Polyamide Thin Film Composite Membranes Research Articles

Silk fibroin-coated polyamide thin-film composite membranes with anti-scaling properties

Scaling inevitably occurs on the reverse osmosis (RO) membrane's surface due to the increased salt concentration during the filtration of a saline solution containing various kinds of ions. Particularly, scaling becomes more likely when an RO membrane's surface possesses many carboxyl groups capable of interacting with multivalent cations. Herein, we developed a thin-film composite (TFC) membrane by coating silk fibroin (SF) on a polyamide (PA) active layer. Since SF consists of a large number of hydroxyl groups, the SF-coated PA TFC membrane (SF-PA-TFC) revealed a smaller absolute value (−17.7 mV) of surface zeta potential than half of that (−40.3 mV) of the PA TFC membrane (PA-TFC), thereby effectively preventing carboxyl groups from stepping in scaling. Furthermore, SF coating made a PA active layer more hydrophilic and smoother. Thanks to the desirable features, the SF-PA-TFC was accompanied by several strengths such as 5 times lower irreversible scaling resistance, 50% higher flux recovery ratio, and 4 times longer operation duration till cleaning under the condition for heterogeneous nucleation. We hope this finding could facilitate the development of anti-scaling RO membranes by making the most of natural resources that can minimize the economic and environmental burdens imposed by a manufacturing process.

Boosting the Performance of Nanofiltration Membranes in Removing Organic Micropollutants: Trade-Off Effect, Strategy Evaluation, and Prospective Development.

In view of the high risks brought about by organic micropollutants (OMPs), nanofiltration (NF) processes have been playing a vital role in advanced water and wastewater treatment, owing to the high membrane performance in rejection of OMPs, permeation of water, and passage of mineral salts. Though numerous studies have been devoted to evaluating and technically enhancing membrane performance in removing various OMPs, the trade-off effect between water permeance and water/OMP selectivity for state-of-the-art membranes remains far from being understood. Knowledge of this effect is significant for comparing and guiding membrane development works toward cost-efficient OMP removal. In this work, we comprehensively assessed the performance of 88 NF membranes, commercialized or newly developed, based on their water permeance and OMP rejection data published in the literature. The effectiveness and underlying mechanisms of various modification methods in tailoring properties and in turn performance of the mainstream polyamide (PA) thin-film composite (TFC) membranes were quantitatively analyzed. The trade-off effect was demonstrated by the abundant data from both experimental measurements and machine learning-based prediction. On this basis, the advancement of novel membranes was benchmarked by the performance upper-bound revealed by commercial membranes and lab-made PA membranes. We also assessed the potentials of current NF membranes in selectively separating OMPs from inorganic salts and identified the future research perspectives to achieve further enhancement in OMP removal and salt/OMP selectivity of NF membranes.

Trimethylamine N-oxide-derived zwitterionic polyamide thin-film composite nanofiltration membranes with enhanced anti-dye deposition ability for efficient dye separation and recovery

Organic dyes from textile industries are becoming the second largest pollutants in the world. In this study, inspired by the seawater fish, a new diamine monomer, N,N-bis(3-aminopropyl)methylamine N-oxide (DNMAO) with a trimethylamine N-oxide (TMAO)-derived “N+─O−” zwitterionic functionality, has been designed for the fabrication of polyamide thin-film composite (TFC) membranes to purify dye-contaminated water and recover organic dyes. The fabricated membranes show enhanced permeability and improved anti-dye-deposition performance. The optimum membrane fabricated at 0.5 wt% of DNMAO feed solution exhibits an ultrahigh pure water permeability (PWP) of 37.5 LMH bar−1, a superior Congo red (CR) rejection of 99.93%, and a low sodium chloride (NaCl) rejection of 9.3%, indicating its outstanding performance for dye/salt separation. It can also achieve the complete CR removal from a feed with a low CR concentration of 1 ppm, demonstrating its superior separation performance for the production of clean potable water. In addition, the low dye loss rate (6.22%) and high salt removal rate (85.6%) are achieved during the purification and recovery test with CR/NaCl mixtures. Furthermore, the optimum membrane possesses an excellent anti-dye-deposition performance with a flux recovery ratio (FRR) of 92.1%. All these results demonstrate its potential for applications in not only textile wastewater treatment but also organic dye purification and recovery.

Permeability improvement of reverse osmosis membranes by addition of dimethyl sulfoxide in the interfacial polymerization media

In this study, it is presented a solvent addition method to significantly increase the performance of reverse osmosis (RO) membranes. Polyamide (PA) thin film composite RO membranes were prepared by interfacial polymerization (IP) method with a mixture containing dimethyl sulfoxide (DMSO) in different weight percentages. With the addition of DMSO, the selective PA layer was successfully activated, increasing its water flux to 41.7 L/m2 h while preserving a NaCl rejection of up to 95.7%. Morphological characteristics and properties of the model PA film under the influence of solvent with different weight percentages of DMSO showed the structural deformation caused by the activation of the PA layer, which affects the pore size and separation properties of the membrane. The research provides an expandable way to fabricate high-performance membranes in terms of flux and desalination with good resistance to fouling agents of polymeric membranes.

Fabrication of superhydrophilic/underwater superoleophobic functionalized-nanoparticles/PVDF-supported thin film composite polyamide membranes for efficient water purification

For water treatment, membrane-based separation methods are very essential owing to long-term efficiency, high mechanical stability and durability. The filtration process with polymer-inorganic and organic composite is an outstanding strategy that enhances the properties of both inorganic materials such as thermal and mechanical stability and organic material including flexibility and processability of the membranes. Therefore, the surface wettability of the membranes is vital for pollutants separation. Here, the high hydrophobic behavior of polyvinylidene fluoride (PVDF) membranes is altered to superhydrophilicity and underwater superoleophobicity via single-step coating. This PVDF membrane has high molecular separation due to the ultrathin thickness and good controllable interlayer. In this study, the PVDF membrane was by interfacial polymerization coated with a polyamide (PAm) layer, modified alumina nanoparticles (Al-NPs), (aminopropyl)triethoxysilane (APTES), and folic acid (FA) through a chemical grafting reaction. The influence of the PAm and Al-APTES-FA content on the morphology, structure, antifouling, and superhydrophilicity of the PVDF-g-PAm@Al-APTES-FA membrane has been investigated which has enhanced the oil and salt rejection as well as filtration performance. Fourier Transform Infrared (FTIR) spectroscopy showed the specific functional groups from the obtained results indicating the successful preparation. Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX), and AFM (Atomic Force Microscope) techniques were conducted to observe the membrane surface morphology, roughness, and elemental adsorption after the filtration process. Furthermore, this modified PVDF membrane exhibited an excellent superoleophobicity with underwater oil contact angle (OCA~145°), and superhydrophilic visualization with water contact angle (WCA ~ 0°) after being functionalized. Additionally, the parameters of membrane performance such as permeate flux, heavy metal ions, oil and salts rejection, were assessed. The modified material on the PVDF membrane enhanced the membrane efficiency under high operating pressure of 10 bar with 53 LMH (L.m−2 h−1, while it is ≈0 for PVDF membrane), permeate flux, over 90 % salt rejection, and almost 100 % hydrocarbons and heavy metal ions rejection, owing to membrane surface changes, hydrophilicity, and roughness. This research will provide new insights on porous surface transformation to improve the separation and antifouling properties of PVDF membranes used in water purification.

Enhanced Removal of Endocrine-Disrupting Compounds from Wastewater Using Reverse Osmosis Membrane with Titania Nanotube-Constructed Nanochannels.

This paper presents a comprehensive study of the performance of a newly developed titania nanotube incorporated RO membrane for endocrine-disrupting compound (EDC) removal at a low concentration. EDCs are known as an emerging contaminant, and if these pollutants are not properly removed, they can enter the water cycle and reach the water supply for residential use, causing harm to human health. Reverse osmosis (RO) has been known as a promising technology to remove EDCs. However, there is a lack of consensus on their performance, especially on the feed concentrations of EDC that vary from one source to another. In this study, polyamide thin-film composite (PA TFC) membrane was incorporated with one-dimensional titania nanotube (TNT) to mitigate trade-off between water permeability and solute rejection of EDC. The characterization indicated that the membrane surface hydrophilicity has been greatly increased with the presence of TNT. Using bisphenol A (BPA) and caffeine as model EDC, the removal efficiencies of the pristine TFC and thin-film nanocomposite (TFN) membranes were evaluated. Compared to TFC membrane, the membrane modified with 0.01% of TNT exhibited improved permeability of 50% and 49% for BPA and caffeine, respectively. A satisfactory BPA rejection of 89.05% and a caffeine rejection of 97.89% were achieved by the TNT incorporated TFN membranes. Furthermore, the greater hydrophilicity and smoother surface of 0.01 TFN membrane led to lower membrane fouling tendency under long-term filtration.

Characterization of polyamide thin film composite membranes incorporated silver nanoparticles

AbstractIn this study, the polyamide thin film composite membrane surface has been modified by anti‐microbial silver nanoparticles (AgNPs). The membrane surfaces were interwoven with AgNPs by ultraviolet grafting polymerization method using AgNPs with or without poly(ethylene glycol) (PEG). The membrane surface characteristics were determined by scanning electron microscopy–energy dispersive x‐ray spectrometry images, attenuated total reflection–Fourier transforms infrared spectroscopy, water contact angle values, and anti‐bacterial property. The separation performance was determined based on the flux and the ability to remove calcium ions in water. The anti‐biofouling property was appraised through the maintained flux ratios and the irreversible fouling factors of unmodified and modified membranes during 10 h‐filtration of protein bovine serum albumin (BSA) in an aqueous solution, in which, before filtration of BSA, all membranes were immersed in E. coli bacteria solution for 4 days. The results of the experiments corroborated the hydrophilicity and more anti‐microbial property of the membrane surfaces after being incorporated into AgNPs. The water contact angle decreased from around 49° for the unmodified membrane to 36° and 23° for the AgNP‐modified membranes without/with PEG, while no colonies appeared in the medium containing the AgNP‐modified membranes. The separation property of modified membranes was improved, with both membrane flux and antifouling properties, along with the substantial surge of the anti‐biofouling property. After 10 h of BSA filtration, the fluxes of the modified membranes were maintained at 68% and 78% for AgNP‐modified membranes without and with PEG, respectively. Conversely, this value was only 46% for the unmodified one.

Complexation of tannic acid/silver nanoparticles on polyamide thin film composite reverse osmosis membrane for enhanced chlorine resistance and anti-biofouling properties

Reverse osmosis (RO) is a well-established and reliable desalination method that has been widely implemented on a commercial scale to resolve water scarcity issues. Constant efforts have been made to develop thin film composite membranes that can strike a balance between selectivity and permeability, while maintaining high durability towards fouling and chlorine attack. In this work, the surface of thin film composite RO membrane was modified by complexing tannic acid (TA) and silver nanoparticles (Ag NPs). TA was used for enhancing the chlorine resistance while Ag NPs act as a biocide to mitigate biofouling. Upon the formation of PA layer through interfacial polymerization, TA was chemically grafted, proceeded by in-situ reduction of Ag NPs. Transmission electron microscopy (TEM) image revealed that Ag NPs were deposited on top of the TA-PA interlayer and reduced as discrete spherical Ag NPs with diameter <15 nm. The greatest flux of 20.57 L/m2·h was produced by TFC-TA/Ag1, representing a 60 % improvement as compared to neat TFC membrane. The NaCl rejection of TFC-TA membrane was 97.83 %, which was slightly increased compared to neat TFC membrane with rejection of 95.14 %. Improved chlorine resistance and improved antibacterial properties against Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli) were witnessed for the TFC-TA/Ag1 membranes. This study demonstrates a facile chemical grafting and deposition to introduce multiple functionalities for improving the physical and separation properties of TFC RO membrane.

Fabrication of fluorinated polyamide seawater reverse osmosis membrane with enhanced boron removal

Developing a reverse osmosis membrane with desirable water/salt selectivity and boron removal has been recognized as crucial for high-efficient seawater desalination. Herein, fluorinated seawater reverse osmosis (SWRO) membranes were fabricated via fluorine-containing monomers-mediated interfacial polymerization or surface modification by grafting fluorine-containing monomers atop nascent polyamide (PA) layer via a second interfacial reaction. The fluorinated molecules, 5-(trifluoromethyl)-1.3-phenylenediamine (TFPD), 3,5-bis(trifluoromethyl) benzoyl chloride (TFBC) or 2,2,2-trifluoroethylamine (TFEA), were confirmedly integrated into the PA matrix presumably via strong chemical covalent bonds, which manipulated the physicochemical properties of the PA layer, including surface hydrophilicity, pore size distribution, cross-linking degree and interactions between membrane and solutes, thereby producing a high-selectivity thin-film composite (TFC) membrane. The optimized membranes, i.e., TFC-TFPD, TFC-TFBC and TFC-TFEA, presented significantly excellent separation performance than the control and commercial membrane, both in water/salt selectivity and boron removal capability, accompanied by a comparable water permeance. Among the three proposed incorporation method of fluorinated monomers, direct grafting of TFEA upon the nascent PA layer demonstrates the best efficiency in introducing fluorine elements in the TFC PA membranes, compared to the addition of TFPD and TFBC into aqueous and organic phases during IP process, respectively. The fluorine-incorporated strategy employed in this present work offered a new design of the PA layer containing fluorinated molecules to obtain the desired permselectivity of TFC SWRO membranes towards efficient removal of salt and boron acid in seawater desalination.

Distinct impact of substrate hydrophilicity on performance and structure of TFC NF and RO polyamide membranes

Substrate properties have profound impacts on the structure and performance of both thin-film composite (TFC) nanofiltration (NF) and reverse osmosis (RO) polyamide (PA) membranes. Some studies have previously investigated the impact of substrate hydrophilicity on PA formation and TFC membrane performance. However, the observed phenomena and explanations remain contradictory in literature. Herein, we performed interfacial polymerization (IP) reactions of both piperazine (PIP)-trimesoyl chloride (TMC) and m-phenylenediamine (MPD)-TMC systems on substrates with different hydrophilicity. We found that the TFC RO membrane showed higher water permeance and NaCl rejection on the relatively hydrophobic substrate, while the TFC NF membrane favored the relatively hydrophilic substrate. The critical importance of interfacial degassing and local monomer concentration was highlighted to dissect the distinct impact of substrate hydrophilicity. For the MPD-TMC system, interfacial nanobubble generation was inhibited because of the decreased local MPD concentration and heat production for the more hydrophilic substrates, resulting in a decrease in the roughness feature and compromised water permeance of RO membranes. In contrast, interfacial degassing was not a dominant mechanism in the PIP-TMC system due to the slower reaction rate of PIP-TMC than MPD-TMC. Consequently, the PA layer of NF membrane became thinner and looser when the substrate became more hydrophilic, resulting from the diluted local PIP concentration. Our study unveils the fundamental relationship among substrate hydrophilicity, PA structure, and separation performance of both TFC NF and RO PA membranes, providing important guides on their design and synthesis.

Toward the truth of condensing-water membrane for efficient biogas purification: Experimental and modeling analyses

Facilitated transport membranes with high CO2/CH4 separation performance under humidified state have shown great prospects for biogas purification. The role of water might include the formation of condensed water film on membrane surface, but it was seldom verified and investigated. In this study, the condensation of water film on polyamide (PA) thin-film composite membrane was performed and regulated. Thanks to the absence of active carrier groups that can reversibly with CO2, the contribution of water to facilitated transport can be neglected, and the truth of condensing-water membrane was allowed to be explored. The PA layer was fabricated by interfacial polymerization with its hydrophilicity tuned by polyvinyl alcohol. The regulation of water film is based on three operational approaches: simple humidifying the feed gas, pre-wetting the membrane, or heating the humidifier. The remarkable increment of selectivity along with the improvement of water-condensing conditions implied the formation of condensed water film. Fortunately, the series of gas permeation data allowed the estimation of water film thickness according to the mass transfer resistance model for multilayer composite membranes. The decline of selectivity over time under elevated pressure was found effective to evaluate the stability of such condensing water membranes. The results show that a polyamide thin-film composite membrane with poor CO2/CH4 selectivity under dry state can achieve rather high performance (CO2 permeance 374 GPU and CO2/CH4 selectivity 31 for 16 days under 3.25 bar) with the aid of a simple condensed water layer. Hopefully, it provides a method to re-evaluate the effect of water on a given facilitated transport membrane, and possibilities of further enhancing its separation performance by fine tuning the condensed water film.

Thermo-Responsive Hydrophilic Support for Polyamide Thin-Film Composite Membranes with Competitive Nanofiltration Performance.

Poly(N-isopropylacrylamide) (PNIPAAm) was introduced into a polyethylene terephthalate (PET) nonwoven fabric to develop novel support for polyamide (PA) thin-film composite (TFC) membranes without using a microporous support layer. First, temperature-responsive PNIPAAm hydrogel was prepared by reactive pore-filling to adjust the pore size of non-woven fabric, creating hydrophilic support. The developed PET-based support was then used to fabricate PA TFC membranes via interfacial polymerization. SEM–EDX and AFM results confirmed the successful fabrication of hydrogel-integrated non-woven fabric and PA TFC membranes. The newly developed PA TFC membrane demonstrated an average water permeability of 1 L/m2 h bar, and an NaCl rejection of 47.0% at a low operating pressure of 1 bar. The thermo-responsive property of the prepared membrane was studied by measuring the water contact angle (WCA) below and above the lower critical solution temperature (LCST) of the PNIPAAm hydrogel. Results proved the thermo-responsive behavior of the prepared hydrogel-filled PET-supported PA TFC membrane and the ability to tune the membrane flux by changing the operating temperature was confirmed. Overall, this study provides a novel method to fabricate TFC membranes and helps to better understand the influence of the support layer on the separation performance of TFC membranes.

Fabrication of thin film composite polyamide membrane for water purification via inkjet printing of aqueous and solvent inks

Thin film composite (TFC) polyamide (PA) membranes are typically prepared using the interfacial polymerization (IP) method, which synthesizes the PA layer by soaking in aqueous diamine and organic acyl chloride solutions and allowing the occurrence of amidation. The conventional IP process has been used over several decades in the industrial production of TFC membranes for water purification and excess amounts of monomer solutions are used for PA thin film layer synthesis, generating a lot of chemical wastes. In this work, we first demonstrated the TFC PA membrane fabrication using simple inkjet printing of aqueous and organic inks to effectively prepare a PA layer with no chemical wastes. The organic acyl chloride ink was newly formulated by the combination of dodecane and toluene solvents to allow printability. Precise and uniform depositions of monomer inks via the inkjet printing approach were able to coat a dense and defect-free PA film onto the support membrane using only small volumes of chemicals. After multiple printing numbers of inks, the PA layer was optimized with two printing cycles (30.17 mL m−2) and three printing cycles (8.36 mL m−2) of diamine and triacyl chloride inks, respectively, followed by heat treatment. The inkjet-printed TFC-M2T3-15 membrane exhibited a high salt rejection (95.33 %) which showed higher performance compared to that of the conventional IP-prepared TFC membrane (89.64 %).

Revisiting the alkali hydrolysis of polyamide nanofiltration membranes

High flux membranes are required for energy-efficient separation processes. Chemical treatments of conventionally prepared polyamide thin film composite (TFC) membranes, including alkali hydrolysis of polyamide, have been found suitable for achieving higher membrane permeance without significant loss in solute rejection. However, polyamide-based membranes are known to be stable in alkaline conditions during chemical cleaning. Hence, we revisited the possibility of alkali hydrolysis post-treatment of the polyamide layer of a commercial nanofiltration membrane upon short-term exposures at a wide range of pH exceeding the recommended value (up to pH 13). We optimized the post-treatment parameters using the Box Behnken design (BBD) of Response Surface Methodology (RSM) to achieve maximum pure water permeance. We observed that the pure water permeance (PWP) of the post-treated (optimum) membrane increased to 21.1 ± 0.4 LMH/bar from 12.3 ± 0.4 LMH/bar of the pristine membrane while retaining the same salt rejection. However, the chemical composition, thickness, surface charge, and pore size of the polyamide layer in the pristine and post-treated membranes were found identical. Hence, it was concluded that the increase in PWP might be attributed to the physical restructuring of the polyamide layer or restructuring of the support layer and interface, making the membrane more permeable, rather than hydrolysis of the polyamide layer.

Mussel inspired surface functionalization of polyamide membranes for the removal and adsorption of crystal violet dye

In this work, we report the adsorptive membrane technology with remarkable dynamic adsorption capacity (DAC) and selectivity towards crystal violet dye synthesized by mussel inspired co-deposition of dopamine (DP) and polyethyleneimine (PEI) on to the polyamide thin film composite (TFC) membrane. The dopamine coated TiO2 (TiO2-DP) acts as filler in which polydopamine (PDA) formation via the oxidative self-polymerization of dopamine facilitates high adhesion with the substrate. On the other hand, PEI offers abundant of amino groups that have separative and adsorption ability along with having both Schiff base reaction and Michael addition with dopamine to prompt covalent based interaction for greater stability. The invention of such structural design offers eminent dynamic adsorption capacity (up till 200 mg g−1) along with excellent selectivity (96%) towards crystal violet dye. Not only has the membrane offered high selectivity and dynamic adsorption capacity. More importantly, the membranes exhibits high chlorine resistivity and antifouling property. The data depicted in paper not solely facilitates novel approach to fabricated nanofiltration membranes, but also offers mussel inspired layer by layer strategical design composed of advanced material mainly for environmental based application.

Sustainable electrospray polymerization fabrication of thin-film composite polyamide nanofiltration membranes for heavy metal removal

Thin-film composite polyamide (TFC-PA) nanofiltration membrane is promising in heavy metal removal due to its excellent performance and high economic benefits. However, the common interfacial polymerization (IP) fabrication method requires abundant toxic and harmful solvents, causing harm to the environment and humans. Therefore, novel green, low-carbon and sustainable fabrication methods are urgently needed. Here, we reported a sustainable electrospray polymerization (SEP) technique for TFC-PA membrane preparation via electrospray featuring no toxic solvent, near-complete monomer conversion, and zero waste liquid discharge. In this process, 2-methyl-tetrahydrofuran and ethanol were used as green solvents, and its greenness was assessed by green metrics and toxicity bioassays. Physical features and physicochemical properties of SEP membranes were characterized by SEM, TEM, AFM and XPS. Membranes with different surface charges and pore sizes could be tailored by varying the monomer concentration. The optimal membrane exhibited excellent removal efficiency of toxic heavy metal ions, in which the rejection rates of Cu2+ and Ni2+ were higher than 97.0 %. In addition, the permeability and salt rejection of SEP membranes were better than those of IP membranes. Our sustainable electrospray polymerization method provides a versatile green platform for fabricating TFC membranes and may facilitate the development of sustainable nanofiltration membranes.

Nanofiltration Membranes Modified with a Clustered Multiquaternary Ammonium-Based Ionic Liquid for Improved Magnesium/Lithium Separation.

Lithium separation is of great significance to overcome the lithium supply shortage resulting from a heightened demand in the energy sector. The low selectivity of polymer nanofiltration membranes for lithium extraction from concentrated Mg/Li mixtures caused by miniaturized pore structures and weak and unstable positive surface charges limits their practical implementation. To address the surface charge strength and stability, a novel ionic liquid monomer, N1-(6-aminohexyl)-N1,N1,N6,N6,N6-pentamethylhexane-1,6-diaminium bromide (denoted as DABIL), is first synthesized and covalently anchored on a pristine polyamide thin-film composite (TFC) membrane via a secondary amidation reaction for improved selective lithium separation from Mg/Li mixtures. DABIL modification of the polyamide network contributes to increased surface hydrophilicity, an enlarged membrane pore structure, and reinforced Donnan exclusion effects. Molecular dynamics simulation confirmed that the difference of the interaction energies between water and the multication groups dominates the surface properties. The DABIL membrane exhibits sixfold enhancement of water permeability compared to the unmodified membrane and outperforms the recently reported state-of-the-art positively charged membranes. It presents an improved Li+/Mg2+ selectivity of 26.49, suggesting the membranes' potential for lithium recovery. Moreover, the membrane shows efficient antibacterial activity for mitigating biofilm formation. We establish that functionalization of TFC membranes with ionic liquids containing multication side chains could be a promising approach to achieve improved and sustainable permselectivity for the recovery of critical metal resources.

Phenolic compounds from passion fruit rinds using ultrasound-assisted pressurized liquid extraction and nanofiltration

Ultrasound-Assisted Pressurized Liquid Extraction (UAPLE) and Nanofiltration (NF) were performed in 70% ethanol to recover and concentrate bioactive compounds from passion fruit rinds. Polyamide Thin-Film Composite membranes with nominal MWCO between 150 and 300 Da provided good retention of phenolic compounds (74–89%) and antioxidant capacity (84–96%) with a maximum mass concentration factor 1.4. The membrane surface showed particle deposition and fouling after filtration using AFM, SEM and FTIR, resulting in reductions of permeate mass fluxes of 50–57%. Isoorientin was the main phenolic compound found in the retentates. Integrated UAPLE and NF is a promising process to recover and concentrate phenolic compounds from passion fruit rinds.

Fabrication and characterization of high-performance acetone-assisted polyamide thin-film composite membranes for fluoridated saline water treatment

Nanofiltration (NF) and reverse osmosis (RO) membrane show promising potential for treating fluoridated brackish water and wastewater. We assessed the water flux and rejection performance of a self-fabricated membrane with various acetone concentrations as co-solvent for the treatment of fluoridated brackish water. The membrane performance was studied at different pH and pressure levels using a crossflow RO test cell with a single fluoride feed solution, brackish water composition, and real seawater. The addition of acetone to the organic and aqueous solutions during interfacial polymerization reduced the solubility difference and formed a narrower miscibility zone, resulting in a thicker reaction zone and a multilayer polyamide structure with larger pores. The water flux performance improved as the acetone concentration rose, with just a minor loss in fluoride solute rejection. Additionally, the fluoride removal efficiency increased with pH increase as the membrane became highly negatively charged. The performance of acetone added membrane was compared with commercial RO/NF membranes under the same conditions, and the acetone-added membrane exhibited higher flux and rejection. This work illustrates the utility of an acetone-assisted membrane as a suitable stand for fluoride removal and brackish water treatment.

Cucurbit[n]uril-rotaxanes functionalized membranes with heterogeneous channel and regenerable surface for efficient and sustainable nanofiltration

Nanofiltration membranes with high permeability and antifouling ability is favor of efficient and sustainable separation. However, simultaneous enhancement of above performances faces formidable challenges. Herein, we present a facile method to obtain ultrapermeable antifouling nanofiltration membranes via surface binding binary complex of dihydroxyl viologen (HV2+) axis molecule and cucurbit[n]uril (CB[n]) on the freshly prepared polyamide (PA) thin-film composite membranes in a rotaxane manner. CB[n]-rotaxanes feature three-dimensional hydrophilic structure and create heterogeneous channel in PA selective layer, which favors water transport resistance decrease. Meanwhile, CB[n]-rotaxanes as host molecules enhance superficial grafting ability of membranes towards guest-labelled antifouling materials through supramolecular recognition. Inspiringly, adopting stimuli-responsive guest, such as azobenzene, endows grafted antifouling layer with photo-activated regeneration capability, which further improves fouling reversibility of membranes. The optimal membrane exhibits a 3-fold increase of permeance, maintained Na2SO4 rejection and enhanced antifouling properties compared to the pristine, which overmatches most of the state-of-the-art nanofiltration membranes. The proposed construction strategy may pave a novel avenue to develop ultrapermeable antifouling membranes for treating complex wastewater.