Fabrication of Janus PTFE nanofibrous membrane with superhydrophilic hydrogel coating for robust membrane distillation

A calcium alginate hydrogel layer was ionically crosslinked on electrospun PTFE to form a Janus membrane. • A PVDF interlayer was introduced to improve interfacial adhesion. • The dense hydrogel layer provided a hydration barrier and molecular sieving functions. • The Janus membrane showed superior anti-wetting, anti-fouling and anti-scaling performance to that of pristine PTFE. Membrane distillation (MD) holds great promise for high-salinity wastewater treatment, yet membrane wetting, fouling, and scaling severely restrict its practical application. In this study, an electrospun polytetrafluoroethylene (PTFE) nanofibrous membrane was used as the hydrophobic substrate, a polyvinylidene fluoride (PVDF) interlayer was introduced to enhance interfacial adhesion, and a hydrophilic calcium alginate hydrogel layer was constructed via one-side ionic crosslinking of sodium alginate with calcium chloride (SA-CaCl 2 ). Consequently, an SA-CaCl 2 /PVDF/PTFE Janus membrane with superhydrophobic/superhydrophilic asymmetric wetting characteristics was successfully prepared. The sodium alginate concentration (1 mg mL −1 ) and crosslinking time (5 min) were optimized, and the resulting JM-1-5 membrane possessed a dense, uniform, and firmly attached hydrophilic gel layer. Direct contact membrane distillation (DCMD) evaluation showed that the membrane maintained a stable permeate flux (approximately 18 kg·m −2 ·h −1 ) and nearly 100% salt rejection when treating pure saline water, SDS-containing saline water, and oily simulated wastewater. In a long-term concentration experiment with 3.5 wt% NaCl, the JM-1-5 membrane operated stably for about 30 h and achieved a concentration efficiency of 73%, exhibiting significantly better anti-wetting, anti-fouling, and anti-scaling performance than the pristine PTFE membrane. Mechanistic analysis revealed that the hydration effect, size-exclusion effect, and high capillary pressure of the hydrophilic layer act synergistically to effectively inhibit contaminant adsorption and salt crystallization nucleation. This study provides a new approach for the design of high-performance composite membranes for membrane distillation. Download: Download high-res image (124KB) Download: Download full-size image