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One of the major reasons for the limited commercial availability of the TFN membranes is the poor compatibility and adhesion between the embedded nanoparticles and polyamide matrix. Herein, we addressed this issue by functionalization of nanoscale additives to enhance their interactions with the polymer matrix and thereby reducing their leachability. Reverse osmosis TFN membranes were fabricated by in-situ interfacial polymerization of MPD and TMC, and incorporation of functionalized Halloysite Nanotubes (HNT). Exterior surfaces of the HNT were modified by adding three different functional groups: amine groups (HNT-NH2), the first generation of poly(amidoamine) (PAMAM) dendrimers (HNT-G1), and carboxylic acid (HNT-COOH). The modified HNT were characterized by ATR-FTIR, TEM, SEM, zeta potential, and thermogravimetric TGA analyses. Surface morphology and physicochemical properties of the HNT-based TFN membranes were investigated by SEM, ATR-FTIR, XPS, and contact angle measurements. Potential reactions of the functionalized HNT with TMC were investigated by ATR-FTIR. Also, the leachability of HNT from the membranes was studied by using a leaching test in a batch incubator followed by their tracing with ICP-MS. Furthermore, membrane selectivity and permeate flux were evaluated in cross-flow reverse osmosis (RO) desalination experiments using a synthetic brackish water. The water flux of all HNT-based TFN membranes compared to the reference TFC membrane increased without sacrifice of salt rejection. The maximum increase of nearly 100% was observed for HNT-COOH-based TFN membrane with salt rejection of 99.1% ± 0.1%. The TFN membranes with HNT-NH2 and HNT-G1 exhibited significantly lower leaching of nanoparticles in comparison to other TFN membranes. Decreased leachability of these membranes is attributed to the formation of covalent bonds between the amine groups of HNT-NH2 and HNT-G1, and the acyl chloride of TMC monomers.

A novel TFN membrane was fabricated by embedding Cellulose Nanocrystals (CNCs) into the polyamide active layer. Membranes were synthesized by in-situ interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) containing different amounts of CNCs. Successful incorporation of CNCs into the polyamide layer was confirmed by XRD analyses. Surface morphology of the membranes was characterized by SEM and AFM. Water contact angle measurements showed improved hydrophilicity of the TFN membranes. Desalination experiments with synthetic brackish water at 20 bar(g) revealed doubling of the water flux from 30 to 63 ± 10 L/m2·h, without significantly compromising the salt rejection (97.8%) for 0.1% (w/v) CNCs loading. In the fouling/filtration experiments with 300 ppm of Bovine Serum Albumin (BSA) in the feed solution, the TFN membrane had 11% smaller water flux reduction compared to the control TFC membrane. The promising performance of the CNCs-based TFN membranes and the fact that CNCs are inexpensive and abundant nanoparticles indicates their potential for a large-scale use in water desalination. Moreover, since CNCs are safe and environmentally friendly nanoparticles their possible leaching out during membrane operation would not impose health and environmental concerns.

In this work, a new type of mixed matrix membranes (MMMs) composed of dual-nanofillers at different ratios of hydrous manganese oxide (HMO) and titanium dioxide (TiO2) was fabricated with the objective of improving properties of polyethersulfone (PSF)-based membrane for oil-water separation process. The morphology and surface chemistry of the resultant MMMs were characterized by several analytical instruments, i.e., SEM-EDX, contact angle goniometer and FTIR spectrometer prior to separation performance evaluation using oily solution composed of 500 or 2000 ppm. The results showed that the membrane surface hydrophilicity was greatly improved upon addition of hydrophilic nanofillers and HMO in particular showed greater extent of hydrophilicity enhancement owing to the fact that it is associated with higher amount of OH functional groups compared to TiO2. The improved surface hydrophilicity coupled with formation of long finger-like voids in the membrane structure are the main factors leading to greater water flux of MMMs in comparison to control PES membrane. MMM2 (membrane made of HMO:TiO2 ratio of 0.75:0.25) and MMM4 (HMO:TiO2 ratio of 0.25:0.75) in particular were the best two performing nanofillers-incorporated membranes owing to their good balance between water flux and oil removal rate. They achieved 31.73% and 26.41% higher water flux than that of the control membrane without sacrificing oil removal rate. Most importantly, these nanofillers-incorporated membranes showed significantly lower degree of flux decline as a result of improved surface resistance against oil fouling and are of potential for long-term operation with extended lifespan.

The water sources contaminated by toxic dyes would pose a serious problem for public health. In view of this, the development of a simple yet effective method for removing dyes from industrial effluent has attracted interest from researchers. In the present work, flat sheet mixed matrix membranes (MMMs) with different physiochemical properties were fabricated by blending P84 polyimide with different concentrations of cadmium-based metal organic frameworks (MOF-2(Cd)). The resultant membranes were then used for simultaneous removal of eosin y (EY), sunset yellow (SY) and methylene blue (MB) under various process conditions. The findings indicated that the membranes could achieve high water permeability (117.8–171.4 L/m2.h.bar) and promising rejection for simultaneous dyes removal, recording value of 99.9%, 81.2% and 68.4% for MB, EY and SY, respectively. When 0.2 wt% MOF-2(Cd) was incorporated into the membrane matrix, the membrane separation efficiency was improved by 110.2% and 213.3% for EY and SY removal, respectively when compared with the pristine membrane. In addition, the optimization and modeling of membrane permeate flux and dye rejection was explored using response surface methodology. The actual and model results are in good agreement with R2 of at least 0.9983 for dye rejection and permeate flux. The high flux of the developed MMMs coupled with effective separation of dyes suggests a promising prospect of using P84 polyimide MMMs incorporated with MOF-2(Cd) for water purification.

Novel forward osmosis (FO) is a membrane-based separation process with significant potentials for low energy desalination. While this technology offers various benefits, overcoming its low water flux performance caused by internal concentration polarization (ICP) of solutes in porous substrates remains a challenge. This study aims at addressing this issue by introducing hydrophilic halloysite nanotubes (HNTs) into substrate made of polysulfone (PSF). The thin film nanocomposite (TFN) membranes suitable for FO applications were prepared via interfacial polymerization on the top surface of PSF-HNT nanocomposite substrates. The results obtained from filtration experiments showed that the TFN membrane prepared with 0.5 wt% HNTs (TFN0.5 membrane) demonstrated the most satisfactory results by exhibiting high water permeability and low reverse solute flux. Furthermore, TFN0.5 membrane exhibited remarkably higher water flux than that of control TFC membrane in both FO (27.7 vs 13.3 L/m 2 h) and PRO (42.3 vs 26.0 L/m 2 h) configurations when they were tested with 10 mM NaCl as feed solution and 2 M NaCl as draw solution. This improvement can be ascribed to the fact that the structural parameter of TFN0.5 is much lower compared to control TFC membrane (0.37 vs 0.95 mm), leading to reduced ICP effect.

In this work, titanate nanotubes (TNTs) were self-synthesized and amino functionalized to produce titanate nanotubes (NH2-TNTs) for thin film nanocomposite (TFN) reverse osmosis (RO) membrane fabrication. The novel RO membranes were fabricated by embedding NH2-TNTs of different quantities into polyamide (PA) layer. The nanotubular morphology of NH2-TNTs was studied using TEM while FTIR was employed to confirm the reaction of TNTs with [1-(2-amino-ethyl)-3-aminopropyl] trimethoxysilane. The effect of NH2-TNTs on the PA layer of TFN with respect to surface morphology, separation performance and antifouling properties was thoroughly investigated and discussed. The presence of NH2-TNTs in PA layer was verified using XPS while the “leaf-like” outgrowth morphology of PA layer was observed using FESEM. Results showed that the TFN membrane with 0.05% NH2-TNTs embedded was the most promising membrane as it exhibited 93% higher water flux than the control thin film composite (TFC) membrane, without compensating NaCl rejection. In terms of organic fouling tendency, the TFN0.05 membrane also showed higher tolerance compared to the control membrane during RO process. Furthermore, as high as 94% of the water flux of TFN0.05 was able to retrieve by a simple water rinse process, which suggests that organic fouling in TFN0.05 is highly reversible.

Antifouling properties of the polysulfone (PSf) and titanium nanotube (TNT) mixed matrix ultrafiltration membrane were investigated. The membrane was prepared by phase separation process using different concentrations of TNT and PSf. The pure water flux, protein removal and fouling parameters were studied to analyze the performance of the membrane. Morphology of the membrane was characterized by using scanning electron microscopy and atomic force microscopy. The most prominent observation was the significant improvement in water flux which attributed to improved hydrophilicity. The improvement of hydrophilicity was confirmed by water contact angle measurement and porosity measurements. This improvement in hydrophilicity is because of hydroxyl group present on TNT as determined by ATR-IR spectra. Fouling resistance of the membranes assessed by BSA solution filtration showed that 0.3 and 0.5 wt.% TNT loading membrane exhibited the best antifouling property that resulted in 100% flux recovery. The results also showed that 0.3 wt.% TNT loading membrane possessed the highest mean pore radius, porosity, and water flux. The effect of different washing directions in fouling experiment was reported. The perpendicular washing and parallel washing were carried out during fouling experiment and effects were discussed. The TNT nanocomposite membrane with parallel washing showed significant reusability during filtration.

Electrospinning was used to fabricate beadless microfibrous polyacrylonitrile (ePAN) mats with an average fiber diameter of 1448 ± 380 nm from a 10 wt.% PAN in dimethylformamide (DMF) dope solution at applied voltage of 18 kV and 20 cm fiber collection distance. Urease (EC 3.5.1.5) was then covalently immobilized on dispersed microfibrous ePAN mats following the chemical treatment of fibers with ethylenediamine (EDA) and glutaraldehyde (GA). The optimal concentration of GA for immobilization was 5%. The amount of loaded urease reached 157 μg/mg mat, exhibiting 54% of the free urease activity. The surface chemistry of as-spun and chemically treated fibers was examined with Fourier transform infrared (FTIR) spectroscopy. Field emission scanning electron microscopy (FESEM) was used to study the morphology and diameter of the pristine, chemically treated, and urease-immobilized microfibrous mats. Immobilized urease showed increased temperature for maximum activity (from 37 to 50 °C for free and immobilized urease, respectively) and improved storage stability (20 days). The immobilized urease was also less sensitive to the changes in pH, especially in acid conditions. In addition, nearly 70% of initial activity of the immobilized urease was retained after 15 cycles of reuse, which proved the applicability of the electrospun fibers as successful enzyme carriers.

In this study, a new type of thin film nanocomposite (TFN) forward osmosis (FO) membranes was prepared by incorporating different quantities of halloysite nanotubes (HNTs) into the polyamide layer via interfacial polymerization. The FO performance of all fabricated TFN membranes in terms of water permeability and reverse solute flux was compared and the best performing membrane which showed good balance between permeability and solute flux, among all, was selected for further organic fouling investigation. Using 10 mM NaCl concentration in feed solution and draw solution of 2 M NaCl, the TFN membrane that was embedded with 0.05% HNTs (i.e. TFN0.05) was identified as the best performing membrane due to its high water permeability and low reverse solute flux. Confirmed by the results of BSA removal in the presence of Ca 2 + , the TFN0.05 membrane also exhibited significantly higher fouling resistance compared to a typical TFC membrane. As an indication to the TFN0.05 fouling reversibility, it was found that > 96% permeate flux could be recovered after a simple water rinse process. Overall, it can be concluded that the addition of an appropriate amount of HNTs into the polyamide layer can remarkably improve the antifouling affinity of conventional TFC membranes for FO applications.

A major limiting factor of forward osmosis (FO) membrane, particularly in pressure retarded osmosis (PRO) mode, is fouling by natural organic matters. In this work, we investigated the effect of the nanocomposite substrate on the fouling of a thin film nanocomposite (TFN) membrane due to organic foulants in PRO mode. The TFN membrane was synthesized by coating a polyamide film over the surface of substrate made of polysulfone–titanium dioxide. The TFN membrane always showed much higher FO water flux than the typical thin film composite TFC membrane prepared from the pristine polysulfone substrate. Reduced internal concentration polarization following a significant decrease of the structural parameter in the nanocomposite substrate causes the mass transfer coefficient of the substrate to increase. In the PRO mode, BSA removal in the presence of Ca2 + confirmed that the TFN FO membrane could significantly mitigate fouling tendency compared to a typical TFC membrane. Results also showed that fouling in TFN FO is highly reversible, recovering > 92% permeate flux after a simple water rinse process. A complete study of the membrane fouling was reported with detailed scientific discussion. To the best of our knowledge, this is the first report on the effect of the nanocomposite membrane on membrane fouling in PRO mode.

Dry–wet phased inversion method was used to fabricate polyvinylidene fluoride (PVDF) hollow fiber membranes. Different concentration of surface modifying macromolecules (SMM) i.e., 2, 4 and 6 wt.% were used as additives in the spinning dope. In the phase inversion SMM migrates to the membrane surface and changes the surface morphology with chemical properties on the membrane surface. This modification results into larger pore size, higher gas permeance, effective surface porosity and water contact angle. The surface modified membrane was used in membrane contactor for CO 2 stripping from water by using self-fabricated gas–liquid membrane contactor module. The result of CO 2 stripping experiment shows that the performance of surface modified membrane is better than plain PVDF membrane. CO 2 desorption flux increased with respect to SMM concentration, considerably. The membrane fabricated with 6 wt.% SMM as additive showed higher CO 2 desorption flux and efficiency of 2.1 × 10 −3 (mol m −2 s −1 ) and 80%, respectively at 200 ml/min of liquid flow rate. For this membrane CO 2 stripping flux was investigated for different liquid phase temperature. It was found that desorption flux increased by increasing liquid temperature and the highest stripping flux was obtained in the temperature of 90 °C. The enhancement of the gas flow rate increased the CO 2 desorption flux but this change was negligible.

In this work, a novel forward osmosis (FO)-ultrafiltration (UF) hybrid membrane is designed, constructed and its performance tested. The membrane consists of FO and UF membrane bilayer, between which highly concentrated sodium polyacrylate (SPAA) solution is sandwiched as a draw solution. When the FO side of the hybrid membrane is brought into contact with waste water, seawater or brackish water, clean water is drawn into the SPAA solution through FO membrane. The clean water is then squeezed out of the SPAA solution through the UF membrane by applying pressure, which can be either hydraulic or mechanical. Experiments were carried out to prove the validity of the design concept. Some model equations were derived to simulate the performance of the hybrid membrane and the experimental data were analyzed based on the model equations. The novel hybrid membrane is believed to allow the production of RO quality water at the UF pressure that is much lower than the pressure for RO, thus leading to significant reduction of energy consumption for water production.

In this work, polysulfone (PSf)–titanium dioxide (TiO2) nanocomposite substrates were prepared by incorporating different amounts of TiO2 nanoparticles (ranging from zero to 1 wt%) into PSf matrix. The nanocomposite substrates so prepared were then characterized with respect to hydrophilicity, overall porosity, surface roughness and cross-sectional morphology. It was found that both hydrophilicity and porosity of the substrate were increased upon addition of TiO2. In addition, long finger-like structures were developed by increasing the TiO2 loading, leading to water permeability enhancement. In order to fabricate thin film nanocomposite (TFN) membranes for forward osmosis (FO) application, a thin polyamide layer was formed by interfacial polymerization of 1,3-phenylendiamine and 1,3,5-benzenetricarbonyl trichloride on the top surface of PSf–TiO2 nanocomposite substrates. Under the conditions for FO performance evaluation (10 mM NaCl concentration in feed solution, 0.5 and 2.0 M NaCl concentration in draw solution, and both active layer facing the feed solution (AL–FS) and active layer facing the draw solution (AL–DS) orientations), the TFN membrane prepared using PSf substrate embedded with 0.5 wt% TiO2 nanoparticles (denoted as TFN0.5) exhibited the most promising results by showing high water permeability and low reverse solute flux. In comparison with control TFC membrane, the water flux of TFN0.5 membrane was improved by 86–93%, depending on the membrane orientation and draw solution concentration. The increase in water permeability can be attributed to decrease in structural parameter which resulted in decreased internal concentration polarization (ICP). Although further increase in TiO2 nanoparticles loading to 0.75 and 1 wt% could result in higher water permeability, their FO performances were compromised by a significant increase in reverse solute flux. Based on the results obtained in this work, it can be concluded that adding an appropriate amount of TiO2 nanoparticles into PSf substrate could potentially improve the performance of TFC membrane during FO applications.

Realizing that one of the most important challenges in the forward osmosis (FO) membrane is internal concentration polarization (ICP), thin film nanocomposite (TFN) membranes were prepared by incorporating different loadings of titanium dioxide (TiO 2 ) nanoparticles (ranging from 0 to 0.90 wt%) into the polysulfone (PSf) substrate in order to reduce ICP. The nanocomposite substrates prepared were characterized with respect to hydrophilicity, overall porosity, surface roughness and cross-sectional morphology by different methods. Results revealed that both hydrophilicity and porosity of the substrate were increased upon addition of TiO 2 nanoparticles. Moreover, a large number of finger-like macrovoids were developed by increasing the loading of TiO 2 nanoparticles, leading to enhancement in water permeability. As for the FO performance tested at AL-FS orientation and with DI water as feed and 0.5 M NaCl as draw solution, the TFN membrane prepared using PSf substrate embedded with 0.60 wt% TiO 2 nanoparticles (designated as TFN0.60) exhibited the most promising result by showing water flux of 18.81 L/m 2 h, i.e. 97% higher than the control TFC membrane prepared by substrate without TiO 2 incorporation (designated as TFC), with no significant change in reverse solute flux. Compared to the control TFC membrane, the FO water flux of TFN0.60 was also reported to increase significantly from 4.2 to 8.1 L/m 2 h (AL-FS orientation) and from 6.9 to 13.8 L/m 2 h (AL-DS orientation) when seawater was used as feed solution and 2 M NaCl was used as draw solution. The increase in water flux can be attributed to the decrease in structural parameter ( S value=0.39 mm), mainly due to the formation of finger-liked macrovoids that connect the top and bottom layer of the substrate and reduce the tortuosity, resulting in decreased ICP. Although further increasing TiO 2 nanoparticles loading to 0.90 wt% could increase membrane water permeability, the FO performance was compromised by a significant increase in reverse solute flux. To the best knowledge of the authors, this is the first report on TFN membrane using PSf-TiO 2 nanocomposite substrate for FO applications.

In this study, thin film nanocomposite (TFN) membrane was developed using novel polysulfone–titanium dioxide (PSf–TiO 2 ) nanocomposite substrate. The effects of TiO 2 on the PSf substrate morphologies, hydrophilicity and water permeability were investigated and discussed. The results revealed that the hydrophilicity and the porosity of the substrate were improved upon the TiO 2 addition, leading to significant enhancement in water flux. TFN membrane was then fabricated by establishing a polyamide layer made of 1,3-phenylendiamine and 1,3,5-benzenetricarbonyl trichloride monomers over the surface of the modified substrate. Compared with the typical TFC and commercial CTA membranes, the TFN membrane prepared always demonstrated much higher FO water flux without showing a significant increase in reverse solute flux when tested under same conditions. When tested in AL–FS orientation using 0.5 M NaCl as a draw solution and 10 mM NaCl as feed solution, the water flux of the TFN membrane was ∼ 120% and ∼ 87% higher than that of the commercial membrane and typical TFC membrane, respectively. The water flux of the TFN membrane was also reported to be much higher under prolonged filtration time, mainly due to the improved properties of substrate upon addition of TiO 2 .

Surface modified polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated via a dry–wet phased inversion process. Surface modifying macromolecules (SMMs) (0, 2, 4 and 6 wt.%) were used as additives in the spinning dope. During phase inversion SMM migrates to the membrane surface, resulting in different surface morphology and surface chemistry. The surface modified PVDF membranes showed the larger pore size, higher gas permeance, effective surface porosity, contact angle and overall porosity but lower critical water entry pressure compared to the PVDF hollow fiber membrane without SMM. The performance of the surface modified membrane in contactor application for physical CO 2 absorption was investigated by the fabricated gas–liquid membrane contactor module, where distilled water was used to dissolve CO 2 . It was found that the liquid phase resistance was dominant in the absorption experiment. The results show that the surface modified PVDF membrane has a higher performance compared to control PVDF membrane. By increasing SMM concentration in the spinning dope, the CO 2 absorption flux increased significantly. With the membrane prepared from 6 wt.% of SMM in the spinning dope, a maximum CO 2 absorption flux of 5.4 × 10 −3 mol/m 2 s was achieved at 300 ml min −1 of absorbent flow rate, which was almost 650% more than the fabricated membrane without SMM.

Carbon dioxide (CO2) stripping from water was conducted through the porous asymmetric polysulfone (PSf) hollow fiber membrane contactor. The effect of the liquid and gas flow rates on the stripping performance, the liquid phase CO2 concentration and the CO2 stripping efficiency of the membrane module and the effect of liquid phase temperature on CO2 stripping flux were studied. The experimental results showed that the stripping gas velocity had a minor effect on the CO2 desorption flux while the increase in the liquid velocity could enhance CO2 desorption flux in the gas stripping membrane contactor. By increasing liquid flow rate to 200 ml/min, the maximum CO2 stripping efficiency of almost 66% was achieved. Enhancement of liquid flow rate from 50 to 200 ml/min increased the CO2 flux around 482%. It was found that the CO2 stripping flux was significantly affected by the liquid phase temperature. By increasing liquid temperature from 80 to 90 °C, the CO2 stripping flux increased from 1.3 × 10−4 to 4.9 × 10−4 mol m−2 s−1 at liquid velocity of 200 ml min−1. Hence, the higher stripping efficiency can be achieved by applying the higher liquid flow rate in the membrane contactor module. As well, the liquid phase temperature is a key parameter that needs to be controlled.