weak interfacial interaction, moderate water transport ability and salt precipitation should be addressed for high efficiency solar driven interface evaporation. Here, carbon modified halloysite nanotubes (CHTs) are firmly anchored onto the skeleton of Polyvinyl alcohol (PVA) sponges for preparation of compressible and superhydrophilic CHTs/PVA evaporators (CPEs). CHTs endow the evaporator with outstanding light absorption and photothermal conversion performance. In addition, the hierarchically porous and hollow structures inside CPEs ensure the evaporator powerful water transport capability and hence excellent salt rejection behavior. Benefiting from the strong interfacial interaction between CHTs and the PVA sponge, CPEs possess superior surface stability and durability. The synergy of the solar driven interface evaporation and natural evaporation from the side walls contributes to a high evaporation rate (up to 3.49 kg m−2 h−1). The evaporation rate is maintained when CPE is mechanically compressed. Also, the sponge composite can be used for cleanup of crude oil, based on the photothermally induced decrease of oil viscosity. This study can provide inspiration to develop solar evaporators for high performance desalination and water purification.

Phospho-modified polyamide nanofiltration membranes with high permeability by using alendronate sodium as additives

The conventional in-situ interfacial polymerization (IP) process, characterized by its rapid reaction rate, is known to be an uncontrollable process that can lead to defects in the performance of nanofiltration (NF) membranes. Herein, a novel NF membrane with a phosphorylated polyamide (PA) network was prepared through a controlled IP process with the addition of alendronate sodium (AS). The phosphoric acid groups of AS can restrain the diffusion of PIP, due to the synergistic interactions with piperazine (PIP) including electrostatic interaction and hydrogen bonding. Moreover, the amine groups of AS could react with trimesoyl chloride (TMC) in organic phase, which incorporated AS into the PA networks. Consequently, a more negatively-charged ionic PA layer with looser, rougher and more hydrophilic structure was obtained. The prepared membrane exhibited a water permeance of 25.0 L·m−2·h−1·bar−1 which was almost two-fold higher than that of NF membranes prepared without additives, while keeping an excellent salt rejection performance (Na2SO4 rejection >97 %), even in a high salt concentration (7.0 g/L). Furthermore, the membrane demonstrated high rejections for different dyes, long-term operation stability and comparable anti-fouling ability against typical contaminants. This work provided a facile and rational approach to preparing ionic NF membranes with high permeability.

3D carbonized orange peel: A self-floating solar absorber for efficient water evaporation

Interfacial solar steam generation (ISSG) is a sustainable and promising technology. Solar energy is used to desalinate seawater and purify industrial wastewater. Solar absorbers based on carbonized biowaste have received increasing attention because they are biocompatible, carbon-rich, hydrophilic, have low thermal conductivity, and exhibit excellent solar absorption. We fabricated a three-dimensional (3D) photothermal material based on carbonized orange peel (COP) for ISSG. The microscopic pores of COP ensured excellent thermal insulation, and the upward-concave shape enhanced light absorption and the self-floating capacity. COP exhibited an evaporation rate of 1.86 kg m−2 h−1 and energy efficiency of 87.90 % under 1 sun irradiation. Additionally, the salt rejection rate was 99.99 % during desalination, and the dye removal rate was 100 % during water purification. Our solar evaporator is thus a low-cost and efficient means of ISSG, and it shows that biowastes can serve as effective photothermal materials.

In‐situ generated ZnO nanoparticles for enhanced performance of thin film nanocomposite membrane in forward osmosis process

AbstractThis work developed a novel approach to the in‐situ synthesis of ZnO nanoparticles to modify the polysulfone (PSf) porous membrane substrate. The zinc acetate was added to the casting solution, and ZnO nanoparticles were synthesized during phase inversion. The non‐solvent pH and zinc acetate concentration controlled the ZnO synthesis and loading. Their effect on the substrates properties in terms of morphology, hydrophilicity and porosity was studied thoroughly. The result shows that the ZnO nanoparticles was not formed in acidic pH, while ZnO nanoparticles with size of 20 nm could be easily formed in basic pH. The successful synthesis of ZnO nanoparticles was investigated using FTIR and EDX analysis. The EDX images verify that in‐situ synthesis led to a more uniform dispersion than conventional incorporation method. Then the effect of ZnO loading on the interfacial reaction and polyamide (PA) structure was investigated. SEM images verify the successful synthesis of a uniform and defect‐free PA thin film on ZnO modified substrates. FO performance results show an enhancement in water flux and salt rejection as a result of ZnO incorporation in thin film nanocomposite (TFN) membranes, where TFN 1 wt.% in‐situ membrane showed 40% higher water flux than the control TFC membrane. The porous and hydrophile substrate in TFN 1 wt.% in‐situ membrane is responsible for improved separation performance. These modified membranes displayed uniform dispersion of ZnO nanoparticles within substrates, confirming that this method could effectively restrain the aggregation of the nanoparticles.

Desalination of produced water via carbon dioxide hydrate using filter-based hydrate desalination reactor

This paper emphasizes sustainable development goal 6 and accepts that social progress and economic prosperity depend on the appropriate management of produced water.Produced water being the largest source of wastewater, several conventional desalination methods (thermal, membrane and freeze–thaw), are applied to obtain treated water. Nevertheless, the methods are highly energy intensive. Prospective utilization of hydrate-based desalination was proposed with a novel filter-based apparatus design to separate hydrate crystals from residual water and enhance the gas–liquid contact with all the unit operations (hydrate formation, and dissociation) occurring inside a single reactor. Experimentations were implemented to obtain the optimum conditions for CO2hydrate formation and compared with pure water. CO2 hydrate formation kinetics revealed induction time, moles consumed, water-to-hydrate conversion, and water recovery were 57 mins, 1.28 mol, 27.72 %, and 50.65 % at optimum conditions of 500 ml, 3.0 MPa, 450 rpm, and 275.15 K for purification of produced water. A desalination efficiency of 62–80 % is achieved with each of the metal ions in the sequence K+>Na+>Mg2+>Ca2+, and anionsSO42-> Cl- without any pre and post-treatment. Also, demonstrated that the ionic charge and size have a significant impact on the ion rejection mechanism. The findings disclosed that with an upsurge in the temperature to 277.15 K the desalination efficiency enhanced nevertheless the volume of formed hydrate is less resulting in less driving force. The total dissolved solids and electrical conductivity results indicate that the treated water meets Malaysia's water quality standards for irrigation purposes. This showcases the execution of the hydrate-based desalination process, investigating salt rejection and yield with our custom reactor design. The proposed reactor design may be utilized for the effective separation of hydrate and effectively desalinating waters of higher salinities. Hydrate-based desalination integrated with membrane reactors could lead to a sustainable source of clean water by treating produced water.

The role of microporous metal–organic frameworks in thin-film nanocomposite membranes for nanofiltration

Endowed with amendable pore apertures and chemistries as well as customized topologies, metal–organic frameworks (MOFs) have displayed a promise to improve the separation efficacy of thin-film nanocomposite (TFN) membranes. In this study, the microporous MOF-801 nanoparticles (NPs) with robust water stability were synthesized using a green synthesis approach at room temperature. Subsequently, the MOF-801 NPs were positioned atop the polysulfone (PSf) membrane support via vacuum-assisted filtration, followed by interfacial polymerization to construct TFN membranes. A wide array of characterizations was conducted to analyze the physicochemical properties and morphological characteristics of the MOF-801 and the modified polyamide (PA) membranes. Results revealed the successful synthesis of MOF-801 nanocrystals with abundant micropores and a high crystallinity. The incorporation of MOF-801 NPs to the PA layer was found to induce substantial improvements in surface hydrophilicity and roughness as well as thinner PA layers, which are favorable for rapid water molecule transport. The water permeability of TFN membranes presented a notable 98% increment compared to the thin-film composite (TFC) membrane with only a small compromise for salt rejection. This work underscores the promising potential of nanoporous and acid-base stable MOF-801 as an efficient nanofiller for constructing nanofiltration membranes with admirable performance.

Modification of PVDF hollow fiber membrane with ZnO structure via hydrothermal for enhanced antifouling property in membrane distillation

This study aims to provide a close insight into the possibilities and constraints associated with the development of ZnO structures on polyvinylidene fluoride (PVDF) hollow fiber membranes using the hydrothermal method to enhance membrane surface roughness for improved fouling resistance in membrane distillation (MD). Due to the flexible nature of polymeric hollow fiber membranes, there is a considerable risk of the ZnO structure detaching from the membrane surface when the membrane is bent. To address this issue, the hydrothermal duration was varied between 4 and 16 h to optimize the ZnO structure for high integrity, followed by fluorination. The results reveal that the membrane treated with hydrothermal for 8 h exhibits stable coating integrity, imparting the membrane with the highest contact angles with various liquids. This membrane demonstrates a flux of 4.0 kg/m2h and excellent salt rejection (>99.9 %) in direct contact MD (DCMD) when treating a 35 g/L saline solution. Additionally, the membrane exhibits outstanding antifouling performance with minimal flux reduction over 24 h when treating a saline solution containing humic acid. However, the upscaling of the hydrothermal approach may pose challenges due to the difficulty in maintaining the consistency of ZnO structure formation.

Preparation of solvent-resistant polyimide membranes for efficient separation of dyes and salts via an “internal drive” strategy

It is extremely difficult to separate salts and dyes from high-salinity printing and dyeing wastewater. In this study, modified montmorillonite (EPTAC-CD-MMT) was obtained by intercalation of 2,3-epoxypropyltrimethylammonium chloride (EPTAC) modified cyclodextrin (CD). PI/EPTAC-CD-MMT membrane was prepared by blending EPTAC-CD-MMT with polyimide (PI). The addition of EPTAC-CD-MMT could inhibit the motion of PI molecular chains and increase the solvent resistance of the membrane. Additionally, EPTAC-CD-MMT exhibited spontaneous “internal drive” during the phase transition and segregated to the membrane surface. The pore structure of the membrane was adjusted to a well-developed “side pore” structure. Thus, solvent-resistant membranes for dye/salt separation with high flux were finally obtained. The successful modification of MMT was demonstrated by FTIR, XRD, TGA and XPS. EDX and SEM were used to characterize the surface segregation phenomena and well-developed pore structures of the membranes. When EPTAC-CD-MMT was added at 3 wt%, the membranes showed a significant increase in pure water flux (138.0 L·m−2·h−1·bar−1), high dye rejection (>98.5 %), low salt rejection (<10.0 %), and good solvent resistance in six organic solvents. This demonstrated the potential of PI/EPTAC-CD-MMT separation membranes for the treatment of dye wastewater containing sophisticated organic solvents.

Continuous solar-driven saturated brine separation using sawtooth photothermal fabrics with asymmetrical wetting property

Eco-friendly solar-driven water evaporation is emerging as a promising strategy for saline wastewater separation. However, due to the severe decline in evaporation performance caused by salt fouling, complete separation of water and solute for saturated brine from industrial sectors calls for alternative efficient strategies. Here, the present study proposes a sawtooth photothermal fabric with asymmetrical wetting properties for high-efficiency and continuous solar-driven saturated brine separation. The proposed sawtooth photothermal fabric comprises a hydrophobic upper layer and a hydrophilic lower layer, which together enable efficient salt rejection and continuous water transport. In addition, the sawtooth structure of the photothermal fabric creates a dual escape path for the vapor to travel from the absorber to the environment, which improves the evaporation rate and provides appropriate conditions for salt collection. The experimental results revealed that the sawtooth photothermal fabric with asymmetrical wetting properties achieved an evaporation rate of 1.43 kg m–2 h−1 for 25 wt% brine under 1 sun illumination and recovery of a considerable amount of salt. Notably, in the outdoor experiment, the evaporation rate achieved using the fabric did not decline throughout the eight days of continuous solar-driven saturated brine separation. The present study has therefore provided a simple and economical method for the treatment of high-concentration waste brine with considerable salt recovery.