Developing a feasible and efficient separation membrane for the purification of highly emulsified oily wastewater is of significance but challenging due to the critical limitations of low flux and ...serious membrane fouling. Herein, a biomimetic and superwettable nanofibrous skin on an electrospun fibrous membrane via a facile strategy of synchronous electrospraying and electrospinning is created. The obtained nanofibrous skin possesses a lotus‐leaf‐like micro/nanostructured surface with intriguing superhydrophilicity and underwater superoleophobicity, which are due to the synergistic effect of the hierarchical roughness and hydrophilic polymeric matrix. The ultrathin, high porosity, sub‐micrometer porous skin layer results in the composite nanofibrous membranes exhibiting superior performances for separating both highly emulsified surfactant‐free and surfactant‐stabilized oil‐in‐water emulsions. An ultrahigh permeation flux of up to 5152 L m−2 h−1 with a separation efficiency of >99.93% is obtained solely under the driving of gravity (≈1 kPa), which was one order of magnitude higher than that of conventional filtration membranes with similar separation properties, showing significant applicability for energy‐saving filtration. Moreover, with the advantage of an excellent antioil fouling property, the membrane exhibits robust reusability for long‐term separation, which is promising for large‐scale oily wastewater remediation.
A biomimetic and superwettable nanofibrous skin is constructed in situ. The membrane equipped with the skin layer exhibits sub‐micrometer pores, superhydrophilicity, and underwater superoleophobicity, which is effective in separating the highly emulsified oil‐in‐water emulsions with excellent separation efficiency, has high permeation fluxes at a low driving pressure, along with an intriguing antifouling property and good reusability.
The separation of oil and water is a worldwide challenge due to the ever-increasing amount of oily industrial wastewater and polluted oceanic waters, as well as the increasing frequency of oil spill ...accidents. As the leader of advanced fibrous materials, electrospun nanofibers combine the properties of tunable wettability, large surface area, high porosity, good connectivity, fine flexibility, and ease of scalable synthesis from various materials (polymer, ceramic, carbon, etc.), and they hold great potential for many emerging environmental applications, including the separation of oily wastewater. In this review, the recent progress in the design and fabrication of electrospun nanofibrous materials with tunable surface wettability for oil/water separation applications is summarized and highlighted. This review covers the research and development starting from the design concepts and the synthesis of nanofibrous sorbents, nanofibrous membranes, and nanofibrous aerogels for effective oil/water separation. The review concludes with a brief forecast of challenges and future directions in this rapidly expanding field.
Abstract
Desiccants play vital roles in dehumidification and atmospheric water harvesting; however, current desiccants have mediocre hygroscopicity, limited recyclability, and high energy ...consumption. Herein, we report a wood-inspired moisture pump based on electrospun nanofibrous membrane for solar-driven continuous indoor dehumidification. The developed moisture pump with multilayer wood-like cellular networks and interconnected open channels is composed of a desiccant layer and a photothermal layer. The desiccant layer exhibits an unprecedented moisture absorption capacity of 3.01 g g
−1
at 90% relative humidity (RH), fast moisture absorption and transport rates, enabling atmospheric water harvesting. The photothermal layer shows a high solar absorption of 93%, efficient solar thermal conversion, and good moisture permeability, thus promoting water evaporation. The moisture pump efficiently reduces the indoor relative humidity to a comfort level (40‒60% RH) under one-sun illumination. This work opens the way to develop new-generation, high-performance nanofibrous membrane-based desiccants for energy-efficient humidity control and atmospheric water harvesting.
A direct approach for fabricating nanoporous polymer fibers via electrospinning has been demonstrated. Polystyrene (PS) fibers with micro- and nanoporous structures both in the core and/or on the ...fiber surfaces were electrospun in a single process by varying solvent compositions and solution concentrations of the PS solutions. The porous structures of the fibrous mats were characterized by field emission scanning electron microscopy and Brunauer−Emmett−Teller measurements to confirm that they could be accurately controlled by tuning vapor pressure of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) solvent mixtures and PS concentrations in the solutions. As the solution concentration decreased, the average fiber diameter decreased, whereas the bead density increased dramatically to show a beads-on-string morphology. Both the specific surface area and pore volume of the fibrous mats showed a unimodal distributions centered at 1/3 THF /DMF mix ratio. Fibers formed from 5 wt % PS in the 1/3 THF and DMF mixtures had the largest specific surface area of 54.92 m2 g−1 and a pore volume of 0.318 cm3g−1, respectively.
Particulate matter (PM) pollution has become a serious public health issue, especially with outbreaks of emerging infectious diseases. However, most present filters are bulky, opaque, and show ...low‐efficiency PM0.3/pathogen interception and inevitable trade‐off between PM removal and air permeability. Here, a unique electrospraying–netting technique is used to create spider‐web‐inspired network generator (SWING) air filters. Manipulation of the dynamic of the Taylor cone and phase separation of its ejected droplets enable the generation of 2D self‐charging nanostructured networks on a large scale. The resultant SWING filters show exceptional long‐range electrostatic property driven by aeolian vibration, enabling self‐sustained PM adhesion. Combined with their Steiner‐tree‐structured pores (size 200–300 nm) consisting of nanowires (diameter 12 nm), the SWING filters exhibit high efficiency (>99.995% PM0.3 removal), low air resistance (<0.09% atmosphere pressure), high transparency (>82%), and remarkable bioprotective activity for biohazard pathogens. This work may shed light on designing new fibrous materials for environmental and energy applications.
A spider‐web‐inspired network generator (SWING)‐based air filter constructed from 2D electrostatic nanostructured networks is created by a unique electrospraying–netting technique. Due to the self‐sustained electrostatic adhesion driven by aeolian vibration and Steiner‐tree‐structured pores (size 200–300 nm) consisting of nanowires (diameter 12 nm), the SWING filters achieve >99.995% PM0.3 removal, <0.09% atmosphere pressure, >82% transmittance, and remarkable bioprotective activity.
Many applications proposed for functional nanofibers require their assembly into a monolithic cellular structure. The ability to maintain structural integrity upon large deformation is essential to ...ensure a macroscopic cellular material that functions reliably. However, it remains a great challenge to achieve high elasticity in three-dimensional (3D) nanofibrous networks. Here, we report a strategy to create fibrous, isotropically bonded elastic reconstructed (FIBER) aerogels with a hierarchical cellular structure and superelasticity by combining electrospun nanofibers and the freeze-shaping technique. Our approach allows the intrinsically lamellar deposited electrospun nanofibers to assemble into elastic bulk aerogels with tunable porous structure and wettability on a large scale. The resulting FIBER aerogels exhibit the integrated properties of ultralow density (<30 mg cm–3), rapid recovery from 80% compression strain, superhydrophobic-superoleophilic wettability, and high pore tortuosity. More interestingly, the FIBER aerogels can effectively separate surfactant-stabilized water-in-oil emulsions, solely using gravity, with high flux (maximum of 8140 ± 220 L m–2 h–1) and high separation efficiency, which match well with the requirements for treating the real emulsions. The synthesis of FIBER aerogels also provides a versatile platform for exploring the applications of nanofibers in a self-supporting, structurally adaptive, and 3D macroscopic form.
Waterproof and breathable macroporous membranes that are both completely resistant to liquid water penetration and easily allowable to vapor transmission would have significant implication for ...numerous applications; however, fabrication of such materials has proven to be tremendously challenging. Herein, we reported novel electrospun composite fibrous membranes with high waterproof and breathable performance, which consisted of polyurethane (PU), terminal fluorinated polyurethane (FPU), and carbon nanotubes (CNTs). Benefiting from the utilization of FPU and CNTs, the fibrous membranes were endowed with superhydrophobic surface, optimized pores size and porosity, along with enhanced fibers, which resulted in excellent waterproof, breathable and mechanical properties. Significantly, the relationship among waterproofness, pore structure and surface wettability has been confirmed finely accordance with Young–Laplace equation. Ultimately, the resultant membranes presented high waterproofness with hydrostatic pressure up to 108 kPa, good breathability with water vapor transmission rate over 9.2 kg m–2 d–1, as well as robust mechanical properties with bursting strength of 47.6 kPa and tensile strength of 12.5 MPa, suggesting them as promising alternatives for a number of potential applications, such as protective clothing.
Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting ...process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author's research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued.
Abstract
Two-dimensional network-structured carbon nanoscale building blocks, going beyond graphene, are of fundamental importance, and creating such structures and developing their applications have ...broad implications in environment, electronics and energy. Here, we report a facile route, based on electro-spraying/netting, to self-assemble two-dimensional carbon nanostructured networks on a large scale. Manipulation of the dynamic ejection, deformation and assembly of charged droplets by control of Taylor cone instability and micro-electric field, enables the creation of networks with characteristics combining nanoscale diameters of one-dimensional carbon nanotube and lateral infinity of two-dimensional graphene. The macro-sized (meter-level) carbon nanostructured networks show extraordinary nanostructural properties, remarkable flexibility (soft polymeric mechanics having hard inorganic matrix), nanoscale-level conductivity, and outstanding performances in distinctly different areas like filters, separators, absorbents, and wearable electrodes, supercapacitors and cells. This work should make possible the innovative design of high-performance, multi-functional carbon nanomaterials for various applications.
Waterproof and breathable membranes (WBMs) with simultaneous environmental friendliness and high performance are highly desirable in a broad range of applications; however, creating such materials ...still remains a tough challenge. Herein, we present a facile and scalable strategy to fabricate fluorine-free, efficient, and biodegradable WBMs via step-by-step dip-coating and heat curing technology. The hyperbranched polymer (ECO) coating containing long hydrocarbon chains provided an electrospun cellulose acetate (CA) fibrous matrix with high hydrophobicity; meanwhile, the blocked isocyanate cross-linker (BIC) coating ensured the strong attachment of hydrocarbon segments on CA surfaces. The resulting membranes (TCA) exhibited integrated properties with waterproofness of 102.9 kPa, breathability of 12.3 kg m–2 d–1, and tensile strength of 16.0 MPa, which are much superior to that of previously reported fluorine-free fibrous materials. Furthermore, TCA membranes can sustain hydrophobicity after exposure to various harsh environments. More importantly, the present strategy proved to be universally applicable and effective to several other hydrophilic fibrous substrates. This work not only highlights the material design and preparation but also provides environmentally friendly and high-performance WBMs with great potential application prospects for a variety of fields.
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