Ronghua Ma,Xiaolong Lu,Shaozhe Zhang,Kai Ren,Jie Gu,Chao Liu,Ziqiang Liu,Hanli Wang
In recent years, membrane separation technology has been widely used in various fields. And for the increasingly severe oily wastewater system, there is an increasing demand for the anti-fouling properties of the membranes. Based on the concept of fluorine-free, non-toxic, environmental-friendly and low-cost, this study constructed a discontinuous silicon-island structure with low surface energy on the surface of the hydrophilic membrane, which endows the PVDF-CTFE membrane with fouling resistance and cleaning pH-responsiveness. The discontinuous silicon-island structures were constructed by introducing SiO 2 nanoparticles on the super-hydrophilic layer of the PVDF-CTFE membrane modified by itaconic acid, and then hydrophobically treated with polydimethylsiloxane (PDMS). The experimental results exhibited that the modified membrane reached the hydrophobic and underwater super-oleophobic state when treated by PDMS for 1.0 h. The water contact angle (WCA) and the underwater oil contact angle (OCA) were 124° and 151°, respectively. Furthermore, the water flux remained at 186 L m −2 h −1 with no serious pore-plugging. Moreover, the water flux decay rate (FDR) remained below 19.6%, when modified membrane treating soybean oil/water emulsion for 6 cycles, presenting an excellent anti-fouling performance. Additionally, the water flux recovery rate (FRR) was over 99.3% after alkali cleaning, indicating the modified membrane possessed excellent cleaning pH-responsiveness. The above analysis exhibited that the synergistic effect of hydrophilic micro-domains and oleophobic micro-domains not only slows down the attachment of hydrophobic pollutants but also promotes the separation of hydrophobic pollutants during chemical cleaning, which greatly improves its anti-fouling performance and expands its application prospect.
Wenyi Ma,Wanzheng Ren,Xiaoyu Bai,Jian Pan,Lilan Huang,Qinglin Huang,Zengge Guo,Xinyan Wang
Poly (vinylidene fluoride) (PVDF) has been widely implemented in fabricating membranes, but pure PVDF membrane need to be modified by blending or copolymerization to cope with its weak alkali resistance. In this work, the function of chlorotrifluoroethylene (CTFE) chain segment was studied, PVDF/ECTFE blending membranes and poly (vinylidene difluoride- co -chlorotrifluoroethylene) (PVDF-CTFE) membranes were prepared via non-solvent induced phase separation (NIPS) method. The effect of modification methods and solvents on the membrane morphology, micropore and physicochemical structure, permeability, ultrafiltration performance, anti-fouling property and alkali resistance were investigated systematically. More than that, the surface charge and roughness of membrane prepared by different solvents were determined in the varying environment to better understand the anti-fouling property. The result presented that the comprehensive properties of PVDF-CTFE copolymerization membrane were better than that of PVDF/ECTFE blending membrane. The microporous structure of PVDF-CTFE membrane surface and sublayer was optimized by adjusting the solvent. The effect of solvent on the rate of L-L de-mixing during phase inversion was investigated from thermodynamic and kinetic factors. The prepared PVDF-CTFE membrane using N -methylpyrrolidone (NMP) as solvent broke the trade-off between the permeability and selectivity, so it was simultaneously possessed superior pure water flux (306.5 L·m −2 ·h −1 ) and higher BSA rejection rate (98.4%). The combination of NMP and PVP significantly decreased the rate of phase inversion without changing the polymer content, and provided a simple and feasible improvement idea for non-solvent-induced phase separation. In addition, the PVDF-CTFE membranes possessed better alkali resistance compared to PVDF membranes, demonstrating its promising potential in harsh environment.
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