A novel method of surface modification on thin-film composite reverse osmosis membrane by grafting poly(ethylene glycol)

Polyethylene glycol-grafted graphene oxide nanosheets in tailoring the structure and reverse osmosis performance of thin film composite membrane

Introducing hydrophilic polymers such as polyethylene glycol (PEG) within the polyamide (PA) layer of thin film composite (TFC) membranes helps achieve high water desalination performance. Here, PEGs of different molecular weights (X: 1500, 6000, 16,000 g/mol) are effectively introduced into the PA layer of TFC membranes utilizing PEG-grafted graphene oxide (GOPX) nanosheets and their effects on the physicochemical properties and reverse osmosis (RO) performance of the thin film nanocomposite (TFN) membranes are investigated. Among the TFNs prepared the GOP16000/TFN exhibits the best performance with 68% improvement in water flux and almost constant salt rejection compared to those of the bare TFC. The influence of PEG molecular weight on the RO performance of the membranes is interpreted by different surface and bulk hydrophilicity as well as thickness and surface roughness of PA layers of GOPX/TFNs. Furthermore, TFNs with thinner and smoother PA layers and thus higher water flux are obtained by dispersing GOPXs in the aqueous phase of the PA interfacial polymerization reaction than by dispersing them in the organic phase of the reaction. Finally, the high antifouling potential of TFNs containing PEG-grafted GOs is demonstrated.

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.

Removal of natural organic matter from surface water sources by nanofiltration and surface engineering membranes for fouling mitigation - A review

Given that surface water is the primary supply of drinking water worldwide, the presence of natural organic matter (NOM) in surface water presents difficulties for water treatment facilities. During the disinfection phase of the drinking water treatment process, NOM aids in the creation of toxic disinfection by-products (DBPs). This problem can be effectively solved using the nanofiltration (NF) membrane method, however NOM can significantly foul NF membranes, degrading separation performance and membrane integrity, necessitating the development of fouling-resistant membranes. This review offers a thorough analysis of the removal of NOM by NF along with insights into the operation, mechanisms, fouling, and its controlling variables. In light of engineering materials with distinctive features, the potential of surface-engineered NF membranes is here critically assessed for the impact on the membrane surface, separation, and antifouling qualities. Case studies on surface-engineered NF membranes are critically evaluated, and properties-to-performance connections are established, as well as challenges, trends, and predictions for the field's future. The effect of alteration on surface properties, interactions with solutes and foulants, and applications in water treatment are all examined in detail. Engineered NF membranes containing zwitterionic polymers have the greatest potential to improve membrane permeance, selectivity, stability, and antifouling performance. To support commercial applications, however, difficulties related to material production, modification techniques, and long-term stability must be solved promptly. Fouling resistant NF membrane development would be critical not only for the water treatment industry, but also for a wide range of developing applications in gas and liquid separations.

Anti-Fouling Surfaces for Extracorporeal Membrane Oxygenation by Surface Grafting of Hydrophilic Sulfoxide Polymers

Non-thrombogenic surfaces for extracorporeal membrane oxygenation (ECMO) devices are important to increase their duration of usage and to enable long-term life support. However, the contact of blood with the hydrophobic synthetic ECMO membrane materials such as poly(4-methyl-1-pentene) (PMP) can activate the coagulation cascade, causing thrombosis and a series of consequent complications during ECMO operation. Targeting this problem, we proposed to graft highly hydrophilic sulfoxide polymer brushes onto the PMP surfaces via gamma ray irradiation-initiated polymerization to improve the hemocompatibility of the membrane. Through this chemical modification, the surface of the PMP film is altered from hydrophobic to hydrophilic. The extent of plasma protein adsorption and platelet adhesion, the prerequisite mediators of the coagulation cascade and thrombus formation, are drastically reduced compared with those of the unmodified PMP film. Therefore, the method provides a facile approach to modify PMP materials with excellent antifouling properties and improved hemocompatibility demanded by the applications in ECMO and other blood-contacting medical devices.

Improvement of Antibacterial and Antifouling Properties of a Cellulose Acetate Membrane by Surface Grafting Quaternary Ammonium Salt

Through etherification reaction, epoxy propyl dimethyl dodecyl ammonium chloride (EPDMDAC) was grafted onto the surface of a cellulose acetate (CA) membrane to prepare a stable nonleaching antibacterial antifouling membrane (QCA-X). The results showed that with the extension of grafting reaction time, the quaternary ammonium salt groups on the membrane surface increased and the hydrophilicity was enhanced. Compared with those of the CA membrane, the filtration capacity and antifouling performance of the QCA-X membrane are improved. When the grafting time is 4 h, the water permeability and flux recovery rate of the QCA-4 membrane are increased by 139 and 21.5%, respectively. The QCA-X membrane showed excellent antibacterial performance, and the sterilization rate against S. aureus and E. coli was more than 99.99%. After four repeated antibacterial cycles, the bactericidal rates against S. aureus and E. coli were maintained at about 99.69 ± 0.02 and 99.98 ± 0.02%, respectively, with good antibacterial persistence. Moreover, the QCA-X membrane can effectively inhibit bacterial adhesion. Mild and simple EPDMDAC grafting modifications improve the antibacterial, antifouling, and antibioadhesion properties of the CA membrane, showing its application potential in long-term water treatment, especially in biofouling water treatment.

In Situ Chemical Modification with Zwitterionic Copolymers of Nanofiltration Membranes: Cure for the Trade-Off between Filtration and Antifouling Performance

Breaking the trade-off between filtration performance and antifouling property is critical to enabling a thin-film nanocomposite (TFC) nanofiltration (NF) membrane for a wide range of feed streams. We proposed a novel design route for TFC NF membranes by grafting well-defined zwitterionic copolymers of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) and 2-aminoethyl methacrylate hydrochloride (AEMA) on the polyamide surfaces via an in situ surface chemical modification process. The successful grafting of a zwitterionic copolymer imparted the modified NF membranes with better surface hydrophilicity, a larger actual surface area (i.e., nodular structures), and a thinner polyamide layer. As a result, the water permeability of the modified membrane (i.e., TFC-10) was triple that of the pristine TFC membrane while maintaining high Na₂SO₄ rejection. We further demonstrated that the TFC-10 membrane possessed exceptional antifouling properties in both static adsorption tests and three cycles of dynamic protein and humic acid fouling tests. To recap, this work provides valuable insights and strategies for the fabrication of TFC NF membranes with simultaneously enhanced filtration performance and antifouling property.

Improved anti-biofouling resistances using novel nanocelluloses/cellulose acetate extracted from rice straw based membranes for water desalination

Cellulose and Nanocellulose acetate (NCA) have attractive novel properties like excellent mechanical properties, rich hydroxyl groups for modification, and natural properties with environmental friendliness. Cellulose was extracted from rice straw wastes as an extra value, then it had been further transformed into NCA using the acidic hydrolysis technique. The structural, crystalline, morphological, were characterized by Fourier transform infrared spectroscopy (FTIR), Proton nuclear magnetic resonance (¹HNMR), X-ray diffraction (XRD), Scanning microscopy, respectively. The particle size of the Nanocellulose extracted from rice straw was about 22 nm with a spherical shape. Development membranes were prepared with different concentrations of NCA to improve the performance and the anti-biofouling properties of cellulose acetate reverse osmosis (RO) membranes using a phase inversion technique. The structural of membranes were characterized by FTIR, water contact angle measurements, while the anti-biofouling properties were studied by static protein adsorption. The results indicated the development membrane features a lower contact angle accomplished with exhibits pore-forming ability and enhanced hydrophilicity of prepared membrane, furthermore the development cellulose acetate reverse osmosis (CA-RO) membranes with 40:60% RNCA:CA produced a salt rejection of 97.4% and a water flux of 2.2 L/m² h. the development membrane have resists effectively protein adsorption and microbial growth showed from the results of Static protein adsorption.

Fabrication of highly permeable and anti-fouling performance of Poly(ether ether sulfone) nanofiltration membranes modified with zinc oxide nanoparticles

Membrane fouling is one of the challenging bottleneck problems in waste water treatment by membrane process. The present study constructed a nanofiltration membrane based on the zinc oxide nanoparticle (n-ZnO) integrated Poly(ether ether sulfone) (PEES) membranes. The developed membranes were characterized by X-ray diffraction (XRD), attenuated total reflectance - fourier transform infrared spectroscopy (AT-FTIR), atomic force microscopy (AFM) and scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX) analysis. Pure water flux, contact angle, molecular weight cut-off, mean pore size and porosity were determined to investigate the influence of n-ZnO on the properties of the membranes. The characterization showed asymmetric configuration of membranes after n-ZnO incorporation. This incorporation also enhanced the hydrophilicity of PEES membrane. The fouling-resistant potential of the membranes was investigated by the model foulant humic acid (HA) and an enhanced anti-fouling irreversible property with a corresponding flux recovery rate of 92.43 % was noted for the prepared membrane. The rejection performance and permeability of HA was 98.03 % and 166.73 L m^-2 h^-1, respectively, owing to the hydrophilic nature of ZnO particles. Further, modified PEES membrane exhibited superior separation performance for monovalent and divalent anions. PEES/n-ZnO hybrid membrane assisted nanofiltration is an effective process for the improvement of membrane performance and anti-fouling property, demonstrating its immense use in water reclamation.

Dynamic Modeling of Fouling in Reverse Osmosis Membranes

During reverse osmosis (RO) membrane filtration, performance is dramatically affected by fouling, which concurrently decreases the permeate flux while increasing the energy required to operate the system. Comprehensive design and optimization of RO systems are best served by an understanding of the coupling between membrane shape, local flow field, and fouling; however, current studies focus exclusively on simplified steady-state models that ignore the dynamic coupling between fluid flow, solute transport, and foulant accumulation. We developed a customized solver (SUMs: Stanford University Membrane Solver) under the open source finite volume simulator OpenFOAM to solve transient Navier-Stokes, advection-diffusion, and adsorption-desorption equations for foulant accumulation. We implemented two permeate flux reduction models at the membrane boundary: the resistance-in-series (RIS) model and the effective-pressure-drop (EPD) model. The two models were validated against filtration experiments by comparing the equilibrium flux, pressure drop, and fouling pattern on the membrane. Both models not only predict macroscopic quantities (e.g., permeate flux and pressure drop) but also the fouling pattern developed on the membrane, with a good match with experimental results. Furthermore, the models capture the temporal evolution of foulant accumulation and its coupling with flux reduction.

Recent development of pressure retarded osmosis membranes for water and energy sustainability: A critical review

With the goal of zero-liquid discharge and green energy harvest, extraction of abundant green energy from saline water via pressure retarded osmosis (PRO) technology is a promising but challenging issue for water treatment technologies to achieve water and energy sustainability. Development of high performance PRO membranes has received increased concerns yet still under controversy in practical applications. In this review, a comprehensive and up-to-date discussion of some key historical developments is first introduced covering the major advances of PRO engineering applications and novel membranes especially made in recent years. Then the critical performance indicators of PRO membranes including water flux and power density are briefly discussed. Subsequently, sufficient discussion on four performance limiting factors in PRO membrane and process is presented including concentration polarization, reverse solute diffusion, membrane fouling and mechanical stability. To fully address these issues, an updated insight is provided into recent major progresses on advanced fabrication and modification techniques of novel PRO membranes featuring enhanced performance with different configurations and materials, which are also reviewed in detail based on the viewpoint of design rationales. Afterwards, antifouling strategies and engineering applications are critically introduced. Finally, conclusions and future perspective of PRO membrane for practical operation are briefly discussed.

Carbodiimide-assisted zwitterionic modification of poly(piperazine amide) thin-film composite membrane for enhanced separation and anti-depositing performances to cationic/anionic dye aqueous solutions

In this work, a novel method of carbodiimide-assisted zwitterionic modification was proposed and implemented to incorporate zwitterionic moieties onto poly(piperazine amide) membrane for improved water permeability and anti-depositing property, which are crucial for highly efficient nanofiltration of dye-contained effluents. Carboxyl groups of polyamide layer were firstly transferred into N-acylurea using excess l-ethyl-3-(3-(dimethylamino)propyl)-carbodiimide. Zwitterions were then incorporated through ring-opening reaction between tertiary amine groups of N-acylurea and 1, 4-butanesultone. Carbodiimide-assisted zwitterionic modification was verified by ATR-IR and XPS analyses and was found to not affect membrane pore size but significantly enhance membrane's permeation and anti-dye-deposition performances. Compared with those of virgin membrane, water permeabilities of the desired zwitterionic membrane to pure water, Congo red aqueous solution and Victoria blue B aqueous solution were higher by 42.9, 62.3 and 95.2 %, respectively, hydraulic resistances from irreversible deposition of Congo red and Victoria blue B molecules were dramatically lowered by 68.4 and 91.8 %, respectively. Furthermore, the perm-selectivity performance of the desired zwitterionic membrane in terms of molecular weight cut-off and pure water permeability was better than most of the reported zwitterionic membranes, and the separation and anti-depositing performances to both anionic and cationic dye aqueous solutions were better than commercial membrane NF270.

Surface Grafting of Reverse Osmosis Membrane with Chlorhexidine Using Biopolymer Alginate Dialdehyde as a Facile Green Platform for In Situ Biofouling Control

We report a new robust and green facile platform for nonoxidizing chemical grafting to simultaneously improve antifouling and antibacterial properties of thin film composite (TFC) polyamide (PA) reverse osmosis (RO) membranes. In this work, alginate dialdehyde (ADA) was used as a green platform to graft chlorhexidine (CH), a nonoxidizing chemical, on TFC-RO membrane surface. A synergistic effect due to ADA and CH grafting was revealed. The modified membrane surfaces were characterized using XPS, FT-IR, AFM, SEM-EDS, contact angle, and zeta potential analysis. A simple two-step Schiff base reaction was performed. Improved salt rejection performances were observed for the grafted PA membranes at the expense of negligible flux drop for the CH-ADA-PA membranes (38 to 42 L m^-2 h^-1) compared with the pristine PA membrane (45 L m^-2 h^-1). All the CH-ADA-PA membranes had excellent antibacterial activity against E. coli along with a highly superior resistance to the formation of biofilms. Organic fouling behaviors with a protein (bovine serum albumin, BSA) and a surfactant (dodecyl trimethylammonium bromide, DTAB) were investigated as typical foulants for the grafted PA membranes. The results indicated that the CH-ADA-PA membranes showed the best antifouling performance followed by the ADA-PA membranes, the pristine membrane being the most inferior. Hence, these results pave the way for a new robust and green bioinspired route for practical application in RO membrane fouling control.

Integration of PEGylated Polyaniline Nanocoatings with Multiple Plastic Substrates Generates Comparable Antifouling Performance

Conducting polymer nanocoatings render plastics to possess interesting optical, chemical, and electrical properties. It nevertheless remains technically challenging to deposit uniform conducting polymer nanocoatings on ambient plastic substrates ascribed to the inert and varied chemical properties of plastics and the notorious processability of conducting polymers. Previous studies have made progress in delivering various conducting polymer thin films via oxidative chemical vapor deposition. Herein, we develop a solution-based approach to polyaniline (PANI) and PEGylated PANI nanocoatings on multiple engineering plastics followed by evaluating their antifouling performance. The procedure relies on the formation of uniform, lyotropic V₂O₅·nH₂O thin films on plastics assisted by a surfactant-sodium N-lauroylsarcosinate. Next, in situ, oxidative polymerization causes the formation of nanofibrous PANI nanocoatings. Finally, interfacial functionalization leads to PEGylated PANI nanocoatings, and the steric nanolayer effectively repels the adsorption of bovine serum albumin and the attachment of the bacterium Pseudoalteromonas sp. on the surface. It is worth noting that the antifouling properties rely mainly on the presence of PEGylated PANI nanocoatings, irrespective of the type of plastic substrates underneath. The current study therefore opens an avenue for the solution-based delivery of conducting polymer-based, functional nanocoatings on hydrophobic substrates in a controllable manner with the availability of further modification.

Versatile biomimetic medical device surface: hydrophobin coated, nitric oxide-releasing polymer for antimicrobial and hemocompatible applications

In medical device design, there is a vital need for a coating that promotes treatment of the patient and simultaneously prevents fouling by biomacromolecules which in turn can progress to infections, thrombosis, and other device-related complications. In this work, hydrophobin SC3 (SC3), a self-assembling amphiphilic protein, was coated on a nitric oxide (NO) releasing medical grade polymer to provide an antifouling layer to work synergistically with NO's bactericidal and antiplatelet activity (SC3-NO). The contact angle of SC3 samples were ∼30% lesser than uncoated control samples and was maintained for a month in physiological conditions, demonstrating a stable, hydrophilic coating. NO release characteristics were not adversely affected by the SC3 coating and samples with SC3 coating maintained NO release. Fibrinogen adsorption was reduced over tenfold on SC3 coated samples when compared to non-SC3 coated samples. The viable cell count of adhered bacteria (Staphylococcus aureus) on SC3-NO was 79.097 ± 7.529% lesser than control samples and 49.533 ± 18.18% lesser than NO samples. Platelet adherence on SC3-NO was reduced by 73.407 ± 14.59% when compared to control samples and 53.202 ± 25.67 when compared to NO samples. Finally, the cytocompatibility of SC3-NO was tested and proved to be safe and not trigger a cytotoxic response. The overall favorable results from the physical, chemical and biological characterization analyses demonstrate the novelty and importance of a naturally-produced antifouling layer coated on a bactericidal and antiplatelet polymer, and thus will prove to be advantageous in a multitude of medical device applications.

Synthesis, characterization and enzymatic surface roughing of cellulose/xylan composite films

Upgrading renewable cellulose biopolymer to various high-value material/chemical is of great importance in building a sustainable bio-economy. This work assessed the technical feasibility of fabricating transparent cellulose/xylan composite films using facile solution-casting method. More importantly, this work also initially assessed the technical potential of xylanase treatment to selectively modify the surface of the obtained composite films with the goal of extending their applications. When bleached Kraft xylan addition was lower than 20 wt%, the composite films could still retain their original mechanical and structural advantages. Xylanase treatment specifically removed 26.0% and 32.3% xylan of the composite films with an enzyme loading of 2 and 5 mg g^-1 cellulose, respectively. It was shown that xylan component was heterogeneously located in the surface of the composite films during film-casting process, which allowed the subsequent surface etching/roughing at nanoscale using facile xylanase treatment without compromising their structural advantages.

Toward Enhancing the Chlorine Resistance of Reverse Osmosis Membranes: An Effective Strategy via an End-capping Technology

Polyamide reverse osmosis (RO) membranes suffer performance decay when exposed to free chlorine because of their unique chemical structure. The decay limits their lifespan and increases operating cost. Herein, the secondary interfacial polymerization method was performed, for the first time, using isophthaloyl chloride (IPC) as the chain-terminating reagent, to eliminate the negative effect when the unreacted amino groups interact with chlorine. The surface zeta potential of the as-prepared membrane remained almost constant over a wide pH range, which greatly demonstrated the high conversion ratio of the end-capping procedure. However, neither the surface morphology nor the separation properties were conspicuously influenced. Because of the absence of the terminated amino groups in the polyamide layer, the IPC-modified membrane exhibited significantly improved chlorine resistance, particularly at high pH. Its desalination performance remained unchanged as the total chlorine exposure approached 10 000 ppm·h, whereas only 80.3% of the NaCl was rejected by the unmodified membrane under the same conditions. Such SIP technology can be applied directly to the commercial SW30 seawater desalination membrane, making it more tolerant to free chlorine. Overall, our results strongly proved the IPC-assisted end-capping process as a promising, practicable, and scalable technology for enhancing the chlorine resistance of an RO membrane.