Fabrication of monolithic omniphobic PVDF membranes based on particle stacking structure for robust and efficient membrane distillation

Robust omniphobic membranes have attracted great attention in improving the continuous service performance of the membrane distillation (MD) in treating high salinity wastewater. However, the fabrication of omniphobic membranes commonly undergoes complex procedures of modification including the construction of rough structures and post-modification using low-surface-energy substances. Herein, monolithic omniphobic polyvinylidene fluoride (PVDF) membranes were conveniently constructed by the combination of porous membranes possess particle stacking structure generated by a one-step vapor-induced phase separation (VIPS) procedure with subsequent surface perfluorination modification. The water contact angle, soybean oil contact angle, and low-surface-tension ethanol contact angle of the perfluorinated modified membrane increased from 139.6°, 45°, and ~0° of the original membrane to 153°, 141°, and 110°, respectively. In addition, the LEP of the perfluorinated membrane is as high as 0.32 MPa, which is higher than the 0.22 MPa of the original membrane. More importantly, the monolithic omniphobic membrane can maintain a stable water flux without deteriorating salt rejection rate during the entire MD testing due to its high specific surface area, high porosity, three-dimensional micro/nano hierarchical structure, and adjustable pore size. This study offers useful insights for constructing monolithic omniphobic membranes for efficient and robust MD processes without additional nanoparticle loading procedure.