In Situ Electrospun Porous MIL-88A/PAN Nanofibrous Membranes for Efficient Removal of Organic Dyes.

In recent years, metal-organic framework (MOF)-based nanofibrous membranes (NFMs) have received extensive attention in the application of water treatment. Hence, it is of great significance to realize a simple and efficient preparation strategy of MOF-based porous NFMs. Herein, we developed a direct in situ formation of MOF/polymer NFMs using an electrospinning method. The porous MOF/polymer NFMs were constructed by interconnecting mesopores in electrospun composite nanofibers using poly(vinylpolypyrrolidone) (PVP) as the sacrificial pore-forming agent. MOF (MIL-88A) particles were formed inside the polyacrylonitrile (PAN)/PVP nanofibers in situ during electrospinning, and the porous MIL-88A/PAN (pMIL-88A/PAN) NFM was obtained after removing PVP by ethanol and water washing. The MOF particles were uniformly distributed throughout the pMIL-88A/PAN NFM, showing a good porous micro-nano morphological structure of the NFM with a surface area of 143.21 m2 g-1, which is conducive to its efficient application in dye adsorption and removal. Specifically, the dye removal efficiencies of the pMIL-88A/PAN NFM for amaranth red, rhodamine B, and acid blue were as high as 99.2, 94.4, and 99.8%, respectively. In addition, the NFM still showed over 80% dye removal efficiencies after five adsorption cycles. The pMIL-88A/PAN NFM also presented high adsorption capacities, fast adsorption kinetics, and high cycling stabilities during the processes of dye adsorption and removal. Overall, this work demonstrates that the in situ electrospun porous MOF/polymer NFMs present promising application potential in water treatment for organic dyestuff removal.

Removal of Acidic Organic Ionic Dyes from Water by Electrospinning a Polyacrylonitrile Composite MIL101(Fe)-NH2 Nanofiber Membrane.

A nanofiber metal-organic framework filter, a polyacrylonitrile (PAN) nanofiber membrane composite with an iron/2-amino-terephthalic acid-based metal-organic framework (MIL101(Fe)-NH2), was prepared by one-step electrospinning. MIL101(Fe)-NH2 was combined into the polymer nanofibers in situ. PAN-MIL101(Fe)-NH2 composite nanofiber membranes (NFMs) were prepared from a homogeneous spinning stock containing MIL101(Fe)-NH2 prebody fluid and PAN. Crystallization of MIL101(Fe)-NH2 and solidification of the polymer occurred simultaneously during electrospinning. The PAN-MIL101(Fe)-NH2 composite NFM showed that MIL101(Fe)-NH2 was uniformly distributed throughout the nanofiber and was used to adsorb and separate acidic organic ionic dyes from the aqueous solution. The results of Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis showed that MIL101(Fe)-NH2 crystals were effectively bonded in the PAN nanofiber matrix, and the crystallinity of MIL101(Fe)-NH2 crystals remained good, while the distribution was uniform. Owing to the synergistic effect of PAN and the MIL101(Fe)-NH2 crystal, the PAN-MIL101(Fe)-NH2 composite NFM showed a fast adsorption rate for acidic ionic dyes. This study provides a reference for the rapid separation and purification of organic ionic dyes from wastewater.

Electrospun Nanofiber Membranes from 1,8-Naphthimide-Based Polymer/Poly(vinyl alcohol) for pH Fluorescence Sensing.

Accurately and sensitively sensing and monitoring the pH in the environment is a key fundamental issue for human health. Nanomaterial and nanotechnology combined with fluorescent materials can be emerged as excellent possible methods to develop high-performance sensing membranes and help monitor pH. Herein, a series of fluorescent nanofiber membranes (NFMs) containing poly-1,8-naphthimide derivative-3-[dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azaniumyl]propane-1-sulfonate (PNI-SBMA) are fabricated by electrospinning the solution of PNI-SBMA blended with poly(vinyl alcohol) (PVA). The surfactant-like functionalities in side chains of PNI-SBMA endow the NFMs with outstanding hydrophilicity, and the naphthimide derivatives are sensitive to pH by photoinduced electron transfer effect, which contribute to highly efficient pH fluorescence sensing applications of NFMs. Specifically, the PNI-SBMA/PVA NFM with a ratio of 1:9 (NFM2) shows high sensitivity and good cyclability to pH. This work demonstrates an effective strategy to realize a fluorescent sensor NFM that has a fast and sensitive response to pH, which will benefit its application of pH sensor monitoring in the water treatment process.

Gradient structured micro/nanofibrous sponges with superior compressibility and stretchability for broadband sound absorption.

Ultrafine fibrous porous materials obtained by electrospinning technology have broad application prospects in the field of noise reduction. However, the two-dimensional fibrous membranes faced low thickness and dense structure, resulting in a single internal structure and narrow sound absorption band. Here, we report a simple and robust strategy to prepare gradient structured fiber sponges with superelasticity and stretchability by combining humidity-assisted multi-step electrospinning and a unique physical/chemical dual cross-linking method. The prepared gradient structured fibrous sponge has a maximum tensile strength of 169 kPa and can lift a weight 10,000 times its weight without breaking. Besides, the material can still maintain a stable structure after 500 compression cycles at 60% strain. Meantime, the material has lightweight properties (density of 13.8 mg cm-3) and hydrophobicity (water contact angle of 152°). More importantly, the gradient change of porosity and pore diameter in the Z direction endowed the fibrous sponge material with high-efficiency absorption of broadband sound waves (with a noise reduction coefficient up to 0.53). The design of this gradient structured fiber sponge opens a new way for the development of ideal sound-absorbing materials.

Multi-scaled interconnected inter- and intra-fiber porous janus membranes for enhanced directional moisture transport.

HYPOTHESIS: Growing use of comfortable functional textiles has resulted in increased demand of excellent directional moisture (sweat) transport feature in textiles. However, designing such anisotropic functional textiles that allow fast penetration of sweat through one direction but prevent its movement in the reverse direction is still a challenging task. In this regard, fabrication of a novel Janus membrane with multi-scaled interconnected inter- and intra-fiber pores for enhanced directional moisture transport designed by a rational combination of superhydrophilic hydrolyzed porous polyacrylonitrile (HPPAN) nanofibers and hydrophobic polyurethane (PU) fibers via electrospinning may be a very useful approach. EXPERIMENT: PAN/PVP composite nanofibers were electrospun using PAN/PVP composite solution dissolved in DMF. After electrospinning, electrospun fibers were subjected extensive washing process to selectively remove PVP from the fiber matrix to develop highly rough and porous PAN (PPAN) nanofibers. The resultant PPAN nanofibers were then hydrolyzed to further improve their wettability. Finally, a layer of PU fibers was directly deposited on the HPPAN nanofibers via electrospinning to fabricate the subsequent Janus membrane. FINDINGS: The resultant PU/HPPAN Janus membranes display instant moisture transport in the positive direction with exceptional directional moisture transport index (R = 1311.3%), whereas, offer superior resistance (i.e. breakthrough pressure ≥17.1 cm H2O) to the moisture movement in the reverse direction. Moreover, a plausible mechanism articulating the role of inter- and intra-porosity for the enhanced directional moisture transport has been proposed. Successful fabrication of such fascinating Janus membranes based on the proposed coherent mechanism opens a new insight into the engineering of novel functional textiles for fast sweat release and personal drying applications.

Constructing Ionic Gradient and Lithiophilic Interphase for High-Rate Li-Metal Anode.

Li metal is the optimal choice as an anode due to its high theoretical capacity, but it suffers from severe dendrite growth, especially at high current rates. Here, an ionic gradient and lithiophilic inter-phase film is developed, which promises to produce a durable and high-rate Li-metal anode. The film, containing an ionic-conductive Li0.33 La0.56 TiO3 nanofiber (NF) layer on the top and a thin lithiophilic Al2 O3 NF layer on the bottom, is fabricated with a sol-gel electrospinning method followed by sintering. During cycling, the top layer forms a spatially homogenous ionic field distribution over the anode, while the bottom layer reduces the driving force of Li-dendrite formation by decreasing the nucleation barrier, enabling dendrite-free plating-stripping behavior over 1000 h at a high current density of 5 mA cm-2 . Remarkably, full cells of Li//LiNi0.8 Co0.15 Al0.05 O2 exhibit a high capacity of 133.3 mA h g-1 at 5 C over 150 cycles, contributing a step forward for high-rate Li-metal anodes.

High-water-absorbing calcium alginate fibrous scaffold fabricated by microfluidic spinning for use in chronic wound dressings.

More and more water-absorbing wound dressings have been studied since moist wound-healing treatment can effectively promote the healing of wounds. In this work, we introduce a novel method to produce improved wound dressings with high-water-absorbance. A high-water-absorbing calcium alginate (Ca-Alg) fibrous scaffold was fabricated simply by microfluidic spinning and centrifugal reprocessing. The structure and physical properties of the scaffold were characterized, and its water-absorbing, cytotoxicity properties and other applicability to wound dressings were comprehensively evaluated. Our results indicate that this material possesses high water-absorbing properties, is biocompatible, and has a 3D structure that mimics the extracellular matrix, while Ca-Alg fibers loaded with silver nanoparticles (AgNPs) exhibit broad-spectrum antibacterial activities; these properties meet the requirements for promoting the healing of chronic wounds and are widely applicable to wound dressings.

Cellulose acetate nanofibers coated layer-by-layer with polyethylenimine and graphene oxide on a quartz crystal microbalance for use as a highly sensitive ammonia sensor.

A novel approach to the preparation of a sensing coating on a quartz crystal microbalance (QCM) to realize rapid and accurate ammonia detection is reported in this study. Positively charged polyethylenimine (PEI) and negatively charged graphene oxide (GO) were successively assembled on the surfaces of negatively charged electrospun cellulose acetate (CA) nanofibers, using the electrostatic layer-by-layer (LBL) self-assembly technique. Scanning electron microscopy (SEM) images demonstrated the nanofibrous morphology of the as-prepared CA/PEI/GO membrane. Fourier-transform infrared (FT-IR) and Raman analyses indicated that the PEI and GO were successfully assembled on the surfaces of the CA nanofibers. In gas-sensing tests, the CA/PEI/GO-based QCM sensor not only exhibited a low detection limit and rapid response, but also performed with good reversibility and selectivity with respect to ammonia detection.

Regulation of biphasic drug release behavior by graphene oxide in polyvinyl pyrrolidone/poly(ε-caprolactone) core/sheath nanofiber mats.

One of the key issues for drug delivery systems is to develop a drug carrier with a time-programmed, biphasic release behavior. Using vancomycin hydrochloride (VAN) as a model drug, polyvinyl pyrrolidone (PVP) blended with graphene oxide (GO) sheets as the core matrix, and poly(ε-caprolactone) (PCL) as the sheath polymer, core/sheath PVP/PCL nanofiber mats were fabricated via a coaxial electrospinning process. We hypothesized that the addition of GO sheets would lead to their molecular interactions with VAN molecules, thereby adjusting the VAN release behavior. Field emission scanning electron microscopy and transmission electron microscopy of the fiber mats revealed their nanofibrous structure and clear core/sheath boundary. Raman analysis demonstrated the presence of GO sheets in the PVP/PCL nanofiber mats. Fourier transform infrared spectroscopy indicated the formation of hydrogen bonds between GO sheets and VAN molecules. In vitro studies showed that the PVP/PCL nanofiber mats were biocompatible, despite the addition of GO sheets, and exhibited typical biphasic drug release profiles, which were tailored by adjusting the content of GO sheets. Furthermore, an antimicrobial test showed different antimicrobial activities of the medicated nanofiber mats, depending on the GO content. Collectively, the results of the present study provide a simple approach to obtaining time-programmed drug release profiles.

Electrospun nanofibrous chitosan membranes modified with polyethyleneimine for formaldehyde detection.

Here we describe a formaldehyde sensor fabricated by coating polyethyleneimine (PEI) functionalized chitosan nanofiber-net-binary structured layer on quartz crystal microbalance (QCM). The chitosan fibrous substrate comprising nanofibers and spider-web-like nano-nets constructed by a facile electro-spinning/netting process provided an ideal structure for the uniform PEI modification and sensing performance enhancement. Benefiting from the fascinating nanostructure, abundant primary amine groups of PEI, and strong adhesive force to the QCM electrode of PEI-chitosan membranes, the developed formaldehyde sensor presented rapid response and low detection limit (5 ppm) at room temperature. These findings have important implications in fabricating multi-dimensional nanostructures on QCM for gas sensing and chemical analysis.

PCL/PEG core/sheath fibers with controlled drug release rate fabricated on the basis of a novel combined technique.

A novel core/sheath fiber preparation method, which included the processes of blend electrospinning to produce the core fiber and UV-induced graft polymerization to fabricate the outer polymeric shell, was presented to provide designated fibers with different shell thicknesses. A hydrophilic drug, salicylic acid (SA), was loaded in the representative poly(ϵ-caprolactone) (PCL)/polyethylene glycol (PEG) core/sheath fibers, performed according to this combined technique. FTIR analysis indicated that the existence of hydrogen bonds between SA and the PCL matrix improved drug compatibility. Field emission scanning electron microscopy (FESEM) images indicated that the morphology and the diameter distribution of fibers changed significantly after the graft polymerization procedure. All the core/sheath fibers became more flexible and thicker compared with the core fiber. The water contact angle (WCA) test also noted the differences of these two fibers: PCL/PEG core/sheath fibers with cross-linked PEG surface exhibited more hydrophilic property. Moreover, in vitro SA release tests were conducted to explore the relationship between the PEG shell thickness and the drug release rate. A typical biphasic release mechanism was observed for the PCL/PEG core/sheath fibers, and their sustained release rates were controlled by the PEG shell thickness in a linear correlation.