Factors affecting the sieving behavior of anti-fouling thin-layer cross-linked hydrogel polyethersulfone composite ultrafiltration membranes

Advances in Membrane Separation for Biomaterial Dewatering

Biomaterials often contain large quantities of water (50-98%), and with the current transition to a more biobased economy, drying these materials will become increasingly important. Contrary to the standard, thermodynamically inefficient chemical and thermal drying methods, dewatering by membrane separation will provide a sustainable and efficient alternative. However, biomaterials can easily foul membrane surfaces, which is detrimental to the performance of current membrane separations. Improving the antifouling properties of such membranes is a key challenge. Other recent research has been dedicated to enhancing the permeate flux and selectivity. In this review, we present a comprehensive overview of the design requirements for and recent advances in dewatering of biomaterials using membranes. These recent developments offer a viable solution to the challenges of fouling and suboptimal performances. We focus on two emerging development strategies, which are the use of electric-field-assisted dewatering and surface functionalizations, in particular with hydrogels. Our overview concludes with a critical mention of the remaining challenges and possible research directions within these subfields.

Efficient removal of bovine serum albumin from water by cellulose acetate membranes modified with clay and titania nano particles

Modified cellulose acetate membranes with bentonite clay (CA/bent) and TiO₂ nanoparticles (CA/TiO₂) using the phase inversion method are successfully prepared and characterized. These Membranes are favored due to their high salt rejection properties and recyclability. The IR and EDX spectral data indicate the formation of modified membranes. The Scan Electron Microscope micrographs show that the modified membranes have smaller particle sizes with higher porosity than the neat membrane. The average pore diameter is 0.31 µm for neat cellulose acetate membrane (CA) and decreases to 0.1 µm for CA/0.05bent. All modified membranes exhibit tensile strengths and elongation percentages more than the neat membrane. The higher tensile strength and the maximum elongation% are 15.3 N/cm² and 11.78%, respectively, for CA/0.05bent. The thermogravimetric analysis of modified membranes shows higher thermal stability than the neat membrane. The modified membranes exhibit enhanced wettability and hydrophilicity compared with cellulose acetate, by measuring the contact angle which decreases from 60° (CA) to 40° (CA/0.1bent). The ultrafiltration tests indicated that the CA/bent and CA/TiO₂ are better than CA. The most efficient nanocomposite membrane is CA/0.05bent with 100% removal of (BSA) from industrial water with a flux equal to 9.5 mL/min under an applied pressure of 20 bar. Thus, this study introduces a novel ultrafiltration membrane (CA/0.05bent) that can be used effectively to completely remove bovine serum albumin from contaminated water.

Thermoresponsive Microgel-Based Free-Standing Membranes: Influence of Different Microgel Cross-Linkers on Membrane Function

In this study we show a possibility to produce thermoresponsive, free-standing microgel membranes based on N-isopropylacrylamide (NIPAM) and the UV-sensitive comonomer 2-hydroxy-4-(methacryloyloxy)benzophenone (HMABP). To influence the final network structure and functionality of the membranes, we use different cross-linkers in the microgel syntheses and characterize the resulting structural microgel properties and the swelling behavior by means of AFM, FTIR, and PCS measurements. Varying the cross-linker results in significant changes in the structure and swelling behavior of the individual microgels and has an influence on the incorporation of the comonomer, which is essential for subsequent photochemical membrane formation. We investigate the ion transport through the different membranes by temperature-dependent resistance measurements revealing a sharp increase in resistance when the copolymer microgels reach their collapsed state. The resistance of the membranes can be adjusted by different cross-linkers and the associated incorporation of the comonomer. Furthermore, we show that transferring a reversible cross-linker from a cross-linked state to an un-cross-linked state strongly influences the membrane properties and even reverses the switching behavior, while the mechanical stability of the membrane is maintained.

Antiviral Nanomaterials for Designing Mixed Matrix Membranes

Membranes are helpful tools to prevent airborne and waterborne pathogenic microorganisms, including viruses and bacteria. A membrane filter can physically separate pathogens from air or water. Moreover, incorporating antiviral and antibacterial nanoparticles into the matrix of membrane filters can render composite structures capable of killing pathogenic viruses and bacteria. Such membranes incorporated with antiviral and antibacterial nanoparticles have a great potential for being applied in various application scenarios. Therefore, in this perspective article, we attempt to explore the fundamental mechanisms and recent progress of designing antiviral membrane filters, challenges to be addressed, and outlook.

2D MoS2 nanoplatelets for fouling resistant membrane surface

2D Molybdenum disulfide (MoS₂) nanoplatelets were synthesized via a green bottom-up strategy using non-toxic l-Cysteine as sulfur source. Thehydrophobic MoS₂ nanoplatelets assisted by hydrophilic 3-(3, 4-dihydroxyphenyl)-l-alanine (l-DOPA) were coated on a thin film composite nanofiltration (TFC-NFG) membrane. The accelerated fouling experiments were conducted by usingbovine serum albumin (BSA) asmodel organic foulant,and MoS₂ coated membrane demonstrated excellent resistance with almost no flux decline within first hour of filtration, whereas the uncoated membrane showed flux decline immediately from the beginning of the experiment. After 5-hour filtration, the flux reduced by only 26% for MoS₂ coated membrane with a higher flux recovery rate of 85.4% after washing by de-ionized (DI) water, whereas 45% flux decline was observed for uncoated membrane with lower flux recovery of 68%.These antifouling effects attributed by MoS₂coated membrane were underpinned by combined unique interfacial properties offered by 2D tri-atomic layered MoS₂morphology including dispersive surface tension, reduced surface roughness, weaker MoS₂-foulant interactive forces, and negatively charged surface. This research positively confirms the role of 2D MoS₂ nanoplatelets as an anti-fouling coating on membranes and brings up more possibility for applying other nanomaterials in 2D family in water applications such as desalination and water treatment.

Antifouling Membranes Prepared from Polyethersulfone Grafted with Poly(ethylene glycol) Methacrylate by Radiation-Induced Copolymerization in Homogeneous Solution

To synthesize evenly grafted copolymers, gamma radiation of homogeneous solutions was employed to graft poly(ethylene glycol) methacrylate (PEGMA) onto polyethersulfone (PES). The grafting was verified by Fourier transform infrared spectroscopy, and the degrees of grafting (DGs) were determined by elementary analysis. The PES-g-polyPEGMA copolymers with different DGs were obtained by changing the monomer concentration. Membranes were cast from pristine PES, PES/PEG blends, and PES-g-polyPEGMA with different DGs, respectively, via nonsolvent-induced phase separation. Results from water contact angle measurements and scanning electron microscopy analysis indicated that increasing DGs led to PES-g-polyPEGMA membranes with increasing hydrophilicity and porousness. Filtration experimental results showed that increasing DGs without adding pore-forming agents caused PES-g-polyPEGMA membranes with higher permeability. Compared with PES/PEG membranes with analogous permeation characteristics, in which PEG is added as a pore-forming agent, PES-g-polyPEGMA membranes exhibited superior antifouling properties.

Advanced Treatment of Real Grey Water by SBR Followed by Ultrafiltration—Performance and Fouling Behavior

Grey water has been identified as a potential source of water in a number of applications e.g., toilet flushing, laundering in first rinsing, floor cleaning, and irrigation. The major obstacle to the reuse of grey water relates to pathogens, nutrients, and organic matter found in grey water. Therefore, much effort has been put to treat grey water, in order to yield high-quality water deprived of bacteria and with an appropriate value in a wide range of quality parameters (Total Organic Carbon (TOC), nitrate, phosphate, ammonium, pH, and absorbance), similar to the values for tap water. The aim of this study was to treat the real grey water, and turn it into high-quality, safe water. For this purpose, the real grey water was treated by means of a sequential biological reactor (SBR) followed by ultrafiltration. Initially, grey water was treated in a laboratory SBR reactor with a capacity of 3 L, operated in a 24 h cycle. Then, SBR effluent was purified in a cross-flow ultrafiltration setup. Treatment efficiency in SBR and ultrafiltration was assessed using extended physicochemical and microbiological analyses (pH, conductivity, color, absorbance, Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD5), nitrate, phosphate, ammonium, total nitrogen, phenol index, nonionic and anionic surfactants, TOC, Escherichia coli, and enterococci). Additionally, ultrafiltration was evaluated in terms of fouling behavior for three polymer membranes with different MWCO (molecular weight cut-off). The values of quality parameters (pH, conductivity, COD, BOD5, TOC, N-NH4+, N-NO3−, Ntot, and P-PO43−) measured in SBR effluent did not exceed permissible values for wastewater discharged to soil and water. Ultrafiltration provided the high-quality water with very low values of COD (5.8–18.1 mg/L), TOC (0.47–2.19 mg/L), absorbanceUV254 (0.015–0.048 1/cm), color (10–29 mgPt/L) and concentration of nitrate (0.18–0.56 mg/L), phosphate (0.9–2.1 mg/L), ammonium (0.03–0.11 mg/L), and total nitrogen (3.3–4.7 mg/L) as well as lack of E. coli and enterococci. Membrane structural and surface properties did not affect the treatment efficiency, but did influence the fouling behavior.

Radical polymerization as a versatile tool for surface grafting of thin hydrogel films

The surface of solid substrates is the main part that interacts with the environment.

Nano/microplastics in water and wastewater treatment processes - Origin, impact and potential solutions

The presence of nano and microplastics in water has increasingly become a major environmental challenge. A key challenge in their detection resides in the relatively inadequate analytical techniques available preventing deep understanding of the fate of nano/microplastics in water. The occurrence of nano/microplastics in water and wastewater treatment plants poses a concern for the quality of the treated water. Due to their broad but small size and diverse chemical natures, nano/microplastics may travel easily along water and wastewater treatment processes infiltrating remediation processes at various levels, representing operational and process stability challenges. This review aims at presenting the current understanding of the fate and impact of nano/microplastics through water and wastewater treatment plants. The formation and fragmentation mechanisms, physical-chemical properties and occurrence of nano/microplastics in water are correlated to the interactions of nano/microplastics with water and wastewater treatment plant processes and potential solutions to limit these interactions are comprehensively reviewed. This critical analysis offers new strategies to limit the number of nano/microplastics in water and wastewater to keep water quality up to the required standards and reduce threats on our ecosystems.

A substrate-independent ultrathin hydrogel film as an antifouling and antibacterial layer for a microfiltration membrane anchored via a layer-by-layer thiol-ene click reaction

Herein, a substrate-independent ultrathin hydrogel film was constructed on a microfiltration membrane through layer-by-layer (LbL) thiol-ene click chemistry to improve the antifouling and antibacterial properties. In our strategy, ene-functionalized dopamine was synthesized and coated onto a model substrate (polyethersulfone membrane) to introduce double bonds as anchoring sites for the hydrogel film; thiol-functionalized poly[oligo(ethylene glycol)mercaptosuccinate] (POEGMS) and ene-functionalized P(SBMA-co-AA) were synthesized as hydrogel precursors. The membrane was alternately immersed in the precursor solutions to form the ultrathin hydrogel film. Finally, Ag nanoparticles (AgNPs) were loaded into the hydrogel layer by adsorption and reduction procedures. By coating the hydrogel films, the loaded AgNPs could kill almost all the contacting bacteria and the bacteria in the surroundings, and the enhanced hydrophilicity of the modified membrane could effectively prevent the attachment of the bacteria. The membrane flux showed no significant decrease, the rejection ratio of BSA increased from 51% to 89%, and the F_RR increased from 36% to 90%. Moreover, the improvement of the hemocompatibility was confirmed by the decline in the plasma protein adsorption, prolonged clotting times, low hemolysis ratio, and prevention of platelet adhesion. Compared with that of other techniques for attaching hydrogel films, the main advantage of the current technique is that the hydrogel film thickness could be well controlled within the nanometer range; thus, it could significantly improve the antifouling and antibacterial properties of the membrane, but without compromising its permeability. Another advantage is that it is versatile for various substrates such as PVDF, PAN, and CA. This study opens up a facile and versatile route for anchoring ultrathin hydrogel film onto polymeric membranes to achieve excellent antifouling, antibacterial and hemocompatible properties.

Self-Healing Hydrogel Pore-Filled Water Filtration Membranes

Damages to water filtration membranes during installation and operation are known to cause detrimental loss of the product water quality. Membranes that have the ability to self-heal would recover their original rejection levels autonomously, bypassing the need for costly integrity monitoring and membrane replacement practices. Herein, we fabricated hydrogel pore-filled membranes via in situ graft polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto microporous poly(ether sulfone) (PES) substrates and successfully demonstrated their self-healing ability. Covalent attachment of the hydrogel to the substrate was essential for stable membrane performance. The membranes autonomously restore their particle rejection up to 99% from rejection levels as low as 30% after being physically damaged. We attribute the observed self-healing property to swelling of the pore-filling hydrogel into the damage site, strong hydrogen bonding, and molecular interdiffusion. The results of this study show that hydrogel pore-filled membranes are a promising new class of materials for fabricating self-healing membranes.

Highly fouling-resistant brominated poly(phenylene oxide) membranes using surface grafted diethylenetriamine

Composite BPPO/DETA ultrafiltration membranes show decreased membrane fouling and enhanced protein rejection with very high flux recovery ratios.

Decoration of heparin and bovine serum albumin on polysulfone membrane assisted via polydopamine strategy for hemodialysis

Renal failure brings about abnormality of waste and toxins and deposition in the body. In clinic, the waste and toxins in vitro are eliminated by hemodialysis device with polysulfone (PSF) porous membranes. In the work, decoration of heparin (Hep) and bovine serum albumin (BSA) on PSF membranes would be beneficial to improve the hemocompatibility and reduce the anaphylatoxin formation during hemodialysis. The PSF porous membranes are surface-modified by simply dipping them into dopamine aqueous solution for 8 h. Then, Hep and BSA are immobilized covalently onto the resultant membrane. Attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR) confirms that Hep and BSA are successfully introduced onto the surface of PSF membranes. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) display the changes of surface morphologies after modification. The result of water contact angle measurement shows that the hydrophilicity of PSF membranes is remarkably improved after coating polydopamine (pDA) and binding Hep and BSA. The experiments of hemocompatibility indicate that Hep and BSA grafted onto membranes suppress the adhesion of platelet and enhance the anticoagulation ability of PSF membranes. Furthermore, the protein adsorption tests reveal that Hep and BSA immobilized onto membranes depress the protein absorption and develop antifouling-protein ability of pristine membrane. This study proves a convenient and simple approach to graft two functional organic polymers which, respectively, play a vital role and then improve the hemocompatibility and biocompatibility of PSF membranes for their biomedical and blood-contacting applications.

Nanoporous block copolymer membranes for ultrafiltration: a simple approach to size tunability

Nanoporous structures were obtained by the self-assembly of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymers (BCP) where, in thick films, cylindrical microdomains were oriented normal to the substrate and air interfaces, and in the interior of the films, the microdomains were randomly oriented. Continuous nanopores that penetrated through the film were readily produced by a simple preferential swelling of the PMMA microdomains. The confined swelling and rapid contraction of PMMA microdomains generated well-defined uniform pores with diameters to 17.5 nm. The size selectivity and rejection of Au nanoparticles (NPs) for these ultrafiltration (UF) membranes were demonstrated, suggesting an efficient route to tunable, noncomponent-degradative UF membranes.