Rheologically controlled design of nature-inspired superhydrophobic and self-cleaning membranes for clean water production

Abstract

Conventional fabrication technologies of superhydrophobic and self-cleaning membranes for wastewater treatment often involve complex surface modifications, and massive usage of nanomaterials or organic solvents. In this work, we developed a pure rheological spray-assisted nonsolvent induced phase separation (SANIPS) approach to fabricate self-cleaning polyvinylidene fluoride (PVDF) membranes with high porosity and hierarchical micro/nanostructures. The resultant membranes exhibit water contact angles and sliding angles in the range of 151.9–156.2° and 9.6–22.6°, respectively. We found that the spraying step caused local distortion of the membrane surface and induced a two-stage phase inversion, leading to the formation of multilevel polymeric crystal structures. Moreover, the morphological structures and other membrane properties (e.g., mechanical strength and liquid entry pressure) could be tuned by applying spraying materials with different physicochemical properties. The superior anti-wetting and self-cleaning properties of the resultant membranes have been demonstrated by treating hypersaline wastewater, comprising 10% sodium chloride and 2000 p.p.m. Rose Bengal dye via direct contact membrane distillation (DCMD) tests. The SANIPS membrane showed a remarkably stable vapor flux of 36.0 kg m−2 h at a feed temperature of 60 °C, and a salt rejection over 99.9% throughout the long-term test of 100 h. We envision this facile and green fabrication method will pave the way for large-scale production of superhydrophobic and self-cleaning membranes for diverse water treatment processes.