Unlock the secret of air blowing in developing high strength and superhydrophobic membranes for membrane distillation

Abstract

Superhydrophobic polyvinylidene fluoride (PVDF) membranes with high mechanical strength are highly desirable for multiple applications. Nevertheless, they can hardly be fabricated using conventional phase separation technologies without post-treatment. In this work, the goal has been achieved by a novel spray-assisted nonsolvent induced phase separation (SANIPS) method with the aid of air blowing. Without any membrane modification, a superhydrophobic membrane (water contact angle: 166.0°, water sliding angle: 20.0°) with excellent mechanical strength (maximum tensile strength: 3.09 MPa, maximum tensile strain: 104.80%, and Young's modulus: 71.29 MPa) can be produced. The resultant membrane exhibits a remarkable liquid entry pressure of 3.25 bar, and a stable direct contact membrane distillation (DCMD) performance over 400 h when being subjected to a hypersaline dye wastewater. The newly developed method has been compared with conventional nonsolvent induced phase separation (NIPS) and vapor induced phase separation (VIPS) methods to reveal its underlying mechanism. We believe this work would shed a new light on large scale production of PVDF membranes with both high strength and superhydrophobicity for clean water production via membrane distillation.