CF4 plasma-modified omniphobic electrospun nanofiber membrane for produced water brine treatment by membrane distillation

This study describes the development and performance of an omniphobic poly(vinylidene fluoride) (PVDF) membrane by electrospinning and CF4 plasma surface modification for, air gap membrane distillation (AGMD). The effect of different duration of plasma treatment on the nanofiber membrane characteristics was investigated. The AGMD performance of the membranes was evaluated using real reverse osmosis (RO) brine produced from coal seam gas (CSG) water that was added with low surface tension liquid (surfactant) as feed solution. Results indicated the formation of new CF2-CF2 and CF3 bonds after plasma treatment, which lowered the surface energy of the membrane, providing omniphobic property, as indicated by its wetting resistance to different low surface tension liquids such as methanol, mineral oil and ethylene glycol. Though no appreciative changes in morphology of the membrane were observed after plasma treatment, optimal treatment condition of 15 min (i.e., P/CF-15 membrane) exhibited lotus effect membrane surface with increased liquid entry pressure of 187 kPa compared to 142 kPa for neat membrane. AGMD performance showed stable normalized flux (initial flux of 15.3 L/m(2)h) and rejection ratio (100%) for P/CF-15 even with the addition of up to 0.7 mM sodium dodecyl sulfate surfactant to the RO brine from CSG produced water feed, while commercial PVDF membrane suffered membrane wetting after 0.3 mM of surfactant addition. Based on the results, the present omniphobic membrane has good potential for producing clean water from challenging waters containing high salinity and organic contaminants.