Antifouling polysulfone ultrafiltration membranes with pendent sulfonamide groups

Increased hydrophilicity of lignin-derivable vs. bisphenol-based polysulfones for potential water filtration applications

The functionality inherent in lignin-derivable aromatics (e.g., polar methoxy groups) can provide a potential opportunity to improve the hydrophilicity of polysulfones (PSfs) without the need for the additional processing steps and harsh reagents/conditions that are typically used in conventional PSf modifications. As determined herein, lignin-derivable PSfs without any post-polymerization modification exhibited higher hydrophilicity than comparable petroleum-based PSfs (commercial/laboratory-synthesized) and also demonstrated similar hydrophilicity to functionalized BPA-PSfs reported in the literature. Importantly, the lignin-derivable PSfs displayed improved thermal properties relative to functionalized BPA-PSfs in the literature, and the thermal properties of these bio-derivable PSfs were close to those of common non-functionalized PSfs. In particular, the glass transition temperature (T g) and degradation temperature of 5% weight loss (T d5%) of lignin-derivable PSfs (T g ∼165-170 °C, T d5% ∼400-425 °C) were significantly higher than those of typical functionalized BPA-PSfs in the literature (T g ∼110-160 °C, T d5% ∼240-260 °C) and close to those of unmodified, commercial/laboratory-synthesized BPA-/bisphenol F-PSfs (T g ∼180-185 °C, T d5% ∼420-510 °C).

MOF@MXene nanocomposite as a novel modifier to extend the application of PES mixed-matrix nanofiltration membranes for water treatment

MXene-based membranes, as a type of modified membrane, have unique structures that attract attention for water treatment but suffer from low water flux. To address this, MXene was manipulated with UiO-66-NH2 nanoparticles to create UiO-66-NH2@MXene 2D-nanocomposites for the modification of the PES membrane. Herein, we synthesized a novel modified MXene-based PES membrane. The MXene, UiO-66-NH2, and UiO-66-NH2@MXene were assessed using the Fourier transform infrared, X-ray diffraction pattern, X-ray photoelectron spectroscopy, and zeta potential analysis. Field emission scanning electron microscopy was used to evaluate the MXene-based materials and prepared membranes, and the surface topography of the fabricated membranes was studied using atomic force microscopy. The membrane modified by 0.25 wt% of modifier was able to not only remove 72% and 81% of methylene blue and crystal violet cationic dyes, but also recorded more than 91% rejections for methyl blue, methyl orange, acid fusion, and Congo red anionic dyes. Using the same membrane, salt rejections of 91%, 87%, 79%, and 62% were achieved for Na2SO4, MgSO4, MgCl2, and NaCl, respectively. Water flux was also increased by more than 4 times in the membrane modified with 0.25 wt% of the novel nanocomposite modifier, and the water contact angle of the membrane with 0.5 wt% decreased from 65° to 38° compared to the pristine PES membrane. Besides, the anti-fouling properties were exceptionally improved in the membranes modified by the introduced UiO-66-NH2@MXene nanocomposite modifier.

Facile Preparation of Dense Polysulfone UF Membranes with Enhanced Salt Rejection by Post-Heating

Polysulfone (PSf) membranes typically have a negligible rejection of salts due to the intrinsic larger pore size and wide pore size distribution. In this work, a facile and scalable heat treatment was proposed to increase the salt rejection. The influence of heat treatment on the structure and performance of PSf membranes was systematically investigated. The average pore size decreased from 9.94 ± 5.5 nm for pristine membranes to 1.18 ± 0.19 nm with the increase in temperature to 50 °C, while the corresponding porosity decreased from 2.07% to 0.13%. Meanwhile, the thickness of the sponge structure decreased from 20.20 to 11.5 μm as the heat treatment temperature increased to 50 °C. The MWCO of PSf decreased from 290,000 Da to 120 Da, whereas the membrane pore size decreased from 5.5 to 0.19 nm. Correspondingly, the water flux decreased from 1545 to 27.24 L·m-2·h-1, while the rejection ratio increased from 3.1% to 74.0% for Na2SO4, from 1.3% to 48.2% for MgSO4, and from 0.6% to 23.8% for NaCl. Meanwhile, mechanism analysis indicated that the water evaporation in the membranes resulted in the shrinkage of the membrane pores and decrease in the average pore size, thus improving the separation performance. In addition, the desalting performance of the heat-treated membranes for real actual industrial wastewater was improved. This provides a facile and scalable route for PSf membrane applications for enhanced desalination.

Designing a novel poly (methyl vinyl ether maleic anhydride) based polymeric membrane with enhanced antifouling performance for removal of pentachlorophenol from aqueous solution

In this current study, poly (methyl vinyl ether maleic anhydride) (PMVEAMA), a sustainable additive, was incorporated into poly (ether-ether sulfone) (PEES) polymer to design a novel polymeric hybrid membrane for the efficient filtration of toxic pentachlorophenol (PCP) from an aqueous medium. Hydrophilic additives significantly altered the membrane's morphology, structure, porosity, water content, and flux performance compared to the bare PEES membrane. The influence of PMVEAMA on the structural modification of the synthesized polymer membrane was confirmed by SEM, ATR-FTIR, XRD, AFM, zeta potential and contact angle. Findings revealed that the addition of PMVEAMA to the PEES polymer enhances the porosity (17.7%-28.9%), water content (29.8%-39.8%), and pure water flux (186 Lm^-2h^-1 to 349 Lm^-2h^-1). The effect of PMVEAMA concentration on the PEES membrane exhibited more finger like pores, better porosity and hydrophilicity, reduced surface roughness, fouling and increased permeability. The fouling studies exhibit an improved 57% PCP rejection and permeation flux of 22.3 Lm^-2h^-1 due to the addition of the hydrophilic additive. Surprisingly, the incorporation of PMVEAMA into the bare PEES membrane resulted in a high flux recovery ratio of 73.7%. The antifouling properties and enhanced permeability of the PEES/PMVEAMA membrane indicates its potential application in water purification sectors for the efficient separation of contaminants.

Next-generation ultrafiltration membranes: A review of material design, properties, recent progress, and challenges

Membrane technology utilizing ultrafiltration (UF) processes has emerged as the most widely used and cost-effective simple process in many industrial applications. The industries like textiles and petroleum refining are promptly required membrane based UF processes to alleviate the potential environmental threat caused by the generation of various wastewater. At the same time, major limitations such as material selection as well as fouling behavior challenge the overall performance of UF membranes, particularly in wastewater treatment. Therefore, a complete discussion on material design with structural property relation and separation performance of UF membranes is always exciting. This state-of-the-art review has exclusively focused on the development of UF membranes, the material design, properties, progress in separation processes, and critical challenges. So far, most of the review articles have examined the UF membrane processes through a selected track of paving typical materials and their limited applications. In contrast, in this review, we have exclusively aimed at comprehensive research from material selection and fabrication methods to all the possible applications of UF membranes, giving more attention and theoretical understanding to the complete development of high-performance UF systems. We have discussed the methodical engineering behind the development of UF membranes regardless of their materials and fabrication mechanisms. Identifying the utility of UF membrane systems in various applications, as well as their mode of separation processes, has been well discussed. Overall, the current review conveys the knowledge of the present-day significance of UF membranes together with their future prospective opportunities whilst overcoming known difficulties in many potential applications.

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.

A Biofouling Resistant Zwitterionic Polysulfone Membrane Prepared by a Dual-Bath Procedure

This study introduces a zwitterionic material to modify polysulfone (PSf) membranes formed by a dual bath procedure, in view of reducing their fouling propensity. The zwitterionic copolymer, derived from a random polymer of styrene and 4-vinylpyrridine and referred to as zP(S-r-4VP), was incorporated to the PSf solution without any supplementary pore-forming additive to study the effect of the sole copolymer on membrane-structuring, chemical, and arising properties. XPS and mapping FT-IR provided evidence of the modification. Macrovoids appeared and then disappeared as the copolymer content increased in the range 1-4 wt%. The copolymer has hydrophilic units and its addition increases the casting solution viscosity. Both effects play an opposite role on transfers, and so on the growth of macrovoids. Biofouling tests demonstrated the efficiency of the copolymer to mitigate biofouling with a reduction in bacterial and blood cell attachment by more than 85%. Filtration tests revealed that the permeability increased by a twofold factor, the flux recovery ratio was augmented from 40% to 63% after water/BSA cycles, and irreversible fouling was reduced by 1/3. Although improvements are needed, these zwitterionic PSf membranes could be used in biomedical applications where resistance to biofouling by cells is a requirement.

Preparation of Low-Lactose Milk Powder by Coupling Membrane Technology

Due to lactose intolerance, there is a growing need for lactose-free or low-lactose dairy products. Herein, a combination of three membrane technologies (UF, electrodialysis (ED), and nanofiltration (NF)) was used as a novel green technology to replace the enzymatic preparation of low-lactose milk powder in the traditional industry. In which, large molecules such as proteins and fats are first retained using UF, mineral salt was intercepted and re-added into milk by electrodialysis, and finally, lactose is recovered by NF. Finally, low-lactose milk powder with a lactose content of less than 0.2% was obtained; meanwhile, the high purity (95.7%) of lactose powder could be effectively reclaimed from the NF concentrate (lactose concentrate). The whole membrane process is based on the physical pore size screening mechanism, without adding any chemical reagents with minimal impact on the physical and chemical properties of milk. These results indicate that process development and optimization coupling of three membrane technologies is very promising in preparing low-lactose milk powder and recovering lactose.

Preparation of a novel zwitterionic striped surface thin-film composite nanofiltration membrane with excellent salt separation performance and antifouling property

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the co-deposition of taurine, tannic acid (TA), and polyethyleneimine (PEI), followed by subsequent interfacial polymerization with trimesoyl chloride (TMC) on the surface of the polysulfone ultrafiltration substrates. The surface properties, including the roughness, hydrophilicity, surface potential, and NF performances were facilely tuned by varying the taurine content for the prepared TFC membranes. In addition, the as-prepared TFC NF membranes had an excellent antifouling property and flux recovery ratio (FRR) in humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA) filtration tests. These results also revealed that the taurine content controlled the formation of the striped surface. Thus, this work provided a viable strategy for fabricating TFC NF membranes with high selectivity and outstanding antifouling ability.

Thin-film composite (TFC) nanofiltration (NF) membranes with zwitterionic striped surface were fabricated via the co-deposition and interfacial polymerization.

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.

Amphiphilic Block Copolymer of Poly(dimethylsiloxane) and Methoxypolyethylene Glycols for High-Permeable Polysulfone Membrane Preparation

Poly(dimethylsiloxane)-block-methoxypolyethylene glycols (PDMS-b-mPEG) were synthesized by Steglich esterification. The high-permeable membrane (PSf/PDMS-b-mPEG) was prepared by using PDMS-b-mPEG as additives. The successful synthesis of PDMS-b-mPEG was confirmed by nuclear magnetic resonance. Field emission scanning electron microscopy images show that the distribution of finger-like macroporous and sponge-like macroporous can be modulated by controlling the ratio of the hydrophilic/hydrophobic components of additives. The distribution of additives and membrane wettability are validated with X-ray photoelectron spectroscopy and water contact angle test. The permeability of the blended membrane, especially for the membrane PSf/PDMS-b-mPEG1900 (M3), was remarkably improved. The water permeability of M3 (239.4 L/m²·h·bar) was 6.6 times that of the unblended membrane M0 (42.5 L/m²·h·bar). The findings of protein BSA filtration show that the flux recovery ratio of M3 is 89.2% at a BSA retention rate of about 80%, which demonstrates that the polysulfone membranes blended with PDMS-b-mPEG have excellent antifouling performance and extraordinary permeability.