Janus composite membranes for suppressing thermal wetting in membrane distillation of flue gas desulfurization wastewater

The PIP Janus membrane with crater-like structures boosted flux to 72 LMH at 70 °C. • The dense PIP layer decoupled surface scaling from pore wetting to stop salt leakage. • Interfacial polymerization surface modification turned internal wetting into surface fouling. Membrane distillation (MD) is a promising technology for zero-liquid discharge (ZLD) treatment of flue gas desulfurization wastewater (FGDW), but its industrial application is hindered by membrane wetting induced by the combined effects of inorganic scaling and thermal stress. In this study, Janus composite membranes were fabricated on PTFE substrates via interfacial polymerization (IP) to improve wetting resistance. Two polyamide barriers were constructed using piperazine (PIP) and m -phenylenediamine (MPDA). The pristine PTFE membrane exhibited a critical failure at 70 °C, where accelerated gypsum crystallization promoted crystal intrusion into membrane pores, leading to rapid wetting. In contrast, the IP-modified membranes significantly enhanced MD stability. Notably, the PIP@PTFE membrane formed a crater-like nanostructure and exhibited a high initial flux (∼72 L m −2  h −1 at 70 °C). The flux enhancement may be associated with favorable surface morphology and interfacial transport characteristics. Moreover, its dense polyamide layer confined gypsum crystallization to the membrane surface, maintaining excellent permeate quality (<200 μS cm −1 ) despite severe scaling and preventing the massive saline breakthrough observed in pristine membranes. These results demonstrate that PIP-based interfacial polymerization effectively suppresses thermally induced wetting, maintains permeate quality, and improves short-term wetting resistance under severe thermal-scaling conditions of MD for hypersaline wastewater treatment. Download: Download high-res image (163KB) Download: Download full-size image