Rational design of phase inversion membranes by tailoring thermodynamics and kinetics of casting solution using polymer additives

Analysis of Metal-Organic Framework and Polyamide Interfaces in Membranes for Water Treatment and Antibacterial Applications

Integrating biocidal nanoparticles (NPs) into polyamide (PA) membranes shows promise for enhancing resistance to biofouling. Incorporating techniques can tailor thin-film nanocomposite (TFN) membranes for specific water purification applications. In this study, silver-based metal-organic framework Ag-MOFs (using silver nitrate and 1,3,5-benzentricarboxylic acid as precursors) are incorporated into PA membranes via three different methods: i) incorporation, ii) dip-coating, and iii) in situ ultrasonic techniques. The characterizations, such as top-surface and cross-section scanning and transmission microscopy, reveal that the incorporation methods for the modified TFN membranes substantially control morphology and surface characteristics. For example, the in situ ultrasonically interlayered Ag-MOFs showed the largest pores (average pore diameter of 14 Å ± 0.1), resulting in the highest water permeance (water flux of 10.9 LMH/bar for Na2SO4). It also show superior antifouling and anti-biofouling performance, with a flux recovery ratio (FRR) of 94.1% in both fouling tests due to its improved surface hydrophilicity and the antibacterial properties of incorporated Ag-MOFs. Conversely, the surface-grafted dip-coated Ag-MOFs offered the highest salt rejection, attributed to its highly negatively charged surface and a dense PA network with narrow pores (average pore diameter of 10 Å ± 0.06).

Conversion of waste PET bottles into supported ionic liquid membranes for heavy metal separation from wastewater

Plastic waste poses a significant and persistent environmental challenge, creating a division between producers and consumers. Addressing this issue requires exploring various techniques, including thermal processing, landfilling, and recycling. Plastic waste recycling, a complex approach, depends on particle size, location, and source material. This study focuses on recycling plastic waste bottles made of polyethylene terephthalate (PET). The phase inversion method converts discarded PET bottles into polymeric membranes. Subsequently, the performance of the membrane is enhanced by infusing ionic liquid into its pores. The modified membrane, referred to as a supported ionic liquid membrane (SILM), was subsequently employed for the removal of heavy metal contaminants, specifically Pb (II), Cd (II), and As (V), within a specially designed H-cell system. The H-cell setup includes feed and stripping phase compartments, separated by the modified membrane. Metal ion separation efficiency is evaluated under varying operating conditions, including carrier concentration, feed phase concentration, stripping phase concentration, stirring rate, and temperature. Removal efficiency is optimized using the Box-Behnken design in response surface methodology. After optimizing the parameters of the modified plastic waste membrane, exceptional removal efficiencies are attained, with removal rates exceeding 95% for Pb (II), 88% for Cd (II), and 78% for As (V). This study highlights the potential of recycled PET plastic waste as a valuable resource for developing highly efficient and sustainable membranes for heavy metal removal.

Polyethersulfone mixed matrix membranes modified with pore formers and Ag-titanate nanotubes: physicochemical characteristics and (bio)fouling study

In the presented studies it was hypothesized that the modification of a polymeric membrane with a pore former and a hybrid nanomaterial composed of titanate nanotubes with deposited Ag nanoparticles (Ag-TNTs NPs) can protect the membrane from the microbial growth, and thus enhance its resistance to biofouling. Polyethersulfone (PES) membranes were prepared by the wet phase inversion, and polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) were used as pore formers. The membranes were characterized in terms of morphology, topography, permeability, separation characteristics, and anti-(bio)fouling properties as well as antibacterial activity. The membranes modified with porogens and Ag-TNTs revealed improved hydrophilicity and water permeability compared to the unmodified membrane, from 58 to 66%. Moreover, the improvement in rejection of model dextrans and PEG upon application of the NPs was found. However, the use of PVP or PEG had a negative influence on the resistance to fouling by bovine serum albumin, i.e., ca. 35% of decline of permeate flux was noticed after 2 h of ultrafiltration of BSA. On the contrary, both porogens and NPs contributed to biofouling mitigation. The introduction of pore formers had a positive effect on the inhibition of Escherichia coli growth by the membrane containing Ag-TNTs. The log reduction of bacteria varied from 3.17 to 3.3 in case of stirred and filtration system.

Tailoring the characteristics of polyacrylonitrile nanofiltration membranes for nickel removal from wastewater: The influence of binary solvents and pore-forming agents

This work presents the results of an investigation on the physiochemical and structural characteristics of polyacrylonitrile (PAN) nanofiltration (NF) membranes prepared using a novel concept of binary solvents for nickel (Ni) removal from wastewater streams. The thermodynamic and kinetic aspects are emphasized aiming to optimize dope formulation, membrane performance, and durability. The fabricated membranes were characterized by scanning electron microscopy (SEM), porosimetry, tensile stress/strain, and flux and rejection. Results revealed that the use of an equal (1:1) mixture of n-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) as dope solvents led to the formation of membranes with enhanced performance, offering pure water flux of 2.33 L·m-2·h-1·bar-1 and Ni rejection of 90.84%. Moreover, the incorporation of 0.5 wt.% PEG as a pore-forming agent to the dope solution further boosted pure water flux to 4.97 L·m-2·h-1·bar-1 with negligible impact on Ni rejection. Besides attractive performance, the adopted strategy offered membranes of exceptionally high flexibility with no sign of defect or failure especially during module fabrication and testing enabling smooth and hassle-free scale-up and extension to other applications. PRACTITIONER POINTS: Optimized solvent mixture: A 1:1 blend of n-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) as solvents resulted in enhanced membrane performance. High flux and Ni rejection: The fabricated membranes exhibited a pure water flux of 2.33 L·m-2·h-1·bar-1 and a remarkable Ni rejection of 90.84%. PEG enhancement: Incorporating 0.5 wt.% PEG as a pore-forming agent further improved the membrane's pure water flux to 4.97 L·m-2·h-1·bar-1, without compromising Ni rejection. Exceptional flexibility: The adopted strategy yielded membranes with exceptional flexibility, making them suitable for scale-ups and other applications.

Morphology and Thermodynamic Study of a Novel Composite Membrane from Waste Polystyrene/Slag: Experimental Investigation

The development of the membrane surface and cross-sectional morphology is pivotal in influencing the effectiveness of membrane separation. In this study, evaluating the separation rates between the solvent and nonsolvent in the casting solution and the related thermodynamic alteration analysis were illustrated. Additionally, the rheological variations were determined by measuring the viscosity of the resulting dope solutions, providing an initial estimation of the phase separation kinetics. Asymmetric polystyrene (PS)/slag composite membrane, incorporating slag waste as an inorganic additive, was developed. Dimethylformamide (DMF) was utilized as the solvent, and sodium dodecyl sulfate (SDS) was employed as an anionic surfactant to facilitate the casting process. A tertiary system diagram approach involving waste PS, DMF, and water introducing slag as an inorganic additive and SDS as a surfactant was attained to promote the separation of the solvent and nonsolvent in the casting solution. These novel composite mixtures exhibited increased thermodynamic instability within the coagulation bath, facilitating the rapid separation of solid membranes from the dope solutions and forming composite membranes with significantly increased porosity (exceeding a 20% increase) compared to that of plain waste materials. The composite membrane characteristics were assessed with the widely used poly(vinylidene difluoride) (PVDF) membrane, showing comparative features and performance when tested on a membrane distillation (MD) cell; it gave a flux of 1 kg/m2·h. These promising characteristics positioned this novel PS/slag composite membrane as a candidate for various water-related applications.

From environmental issue to purification aid: Novel positively charged functionalized algal biochar as robust modifier of composite nanofiltration membranes

Robust membrane modifiers were achieved for the first time by functionalizing the algal biochar of unique porous structure. The biochar was prepared through the pyrolysis of Cladophora glomerata, the most widespread freshwater macroalga, functionalized by diethylenetriamine and dendrimer poly(amidoamine), and employed to fabricate positively charged composite nanofiltration membranes. The presence of hydrophilic functionalizers of positive charge on the membrane was verified through Fourier transform infrared and energy dispersive X-ray analyses and atomic force microscopy and zeta potential measurements were performed to determine surface roughness and confirm positive charge of the modified membranes. Dispersion of modifiers on the surface and morphology of the were also revealed through field-emission scanning electron microscopy images. It has shown that, compared to the pristine membrane, pure water fluxes were increased by 214% and 185%, and water contact angles were reduced from 66.1° to 39.5° and 43.3° in those modified by biochar functionalized with dendrimer poly(amidoamine) and diethylenetriamine, respectively. More than 90% dye rejections and salt and heavy metals removals were recorded for the membranes possessed 0.6 wt% of modifiers. Finally, a comparative study conducted between the novel modifier introduced in this study and those reported in the literature, indicated that C. glomerata biochar decorated with amine functional groups could be considered as a robust and practical alternative to the common modifiers used to manipulate nanocomposite membranes characteristics.

Influence of citric acid concentrations on the porosity and performance of cellulose acetate-based porous membranes: A comprehensive study

This study investigates the influence of citric acid concentration on the fabrication of porous cellulose acetate (CA) membranes using the Non-Solvent Induced Phase Separation (NIPS) method. A notable aspect is the precise control over membrane properties, particularly pore size and porosity, achieved solely through the adjustment of citric acid concentration, serving as the additive. Higher concentrations of citric acid increase pore size by rendering polymer chains more pliable, whereas lower concentrations lead to smaller, denser pores due to improved dispersion in the CA matrix and altered water interactions during phase separation. A decrease in porosity and Gurley values with reducing citric acid concentrations (from 5 × 10-2 to 1 × 10-3 M ratios) indicates less plasticization of CA chains. However, at very low concentrations (1 × 10-4 and 1 × 10-5), porosity increases, despite the presence of smaller pores, and Gurley values approach those of pure CA in terms of gas permeability. Fourier Transform Infrared (FT-IR) spectroscopy confirms the presence of citric acid and its interaction with carbonyl groups, consistent with the pore size observations from Scanning Electron Microscopy (SEM). Spectral data deconvolution reveals weakened carbonyl bonds due to the reduced presence of citric acid, correlating with the smaller pores observed in SEM. Thermal Gravimetric Analysis (TGA) demonstrates that composite membranes are more thermally stable than pure CA, attributed to the citric acid-induced crosslinking within the polymer chains. Stability increases with decreasing citric acid concentration, with some anomalies at the lowest levels. In conclusion, this study highlights the capability of adjusting citric acid concentration to tailor membrane properties, offering valuable insights for the creation of porous materials across diverse industrial applications.

Novel partially cross-linked nanoparticles graft co-polymer as pore former for polyethersulfone membranes for dyes removal

A newly developed water-soluble polymeric nano-additive termed "partially cross-linked nanoparticles graft copolymer (PCLNPG)" has been successfully synthesized and harnessed as a pore former for modifying a polyethersulfone ultrafiltration membrane for dyes removal. The PCLNPG content was varied in the PES polymeric matrix aiming to scrutinize its impact on membrane surface characteristics, morphological structure, and overall performance. Proposed interaction mechanism between methylene blue (MB), methyle orange (MO), and malachite green (MG) dyes with PES membrane was presented as well. Hydrophilicity and porosity of the novel membrane increased by 18 and 17 %, respectively, when manufactured with a 3 Wt. % PCLNPG, according to the findings. Besides this, the disclosed increased porosity, rather than the hydrophilic properties of the water-soluble PCLNPG, was the principal cause of the diminished contact angle. Meanwhile, raising the PCLNPG content in the prepared membrane made worthy shifts in its structure. A sponge-like region was materialized near the bottom surface as well. The membrane's pure water flux (PWF) synthesized with 3 Wt.% PCLNPG recorded 628 LMH, which is estimated 3.95 fold the pristine membrane. MG, MB, and MO dyes were rejected by 90.6, 96.3, and 97.87 %, respectively. These findings showed that the performance characteristics of the PES/PCLNPG membrane make it a potentially advantageous option to treat the textile wastewater.

Thermodynamics and kinetic analysis of membrane: Challenges and perspectives

The ultimate structure of the membrane is determined using two important effects: (i) thermodynamic effect and (ii) kinetic effect. Controlling the mechanism of kinetic and thermodynamic processes in phase separation is essential for enhancing membrane performance. However, the relationship between system parameters and the ultimate membrane morphology is still largely empirical. This review focuses on the fundamental ideas behind thermally induced phase separation (TIPS) and nonsolvent-induced phase separation (NIPS) methods, including both kinetic and thermodynamic elements. The thermodynamic approach to understanding phase separation and the effect of different interaction parameters on membrane morphology has been discussed in detail. Furthermore, this review explores the capabilities and limitations of different macroscopic transport models used for the last four decades to explore the phase inversion process. The application of molecular simulations and phase field to understand phase separation has also been briefly examined. Finally, it discusses the thermodynamic approach to understanding phase separation and the consequence of different interaction parameters on membrane morphology, as well as possible directions for artificial intelligence to fill the gaps in the literature. This review aims to provide comprehensive knowledge and motivation for future modeling work for membrane fabrication via new techniques such as nonsolvent-TIPS, complex-TIPS, non-solvent assisted TIPS, combined NIPS-TIPS method, and mixed solvent phase separation.

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.

Scale Design of Dual-Layer Polyphenylsulfone/Sulfonated Polyphenylsulfone Hollow Fiber Membranes for Nanofiltration

This study focuses on the synthesis and characterization of dual-layer sulfonated polyphenylenesulfone (SPPSu) nanocomposite hollow fiber nanofiltration membranes incorporating titanium dioxide (TiO2) nanoparticles through the phase inversion technique. Advanced tools and methods were employed to systematically evaluate the properties and performance of the newly developed membranes. The investigation primarily centered on the impact of TiO2 addition in the SPPSu inner layer on pure water permeability and salt rejection. The nanocomposite membranes exhibited a remarkable three-fold increase in pure water permeability, achieving a flux of 5.4 L/m2h.bar compared to pristine membranes. The addition of TiO2 also enhanced the mechanical properties, with an expected tensile strength increase from 2.4 to 3.9 MPa. An evaluation of salt rejection performance using a laboratory-scale filtration setup revealed a maximal rejection of 95% for Mg2SO4, indicating the effective separation capabilities of the modified dual-layer hollow fiber nanocomposite membranes for divalent ions. The successful synthesis and characterization of these membranes highlight their potential for nanofiltration processes, specifically in selectively separating divalent ions from aqueous solutions, owing to their improved pure water flux, mechanical strength, and salt rejection performance.

The Effect of Non-Solvent Nature on the Rheological Properties of Cellulose Solution in Diluted Ionic Liquid and Performance of Nanofiltration Membranes

The weak point of ionic liquids is their high viscosity, limiting the maximum polymer concentration in the forming solutions. A low-viscous co-solvent can reduce viscosity, but cellulose has none. This study demonstrates that dimethyl sulfoxide (DMSO), being non-solvent for cellulose, can act as a nominal co-solvent to improve its processing into a nanofiltration membrane by phase inversion. A study of the rheology of cellulose solutions in diluted ionic liquids ([EMIM]Ac, [EMIM]Cl, and [BMIM]Ac) containing up to 75% DMSO showed the possibility of decreasing the viscosity by up to 50 times while keeping the same cellulose concentration. Surprisingly, typical cellulose non-solvents (water, methanol, ethanol, and isopropanol) behave similarly, reducing the viscosity at low doses but causing structuring of the cellulose solution and its phase separation at high concentrations. According to laser interferometry, the nature of these non-solvents affects the mass transfer direction relative to the forming membrane and the substance interdiffusion rate, which increases by four-fold when passing from isopropanol to methanol or water. Examination of the nanofiltration characteristics of the obtained membranes showed that the dilution of ionic liquid enhances the rejection without changing the permeability, while the transition to alcohols increases the permeability while maintaining the rejection.

Printability of Poly(lactic acid) Ink by Embedded 3D Printing via Immersion Precipitation

Immersion precipitation three-dimensional printing (ip3DP) and freeform polymer precipitation (FPP) are unique and versatile methods of 3D printing to fabricate 3D structures based on nonsolvent-induced phase separation via direct ink writing (DIW). Immersion precipitation involves complex dynamics among solvents, nonsolvents, and dissolved polymers, and the printability of 3D models in these methods requires further understanding. To this end, we characterized these two methods of 3D printing using polylactide (PLA) dissolved in dichloromethane (7.5-30% w/w) as model inks. We analyzed the rheological properties of the solutions and the effect of printing parameters on solvent-nonsolvent diffusion to achieve printability. The PLA inks exhibited shear-thinning properties, and their viscosities varied over three orders of magnitude (10^-1∼10² Pa·s). A processing map was presented to understand the ideal ranges of the concentration of PLA in inks and the nozzle diameter to ensure printability, and the fabrication of complex 3D structures was fabricated with adequate applied pressure and nozzle speed. The processing map also highlighted the advantages of embedded 3D printing over solvent-cast 3D printing based on solvent evaporation. Lastly, we demonstrated that the porosity of the interface and inner structure of the printed objects was readily tailored by the concentration of the PLA and the porogen added to the ink. The methods presented here offer new perspectives to fabricate micro-to-centimeter objects of thermoplastics with nanometer-scale inner pores and provide guidelines for successful embedded 3D printing based on immersion precipitation.

Ultra-low pressure PES ultrafiltration membrane with high-flux and enhanced anti-oil-fouling properties prepared via in-situ polycondensation of polyamic acid

Polyamic acid (PAA) is a flexible polymer and has abundant valuable hydrophilic groups. Herein, we developed an ultra-low pressure ultrafiltration (UF) membrane by integrating PAA into the polyethersulfone (PES) matrix via the "in-situ polycondensation" method. PAA was well compatible with PES and distributed uniformly in the membrane. The introduction of PAA improved membrane hydrophilicity. Meanwhile, the membrane pore structures were also refined. The membrane exhibited an excellent permeability under ultra-low pressure due to its improvement of hydrophilicity and pore structures. Under 0.3 bar, compare with the water flux of PES membrane, PES/PAA membrane improved nearly 2 times (571.05 L/(m²·h)), with a high BSA rejection (≥90%). Even under a lower pressure, 0.1 bar, >300 L/(m²·h) still can be achieved. Interestingly, the membrane we developed could maintain a high performance after drying, and then is very suitable for dry preservation. PES/PAA membrane showed a high oil removal (≥92%) and could remove oil from water effectively. Besides, the membrane exhibited excellent anti-oil-fouling properties. The flux recovery rate of PES/PAA (70.0%) far exceeds that of PES (37.9%) after three filtration and cleaning cycles. The membrane we developed is very valuable in oily wastewater treatment.

Preparation of composite polyethersulfone membrane containing basalt powder and optimization of the parameters using response surface methodology

In this study, environmental-friendly composite polyethersulfone (PES) membranes based on basalt powder were prepared by phase inversion method. The effects of polymer percentage, the basalt percentage, and the thickness of the membrane were investigated on the distilled water flux, compaction factor, bovine serum albumin (BSA) rejection, contact angle, fouling factor and the parameters were modelled by response surface methodology (RSM). The distilled water flux increased when the basalt was added to the membrane up to 6% percentage of the polymer amount. The blending of basalt also provided resistance against the membrane compaction. The BSA rejection experiments approved the positive effects of basalt on the rejections efficiencies. At higher basalt percentages, the rejection efficiencies increased from 78% at the raw membrane to 99% for the composite membranes had 10% basalt. The adding of basalt to the membranes decreased the contact angles. The hydrophilicity of the membranes contained basalt in their structures was higher than those which had not basalt. By comparison with the neat membranes and the basalt added membrane, it can be said that the basalt increased the flux recovery and decreased the irreversible fouling factors. The basalt increased the antifouling properties for the composite membranes. Finally, the prepared membranes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).

Recent progress in nanomaterial-functionalized membranes for removal of pollutants

Membrane technology has gained tremendous attention for removing pollutants from wastewater, mainly due to their affordable capital cost, miniature equipment size, low energy consumption, and high efficiency even for the pollutants present in lower concentrations. In this paper, we review the literature to summarize the progress of nanomaterial-modified membranes for wastewater treatment applications. Introduction of nanomaterial in the polymeric matrix influences membrane properties such as surface roughness, hydrophobicity, porosity, and fouling resistance. This review also covers the importance of functionalization strategies to prepare thin-film nanocomposite hybrid membranes and their effect on eliminating pollutants. Systematic discussion regarding the impact of the nanomaterials incorporated within membrane, toward the recovery of various pollutants such as metal ions, organic compounds, dyes, and microbes. Successful examples are provided to show the potential of nanomaterial-functionalized membranes for regeneration of wastewater. In the end, future prospects are discussed to develop nanomaterial-based membrane technology.

Cellulose acetate in fabrication of polymeric membranes: A review

Developing biodegradable polymers to fabricate filtration membranes is one of the main challenges of membrane science and technology. Cellulose acetate (CA) membranes, due to their excellent film-forming property, high chemical and mechanical stability, high hydrophilicity, eco-friendly, and suitable cost, are extensively used in water and wastewater treatment, gas separation, and energy generation purposes. The CA is one of the first materials used to fabricate filtration membranes. However, in the last decade, the possibility of modification of CA to improve permeability and stability has attracted the researcher's attention again. This review is focused on the properties of cellulose derivatives and especially CA membranes in the fabrication of polymeric separation membranes in various applications such as filtration, gas separation, adsorption, and ion exchange membranes. Firstly, a brief introduction of CA properties and used molecular weights in the fabrication of membranes will be presented. After that, different configurations of CA membranes will be outlined, and the performance of CA membranes in several applications and configurations as the main polymer and as an additive in the fabrication of other polymer-based membranes will be discussed.

A smart and responsive crystalline porous organic cage membrane with switchable pore apertures for graded molecular sieving

Membranes with high selectivity offer an attractive route to molecular separations, where technologies such as distillation and chromatography are energy intensive. However, it remains challenging to fine tune the structure and porosity in membranes, particularly to separate molecules of similar size. Here, we report a process for producing composite membranes that comprise crystalline porous organic cage films fabricated by interfacial synthesis on a polyacrylonitrile support. These membranes exhibit ultrafast solvent permeance and high rejection of organic dyes with molecular weights over 600 g mol^-1. The crystalline cage film is dynamic, and its pore aperture can be switched in methanol to generate larger pores that provide increased methanol permeance and higher molecular weight cut-offs (1,400 g mol^-1). By varying the water/methanol ratio, the film can be switched between two phases that have different selectivities, such that a single, 'smart' crystalline membrane can perform graded molecular sieving. We exemplify this by separating three organic dyes in a single-stage, single-membrane process.

Antifouling improvement of a polyacrylonitrile membrane blended with an amphiphilic copolymer

The amphiphilic copolymer polyacrylonitrile-co-poly(hydroxyethyl methacrylate) (PAN-co-PHEMA) was readily blended with polyacrylonitrile (PAN) to fabricate a flat-sheet blending membrane through non-solvent induced phase separation (NIPS). In the membrane-forming process, the hydrophilic PHEMA chains are uniformly distributed on the surface, as revealed by the energy-dispersive X-ray tests. The sponge-like sub-layer embedded with droplet-shaped structures is formed at the cross-sections of membranes, because of the high viscosity of the casting solution. With the increase of copolymer concentration, the mean pore size of the blending membranes increases from 26.9 to 99.8 nm, leading to the increase of membrane flux from 93.6 to 205.4 l/(m2h). The incorporation of PAN-co-PHEMA copolymer endows the blending membrane with a rough surface microstructure and enhanced hydrophilicity. The rejection ratio of membranes for emulsified pump oil reaches 99.9%, indicating a prominent separation performance. In the cycle permeation experiments, the flux recovery ratio of the blending membranes is as high as 99.6%, which is much higher than those of PAN membrane. The irreversible fouling of blending membranes induced by oil adsorption is alleviated, and converted into reversible fouling, owing to the reduction of the adhesion force between foulant and membrane surface. These results suggest that the anti-fouling property of PAN membranes has been dramatically strengthened via the addition of PAN-co-PHEMA copolymer.

Recent Advancements in Polyphenylsulfone Membrane Modification Methods for Separation Applications

Polyphenylsulfone (PPSU) membranes are of fundamental importance for many applications such as water treatment, gas separation, energy, electronics, and biomedicine, due to their low cost, controlled crystallinity, chemical, thermal, and mechanical stability. Numerous research studies have shown that modifying surface properties of PPSU membranes influences their stability and functionality. Therefore, the modification of the PPSU membrane surface is a pressing issue for both research and industrial communities. In this review, various surface modification methods and processes along with their mechanisms and performance are considered starting from 2002. There are three main approaches to the modification of PPSU membranes. The first one is bulk modifications, and it includes functional groups inclusion via sulfonation, amination, and chloromethylation. The second is blending with polymer (for instance, blending nanomaterials and biopolymers). Finally, the third one deals with physical and chemical surface modifications. Obviously, each method has its own limitations and advantages that are outlined below. Generally speaking, modified PPSU membranes demonstrate improved physical and chemical properties and enhanced performance. The advancements in PPSU modification have opened the door for the advance of membrane technology and multiple prospective applications.

Influence of Preparation Temperature on the Properties and Performance of Composite PVDF-TiO2 Membranes

Composite PVDF-TiO₂ membranes are studied extensively in literature as effective anti-fouling membranes with photocatalytic properties. Yet, a full understanding of how preparation parameters affect the final membrane structure, properties and performance has not been realized. In this study, PVDF-TiO₂ membranes (20 wt% TiO₂/PVDF) were fabricated via the non-solvent-induced phase separation (NIPS) method with an emphasis on the preparation temperature. Then, a systematic approach was employed to study the evolution of the membrane formation process and membrane properties when the preparation temperature changed, as well as to establish a link between them. Typical asymmetric membranes with a high porosity were obtained, along with a vast improvement in the permeate flux compared to the neat PVDF membranes, but a reduction in mechanical strength was also observed. Interestingly, upon the increase in preparation temperature, a significant transition in membrane morphology was observed, notably the gradual diminution of the finger-like macrovoids. Other membrane properties such as permeability, porosity, thermal and mechanical properties, and compression behavior were also influenced accordingly. Together, the establishment of the ternary phase diagrams, the study of solvent-nonsolvent exchange rate, and the direct microscopic observation of membrane formation during phase separation, helped explain such evolution in membrane properties.

Antimicrobial Hydrophilic Membrane Formed by Incorporation of Polymeric Surfactant and Patchouli Oil

Membrane properties are highly affected by the composition of the polymer solutions that make up the membrane material and their influence in the filtration performance on the separation or purification process. This paper studies the effects of the addition of pluronic (Plu) and patchouli oil (PO) in a polyethersulfone (PES) solution on the membrane morphology, membrane hydrophilicity, and filtration performance in the pesticide removal compound in the water sample. Three types of membranes with the composition of PES, PES + Plu, and PES + Plu + patchouli oil were prepared through a polymer phase inversion technique in an aqueous solvent. The resulting membranes were then analyzed and tested for their mechanical properties, hydrophilicity, antimicrobial properties, and filtration performance (cross-flow ultrafiltration). The results show that all of the prepared membranes could reject 75% of the pesticide. The modification of the PES membrane with Plu was shown to increase the overall pore size by altering the pore morphology of the pristine PES, which eventually increased the permeation flux of the ultrafiltration process. Furthermore, patchouli oil added antimicrobial properties, potentially minimizing the biofilm formation on the membrane surface.

Developing a Thin Film Composite Membrane with Hydrophilic Sulfonated Substrate on Nonwoven Backing Fabric Support for Forward Osmosis

This study describes the fabrication of sulfonated polyethersulfone (SPES) as a super-hydrophilic substrate for developing a composite forward osmosis (FO) membrane on a nonwoven backing fabric support. SPES was prepared through an indirect sulfonation procedure and then blended with PES at a certain ratio. Applying SPES as the substrate affected membrane properties, such as porosity, total thickness, morphology, and hydrophilicity. The PES-based FO membrane with a finger-like structure had lower performance in comparison with the SPES based FO membrane having a sponge-like structure. The finger-like morphology changed to a sponge-like morphology with the increase in the SPES concentration. The FO membrane based on a more hydrophilic substrate via sulfonation had a sponge morphology and showed better water flux results. Water flux of 26.1 L m⁻² h⁻¹ and specific reverse solute flux of 0.66 g L⁻¹ were attained at a SPES blend ratio of 50 wt % when 3 M NaCl was used as the draw solution and DI water as feed solution under the FO mode. This work offers significant insights into understanding the factors affecting FO membrane performance, such as porosity and functionality.

Visible Light-Driven GO/TiO2-CA Nano-Photocatalytic Membranes: Assessment of Photocatalytic Response, Antifouling Character and Self-Cleaning Ability

Photocatalysis and membrane technology in a single unit is an ideal strategy for the development of wastewater treatment systems. In this work, novel GO (x wt%)/TiO2-CA hybrid membranes have been synthesized via a facile non-solvent induced phase inversion technique. The strategy aimed to address the following dilemmas: (1) Effective utilization of visible light and minimize e-/h+ recombination; (2) Enhanced separation capability and superior anti-fouling and self-cleaning ability. The experimental results reveal that the integration of nano-composite (GO/TiO2) boosts the membrane properties when compared to pristine CA and single photocatalyst employed membrane (GO-CA and TiO2-CA). The effect of GO content on the properties of the photocatalytic membrane has been determined by utilizing three different ratios of GO, viz. 0.5 wt%, 1 wt%, and 2 wt% designated as NC(1)-CA, NC(2)-CA, and NC(3)-CA, respectively. Amongst them, NC(3)-CA membrane showed state-of-the-art performance with an elevated photocatalytic response (four times higher than pristine CA membrane) toward methyl orange. Moreover, the water flux of NC(3)-CA membrane is 613 L/m2h, approximately three times higher than bare CA membrane (297 L/m2h), while keeping the MO rejection high (96.6%). Besides, fouling experiments presented the lowest total and fouling resistance ratios and a higher flux recovery ratio (91.78%) for the NC(3)-CA membrane, which endows the membrane with higher anti-fouling and self-cleaning properties. Thus, NC(3)-CA membrane outperforms the other as synthesized membranes in terms of separation efficiency, visible light photo-degradation of pollutant, anti-fouling and self-cleaning ability. Therefore, NC(3)-CA membrane is considered as the next generation membrane for exhibiting great potential for the wastewater treatment applications.

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.

Express Method of Preparation of Hollow Fiber Membrane Samples for Spinning Solution Optimization: Polysulfone as Example

This article describes a new technique for the preparation of hollow fiber (HF) membrane samples using an automatic manipulator unit. The manipulator uses a syringe needle to form a HF of a given geometry. The needle in automatic mode is sequentially immersed, first into the polymer solution and then into the coagulation bath. The possibility of using a manipulator to obtain HF samples was studied on the known polysulfone (PSf)/N-methylpyrrolidone (NMP)/pore-forming additive system. A series of HF membrane samples were made within 29 h from twelve 1 mL PSf casting solutions. This was 15 times faster than obtaining samples of HF membranes at the multifunctional research laboratory facility. From the point of view of the consumption of the components of the casting solution, the use of the manipulator was 30 times more economical, and the consumption of water for precipitation and washing was 8000 times less. The developed method made it possible to study samples of HF by scanning electron microscopy (SEM), ultrafiltration, and evaluate its mechanical properties without spinning the membranes. Using the new technique, the optimal composition of the casting solution for the wet spinning of HF PSf membranes was selected during two weeks. Thus, the manipulator makes it possible to significantly reduce the time of the new membrane preparation, reduce the volume of used polymer, and thus makes it promising to study expensive or new membrane materials.

Decimeter-Scale Atomically Thin Graphene Membranes for Gas-Liquid Separation

Graphene holds great potential for fabricating ultrathin selective membranes possessing high permeability without compromising selectivity and has attracted intensive interest in developing high-performance separation membranes for desalination, natural gas purification, hemodialysis, distillation, and other gas-liquid separation. However, the scalable and cost-effective synthesis of nanoporous graphene membranes, especially designing a method to produce an appropriate porous polymer substrate, remains very challenging. Here, we report a facile route to fabricate decimeter-scale (∼15 × 10 cm²) nanoporous atomically thin membranes (NATMs) via the direct casting of the porous polymer substrate onto graphene, which was produced by chemical vapor deposition (CVD). After the vapor-induced phase-inversion process under proper experimental conditions (60 °C and 60% humidity), the flexible nanoporous polymer substrate was formed. The resultant skin-free polymer substrate, which had the proper pore size and a uniform spongelike structure, provided enough mechanical support without reducing the permeance of the NATMs. It was demonstrated that after creating nanopores by the O₂ plasma treatment, the NATMs were salt-resistant and simultaneously showed 3-5 times higher gas (CO₂) permeance than the state-of-the-art commercial polymeric membranes. Therefore, our work provides guidance for the technological developments of graphene-based membranes and bridges the gap between the laboratory-scale "proof-of-concept" and the practical applications of NATMs in the industry.