Dual resistance Janus PDA/patterned PVDF membrane for membrane distillation with early wetting detection using electrochemical impedance spectroscopy

Abstract

Membrane distillation (MD) is highly efficient in separating and removing water pollutants; however, it is susceptible to membrane wetting and fouling especially when treating low-surface tension pollutants such as oils and surfactants. To address these limitations, we fabricated a Janus polydopamine (PDA)/patterned polyvinylidene fluoride (PVDF) membrane with anti-wetting and anti-fouling properties via non-solvent- and vapor-induced phase separation. In the MD test with a NaCl feed solution with hourly sodium dodecyl sulfate injection, the Janus membrane with the hydrophobic patterned PVDF layer significantly delayed membrane wetting with only a slight trade-off in flux - an 8.6 % decrease in water vapor flux. Also, in the MD test using a NaCl feed solution containing 1000 mg L−1 of canola oil, the hydrophilic PDA layer of the Janus membrane effectively prevented the interaction between oil and the membrane surface. The wetting progression of the Janus membrane was systemically monitored using electrochemical impedance spectroscopy to identify the mechanism of its wetting behaviour and to detect and analyse the different wetting stages (i.e., non-wetting, partial wetting, and full wetting). Therefore, unlike conventional electrical conductivity measurement methods, the wetting front estimated using EIS enabled a more precise wetting detection during the DCMD operation.