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.

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.