Nanostructure depositions on alumina hollow fiber membranes for enhanced wetting resistance during membrane distillation

Omniphobic alumina hollow fiber membranes were developed for direct contact membrane distillation (DCMD) with a low surface tension feed in this study. Alumina hollow fiber (HF) membranes were prepared as the membrane substrates, and chemical bath deposition methods were applied to deposit ZnO nanorods and nanoparticles on the HF membranes. The SEM, EDX, and AFM analyses showed that the ZnO nanostructures were effectively deposited on the membrane surfaces and able to increase the surface roughness. After surface fluorination by FAS17, the HF membranes deposited by ZnO nanorods and nanoparticles demonstrated contact angles of 128.7 degrees and 138.1 degrees for a 90% v/v ethanol/water mixture, both of which were higher than 114.8 degrees for the pristine HF membrane without ZnO nanostructures. In the DCMD experiments with the sequential addition of SDS from 0.2 to 2.0 mM, the HF membranes with ZnO nanostructures exhibited superior wetting resistances with low surface tension feeds compared to that of the pristine HF membranes. Moreover, the HF membranes with the deposited ZnO nanoparticles had the best wetting resistance, and the permeate water flux was maintained for 24 h using a 2.0mM SDS (70 degrees C 1M NaCl) solution as an initial feed. The results not only suggested that the deposition of nanostructures enhanced the wetting resistance of the alumina hollow fiber membranes to low surface tension liquids but also showed the promise of utilizing these membranes for the desalination of low surface tension wastewaters.