Electret treatment was a simple method to enhance the charge-electrode properties of polyvinylidene fluoride (PVDF) materials due to the increase of space charge and polarization charge of PVDF materials. The polarization charge was due to the electric dipole orientation change in loose nanofiltration PVDF membrane, which increased the electric dipole moment and improved the polarity of surface potential. Importantly, electret charges were less affected by ambient humidity. Therefore, the electret treatment could improve the surface negative potential of loose nanofiltration PVDF membrane, so as to improve its anti-fouling performance under certain conditions. Based on the above theoretical analysis, the influence and mechanism of the electret treatment on the surface potential, morphology, structure, hydrophilicity and anti-pollution performance of PVDF membrane were studied in this manuscript. When the electret time was 7.5 min and the electret voltage was 30 kV, the surface negative potential was the highest. The content of β phase crystals was 39.1%, which was 12.18% higher than that of untreated membrane. In addition, the surface morphology of PVDF membrane did not change significantly, but the water contact angle decreased slightly, and the pore size increased by 0.36–0.75 nm. Importantly, the flux and the rejection of dye and BSA increased to some extent, and the maximum rejection rate and water flux were increased by 10.34% and 20.25%, respectively. Through the cyclic filtration test and analysis, the anti-fouling performance of membrane was increased due to electrostatic repulsion.
Quan Li,Huan Liu,Benqiao He,Wenxiong Shi,Yanhong Ji,Zhenyu Cui,Feng Yan,Younas Mohammad,Jianxin Li
Efficient separation of Mg 2+ and Li + remains a major challenge in the extraction of lithium from salt lake brine. In this work, an electro-nanofiltration (NF) process was employed to separate Mg 2+ and Li + from the MgCl 2 /LiCl feed solution under a current density of 0–2.83 mA cm −2 and at an operating pressure of 5 bar. The surface chargeability of the NF membrane under an electric field (EF) was investigated in detail by combination of the experiment and theoretical simulation. It was found that Mg 2+ ions were almost completely rejected (no Mg 2+ detected by an ICP-OES with a determination limit of 0.01 ppm). A high permeance of Li + (0.55 molm −2 h −1 ) and a stable solution flux of 75 ± 2 Lm −2 h −1 were achieved. The separation performance was far better than the results reported in the literature until now. It was believed that high positive charges on the negative-charged NF membrane surface were in-situ reconstructed and enhanced with the increase in current density due to the complexion and enrichment of Mg 2+ on the membrane surface, leading to the high rejection for Mg 2+ . The dehydration of Li + ions with a low hydration energy under EF promoted the permeance of Li + . This work provides a practical route for efficient separation of Mg 2+ /Li + , and would have a huge potential in the extraction of high-pure Li + salt from salt lakes.
Lulu Liu,Yuxuan Liu,Yinhua Wan,Weijie Song,Hongwei Lu,Jianquan Luo
Surface grafting has been widely used to tune hydrophilicity and chargeability of nanofiltration membranes for reducing membrane fouling potential. However, surface grafting typically leads to a significant pore narrowing and resultant permeability loss, and monocharged surface still struggles to resist mixed foulants with different charges. Herein, ionic liquid (IL)-ethanol (EtOH) solution containing polyethyleneimine (PEI) is used to rearrange the nascent polyamide layer. The high affinity of IL to the PA layer and the low diffusion steric hindrance of EtOH contribute to the polyamide swelling and PEI deep grafting, during which the “self-regulation” effect (larger pores would be filled with more PEI molecules) narrows the pore size distribution and enhances hydrophilicity. The nearly charge-neutral and smooth separation layer shows impressive antifouling capacity to hydrophobic macromolecules and mixed charged molecules, along with long-term operating stability for real wastewater treatment. This study emphasizes the importance of solvent properties on the membrane grafting behavior.
危险品化学品经营许可证（带存储）