Fabrication of robust green superhydrophobic hybrid nanofiber-nanosphere membrane for membrane distillation

To solve the fouling and wetting issues in membrane distillation (MD), the preparation of membranes with a superhydrophobic surface has been a significant focus of researchers. In this study, an innovative biaxial electrospinning technology combined with a single PVDF-co-HFP polymer was employed to prepare a green superhydrophobic, monolayer hybrid membrane without using long-chain perfluorinated additives in one-step. Compared with nanofiber (NF) membranes, the surface roughness of the nanosphere-nanofiber (NF-NS) hybrid membranes increased 3.58 times, achieving a superhydrophobic surface (CA:153.8 ± 0.19°) while the single layer structure imparted good surface stability to the membrane. The introduction of nanospheres reduced the membrane's pore size, improved tensile strength, imparted a firmer pore structure, and reduced thermal conductivity, which contributed to a higher LEP value and average water flux. In MD testing, optical coherence tomography (OCT) technology was applied to monitor the foulant growth process in-situ on the membrane surface non-destructively and in real-time. Furthermore, a 7-day membrane distillation test was conducted with a water flushing operation, which demonstrated the outstanding long-term performance of the superhydrophobic NS-NF hybrid membrane, with a rejection rate of 99.8 ± 0.13% and average water flux of 29.6 ± 0.19LHM. These results represent valuable evidence for promoting the industrial development of MD technology by addressing stability and pollutant concerns.