Constructing discontinuous silicon-island structure with low surface energy based on the responsiveness of hydrophilic layers to improve the anti-fouling property of membranes

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 SiO2 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.