A self-cleaning zwitterionic nanofibrous membrane for highly efficient oil-in-water separation

High-flux nanofiltration membrane with modified highly dispersed MOF particles as nano filler

The synthesis of optimized thin film nanocomposite (TFN) membrane with no or few defects is an efficacious method which can improve nanofiltration performance. However, poor dispersion of fillers in the organic phase and wrong compatibility between fillers and polymerizate are still a serious problem. In this study, the particle size of metal organic framework (MOF), aluminum-based metal-organic frameworks (CAU-1) was modulated and for the first time, dodecyl aldehyde was used to modify the surface hydrophobicity of CAU-1, which improved the dispersibility and inhibited the aggregation in the trimesoyl chloride (TMC)/n-hexane solution; later CAU-1 and modified CAU-1 were incorporated into the polyamide (PA) selective layer to synthesize TFN membrane by interfacial polymerization (IP). The particle size modulation and modification of the CAU-1 were demonstrated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) characterization. The characterization showed that PA selective layer was synthesized on the top layer of polysulfone (PSF) substrate. The pure water flux of the TFN membrane was increased to 79.89 ± 1.24 L·m^-2·h^-1·bar^-1 compared to the original thin film composite (TFC) membrane, which was due to the polymerization of 100 nm modified CAU-1 on the PA layer to form a new water molecular channel, thus increasing the water flux by about 70%.

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.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Electrospun Nanofiber-Based Membranes for Water Treatment

Water purification and water desalination via membrane technology are generally deemed as reliable supplementaries for abundant potable water. Electrospun nanofiber-based membranes (ENMs), benefitting from characteristics such as a higher specific surface area, higher porosity, lower thickness, and possession of attracted broad attention, has allowed it to evolve into a promising candidate rapidly. Here, great attention is placed on the current status of ENMs with two categories according to the roles of electrospun nanofiber layers: (i) nanofiber layer serving as a selective layer, (ii) nanofiber layer serving as supporting substrate. For the nanofiber layer’s role as a selective layer, this work presents the structures and properties of conventional ENMs and mixed matrix ENMs. Fabricating parameters and adjusting approaches such as polymer and cosolvent, inorganic and organic incorporation and surface modification are demonstrated in detail. It is crucial to have a matched selective layer for nanofiber layers acting as a supporting layer. The various selective layers fabricated on the nanofiber layer are put forward in this paper. The fabrication approaches include inorganic deposition, polymer coating, and interfacial polymerization. Lastly, future perspectives and the main challenges in the field concerning the use of ENMs for water treatment are discussed. It is expected that the progress of ENMs will promote the prosperity and utilization of various industries such as water treatment, environmental protection, healthcare, and energy storage.

Review of the Recent Advances in Electrospun Nanofibers Applications in Water Purification

Recently, nanofibers have come to be considered one of the sustainable routes with enormous applicability in different fields, such as wastewater treatment. Electrospun nanofibers can be fabricated from various materials, such as synthetic and natural polymers, and contribute to the synthesis of novel nanomaterials and nanocomposites. Therefore, they have promising properties, such as an interconnected porous structure, light weight, high porosity, and large surface area, and are easily modified with other polymeric materials or nanomaterials to enhance their suitability for specific applications. As such, this review surveys recent progress made in the use of electrospun nanofibers to purify polluted water, wherein the distinctive characteristics of this type of nanofiber are essential when using them to remove organic and inorganic pollutants from wastewater, as well as for oil/water (O/W) separation.

Simultaneously achieving high-effective oil-water separation and filter media regeneration by facile and highly hydrophobic sand coating

Efficient oil-water separation, including of emulsified oil separation, is one of the problems restricting the green development of the petrochemical industry. Herein, highly hydrophobic sand was fabricated in one-step, followed by an investigation of adsorption capacity for various oils of hexane, petroleum ether, diesel, tetrachloroethylene and tetrachloromethane. The modified sand (MS) filter bed was subsequently set up to investigate the oil separation efficiency for oil-water mixtures, emulsions and actual petroleum refinery wastewater, respectively. Moreover, the capture process of the oil droplet by the MS was observed by a high-speed camera system, and the oil removal mechanism was explored. The removal feasibility of the oil adhered to the MS in a hydrocyclone was also investigated. The oil could be quickly adsorbed by the MS, and the adsorption capacity was positively correlated with oil density. A high flux of 14,436 L·m^-2·h^-1 and a considerable separation efficiency of 99% were obtained when the MS was applied for oil-water mixture separation. Additionally, the highest separation efficiency of various emulsions was up to 99.3%. Regrading actual petroleum refinery wastewater, the oil removal efficiency of the MS reached 90% rather than 57.8% of raw sand. The oil droplets in the wastewater were efficiently separated by the MS based on the mechanism of adsorption and coalescence. Additionally, the oil adhered on the MS could be removed, and the oil concentration decreased from 17.6% to 5.2%, which was ascribed to the MS spinning in a hydrocyclone. A novel oil-water separation method of hydrocyclone-intensified filtration by facile and highly hydrophobic sand coating was proposed, and simultaneously the filter media can be effectively regenerated. It is believed that this work might provide a low cost, recyclable and efficient strategy for oil removal, which shows high promise for industrial oily wastewater treatment.

Multifunctional filtration membrane with anti-viscous-oils-fouling capacity and selective dyes adsorption ability for complex wastewater remediation

Multifunctional filtration membranes (MFMs), which can both effectively separate oil and selectively remove dyes from polluted aquatic system with robust anti-viscous-oil-fouling capacity, strong chemical/physical resistance, and long cycled stability, are highly required but still a challenge to be realized. Herein, a simple route has been demonstrated to address this challenge aforementioned by decorating both halloysite nanotubes (HNTs) and zwitterionic poly (sulfobetaine methyl methacrylate) (PSBMA) on the microporous polyvinylidene fluoride (PVDF) membrane surface via modified polydopamine (PDA) coating route. The as-prepared membrane exhibits super-hydrophilic/underwater super-oleophobic performance and high water permeation flux (32529 ± 278 L m^-2 h^-1 at 0.85 bar) to purify the diverse viscous oil-in-water emulsions from oily wastewater accompanying with good cycled stability (the recovery rate of permeate flux is close to 100% after 5 cycles). Moreover, the as-prepared MFM possesses not only strong chemical resistance under wide range of pH value (from 1 to 12) and high saline (NaCl: 10 wt%) environment, but also physical resistance against ultrasound bath for 30 min. Given the presence of HNTs, PDA, and PSBMA, our MFM shows enough active sites to adsorb the soluble dyes and metallic ions in wastewater. These excellent properties endow our MFM with great potential for the remediation of complex wastewater.

Enhancing the Oil-Fouling Resistance of Polymeric Membrane Ion-Selective Electrodes by Surface Modification of a Zwitterionic Polymer-Based Oleophobic Self-Cleaning Coating

Due to the frequent oil spill accidents and pollution of industrial oily wastewater, oil fouling has become a great challenge to polymeric membrane ion-selective electrodes (ISEs) for applications in oil-contaminated areas. Herein, a simple approach is proposed to enhance the oil-fouling resistance of polymeric membrane ISEs by surface modification of a zwitterionic polymer-based underwater oleophobic coating. As a proof-of-concept, a classical poly(vinyl chloride) membrane-based calcium ion-selective electrode (Ca²⁺-ISE) is chosen as a model sensor. The zwitterionic polymer-based coating can be readily modified on the sensor's surface by immersion of the electrode into a mixture solution of dopamine and a zwitterionic acrylate monomer (i.e., sulfobetaine methacrylate, SBMA). The formed poly(SBMA) (PSBMA) coating alters the oleophilic membrane surface to an oleophobic one, which endows the surface with excellent self-cleaning properties without loss of the sensor's analytical performance. Compared to the pristine Ca²⁺-ISE, the PSBMA-modified Ca²⁺-ISE exhibits an improved analytical stability when exposed to oil-containing wastewater. The proposed approach can be explored to enhance the oil-fouling resistance of other polymeric membrane-based electrochemical sensors for use in the oil-polluted environment.

A tunable amphiphilic Enteromorpha-modified graphene aerogel for oil/water separation

Three-dimensional graphene aerogel materials used for treatment of oily wastewater with sophisticated composition remains a challenge due to volume shrinkage, resulting in single-function and low adsorption capacity. In this work, renewable Enteromorpha was introduced into the graphene aerogel via facile hydrothermal-freeze casting treatment, forming the compression, ultralight and amphiphilic adsorbent for oil spill cleanup and water pollution remediation. Meanwhile, further freeze casting avoids aerogel collapse for capillary tension during drying and produce more hierarchical pores. As for oil spill clean up, the Enteromorpha modified graphene aerogel (EGA) exhibits excellent adsorption capacity towards oil and organic solvents than pristine graphene aerogel (GA). Even after several cycles by compression and heat treatment, it still has a stable adsorption capacity for oil and organic solvents. The EGA also showed high ability to absorb water-soluble pollutants, such as dyes through hydrogen bonding and electrostatic reactions between dye molecules and aerogel. The facile strategy to fabricate the Enteromorpha-based amphiphilic EGA broadens the applications in water treatment through the high-value utilization of Enteromorpha.

Sacrifice Template Strategy to the Fabrication of a Self-Cleaning Nanofibrous Membrane for Efficient Crude Oil-in-Water Emulsion Separation with High Flux

The superhydrophilic/underwater superoleophobic membrane materials have attracted considerable attention in oil/water separation. However, most materials are extremely susceptible to pollution during oil-water separation, which drastically restricts their widespread applications. Herein, a momordica-charantia-like nanofibrous membrane (MCNM) with underwater superoleophobic performance was fabricated through a sacrifice template strategy by the electrospinning solution of zeolitic imidazolate framework-8 (ZIF-8) and polyacrylonitrile particles. The opened voids and wrinkles left after removing the template of nanocrystals ZIF-8 not only increased the porosity and roughness of the as-prepared fibrous membrane but also tremendously improved the underwater superoleophobicity. Therefore, the as-prepared MCNM showed excellent self-cleaning performance toward crude oil under water, avoiding the decrease of the separation efficiency and flux caused by membrane fouling during oil-water separation. Meanwhile, the separation efficiency of various surfactant-stabilized oil-in-water emulsions was higher than 99.6% with a flux up to 1580 ± 30 L m^-2 h^-1 solely driven by gravity. Moreover, no obvious wrinkles and cracks were observed on the resulted nanofibrous membrane after the sand impact and bent testing. More importantly, the as-prepared MCNM still maintained exceptional underwater superoleophobicity in harsh environment (3.5 wt % NaCl, 4 M HCl, 50 °C hot water) even after ultrasound for 1 h. The robust mechanical and chemical stability makes the antifouling MCNM exhibit tremendous potential for practical applications in dealing with oily wastewater in the future.

Energy-Saving Electrospinning with a Concentric Teflon-Core Rod Spinneret to Create Medicated Nanofibers

Although electrospun nanofibers are expanding their potential commercial applications in various fields, the issue of energy savings, which are important for cost reduction and technological feasibility, has received little attention to date. In this study, a concentric spinneret with a solid Teflon-core rod was developed to implement an energy-saving electrospinning process. Ketoprofen and polyvinylpyrrolidone (PVP) were used as a model of a poorly water-soluble drug and a filament-forming matrix, respectively, to obtain nanofibrous films via traditional tube-based electrospinning and the proposed solid rod-based electrospinning method. The functional performances of the films were compared through in vitro drug dissolution experiments and ex vivo sublingual drug permeation tests. Results demonstrated that both types of nanofibrous films do not significantly differ in terms of medical applications. However, the new process required only 53.9% of the energy consumed by the traditional method. This achievement was realized by the introduction of several engineering improvements based on applied surface modifications, such as a less energy dispersive air-epoxy resin surface of the spinneret, a free liquid guiding without backward capillary force of the Teflon-core rod, and a smaller fluid-Teflon adhesive force. Other non-conductive materials could be explored to develop new spinnerets offering good engineering control and energy savings to obtain low-cost electrospun polymeric nanofibers.