Investigation of the performance of dual-layered omniphobic electrospun nanofibrous membranes for direct contact membrane distillation

Abstract

Direct contact membrane distillation (DCMD) is a viable one-stop solution for sustainable seawater desalination and wastewater recovery. In this study, robust dual-layered omniphobic electrospun nanofibrous membranes (ENFMs) were fabricated with a re-entrant architecture and low surface free energy. This was achieved by incorporating hydrophobic mesocellular silica foam (MCF-5) into the top layer, followed by the surface functionalisation with 1 H, 1 H, 2 H, 2 H Perfluorodecyltriethoxysilane to improve the membrane anti-wetting and anti-fouling resistance. The dual-layered ENFMs exhibited a high porosity and a water contact angle ≃ of 143˚ and displayed an excellent vapour flux of ∼ 8.5 Lm−2h−1 and NaCl rejection > 99.99% when tested with synthetic seawater. The long-term desalination of natural seawater revealed that the normalised permeate flux was > 0.98 (NaCl rejection > 99.97%), and a simple water wash could recover the loss of membrane hydrophobicity and performance caused by the membrane scaling. The fabricated ENFMs displayed excellent permeate quality (< 1 ppm organic content and < 30 µS/cm) when evaluated with synthetic wastewater containing pharmaceutical compounds (acetaminophen, diclofenac sodium, ibuprofen and amoxicillin). The dual-layered membranes demonstrated outstanding anti-wetting ability when challenged with increasing concentration of cationic surfactant cetyltrimethylammonium bromide (CTAB 1.5 mM) in saline oily wastewater. The preliminary investigations revealed that these ENFMs hold great potential to be further investigated for enhanced water recovery.