Regulating the aqueous phase monomer balance for flux improvement in polyamide thin film composite membranes

Comprehensive Characterization of Commercial Reverse Osmosis Membranes through High-Temperature Cross-Flow Filtration

Developing thermally stable reverse osmosis membranes is a potential game-changer in high-temperature water treatment. In this work, the performance of three commercial reverse osmosis membranes was evaluated with a series of high-temperature filtrations. The membranes were tested with different filtration methodologies: long-term operation, cyclic tests, controlled stepwise temperature increment, and permeability tests. The morphological and physiochemical characterizations were performed to study the impact of high-temperature filtration on the membranes' chemical composition and morphological characteristics. An increase in the temperature deteriorated the membrane performance in terms of water flux and salt rejection. Flux decline at high temperatures was recognized as the primary concern for high-temperature filtrations, restricting the applications of commercial membranes for long-term operations. This research provides valuable insights for researchers aiming to thoroughly characterize reverse osmosis membranes at high temperatures.

New Insights into the Mechanical Behavior of Thin-Film Composite Polymeric Membranes

Limited predictions of thin-film composite (TFC) membranes’ behavior and functional life exist due to the lack of accurate data on their mechanical behavior under different operational conditions. A comprehensive investigation of the mechanical behavior of TFC membranes addressing deformation and failure, temperature and strain rate sensitivity, and anisotropy is presented. Tensile tests were conducted on commercial membranes as well as on individual membrane layers prepared in our laboratories. The results reveal the overall mechanical strength of the membrane is provided by the polyester layer (bottom layer), while the rupture stress for the middle and top layers is at least 10 times smaller than that of the polyester layer. High anisotropic behavior was observed and is attributed to the nonwoven structure of the polyester layer. Rupture stress in the transverse (90°) direction was one-third of the rupture stress in the casting direction. Limited temperature and strain rate dependence was observed in the temperature range that exists during operation. Scanning electron microscopy images of the fractured surfaces were also analyzed and correlated with the mechanical behavior. The presented results provide new insights into the mechanical behavior of thin-film composite membranes and can be used to inform novel membrane designs and fabrication techniques.

3D Printed and Conventional Membranes—A Review

Polymer membranes are central to the proper operation of several processes used in a wide range of applications. The production of these membranes relies on processes such as phase inversion, stretching, track etching, sintering, or electrospinning. A novel and competitive strategy in membrane production is the use of additive manufacturing that enables the easier manufacture of tailored membranes. To achieve the future development of better membranes, it is necessary to compare this novel production process to that of more conventional techniques, and clarify the advantages and disadvantages. This review article compares a conventional method of manufacturing polymer membranes to additive manufacturing. A review of 3D printed membranes is also done to give researchers a reference guide. Membranes from these two approaches were compared in terms of cost, materials, structures, properties, performance. and environmental impact. Results show that very few membrane materials are used as 3D-printed membranes. Such membranes showed acceptable performance, better structures, and less environmental impact compared with those of conventional membranes.

Development of Novel Composite Membranes in Water/Wastewater Treatment

Composite membranes have attracted significant attention due to their flexibility in having more than one layer, with many materials being used to form the membrane [...]

Functional GO-based membranes for water treatment and desalination: Fabrication methods, performance and advantages. A review

Graphene oxide (GO) and GO-based materials have gained a significant interest in the membrane synthesis and functionalization sector in the recent years. Inspired by their unique and tuneable properties, several GO-based nanomaterials have been investigated and utilized as effective nanofillers for various membranes in the water treatment, purification and desalination sectors. This paper comprehensively reviews the recent advances of GO utilization in pressure, concentration and thermal-driven membrane processes. A brief overview on GO particles, properties, synthesis and functionalization methods was provided. The conventional and the state-of-art fabrication methods of GO-based membranes were summarized and discussed, and consequently the GO-based membranes were classified into different categories. The applications, types, and the performance in terms of flux and rejection were summarized and reviewed. The advantages of GO-based membranes in terms of antifouling properties, bactericidal effects, mechanical strength and stability have been reviewed, too. The review gives insights on the future perspectives of GO functional materials and their potential use in the various membrane processes discussed herein.

Toward Sustainable Tackling of Biofouling Implications and Improved Performance of TFC FO Membranes Modified by Ag-MOF Nanorods

In this work, nanorods with high antibacterial properties were synthesized with silver acetate as the metal source and 2-aminoterephthalic acid as the organic linker and were then embedded into thin-film composite (TFC) membranes to amend their performance as well as to alleviate biofouling. Silver metal-organic framework (Ag-MOF) nanorods with a length smaller than 40 nm were incorporated within the polyamide thin selective layer of the membranes during interfacial polymerization. The interaction of the synthesized nanorods with the polyamide was favored because of the presence of amine-containing functional groups on the nanorod's surface. The results of X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy characterizations proved the presence of Ag-MOF nanorods in the selective layer of thin-film nanocomposite (TFN) membranes. TFN membranes demonstrated improved water permeance, salt selectivity, and superior antibacterial properties. Specifically, the increased hydrophilicity and antibacterial potential of the TFN membranes led to a synergetic effect toward biofouling mitigation. The number of live bacteria attached to the surface of the neat TFC membrane decreased by more than 92% when a low amount of Ag-MOF nanorods (0.2 wt %) was applied. Following contact of the TFN membrane surface with Escherichia coli and Staphylococcus aureus, full inactivation, and degradation of bacteria cells were observed with microscopy, colony-forming unit tests, and disc inhibition zone analyses. This result translated to a negligible amount of the biofilm formed on the active layer. Indeed, the incorporation of Ag-MOF nanorods decreased the metal-ion release rate and therefore provided prolonged antibacterial performance.

Flexible and Hydrophilic Copolyamide Thin-Film Composites on Hollow Fiber Membranes for Enhanced Nanofiltration Performance

Flexible and hydrophilic copolyamide (Co-PA) thin-film composite (TFC) membranes were fabricated as a selective layer on the outer surface of the polyvinylidene fluoride hollow fiber membrane substrate. The fabrication process was carried out by the dip-coating method to create three TFC membranes. The first layer is tannic acid and the second layer is (3-aminopropyl)triethoxysilane, which is followed by Co-PA as a final selective layer. The Co-PA TFC membrane was prepared through interfacial polymerization via the combination of various short-chain aliphatic diamines and conventional aromatic diamines with trimesoyl chloride. The influence of coating layers and total diamine concentration on the Co-PA TFC membrane was investigated in terms of the membrane's physicochemical and mechanical properties, morphology, surface thickness and roughness, water contact angle, surface charge, and nanofiltration (NF) performance. The obtained Co-PA TFC membrane system was operated under low pressure (2 bar) with pure water flux in the range of 23.8-83.9 L m^-2 h^-1 and exhibited better hydrophilicity, flexibility, molecular weight cutoff, and NF performance compared to the conventional PA TFC membrane. The superior properties of Co-PA are due to the increased chain mobilities provided by short-chain aliphatic diamines in its structure. The best Co-PA TFC membranes, which were synthesized using diamines containing four carbon atoms, achieved a significant improvement in NF membrane performance and selectivity (pure water flux = 56.9 L m^-2 h^-1 and salt and dye rejection in the range of 46.2-99.2%). This Co-PA TFC membrane is a promising membrane for its high flexibility, hydrophilicity, and selectivity of the NF membrane.

Influence of l-arginine on performances of polyamide thin-film composite reverse osmosis membranes

To prepare polyamide thin-film composite reverse osmosis (PA-TFC-RO) membranes with high performance, l-arginine (Arg) was used as an additive in m-phenylenediamine (MPD) aqueous solution. Arg with active amine groups can react with 1,3,5-benzenetricarboxylic chloride (TMC) to be incorporated into the polyamide selective layer during interfacial polymerization. X-ray photoelectron spectroscopy verified the successful introduction of Arg into the polyamide selective layer. Scanning electron microscopy, atomic force microscopy, contact angle and zeta potential measurements manifested that the polyamide selective layer was thinner, smoother, more hydrophilic and less negatively charged after the incorporation of Arg. The thinner and more hydrophilic polyamide selective layers favor the boosting of the permeability of the RO membrane by decreasing the hydraulic resistance to water permeation. Consequently, when the content of Arg was 0.5 wt%, the water flux and salt rejection of the resulting membranes increased from the original 46.46 L m⁻² h⁻¹ and 96.34% to 54.13 L m⁻² h⁻¹ and 98.36%. Besides, the modified membranes showed excellent fouling-resistance and easy-cleaning properties when tested by using bovine serum albumin (BSA) and dodecyltrimethyl ammonium bromide (DTAB) as model foulants.

l-Arginine (Arg) as an aqueous additive was incorporated into the polyamide selective layer during interfacial polymerization, thereby the separation performance and anti-fouling properties of the resulting RO membranes were enhanced.

Study of polyamide thin film characteristics impact on permeability/selectivity performance and fouling behavior of forward osmosis membrane

In recent years, forward osmosis (FO) has received considerable attention due to its huge potentials in water desalination. The thin film composite (TFC) membrane used in the FO desalination consists of a bottom support layer covered by an active layer on top. Polyamide (PA) is commonly employed as an active layer forming via interfacial polymerization between m-phenylenediamine (MPD) and trimesoyl chloride (TMC) monomers. In this study, the effects that the MPD and TMC concentrations could have on the performance and anti-fouling behavior of the obtained FO membrane have been investigated. Results showed that there is a trade-off relationship between the water flux and salt rejection, which by increasing MPD concentration, the water flux was reducedو while the salt rejection was enhanced. Also, by increasing the TMC concentration, an opposite trend was observed. Using 0.20 wt.% of TMC monomer, the highest water fluxes of 21.6 LMH and 29.3 LMH were achieved in two different membrane configurations. Furthermore, higher TMC concentration caused better anti-fouling property, when PA active layer of the membrane was in a high fouling potential environment.

Influence of l-lysine on the permeation and antifouling performance of polyamide thin film composite reverse osmosis membranes

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study. l-Lysine is used as a type of aqueous additive during interfacial polymerization. As a result, the pure water flux (PWF) of the resulting membranes increased by around 18% and their salt rejection improved from 98.17% to 98.40% at an optimum l-lysine dosage of 0.1 wt%. Additionally, the anti-fouling properties of the resulting membranes were enhanced. The chemical structure of the membranes was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The morphologies of the top surface and cross-section of the membranes were revealed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, contact angle (CA) and zeta potential measurements were carried out to determine the surface properties of the membranes. The results showed that the TFC RO membrane became thinner, smoother, smaller in surface area, more hydrophilic and more negatively charged after the introduction of l-lysine. Accordingly, the reason for the enhancement in the PWF and anti-fouling properties of the TFC RO membranes with the introduction of l-lysine was analyzed. The thinner selective layer (increase in concentration gradient across the membrane) with carboxyl groups (hydrogen bond interactions) and loose structure (greater free volume and sub-nanometer pores) resulted in low hydraulic resistance to the permeability of the polyamide selective layer, which led to the enhancement in PWF. Also, the smoother and more hydrophilic top surface and the increase in negative charges in the selective layer contribute to the improvement in anti-fouling property.

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study.

A critical review on recent polymeric and nano-enhanced membranes for reverse osmosis

Current and recent advances in polymeric and nano-enhanced membrane developments for reverse osmosis are reported in terms of membrane performance and fouling.