High-performance Thin Film Nanocomposite Research Articles

Tannic acid etched ZIF-8 incorporated thin-film nanocomposite nanofiltration membrane with enhanced performance

Incorporating functionalized nanomaterials in the selective layer of conventional polyamide nanofiltration (NF) membrane is a promising strategy for overcoming the trade-off between permeability and selectivity. Highly hydrodispersible TA/ZIF-8 composite nanomaterials were prepared by etching ZIF-8 with tannic acid, and the thin-film nanocomposite (TFN) NF membranes were prepared by introducing TA/ZIF-8 into the interfacial polymerization aqueous phase solution. The nanomaterials and NF membranes' structure, chemical composition, and hydrophilicity were comprehensively characterized. The influence and mechanism of introducing TA/ZIF-8 into the polyamide layer on the separation performance of the TFN membranes were discussed by separating typical mono- and divalent salts. The optimal TFN membrane had a water flux of 26.59 LMH-bar−1 (increased by 86.6% than that of the TFC-blank membrane) with 94.95% rejection of Na2SO4 while having good antifouling performance and stability. Furthermore, the inverse size exclusion phenomenon of chlorine-contained salts was explored through relevant control experiments. This work is valuable for expanding the application of 3D nanomaterials in membrane separation technology and preparing high-performance TFN nanofiltration membranes.

A novel ZIF-L/PEI thin film nanocomposite membrane for removing perfluoroalkyl substances (PFASs) from water: Enhanced retention and high flux

Membrane separation technology is widely recognized as an effective method for removing perfluoroalkyl substances (PFASs) in water treatment. ZIF-L, a metal-organic framework (MOF) family characterized by its mat-like cavities and leaf-like morphology, has garnered considerable interest and has been extensively employed in fabricating thin-film nanocomposite (TFN) membranes. In this study, a robust, high-performance TFN membrane to remove PFASs in a nanofiltration (NF) process was created through an interfacial polymerization approach on the surface of polysulfone (PSF), incorporating ZIF-L within the selective layer. The TFN membrane modified by adding 5 wt% ZIF-L (relative to the weight of ethylene imine polymer (PEI)) exhibits 2.3 times higher water flux (up to 47.56 L·m−2·h−1·bar−1) than the pristine thin film composite membrane (20.46 L·m−2·h−1·bar−1), and the rejection for typical PFASs were above 95 % (98.47 % for perfluorooctanesulfonic acid (PFOS) and 95.85 % for perfluorooctanoic acid (PFOA)). The effectiveness of the ZIF-L/PEI TFN membrane in retaining representative PFASs was examined under various conditions, including different pressures, feed concentrations, aqueous environments, and salt ions. Notably, the experiments demonstrated that even after contamination with humic acid (HA), >88 % of the water flux could be restored by washing. Additionally, density functional theory (DFT) calculations were employed to predict the distinct intermolecular interactions between PFASs and ZIF-L as well as PEI. These calculations provide additional insights into the interception mechanism of TFN membranes towards PFASs. Based on this study, TFN membranes incorporating MOF as nanofillers show great potential as an effective method for purifying PFASs from aqueous environments and possess superior environmental sustainability and cost-effectiveness.

In-situ interfacial polymerization of polyamide TFN membranes by adding a diamino-silane coupling agent: Toward enhanced desalination performance

The primary challenge faced by thin film nanocomposite (TFN) membrane in nanofiltration (NF) process is to effectively resolve the trade-off effect between permeability and selectivity. Herein, a polyamide (PA) TFN membrane with enhanced NF performance was prepared through in-situ interfacial polymerization (in-situ IP) method, using piperazine (PIP) and 3-diamino-methyl-cyclohexyl triethoxysilane (DTES) as co-amine monomers to undergo a reaction with 1,3,5-benzenetricarbonyl trichloride (TMC). This study investigated the effects of DTES on the surface chemical composition, morphologies, hydrophilicity, separation efficiency, and anti-fouling properties of the novel DTES/PIP/TMC TFN membranes. It was found that SiO2 nanoparticles were generated in-situ from the reacted DTES through hydrolysis and self-condensation, resulting in their uniform distribution within the formed PA selective layer with high compatibility and without aggregation. The optimal PA TFN membrane was achieved by adjusting the ration of Si-OH group in formed SiO2 nanoparticles through varying the concentration of DTES concentration. Meanwhile, the induction of SiO2 into the PA layer resulted in an enlargement in membrane pore size and improved surface hydrophilicity. When the concentration of added DTES was 0.333 wt%, the optimal PA TFN membrane (TFN-4) exhibited the highest quantity of formed Si-OH groups, resulting in the excellent performance, including a markedly enhanced water permeability flux of 76.8 L·m−2·h−1 (2-fold larger than that of the pure TFC membrane), a great Na2SO4 rejection of 97.5 %, and a superior Cl−/SO42− permeation selectivity of 46.0. Moreover, the TFN-4 membrane exhibited exceptional stability and superior antifouling properties attributed to its unparalleled hydrophilicity. This work provided a strategy for preparing uniform and high-performance TFN membranes.

Solvent-activated thin-film nanocomposite membranes molecularly tuned with macrocyclic cavities for efficient water desalination and boron removal

Tuning the permeation properties of thin-film nanocomposite (TFN) membranes through the molecular redesign of their underlying nanoarchitecture is a challenging but important task for realizing reverse osmosis (RO) desalination performance above the trade-off limit. Activation by organic solvents, as one of the most facile methods to rearrange the microstructure of RO membranes, can effectively boost the water permeability but is constrained by the significant rejection loss. Here, we innovated an integrative approach whereby soluble organic macrocyclic cavitands (OMCs) with molecular-sieving open cavities were simultaneously dissolved in the activating solvent during membrane post-treatment such that their infiltration into the interfacially polymerized (IP) polyamide (PA) layer enabled the formation of a nanocomposite structure with recovered or even enhanced salt rejections. In this work, prefabricated polysulfone-supported pristine PA membranes were transformed into cavity-bearing nanocomposites after being treated with methanol solutions containing 4-sulfocalix[4]arene (SCA4), an OMC structure with a strongly size-sieving ∼ 3.0 Å cavity opening. This integrative solvent-cavitand treatment allowed their water permeability to increase by up to 129% from 1.98 to 4.53 Lm−2h−1bar−1 with uncompromised or even enhanced NaCl rejection, leading to overall separation performances that well surpassed the permeability-selectivity trade-off line. Meanwhile, these SCA4-infiltrated TFN membranes also demonstrated promising boron removal efficiency with an increase in both the water permeability and boron rejection from 1.95 to 4.17 Lm−2h−1bar−1 and 96.9% to 97.4% at pH = 10, respectively. With the wide array of solvent and soluble nanoarchitecture options, this study could provide a new and versatile direction in designing high-performance TFN membranes for environmentally important separations.

Correlating the role of nanofillers with active layer properties and performance of thin-film nanocomposite membranes

Thin-film nanocomposite (TFN) membranes are emerging water-purification membranes that could provide enhanced water permeance with similar solute removal over traditional thin-film composite (TFC) membranes. However, the effects of nanofiller incorporation on active layer physico-chemical properties have not been comprehensively studied. Accordingly, we aimed to understand the correlation between nanofillers, active layer physico-chemical properties, and membrane performance by investigating whether observed performance differences between TFN and control TFC membranes correlated with observed differences in physico-chemical properties. The effects of nanofiller loading, surface area, and size on membrane performance, along with active layer physico-chemical properties, were characterized in TFN membranes incorporated with Linde Type A (LTA) zeolite and zeolitic imidazole framework-8 (ZIF-8). Results show that nanofiller incorporation up to ~0.15 wt% resulted in higher water permeance and unchanged salt rejection, above which salt rejection decreased 0.9–25.6 % and 26.1–48.3 % for LTA-TFN and ZIF-8-TFN membranes, respectively. Observed changes in active layer physico-chemical properties were generally unsubstantial and did not explain observed changes in TFN membrane performance. Therefore, increased water permeance in TFN membranes could be due to preferential water transport through porous structures of nanofillers or along polymer-nanofiller interfaces. These findings offer new insights into the development of high-performance TFN membranes for water/ion separations.

Nano-striped polyamide membranes enabled by vacuum-assisted incorporation of hierarchical flower-like MoS2 for enhanced nanofiltration performance

Introducing nanomaterials into the polyamide layer of thin-film composite (TFC) membranes during interfacial polymerization process can customize the physicochemical properties of membranes and further enhance the membrane permeability without sacrificing selectivity. In this study, we prepared novel thin-film nanocomposite (TFN) nanofiltration membranes by varying the deposition density of hierarchical flower-like structured molybdenum disulfide (HF–MoS2) with the assistance of vacuum filtration. Ascribed to the unique 3D hierarchical structure of HF–MoS2, a nano-sized striped polyamide film with a decreased thickness of 30–40 nm was formed, which increased the membrane effective filtration area and reduced the mass transfer resistance for water permeation. In addition, compared to the control TFC membrane, the TFN membranes possessed relatively looser polyamide layers with higher surface hydrophilicity and more negative surface charges. When the deposition density of HF–MoS2 was 10 μg/cm2, the optimal performance of the TFN membranes was obtained, i.e., a water permeability of 18.4 L m−2 h−1 bar−1 and rejections above 98% for Na2SO4 and MgSO4. Moreover, the optimal TFN membrane demonstrated an excellent separation performance and structure stability in the mixed salt solution and the long-term filtration test of 120 h, respectively. This work provides a novel approach to design high-performance TFN membranes applied for water/wastewater treatment.

Ionic liquid modified COF nanosheet interlayered polyamide membranes for elevated nanofiltration performance

Presently, advanced Thin-film nanocomposite (TFN) nanofiltration membranes fabricated using microporous materials displayed distinctly enhanced separation performance. Herein, tetrakis(hydroxymethyl) phosphonium chloride (THPC)-modified COF nanosheets (termed as IL@COF-367 NSs) were designed as the intermediate layer to construct a high-hydrophilic membrane support, with the purpose of regulating interfacial polymerization (IP) to optimize the physicochemical characters of polyamide films. Due to the high hydrophilicity and favored dispersion of IL@COF-367 NSs in aqueous phase, the as-fabricated COF nanosheet interlayer not only promotes uniform distribution of amine monomers, but also slows down their diffusion toward the organic interface. Compared pristine thin-film composite (TFC) membranes, the IC-TFN membranes yield a nodular polyamide film with a higher surface roughness (from 14.5 to 54.5 nm) and a lower film thickness (from 95 to 30 nm). Introducing IL@COF-367 NSs additionally improves the pore size (from 0.31 to 0.47 nm) of the functionalized TFN membrane revealed by the MWCO measurement. Consequently, IL@COF-367 NSs-interlayer polyamide (IC-TFN) membrane manifests a high permeability of 36.5 L m−2 h−1 bar−1 and satisfactory Na2SO4 rejection of 98.5 %. The usage of 2D hydrophilic COF nanosheet as an interlayer to optimize the polyamide membranes offers a guideline for the design of high-performance TFN membrane.

Regulating interfacial polymerization via constructed 2D metal-organic framework interlayers for fabricating nanofiltration membranes with enhanced performance

Interlayered thin-film nanocomposite (TFN) membranes have been proven to achieve enhanced water permeance for desalination applications, while those lacking effective control over the construction of interlayers were prone to unsatisfactory permselectivity. In this study, a high-performance TFN membrane was constructed via interfacial polymerization on a Metal-Organic Frameworks (MOFs)-interlayered polyethersulfone substrate. Regulating the thickness of the MOFs (copper-tetrakis(4-carboxyphenyl) porphyrin, Cu-TCPP) interlayer could effectively tailor the structural parameters (effective filtration area, selective layer thickness, and pore size) and physicochemical properties of the membrane. A resistance-in-series model was applied to analyze the hydraulic resistance distribution and the specific value of the intrinsic solution permeability of each layer of the TFN membranes. Results showed that the interlayer with a proper deposition density of MOFs nanosheets could simultaneously increase the cross-linking degree by adsorbing the PIP monomers and reduce the thickness of the PA layer to enhance the intrinsic permeability. The optimal membrane with a thin PA film (20 nm) displayed an excellent water permeance of 32.7 L·m−2·h−1·bar−1 and an ultrahigh NaCl/Na2SO4 selectivity of 271.7. Moreover, the membrane demonstrated remarkable stability during 120 h filtration. This work provides a promising strategy for fabricating TFN membranes with higher selectivity and enhanced comprehensive performance.

Thin film nanocomposite membrane incorporated with 2D-MOF nanosheets for highly efficient reverse osmosis desalination

Metal-organic frameworks (MOFs) have drawn significant attention in the fabrication of thin film nanocomposite (TFN) membranes. In particular, two-dimensional MOFs (2D-MOFs) are advantageous in improving compatibility and molecular sieving performance depending on the sub-atomic surface thickness, high exposure of surface functional groups and controllable pore structure properties. In this study, a robust high performance TFN membrane for reverse osmosis (RO) desalination was fabricated using an interfacial polymerization strategy on the surface of polysulfone (PSF) substrate with embedded ultrasonically exfoliated nickel-based 2D-MOF nanosheet in the selective layer. The TFN membrane modified by adding 0.015 wt% 2D-MOF nanosheet to the aqueous phase exhibits a 2.5 times higher water permeability with a well-maintained salt rejection (water permeance up to 50.0 L m−2 h−1·MPa−1, NaCl rejection of 99.2%) compared to pristine thin film composite (TFC) membrane (water permeance 20.6 L m−2 h−1·MPa−1, NaCl rejection 99.3%). Meanwhile, the modified TFN membrane features outstanding anti-fouling properties against 500 ppm humic acid with a high water permeance recovery ratio of 96.9%. In addition, the diffusions of water molecules both in pristine TFC membrane and modified TFN membrane were investigated by the molecular dynamics (MD) simulation, showing good agreement with the experimental results. The simulation results reveal that the incorporation of 2D-MOF nanosheets can reduce transfer resistance and increase water diffusion because of the extra pores of 2D-MOF and H bonds between free water molecules and the coordination water of 2D-MOF. This study presents a new strategy to fabricate high-performance RO membranes, and also provides further insights into the great potential of 2D-MOFs in the water-treatment field.

Thin film nanocomposite membrane incorporated with clay-ionic liquid framework for enhancing rejection of epigallocatechin gallate in aqueous media

Tea catechins are the major ingredients in tea polyphenols. The design of nanomaterials from natural resources for versatile applications is a global topic of research. Here, we have reported a new and versatile Thin Film Nanocomposite (TFN) membrane that was developed from ionic liquid functionalized bentonite clay. Clay-[1-hexyl-3-methylimidazolium chloride] framework was introduced as a nano additive to prepare high performance TFN membranes of thermal stability 630 ºC. The polyamide layer was designed over the membrane surface for selective separation of epigallocatechin gallate (EGCG). In this work, diffusive mass transfer across porous hydrophilic surfaces is significant in an emerging trade-off between membrane flux and permeability for selective separation of EGCG. The membrane showed 94% rejection at pressure 5 bar, flow rate of 23 mL.min−1 and feed concentration of 1.5 mmol.L−1. The membrane showed its efficiency for its reusability. This study confirms the desirable applicability of novel functionalized bentonite (FBn) based TFN membranes for selective separation of biomolecule in aqueous media.

Multilayer assembly of thin-film nanocomposite membranes with enhanced NaCl and antibiotic rejection

Reverse osmosis and nanofiltration by thin-film nanocomposite (TFN) membranes are energy-efficient processes for water purification. However, it is difficult to fabricate high-performance TFN membranes in controllable manner. In this work, the uniform and multilayered polyamide (PA)-graphene oxide (GO) TFN membranes were assembled by a simple and controllable strategy, named as multilayer deposition, which was performed by consecutively spin-coating GO, meta-phenylene diamine (MPD)/piperazine (PIP), and trimesoyl chloride (TMC) solutions on the substrates. The introduction of GO could reduce defects, resulting in formation of smooth and defect-free reverse osmosis/nanofiltration membranes with significantly increased NaCl and antibiotic rejection. For example, the TFN reverse osmosis membrane showed NaCl rejection of 99.1% and water permeance of 1.83 L m−2 h−1 bar−1, accompanied by substantially enhanced antifouling property.

Fabrication of high performance TFN membrane incorporated with graphene oxide via support-free interfacial polymerization

A high-performance thin film nanocomposite (TFN) membrane containing graphene oxide (GO) nanosheets was constructed using a support-free interfacial polymerization (SFIP) technique. In this study, an ultrathin composited polyamide (PA) nanofilm was synthesized at the free piperazine (PIP)-GO suspension/trimesoyl chloride (TMC) interface, followed by transfer onto a polysulfone (PSf) UF substrate. The impact of GO loading (0, 0.1, 0.5, or 1 mg/mL) on the physiochemical properties, surface morphology, and hydrophilicity of the composited PA layer and membrane separation performance was investigated. It was found that the GO-modified TFN membranes showed ultra-high hydrophilicity due to the increase in the number of carboxyl and hydroxyl groups in the PA layer. We propose that GO nanosheets play a key role in improving membrane permeability because a strong hydration layer is formed between the water molecules and GO (embedded in the PA layer), acting as a protective film and minimizing the chance of foulants contacting the membrane surface. Compared with TFC, TFN-GO-0.5 simultaneously exhibited a higher water permeability of up to 12.8 L·m−2·h−1·bar−1 (58.1% higher than the TFC membrane) and a higher Na2SO4 rejection of approximately 98.4%. Moreover, the introduction of GO nanosheets into TFN membrane resulted in an improved antifouling performance. This facile SFIP method reveals the potential of GO nanosheets for the development of high performance TFN membranes.

High-performance thin-film nanocomposite (TFN) forward osmosis (FO) membranes incorporated with porous hydrophobic-core/hydrophilic-shell nanoparticles

The current article discusses some unprecedented information about the improvement in forward osmosis (FO) performance of polyethersulfone/polyamide (PES/PA) membranes, mainly focused on water flux and selectivity along with resistance to fouling phenomenon; which itself is brought in by the introduction of pre-modified zeolitic imidazolate framework-8 MOF nanoparticles. An investigation has been conducted on ZIF-8 nanoparticles surface with hydrophilicity feature to evaluate their potential for utilization in active polyamide layer of FO membranes for the first time, free from any decrease in water flux value (when hydrophobic ZIF-8 is exploited solely) and selectivity (when mSiO2 with unselective channels is employed). Correspondingly, to fulfill the desired goal, MOF nanocrystals were coated with a thin mSiO2 shell at first, so they can be modified in the next step by GPTMS and ultimately aspartic acid. Feasibility of applied strategy (using hydrophobic-core/hydrophile-shell nanofillers) in FO membranes' desalination performance was assessed after incorporating ZIF-8@mSiO2-GPTMS-Asp nanoparticles of various concentrations in the polyamide rejection layer throughout the interfacial polymerization (IP) process. The obtained results divulge that the optimal membrane (TFN400) has the highest water flux and selectivity as well as superior resistance to BSA and SA foulant.

Electrophoretic nuclei assembly of MOFs in polyamide membranes for enhanced nanofiltration

Thin film nanocomposite (TFN) polyamide (PA) membranes has drawn increasing attention due to the improved physicochemical properties of the top layer for versatile separation performance. However, the commonly used fabrication approach, lacking a controllable loading of nanofillers, leads to a random and insufficient distribution of nanofillers into the PA layer and generates interfacial defects that deteriorate the membrane performance. Herein, a rational strategy for incorporating metal-organic frameworks (i.e., ZIF-8) into the PA layer via electrophoretic deposition (EPD) was proposed. Driven by an external direct current field, the ZIF-8 nanoparticles were uniformly assembled onto a porous ultrafiltration (UF) substrate for fabrication of high-performance TFN nanofiltration membranes by vacuum-assisted interfacial polymerization (IP). The resultant TFN nanofiltration membrane yielded an enhanced water permeability of 22.4 ± 1.2 L·m−2·h−1·bar−1, due to incorporation of ZIF-8 nanoparticles which created extra nano-channels for fast water permeation. Additionally, such an EPD process effectively tailored the membrane surface properties (e.g., zeta potential) and conferred a considerably high rejection for Na2SO4 (96.9 ± 0.7%) but a low rejection for NaCl (18.9 ± 2.5%), demonstrating an excellent selectivity between SO42− and Cl− ions. This study highlights the impressive efficacy of the EPD process in precisely anchoring nanomaterials to design high-performance TFN nanofiltration membranes for target separations.

Polyamide-MIL-101(Cr) Thin Films Synthesized on Either the Outer or Inner Surfaces of a Polysulfone Hollow Fiber for Water Nanofiltration.

High-performance thin film nanocomposite (TFN) hollow fiber (HF) membranes, with MIL-101(Cr) MOF nanoparticles (52 ± 13 nm) embedded, have been synthesized with the polyamide layer formed either on the outer or inner surface of a polysulfone HF (250 and 380 μm ID and OD, respectively). The TFN_out membrane was developed using the conventional interfacial polymerization method, typically applied to obtain TFN flat membranes (MOF particles added to the thin layer by deposition). This membrane gave a water permeance value of 1.0 ± 0.7 L·m–2·h–1·bar–1 and a rejection of 90.9 ± 1.2% of acridine orange (AO, 265 Da). In contrast, the TFN_in membrane was synthesized by microfluidic means and gave a significantly higher water permeance of 2.8 ± 0.2 L·m–2·h–1·bar–1 and a slightly lower rejection of 87.4 ± 2.5% of the same solute. This remarkable increase of flux obtained with small solute AO suggests that the HF membranes developed in this work would exhibit good performance with other typical solutes with higher molecular weight than AO. The differences between the performances of both TFN_in and TFN_out membranes lay on the distinct superficial physicochemical properties of the support, the synthesis method, and the different concentrations of MOF present in the polyamide films of both membranes. The TFN_in is more desirable due to its potential advantages, and more effortless scalability due to the microfluidic continuous synthesis. In addition, the TFN_in membrane needs much fewer quantities of reactants to be synthesized than the TFN_out or the flat membrane version.

Nanodiamond-Enabled Thin-Film Nanocomposite Polyamide Membranes for High-Temperature Water Treatment

Despite growing demands for high-temperature wastewater treatment, most available polymeric membranes are limited to mild operating temperatures (<50 °C) and become less efficient at high temperatures. Herein we show how to make thermally stable reverse osmosis thin-film nanocomposite (TFN) membranes by embedding nanodiamond (ND) particles. Polyamide composite layers containing different loadings of surface-modified ND particles were synthesized through interfacial polymerization. The reactive functional groups and the hydrophilic surface of the NDs intensified the interactions of the nanoparticles with the polymer matrix and increased the surface wettability of the TFN membranes. Contact angle measurement showed a maximum decrease from 88.4° for the pristine membrane to 58.3° for the TFN membrane fabricated with 400 ppm ND particles. The addition of ND particles and ethyl acetate created larger surface features on the polyamide surface of TFN membranes. The average roughness of the membranes increased from 108.4 nm for the pristine membrane to 177.5 nm for the TFN membrane prepared with highest ND concentration. The ND-modified TFN membranes showed a higher pure water flux (up to 76.5 LMH) than the pristine membrane (17 LMH) at ambient temperature at 220 psi and room temperature. The TFN membrane with the highest loading of ND particles overcame the trade-off relation between the water flux and NaCl rejection with 76.5 LMH and 97.3% when 2000 ppm of NaCl solution was filtered at 220 psi. Furthermore, with increasing ND concentration, the TFN membrane showed a lower flux decline at high temperatures over time. The TFN400 prepared with 400 ppm of m-phenylene diamine functionalized ND particles had a 13% flux decline over a 9 h filtration test at 75 °C. This research provides a promising path to the development of high-performance TFN membranes with enhanced thermal stability for the treatment of wastewaters at high temperatures.

Effects of colloidal TiO2 and additives on the interfacial polymerization of thin film nanocomposite membranes

Highly stable, well suspended TiO2 nanoparticles (NPs) were synthesized by a sol-gel method and directly mixed with an aqueous amine solution to react at the interface with trimesoyl chloride, forming polyamide (PA) thin film nanocomposite (TFN) membranes with a uniform distribution of the nanoparticles in the PA film. Besides the presence of TiO2 NPs, the influence of remaining chemicals such as ethanol and acid from the synthesis of the TiO2 colloids on the film formation was also investigated. The residual ethanol and acid were found to play a role in thin film formation and properties of the final membranes. The presence of TiO2 NPs, ethanol, and acid had a positive impact on membrane wettability, water flux, and salt rejection. Compared to the unmodified membrane, the TiO2-TFN membranes achieved a good separation performance with around 12% and 19% improvement in water permeability and NaCl rejection, respectively. In addition, the developed TFN membranes possessed an improved anti-fouling property with low flux decay and high flux recovery up to 94%. This simple one-pot synthesis procedure of TiO2 NPs combined with the in-situ integration during the interfacial polymerization showed great potential for economic scaling up in industrial production of high-performance TFN membranes.

High-performance thin film nanocomposite membranes enabled by nanomaterials with different dimensions for nanofiltration

The incorporation of nanomaterials into a polyamide (PA) matrix has been demonstrated to be effective in the design of advanced thin film nanocomposite (TFN) membranes. In this study, a novel TFN membrane was developed by simultaneous introduction of two nanofillers with different dimensions. Graphitic carbon nitride (g-C3N4) and halloysite nanotubes (HNTs) were co-deposited onto a substrate surface with piperazine (PIP) monomers via vacuum filtration, followed by interfacial polymerization (IP) with trimesoyl chloride (TMC). A series of characterizations showed that the pre-loaded g-C3N4 was present as nanoaggregates wrapped by the formed PA film, while one-dimensional HNTs inclined to be horizontally aligned as a hydrophilic interlayer. This unique architecture led to a crumpled membrane surface with convex and ridged structures, and provided additional water transport channels. The surface roughness and hydrophilicity of the TFN membranes were also enhanced with the addition of nanomaterials. Although g-C3N4 and HNTs were able to elevate the water permeance, a superior separation performance could only be achieved by simultaneously incorporating these two nanofillers. The best performing TFN membrane containing 16.4 μg cm−2 g-C3N4 and 19.7 μg cm−2 HNTs exhibited a water permeance of 20.5 L m−2 h−1 bar−1, nearly twice as high as that of the thin film composite (TFC) membrane, while maintaining a comparably high Na2SO4 rejection of 94.5%. This demonstrated the effectiveness of g-C3N4 and HNTs in developing high-performance TFN membranes, which were ascribed to their respective advantages as well as the combined effect in the regulation of the PA layer microstructure.

Hydrophilic polymers of intrinsic microporosity as water transport nanochannels of highly permeable thin-film nanocomposite membranes used for antibiotic desalination

Nanofiltration (NF) membranes with superior perm-selectivity are highly desirable in separation and purification processes. In this work, a highly permeable thin film nanocomposite (TFN) NF membrane containing hydrophilic polymer nanoparticles of intrinsic microporosity (PIM NPs) in polyamide (PA) separation layer is developed for antibiotic desalination. The hydrophilic PIM NPs were synthesized by one-pot polycondensation with hydrophilic β-cyclodextrin (β-CD) as one of building units and used as an additive of aqueous phase in the preparation TFN membranes by interfacial polymerization. Unlike commonly-used inorganic nanomaterials, the β-CD-PIM NPs are well compatible with PA matrix due to their polymer characteristic. Moreover, the hydroxyl groups in β-CD can participate in interfacial polymerization and thus the interfacial defects between β-CD-PIM NPs and PA matrix are effectively eliminated. As a result, the TFN membranes exhibit not only high water permeance (15.3 L m−2 h−1 bar−1), about three times as large as that of the prinstine membrane, but also high divalent salt rejection (RNa2SO4 = 95.1%). It is believed that the interior micropores inside β-CD-PIM NPs play a role of water transport nanochannels and contribute to high water permeance of the membranes. The long-term durability of the membranes are superior due to the chemical bonding between β-CD-PIM NPs and PA matrix. In addition, the TFN membranes were used for antibiotics desalination due to their high rejection towards antibiotics, but low rejection towards sodium chloride. This work offers a new strategy for constructing water transport nanochannels in separation layer to develop high performance TFN NF membranes.

Graphene quantum dots (GQDs)-polyethyleneimine as interlayer for the fabrication of high performance organic solvent nanofiltration (OSN) membranes

Novel thin film nanocomposite (TFN) organic solvent nanofiltration (OSN) membranes with sandwich-like structure were developed via interfacial polymerization (IP) using both low concentration m-phenylenediamine (MPD) and trimesoyl chloride (TMC), on graphene quantum dots (GQDs)-polyethyleneimine (PEI) modified polyimide substrate surface, and followed by post-IP crosslinking and solvent activation. Such GQDs-interlayered OSN membranes have exhibited a remarkable reduced thickness (about 25 nm) and an ultra-low average surface roughness (less than 2 nm) of their IP skin layers, respectively. Both material features are rarely reported in literature. Meanwhile, our GQDs-interlayered OSN membranes have shown an increased Rhodamine B (479 Da) rejection (from 87.4% to 98.7%) and an increased ethanol permeance (from 33.5 to 40.3 L m−2 h−1 MPa−1) compared with the pristine OSN membrane. Superior solvent resistance was demonstrated after long immersion in pure N, N-dimethylformamide (DMF) at room temperature for 81 days, and at 80 °C for 45 days, and after a long-term consecutively filtration with Rose Bengal (1017 Da) DMF solution at 25 °C for 5 days, without scarifying solute rejection. Antifouling properties during the long-term filtration were also indicated. This paper presents a novel GQDs-interlayered strategy in developing high-performance TFN membranes for OSN application.