Novel ultrafiltration membranes with excellent antifouling properties and chlorine resistance using a poly(vinyl chloride)-based copolymer

Construction of PDA-PEI/ZIF-L@PE tight ultra-filtration (TUF) membranes on porous polyethylene (PE) substrates for efficient dye/salt separation

Tight ultra-filtration (TUF) membranes were constructed by in situ growing zinc imidazole frameworks micro-crystalline leaves (ZIF-L) in polyethylene imine (PEI) and polydopamine (PDA) deposit layers on porous polyethylene (PE) substrates. The effects of preparation conditions on the surface physical and chemical structures as well as on the dye/salt separation performance of the formed TUF membranes were systematically investigated. By inserting selective water permeation channels and increasing contacting surface areas, in situ-grown ZIF-L arrays tightly cross-linked in the coating matrix greatly increased water permeation without trading off dye/salt retention selectivity. The morphology of the included ZIF-L particles could be varied by adjusting the ligand/Zn molar ratio (α) in the preparation processes. Optimized PDA-PEI/ZIF-L@PE TUF membranes containing ZIF-L of cross-cross block morphology showed very high pure water permeability of 180 ± 20 L·m-2·h-1·bar-1 (LMHB) and retention selectivity (SCR/Na2SO4 and SMB/Na2SO4) of 267 and 43, respectively, as well as excellent stability and anti-fouling properties.

Sustainability in Membrane Technology: Membrane Recycling and Fabrication Using Recycled Waste

Membrane technology has shown a promising role in combating water scarcity, a globally faced challenge. However, the disposal of end-of-life membrane modules is problematic as the current practices include incineration and landfills as their final fate. In addition, the increase in population and lifestyle advancement have significantly enhanced waste generation, thus overwhelming landfills and exacerbating environmental repercussions and resource scarcity. These practices are neither economically nor environmentally sustainable. Recycling membranes and utilizing recycled material for their manufacturing is seen as a potential approach to address the aforementioned challenges. Depending on physiochemical conditions, the end-of-life membrane could be reutilized for similar, upgraded, and downgraded operations, thus extending the membrane lifespan while mitigating the environmental impact that occurred due to their disposal and new membrane preparation for similar purposes. Likewise, using recycled waste such as polystyrene, polyethylene terephthalate, polyvinyl chloride, tire rubber, keratin, and cellulose and their derivates for fabricating the membranes can significantly enhance environmental sustainability. This study advocates for and supports the integration of sustainability concepts into membrane technology by presenting the research carried out in this area and rigorously assessing the achieved progress. The membranes' recycling and their fabrication utilizing recycled waste materials are of special interest in this work. Furthermore, this study offers guidance for future research endeavors aimed at promoting environmental sustainability.

Characterization of a chlorine resistant and hydrophilic TiO2/calcium alginate hydrogel filtration membrane used for protein purification maintaining protein structure

The development of membranes for protein purification has stringent requirement of disinfection resistance, low protein adsorption and anti-fouling, without changing protein structure. In this study, hydrophilic titanium dioxide (TiO2)/calcium alginate (TiO2/CaAlg) hydrogel membranes were prepared by a simple ionic cross-linking method. The effects of the porogenic agent polyethylene glycol (PEG) concentration, the molecular weight of PEG, and the concentration of TiO2 on the filtration properties were systematically investigated. The TiO2/CaAlg membrane exhibited excellent bovine serum albumin (BSA) rejection and anti-fouling properties. The mechanical properties and surface energy of the TiO2/CaAlg membrane were significantly improved. The chemical bonding mechanism of TiO2 and NaAlg was investigated by molecular dynamic simulation. The TiO2/CaAlg membrane had good chlorine resistance and could be disinfected or cleaned with sodium hypochlorite. The TiO2/CaAlg hydrogel membrane loaded with polyhydroxybutyrate (PHB) nanofibers maintained high flux (136.7 L/m2h) and high BSA rejection (98.0 %) at 0.1 MPa. The results of circular dichroism and synchronous fluorescence indicated that the secondary structure of BSA was maintained after membrane separation. This study provides one method for the preparation of green and environmentally friendly membrane for protein purification.

Surface-engineered polyethersulfone membranes with inherent Fe-Mn bimetallic oxides for improved permeability and antifouling capability

In recent years, bimetallic oxide nanoparticles have garnered significant attention owing to their salient advantages over monometallic nanoparticles. In this study, Fe₂O₃-Mn₂O₃ nanoparticles were synthesized and used as nanomodifiers for polyethersulfone (PES) ultrafiltration membranes. A NIPS was used to fabricate asymmetric membranes. The effect of nanoparticle concentration (0-1 wt.%) on the morphology, roughness, wettability, porosity, permeability, and protein filtration performance of the membranes was investigated. The membrane containing 0.25 wt% nanoparticles exhibited the lowest water contact angle (67°) and surface roughness (10.4 ± 2.8 nm) compared to the other membranes. Moreover, this membrane exhibited the highest porosity (74%) and the highest pure water flux (398 L/m² h), which was 16% and 1.9 times higher than that of the pristine PES membrane. The modified PES membranes showed an improved antifouling ability, especially against irreversible fouling. Bovine serum albumin protein-based dynamic five-cycle filtration tests showed a maximum flux recovery ratio of 77% (cycle-1), 67% (cycle-2), and 65.8% (cycle-5) for the PES membrane containing 0.25 wt% nanoparticles. Overall, the biphasic Fe₂O₃-Mn₂O₃ nanoparticles were found to be an effective nanomodifier for improving the permeability and antifouling ability of PES membranes in protein separation and water treatment applications.

Effects of Benzalkonium Chloride Contents on Structures, Properties, and Ultrafiltration Performances of Chitosan-Based Nanocomposite Membranes

The effects of benzalkonium chloride (BKC) contents on the structure, properties, and ultrafiltration performance of chitosan-based nanocomposite membranes containing poly(ethylene glycol) and multi-walled carbon nanotube (chitosan/BKC/PEG/CNT) were examined. The membranes were prepared by a mixing solution method and phase inversion before being characterized with microscopic techniques, tensile tests, thermogravimetric analysis, water contact angle, and porosity measurements. The performance of the nanocomposite membranes in regard to permeability (flux) and permselectivity (rejection) was examined. The results show that the incorporation of BKC produced nanocomposite membranes with smaller pore structures and improved physico-chemical properties, such as an increase in porosity and surface roughness (Ra = 45.15 to 145.35 nm and Rq = 53.69 to 167.44 nm), an enhancement in the elongation at break from 45 to 109%, and an enhancement in the mechanical strength from 31.2 to 45.8 MPa. In contrast, a decrease in the membrane hydrophilicity (water contact angle increased from 56.3 to 82.8°) and a decrease in the average substructure pore size from 32.64 to 10.08 nm were observed. The membrane rejection performances toward Bovine Serum Albumin (BSA) increased with the BKC composition in both dead-end and cross-flow filtration processes. The chitosan/BKC/PEG/CNT nanocomposite membranes have great potential in wastewater treatments for minimizing biofouling without reducing the water purification performance.

Fabrication of an antifouling PES ultrafiltration membrane via blending SPSF

Sulfonated polysulfone (SPSF) with different sulfonation degrees (10%, 30%, and 50%) was added to polyethersulfone (PES) to improve the separation and antifouling performance of polyethersulfone ultrafiltration membranes. The PES/SPSF blend ultrafiltration membrane was prepared by the non-solvent induced phase inversion method (NIPS), and the effect of sulfonation degree on the ultrafiltration performance was studied. The compatibility of SPSF and PES was calculated by the group contribution method, and confirmed by differential scanning calorimetry (DSC). The morphology and surface roughness of the membrane were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), the chemical composition of the membrane was analyzed by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR), and the permeability and anti-fouling performance of the blend membrane were studied through filtration experiments. The research shows that the flux and anti-fouling performance of the blend membrane have been improved after adding SPSF. When the sulfonation degree of the SPSF is 30%, the pure water flux of the blend membrane can reach 530 L m⁻² h⁻¹, the rejection rate of humic acid (HA) is 93%, the flux recovery rate of HA increases from 69.23% to 79.17%, and the flux recovery rate of BSA increases from 72.56% to 83%.

The chemical structures of (a) PES and (b) SPSF.

Ultrasonic Synthesis of Nanochitosan and Its Size Effects on Turbidity Removal and Dealkalization in Wastewater Treatment

A detailed study on the synthesis of chitosan nanoparticles under ultrasonication is reported in this paper. By using this simple technique, chitosan particles in nanometer range can be easily prepared without using any harmful and expensive chemicals. The results show that increasing the ultrasonic irradiation time and ultrasonic wave amplitude are the key factors for producing discrete chitosan nanoparticles with narrow particle size distribution. The resulting nanoparticles show superior turbidity removal efficiency (75.4%) and dealkalization (58.3%) in wastewater treatment than the bulk chitosan solid (35.4% and 11.1%, respectively), thus offering an eco-friendly and promising approach for treating wastewater via the coagulation/flocculation process.

Waste Reutilization in Polymeric Membrane Fabrication: A New Direction in Membranes for Separation

In parallel to the rapid growth in economic and social activities, there has been an undesirable increase in environmental degradation due to the massively produced and disposed waste. The need to manage waste in a more innovative manner has become an urgent matter. In response to the call for circular economy, some solid wastes can offer plenty of opportunities to be reutilized as raw materials for the fabrication of functional, high-value products. In the context of solid waste-derived polymeric membrane development, this strategy can pave a way to reduce the consumption of conventional feedstock for the production of synthetic polymers and simultaneously to dampen the negative environmental impacts resulting from the improper management of these solid wastes. The review aims to offer a platform for overviewing the potentials of reutilizing solid waste in liquid separation membrane fabrication by covering the important aspects, including waste pretreatment and raw material extraction, membrane fabrication and characterizations, as well as the separation performance evaluation of the resultant membranes. Three major types of waste-derived polymeric raw materials, namely keratin, cellulose, and plastics, are discussed based on the waste origins, limitations in the waste processing, and their conversion into polymeric membranes. With the promising material properties and viability of processing facilities, recycling and reutilization of waste resources for membrane fabrication are deemed to be a promising strategy that can bring about huge benefits in multiple ways, especially to make a step closer to sustainable and green membrane production.

Research and application progress of lignin-based composite membrane

In view of the serious environmental pollution, which is the greatest problem the world is facing, and the continuous consumption of raw materials, it is imminent to search for green and sustainable resources. Lignin is an organic polymer that exists widely in nature, and if it can be transformed from traditional low-value waste product with low range of applications to functional materials with high application prospects, it can be of great significance to alleviate environmental pollution and shortage of fossil resources. One of the functional applications of lignin involves its use to fabricate composite with other polymeric materials, which can then be used to prepare membrane materials. This review summarizes the recent research and application progress of combining lignin with polypropylene, polyvinyl alcohol, starch, cellulose, chitosan, and other polymeric materials to prepare composite membranes; and summarizes the future development direction of lignin-based composite membranes. We hope this review may provide a new perspective to the understanding of lignin-based composite membranes and a useful reference for future research.

Green and sustainable method of manufacturing anti-fouling zwitterionic polymers-modified poly(vinyl chloride) ultrafiltration membranes

The nonsolvent induced phase separation (NIPS) method for ultrafiltration (UF) membrane fabrication relies on the extensive use of traditional solvents, thus ranking first in terms of ecological impacts among all the membrane fabrication steps. Methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean), as a green solvent, was utilized in this study to fabricate poly(vinyl chloride) (PVC) UF membranes. Subsequently, in post-treatment process, zwitterionic polymer, [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS), was grafted onto the membrane surface to enhance its anti-fouling properties using a greener surface-initiated activator regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) reaction. This novel method used low toxicity chemicals, avoiding the environmental hazards of traditional ATRP, and greatly improving the reaction efficiency. We systematically studied the grafting time effect on the resulted membranes using sodium alginate as the foulant, and found that short grafting time (30 min) achieved excellent membrane performance: pure water permeability of 2872 L m^-2 h^-1 bar^-1, flux recovery ratio of 86.4% after 7-hour fouling test, and foulant rejection of 96.0%. This work discusses for the first time the greener procedures with lower environmental impacts in both fabrication and modification processes of PVC UF membranes.

Antifouling and antibacterial behavior of membranes containing quaternary ammonium and zwitterionic polymers

To overcome the organic-/bio- fouling of the membrane, a dual-functional ultrafiltration membrane containing quaternary ammonium and zwitterionic polymers via quaternization and surface radical polymerization was designed, and its antifouling and antibacterial behavior was studied. In this work, poly(vinylidene fluoride)/poly(methyl methacrylate-co-dimethylamino-2-ethyl methacrylate) (PVDF/P(MMA-co-DMAEMA)) blend membrane was quaternized by p-chloromethyl styrene (p-CMS), and the double bonds were introduced onto the membrane surface, which further participated in the polymerization of zwitterionic monomers on the membrane surface. The results indicated that the resultant membrane exhibited obviously improved hydrophilicity and weak positive charge (isoelectric point, 7.49). The membrane presented higher flux recovery ratio and lower protein adhesion compared with the pure PVDF membrane. Meanwhile, the membrane showed high-efficiency broad-spectrum antibacterial performance, that is, the bacteria killing efficiency of S. aureus and E. coli reached 98.2% and 97.0%, respectively. Moreover, the membrane effectively inhibited bacterial adhesion, which is important for the long-term antibacterial properties of membrane. This antifouling and antibacterial PVDF membrane may have potential in the long-term filtration process, especially when dealing with microbiologically contaminated water.

Superhydrophilicity and strong salt-affinity: Zwitterionic polymer grafted surfaces with significant potentials particularly in biological systems

In recent years, zwitterionic polymers have been frequently reported to modify various surfaces to enhance hydrophilicity, antifouling and antibacterial properties, which show significant potentials particularly in biological systems. This review focuses on the fabrication, properties and various applications of zwitterionic polymer grafted surfaces. The "graft-from" and "graft-to" strategies, surface grafting copolymerization and post zwitterionization methods were adopted to graft lots type of the zwitterionic polymers on different inorganic/organic surfaces. The inherent hydrophilicity and salt affinity of the zwitterionic polymers endow the modified surfaces with antifouling, antibacterial and lubricating properties, thus the obtained zwitterionic surfaces show potential applications in biosystems. The zwitterionic polymer grafted membranes or stationary phases can effectively separate plasma, water/oil, ions, biomolecules and polar substrates. The nanomedicines with zwitterionic polymer shells have "stealth" effect in the delivery of encapsulated drugs, siRNA or therapeutic proteins. Moreover, the zwitterionic surfaces can be utilized as wound dressing, self-healing or oil extraction materials. The zwitterionic surfaces are expected as excellent support materials for biosensors, they are facing the severe challenges in the surface protection of marine facilities, and the dense ion pair layers may take unexpected role in shielding the grafted surfaces from strong electromagnetic field.

High-Flux, Antifouling Hydrophilized Ultrafiltration Membranes with Tunable Charge Density Combining Sulfonated Poly(ether sulfone) and Aminated Graphene Oxide Nanohybrid

In this work, a new protocol was developed for creating charge-tuned, hydrophilic hybrid ultrafiltration (UF) membranes with high flux, rejection rate, and fouling resistance. The membranes were fabricated using a combination of sulfonated poly(ether sulfone) (SPES) and aminated graphene (GO-SiO₂-NH₂) nanohybrid via the non-solvent-induced phase separation (NIPS) method. The GO-SiO₂-NH₂ nanohybrid was first synthesized using GO nanosheets and 3-aminopropyl triethoxysilane (APTES) through the covalent condensation reaction at 80 °C and was thoroughly characterized. Then, 2-8 wt% of the nanohybrid was incorporated into the matrix of SPES for the fabrication of the hybrid membranes. The resulting membranes were characterized using an electrokinetic analyzer, a contact angle goniometer, and Raman, field emission scanning electron microscopy-energy-dispersive X-ray spectrometry (FESEM-EDX), and atomic force microscopy experiments. The porosity, charge density, and surface morphology were altered, and the hybrid membranes became more hydrophilic after the incorporation of the nanohybrid. The pure water flux of the hybrid membranes systematically increased with the loading amount of the nanohybrid. The pure water flux of the hybrid membrane containing 6 wt% GO-SiO₂-NH₂ nanohybrid at a 2 bar feed pressure was 537 L m^-2 h^-1, about 3-fold that of pristine membrane (186 L m^-2 h^-1). The fouling resistance of the hybrid membranes was evaluated and confirmed using several representative foulants, including bovine serum albumin, humic acid, sodium alginate, and a synthetic solution of natural organic matter (NOM). The fabricated membranes were capable of removing more than 97% of NOM, without a compromise of their rejection rate.

Electrostatic Adsorption Behavior of Zwitterionic Copolymers on Negatively Charged Surfaces

To investigate the effect of the surface properties and the coating layer properties on surface modification via electrostatic adsorption, the electrostatic adsorption behavior of zwitterionic copolymers on negatively charged surfaces was studied. A series of positively charged zwitterionic copolymers and a series of negatively charged surfaces, including porous substrates and dense films, were fabricated. The electrostatic adsorption behavior of the zwitterionic copolymers on the negatively charged porous substrates was confirmed using the contact angles and fluorescently labeled protein adsorption experiments. The adsorption behavior of the zwitterionic copolymers on the negatively charged dense films was confirmed using quartz crystal microbalance determination and a fluorescently labeled protein adsorption experiment. The results indicated that a lower charge density on the zwitterionic copolymer brings about a higher adsorption mass on the charged surface, whereas an extremely low charge density on the coating layer results in a lower adsorption mass on the charged surface, due to weak interaction. A high density of the film surface charge is beneficial for surface adsorption, whereas an extremely high density of the film surface charge leads to low surface adsorption due to steric hindrance of the negatively charged sites. This work provides an insight into the best strategy for surface modification via electrostatic adsorption.