Treatment of copper-electroplating wastewater by UiO-66-Keratin functionalized PES ultrafiltration membrane.

Thermo-osmosis and enhanced ion rejection rate in Janus nanochannels under the external electric field

Nanoconfinement reduces the favorable hydration free energies of single ions, and is correlated with ion rejection and modified chemical reactivity in water-filled nanopores. Many factors contribute to the magnitude of the observed confinement effect. Here we use simple classical force fields and nonpolarizable carbon nanotubes filled with water as minimal, hydrogen-atom-like models to evaluate the single-ion intrinsic confinement hydration free energy penalty (ΔΔGhyd). In tubes of radius R = 7.5 Å, we predict ΔΔGhyd values that are up to 7.8 kcal/mol, are much larger for Cl- than the smaller Na+ ion, and contradict the canonical Born equation for ion solvation. Adding a 1.0 M background electrolyte reduces ΔΔGhyd for the Na+/Cl- pair by an amount exceeding the Debye-Hückel estimate in unconfined media by almost an order of magnitude. We identify concentration-dependent ion-screening of confinement effects as a major, unheralded consequence of electrolytes in cylindrical nanopores.

Desalination based on carbon nanomembranes offers high water permeance and salt rejection, making them promising for addressing global freshwater shortages and energy demands in reverse osmosis (RO) desalination. Enhancing ion rejection by modulating the energy barrier for ion transport through wide carbon nanotubes (CNTs) is a critical challenge for highly efficient desalination. We perform molecular dynamics simulations on water desalination using CNTs membranes, highlighting the key role of nanoconfinement coupled with an electric field. The results show that the electric field extends the threshold of CNT diameter required for complete ion rejection from 1.10 nm to 1.50 nm, achieving ∼100% ion rejection while maintaining water permeance of ∼97 L cm-2 day-1 MPa-1. The calculated energy barriers for ion transport demonstrate that the applied electric field significantly increases the inhibitory effect of wide CNTs on ion permeation. We elucidate that the molecular mechanism governing the free energy barrier of ion arises from the polarization of confined water induced by the coupling of the electric field and CNTs, leading to the stripping and reorganization of the ion hydration shell. This approach achieves water permeance that is up to three orders of magnitude higher than that of commercial RO membranes, enhancing the application potential of CNTs membranes coupled with external fields for water desalination. We expect this work to be valuable for understanding the thermodynamic and kinetic behaviors of solute transport and separation induced by molecular mechanisms.

ConspectusNanofiltration (NF), regulating the pass and rejection of molecules and ions through membranes carrying sub-2 nm pores, has been used in numerous applications from water softening and Li+ extraction to pharmaceutical purification and petroleum fractionation. The presently used NF membranes are mostly made of cross-linked polyamides developed over 60 years ago, inherently suffering from tortuous transport paths and scattering pore sizes. Hopefully, covalent-organic frameworks (COFs) are opening the door to the next generation of NF and the corresponding membranes. Their inherent monodispersive sub-2 nm pore channels, customizable pore chemistry, and good chemical and thermal stability promise unprecedented selective and fast transport of molecules and ions, mitigating the frustrated "trade-off" effect between permeability and selectivity in traditional polyamide NF membranes.We first performed molecular dynamic simulations on COFs to decode how the pore structure and chemistry govern molecular and ionic transport behaviors. By analyzing the synergistic effect of pore-entrance sieving and pore-interior diffusion, we identified the critical factors affecting mass transfer such as pore sizes and geometry and charge density and surprisingly discovered that ideally structured COFs exhibit remarkable water permeance 1-2 orders of magnitude higher than traditional polyamide NF membranes. However, experimentally prepared thin films of aggregated COF crystallites usually contain defects, amorphous regions, and poorly defined grain boundaries, significantly weakening the selectivity of nanofiltration. Considering that COFs are practically condensation polymers, we envision that their structural imperfection can be fixed or minimized by regulating the condensation reactions or by changing the conformation of the formed polymer chains/networks. We manipulated the nucleation and crystallization kinetics via the controlled release of activators and temperature-swing synthesis. Monomers and crystallites can fully preorganize before epitaxial growth, ultimately forming highly crystallized, continuous films. Furthermore, we reorganized COF skeletons into the favored face-on orientation by vapor annealing to increase the mobility of the COF segments. The long-desired perpendicular alignment of COF films was thus realized, enabling sharpened rejection and simultaneously enhanced permeance compared with those of randomly oriented counterparts.To realize adaptive control over mass transport in specific NF applications, we incorporated dangling azobenzene units into COF skeletons as intrapore groups. Light activation induces precise regulation of pore sizes at the angstrom magnitude in a continuous manner. Furthermore, azobenzene isomerization allows drastic changes in intrapore polarity, which exerts a profound effect on the intermolecular affinity through dipole interactions. These distinctive features enable COF membranes to smartly sieve molecules or ions with close kinetic diameters.We conclude this Account by discussing the remaining challenges and future directions to be explored to push COFs from potential game changers to real leading players in the field of nanofiltration. This Account aims to provide insights into advancing next-generation NF membranes and may inspire growing interest in multidisciplines crossing reticular chemistry, porous materials, polymer science, and separation technologies.

Clean water remains a pressing global challenge and developing membranes that are both efficient and durable is critical. This study combined two polymers, polyethersulfone (PES) and sulfone-modified polysulfone (SPSf), with NiFe-layered double hydroxides (LDHs) to create a new class of multifunctional membranes. The membranes were characterized using FTIR, SEM, water contact angle, and zeta potential. The addition of NiFe-LDH fillers improved the hydrophilicity and surface structure of the membranes and enhanced the separation performance of the resulting membranes. The best-performing membrane (M3, with 2 wt.% NiFe-LDH) delivered pure water flux of about 218 L.m-2h-1, which was nearly three times higher than that of the pristine PES/SPSf membrane. Furthermore, M3 removed approximately 92.4% of bovine serum albumin (BSA), attributed to the synergistic combination of size exclusion, electrostatic repulsion, and hydrophilicity. The membrane also showed excellent antifouling properties, maintaining over 65.9% and 71.2% flux recovery after three fouling-cleaning cycles for BSA solution and surface water, respectively. Importantly, the M3 membrane achieved high removal efficiencies for heavy metals, rejecting 91% of Cd2+, 93% of Pb2+, and 88% of Cu2+. These results highlight how the synergy between PES/SPSf and NiFe-LDH can overcome the common challenges of fouling and low metal ion rejection, offering a promising route toward practical and sustainable water treatment solutions.

Enhancing ion rejection rate in freeze desalination through vibrations

The current research intends to conduct an experimental work to study the removal efficiency of Magnesium (Mg2+), Potassium (K1+), Sodium (Na1+), Bromide (Br1-) and Chloride (Cl1-) ions from different prepared solutions using a ceramic Nanofiltration (NF) membrane with a molecular weight cut-off of 1 kDa. Specifically, the solutions are prepared using double ions and triple ions and the filtration is conducted using different operating conditions of the trans-membrane pressure (TMP) and ions concentrations. In this regard, the TMP ranges between 1 to 5 bar and the ion concentration ranged between 0.01 to 1.0 M (equivalent to 1.0 to 1000 mol/m3). The results demonstrate that the highest ion rejection can be attained with the maximum applied TMP. However, this is not the case for the NaBr and KBr solutions, demonstrating the reverse action. Variable ion rejection patterns are experimentally identified in the current research, which varies between 90% to 99.7%.

Graphene-based materials, with their exceptional physicochemical properties, have demonstrated great potential in desalination. However, conventional graphene membranes face a trade-off between water permeability (WP) and salt rejection, which imposes certain limitations on their overall water treatment performance. In this study, we employ molecular dynamics simulations to demonstrate a strategically engineered intercalated-graphene channel that synergistically combines ultra-high water transport capacity with exceptional ion rejection (IR) capabilities. An interesting phenomenon we observed is that as the intercalation position changes, the salt rejection of the device exhibits a pronounced peak behavior. For small-sized channels, this can be primarily attributed to the high energy barrier for ion transport caused by the dehydration-reassociation process, which effectively blocks ions. For large-sized channels, where the dehydration process is weak, the primary barrier to ion diffusion arises from changes in the water layer structures, because water and ions are coupled, moving together as a co-transport system. Additionally, both water and ion flux exhibit a linear increase with pressure difference (ΔP), aligning with the predictions of the ideal Hagen-Poiseuille equation. Overall, in the best-performing system, the IR remains above 93.1% even as the ΔPincreases, while maintaining high WP, effectively achieving a balance between both factors. Our findings highlight how sub-nanometer geometric structure control can fundamentally alter transport physics in desalination meters.

Lignosulfonate and chitosan-based nanoparticles for heavy metal ions removal via forward osmosis process.

Abstract The development of efficient and regenerable membranes for heavy metal removal remains a major challenge in water purification. This study presents a synergistic strategy to enhance polysulfone (PSf) membranes via the incorporation of zeolite Y, polyethylene glycol (PEG), and the surfactant Tween 20 using the phase inversion method. The combined use of these additives was investigated to overcome the interfacial and structural limitations of conventional PSf membranes. The prepared hybrid membranes were comprehensively characterized by ATR-FTIR, SEM, AFM, XRD, TGA, nanoindentation, and contact angle measurements. Results revealed that the additives incorporation generated a highly porous and interconnected morphology with enhanced surface hydrophilicity (contact angle: 62.2° ± 0.4) and improved roughness (Ra = 38.1 nm). Mechanical testing indicated a balanced flexibility (Young’s modulus: 39.95 ± 3 MPa; hardness: 4.32 ± 0.4 MPa) while maintaining good thermal stability. The PSf/3 wt% zeolite/PEG/Tween 20 membrane exhibited the best performance, achieving a pure water flux of 219.65 L m −2 h −1 , cadmium removal of 98.49 % at pH = 10, and a flux recovery ratio of 87.49 %. These results demonstrate that the combined modification approach effectively enhances both antifouling behavior and metal ion rejection, providing a promising route toward advanced, regenerable membranes for wastewater treatment applications.

In recent years, the development of high-performance membranes for seawater desalination has attracted significant attention. This work proposes a novel model by employing a boron nitride nanotube (BNNT) as a support in lamellar boron nitride (BN) membranes. The effects of structural parameters as well as the role of nanotubes on seawater desalination performance are explored systematically via nonequilibrium molecular dynamics simulations (NEMD). In addition, the transport mechanism for water molecules and the separation mechanism for ions transmitted through the BN-BNNT membranes are elucidated at the molecular level. Simulation results indicate that the BN-BNNT membrane exhibits a higher water flux rate compared to the BN membrane. Additionally, reducing the gap width from 10 Å to 8 Å leads to a higher ion rejection rate but a significant decrease in water flux rate. The rejection rates for Na+ and Cl- ions are promoted by increasing the interlayer spacing to larger values. This phenomenon can be attributed to the trapping of water molecules and hydration ions in the interfacial regions formed between the BN and BNNT nanosheets. It is possible to simultaneously increase the water flux and interception by inserting nanotubes and adjusting the distance of the interlayer spacing. This study suggests that the stability of lamellar nanomembranes can be enhanced through the incorporation of nanotubes as a support. Simultaneously, it is possible to enhance the rejection rate in such membranes without decreasing the water flux rate by adjusting the relevant structural parameters.

The increasing concentration of phosphate in industrial and agricultural waste is a major cause of eutrophication, which threatens the balance of aquatic ecosystems. Membrane technology offers an effective approach for phosphate ion removal through the combined mechanisms of filtration and adsorption. In this study, chitosan membranes were modified with polyvinylpyrrolidone K30 (PVP K30) at four different concentrations using the phase inversion method. Increasing the PVP K30 content in the chitosan membrane enhanced water absorption, porosity, and hydrophilicity. These improvements significantly influenced phosphate ion filtration performance, resulting in a flux increase of 33–48% and an enhancement in phosphate ion rejection of 32–39% compared to the unmodified chitosan membrane. Furthermore, phosphate ion adsorption on the membrane surface was observed, which is likely attributed to the presence of surface functional groups with different charges and to membrane pore sizes comparable to the size of phosphate ions.

All-cellulose-based solar evaporators with improved wet mechanical integrity via mercerization.

Electrolysis of low-grade impure water offers a sustainable approach to hydrogen production. However, unstable interfacial pH caused by electrochemical reactions accelerates ion-induced electrode degradation. Here, we show an ion-selective gate strategy, in which ion-conducting polymer coatings are applied onto commercial platinum carbon and iridium oxide catalysts to enable selective ion transport and to stabilize the interfacial pH. Compared with conventional aqueous electrolytes, this solid-state configuration effectively suppresses local pH fluctuations and blocks the migration of detrimental impurity ions. The ion-selective gate achieves nearly complete rejection of common ions found in seawater, river and lake water, and industrial wastewater, demonstrating broad adaptability to impurity-rich environments. In untreated seawater, the ion-selective gate engineered electrode operates stably for 1500 h at 200 mA cm−2, with a degradation rate of 5.2 mV kh−1, approaching the durability of pure water electrolysis. This design is compatible with both proton exchange membrane and anion exchange membrane electrolyzers, providing a scalable route for sustainable hydrogen generation from natural water sources.

The growing global water crisis, driven by rising population and shrinking freshwater resources, calls for new and improved purification technologies. Polymeric membranes offer immense promise for potable water production but are often hampered by critical limitations: persistent fouling, chemical degradation, and the inherent selectivity-permeability trade-off. This review highlights recent advances in modifying polyvinylidene fluoride (PVDF) membranes, with a focus on new strategies for achieving ultra-pure water. PVDF serves a versatile role in membrane technology, serving as a support material, a blend matrix, or a platform for surface modifications. Its mechanical stability, chemical resistance, and tunable properties are key components in advanced membrane design. We discuss the transformative potential of integrating next-generation nanomaterials. Novel insights are drawn from nanoparticle-incorporated polyamide (PA) and interpenetrating polymeric network (IPN) membranes, which offer improved ion rejection and durability even in harsh, chlorine-rich environments. The unprecedented molecular precision and exceptional compatibility of covalent organic frameworks (COFs) within the PA matrix are highlighted as a key enabler for superior selectivity and mechanical robustness. Furthermore, the review meticulously details how the unique lamellar structure and tunable nanochannels of two-dimensional (2D) nanomaterials, notably graphene oxide (GO)-based membranes, deliver outstanding antifouling properties and remarkable chlorine resistance without compromising vital water flux or rejection efficiency-a critical breakthrough that overcomes long-standing performance limitations. This review uniquely consolidates diverse modification strategies, offering a rational design framework for next-generation, multi-functional GO-based polymeric membranes. By dissecting the intricate interplay between material science and membrane performance, we aim to empower researchers to engineer membranes with unparalleled chemical resilience, superior structural stability, enhanced energy efficiency, and enduring long-term performance, thereby securing a sustainable global water future.

Water contamination by heavy metal ions poses a significant environmental and public health challenge, necessitating the development of advanced and efficient treatment technologies. This study explores the advanced modification of thin-film composite (TFC) polyvinylidene fluoride (PVDF) membranes through cross-linking with glutaraldehyde (GA) and surface functionalization via a graphene oxide Nanoparticles (GONPs)/polyvinyl alcohol (PVA) coating using a dip-coating technique. The incorporation of GA as a cross-linking agent significantly enhanced the chemical and thermal stability of the thin-film coating, while the addition of GONPs improved the membrane’s hydrophilicity and metal ion rejection efficiency. The mechanical strength of the modified membranes exhibited a notable increase, with the tensile strength rising from 3.58 MPa to 6.15 MPa as the PVA/GONPs loading increased. The performance of the functionalized membranes in removing Mn2+ and Fe2+ ions as the main contaminants was systematically evaluated under varying GONPs loadings. Results demonstrated that for an initial metal ion concentration of 100 ppm, the modified PVDF membranes achieved a removal efficiency of 95.5% for Mn2+ and 94.6% for Fe2+ in the first filtration cycle. Even after five successive filtration cycles, removal rates remained above 60%, highlighting the membranes’ durability and sustained performance. This study presents a promising strategy for enhancing polymeric membranes, offering an efficient and scalable solution for heavy metal removal in wastewater treatment applications.

The effective removal of toxic heavy metals and synthetic dyes from wastewater remains a critical challenge in environmental remediation. In this study, we present a hierarchically engineered nanocomposite membrane that integrates zeolitic imidazolate framework-8 (ZIF-8) and sulfobetaine methacrylate (SBMA) into a polyacrylonitrile-polyvinylpyrrolidone (PAN-PVP) matrix. The membrane exhibits a high pure water flux of 71.96 L·m-2·h-1 and strong rejection efficiencies for cadmium (95.6%), copper (93.3%), and lead (97.8%) ions as well as methyl orange (98.9%) and methylene blue (98.4%) across different pH conditions. Importantly, the membrane retained ∼93% of its performance after 10 continuous cycles, underscoring its durability. A combination of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements confirmed the successful integration and chemical stability of ZIF-8 and SBMA within the membrane. In addition, density functional theory (DFT) and classical all-atom molecular dynamics (MD) simulations were employed to gain molecular-level insights into structural features and intermolecular interactions between contaminants and the ZIF-8/SBMA membrane system. This work introduces a tunable and scalable membrane platform with high flux, selectivity, and robustness, offering both mechanistic insights and practical applications for advanced water purification technologies targeting a wide range of contaminants.

As clean, conventional freshwater resources decrease, treating unconventional water is a global priority. While membrane technologies such as reverse osmosis enable the use of seawater and brackish waters, their relatively high energy demands, particularly the external pressure required to overcome osmotic gradients and infrastructure requirements, limit broader adoption. Among alternative technologies, stimuli-responsive hydrogels provide a promising approach to address such limitations. In particular, thermally responsive hydrogels that can effectively reject ions while saturating (swelling) with water and then dewatering (recovery) under low-energy, controlled conditions hold considerable promise. In this work, enhanced thermoresponsive hydrogels were developed, via graphene oxide addition, and a shell-core strategy whereby the modified hydrogel core drives flow in and out (i.e., pull-push) as a function of temperature, while a thin polymer shell enhances ion (salt) rejection. This multifunctional approach allows for system tunability and thus optimization for treated water recovery. Driven by near room-temperature swings (20-40 °C), composite materials described here desalinate water at 57-78% salt rejection for varying ionic strengths (17-550 mM) and types (NaCl, CaCl2, MgCl2) with ∼5 times swelling/recovery ratios consistently for five relatively rapid treatment cycles, with a water collection rate of 7.7 kg m-2 h-1.

Layered graphene oxide (GO) has emerged as an ideal membrane structure for water desalination. In GO-stacked structures, the slit gaps between GO nanosheets can serve as critical pathways for molecule permeation. Exploring the permeation mechanisms of functionalized GO nanoslits is critical for improving the separation performance. Herein, molecular simulations were performed to investigate the water permeation and ion rejection for six types of ionic solutions by considering edge-amino functionalized GO (NGO) slit membranes. The NGO slit exhibits higher ion retention while maintaining reasonable water permeability. Edge amine groups can interact strongly with water molecules and immobilize ions, thus enhancing ion rejection. The thermodynamic free energy for ion passing was simulated to explain the unique ion rejection mechanism of amine-functionalized GO slits. The thermodynamic barrier for ion rejection can be considered as the delicate combination of the ion dehydration effect and the slit-generated attraction. The ion dehydration accounts for a repulsive contribution, which is the controlling portion in governing the free-energy profile. Overall, our work is important and valuable for the development and design of new-type layered GO membranes.