Superhydrophilic In-Situ-Cross-Linked Zwitterionic Polyelectrolyte/PVDF-Blend Membrane for Highly Efficient Oil/Water Emulsion Separation

Zero-Oil-Fouling Membrane With High Coverage of Grafted Zwitterionic Polymer for Separation of Oil-in-Water Emulsions

Current hydrophilic modification strategies improve the antifouling ability of membranes but fail to completely eliminate the fouling of emulsified oil droplets with a wide size distribution. Constructing membranes with superior anti-oil-fouling ability to resist various oil droplets especially at high permeation fluxes is challenging. Here, the fabrication of a zero-oil-fouling membrane by grafting considerably high coverage of zwitterionic polymer and building defect-free hydration defense barrier on the surface is reported. A uniform layer of protocatechuic acid with COOH as abundant as existing in every molecule is stably deposited on the membrane so as to provide sufficient reactive sites and achieve dense grafting of the zwitterionic polymer. The coverage of zwitterionic polymer on the membrane plays a crucial role in promoting the antifouling ability to emulsified oil droplets. The poly(vinylidene fluoride) membrane with 93% coverage of the zwitterionic polymer exhibits zero oil fouling when separating multitudinous oil-in-water emulsions with ≈0% flux decline, ≈100% flux recovery, and a high water flux of ≈800 L m-2 h-1 bar-1. This membrane outperforms almost all of the reported membranes in terms of the comprehensive antifouling performance. This work provides a feasible route for manufacturing super-antifouling membranes toward oil/water separation application.

On the Disproportionate Contribution of Membrane Electron Donor Functionality in Membrane Biofouling

This study set out to uncover which interfacial properties have the greatest impact on membrane organic fouling, biofouling, and fouling resistance. A relatively simple manipulation of the basic equations used in determining Lifshitz-van der Waals (LW) and Lewis acid-base (AB) surface tensions for solid materials reveals that the high electron accepticity of water makes the electron donicity of membrane and biofouling materials the key component governing their interfacial free energy of adhesion (ΔG132), which defines the favorability (or unfavorability) of one material (1) adhering to another (2) when immersed in a liquid (3). Various biofoulant and membrane LW and AB surface tensions were systematically characterized. Static bacterial adhesion, alginic acid filtration, and wastewater filtration tests were conducted to determine the fouling propensities of three different polymeric membrane materials. Experimental results of microbial adhesion, alginate fouling, and biofouling tests all correlated well with membrane electron density, where higher electron density produced less organic fouling or biofouling. These combined theoretical and experimental results confirm the importance of surface electron donicity in determining the fouling propensity of polymeric membranes.

Surface Segregation Methods toward Molecular Separation Membranes

As a highly promising approach to solving the issues of energy and environment, membrane technology has gained increasing attention in various fields including water treatment, liquid separations, and gas separations, owing to its high energy efficiency and eco-friendliness. Surface segregation, a phenomenon widely found in nature, exhibits irreplaceable advantages in membrane fabrication since it is an in situ method for synchronous modification of membrane and pore surfaces during the membrane forming process. Meanwhile, combined with the development of synthesis chemistry and nanomaterial, the group has developed surface segregation as a versatile membrane fabrication method using diverse surface segregation agents. In this review, the recent breakthroughs in surface segregation methods and their applications in membrane fabrication are first briefly introduced. Then, the surface segregation phenomena and the classification of surface segregation agents are discussed. As the major part of this review, the authors focus on surface segregation methods including free surface segregation, forced surface segregation, synergistic surface segregation, and reaction-enhanced surface segregation. The strategies for regulating the physical and chemical microenvironments of membrane and pore surfaces through the surface segregation method are emphasized. The representative applications of surface segregation membranes are presented. Finally, the current challenges and future perspectives are highlighted.

Compressible Separator and Catalyst for Simultaneous Separation and Purification of Emulsions and Aqueous Pollutants

Oily wastewater, a global environmental concern, demands efficient oil/water separation and pollutant removal. Our compressible separator and catalyst (CSC) balls, prepared through sponge etching and metal nanoparticle synthesis, exhibited efficient degradation of dyes of varying sizes, spanning a molecular weight range from 139 to 696 g/mol during the oil/water separation. Control over the distance between catalysts was achieved by incorporating Ag-Pt-Pd catalysts into the sponge skeleton and by adjusting the compression rates. The dispersion of the catalysts improved degradation efficiency for larger dyes, while concentrating the catalysts proved to be more effective for the smaller ones. By optimizing the compression rates of CSC balls, we successfully achieved the effective removal of emulsions of different sizes and precise control of flux. Our CSC ball-loaded system offers efficient and versatile solutions for concurrent separation and purification of emulsions and pollutants with potential environmental benefits.

Tough and Recyclable Phase-Separated Supramolecular Gels via a Dehydration-Hydration Cycle

Hydrogels are compelling materials for emerging applications including soft robotics and autonomous sensing. Mechanical stability over an extensive range of environmental conditions and considerations of sustainability, both environmentally benign processing and end-of-life use, are enduring challenges. To make progress on these challenges, we designed a dehydration-hydration approach to transform soft and weak hydrogels into tough and recyclable supramolecular phase-separated gels (PSGs) using water as the only solvent. The dehydration-hydration approach led to phase separation and the formation of domains consisting of strong polymer-polymer interactions that are critical for forming PSGs. The phase-separated segments acted as robust, physical cross-links to strengthen PSGs, which exhibited enhanced toughness and stretchability in its fully swollen state. PSGs are not prone to overswelling or severe shrinkage in wet conditions and show environmental tolerance in harsh conditions, e.g., solutions with pH between 1 and 14. Finally, we demonstrate the use of PSGs as strain sensors in air and aqueous environments.

Effects of Different TiO2/CNT Coatings of PVDF Membranes on the Filtration of Oil-Contaminated Wastewaters

Six different TiO2/CNT nanocomposite-coated polyvinylidene-fluoride (PVDF) microfilter membranes (including -OH or/and -COOH functionalized CNTs) were evaluated in terms of their performance in filtering oil-in-water emulsions. In the early stages of filtration, until reaching a volume reduction ratio (VRR) of ~1.5, the membranes coated with functionalized CNT-containing composites provided significantly higher fluxes than the non-functionalized ones, proving the beneficial effect of the surface modifications of the CNTs. Additionally, until the end of the filtration experiments (VRR = 5), notable flux enhancements were achieved with both TiO2 (~50%) and TiO2/CNT-coated membranes (up to ~300%), compared to the uncoated membrane. The irreversible filtration resistances of the membranes indicated that both the hydrophilicity and surface charge (zeta potential) played a crucial role in membrane fouling. However, a sharp and significant flux decrease (~90% flux reduction ratio) was observed for all membranes until reaching a VRR of 1.1-1.8, which could be attributed to the chemical composition of the oil. Gas chromatography measurements revealed a lack of hydrocarbon derivatives with polar molecular fractions (which can act as natural emulsifiers), resulting in significant coalescent ability (and less stable emulsion). Therefore, this led to a more compact cake layer formation on the surface of the membranes (compared to a previous study). It was also demonstrated that all membranes had excellent purification efficiency (97-99.8%) regarding the turbidity, but the effectiveness of the chemical oxygen demand reduction was slightly lower, ranging from 93.7% to 98%.

A comprehensive review on the behavior and evolution of oil droplets during oil/water separation by membranes

Membrane separation technology has significant advantages for treating oil-in-water emulsions. Understanding the evolution of oil droplets could reveal the interfacial and colloidal interactions, facilitate the design of advanced membranes, and improve the separation performances. This review on the characteristic behavior and evolution of oil droplets focuses on the advanced analytical techniques, and the subsequent fouling as well as demulsification effects during membrane separation. A detailed introduction is provided on microscopic observations and numerical simulations of the dynamic evolution of oil droplets, featuring real-time in-situ visualization and accurate reconstruction, respectively. Characteristic behaviors of these oil droplets include attachment, pinning, wetting, spreading, blockage, intrusion, coalescence, and detachment, which have been quantified by specific proposed parameters and criteria. The fouling process can be evaluated using Hermia and resistance models. The related adhesion force and intrusion pressure as well as droplet-droplet/membrane interfacial interactions can be accurately quantified using various force analysis methods and advanced force measurement techniques. It is encouraging to note that oil coalescence has been achieved through various effects such as electrostatic interactions, mechanical actions, Laplace pressure/surface free energy gradients, and synergistic effects on functional membranes. When oil droplets become destabilized and coalesce into larger ones, the functional membranes can overcome the limitations of size-sieving effect to attain higher separation efficiency. This not only bypasses the trade-off between permeability and rejection, but also significantly reduces membrane fouling. Finally, the challenges and potential research directions in membrane separation are proposed. We hope this review will support the engineering of advanced materials for oil/water separation and research on interface science in general.

Facile, green and scalable preparation of low-cost PET-PVDF felts for oil absorption and oil/water separation

3D felt materials with pore structures have the advantages of high absorption performance and recyclability in oily wastewater treatment and chemical leakage. However, most of them were fabricated using either toxic organic solvents or complicated procedures. Herein, we report a facile, green, and scalable route for the fabrication of 3D composite felts with large pore structures by sequentially stirring and heating polyethylene terephthalate (PET) fibers and polyvinylidene fluoride (PVDF). The resulting PET-PVDF felt exhibits high oil absorption capacity to a variety of oil and organic solvents with a maximum saturated absorption capacity of 32 g/g. Additionally, it can be used to separate oil/water mixtures with a separation efficiency of 99.9% and separation flux of 89570 L m^-2 h^-1. Moreover, this felt shows excellent mechanical durability and chemical stability under acid, base, salt solution, and other harsh environments. The current study provides a promising approach for large-scale industrial oily wastewater separation.

Separation of Oil from an Oil/Water Mixed Drop under a Lamb Wave Field: A Review

Oil separation from oil/water mixed drop under a Lamb wave field is one of the emerging acoustofluidic technologies that integrate acoustics and microfluidics. In recent years, this technology has attracted significant attention due to its effective, fast, contactless, and pollution-free. It has been validated in the separation of oil/water mixture on different non-piezoelectric substrates and shows great potential in incompatible liquids applications. Here, we summarize our recent progress in this exciting field and show great potential in different applications. This review introduces the theories and mechanisms of oil/water mixed drop separation induced by Lamb waves, the applications of this technology in the separation of oil/water mixed drop, and discusses the challenges and prospects of this field.

Quick-Release Antifouling Hydrogels for Solar-Driven Water Purification

Hydrogels are promising soft materials for energy and environmental applications, including sustainable and off-grid water purification and harvesting. A current impediment to technology translation is the low water production rate well below daily human demand. To overcome this challenge, we designed a rapid-response, antifouling, loofah-inspired solar absorber gel (LSAG) capable of producing potable water from various contaminated sources at a rate of ∼26 kg m^-2 h^-1, which is sufficient to meet daily water demand. The LSAG-produced at room temperature via aqueous processing using an ethylene glycol (EG)-water mixture-uniquely integrates the attributes of poly(N-isopropylacrylamide) (PNIPAm), polydopamine (PDA), and poly(sulfobetaine methacrylate) (PSBMA) to enable off-grid water purification with enhanced photothermal response and the capacity to prevent oil fouling and biofouling. The use of the EG-water mixture was critical to forming the loofah-like structure with enhanced water transport. Remarkably, under sunlight irradiations of 1 and 0.5 sun, the LSAG required only 10 and 20 min to release ∼70% of its stored liquid water, respectively. Equally important, we demonstrate the ability of LSAG to purify water from various harmful sources, including those containing small molecules, oils, metals, and microplastics.

Superhydrophilic quaternized calcium alginate based aerogel membrane for oil-water separation and removal of bacteria and dyes

In recent years, frequent oil spills and increasing industrial wastewater discharge have caused serious water pollution problems. In addition, there are often microbial and dye pollutants in oil-containing wastewater. The development of materials that can simultaneously treat these three pollutants is very important for the safe treatment and recovery of wastewater. In this work, a modified calcium alginate-based aerogel membrane (CTW) was prepared through sol spraying, Ca²⁺ crosslinking and freeze drying by using tetrabutylammonium hydroxide (TBA) quaternary ammonium salt modified sodium alginate (SA) as raw material and waterborne polyurethane (WPU) as adhesive. The results show that CTW membrane has super hydrophilic and underwater super-oleophobic properties, and can realize the separation oil-water emulsions under gravity, with the separation efficiency of >99 %. CTW membrane can also remove bacteria and dye such as Congo red from water by filtration, with removal rates of 100 % and 99 % respectively. The filtration results of mixed wastewater show that CTW membrane can realize one-step separation of oil, bacteria and dye in wastewater, and can also be recycled, having potential application prospect.

Cellulose nanofiber-poly(ethylene terephthalate) nanocomposite membrane from waste materials for treatment of petroleum industry wastewater

Petroleum industry wastewater contains high level of crude oil and other types of organic substances that can cause immense harm to the agriculture, aquatic as well as terrestrial organisms. Organic solvent resistance of membranes is very important to treat such wastewater that contains high level of organic pollutants. This work reports the designing of a superhydrophilic and organic solvent resistant nanocomposite membrane using waste bottles made of poly(ethylene terephthalate) (PET) and cellulosic papers. Using in-situ synthesized cellulose nanofibers we could successfully fabricate porous membranes which is not possible for bare PET matrix using water as nonsolvent. Thus, we could successfully replace methanol which was used as a suitable non-solvent in earlier reports by distilled water. We successfully used the membrane for separation of synthetic crude oil-water emulsion. The membrane showed permeability up to 98 Lm^-2h^-1 applying pressure of 1.5 bar. The membrane also achieved removal of more than 97 % of organic substances from a crude oil-water emulsion system. The optimum membrane also showed good thermal stability with initial degradation temperature ∼350 °C and tensile strength of 0.86 MPa. The antimicrobial property of the nanocomposite membranes could be achieved by coating its surface with carbon dots rooted graphene oxide.

Synthesis of Superhydrophobic/Superoleophilic stearic acid and Polymer-modified magnetic polyurethane for Oil-Water Separation: Effect of polymeric nature

The superhydrophobic/superoleophilic materials based on polyurethane foams have been layered with three different polymers and extensive modification with iron/magnetic nanocomposite. The general desires are to study the effect of the polymer layer and to eliminate the oil contaminant from the oil-water system which is crucial due to the development of environmental technologies. These materials were generated by facile dip-coating two-step method on the polyurethane foams (PUF) surface. PUF was directly layered with polydopamine/polypyrrole/polyaniline (PDA/PPy/PANI) and incorporated with Fe-SA (stearic acid) nanocomposites by ultrasonication and refluxing. In addition, characterization by FTIR, SEM/EDX, XRD, and TGA presented that the polymer layer and Fe-SA nanocomposites successfully covered the PUF surface caused by the chelating interaction between the carboxylates and active sites on iron particles due to intermolecular hydrogen bond interaction. Interestingly, the water contact angle (WCA) measurement of the nanocomposites displayed that the contact angle significantly improved up to 164°. After 20 cycles of oil absorption capacity, the WCA steadily remained up to 153° indicating powerful superhydrophobic properties of the materials. Furthermore, the oil absorption capacity of the materials was evaluated using typical oil-water separation methods such as reusability, separation efficiency, and oil permeate flux. The results exhibited that the modified PUFs have enhanced the absorption capacity up to 44 times the foam weight, 99 % separation efficiency, and about 8000 L.m-2.h-1 oil flux. For oil removal, the dyed oil phase was rapidly absorbed within 2 s confirming the highly used products for a wide area of oil-water separation. PDA-coated PUF nanocomposites obtained the most outstanding results due to their remarkable interfacial adhesion properties which provide larger active functional groups for hydrogen bonding interaction on PUF surface and Fe-SA nanocomposites.

Interface Optimization of Metal Quantum Dots/Polymer Nanocomposites and their Properties: Studies of Multi-Functional Organic/Inorganic Hybrid

Nanomaterials filled polymers system is a simple method to produce organic/inorganic hybrid with synergistic or complementary effects. The properties of nanocomposites strongly depend on the dispersion effects of nanomaterials in the polymer and their interfaces. The optimized interface of nanocomposites would decrease the barrier height between filler and polymer for charge transfer. To avoid aggregation of metal nanoparticles and improve interfacial charge transfer, Pt nanodots filled in the non-conjugated polymer was synthesized with an in situ method. The results exhibited that the absorbance of nanocomposite covered from the visible light region to NIR (near infrared). The photo-current responses to typical visible light and 808 nm NIR were studied based on Au gap electrodes on a flexible substrate. The results showed that the size of Pt nanoparticles was about 1-2 nm and had uniformly dispersed in the polymer matrix. The resulting nanocomposite exhibited photo-current switching behavior to weak visible light and NIR. Simultaneously, the nanocomposite also showed electrical switching responses to strain applied to a certain extent. Well-dispersion of Pt nanodots in the polymer is attributable to the in situ synthesis of metal nanodots, and photo-current switching behavior is due to interface optimization to decrease barrier height between metal filler and polymer. It provided a simple way to obtain organic/inorganic hybrid with external stimuli responses and multi-functionalities.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Smart Superhydrophobic Filter Paper for Water/Oil Separation and Unidirectional Transportation of Liquid Droplet

Water/oil separation from their mixture and emulsion has been a prominent topic in fundamental research and in practical applications. In this work, a smart superhydrophobic membrane (SHP) was obtained by dipping an off-the-shelf laboratory filter paper in an ethanol suspension of trichloro (1H,1H,2H,2H-tridecafluoro-n-octyl) silane, tetraethyl orthosilicate, and titanium dioxide nanoparticles with different dimensions of 20 and 100 nm. The selection of membrane substrates was optimized including different quantitative and quantitative filter papers with different filtration velocity (slow, intermediate, and fast). The as-prepared SHP was demonstrated to be superhydrophobic and photosensitive, which was used in the separation of carbon tetrachloride and water from their mixture and emulsion. Moreover, orderly aligned micropores were formed for the modified superhydrophobic filter papers by using nanosecond laser. Unidirectional penetration was obtained for the UV-irradiated paper with a bored pore in the range of 50-500 μm in the systems of air/water and water/oil. This study may promote the understanding of unidirectional transportation of liquid droplet and facilitate the design of interfacial materials with Janus-type wettability.

Superhydrophilic Modification of Polyvinylidene Fluoride Membrane via a Highly Compatible Covalent Organic Framework-COOH/Dopamine-Integrated Hierarchical Assembly Strategy for Oil-Water Separation

The integration of membranes with additives such as functionalized nanomaterials can be recognized as an effective method to enhance membrane performance. However, to obtain an efficient nanoparticle-decorated membrane, the compatibility of nanomaterials remains a challenge. Hydrophilic carboxylated covalent organic frameworks (COF-COOH) might be expected to avoid the drawbacks of aggregation and easy shedding of inorganic materials caused by the poor interfacial compatibility. Herein, a highly compatible dip-coating strategy was proposed for the superhydrophilic modification of polyvinylidene fluoride membrane via COF-COOH integrated with dopamine. COF-COOH together with polydopamine nanoparticles were uniformly and stably attached to the membrane due to the high interfacial compatibility, constructing a coating with rough hierarchical nanostructures and abundant carboxyl groups. The synergistic effects of multiscale structures and chemical groups endow the membrane with superhydrophilicity and underwater superoleophobicity, the water contact angle decreased from 123 to 15°, and the underwater oil contact angle increased from 132 to 162°. Accordingly, the modified membrane exhibits an ultrahigh oil rejection ratio (>98%), a high flux (the maximum reaches 1843.48 L m^-2 h^-1 bar^-1), attractive antifouling ability, and impregnable stability. This work would provide a momentous reference for the application of COF-COOH in practical oily wastewater treatment.

Crosslinked biomimetic coating modified stainless-steel-mesh enables completely self-cleaning separation of crude oil/water mixtures

The development of high-flux, durable and completely self-cleaning membranes is highly desired for separation of massive oil/water mixtures. Herein, differently crosslinked poly(2-methacryloyloxylethyl phosphorylcholine) (PMPC) brush grafted stainless steel mesh (SSM) membranes (SSM/PMPCs) were fabricated by integrating of mussel inspired universal adhesion and crosslinking chemistry with surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET-ATRP). The durability and self-cleaning performance of the prepared SSM membranes were evaluated by separating sticky crude oil/water mixtures in a continuous recycling dead-end filtration device. The water filtration flux driven by gravity reached 60,000 L⋅m^-2⋅h^-1 with a separation efficiency of over 99.98%. Furthermore, zero-flux-decline was observed during a 5 h continuous filtration when assisted by mechanical stirring. More significantly, such a completely self-cleaning separation of the well crosslinked SSM/PMPC2 membrane under optimized flux and stirring conditions had been operated cumulatively for 190 h in 30 days without any additional cleaning. These significant advances are more promising for practical applications in crude oil-contaminated water treatments and massive oil/water mixture separation.

Synthesis of a biomimetic zwitterionic pentapolymer to fabricate high-performance PVDF membranes for efficient separation of oil-in-water nano-emulsions

Oily wastewater from industries has an adverse impact on the environment, human and aquatic life. Poly(vinylidene fluoride) (PVDF) membrane modified with a zwitterionic/hydrophobic pentapolymer (PP) with controlled pore size has been utilized to separate oil from water from their nano-emulsions. The PP has been synthesized in 91% yield via pentapolymerization of four different diallylamine salts [(CH₂=CHCH₂)₂NH⁺(CH₂)_x A⁻], bearing CO₂⁻, PO₃H⁻, SO₃⁻, (CH₂)₁₂NH₂ pendants, and SO₂ in a respective mol ratio of 25:36:25:14:100. Incorporating PP into PVDF has shown a substantially reduced membrane hydrophobicity; the contact angle decreased from 92.5° to 47.4°. The PP-PVDF membranes have demonstrated an excellent capability to deal with the high concentrations of nano-emulsions with a separation efficiency of greater than 97.5%. The flux recovery ratio (FRR) of PP-5 incorporated PVDF membrane was about 82%, which was substantially higher than the pristine PVDF.

Polymeric Membranes for Oil-Water Separation: A Review

This review is devoted to the application of bulk synthetic polymers such as polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF) for the separation of oil-water emulsions. Due to the high hydrophobicity of the presented polymers and their tendency to be contaminated with water-oil emulsions, methods for the hydrophilization of membranes based on them were analyzed: the mixing of polymers, the introduction of inorganic additives, and surface modification. In addition, membranes based on natural hydrophilic materials (cellulose and its derivatives) are given as a comparison.

Zwitterionic Polymer Hairy Coating onto Mesh toward Easy Oil/Water Separation

A zwitterionic polymeric hair coated stainless steel mesh membrane is fabricated, which demonstrates efficient separation of oil/water mixtures and the emulsions. The hairy coating of poly(divinylbenzene-co-vinylbenzene chloride) (P(DVB-co-VBC)) is generated by precipitation cationic polymerization, and subsequent grafting a zwitterionic polymer layer by atom transfer radical polymerization (ATRP) of sulfobetaine methacrylate (SBMA). Microstructure of the hairy coating is tunable from array of individual nanofibers to porous network by interweaving of the hairs. The long-range attraction of zwitterionic polymer with water renders the coated mesh with excellent superhydrophilic and underwater superoleophobic performance. The coated mesh is highly antifouling to avoid the pre-hydration in conventional methods. Moreover, the microstructure is demonstrated to be responsible for the high separation efficiency of oil/water emulsion. Therefore, separation of oil/water mixtures and emulsions becomes easier by the coated mesh, which is promising in industrial oil field sewage treatment. This article is protected by copyright. All rights reserved.

Switchable wettability of grain-stacked filter layers from polyurethane plastic waste for oil/water separation

HYPOTHESIS

Polyurethane plastic waste (PUPW), a port-abundant solid waste, is difficult to degrade naturally and poses a severe threat to the environment. Hence, the effective recycling of PUPW remains a challenge.

EXPERIMENTS

Herein, a strategy of converting PUPW into stacked oil/water filtration layer grain through a layer-by-layer (LBL) assembly process is investigated. Notably, such PU-based, grain-stacked, and switchable wettability of the oil/water filter layer is first reported.

FINDINGS

The grain-stacked filter layers are flexible for separating immiscible oil/water mixtures, water-in-oil emulsions (WOE), and oil-in-water emulsions (OWE) under gravity over 10 cycle-usages. They can withstand strong acid/alkali solutions (pH = 1-14) and salt solutions over 12 h. Besides, 100-times scale-up experiments have indicated that the obtained filter layers exhibit an upper to 98.2 % separation efficiency for 10 L real industrial oil/water emulsion in the 24 h continuous operation. The demulsification mechanism for emulsions is that the electrostatic interaction along with adsorption between emulsion droplets and grains leads to the uneven distribution of surfactants on the interface film of the emulsion droplets, increasing the probability of tiny droplets colliding and coalescing into large droplets to achieve oil/water separation. This work proposes an effective and economical method of abundant plastic waste for industrial-scale oil-water separation rather than just on the laboratory-scale.

Zwitterionic silica nanogel-modified polysulfone nanoporous membranes formed by in-situ method for water treatment

We report a simple methodology to prepare nano-porous polysulfone membranes using zwitterionic functionalized silica nanogels with high BSA protein rejection and antifouling properties. The zwitterionic silica precursor was prepared by reacting 1,3-propane sultone with 3-aminopropyl triethoxysilane under an inert atmosphere. The precursor was in situ hydrolyzed and condensed in the polysulfone nanoporous membrane network by one-pot acidic phase inversion. The prepared membranes were characterized to establish their physicochemical nature, morphology, and basic membrane properties such as permeation, rejection, and recovery. The zwitterionic membranes showed improved hydrophilicity, membrane water uptake (∼83.5%), water permeation, BSA protein rejection (>95%), and dye rejection (congo red: >52% (∼6-fold increase); methylene blue: ∼15% (∼2-fold increase)) were improved without compromising the membrane flux and fouling resistance. Overall, we report an easy fabrication method of efficient nanocomposite zwitterionic ultrafilter membranes for water treatment with excellent flux, protein separation, filtration efficiency, and antifouling behavior.