Constructing superhydrophobic ZIF -8 layer with bud -like surface morphology on PDMS composite membrane for highly efficient ethanol/ water separation

Emerging pervaporation technology is very promising to realize clean and renewable bioethanol recovery from biomass fermentation broth. The huge challenge of this technology is the need for a pervaporation membrane with high separation performance. Based on the solution-diffusion mechanism, pervaporation membrane for ethanol recovery should possess hydrophobic selective layer to improve sorption ability toward ethanol mole cules, thereby enhancing the separation performance. In this study, a superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer with a nano-level bud-like surface morphology was grown on polydimethylsiloxane (PDMS) composite membrane via ZIF-8 particle dip-casting, secondary seeded growth, and hydrophobic modification by n-octadecylphosphonic acid for highly efficient ethanol/water separation. The mole ratio of 2-methylimidazole and zinc nitrate (Hmim/Zn2+) in the process of ZIF-8 secondary growth was systematically studied to construct appropriate micro-nano structure on PDMS composite membrane. The resultant optimal composite membrane exhibited a water contact angle of about 163 degrees and an ethanol contact angle of 0 degrees. In addition, it also displayed an outstanding separation factor of 17.4 corresponding to a total flux of 0.64 kg/m(2) h with 5 wt% ethanol aqueous solution at 30 celcius, and thus the superior pervaporation performance to most other reported PDMS-based mixed matrix membranes. The strategy of constructing superhydrophobic layer on PDMS composite membrane may provide a meaningful guidance for preparing high-performance pervaporation membrane for organic recovery from aqueous solution.

Automated summary

This study successfully achieved efficient ethanol/water separation by constructing a superhydrophobic layer on a PDMS composite membrane, demonstrating outstanding pervaporation performance and providing meaningful guidance for organic recovery from aqueous solutions.