Robust dual-layer Janus membranes with the incorporation of polyphenol/Fe3+ complex for enhanced anti-oil fouling performance in membrane distillation

The effective treatment of oily saline wastewater has posed a challenge for membrane distillation (MD) technology due to the severe oil fouling. To address this dilemma, a Janus membrane was successfully developed in this study by incorporating tannic acid (TA)/ferric chloride (FeCl3) complex and polyvinylidene fluoride (PVDF) onto the polytetrafluoroethylene (PTFE) membrane surface via the nonsolvent-induced phase separation (NIPS) method. The characterization results demonstrated that the TA-Fe3+ complex was compatible with the PVDF, and the composite surface layer was firmly attached on the PTFE substrate. Furthermore, the Janus membrane showed a high hydrophilicity and strong underwater superoleophobicity (oil contact angle, 154.80 ± 1.07°), with had an excellent vapor flux (28.30 ± 1.18 Lm−2 h−1) compared with the membrane without the embedding of TA-Fe3+ complex (18.16 ± 1.45 Lm−2 h−1). According to theoretical arithmetic of mass transfer, the evaporation interface of the Janus membrane had transferred during the MD process, contributing to promoting the mass transfer performance and fouling resistance. When treating oily saline emulsion, the Janus membrane exhibited a good desalination and anti-oil fouling stability compared to the control membranes. This study suggests that the fabricated lipophobic Janus MD membrane has great potential in the treatment of oily saline wastewater.