Polyamide Thin Film Nanocomposite Research Articles

Efficient Lithium Recovery from Water Using Polyamide Thin-Film Nanocomposite (TFN) Membrane Modified with Positively Charged Silica Nanoparticles.

The separation of Li+ from Mg2+ in salt-lake brines using nanofiltration (NF) has become the most popular solution to meet the rising demand for lithium, particularly driven by the extensive use of lithium-ion batteries. This study presents the fabrication of a uniquely designed polyamide (PA) thin-film nanocomposite (TFN) membranes with ultrahigh Li+/Mg2+ selectivity and enhanced water flux by covalently incorporating mixed ligands functionalized silica nanoparticles (F-SiO2NPs) into the selective PA layer and covalently bonding them to the membrane surface. In this strategy, bare silica nanoparticles (SiO2NPs) were functionalized with mixed superhydrophilic ligands, including primary amine and quaternary ammonium groups, resulting in a highly positive surface charge primarily from the quaternary ammonium groups and enabling covalent conjugation via amine groups. Among the F-SiO2NP-incorporated membranes, M500 containing 500 ppm of F-SiO2NPs exhibited the best performance. In a solution with 2000 ppm salt concentration (Li+/Mg2+ ratio of 1:20), the M500 membrane showed an improved Li+/Mg2+ selectivity of 7.41 compared to the nonmodified TFC membrane, which had a selectivity of 5.05. Further surface conjugation of the M500 sample with 1500 ppm of F-SiO2NPs resulted in the C1500 membrane, demonstrating the best performance among all of the surface-modified membranes. C1500 showed an outstanding Li+/Mg2+ selectivity of 37.95, with a Mg2+ rejection of 95.7% and a Li+ rejection of -63.2%, and a water flux of 56.0 L m-2 h-1 at 70 psi. Notably, a 7.5-fold improvement in Li+/Mg2+ selectivity over the TFC membrane was achieved without compromising the water flux. This is evident from the nearly identical water flux values of the TFC, M500, and C1500 membranes, which were 57.1, 54.8, and 56.0 L m-2 h-1, respectively. Considering key factors for large-scale applications, such as cost-effectiveness, environmental impact, the abundance of synthetic precursors, and the maturity of synthesis and tailoring technologies, SiO2NP-based modifications outperform all other reported approaches to date.

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.

Polyamide thin film nanocomposite with in-situ co-constructed COFs for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a novel membrane technology, it has great potential for organic solvent separation and purification due to its advantages of low energy consumption and mild operating conditions. High-performance OSN membranes are essential for OSN technology. Herein, we adopted a straightforward one-step in-situ co-polymerization procedure for the fabrication of a thin film nanocomposite (TFN) OSN membrane having a COFs-polyamide selective layer via doping the COFs reaction monomers, p-phenylenediamine (Pa) and 1,3,5-triformylphloroglucinol (Tp), into the aqueous m-phenylenediamine (MPD) solution and organic trimesoyl chloride (TMC) solution, respectively, during the interfacial polymerization (IP) process. With the ultra-low concentrations used in both MPD and COFs reactive monomers, the optimal TFN OSN membrane, TFN-100-75, achieves an ethanol permeance of 65.7 L m−2 h−1 MPa−1 and an Rhodamine B (RDB, 479 Da) rejection of 99.0%. Meanwhile, this OSN membrane has an ultra-smooth surface, corresponding to a roughness of only 2.9 ± 0.3 nm. Also, this membrane has larger porosity, average pore size, and surface pore density compared with the COFs-free thin-film composite (TFC) membrane. Besides, the TFN-100-75 membrane has a pure methanol and ethanol permeance of 184.3 and 105 L m−2 h−1 MPa−1, respectively, and a molecular weight cut-off (MWCO) of about 362 Da. The TFN-100-75 membrane achieved an rifampicin rejection of above 99% during the separation of rifampicin/ethanol solutions with different concentration as well as the continuous concentration experiment, demonstrating its potential in pharmaceutical separation and purification. During a long-time variable temperature immersion test in pure N,N-dimethylformamide (DMF) at 25 °C for 32 days and then at 80 °C for 24 days, the TFN-100-75 membrane demonstrates superior solvent resistance, where the RDB rejection decreased only by 2%, from 99.0% to 97.0%. The TFN OSN membrane fabricated by the simple process in this work shows better separation performance than most OSN membranes reported in literatures, and has bright prospects for industrial organic solvents treatment.

Fabrication of polyamide thin film nanocomposite membranes with enhanced desalination performance modified by silica nanoparticles formed in-situ polymerization of tetramethoxysilane

The high separation performance polyamide (PA) thin film nanocomposite (TFN) reverse osmosis (RO) membrane for desalination was fabricated by incorporating the silica nanoparticles formed by in-situ polymerization of TMOS in the polyamide layer. The different contents and mixing methods of TMOS were investigated. The in-situ synthesized silica was uniformly embedded in the PA layer because TMOS could be fully dissolved in the organic phase solution. The agglomeration and uneven dispersion of traditional nanofillers in the polyamide layer were avoided. The best performance TFN membrane was prepared by mixing 0.8 wt% TMOS in organic phase solution and interfacial polymerization for 2 min. For brackish water desalination and high-pressure seawater desalination, the water flux of best performance membrane reached 58.4 L m−2 h−1 and 72.77 L m−2 h−1 respectively, which was 3 times and 2.6 times of that of pure polyamide thin film composite (TFC) membrane, while maintaining a satisfactory salt rejection (NaCl, 98.5%). The anti-fouling and long-term stability performance of prepared TFN membrane were also superior. This work demonstrated the potential of TMOS in-situ synthesis of nanofillers embedded in PA layer to prepare TFN membrane with high separation performance, and provided a new idea for simple preparation of TFN membrane.

Polyamide thin film nanocomposite membranes with in-situ integration of multiple functional nanoparticles for high performance reverse osmosis

Polyamide (PA) thin film nanocomposite (TFN) reverse osmosis (RO) membranes have been vigorously developed, which could be used in saline water desalination, wastewater treatment and chemicals separation and purification. Aiming at further improving the TFN RO membrane comprehensive performances, such as the perm-selectivity, stability and anti-fouling/-microbial properties remains a great challenge. Herein, we proposed a biomimetic nanoparticle redox strategy to in-situ integration of multiple functional nanoparticles, i.e., biomimetic nanoparticles (BNPs) and silver (Ag) nanoparticles into the PA matrix for simultaneously regulating the membrane microstructure and optimizing the surface property. A much hydrophilic selective layer with interior transporting channel structure renders the resultant RO membrane PA-BNP-Ag with an enhanced water permeance of ∼4.2 L m−2·h−1bar−1 without sacrificing NaCl rejection (∼98.1%). The BNPs induce Ag nanoparticles uniformly distributed within the PA matrix, which significantly improves the membrane anti-fouling/-bacterial property. The water flux recovery ratio of PAM-BNP-Ag was improved to be higher than 96% during several cycles filtration of saline solution containing bovine serum albumin foulants. More importantly, the membrane sterilization rate against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) achieves nearly 100%. This work provides a new strategy for the construction of advanced PA TFN membranes with both high perm-selectivity and anti-fouling/-microbial property in RO desalination.

Post-synthetic modification of MOFs to enhance interfacial compatibility and selectivity of thin-film nanocomposite (TFN) membranes for water purification

Efficient discrimination of ions and small neutral contaminants remains a challenge for polyamide thin-film nanocomposite (TFN) water separation membranes due to the presence of interfacial defects and particle-agglomeration-induced nonselective voids in the polyamide layer. In this work, highly selective TFN membranes were successfully fabricated by leveraging post-synthetic modifications of (3-glycidyloxypropyl)triethoxysilane (GPTES) and trimesoyl chloride (TMC) on MIL-101(Cr)–NH2 MOF filler nanoparticles. GPTES modification suppresses particle agglomeration during interfacial polymerization for membrane formation by forming a stable particle suspension in the organic monomer solution, while TMC-induced in situ chemical crosslinking between filler particles and polyamide addresses the phase compatibility and interfacial issues at the filler–polyamide interface. The resulting TFN membranes show high NaCl, MgCl2, Na2SO4, and MgSO4 rejections of 99.0–99.6% at 150 psi with a water permeance of 0.9 L m−2 h−1 bar−1. Compared to the thin-film composite (TFC) control membrane, the incorporation of the MOF particles yields a 53.0% and 24.5% increase in water permeance and NaCl rejection. Importantly, the TFN membranes also exhibit excellent rejections to small neutral contaminants such as PEG200 (99.2% rejection) and boric acid (89.0% rejection at a pH value of 7.5) at a relatively low pressure of 150 psi, which is higher than the respective value obtained by the commercial Dow SW30XLE TFC control membrane at the same conditions. The outstanding long-term performance stability revealed the robust structure of the MOF TFN membranes. Our results demonstrate a facile strategy to effectively control particle agglomeration and interfacial defects in polyamide TFN membranes by manipulating the surface chemistry of the filler nanoparticles, which can be applied to the fabrication of effective TFN membranes with molecular level size-exclusion selectivity.

Polyamide thin-film nanocomposite membrane containing star-shaped ZIF-8 with enhanced water permeance and PPCPs removal

Pharmaceuticals and personal care products (PPCPs) are universally detected in natural waters, posing potential risks to drinking water safety. Nanofiltration (NF) is an advanced technology for water purification; however, its removals of PPCPs are unsatisfying, especially for hydrophobic species. In this study, the 3D architecture of nanomaterials were used to manipulate the performance the polyamide (PA) thin-film nanocomposite (TFN) membrane. In-situ addition of polyethyleneimine (PEI) successfully induced the assembly of ZIF-8 nanocrystals into star-shaped clusters (ZIF-8-PEI) due to the coordination between PEI and Zn2+. Together with the improved hydrophilicity, these ZIF-8-PEI clusters became excellent scaffolds for water drop retention after discretely loading onto the porous substrate. The conical protrusions of the ZIF-8-PEI clusters supported the defect-free PA film produced by the interfacial polymerization (IP), leaving big interfacial cavities underneath. These cavities worked as gutters for water transport, and the water permeance of the optimal TFN was 79% higher than that of the pristine thin-film composite (TFC) membrane. Moreover, the water impregnated cavities markedly alleviated the hydrophobic interaction between the PA film and hydrophobic PPCPs, impeding the transport of PPCPs across the membrane. Our results demonstrated the importance of the 3D architecture of nanofillers for the improving membrane performance.

Polyamide thin film nanocomposite membrane with internal void structure mediated by silica and SDS for highly permeable reverse-osmosis application

The pursuit of highly permeable thin film nanocomposite (TFNC) membrane is an eternal topic for reverse-osmosis (RO) application. Here, we developed a new avenue based on interfacial polymerization to generate a polyamide TFNC membranes EVOH-SiS-PA by adding silica nanorods (SNRs) and sodium dodecyl sulfate (SDS) in water phase on the surface of EVOH nanofibrous scaffold. The resultant membrane presents a foam-like PA layers with a hierarchical internal voids structure, which is 2–3 μm in thick and distinctly differs to the membranes reported to date. The structure feature can be attributed to the fast reaction between MPD and TMC, Marangoni convection in water phase synergistically determined by SDS molecules on water/hexane interface and SNRs with abundant hydroxyl groups. Comparatively, PA TFNC membranes without SDS and/or SNRs just present a PA layer with smaller thickness (1–2 μm), surface roughness and surface area. As a result, a high permeance of 8.5 L m−2 h−1 bar−1 and a reasonably high rejection to NaCl, CuSO4 and MO feed solution (97.1%–2000 ppm NaCl, 98.2% rejection to 2000 ppm CuSO4 and 99.2% to 20 ppm MO) were obtained towards EVOH-SiS-PA, outperforming the currently reported RO membranes. Here, we provide an approach to fabricate advanced PA TFNC membranes with excellent performance, highlighting their great potential in reverse-osmosis application.

Thin Film Polyamide Nanocomposite Membrane Decorated by Polyphenol-Assisted Ti3C2Tx MXene Nanosheets for Reverse Osmosis

Transition-metal carbides (MXenes), multifunctional 2D materials, have caught the interest of researchers in the fabrication of high-performance nanocomposite membranes. However, several issues regarding MXenes still remain unresolved, including low ambient stability; facile restacking and agglomeration; and poor compatibility and processability. To address the aforementioned challenges, we proposed a facile, green, and cost-efficient approach for coating a stable layer of plant-derived polyphenol tannic acid (TA) on the surface of MXene (Ti3C2Tx) nanosheets. Then, high-performance reverse osmosis polyamide thin film nanocomposite (RO-PA-TFN) membranes were fabricated by the incorporation of modified MXene (Ti3C2Tx-TA) nanosheets in the polyamide selective layer through interfacial polymerization. The strong negative charge and hydrophilic multifunctional properties of TA not only boosted the chemical compatibility between Ti3C2Tx MXene nanosheets and the polyamide matrix to overcome the formation of nonselective voids but also generated a tight network with selective interfacial pathways for efficient monovalent salt rejection and water permeation. In comparison to the neat thin film composite membrane, the optimum TFN (Ti3C2Tx-TA) membrane with a loading of 0.008 wt % nanofiller revealed a 1.4-fold enhancement in water permeability, a well-maintained high NaCl rejection rate of 96% in a dead-end process, and enhanced anti-fouling tendency. This research offers a facile way for the development of modified MXene nanosheets to be successfully integrated into the polyamide-selective layer to improve the performance and fouling resistance of TFN membranes.

Flux enhancement in reverse osmosis membranes induced by synergistic effect of incorporated palygorskite/chitin hybrid nanomaterial

The substrate of RO thin film composite membranes offers support for rejection layer formation. It remarkably affects the physicochemical and structural properties of the developed rejection layer. This denotes the relevance of substrates modification in realizing optimized substrate structure in terms of porosity, thickness and tortuosity with the goal of obtaining highly selective and enhanced hydrophilic membrane. Polyamide thin film nanocomposite (TFN) membranes with its polysulfone (PSF) substrate embedded with palygorskite-chitin (PAL-CH) hybrid nanomaterial have been fabricated in this study. The hybridization of palygorskite and chitin nanofibers was performed under the collision as well as the shear force of ball mill. The TFN membranes with different loadings of PAL-CH in the PSF layer were characterized and applied for desalination process. The incorporation of PAL-CH hybrid increased the finger like structure formation and improved the overall hydrophilicity besides highly cross linked and thinner PA layer. The flux of the neat and PAL-CH membranes was 0.82 L m−2 h−1 and 2.4 L m−2 h−1 respectively. The developed membranes exhibited remarkably improved pure water flux without compromising the salt rejection. Flux enhancement of 192.7% was achieved using 0.01 wt% PAL-CH3 hybrid nanomaterial.

Enhanced Water Permeability and Antifouling Property of Coffee-Ring-Textured Polyamide Membranes by In Situ Incorporation of a Zwitterionic Metal-Organic Framework.

Modulation of the polyamide structure is critically important for the reverse-osmosis performance of thin-film composite (TFC) membranes in the field of water reuse and desalination. Herein, zwitterionic nanoparticles of zeolitic imidazolate framework-8 (PZ@ZIF-8) were fabricated and incorporated into the polyamide active layer through the interfacial polymerization method. A hydrophilic, zwitterionic coffee-ring structure was formed on the surface of polyamide thin-film nanocomposite (TFN) membranes due to the adjusted diffusion rate of m-phenylenediamine (MPD) from the aqueous phase into the organic phase during the interfacial polymerization process. Surface characterization demonstrated that the coffee-ring structure increased the amounts of water transport channels on the membrane surface and the intrinsic pores of PZ@ZIF-8 maintained the salt rejection. Antifouling and bactericidal activities of TFN membranes were enhanced remarkably owing to the bacterial-"defending" and bacterial-"attacking" behaviors of hydrophilic and zwitterionic groups from PZ@ZIF-8 nanoparticles. This work would provide a promising method for the application of MOFs to enhance the bio-/organic-fouling resistance of TFN membranes with high water permeation and salt rejection.

Use of rigid cucurbit[6]uril mediating selective water transport as a potential remedy to improve the permselectivity and durability of reverse osmosis membranes

In spite of many efforts to grasp the nature of porous nanomaterials, it is hard to find research work addressing empirical evidence for selective water permeation through their channels or pores. Herein, we report the experimental proof of selective water permeation through cucurbit[6]uril (CB[6]) with a portal diameter of 3.9 Å along with quantum mechanics calculation results elucidating the mechanisms underlying the selective water transport. CB[6] improved the water/salt permselectivity of CB[6]-polyamide thin-film nanocomposite (CB[6]-TFN) membranes since ion passage was inhibited by a high energy barrier imposed by the CB[6]’s portals while the portals are energetically favorable from the perspective of water transport. This difference in water and salt’s permeabilities stems from its carbonyl-fringed portals, which are cut out for size exclusion and negatively charged for charge repulsion. Due to the rigidity, CB[6]-TFN membranes were found to be more resistant to compaction under elevated pressures. Such unique characteristics of CB[6] allowed CB[6]-TFN membranes to outperform newly developed TFN membranes as well as commercial RO membranes.

High-Performance Nanosilver Thin Film Nanocomposite Membranes Prepared on Carbon Nanotube-Based Supports

Biofouling in membranes is a serious concern as it leads to a severe reduction in membrane performance by increasing the membranes’ resistance to permeate flow. This work describes a facile method for the production of high performance nanosilver polyamide thin-film nanocomposite (TFN) membranes on carbon nanotube-based supports for biofouling control. The TFN membranes were prepared by the interfacial polymerization of a thin polyamide layer over a polyethersulfone (PES) support layer. Nanosilver (nAg) particles were generated in-situ on the surface of the polyamide layer using a reduction reaction between a silver salt and sodium borohydride. The support layer of the TFN membrane contained nitrogen doped multi-walled carbon nanotubes (N-MWCNTs) at various dosages. The SEM/EDS microscopic analyses revealed that nAg particles were present on the polyamide layer and that they were evenly distributed throughout the TFN membrane. Furthermore, the TFN membrane showed an improved water permeability (from 16.74 L/m2.h to 22.86 L/m2.h at 150 Psi) without sever compromise in NaCl rejection (from 98.37% to 99.40%) compared to the bare TFC membrane. This was attributable to the combined hydrophilic effects imparted by the presence of nAg on the TFN polyamide layer and the oxidised CNTs in the support layer. Antibacterial tests conducted using Escherichia coli bacteria demonstrated that the TFN containing nAg particles membranes exude better antibacterial activity compared to the pristine TFC membrane as evidenced by a clear zone of inhibition, in the area surrounding the TFN membrane and the absence of bacterial colonies. The present study demonstrated that the presence of low dosages of CNTs in the support layer is essential in the improvement of mechanical strength and performance properties of the support layer, while nAg plays a crucial role in the enhancement of TFN membrane performance.

Employing the synergistic effect between aquaporin nanostructures and graphene oxide for enhanced separation performance of thin-film nanocomposite forward osmosis membranes

In this study, novel thin-film nanocomposite (TFN) membranes were developed by incorporating graphene oxide (GO) and Aquaporin Z (AqpZ) reconstituting nanostructure (AQN) into the polyamide (PA) active layer to improve the forward osmosis (FO) performances of the PA TFN membranes. First, the AQN loading in the PA layer was optimized, followed by the GO addition in PA layer at various loadings until the optimal FO process performance was attained. Experimental results showed that GO flakes increased membrane water flux but decreased selectivity by creating non-selective voids in PA layer. Whereas, AQN increased membrane selectivity by healing the non-selective PA defects created by the GO flakes. The synergistic effect of GO-AQN improved the water flux without deteriorating the selectivity of the membrane. The TFN membrane with 0.2 wt% AQN and 0.005 wt% GO loading (TFN50) showed almost 3 folds increase in water flux (24.1 L·m−2·h−1) in comparison to the TFC membrane (8.2 L·m−2·h−1), while retaining the membrane selectivity (0.37 g.L−1). Interestingly, the TFN50 membrane demonstrated a 27% lower specific reverse salt flux (SRSF) and a marginal increase in water flux than the TFN membrane embedded with 0.005 wt% GO and no AQN (TFNGO50). The overall experimental results confirmed that the addition of AQN into GO-based PA TFN membranes could improve the membrane selectivity by reducing the non-selective PA defects created by GO flakes. The results of this study could provide strategies to further enhance the selectivity of GO-based TFN membranes by preventing the formation of defective PA layer.

Water and salt transport properties of the cellulose triacetate/reduced graphene oxide nanocomposite membranes

The relationship between desalting membrane and its water/salt transport properties remain largely unknown. This is especially true for polyamide thin film nanocomposite (TFN) membranes which have shown excellent desalination performance and attracted booming attention in recent years. Considering cellulose triacetate (CTA) can be made into dense membranes whose transport properties can be measured based on the solution-diffusion theory, we systematically study the water/salt transport property of the CTA nanocomposite membranes blended with reduced graphene oxide (rGO) of varying reduction degrees, with multilayer graphene oxide (MGO) and single layer graphene oxide (SGO) as control samples. The nanocomposite membranes show enhanced membrane density and glass transition temperature (Tg) due to the interaction of the polar group in GO/rGO with CTA chains. The GO (rGO) frustrates the polymer chain packing and decreases crystallinity of CTA membrane. The adding of rGO increases the water permeability by increasing its diffusivity due to the decreased crystallinity and additional channel from (r)GO, but decreases the salt permeability by decreasing its diffusivity due to membrane densification and the interactions of ions with GO/rGO. The water permeability and diffusivity of the nanocomposites increase when its water sorption decreases, which is against the trend of pure polymers, presumably due to the fact that water sorption is not a good reflection of the free volume in this heterogeneous membrane. Meanwhile, the GO/rGO blending slightly increases water sorption without changing the salt sorption because the newly-introduced polar groups in GO/rGO traps water and suppress its solvation capacity for salt. Both the water permeability and the water/salt selectivity increase with the reduction degree due to the decreased water transport resistance.

TETA-anchored graphene oxide enhanced polyamide thin film nanofiltration membrane for water purification; performance and antifouling properties

This work investigates the performance and structure of polyamide thin film nanocomposite (PA-TFN) membrane incorporated with triethylenetetramine-modified graphene oxide (GO-TETA). The embedment of GO-TETA nanosheets within the structure of PA-TFN membrane was evaluated at different concentrations (0.005, 0.01, 0.03 wt%; in aqueous piperazine (PIP)) through interfacial polymerization (IP). The physicochemical properties of the prepared membrane were investigated by SEM, AFM, water contact angle, and zeta potential as well as ATR-IR spectroscopy. The presence of longer chains of amino groups (in comparison with the directly linked amino ones) among the stacked GO nanosheets was assumed to increase interlayer spacing, resulting in remarkable changes in water permeance and separation behavior of modified polyamide (PA) membrane. It is seen that GO-TETA nanosheets were uniformly distributed in the matrix of PA layer. With increasing the concentration of GO-TETA, the flux of TFN membranes under 6 bar was increased from 49.8 l/m2 h (no additive) to 73.2 l/m2 h (TFN comprising 0.03 wt% GO-TETA. In addition, more loading GO-TETA resulted in a significant decrease in the average thickness of the polyamide layer from ~380 to ~150 nm. Furthermore, addition of GO-TETA improved the hydrophilicity of nanocomposite membranes, resulting in superb water flux recovery (antifouling indicator) as high as 95% after filtration of bovine serum albumin solution. Also, the retention capability of the TFN membranes towards some textile dyes increased as high as 99.6%.

Custom-tailoring metal-organic framework in thin-film nanocomposite nanofiltration membrane with enhanced internal polarity and amplified surface crosslinking for elevated separation property

A polyamide (PA) thin-film nanocomposite (TFN) membrane embedded with post-synthetically functionalized metal-organic framework (MOF) nanofillers of imidazole-2-carbaldehyde (ICA) decorated UiO-66-NH2 nanofillers (ICA_d_UiO-66-NH2) was developed using the interfacial polymerization method. The ICA_d_UiO-66-NH2 nanofiller couples a surface water-capturing ICA decoration, facilitating the rapid transport of water molecules owing to the enhanced internal polarity, while achieving an amplified crosslinking between the terminal amine groups of ICA and trimesoyl chloride, enabling the perfect incorporation of MOF nanofillers within the PA matrix. The resultant ICA_d_UiO-66-NH2@PA TFN membrane with elevated separation property performed comparably high water permeance of 9.4 l m−2 h−1 bar−1 (achieving a nearly 2-fold increase from the initial value of the thin-film composite membrane), and a favorable rejection ratio of 97.4% (Na2SO4). Owing to the unique hierarchical surface microstructure embedded with the intrinsically hydrophilic ICA_d_UiO-66-NH2 nanofillers, the newly-developed TFN membrane exhibited superior antifouling properties. Furthermore, the ICA_d_UiO-66-NH2@PA TFN membrane also retained excellent reusability and durability without significant compromise even after long-term salt, and acid/alkali treatments. Overall, this work provides an insight into the embedding of different functionalized nanofillers inside TFN membranes with elevated separation properties.

Monovalent/Divalent salts separation via thin film nanocomposite nanofiltration membrane containing aminated TiO2 nanoparticles

Nanofiltration is widely used in separation of ions with different sizes and charges. However, thin-film composite nanofiltration membrane is hard to reach satisfied selectivity for monovalent ions from divalent ions. In this study, polyamide thin film nanocomposite (TFN) nanofiltration membranes were prepared via interfacial polymerization of piperazine and trimesoyl chloride on a PES substrate by incorporation of aminated titanium dioxide (APTES-TiO2). Surface morphology, roughness of the TFN membranes with varied concentration of aminated TiO2 were tested by SEM, AFM and Zeta analysis. The results showed membrane containing 0.3(w/v%) amino-modified titanium dioxide with ion-selective properties had greatly improved pure water flux while the Na2SO4 rejection keeps at a relative high level (>95%). For the separation of single salt solution, 0.3(w/v%) TFN has a higher rejection for sodium chloride (23.2%) and sodium sulfate (99.7%). For monovalent/divalent mixed salt solution has a separation factor of 477.89 in terms of chloride ion (Cl−) and sulfate (SO42−) in the mixed solution with a salt concentration ratio of 1:19, which was higher than that of the conventional commercial NF membranes, such as Desal-DL, NF 270. This method provides the possibility of recovering concentrated brine and industrial separation of monovalent and divalent ions.

Influence of incorporating beta zeolite nanoparticles on water permeability and ion selectivity of polyamide nanofiltration membranes

A novel polyamide (PA) thin film nanocomposite (TFN) membrane modified with Beta (β) zeolite was prepared by interfacial polymerization on a poly (ether sulfone) (PES) ultrafiltration membrane. Compared with the PA thin film composite (TFC) membrane, the introduction of β zeolite with porous structure notably increased the water flux of TFN membrane. Because the β zeolite with tiny-sized and well-defined inner-porous acted as prior flow channels for water molecules and a barrier for the sulfate ions. The successful introduction of β zeolite into the (PA) selective layer and their dispersion in the corresponding layer were verified by scanning electron microscope (SEM) and atomic force microscopy (AFM). Water contact angle, zeta potential measurements were used to characterize the changes of membrane surface properties before and after incorporating the β zeolite. With the β zeolite introducing, the water contact angle of modified TFN membrane was decreased to 47.8°, which was benefited to improve the water flux. Meanwhile, the negative charges of the modified TFN membrane was increased, resulting in an enhancement of separation effect on SO42− and Cl−. In term of nanofiltration (NF) experiments, the highest pure water flux of the TFN membranes reached up to 81.22 L m−2 hr−1 under operating pressure of 0.2 MPa, which was 2.5 times as much as the pristine TFC membrane.

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.