Conductive Fe3O4/PANI@PTFE membrane for high thermal efficiency in interfacial induction heating membrane distillation

Conventional membrane distillation (MD) undergoes interfacial temperature polarization and thus may suffer from a reduced thermal efficiency when using the hot saline water as the primary thermal driver. To address this issue, this study employed a conductive Fe3O4/polyaniline (PANI) coated polytetrafluoroethylene (Fe3O4/PANI@PTFE) membrane to achieve local interfacial heating under electromagnetic induction and promote the thermal efficiency of direct-contact MD (DCMD). Induction-responsive Fe3O4 nanoparticles were dispersed in a conductive PANI polymer matrix that binds to the hydrophobic porous PTFE membrane by spray coating. Dispersing Fe3O4 nanoparticles in a conductive PANI polymer matrix doubled the heating efficiency (2.0 °C s−1) than directly dispersing Fe3O4 nanoparticles onto PTFE without PANI (1.1 °C s−1). This enhanced heating efficiency is ascribed to the formation of multiple conductive pathways or eddy current channels via the conductive polymer networks. A parametric study of the DCMD performance revealed that the permeate flux increased from 0.7 to 3.4 L m−2 h−1 with the increase of the coolant flow velocity (1.4–22.9 cm min−1) and induction power (0.9–3.6 kW). However, increasing the feed (3.5 wt% NaCl solution) flow velocity (1.4–8.6 cm min−1) significantly reduced the permeate flux from 5.0 to 1.6 L m−2 h−1 due to the insufficient time of water/membrane contact for mass transfer. Moreover, thermal and mass transport processes at the induction-heated membrane interface were analyzed by finite element analysis (FEA), which matched well the experimental results and determined the thermal efficiency up to 88% as opposed to the reported levels (20–58%) for the conventional DCMD. Our study laid additional foundation for induction-heating DCMD by devising new composite membrane materials and new interfacial thermal and mass transfer mechanisms.