Surface Of Thin-film Composite Membrane Research Articles

Investigating the efficiency of a ceramic-based thin-film composite nanofiltration membrane for dyes removal

This study focuses on producing polyamide thin-film composite (TFC) ceramic membranes using interfacial polymerization, resulting in a polyamide layer on ceramic tubular substrates (Al2O3). These Al2O3 substrates possess robust mechanical and physical traits, featuring a porous surface structure. TFC membranes exhibit a thin, dense structure with root-like nanostructures on the ceramic base, with a thickness of around 260 nm. Atomic force microscopy confirms the smoother surface of TFC membranes with an average roughness value of 18 nm compared to ceramic tubular substrates. TFC membranes exhibit negative zeta potentials within a pH range of 4.7–10, while ceramic tubular substrates show more complex zeta potential behavior. Both substrate and TFC membranes are hydrophilic, with the TFC membrane having a slightly higher water contact angle (approximately 43 ± 1°). Zeta potential analysis reveals a negative potential of around −23 mV for the TFC membrane. In water permeability tests, the ceramic tubular substrate membrane demonstrates high permeability, whereas the TFC membrane displays slightly lower permeability (28 ± 0.8 L/m2 h bar) due to the presence of the polyamide selective layer. Importantly, the TFC membrane significantly enhances organic dye rejection compared to the ceramic tubular substrate, with rejection rates of 95% for CR, 92% for BTB, and 86% for MB. Rejection performance is mainly influenced by size exclusion and dye molecular charge. These novel TFC ceramic nanofiltration membranes offer improved water permeability while maintaining selectivity, holding promise for effectively removing organic pollutants in water treatment applications.

Improving surface characteristics and operational parameters of polyvinyl chloride ultrafiltration membranes: How to manipulate the performance of thin film composite forward osmosis membranes?

The environmental and economic costs are pivotal aspects that should be considered before the commercialization of any membrane separation-based process. Particularly, realizing this goal relies entirely on the key role played by fabrication and operational parameters. Herein, we introduced a systematic investigation for constructing thin-film composite (TFC) - forward osmosis (FO) membranes for direct fertigation applications. To the best of our knowledge, PVC membrane was rarely used as a porous top surface substrate for TFC-FO membranes. The PVC substrate porous structure and polyamide (PA) active layer were manipulated by variating their concentrations and reaction time to optimize the FO membrane performance. All necessary characterization tools were employed to visualize the fabricated TFC membrane's surface characteristics. The influence of feed solution concentration, membrane orientation, flow rate, and draw solutes on the FO work was also methodically tested. Results demonstrated that the porous structure-substrate membrane host polymer content had imparted a significant role in tailoring the TFC-FO performance concerning permeability and back-solute flux. The water flux was improved by 44.3 % with decreasing of the PVC amount, whereas water flux was improved by 48.13 % with decreasing of the M-phenylenediamine monomer (MPD) content from 3 to 1 wt% at constant tri-mesoylchloride monomer (TMC) content of 0.1 wt% in IP reaction conditions of a thin film. This was gone hand in hand with optimal operational conditions harnessed for optimizing the FO process.

Mitigation of biofouling with co-deposition of polydopamine and curcumin on the surface of a thin-film composite membrane

Reverse osmosis (RO) membrane has been widely used in various water treatment fields as an efficient desalination technology, but serious biofouling problem arises in the actual application process. Curcumin is known as a natural compound that can reduce biofouling by inhibiting the growth of microorganisms based on quorum sensing. Dopamine, a molecule with excellent adhesion and functionalization on the material's surface, has high research value for applying a curcumin coating to the membrane surface. Curcumin degrades under alkaline conditions, whereas dopamine must polymerize under alkaline conditions. Simultaneously, a coating may adversely affect curcumin. Therefore, a two-step coating process was considered by self-polymerizing dopamine on the thin-film composite membrane surface and then dip-coating curcumin attached to the polydopamine layer. Furthermore, the effect of time and concentration on the surface modification before and after membrane modification was investigated. The highest permeability of 1.39 L/m2/hr/bar was achieved with the modified membranes. The number of gram-positive bacteria decreased from 6.71 × 106 to 9.67 × 105 CFU/mL. This result is meaningful for antifouling through modification of the membrane surface. Use of curcumin can be applied to reduce biofouling and extend the lifetime of the membrane without pretreatment or membrane cleaning.

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.

Ammonium enrichment and recovery from synthetic and real industrial wastewater by amine-modified thin film composite forward osmosis membranes

In this study, we aimed to recover and enrich NH4+ from real wastewater using forward osmosis (FO). Positively-charged thin film composite (TFC) membranes were developed via chemical grafting with positively-charged polyethyleneimine (PEI). The TFC membrane surface was first activated using 1-ethyl-3-(3-dimethylaminopropyl) carboimide (EDC) and n-hydroxysuccinimide (NHS) to convert the carboxyl groups of polyamide into amine-reactive NHS esters. PEI grafting significantly increased the NH4+ retention in the feed solution. To further improve the NH4+ rejection, quaternization of the amine functional groups of PEI was conducted with iodomethane. Quaternization was found to further increase NH4+ rejection, up to over 98.5%, while maintaining similar water permeability with the PEI-grafted TFC membrane. Fouling control of the pristine and amine-modified TFC membranes were also demonstrated, and the quaternary amine-modified TFC membrane exhibited superior fouling resistance against organic and biological foulants. The amine-modified TFC membranes were evaluated for applicability for dewatering and NH4+ enrichment of real industrial wastewater. NH4+ enrichment using the PEI-grafted membranes was observed following wastewater dewatering, indicating the high NH4+ retention ability of the TFC membranes modified via amine grafting and quaternization. Wastewater dewatering of 90.3 and 92.4% were achieved using TFC-PEI-10 and TFC-qPEI, respectively.

Control of the antagonistic effects of heat-assisted chlorine oxidative degradation on pressure retarded osmosis thin film composite membrane surface

During pressure retarded osmosis (PRO) operation, thin film composite (TFC) membranes are continuously exposed to chemicals present in the stream that can deteriorate the membrane's selective layer with exposure time. Following this observation, TFC membranes are placed in controlled oxidative degradation conditions using aqueous NaOCl solutions. Active chlorine, along with heat, can thin out the dense layer and, when controlled and optimized, can tune the membrane surface properties and separation efficiency as desirable for specific applications. The chlorine oxidative degradation is optimized in terms of chlorine exposure (a factor of both exposure time and chemical dosage), solution pH, and the subsequent heating time. After the chemical modification process, the membrane surface properties were characterized and the PRO performance as well as the osmotic energy harvesting capability were determined. The modified membranes exhibited different levels of polyamide degradation and increase in water permeability, which came along with decrease in selectivity. Optimization of the chlorine oxidative degradation using response surface methodology was performed to maximize the water permeability and extractable osmotic power while keeping salt rejection satisfactory. After performing chlorine oxidation at the following optimized conditions: 3025 ppm Cl2·h, pH 10.72, and 3 min heating time, initial non-pressure retarded water flux of 73.2 L m−2 h−1, specific reverse solute flux of 1.17 g L−1, and power density of 18.71 W m−2 (corresponding to water flux of 56.1 L m-2 h-1) at 12 bar were obtained using 0.6 M NaCl as draw and deionized water as feed.

Effect of graphene oxide quantum dots on the interfacial polymerization of a thin-film nanocomposite forward osmosis membrane: An experimental and molecular dynamics study

We report an ultra-low loading of graphene oxide quantum dots (GQDs) into the polyamide (PA) layer of an outer-selective hollow fiber (OSHF) thin-film composite (TFC) membrane using the vacuum-assisted interfacial polymerization (VAIP) technique to improve the water permeability of OSHF TFC membranes without sacrificing membrane selectivity. Experimental results showed that GQD loading in the PA layer influenced membrane performance. The membrane with a GQD loading of 5 mg L−1 (TFN5) demonstrated an optimal water flux of 30.9 L m−2 h−1 and a specific reverse solute flux (SRSF) of 0.12 g L−1. To investigate the effect of GQDs on the interfacial polymerization (IP) reaction and membrane performance, molecular dynamics (MD) simulation was employed at the water-hexane and water-PA interfaces. The simulation results showed that GQDs decreased the reaction rate during the IP process by reducing the diffusivities of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). Additionally, GQDs reduced water permeability by acting as barriers to water molecules when present at a high concentration near the PA layer surface. At a very high loading, GQDs aggregated at the water-hexane interface and reduced the membrane selectivity by forming non-selective voids at the interface between the PA layer and GQDs. Together with the experimental findings, the MD simulation results delivered a good insight into the GQDs' effect on the TFC membrane's surface and transport properties at both macroscopic and microscopic levels.

Surface versus bulk CaCO3 crystals with ethylene vinyl alcohol co-polymers and polyamide thin-film composite membranes

We conducted experiments to study the influence of material surface chemistry and morphology on the crystallization of calcium carbonate from supersaturated solution containing mixed electrolytes. The study evaluated ethylene vinyl alcohol (EVOH) co-polymers and fluorinated and non-fluorinated polyamide thin film composite membranes to evaluate how surface functional groups impact partitioning of salt crystals between the surface and the bulk fluid. Our methodology and results can aid in developing scaling-resistant thin film composite membranes and in selecting materials for engineered structures exposed to supersaturated solutions. We analyzed turbidity, surface scale deposition, bulk crystal yield, and overall Ca balance to quantify salt crystal adhesion (aka scaling) during exposure to the supersaturated stream and subsequent desupersaturation. Through our studies, we found polyethylene was much more prone to scaling as compared to EVOH. We also show that EVOH containing 56% vinyl alcohol monomer appears to have higher scaling resistance as compared to an EVOH containing 68% vinyl alcohol monomer. These two grades of EVOH were analyzed using atomic force microscopy to elucidate if differences in co-polymer morphology existed; it appears so and this may underlie the measured differences in the salt crystal's surface adhesion. Also, the studies found that the incorporation of fluorine in the polyamide thin film composite membrane surface by means of a novel mono-fluorinated trimesoyl chloride derivative does not impact salt scaling or the total solution de-supersaturation. Our studies provide new insight that not only -OH functional group quantity but also polymer chain configuration and conformation need to be optimized for surfaces that are resistant to calcium carbonate scale buildup.

Fabrication of thin-film composite polyamide nanofiltration membrane based on polyphenol intermediate layer with enhanced desalination performance

Nanofiltration (NF) membrane is of great significance for desalination of light brine and purification of drinking water. Although the development of novel preparation methods and membrane materials has improved the separation performance, it is still a major challenge to promote NF membrane toward industrial production with simpler and more controllable process. Herein, the polyphenol intermediate layer was designed by 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) with twist structure and polyethyleneimine (PEI) co-deposition to increase the surface hydrophilicity and electropositivity of the polysulfone ultrafiltration substrate. Subsequently interfacial polymerization (IP) was carried out on the polyphenol intermediate layer to assemble a polyamide ultrathin selective layer using trimesoyl chloride and piperazine monomer. Through adjusting the co-deposition time of TTSB and PEI, a unique nano-pleated structure was successfully formed on the thin-film composite membrane surface. The water permeance of the membrane was determined as 23.7 L m−2 h−1 bar−1 with 99.4% Na2SO4 rejection, which was almost triple fold of the flux of the controller membrane without the intermediate layer. Our results provide an efficient and convenient way to fabricate the advanced NF membrane with higher divalent/monovalent ion selectivity and water permeance simultaneously, which will provide advices for the gas separation and pervaporation membranes with the IP method.

Characterization and control of membrane fouling during dewatering of activated sludge using a thin film composite forward osmosis membrane

This study investigated the feasibility of applying a thin film composite (TFC) forward osmosis (FO) membrane in the dewatering of activated sludge (AS). Membrane fouling was investigated and controlled to enhance the system’s performance. Investigations showed that the TFC FO membrane provided a water flux that was 120 % higher and a concentration factor that was three times higher compared to a cellulose tri-acetate (CTA) membrane. The foulant layer on the TFC membrane surface was mostly irreversible when 1.44 mg-C/cm2 and 0.13 mg-C/cm2 dissolved organic carbon (DOC) were extracted in sodium hydroxide (NaOH) and deionized (DI) water, respectively. The results of principle component analysis (PCA) revealed that among the operating conditions, the amount of aromatic organic compounds (indicated by UV254 values) followed by their hydrophilicity (specific ultraviolet absorbance (SUVA) indices) were the dominant factors controlling the different fouling potentials. SUVA value indices ranged from 0.4 to 0.6 L/m-mg DOC, illustrating that hydrophilic compounds were more responsible for membrane fouling than hydrophobic components. These results implied that aromatic and hydrophilic substances, in particular protein and polysaccharides were key components of the fouling layers, which need to be considered to enable a reduction of membrane fouling. We thus employed several novel fouling control methods, in which the combination of mono-chloramine pre-treatment and membrane cleaning by NaOH resulted in the recovery up to 86 % of the water from raw AS.

Peranan Oksida Grafin dalam Pengubahsuaian Lapisan Sokongan Membran Komposit Filem Nipis (TFC) untuk Aplikasi Osmosis ke Hadapan

In this work, the effect of graphene oxide (GO) incorporation into the membrane support layer towards the performance of thin-film composite (TFC) membrane was investigated. The support layer was fabricated by phase inversion method with the incorporation of GO as hydrophilic nanoparticles. Next, the active polyamide layer was formed on the membrane support layer via interfacial polymerization between trimesoyl chloride (TMC) and m-Phenylenediamine (MPD). The cross-section images from Field-Emission Scanning Electron Microscope (FESEM) showed the presence of active polyamide layer on the surface of TFC membrane while the FTIR results indicated the existence of bands associated with the amide linkages. The initial study showed that an optimal amount of GO (0.5 wt%) incorporation into the polymer substrate resulted in favourable improvement in TFC membrane performance. The physical and chemical properties of GO helps in enhancing the water transport through the membrane polymer matrix and thus contributing to higher permeate flux. The TFC-FO membrane incorporated with GO showed 44% improvement in terms of water flux (3.72 compared to 2.09 Lm-2 h-1 for pure PSf membrane) and minimal improvement in reverse solute diffusion (0.02 compared to 0.03 g m-2 h-1 for pure PSf membrane). Thus, this study showed that small addition of GO nanoparticles into the membrane support layer leads to an increase in performance of TFC membrane for FO application.

Membrane Fouling: Does Microscale Roughness Matter?

The surface of thin-film composite membranes used for reverse osmosis appears to be rough, known as a peak–valley morphology, and this is believed to cause more severe fouling than would occur for ...

Facile in-situ assembly of silver-based MOFs to surface functionalization of TFC membrane: A novel approach toward long-lasting biofouling mitigation

Surface functionalization of polyamide thin-film composite (TFC) membranes with advanced nanostructure materials suggests tailored control and objective design of surface characteristics which would generate valuable platforms with improved anti-biofouling/antimicrobial properties, excellent selectivity and permeability. This study, for the first time, presents an innovative and facile deposition procedure for covalent bonding of silver-based metal organic frameworks (Ag-MOFs) on the surface of TFC membrane for forward osmosis (FO) application. The binding of Ag-MOFs on the TFC membrane surface was evaluated by FTIR, XPS, FE-SEM, and EDS analyses. After binding of Ag-MOFs on the surface of TFC membrane, the water permeability decreased slightly from 1.1 to 0.94 L/m2 h bar, while the reverse salt flux reduced from 0.334 to 0.275 L/m2 h compared to the nascent TFC membrane. Confocal microscopy analyses showed that Ag-MOF nanoparticles imparted highly potent antibacterial property to the membrane, resulting in a nearly 100% reduction of live bacteria. Moreover, after 7 months immersing of Ag-MOF membrane in water and depletion of silver, the successful regeneration of Ag-MOFs was achieved which can demonstrate the potential of long-term application of this kind of modified membrane without disassembling the module. The simplicity of the technique, the rapid reaction time and the strong antibacterial property highlight the potential of this technique for the development of novel antimicrobial TFC membranes for water treatment.

Recent Advances in Thin Film Composite (TFC) Reverse Osmosis and Nanofiltration Membranes for Desalination

Reverse osmosis (RO) by polymeric membranes is known to be among the successful technologies for brackish and seawater desalination. For the development of these polymeric RO membranes, two different techniques have been used – the phase inversion method for asymmetric membranes, such as cellulose acetate membrane and the interfacial polymerization for thin film composite (TFC) membranes. Despite the high quality of the water produced by TFC–RO process, TFC membranes are susceptible to fouling. After a long period of academic and industrial researches, it is generally accepted that hydrophilicity, surface charge, and surface roughness of the TFC membrane surface are the major factors which affect the membrane susceptibility to fouling. As a result, several recent studies have focused on tailoring these properties with the aim of producing TFC membranes with reduced fouling as well as enhanced flux and salt rejection for use in desalination.In this study, authors present a comprehensive summary of the most recent findings in the literature focusing on the enhancement of TFC RO and nanofiltration membrane performance in desalination applications, by tailoring membrane characteristics. The authors would then present a new concept for the preparation of TFC membranes by interfacial polymerization on porous polysulfone support using novel additives, namely, surface modifying macromolecules (SMMs). Hydrophilic SMMs (LSMMs) were synthesized both ex–situ and in–situ within the organic solvent of the TFC system. The RO performance results showed that the addition of the ex–situ LSMM significantly decreased the salt rejection of the membrane and slightly reduced the flux, while in the case of the in–situ LSMM, salt rejection was improved but the flux declined at different rates for different LSMM concentrations. The membrane prepared by the in–situ LSMM exhibited less flux decay over an extended operational period.

Tris(hydroxymethyl)aminomethane polyamide thin‐film‐composite antifouling reverse osmosis membrane

ABSTRACTFor the applications of reverse osmosis (RO) process, membrane fouling caused by organic molecule adsorption is still a serious problem which significantly decreases membrane lifespan and increases operation costs. In this present article, we report the thin film composite (TFC) RO membrane functionalized with tris(hydroxymethyl)aminomethane (THAM) using one‐step method for improved antifouling property. The results of surface characterization indicated that THAM was successfully grafted onto the active layer of membrane by covalent linkage. Mult‐hydroxyl‐layer was generated and remained steadily on TFC membrane surface after modification. The contact angle decreased from 75.9 ± 3.0° to 46.9 ± 2.3°, which showed a distinct improvement of membrane surface hydrophilicity after modification. The grafted THAM improved water flux by 28.3%, while salt rejection was almost unchanged in membrane property tests. The modified membranes presented preferable antifouling property to foulants of bovine serum albumin, sodium alginate, and dodecyl trimethyl ammonium bromide than that of pristine membranes during dynamic fouling experiments. The method in this study provided an effective way to improve antifouling property of the polyamide thin‐film‐composite RO membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45891.

Graphene oxide modified polyamide reverse osmosis membranes with enhanced chlorine resistance

Improving chlorine resistance of polyamide (PA) reverse osmosis membranes is one of the major challenges in reverse osmosis membrane technology. In this study, few-layered graphene oxide (GO) was assembled onto polyamide thin film composite membrane surfaces through a spin-coating method to address this challenge. The coating solutions were used at different pH values and with different dispersion solvents. It was found that the pH values have great effects on membrane performance including maximizing water flux at a pH value of 6–7. XPS results indicate that the GO layer can protect the PA functional layer by absorbing chlorine radicals to form O–Cl bond. All modified membranes demonstrate a good suppression of membrane degradation in salt rejection upon chlorine exposure, and the degree of resistance to chlorine was enhanced with the increase of the number of GO layers. The GO1-coated membrane with GO nanosheets dispersed in ethanol showed increased water flux and good chlorine resistance. For instance, salt rejection varied from 95.3% to 91.6% for the first two hours, while unmodified membrane dropped to 80%. After 16h of chlorine exposure, measured salt rejection of GO1-coated membrane was 75% but unmodified membrane was a less effective 63%.

Silica scaling in forward osmosis: From solution to membrane interface

Membrane silica scaling hinders sustainable water production. Understanding silica scaling mechanisms provides options for better membrane process management. In this study, we elucidated silica scaling mechanisms on an asymmetric cellulose triacetate (CTA) membrane and polyamide thin-film composite (TFC) membrane. Scaling filtration showed that TFC membrane was subjected to more severe water flux decline in comparison with the CTA membrane, together with different scaling layer morphology. To elucidate the silica scaling mechanisms, silica species in the aqueous solution were characterised by mass spectrometry as well as light scattering. Key thermodynamic parameters of silica surface nucleation on the CTA and TFC membranes were estimated to compare the surface nucleation energy barrier. In addition, high resolution X-ray photoelectron spectroscopy resolved the chemical origin of the silica-membrane interaction via identifying the specific silicon bonds. These results strongly support that silica scaling in the CTA membrane was driven by the aggregation of mono-silicic acid into large silica aggregates, followed by the deposition from bulk solution onto the membrane surface; by contrast, silica polymerised on the TFC membrane surface where mono-silicic acid interacted with TFC membrane surface, which was followed by silica surface polymerisation.

Thin-film composite forward osmosis membranes functionalized with graphene oxide–silver nanocomposites for biofouling control

Innovative approaches to prevent bacterial attachment and biofilm growth on membranes are critically needed to avoid decreasing membrane performance due to biofouling. In this study, we propose the fabrication of anti-biofouling thin-film composite membranes functionalized with graphene oxide–silver nanocomposites. In our membrane modification strategy, carboxyl groups on the graphene oxide–silver nanosheets are covalently bonded to carboxyl groups on the surface of thin-film composite membranes via a crosslinking reaction. Further characterization, such as scanning electron microscopy and Raman spectroscopy, revealed the immobilization of graphene oxide–silver nanocomposites on the membrane surface. Graphene oxide–silver modified membranes exhibited an 80% inactivation rate against attached Pseudomonas aeruginosa cells. In addition to a static antimicrobial assay, our study also provided insights on the anti-biofouling property of forward osmosis membranes during dynamic operation in a cross-flow test cell. Functionalization with graphene oxide–silver nanocomposites resulted in a promising anti-biofouling property without sacrificing the membrane intrinsic transport properties. Our results demonstrated that the use of graphene oxide–silver nanocomposites is a feasible and attractive approach for the development of anti-biofouling thin-film composite membranes.

PEGylation and incorporation of triazine ring into thin film composite reverse osmosis membranes for enhancement of anti-organic and anti-biofouling properties

An approach for the simultaneous enhancement of anti-organic and anti-biofouling properties of polyamide thin film composite (TFC) reverse osmosis (RO) membranes is reported. In situ incorporation of both triazine ring and polyethylene glycol (PEG) into the polyamide network yielded such TFC membranes. The polyamide active layer was fabricated on top of polysulfone support membrane via interfacial polymerization (IFP) between conventionally used trimesoyl chloride (TMC) and mixture of m-phenylenediamine (MPD), melamine and MPD-terminated PEG (MeO-PEG-MPD). The membrane prepared by MPD/melamine/MeO-PEG-MPD exhibited superior overall antifouling properties compared to membrane prepared by MPD/melamine or MPD as sole amine monomer. It turned out that the incorporated PEG enhances anti-organic fouling property and reduces the bacterial adhesion whereas triazine ring only lowers the growth of bacteria on TFC membrane surface. The membrane containing both triazine ring and PEG exhibited pronounced effect on reducing bacterial adhesion than that of membrane containing triazine alone. TFC membrane prepared by IFP between TMC (0.125%, w/v) and mixture of MPD+melamine+MeO-PEG-MPD (MPD:melamine:MeO-PEG-MPD=1:1:0.5 w/w) exhibited enhanced overall antifouling property with permeate flux ca. 38Lm−2h−1 and NaCl rejection ca. 93% from feed solution (containing 2000ppm NaCl) at applied pressure 1.4MPa.

Bidirectional diffusion of ammonium and sodium cations in forward osmosis: role of membrane active layer surface chemistry and charge.

Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4(+)) and sodium (Na(+)) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes.