Abstract
Developing a cost-efficient and high-performance separation membrane for the desalination of hypersaline water is significant but challenging because of the crucial limitations of low permeate flux and serious membrane pore wetting over time. Herein, a unique dual-layer composite membrane consisting of a superhydrophobic selective skin from amorphous polypropylene (aPP) and an electrospun poly(vinylidene fluoride) (PVDF) nanofibrous support was created via a facile vacuum filtration method. Benefitting from the excellent tackiness and low surface free energy of aPP, the robust dual-layer aPP/PVDF membranes not only could exhibit remarkable enhancement in hydrophobicity and liquid entry pressure of water (LEPw) but could also tune the pore size without severely compromising the porosity. The superhydrophobic aPP porous skin acted as an additional barrier to surface wetting and combined with an interconnected nanofibrous support to provide direct paths for vapor transport, leading to superior direct contact membrane distillation (DCMD) performance. Significantly, the optimal superhydrophobic aPP/PVDF membrane exhibited an ultrahigh permeate vapor flux of 53.1 kg m−2 h−1 and stable permeate conductivity for a transmembrane temperature of 40 °C (3.5 wt% NaCl salt feed) over 50 h of operation. This DCMD performance was more than twice that of the typical commercial PVDF (C-PVDF) membrane and even better than those of modified electrospun nanofibrous membranes (ENMs) reported so far, indicating great applicability for MD desalination.