Chitosan-based hollow nanofiber membranes with polyvinylpyrrolidone and polyvinyl alcohol for efficient removal and filtration of organic dyes and heavy metals.

Due to their large specific surface area and numerous diffusion channels, hollow fibers are widely used in wastewater treatment. In this study, we successfully synthesized a chitosan (CS)/polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) hollow nanofiber membrane (CS/PVP/PVA-HNM) via coaxial electrospinning. This membrane demonstrated remarkable permeability and adsorption separation. Specifically, the CS/PVP/PVA-HNM had a pure water permeability of 4367.02 L·m-2·h-1·bar-1. The hollow electrospun nanofibrous membrane exhibited a continuous interlaced nanofibrous framework structure with the extraordinary advantages of high porosity and high permeability. The rejection ratios of CS/PVP/PVA-HNM for Cu2+, Ni2+, Cd2+, Pb2+, malachite green (MG), methylene blue (MB) and crystal violet (CV) were 96.91 %, 95.29 %, 87.50 %, 85.13 %, 88.21 %, 83.91 % and 71.99 %, and the maximum adsorption capacities were 106.72, 97.46, 88.10, 87.81, 53.45, 41.43, and 30.97 mg·g-1, respectively. This work demonstrates a strategy for the synthesis of hollow nanofibers, which provides a novel concept for the design and fabrication of highly efficient adsorption and separation membranes.

Uniaxial MEMS-based 3D reconstruction using pixel refinement.

A uniaxial micro-electro-mechanical systems (MEMS) micro-vibration mirror can be used to construct a new type of fringe projection profilometry (FPP) system. In FPP system calibration, some pixels may be calibrated worse than other pixels due to various error sources, which will affect the final reconstruction accuracy. In addition, there are some difficulties in calibrating the MEMS-based system because a projector using the uniaxial vibration mirror does not have focusing optics and can only project unidirectional fringes. In this paper, we developed an FPP system using a uniaxial MEMS micro-vibration mirror. To solve the calibration problems, we propose a calibration model suitable for the MEMS-based system and a pixel refinement method. These pixels with relatively large calibration errors are called outlier-pixels, which will significantly increase the error of the following 3D mapping. Therefore, the pixel refinement method classifies all pixels based on a frequency distribution histogram of calibration errors during calibration and prevents outlier-pixels from participating in the following 3D mapping. The experimental results show that the proposed method can improve the accuracy of 3D reconstruction, and the feasibility of the self-developed system is verified.

Chitosan/polyvinylpyrrolidone/polyvinyl alcohol/carbon nanotubes dual layers nanofibrous membrane constructed by electrospinning-electrospray for water purification.

Nanofibrous membrane have great potential in the field of water purification due to the high porosity and large specific surface area. Herein, a dual layers nanofibrous membrane was prepared by combining an active layer containing carbon nanotubes (CNTs) with a porous chitosan (CS)/polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) nanofibrous support layer via electrospinning-electrospray technique for highly efficient heavy metal and organic pollutants removal. Incorporating CNTs into the active layer offered additional nanochannels which significantly enhanced pure water permeate flux (1533.26 L·m-2·h-1) and heavy metal ions/dyes rejection (Cu2+ 95.68 %, Ni2+ 93.86 %, Cd2+ 88.52 %, Pb2+ 80.41 %, malachite green 87.20 %, methylene blue 76.33 %, and crystal violet 63.39 %). The optimal membranes were formed with a thickness of 20 µm and a roughness of 142 nm while still showing good perm-selectivity compared with commercial PVDF membrane. Moreover, the constructed membrane exhibited good antifouling property and long-term stability during filtration process. This work provides a new strategy to fabricate advanced separation membranes for water treatment.

Preparation and performance evaluation of chitosan/polyvinylpyrrolidone/polyvinyl alcohol electrospun nanofiber membrane for heavy metal ions and organic pollutants removal.

In this work, a novel electrospun chitosan (CS)/polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) nanofibrous membrane was prepared to remove heavy metal ions and organic pollutants from water. The nanofiber morphologies were adjusted through the optimal electrospinning process parameters. Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations indicated that a well-crosslinked CS/PVP/PVA nanofiber film was formed. Under the optimize conditions, the obtained CS/PVP/PVA nanofiber membranes exhibited porous and uniform nanofibrous structures with an average diameter of 160 nm and a pure water permeability of 4518.91 L·m-2·h-1·bar-1. In addition, the adsorption and separation performance of CS/PVP/PVA nanofiber membranes were evaluated with Cu(II), Ni(II), Cd(II), Pb(II) and Methylene Blue (MB), Malachite Green (MG) as target ions and dyes. The results showed that the retention rate of CS/PVP/PVA nanofiber membranes for Cu(II), Ni(II), Cd(II), Pb(II), MG and MB can reach 94.20%, 90.35%, 83.33%, 80.12%, 84.01% and 69.91%, respectively. The adsorption capacities of Cu(II), Ni(II), Cd(II), Pb(II), MG and MB were 34.79, 25.24, 18.07, 16.05, 17.86 and 13.27 mg g-1. The adsorption kinetics of heavy metal ions and dyes by the nanofiber membranes can be explained by the Langmuir isotherm model and represented by the pseudo-second-order kinetic mechanism that determined the spontaneous chemisorption process. This study provides a synthetic approach to membranes for the removal of organic and heavy metal micropollutants from water.

Development of novel zein-sodium caseinate nanoparticle (ZP)-stabilized emulsion films for improved water barrier properties via emulsion/solvent evaporation.

This work attempted to develop novel high barrier zein/SC nanoparticle (ZP)-stabilized emulsion films through microfluidic emulsification (ZPE films) or in combination with solvent (ethyl acetate) evaporation techniques (ZPE-EA films). Some physical properties, including tensile and optical properties, water vapor permeability (WVP), and surface hydrophobicity, as well as the microstructure of ZP-stabilized emulsion films were evaluated and compared with SC emulsion (SCE) films. The emulsion/solvent evaporation approach reduced lipid droplets of ZP-stabilized emulsions, and lipid droplets of ZP-stabilized emulsions were similar to or slightly lower than that of SC emulsions. However, ZP- and SC-stabilized emulsion films exhibited a completely different microstructure, nanoscalar lipid droplets were homogeneously distributed in the ZPE film matrix and interpenetrating protein-oil complex networks occurred within ZPE-EA films, whereas SCE films presented a heterogeneous microstructure. The different stabilization mechanisms against creaming or coalescence during film formation accounted for the preceding discrepancy of the microstructures between ZP-and SC-stabilized emulsion films. Interestingly, ZP-stabilized emulsion films exhibited a better water barrier efficiency, and the WVP values were only 40-50% of SCE films. A schematic representation for the formation of ZP-stabilized emulsion films was proposed to relate the physical performance of the films with their microstructure and to elucidate the possible forming mechanism of the films.