Acrylic acid-grafted pre-plasma nanofibers for efficient removal of oil pollution from aquatic environment

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.

Improvement strategies for oil/water separation based on electrospun SiO2 nanofibers

Oil spills and oily effluents from industry and daily life pose a great threat to all organisms in the ecosystem, while aggravating the problem of water scarcity, which has developed into a global challenge. Therefore, the development of advanced materials and technologies for oil/water separation has become a focus of attention. One-dimensional (1D) SiO2 nanofibers (SNFs) have become one of the most widely used inorganic nanomaterials in the past due to their stable chemical properties, excellent biocompatibility, and high temperature resistance etc. Meanwhile, electrospinning technique, as an emerging technology for treating oil/water emulsions, electrospun SNFs on this basis also has a number of advantages such as adjustable wettability, diverse structure and good connectivity. This review provides a systematic overview of the research progress of electrospun SNFs in different aspects. In this review, we first introduce the basic principles of electrospun SNFs, then focus on the design structures of various SNFs, propose corresponding strategies for the property improvement of SNFs, also analyze and consider the applications of SNFs. Finally, the challenges faced by electrospun SNFs in the field of oil/water separation are analyzed, and the future directions of electrospun SNFs are summarized and prospected.

Ti2NTx quasi-MXene modified polyamide thin film composite reverse osmosis membrane with effective desalination and antifouling performance

In this study, considering the serious problem of lack of fresh water worldwide and the effectiveness of reverse osmosis (RO) membranes in water purification, we prepared improved RO membranes with two-dimensional quasi-MXene nanosheets. In this study, the MAX phase with the chemical formula of Ti2AlN was prepared through the reactive sintering route. Prosperous preparation of the MAX phase with the hexagonal crystalline structure was approved by an X-ray diffraction pattern. Compacted sheets morphology was recognized for the prepared MAX phase from transmittance electron microscopy and scanning electron microscopy micrographs. Then, Ti2NTx quasi-MXene nanosheets were prepared by selective ultrasonic-assisted exfoliation of the MAX phase. Polyamide (PA) thin-layer composite RO membranes with different weight percentages of Ti2NTx quasi-MXene were fabricated by the interfacial polymerization (IP) method. The addition of ultrasonic-assisted prepared quasi-MXene creates numerous and coherent nanochannels on the surface of the membrane. The optimum membrane with 0.01 wt% of quasi-MXene showed the highest pure water flux of 31.9 L m-2. h-1 with an improved salt rejection of 98.2%. Therefore, these nanosheets showed that they can partially solve the trade-off between water permeability and salt rejection, which is a serious challenge in RO membranes. Also, the membranes containing quasi-MXene showed good resistance against fouling by humic acid. This research can be a scalable development in making high-performance membranes.

Constructing a highly tough, durable, and renewable flexible filter by epitaxial growth of a glass fiber fabric for high flux and superefficient oil-water separation

The separation and purification of complex and stable stubborn oily sewage is extremely challenging. To respond to this challenge, we developed a powerful flexible filter with ultrahigh strength, durability, flux, separation efficiency, and a multiobjective separation function based on a universal epitaxial growth process of glass fiber fabric (Gf). The underwater oil contact angle (UOCA) of the silicate@Gf (MgSi@Gf) filter is 156.3°, so it can achieve both an ultrahigh permeation flux (5632.7 L·m^-2·h^-1) and oil-water separation efficiency (99.5%) under gravity (≈ 1 kPa) in purifying surfactant-stabilized emulsions, actual industrial oily sewage and mechanical cold rolling emulsions. The filter with a high tensile strength (66.5 MPa) and oil invasion pressure (4626 Pa) can withstand the impact of much sewage or intense water flow. The filter can tolerate extreme conditions and can maintain high separation performance in acid or alkaline (pH 1-13), high or low temperature (100 °C, 200 °C, -18 °C) conditions or natural salty waters such as seawater. The filter can remove methylene blue (MB) dye (99.8%) by filtration, and can be repeatedly and easily reconstructed (renewable advantage). The filter shows great potential for efficiently eliminating the hazards of contaminants in actual oily sewage and thus protect human health.

Efficacy of Electrospun Nanofiber Membranes on Fouling Mitigation: A Review

Despite the advantages of high contaminant removal, operational flexibility, and technical advancements offered, the undesirable fouling property of membranes limits their durability, thus posing restrictions on their usage. An enormous struggle is underway to conquer this major challenge. Most of the earlier reviews include the basic concepts of fouling and antifouling, with respect to particular separation processes such as ultrafiltration, nanofiltration, reverse osmosis and membrane bioreactors, graphene-based membranes, zwitterionic membranes, and so on. As per our knowledge, the importance of nanofiber membranes in challenging the fouling process has not been included in any record to date. Nanofibers with the ability to be embedded in any medium with a high surface to volume ratio play a key role in mitigating the fouling of membranes, and it is important for these studies to be critically analyzed and reported. Our Review hence intends to focus on nanofiber membranes developed with enhanced antifouling and biofouling properties with a brief introduction on fabrication processes and surface and chemical modifications. A summary on surface modifications of preformed nanofibers is given along with different nanofiller combinations used and blend fabrication with efficacy in wastewater treatment and antifouling abilities. In addition, future prospects and advancements are discussed.

Functionalized Nanomembranes and Plasma Technologies for Produced Water Treatment: A Review

The treatment of produced water, associated with oil & gas production, is envisioned to gain more significant attention in the coming years due to increasing energy demand and growing interests to promote sustainable developments. This review presents innovative practical solutions for oil/water separation, desalination, and purification of polluted water sources using a combination of porous membranes and plasma treatment technologies. Both these technologies can be used to treat produced water separately, but their combination results in a significant synergistic impact. The membranes functionalized by plasma show a remarkable increase in their efficiency characterized by enhanced oil rejection capability and reusability, while plasma treatment of water combined with membranes and/or adsorbents could be used to soften water and achieve high purity.

Green Synthesis of Silver Nanoparticles as an Effective Antibiofouling Material for Polyvinylidene Fluoride (PVDF) Ultrafiltration Membrane

Silver nanoparticles (AgNPs) were successfully synthesized using the aqueous extract of the Paronychia argentea Lam (P. argentea) wild plant. The results showed that the conversion of Ag⁺ to Ag⁰ nanoparticles ratio reached 96.5% as determined by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), with a negative zeta potential (ζ) of −21.3 ± 7.68 mV of AgNPs expected to improve the stability of synthesized AgNPs. AgNP antibacterial activity has been examined against Streptococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria. The minimum inhibition concentration (MIC) was 4.9 µL/mL for both E. coli and S. aureus bacteria, while the minimum bactericidal concentrations (MBC) were 19.9 µL/mL and 4.9 µL/mL for S. aureus and E. coli, respectively. The synthesized AgNPs were incorporated in ultrafiltration polyvinylidene Fluoride (PVDF) membranes and showed remarkable antibiofouling behavior against both bacterial strains. The membranes were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and X-ray diffraction (XRD). The contact angle and porosity of the membrane were also determined. The efficiency of the membranes regarding rejection rate was assessed using bovine serum albumin (BSA). It was found in the flux experiments that membranes BSA rejection was 99.4% and 98.7% with and without AgNPs, respectively.

Electrospun stereocomplex polylactide porous fibers toward highly efficient oil/water separation

The urgent needs for water protection are not only developing the highly efficient wastewater treatment technologies but also designing the eco-friendly materials. In this work, the eco-friendly composite fibers composed of poly(L-lactide) (PLLA), poly(D-lactide) (PDLA) and maghemite nanoparticles γ-Fe₂O₃ nanoparticles were fabricated through electrospinning technology. Through regulating the processing parameters and introducing additional annealing treatment, nanoscale porous structure and the stereocomplex crystallites (SCs) are simultaneously constructed in the composite electrospun fibers. Physicochemical performances measurements exhibited that the fiber membranes had excellent lipophilicity, good mechanical performances, and high hydrolysis resistance, and all of which endowed the fiber membranes with high oil adsorption capacities, and the maximum oil adsorption capacities achieved 148.9 g/g at 23 °C and 114.8 g/g at 60 °C. Further results showed that the fiber membranes had good oil/water separation ability. The gravity-driven oil flux was 6824.4 L/m²h², and the water rejection ratio was nearly 100% during separating oil/water mixture. Specifically, the fiber membranes showed good stability during the cycling measurements. It is evidently confirmed that the composite PLLA-based fiber membranes with porous structure and SCs can be used in wastewater treatment, especially in some rigorous circumstances.

A review of recent progress in polymeric electrospun nanofiber membranes in addressing safe water global issues

With rapid advancement in water filtration materials, several efforts have been made to fabricate electrospun nanofiber membranes (ENMs). ENMs play a crucial role in different areas of water treatment due to their several advantageous properties such as high specific surface area, high interconnected porosity, controllable thickness, mechanical robustness, and wettability. In the broad field of water purification, ENMs have shown tremendous potential in terms of permeability, rejection, energy efficiency, resistance to fouling, reusability and mechanical robustness as compared to the traditional phase inversion membranes. Upon various chemical and physical modifications of ENMs, they have exhibited great potential for emerging applications in environment, energy and health sectors. This review firstly presents an overview of the limiting factors influencing the morphology of electrospun nanofibers. Secondly, it presents recent advancements in electrospinning processes, which helps to not only overcome drawbacks associated with the conventional electrospinning but also to produce nanofibers of different morphology and orientation with an increased rate of production. Thirdly, it presents a brief discussion about the recent progress of the ENMs for removal of various pollutants from aqueous system through major areas of membrane separation. Finally, this review concludes with the challenges and future directions in this vast and fast growing area.

Design of poly ionic liquids modified cotton fabric with ion species-triggered bidirectional oil-water separation performance

A novel ion species-responsive oil-water separation material was designed: poly ionic liquid (PIL) was carried on the graphene oxide (GO) by free radical polymerization, then the PIL modified GO sheets (GO-PIL) were coated on cotton fabric (CF). The wettability of the obtained GO-PIL coated CF (GO-PIL@CF) could be switched between hydrophilic and hydrophobic state with the exchange of different types of counteranions. Water contact angle of the GO-PIL@CF could be switched between 0 to about 145°; and correspondingly the underwater oil contact angle would change between about 148 to 0°. Because of the switchable wettability, the GO-PIL@CF could selectively separate water or oil from the oil-water mixtures. Meanwhile, due to the loose fibrous structure, the GO-PIL@CF showed relatively high permeate fluxes; in the hydrophilic state the water flux was about 36000 L/m²h, while in the hydrophobic state the fluxes for the low-density oils (n-hexane and toluene) were about 59,000 and 65000 L/m²h, respectively. Consequently, the separation processes could be completed simply by gravity. In addition, because of the soft and flexible mechanical property, the GO-PIL@CF could serve as wrappage of traditional absorbents and be applied directly as absorbent to remove water or oil selectively from their mixtures.

One-step electrospinning cellulose nanofibers with superhydrophilicity and superoleophobicity underwater for high-efficiency oil-water separation

Cellulose nanofibers have been widely applied in many fields because of its unique advantages. However, it is a challenge to prepare cellulose nanofibers by electrospinning directly owing to the special molecular structure of cellulose. This limits the practical applications of cellulose nanofibers. In this work, cellulose nanofibers were successfully prepared directly by design of new electrospinning receiving device and optimization of process parameters. The as-prepared cellulose nanofibers exhibit good oil-water separation performances. Driven solely by gravity, the separation flux of the cellulose nanofibers for mixture of oil and water reaches 34,300.6 L m^-2 h^-1, and the separation flux and efficiency for surfactant-stabilized emulsion of oil and water reach 2503.7 L m^-2 h^-1 and over 98.3%, respectively. The as-prepared cellulose nanofibers also exhibit good mechanical properties and reusability. The breaking strength of the cellulose nanofibers can reach 148.2 cN. The separation fluxes of cellulose nanofibers for mixtures and emulsions of oil and water can be maintained 99.7% and 86.3% of the initial value after being used for 20 times. Furthermore, the as-prepared cellulose nanofibers have good degradability. These properties render as-prepared cellulose nanofibers as promising materials with potential applications in oil-water separation.

Enabling phase transition of infused lubricant in porous structure for exceptional oil/water separation

The fundamental mechanism behind oil/water separation materials is their surface wettability that allows either oil or water to pass through. The conventional materials for oil/water separation generally have extreme wettability, namely superhydrophilic for water separation and superhydrophobic for oil separation. Using easily accessible materials that are medium hydrophobic or even relatively hydrophilic for preparing highly efficient oil/water separators have rarely been reported. In this work, a new strategy by triggering phase transition of infused lubricant from liquid to solid state in porous structure is realized in fabricating slippery lubricant infused porous structure for oil/water separations. By infusing polyester fabric with coconut oil, after phase transition, excellent water repellency and oil permeability by an absorbing-permeating mechanism are achieved, despite the low water contact angle on the new material. Although the new phase transformable slippery lubricant infused porous structure, features much milder hydrophobicity than conventional oil/water separators, it can remove diverse types of oil from water with high efficiencies. The phase transformable slippery lubricant infused porous structure is able to maintain their water repellency after immersing in high concentration salt (10 wt% NaCl), acid (25 % HCl), alkaline (25 % NH₃·H₂O) solutions for 120 h, showing remarkably functional durability in harsh environment. The lubricant phase transition mechanism proposed in this study is universally applicable to porous substrates with various chemical compositions and pore structures, such as porous sponges or even daily life breads, for creating efficient oil/water separators, which can serve as a novel accessible design principle of phase transformable slippery lubricant infused porous structure for eco-friendly oil/water separators.

One-pot fabrication of reusable hybrid sorbents for quick removal of oils from wastewater

The leaking of harmful organic liquids into water resources has had hazardous impacts on living organisms. Herein, we demonstrated the fabrication of hybrid sorbents using s-PPG and organosilane cross-linker. The final product exhibited high, quick absorption capacity, great reusability and excellent oil separation performance from wastewater. They also selectively absorb different oils from the bottom and surface of water without any capacity change, even in harsh conditions like wavy and sub-zero water environment. Experimental results demonstrated that the obtained sorbents are efficient to successfully remove oil from water surface, even at harsh conditions, and float on the water surface before and after oil sorption without any capacity loss and structural change. Simple preparation by avoiding time consuming multistep process, initiator, solvent, activator free reaction medium, high and selective sorption characteristics and great reusability could make these sorbents a promising candidate for the cleaning of water from harmful organic liquids, by absorbing them.

Multifunctional PVDF/CNT/GO mixed matrix membranes for ultrafiltration and fouling detection

Membrane fouling can be effectively addressed by modifying the membrane to realize anti-fouling capability together with real-time fouling detection. Here, we present the synthesis and water treatment testing of a promising candidate for this application, a composite membrane of polyvinylidene fluoride (PVDF) and functionalized carbon nano-materials prepared by a facile phase inversion method. The synergistic effect of oxidized multi-walled carbon nanotubes (OMWCNTs) and graphene oxide (GO) enabled better surface pore structures, higher surface roughness, hydrophilicity, and better antifouling property as compared with that of pristine PVDF membranes. The PVDF/OMWCNT/GO mixed matrix membranes (MMMs) achieved a high water flux of 125.6 L m^-2 h^-1 with high pollutant rejection rate, and their electrical conductivity of 2.11 × 10^-4 S cm^-1 at 100 kHz was sensitive to the amount of pollutant uptake. By using hybrid MMMs, we demonstrate simultaneous pollutant filtering and uptake monitoring, which is an important step in revolutionizing the water treatment industry.

Nature-inspired chemistry toward hierarchical superhydrophobic, antibacterial and biocompatible nanofibrous membranes for effective UV-shielding, self-cleaning and oil-water separation

Fabrication of environmental-friendly, low-cost, and free-standing superhydrophobic nanofibrous membranes with additional functionalities such as self-cleaning and UV-shielding properties is highly demanded for oil-water separation. Herein, we describe the preparation of multifunctional superhydrophobic nanofibrous membrane by using a facile and novel nature-inspired method, i.e., plant polyphenol (tannic acid) metal complex is introduced to generate rough hierarchical structures on the surface of an electrospun polyimide (PI) nanofibrous membrane, followed by modification of poly (dimethylsiloxane) (PDMS). Taking an as-prepared tannic acid - Al³⁺-based superhydrophobic membrane as an example, it not only exhibits anti-impact, low-adhesive and self-cleaning functions, but also presents excellent performance in the separation of various oil-water mixtures. A high flux up to 6935 l m^-2 h^-1 with a separation efficiency of over 99% and the oil contents in water below 5 ppm is obtained even after repeating use for twenty separation cycles. Additionally, the membrane exhibits excellent UV-shielding property, attributing to the inherent UV-absorbing ability of tannic acid. Furthermore, the membrane also possesses additional properties including antibacterial activity, good biocompatibility, robust mechanical strength, and excellent resistance to various harsh conditions. These attractive properties of the as-prepared membrane make it a promising candidate for potential applications in industrial oil-contaminated water treatments and oil-water separation.

Smart nonwoven fabric with reversibly dual-stimuli responsive wettability for intelligent oil-water separation and pollutants removal

This work presents the first fabrication of smart nonwoven fabric (DSR-CZPP) with extraordinary reversible double-stimulus responsive wettability, where carboxyl groups of cellulose nanocrystals/zinc oxide (CNC/ZnO) nanohybrids deposited on fabric surface can bond with hydroxyl group of the PDMAEMA-b-PHEMA-b-PMAAAB triblock polymer brushes that was prepared by using methyl methacrylate (HEMA), dimethylaminoethyl methacrylate (DMAEMA) and methacrylamide-azobenzene monomer (MAAAB) via reversible addition-fragmentation chain transfer (RAFT). The peculiar reversible double-stimulus responsive wettability of the DSR-CZPP can be modulated by triggering hydrophilic/hydrophobic transitions and lipophilic/oleophobic transitions under dual-stimulations of pH and UV light irradiation. The special molecular structure of the triblock polymer brushes enabled DSR-CZPP to intelligent modulation of oil-water separation under the control of "UV & pH double switch", meanwhile CNC/ZnO simultaneously can induce the photocatalytic degradation of organic dyes. Moreover, DSR-CZPP can have high removal ratios of various pollutants, such as metal ion (Cu²⁺) and toxic organic solvent (silicone oil, acetone and chloroform). This smart and multifunctional fabric shows great potentials for treating complicated polluted water from most industrial fields.

Electrospun SiO2-MgO hybrid fibers for heavy metal removal: Characterization and adsorption study of Pb(II) and Cu(II)

SiO₂-MgO hybrid fibers (SMHFs) were fabricated by one-step electrospinning process, characterized, and evaluated in heavy metal adsorption, for the first time. High-pressure steam (HPS) pretreated SMHFs showed high specific surface area (S_BET) and large number of surface basic sites accompanied by the crystallization of MgO. The SMHFs showed high affinities for Pb(II) and Cu(II) with the distribution coefficients K_d>100 L·g^-1 (when pH > 4). Langmuir model and pseudo-second-order kinetic model described the experimental data well, and the maximum adsorption capacities of 787.9 and 493.0 mg·g^-1 for Pb(II) and Cu(II) at 298 K were the highest among those of reported SiO₂-MgO adsorbents. Thermodynamics indicated SMHFs had the spontaneous and physicochemical adsorption nature. SMHFs kept good capacities in the presence of interfering substances and retained their reusability. The SMHFs with the superiority of high efficiency, low cost, easy preparation and environmentally benign, have promising applications in wastewater treatment and relative fields.