Thin-Film Composite Membrane with Interlayer Decorated Metal–Organic Framework UiO-66 toward Enhanced Forward Osmosis Performance

Recent advances in surface tailoring of thin film forward osmosis membranes: A review

The recent advancements in fabricating forward osmosis (FO) membranes have shown promising results in desalination and water treatment. Different methods have been applied to improve FO performance, such as using mixed or new draw solutions, enhancing the recovery of draw solutions, membrane modification, and developing FO-hybrid systems. However, reliable methods to address the current issues, including reverse salt flux, fouling, and antibacterial activities, are still in progress. In recent decades, surface modification has been applied to different membrane processes, including FO membranes. Introducing nanochannels, bioparticles, new monomers, and hydrophilic-based materials to the surface layer of FO membranes has significantly impacted their performance and efficiency and resulted in better control over fouling and concentration polarization (CP) in these membranes. This review critically investigates the recent developments in FO membrane processes and fabrication techniques for FO surface-layer modification. In addition, this study focuses on the latest materials and structures used for the surface modification of FO membranes. Finally, the current challenges, gaps, and suggestions for future studies in this field have been discussed in detail.

Forward Osmosis Membranes: The Significant Roles of Selective Layer

Forward osmosis (FO) is a promising separation technology to overcome the challenges of pressure-driven membrane processes. The FO process has demonstrated profound advantages in treating feeds with high salinity and viscosity in applications such as brine treatment and food processing. This review discusses the advancement of FO membranes and the key membrane properties that are important in real applications. The membrane substrates have been the focus of the majority of FO membrane studies to reduce internal concentration polarization. However, the separation layer is critical in selecting the suitable FO membranes as the feed solute rejection and draw solute back diffusion are important considerations in designing large-scale FO processes. In this review, emphasis is placed on developing FO membrane selective layers with a high selectivity. The effects of porous FO substrates in synthesizing high-performance polyamide selective layer and strategies to overcome the substrate constraints are discussed. The role of interlayer in selective layer synthesis and the benefits of nanomaterial incorporation will also be reviewed.

Construction of PPSU-MoS2/PA-MIL-101(Cr) Membrane with Highly Enhanced Permeance and Stability for Organic Solvent Nanofiltration

Membranes with excellent separation performance and stability are needed for organic solvent nanofiltration in industrial separation and purification processes. Here we reported a newly PPSU-MoS₂/PA-MIL-101(Cr) composite membrane with high permeance, good selectivity and stability. The MIL-101(Cr) was introduced in the polyamide (PA) layer via the PIP/TMC interfacial polymerization process on a microporous PPSU-MoS₂ substrate. At a small doping amount of 0.005 wt% MIL-101(Cr), the PPSU-MoS₂/PA-MIL-101(Cr) composite membrane exhibited a high methanol permeance of 12.03 L m⁻² h⁻¹ bar⁻¹, twice higher than that of the pristine membrane without sacrificing selectivity. Furthermore, embedding MIL-101(Cr) notably enhanced the stability of the composite membrane, with permeance only decreasing by 8% after a long time operation of 80 h (pristine membrane decreased by 25%). This work demonstrated a composite membrane modified by MIL-101(Cr) with superior separation performance, which provides potential application of MOF materials for high-performance membranes in organic solvent nanofiltration and a theoretical foundation for future research in studying MOF’s influence on membrane properties.

Crumpled Globule-Heterotextured Polyamide Membrane Interlayered with Protein-Polyphenol Nanoaggregates for Enhanced Forward Osmosis Performance

Surface modulation of polyamide structures and the development of nanochanneled membranes with excellent water transport properties are crucial for the separation performance enhancement of thin-film composite membranes. Here, we demonstrate the fabrication of a modular nanochannel-integrated polyamide network on a nanoporous interlayer membrane comprising Mxene-reinforced protein-polyphenol nanoaggregates. The research indicates that the confined growth of the polyamide matrix inside this hydrophilic sub-10 nm nanochannel nanoporous intermediate layer stiffened the interfacial channels, leading to the formation of a polyamide layer with a spatial distribution of a network of unique 3D crumpled globule-like nanostructures. The high specific surface area of such a morphology bestowed the membrane with increased filtration area while facilitating the nanofluidic transport of water molecules through the nanochanneled membrane structure, leading to enhanced water flux of up to 26.6 L m^-2 h^-1 (active layer facing the feed solution) and 41.0 L m^-2 h^-1 (active layer facing the draw solution) using 1.0 M NaCl as the draw solution. The membrane equally exhibited good treatment for organic solvent forward osmosis filtration and typical seawater desalination. Moreover, the hierarchical nanostructures induced antimicrobial activity by effectively reducing the biofilm formation of Gram-negative Escherichia coli bacteria. This work provides significant insights into the interfacial engineering and compatibility of the nanomaterials and the polymers in interlayer mixed-matrix membranes, which are environmentally sustainable and cost-effective for the fabrication of advanced forward osmosis membranes for water purification and osmotic energy applications.

Metal organic framework UiO-66 incorporated ultrafiltration membranes for simultaneous natural organic matter and heavy metal ions removal

In this work, a new type of UiO-66 incorporated polysulfone (PSf) ultrafiltration (UF) membranes was fabricated to enhance antifouling properties and heavy metal ions removal efficiency. The UF membranes incorporating different loadings of the UiO-66 filler were prepared via the classical phase inversion process. These membranes unveiled enhanced hydrophilicity, porosity, water uptake, zeta potential, mechanical strength, permeability, and HA removal ratios due to the incorporation of hydrophilic UiO-66 fillers. Particularly, HA rejection ratios were observed to be approximately 93% for all the modified membranes, which was attributed to electrostatic repulsion interactions between the hydrophilic groups of HA and UiO-66. Moreover, the antifouling abilities of the modified membranes were evaluated and found to be much better with a high flux recovery ratio (FRR) of about 88% when compared to the blank PSf membrane (only around 34%). Moreover, the UiO-66 incorporated membranes were highly-effective in the removal of contaminants like heavy metal ions (Sr²⁺, Pb²⁺, Cd²⁺, and Cr⁶⁺) and HA at the same time. Overall, the PSf UF membranes incorporating UiO-66 opened up a new avenue to enhance the membrane hydrophilicity, permeability, antifouling properties as well as heavy metal ions removal abilities.

Preparation and Characterization of a Thin-Film Composite Membrane Modified by MXene Nano-Sheets

MXene nano-sheets were introduced into a thin-film composite membrane (TFC) to reduce the mass transfer resistance (concentration polarization) and improve the membrane performance. The process entailed dissolving the MXene nano-sheets in a membrane casting solution using the blending method and introducing them into the porous support layer to prepare a modified thin-film composite forward osmosis (TFC-FO) membrane. The results showed that the water contact angle decreased by about 16%, indicating that the hydrophilicity was strengthened, and the O/N ratio of the active selective layer decreased by 13%, indicating an increased degree of crosslinking, thereby demonstrating that the introduction of MXene nano-sheets changed the properties of the membrane and played a positive role in its physicochemical properties. In contrast to the unmodified TFC-FO membrane, the modified membrane had a slightly higher reverse solute flux, while its water flux increased by about 80%. Its specific reverse osmosis flux was also significantly optimized (only 0.63 g/L). In conclusion, adding MXene nanosheets to TFC-FO membranes led to the modified membranes with better mass transfer, lessened internal concentration polarization (ICP), and better osmotic separation.

Preparation and Characterization of the Forward Osmosis Membrane Modified by MXene Nano-Sheets

The Forward Osmosis (FO) membrane was the core of FO technology. Obtaining a high water flux while maintaining a low reverse solute flux has historically been considered the gold standard for a perfect FO membrane. In a thin-film composite FO membrane, the performance of the membrane was determined not only by the material and structure of the porous support layer but also by the structural and chemical properties of the active selective layer. Researchers have selected numerous sorts of materials for the FO membranes in recent years and have produced exceptional achievements. Herein, the performance of the modified FO membrane constructed by introducing new two-dimensional nanomaterial MXene nano-sheets to the interfacial polymerization process was investigated, and the performance of these modified membranes was investigated using a variety of characterization and testing methods. The results revealed that the MXene nano-sheets played an important role in improving the performance of the FO membrane. Because of the hydrophilic features of the MXene nano-sheets, the membrane structure may be tuned within a specific concentration range, and the performance of the modified FO membrane has been significantly enhanced accordingly. The optimal membrane water flux was boosted by around 80%, while its reverse solute flux was kept to a minimum of the resultant membranes. It showed that the addition of MXene nanosheets to the active selective layer could improve the performance of the FO membrane, and this method showed promising application prospects.

Zwitterion-functionalized MIL-125-NH2-based thin-film nanocomposite forward osmosis membranes: towards improved performance for salt rejection and heavy metal removal

Incorporating zwitterion-functionalized MIL-125-NH2 nanoparticles in the rejection layer of TFN FO membranes improves their water/ion separation performance and antifouling ability.

Recent advances in metal-organic framework membranes for water treatment: A review

Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

Regulation of electronic structures of MOF-derived carbon via ligand adjustment for enhanced Fenton-like reactions

Peroxymonosulfate (PMS)-based Fenton-like reactions are widely used for wastewater remediation. Metal-free carbonaceous activators can avoid the secondary pollution caused by metal leaching but often suffer from insufficient activity due to limited active centers and mass transfer barriers. Here, we prepared a series of heteroatom (N, S, F)-doped, highly porous carbonaceous materials (UC-X, X = N, S, F) by pyrolyzing UiO-66 precursors assembled by various organic ligands. Density functional theory calculations showed that the heteroatoms modulated the electronic structures of the carbon plane. UC-X exhibited significantly enhanced PMS activation capability compared with the undoped counterpart, in the efficiency order of UC-N > UC-S > UC-F > UC. UC-N (calcined at 1000°C) showed the best PMS activation, exceeding that of commonly used carbocatalysts. The prominent performance of UC-N originated from its unique porous structure and homogeneously dispersed graphitic N moieties. Trapping experiments and electron spin resonance showed a nonradical degradation pathway in the UC-N/PMS system, through which organics were oxidized by donating electrons to UC-N/PMS* metastable complexes. This work not only reports a universal way to access high-performance, metal-free PMS activators but also provides insight into the underlying mechanism of the carbon-activated PMS process.

Developing a Thin Film Composite Membrane with Hydrophilic Sulfonated Substrate on Nonwoven Backing Fabric Support for Forward Osmosis

This study describes the fabrication of sulfonated polyethersulfone (SPES) as a super-hydrophilic substrate for developing a composite forward osmosis (FO) membrane on a nonwoven backing fabric support. SPES was prepared through an indirect sulfonation procedure and then blended with PES at a certain ratio. Applying SPES as the substrate affected membrane properties, such as porosity, total thickness, morphology, and hydrophilicity. The PES-based FO membrane with a finger-like structure had lower performance in comparison with the SPES based FO membrane having a sponge-like structure. The finger-like morphology changed to a sponge-like morphology with the increase in the SPES concentration. The FO membrane based on a more hydrophilic substrate via sulfonation had a sponge morphology and showed better water flux results. Water flux of 26.1 L m⁻² h⁻¹ and specific reverse solute flux of 0.66 g L⁻¹ were attained at a SPES blend ratio of 50 wt % when 3 M NaCl was used as the draw solution and DI water as feed solution under the FO mode. This work offers significant insights into understanding the factors affecting FO membrane performance, such as porosity and functionality.

Interlayered Forward Osmosis Membranes with Ti3C2Tx MXene and Carbon Nanotubes for Enhanced Municipal Wastewater Concentration

Forward osmosis (FO) hybrid systems have the potential to simultaneously recover nutrients and water from wastewater. However, the lack of membranes with high permeability and selectivity has limited the development and scale-up of these hybrid systems. In this study, we fabricated a novel thin-film nanocomposite membrane featuring an interlayer of Ti₃C₂T_x MXene intercalated with carbon nanotubes (M/C-TFNi). Owing to the enhanced confinement effect on interfacial degassing and increased amine monomer sorption by the interlayer, the resulting M/C-TFNi FO membrane has a greater degree of cross-linking and roughness. In comparison with the thin-film composite (TFC) membrane without an interlayered structure, the M/C-TFNi membrane attained a water flux that was four times higher and a lower specific salt flux. Notably, the M/C-TFNi membrane exhibited excellent concentration efficiency for real municipal wastewater and enhanced rejection of ammonia nitrogen, which breaks the permeability-selectivity upper bound. This study provides a new avenue for the rational design and development of high-performance FO membranes for environmental applications.

Thin film nanocomposite membrane with triple-layer structure for enhanced water flux and antibacterial capacity

Triple-layered thin film composite (TFC) forward osmosis (FO) membranes prepared on interlayer-based supports have overcome the limitations of conventional porous substrates due to the formation of ultrathin and highly selective polyamide (PA) layers. However, mitigating the internal concentration polarization (ICP) and biofouling of TFC membranes remain a great challenge. Herein, we designed a novel triple-layered thin film nanocomposite (TFN) FO membrane with incorporation of silver (Ag) decorated graphene oxide quantum dots (GOQD) into PA layer via interfacial polymerization on a carbon nanotube (CNT) interlayer-based polyether sulfone substrate. By contrast with the TFC membranes, the newly developed GOQD/Ag incorporated triple-layered TFN membrane (TFN-GOQD/Ag) exhibited a great alleviation for ICP accompanied with a prominently enhanced water flux of 65.8 L·m^-2·h^-1 and decreased specific reverse salt flux of 1.4 g·m^-2·h^-1 by employing 1 M NaCl solution as draw solution. Moreover, the TFN-GOQD/Ag membrane possessed prominent antibacterial activity against both E. coli (99.8%) and S. aureus (97.3%). Noteworthy, the obtained TFN membrane demonstrated a controlled release of Ag⁺ along with long-term antibacterial potential and outstanding fouling resistance during the FO process. This work provides a new avenue to fabricate newly FO membranes with superior performance for water cleaning treatment.

Synergistic impacts of Cu2+ on simultaneous removal of tetracycline and tetracycline resistance genes by PSF/TPU/UiO forward osmosis membrane

Cu²⁺, tetracycline (TC), and corresponding tetracycline resistance genes (TRGs) are common micropollutants in aquaculture wastewater, which have great impact on environment and human health. In this study, we developed a thin-film nanocomposite (TFN) forward osmosis (FO) membrane with an electrospinning thermoplastic polyurethane/polysulfone (PSF/TPU) substrate and a UiO-66-NH₂ particle interlayer modified active layer. The effects of Cu²⁺ concentration on the synergetic removal of TC and TRGs (e.g., tetA/M/X/O/C, int1, and 16 S rRNA gene) were analyzed to determine the role of Cu²⁺ in FO process. The rejection mechanism was also analyzed in depth. Results demonstrated that the rejection of TC and Cu²⁺ was 99.53% and 97.99%. The rejection of TRGs exceeded 90% (specifically, over 99% for tetC) at a Cu²⁺ concentration of 500 μg/L when 0.5 M (NH₄)₂HPO₄ was used as draw solution. Complexation reaction between Cu²⁺ and TC, electrostatic interaction, and the adsorption of Cu²⁺ on membrane surface were the main contributing factors for the high rejection efficiencies. Altogether, the as-prepared FO membrane holds great potential for simultaneously removing heavy metals, antibiotics, and resistance genes in real wastewater.

Alleviation of Reverse Salt Leakage across Nanofiber Supported Thin-Film Composite Forward Osmosis Membrane via Heat-Curing in Hot Water

Electrospun nanofiber with interconnected porous structure has been studied as a promising support layer of polyamide (PA) thin-film composite (TFC) forward osmosis (FO) membrane. However, its rough surface with irregular pores is prone to the formation of a defective PA active layer after interfacial polymerization, which shows high reverse salt leakage in FO desalination. Heat-curing is beneficial for crosslinking and stabilization of the PA layer. In this work, a nanofiber-supported PA TFC membrane was conceived to be cured on a hot water surface with preserved phase interface for potential “defect repair”, which could be realized by supplementary interfacial polymerization of residual monomers during heat-curing. The resultant hot-water-curing FO membrane with a more uniform superhydrophilic and highly crosslinked PA layer exhibited much lower reverse salt flux (FO: 0.3 gMH, PRO: 0.8 gMH) than that of oven-curing FO membrane (FO: 2.3 gMH, PRO: 2.2 gMH) and achieved ∼4 times higher separation efficiency. It showed superior stability owing to mitigated reverse salt leakage and osmotic pressure loss, with its water flux decline lower than a quarter that of the oven-curing membrane. This study could provide new insight into the fine-tuning of nanofiber-supported TFC FO membrane for high-quality desalination via a proper selection of heat-curing methods.

A Critical Review on Thin-Film Nanocomposite Membranes with Interlayered Structure: Mechanisms, Recent Developments, and Environmental Applications

The separation properties of polyamide reverse osmosis and nanofiltration membranes, widely applied for desalination and water reuse, are constrained by the permeability-selectivity upper bound. Although thin-film nanocomposite (TFN) membranes incorporating nanomaterials exhibit enhanced water permeance, their rejection is only moderately improved or even impaired due to agglomeration of nanomaterials and formation of defects. A novel type of TFN membranes featuring an interlayer of nanomaterials (TFNi) has emerged in recent years. These novel TFNi membranes show extraordinary improvement in water flux (e.g., up to an order of magnitude enhancement) along with better selectivity. Such enhancements can be achieved by a wide selection of nanomaterials, ranging from nanoparticles, one-/two-dimensional materials, to interfacial coatings. The use of nanostructured interlayers not only improves the formation of polyamide rejection layers but also provides an optimized water transport path, which enables TFNi membranes to potentially overcome the longstanding trade-off between membrane permeability and selectivity. Furthermore, TFNi membranes can potentially enhance the removal of heavy metals and micropollutants, which is critical for many environmental applications. This review critically examines the recent developments of TFNi membranes and discusses the underlying mechanisms and design criteria. Their potential environmental applications are also highlighted.

Search for optimal monomers for fabricating active layers in thin-film composite osmosis membranes by conceptual density functional theory

This paper presented an effective way to select monomers to fabricate active layers for the thin-film composite (TFC) membrane at the molecular level. Five types of diamine monomers and six acid chloride monomers were firstly selected by a conformer search process. Then, the conceptual density functional theory (CDFT) method was adopted to examine the properties of these monomers. A few different molecular properties were calculated, including relative energy, hydrogen bond, global/local/difference local softness, hardness, chemical potential, and electrophilicity index. Similarly, polyamides that were the productions of interfacial polymerization reaction were also analyzed by CDFT. Our results showed that the mixture of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) for the interfacial polymerization was ideal synthetic materials to fabricate the active layer of TFC membranes. Graphical abstract Polyamides synthesis by interfacial polymerization.

Improving the Selectivity of ZIF-8/Polysulfone-Mixed Matrix Membranes by Polydopamine Modification for H2/CO2 Separation

Gas separation membranes are essential for the capture, storage, and utilization (CSU) of CO₂, especially for H₂/CO₂separation. However, both glassy and rubbery polymer membranes lead a relatively poor selectivity for H₂/CO₂ separation because the differences in kinetic diameters of these gases are small. The present study establishing the mixed matrix membranes (MMMs) consist of a nano-sized zeolitic imidazolate frameworks (ZIF-8) blended with the polysulfone (PSf) asymmetric membranes. The gas transport properties (H₂, CO₂, N₂, and CH₄) of MMMs with a ZIF-8 loading up to 10 wt% were tested and showing significant improvement on permeance of the light gases (e.g., H₂ and CO₂). Moreover, the depositional polydopamine (PDA) layer further enhanced the ideal H₂/CO₂ selectivity, and the PDA-modified MMMs approach the Robeson upper bound of H₂/CO₂ separation membranes. Hence, the PDA post-modification strategy can effectively repair the defects of MMMs and improved the H₂/CO₂selectivity.

Scalable Ti3C2Tx MXene Interlayered Forward Osmosis Membranes for Enhanced Water Purification and Organic Solvent Recovery

The design of nanosheets interlayer between the substrate and polyamide layer has attracted growing attention to improve the performance of thin-film composite membranes. However, the membrane size is limited by current fabrication methods such as vacuum filtration. Herein, a high-performance MXene (Ti₃C₂T_x) interlayered polyamide forward osmosis (FO) membrane is fabricated based on a combination of a facile and scalable brush-coating of MXene on nylon substrates and the interfacial polymerization process. The as-prepared FO membrane shows high water permeability of 31.8 L m^-2 h^-1 and low specific salt flux of 0.27 g L^-1 using 2.0 mol L^-1 sodium chloride as the draw solution. This is attributed to the adjustment of substrate properties and the polyamide layer by coating of MXene as well as the facilitation of water transportation by the interlayer distances between Ti₃C₂T_x. The membrane also exhibits a good organic solvent forward osmosis performance with high ethanol flux as 9.5 L m^-2 h^-1 and low specific salt flux of 0.4 g L^-1 using 2.0 mol L^-1 lithium chloride as the draw solution. Moreover, the MXene interlayered FO membrane demonstrates a feasible application in real seawater desalination and industrial textile wastewater treatment. This work presents an effective approach to fabricating nanomaterials interlayered FO membranes with superior performance for both desalination and organic solvent recovery.

Ultrathin Thin-Film Composite Polyamide Membranes Constructed on Hydrophilic Poly(vinyl alcohol) Decorated Support Toward Enhanced Nanofiltration Performance

Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES-PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m^-2 h^-1 bar^-1 and a 99.4% Na₂SO₄ rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.

A highly permeable zinc-based MOF/polyphenylsulfone composite membrane with elevated antifouling properties

In this study, for the first time, a highly permeable composite membrane was constructed by incorporating a zinc-based metal-organic framework (Zn-MOF) in a polyphenylsulfone matrix for the elevation of antifouling properties. Owing to the hydrophilic nature and high surface charge, this membrane demonstrated effective bovine serum albumin (a model protein) rejection and antifouling characteristics.

Thin Film Composite Forward Osmosis Membrane with Single-Walled Carbon Nanotubes Interlayer for Alleviating Internal Concentration Polarization

This study reported a series of thin film composite (TFC) membranes with single-walled nanotubes (SWCNTs) interlayers for the forward osmosis (FO) application. Pure SWCNTs with ultrahigh length-to-diameter ratio and without any functional group were applied to form an interconnect network interlayer via strong π-π interactions. Compared to the TFC membrane without SWCNTs interlayer, our TFC membrane with optimal SWCNTs interlayer exhibited more than three times the water permeability (A) of 3.3 L m⁻²h⁻¹bar⁻¹ in RO mode with 500 mg L⁻¹ NaCl as feed solution and nearly three-fold higher FO water flux of 62.8 L m⁻² h⁻¹ in FO mode with the deionized water as feed solution and 1 M NaCl as draw solution. Meanwhile, the TFC membrane with SWCNTs interlayer exhibited significantly reduced membrane structure parameters (S) to immensely mitigate the effect of internal concentration polarization (ICP) in support layer with micro-sized pores in favor of higher water flux. It showed that the pure SWCNTs interlayer could be an effective strategy to apply in FO membranes.

Graphene Oxide Incorporated Forward Osmosis Membranes With Enhanced Desalination Performance and Chlorine Resistance

In this work, grapheme oxide (GO) nano-sheets were synthesized and dispersed in the aqueous phase for the interfacial polymerization (IP) process to develop a new type of thin-film composite (TFC) membranes for forward osmosis (FO) applications. The effects of the GO concentrations on the membrane surfaces and cross-sectional morphologies and FO desalination performances of the as-prepared TFC membranes were investigated systematically. Compared with the control membrane, the optimal GO-incorporated TFC membrane displayed higher water flux, less specific reverse solute flux (SRSF) and lower structure parameter. Moreover, the optimized membrane showed 75.0 times higher chlorine resistance than the control membrane. In general, these new type of membranes could be an effective strategy to fabricate high-performance FO membranes with good desalination performance and chlorine resistance.

Porous Zr-Based Metal-Organic Frameworks (Zr-MOFs)-Incorporated Thin-Film Nanocomposite Membrane toward Enhanced Desalination Performance

Four different thin-film nanocomposite (TFN) membranes were prepared by adding different concentrations of porous Zr-metal-organic frameworks (MOFs) (UiO-66 and UiO-66-NH₂) to piperazine aqueous solution (aqueous phase) or 1,3,5-benzenetricarbonyl trichloride-n-hexane solution (organic phase) by interfacial polymerization. The main purpose is to study the specific effects of different addition methods and addition amounts of nanoparticles on the structure and performance of the TFN membranes by interfacial polymerization. All four TFN membranes exhibited a higher water permeability while maintaining high salt rejection compared to thin-film composite membrane. On the one hand, the TFN membranes behave differently, which are prepared by adding the same kind of nanoparticles to the aqueous phase or organic phase, respectively. The TFN membrane prepared by adding 0.2 w/v% UiO-66 to the organic phase had a high water flux of 87.86 L m^-2 h^-1, compared to 46.31 L m^-2 h^-1 of the membrane prepared by adding 0.3 w/v% UiO-66 in the aqueous phase. This is due to the fact that UiO-66 greatly slows the interfacial polymerization rate when UiO-66 is added to the organic phase, resulting in a thinner and wider-aperture polyamide thin-film layer, reducing the water transmission resistance during filtration. Therefore, it is more economical by adding nanoparticles to organic phase than aqueous phase under the same filtering effect. On the other hand, different nanoparticles can also cause differences in performance and structure of the TFN membranes even in the same preparation manner. TFN membrane with UiO-66-NH₂ in the aqueous phase has higher water permeance than the one with UiO-66 in the aqueous phase, owing to the good hydrophilicity of the amino group, which improves the water dispersibility of UiO-66-NH₂ so that the TFN membrane is more uniform. In addition, UiO-66-NH₂ slows down the process of interface polymerization, making the membrane more porous. The monomers in the aqueous phase and organic phase can be adsorbed in the pores of Zr-MOFs, which makes the interfacial polymerization occur both in the pores and on the surface of the pores. Thus, the compatibility between the polyamide and MOFs was enhanced and less defects were formed in the thin-film layer, resulting in a high salt rejection even when the concentration of Zr-MOFs increased. This is the first time to explain that polyamide membrane has not obvious salt rejection attenuation with increasing porous material content using pore adsorption reaction monomer principle. Also, the Zr-MOFs-based TFN membrane exhibited good heat resistance and antifouling property. This work shows that porous Zr-MOFs nanomaterials have significant advantages in the development of nanofiltration membranes with high water flux and rejection.

Metal-organic framework UiO-66 membranes

Metal-organic frameworks (MOFs) have emerged as a class of promising membrane materials. UiO-66 is a prototypical and stable MOF material with a number of analogues. In this article, we review five approaches for fabricating UiO-66 polycrystalline membranes including in situ synthesis, secondary synthesis, biphase synthesis, gas-phase deposition and electrochemical deposition, as well as their applications in gas separation, pervaporation, nanofiltration and ion separation. On this basis, we propose possible methods for scalable synthesis of UiO-66 membranes and their potential separation applications in the future.

Aluminosilicate Nanotubes Embedded Polyamide Thin Film Nanocomposite Forward Osmosis Membranes with Simultaneous Enhancement of Water Permeability and Selectivity

Nanocomposite membranes are strongly desired to break a trade-off between permeability and selectivity. This work reports new thin film nanocomposite (TFN) forward osmosis (FO) membranes by embedding aluminosilicate nanotubes (ANTs) into a polyamide (PA) rejection layer. The surface morphology and structure of the TFN FO membranes were carefully characterized by FTIR, XPS, FESEM and AFM. The ANTs incorporated PA rejection layers exhibited many open and broad "leaf-like" folds with "ridge-and-valley" structures, high surface roughness and relatively low cross-linking degree. Compared with thin film composite (TFC) membrane without ANTs, the TFN membrane with only 0.2 w/v% ANTs loading presented significantly improved FO water permeability, selectivity and reduced structural parameters. This promising performance can be mainly contributed to the special ANTs embedded PA rejection layer, where water molecules preferentially transport through the nanochannels of ANTs. Molecular dynamic simulation further proved that water molecules have much larger flux through the nanotubes of ANTs than sodium and chloride ions, which are attributed to the intrinsic hydrophilicity of ANTs and low external force for water transport. This work shows that these TFN FO membranes with ANTs decorated PA layer are promising in desalination applications due to their simultaneously enhanced permeability and selectivity.